The technical field of this invention is ballast circuits for controlling current flow through electrical discharge lamps . Background Art

Electrical discharge lamps are widely used in various forms , such as fluorescent lights , neon lights , mercury vapor lights and sodium vapor lights . These and many other types of electrical discharge lamps are known and possible using technology which began in the 1800's when many scientists experimented with electrical discharge lamps .

Electrical discharge lamps are characterized by an envelope of glass or other transparent material which encloses a volume of appropriate gas . The enclosed gas can be of a variety of types and combinations which are capable of being ionized to allow electrical current to flow therethrough. Examples of suitable gases employed in electrical discharge lamps include air , neon and argon . These gases are often combined with small quantities of suitable metals and other materials which improve the ionization or light emissive properties of the lamp . Examples of metals commonly used in discharge lamps are sodium and mercury , which vaporize as a result of the heat generated by the lamps. Discharge lamps are also manufactured using combinations of gases such as neon and argon with metal halides such as mercury iodide and sodium iodide . The variety of gases and added materials used in discharge lamps have widely varying voltage requirements for initiating ionization . The voltage or potential required across the electrodes before ionization will occur depends upon the gas type , internal pressure of the gas , gas temperature , and electrode spacing. After the gas within a discharge lamp becomes ionized , current flows more readily because of the increased number and density of available charge carriers . The increased number of charge carriers greatly reduces the resistance across the electrodes as compared to the starting resistance required when initiating ionization . This decrease in the electrical resistance across the lamp electrodes requires that some form of current limiting device be used in conjunction with the discharge lamp to control the flow of current and prevent the destructive amounts of heat which would be caused thereby. Current control is also desired to reduce power

consumption and optimize the illumination output of the lamp . This current limiting function for discharge lamps has typically been performed by an electrical device termed a ballast.

Prior art discharge lamp ballasts have typically used a transformer or other induction coil between the source of electricity and the discharge lamp in order to limit current flow through the lamp . Such transformer ballasts have also often been used to boost the starting voltage to the lamp . Such prior art inductive ballasts suffer from a number of disadvantages. Transformers are relatively costly to manufacture and are also relatively large and heavy. This increases the total cost of the discharge lamp and further requires that relatively strong standards, poles , overhanging arms and other supporting structures be employed. Increased size and strength for foundations and other structural members must also accordingly be provided. It has also not been practical to remotely mount transformer ballasts at the base of a light pole or otherwise in a remote location because of the relatively high starting or ionization voltage required. Supplying such starting potential has been difficult or impossible to attain when lengths of wire greater than 25-30 feet have been used because of line losses and voltage decreases occurring due to capacitance developed across the supply wiring. Accordingly, it has been standard practice to mount the heavy, bulky transformers immediately adjacent the lamp .

The close mounting of inductive ballasts to discharge lamps typically causes very significant increases in installation and maintenance costs . Installation costs are increased because of the increased size and structural capability which must be provided in any light fixture and supporting structure. Placement of such heavy ballasts in street lighting and other applications also usually entail an overhanging configuration for the added weight of the ballast which further increases the demands placed upon the supporting poles and other structural elements . Since these poles and other supporting structures are often tall, slender, and free standing, the incremental weight of the inductive ballast require a disproportionately large amount of the installation costs . Further aggravating these basic structural problems are the effects of wind upon light standards . The large size of the ballasts and associated hoods are more easily displaced by wind forces striking the units atop typically slender light standards , thus displacing the load further off

center and intensifying the structural loading problem associated with the weight of the ballasts.

Inductive ballasts must also be shielded from the wind and weather thus requiring additional expense for protective hoods or other coverings . Such protective hoods are relatively large thus increasing the wind loading and weight placed upon the structure which still further increases the costs of manufacturing and installation .

The installation costs of discharge lamp lighting is further increased when transformer ballasts are used because of the relatively high costs of crating, shipping and handling the heavy and bulk} transformer . Manufacture of such transformer ballasts also requires relatively large scale heavy industry -in order to produce economically . The materials and costs of constructing inductive ballasts are accordingly high .

Maintenance of transformer ballasts has also proven to be costly and difficult. Transformer ballasts produce substantial amounts of heat which tend to deteriorate the coil winding insulation thus leading to short circuiting of the coils and replacement of the ballast . Since the transformer ballasts cannot be conveniently mounted in remote locations from the lamp , this often requires cranes in order to remove and replace deficient ballasts . This accordingly increases maintenance costs .

Vibration produced by transformer ballasts may also cause fluctuating or cyclical loading on the light fixture supporting structures which requires increased strength, or in some cases premature failure, resulting damage and maintenance costs . The expected service life of transformer ballasts is also sufficiently short for the above and other reasons so that maintenance must be performed on a regular basis where numerous units are in service.

Prior art transformer ballasts also suffer from a tendency to vibrate at 60 Hz and several upper harmonies thereof thus producing very noticeable and often irritating noise. This noise has restricted most types of discharge lamps to exterior uses only . Fluorescent type discharge lamps are widely used in interior applications because they do not produce as much noise as other more efficient types of discharge lamps which are noisier. Considering the widespread use of fluorescent lamps , this results in tremendous increased power costs for using fluorescent type lamps versus sodium vapor and other more efficient lamps .

Prior art inductive ballasts are also disadvantageous in providing an inductive power factor component. Power companies typically experience excess inductive as compared to capacitive reactive power factor component's , thus requiring installation of power factor correcting equipment such as large banks of capacitors . Such equipment is expensive and accordingly increases the cost of power to the consumer. Thus there is a need for discharge lamp ballasts which produce a capacitive power factor which can be used to offset power consumed by inductive devices such as electric motors .

Disclosure of Invention

The applicants appreciation for the above problems and considerations has led to the improved, novel electronic ballasts according to this invention. A preferred form of the invention includes a dual polarity alternating-current-to-direct-current (AC-DC) converter . Such converter provides a source of substantially continuous positive current and a source of substantially continuous negative current. The converter advantageously includes positive primary energy storage means, such as at least one positive capacitor or other positive energy storage means , which receives positive current from the alternating current electrical supply. The converter also advantageously includes negative primary energy storage means, such as at least one negative capacitor or other negative energy storage means , which receives negative current from the alternating current electrical supply . The positive and negative potential portions of the alternating current supply can be divided using diodes and supplied to their respective positive and negative primary energy storage means .

The positive and negative currents supplied by the AC-DC converter are preferably modulated in respective positive and negative current modulators . The current modulators are preferably constructed to provide maximum efficiency while allowing control of the amount of current delivered to the discharge lamp .

Positive current is controllably supplied to the discharge lamp using at least one positive lamp discharge switching means which is advantageously connected between the positive current modulator and the discharge lamp to control the flow of modulated positive current to the lamp. Negative current is controllably supplied to the discharge lamp using at least one negative lamp discharge switching means which is

advantageous^ connected between the negative current modulator and the discharge lamp to control the flow of modulated negative current to the lamp . The positive and negative modulators preferably are pulse width modulators or electronic devices providing high conduction efficiency . The modulators preferably operate at frequencies in excess of the electricity supply and lamp operation . The modulators can be controlled to maintain a desired voltage drop across the respective lamp discharge switches to minimize power loss .

The electronic ballasts can also advantageously include a positive and negative current regulators to regulate the modulated currents. Regulation of the pulsed modulation currents from the preferred pulse width modulators is desired to provide increased performance of the discharge lamp . The current regulators preferably are connected between the output of the modulators and the respective positive and negative lamp discharge switching means .

The positive and negative lamp discharge switching means are advantageously transistors or other suitable solid state switching device .

The positive and negative lamp switches are controlled to operate in an asynchronous manner to prevent simultaneous supply of positive and negative lamp current to the discharge lamp . This is advantageous^ accomplished using independent positive and negative lamp discharge switching control circuitry which are coordinated to operate the positive and negative lamp switches in an alternating manner to provide alternating positive and negative lamp discharge periods . The switches are preferably operated to provide an alternating current mode of operation to the discharge lamp . The alternating current operation of the lamp has substantial benefits and can be provided in a manner compatible to the normal line frequency of the alternating current electricity supply used to power the ballast and discharge lamp . Preferred circuits according to this invention can also preferably include arc initiation subcircuits which provide boosted operating voltages for brief portions of the lamp alternating current cycle for both the positive and negative currents passed therethrough . The relatively higher voltage arc initiation discharge allows more efficient operation of the lamp by initiating discharge with a relatively small amount of higher voltage current .

Benefits of the invention can include lower power loss , physical lightness , reduced noise and interference , compactness , remotely

locatable, low heat output, lower cost mounting structures, less expensive manufacture, lower freight costs , capacitive power factor , and better regulation of current to the needs of the lamp. Some or all of these , and other benefits of the invention which may be recognized below or in the future, may be accomplished using ballast circuits according to this invention. Exemplary preferred forms of the invention will be described below .

Brief Description of the Drawings Preferred embodiments of the invention are shown in the accompanying drawings.

Fig. 1 is a block diagram showing principal functional elements of a preferred form of the invention.

Fig. 2 is a schematic circuit diagram showing a portion of a preferred circuit according to the embodiment of Fig. 1.

Fig. 3 is a schematic circuit diagram showing a further portion of the preferred embodiment showing Fig. 2.

Figs. 4A and 4B are schematic circuit diagrams showing further portions of the embodiment partially shown in Figs . 2 and 3. The portions shown in Figs. 4 A and 4B represent the modulator drive circuitry for the positive side of the electronic ballast .

Figs. 5A and 5B are schematic circuit diagrams showing further portions of the preferred embodiment shown in Figs . 2 , 3 , 4A and 4B . The portions shown in Figs . 5A and 5B represent the modulator drive circuitry for the negative side of the electronic ballast.

Fig. 6 is a graph showing voltage across a discharge lamp operated using the circuitry of Figs . 1-5B .

Fig. 7 is a graph showing current conducted through a discharge lamp operated using the circuitry of Figs . 1-5B . Fig. 8 is a graph showing voltage between the supply side of a discharge lamp and the base of the positive power discharge transistors shown in the circuitry of Figs . 1-5B .

Best Modes for Carrying Out the Invention Fig. 1 shows a preferred embodiment of electronic ballast 600 according to this invention. Ballast 600 , as shown, is adapted for use with 400 watt metal halide lamps , although the concepts described are useful for most, if not all, types of discharge lamps . Ballast

circuitry 600 receives electrical current from an alternating current (AC) source 601. A preferred current source is a nominal 120 volt rms AC current such as widely used in the United States . Connection node 602 represents the voltage-varying side of the alternating current source and terminal 603 represents the neutral or common side of the alternating current source . The voltage-varying current supply conductors are designated with the letter M in the drawings . The neutral or common side of the AC source is designated with the letter N .

Current from electricity source 601 flows to a dual polarity AC-DC converter 610. AC-DC converter 610 can be of a variety of different designs which provide a positive current source terminal 611 and a negative current source terminal 612. AC-DC converter 610 includes both positive and negative converters for producing substantially DC positive and negative current outputs 611 and 612. AC-DC converter 610 can advantageously include a first positive electrical energy storage means , such as a first positive capacitor (not specifically illustrated in Fig. 1) , for storing and converting the alternating positive

AC power to positive DC power and providing positive output 611.

Similarly , the converter 610 can also include a first negative electrical energy storage means , such as a first negative capacitor (not specifically illustrated in Fig. 1) , for storing and converting the negative AC power to negative DC power and providing negative output 612. The use of primary energy storage means which are capacitive provides a capacitive power factor for this device . In the preferred embodiment positive current source or output 611 provides approximately +170 volts DC in the no load condition. The negative current source or output terminal 612 provides approximately -170 volts in the no load condition .

The positive and negative current supplied from terminals 611 and 612 are substantially direct current with some variation possible due to discharge of capacitors or other energy storage device used in the

AC-DC converter.

The positive output 611 from converter 610 is communicated to a positive modulation subcircuit which can advantageously be in the form of a DC-DC converter 620. The negative current output 612 is similarly connected to a negative modulation subcircuit which can advantageously also be in the form of a DC-DC converter 630.

The positive modulator advantageously includes a current modulating element such as a transistor , specifically, field effect transistor

(FET) 621. The positive current modulating transistor 621 is controlled by a positive modulator drive subcircuit 622. An inductor 661 can be utilized as a regulator, choke or filtering device which smooths the modulated positive power which is controllably passed by modulation transistor 621. The resulting current flotv from inductor 661 is communicated through a diode 642 to the collector of positive lamp discharge switching means Q103. Transistor or other switching means Q103 is controlled using a positive lamp discharge switching control circuit 660. A positive current output terminal such as the emitter of transistor Q103 is connected to a supply side of discharge lamp 700 , preferably using a relatively low value resistance indicated by R204.

Fig. 1 also shows a positive high voltage arc initiation circuitry 640. Arc initiation circuitry 640 is connected to receive line AC to provide power thereto. Other sources of power may also be possible, such as output 611. Circuitry 640 generates a relatively high voltage and stores it until an appropriate time during the discharge of positive current through discharge lamp 700. The amount of current provided by positive arc initiation circuitry 640 is preferably made sufficient to initiate discharge within lamp 700 through diode 641 , transistor Q103 and resistor R.204. The energy storage capability of arc initiation circuitry 640 is also preferably made relatively low so that the higher voltage power source is only utilized for a brief portion of a positive lamp discharge period associated with discharge of positive current through lamp 700. This minimizes the energy expended and makes the ballast more efficient.

Negative current from negative output terminal 612 is communicated to a negative current modulator, such as at field effect transistor 631 which acts as a negative modulating element. The negative modulating element is controlled using negative modulator drive subcircuit 632. The current output from modulation transistor 631 is also preferably conducted through an inductive choke 662 to help filter the modulated current and to help regulate current flow therethrough . The negative current output from inductor 662 is conducted through diode 652 and resistor R205 to a negative lamp discharge switching means Q104. Current is controllably conducted through the negative, lamp discharge switch 104 to discharge lamp 700. The negative lamp discharge

switching means is controlled using a negative lamp , discharge switching control subcircuit 670.

The negative side or channel of circuitry 600 is also provided with a negative high voltage arc initiation subcircuit 650. Negative arc initiation circuitry 650 functions in a manner similar to that described above with respect to the positive arc initiation circuitry 640. The relatively high voltage negative current produced by circuitry 650 is passed through diode 651 , resistor R205 and negative lamp discharge switching means Q104 to produce a brief relatively more negative discharge through lamp 700.

Fig. 2 shows a portion of circuitry 600 in greater detail than shown in the abbreviated bloc /schematic diagram presented in Fig. 1. Fig. 2 shows the voltage-varying line current being supplied at terminal M .

Positive and negative current supplied thereto is effectively divided into positive and negative components by diodes 613 and 614 , respectively.

Positive side diode 613 is connected with the anode towards the alternating current source conductor M. Negative diode 614 is connected with the cathode thereof connected to the incoming line voltage via conductor M. The cathode of positive diode 613 is connected to a positive converter storage capacitor C100. The other side of capacitor C100 is connected to the neutral conductor N . Similarly', the anode of negative diode 614 is connected to one side of a main negative converter capacitor C101. The other side of capacitor C101 is connected to the neutral line N . Capacitors C100 and C101 are connected across their terminals using resistors R200 and R201 , respectively , for slowly discharging these capacitors when power is turned off. The voltage produced at the first side of capacitor C100 and on conductor 617 is substantially DC positive current made available to remaining portions of the positive side of the electronic ballast 600. The negative substantially DC current developed on conductor 618 is similarly used to supply negative current to remaining portions of the negative side or channel of circuit 600.

Positive DC conductor 617 is connected to the drain connection of transistor 621. The gate of transistor 621 is connected to the positive modulator drive circuitry 622. The source connection of transistor 621 is also connected to drive circuitry 622. In an analogous manner , negative current conductor 618 is connected to the source connection of negative modulator transistor 631. The gate of transistor 631 is

connected to the negative modulator drive circuitry 632. The negative modulator drive circuitry 632 is also connected to the source connection of transistor 631. The drain connection of transistor 631 functions as a modulated negative current output terminal for the modulator and is connected to remaining portions of the circuitry to supply the primarj ¹ - power for discharge to lamp 700. The source connection of transistor 621 is similarly used as an output for the positive modulator to provide the primary modulated positive current for discharge through lamp 700. The modulated current from transistors 621 and 631 is preferably in the form of pulse width modulated pulses of positive and negative current, respectively. These modulation transistors are preferably turned fully on and fully off in order to minimize power dissipation during modulation of the positive and negative currents .

The positive output of the current modulator is connected to one end of inductor 661 and to the cathode of diode D200. The other end of inductor 661 is connected to resistor R202. The other end of resistor R202 is connected to one side of capacitor C102 and to the anode of diode 642. The other side of capacitor C102 is connected to the anode of diode D200 and to the neutral line N . The cathode of diode 642 is connected to one side of capacitor C104 and to the positive lamp discharge switching transistors 103 , such as at the collectors of parallel bipolar transistors Q103a and Q103b . The other side of capacitor C104 is connected to the neutral conductor N. The emitters of positive lamp discharge transistors Q103a and 103b are connected to resistors R204a and R204b , respectively. The other ends of resistors R204a and R204b are connected to the supply side of discharge lamp 700. The bases of positive switching means Q103 are connected via conductor AA to a suitable positive lamp discharge switching control circuit 660 , such as shown in Fig. 3 and described hereinafter. Modulated negative current from negative modulator transistor 631 is connected to one end of inductor 662 which acts as a filtering and energy storage device for taking the pulse modulated current and converting it back into a substantially DC signal at the opposite or output end thereof. The output end of inductor 662 is connected to resistor R203. The other end of resistor R203 is connected to the cathode of diode 652 and to one side of capacitor C103. The other side of capacitor C103 is connected to the neutral line N . The anode of diode 652 is connected to one side of capacitor C105 and to parallel

resistors R205a and R205b . Negative current is conducted through resistors R205a and b as controlled by the negative lamp discharge switching means which is preferably in the form of parallel bipolar transistors Q104a and Q104b . Transistors Q104a and b are connected with the emitters thereof to ends of resistors R205a and R205b , respectively . The collectors of transistors Q104a and O104b are connected together and to the supply side of discharge lamp 700. The bases of transistors Q104a and b are connected through conductor BB to a negative lamp discharge switching control subcircuit 670 which is shown in greater detail in Fig. 3 and described hereinafter .

The supply and neutral terminals of discharge lamp 700 are preferably connected across using a suitable excess voltage protection device such as a transzorb having zener diodes 708 and 709. Zener diode 708 is connected with the anode thereof to the supply side of discharge lamp 700 and the cathode thereof connected to the cathode of zener diode 709. The anode of zener diode 709 is connected to the neutral side of lamp 700.

Fig. 2 also shows the positive high voltage arc initiation circuitry 640 near the top thereof. Circuitry 640 is connected to the incoming line voltage M using a first side of capacitor C108. The second side of capacitor C108 is connected to the cathode of diode 645. The anode of diode 645 is connected to the neutral conductor N of the alternating current source . A resistor R207 is connected across capacitor C108 to allow slow discharge when power is terminated . The second side of capacitor C108 and the cathode of diode 645 are connected to the anode of diode 641. The cathode of diode 641 is connected to the cathode of diode 642 and to the collectors of the positive lamp discharge transistors Q103.

Fig. 2 also shows the negative high voltage arc initiation circuitry 650. Circuitry 650 includes capacitor C109 which has the first side thereof connected to the incoming voltage-varying line conductor M. The second side of capacitor 109 is connected to the anode of diode 655. The cathode of diode 655 is connected to the neutral line conductor N . Resistor R206 is connected across capacitor C109 to allow slow discharge when power is terminated. The second side of capacitor C109 is connected to the cathode of diode 651. The anode of diode 651 is connected to the anode of diode 652 and to negative lamp discharge switching transistors Q104 via resistors R205a and R205b .

The basic flow of positive and negative current used to power lamp 700 will now be described. During positive portions of the alternating current cycle of electricity source 601 current flows through diode 613 and is stored in capacitor C100. A number of cycles of positive current causes capacitor C100 to become sufficiently charged so as to supply a somewhat fluctuating but substantially DC positive current along conductor 617. Current is modulated through modulator transistor 621 while applying a voltage to the gate of transistor 621 which is sufficient to forwardly bias the transistor relative to the voltage applied at the source of transistor 621. This modulation control signal preferably turns the modulation transistor on and off at a frequency which is substantially greater than the operating frequency of the incoming line current. Preferably the frequency of the modulator is 10 or more times greater than the frequency of the incoming line current and the frequency of the alternating current supplied by the ballast to the discharge lamp . In the preferred embodiment shown the modulating transistor 621 operates at a frequency of approximately 100 KHz.

The modulated current is supplied in the form of DC pulses of brief duration which are conducted through inductor 661 to provide a modulated substantially DC output therefrom . The primary positive lamp discharge current passed through inductor 661 is also conducted through current sensing resistor R202 in order to provide a voltage differential thereacross which is used in control of the modulation circuitry using conductors P and Q. Inductor 661 , capacitor C102 and diode D200 form a current regulating, filtering and secondary energy storing function within the circuit. When positive lamp discharge switches Q103 are conductive, current flows through inductor 661 resistor R202 in a surge with substantially constant DC values being produced through diode 642. However, when switches Q103 are turned off, inductor 661 tends to continue conducting current as the magnetic field collapses thus drawing positive current through diode D200 from the neutral side of capacitor C102. The current flowing through diode D200 and inductor 661 passes through resistor R202 to the first side of capacitor C102. While lamp discharge transistors Q103 are turned off, the modulation transistor 661 continues to pulse reduced amounts of current therethrough in order to fully charge the energy storing and filtering circuit formed by inductor 661 , capacitor C102 and diode D200

to the full DC voltage of capacitor C100 , approximate +170 volts . This allows the circuitry to be in a fully charged condition and ready for discharge when the positive lamp discharge transistors Q103 are turned on for the next surge of positive current through discharge lamp 700. In the preferred embodiment shown the positive discharge transistors Q103 are turned on during positive portions of the line alternating current . The positive lamp discharge period defined by transistors Q103 being conductive is substantially coextensive with the positive portions of the AC cycle in the preferred embodiment . Relatively minor amounts of dead band time are preferably provided at the start of the positive portion of the line AC cycle and at the end of the positive portion of the line AC cycle in order to assure that there is no simultaneous conduction through the positive and negative lamp discharge transistors Q103 and Q104 and maintain their asynchronous operation . During positive lamp discharge periods substantially all current through lamp 700 is controlled by the positive lamp discharge transistors Q103. The substantial^- in-phase operation of positive lamp discharge transistors Q103 with respect to the line alternating current cycles is not necessary but is advantageous . The operation of the high voltage generating circuit 640 used for arc initiation will now be described . During a negative portion of line AC positive current is conducted from the neutral conductor N through diode 645 and on to the second side of capacitor C108. When the line AC current swings positive , the positive potential on the first side of capacitor C108 causes an increase in the voltage on the second side of C108 because the voltage across the capacitor tends to be maintained . In no load conditions the voltage is doubled . In loaded conditions the charge generated and stored on the second side of capacitor C108 is discharged through diode 641 for a brief portion of the lamp discharge cycle until the capacitor C108 is discharged to a point where the anode of diode 641 is at approximately the same voltage as the anode of diode 642. At that point conduction of the primary lamp operating current during the positive lamp discharge periods is provided by the modulated current flow passing through diode 642. The positive arc initiation circuitry 640 provides a relatively short duration flow of higher voltage current which is efficient for initiation of lamp discharge without requiring generation of high voltage current for all of the current used to power the discharge lamp .

Negative current flows from conductor M to lamp 700 in a manner substantially the same as described above with respect to the positive side . Specifically, negative current flow through diode 614 during the negative potential portions of the line alternating current provided on conductor M. The negative charge passed by diode 614 is stored on the first side of capacitor C101. The current modulating switch or gate 631 pulses the substantially DC current provided by conductor 618. The pulsed modulated current from gate 631 is conducted to inductor 662. Inductor 662, capacitor C103 and diode D201 provide the same regulating, filtering and energy storing function as described above with respect to positive inductor 661 , capacitor C102 and diode D200 with opposite polarity. The primary negative operating current passes through inductor 661, resistor R203 and diode 652 when negative lamp discharge switching transistors 104 are turned on. Transistors 104 are controlled by suitable biasing voltage via conductor BB using the negative lamp discharge switching control circuitry 670. Lamp discharge switches Q104 controllably discharge negative current through lamp 700. The discharge of negative current through lamp 700 occurs in asynchronous relationship to the discharge of positive current using lamp discharge switches Q103 , that is , the positive and negative transistors Q103 and Q104 are not conductive at the same time. The negative current discharge through lamp 700 , as shown, advantageously occurs during the negative potential portions of the incoming line alternating current. The negative lamp discharge periods defined by switches Q104 being turned on is preferably substantially coextensive with the negative potential portions of the line current in the preferred embodiment. During negative lamp discharge periods substantially all current through lamp 700 is controlled by the negative lamp discharge transistors Q104. Dead band space at the start and end of the negative lamp discharge period are also preferably provided to assure that no simultaneous conduction occurs through positive and negative lamp discharge switches Q103 and Q104.

Capacitors C104 and C105 serve to reduce noise at the collectors of transistors Q103 and 104, respectively, due to the relatively high impedances which exist at on conductors X and Y.

Although operation of the invention has been described above with respect to the positive lamp discharge periods being substantially coincident with the line AC positive potential portions and the negative

lamp discharge periods being substantially coincident with the negative potential portions of the line current , such is not necessarily required .

It is alternatively possible that the lamp operate at frequencies different from the line using switching transistor control circuitry which is suitably adapted. Other variations in frequency and relationship of the discharge lamp operating phase with respect to the phase of the incoming line current are also possible so long as the asynchronous operation is maintained between the positive and negative lamp discharge switching means Q103 and Q104 , respectively . The above descriptions give a general explanation of the flow of primary and arc initiating boosting current through the positive and negative current flow channels of the circuit 600. Discussion will now turn to the structural interrelationship of the driving circuits 660 and 670 used to control the positive and negative lamp discharge switches Q103 and Q104.

Fig. 3 also shows the positive and negative lamp discharge switching means 103 and Q104 , respectively , for ease of description and consideration. Positive power is supplied to the collectors of switching means Q103 via conductor X and negative current is supplied to the emitters of negative switching means Q104 via conductor Y through resistors R205a and b . The bases of positive lamp discharge switching transistors Q103 are connected to the positive lamp discharge switching control or driving circuitry 660. The bases of negative lamp discharge switching transistors Q104 are connected to the negative lamp discharge switching control circuitry 670. Fig. 3 further shows a power supply subcircuit 680 which is used to generate appropriate voltages on conductors marked T and U . The conductor marked Z is connected directly to the supply terminal 700a of lamp 700. The lamp neutral terminal is 700b . Circuitry 660 includes a suitable transformer 760 which includes a primary coil L20 and a secondary coil L21. The first side of primary coil L20 is connected to the neutral conductor M and the second side of the coil L20 is connected to hot lead M. The secondary coil L21 steps the voltage down to approximately ±8 volts when the primary coil is exposed to ±170 volts . The first side of secondary coil L21 is connected to conductor Z which is connected to the supply side 700a of discharge lamp 700. The second end of coil L21 is connected to the anode of diode 761 and other components . The cathode of diode 761 is connected

to the cathode of diode 762 and to first ends of resistors R210 , R212 and R213. The opposite end of resistor R210 is connected to the first side of capacitor C120 and to an end of a resistor R211. The anode of diode 762 is also connected to the first side of capacitor C120. The other side of capacitor C120 is connected to conductor Z . The other end of resistor R211 is connected to the collector of transistor 774. The base of transistor 774 is connected to resistor R214 with the opposite end of resistor R214 connected to the second end of coil L21. The base of transistor 774 is also connected to the cathode of diode 763 and the anode thereof is connected to conductor Z. The emitter of transistor 774 is also connected to conductor Z. The collector of transistor 774 is also connected to the emitter of PNP transistor 770. The collector of transistor 770 is connected to one end of resistor R215 and to the base of transistor 772. The opposite end of resistor 215 is connected to the emitter of transistor 772 and also to one end of resistor R216 and to one side of capacitor C121. The opposite side of capacitor C121 is connected to conductor Z. The opposite end of resistor R216 is connected to the anode of diode 764 which has the cathode thereof connected to the second end of coil L21. The second end of coil L21 is also connected to resistor R217. The opposite end of resistor R217 is connected to the base of transistor 773 and to one end of resistor R219. The opposite end of resistor R219 is connected to conductor Z. The collector of transistor 773 is connected to conductor Z. The emitter of transistor 773 is connected to the cathode of diode 765. The anode of diode 765 is connected to the collector of transistor 772 , the base of transistor 771, and to the cathode of diode 766. The base of transistor 771 is also connected to the second end of resistor R212. The collector of transistor 771 is connected to the second end of resistor R213 and the emitter of transistor 771 is connected to the anode of diode 766. The emitter of transistor 771 is also connected to a first side of resistor R218. The second end of resistor R.218 is connected to conductor Z-. The emitter of transistor 771 is further connected to a first side of capacitor C122 and to the bases of positive lamp discharge switching transistors Q103a and b . The base node for such transistors has been designated conductor AA which refers to the signal which drives the bases of these positive switching transistors . This designation is used merely for convenience in relating Figs . 10 and 11.

The positive lamp discharge sv/itching control circuitry 660 operates in the following manner. During positive portions of the incoming line current, a positive voltage is generated on the second side of coil L21. This positive voltage is referenced with respect to the first side of coil L21 which is connected to the voltage which is experienced on the supply side of the discharge lamp being powered . Thus the signal generated in coil L21 is superimposed on the alternating voltage existing on the supply side of the lamp . The relatively more positive voltage generated on the second side of L21 during positive portions of line current applies a relatively higher voltage to the base of transistor 774 than to the emitter thereof which is connected to Z which is effectively a control ground . This turns transistor 774 on causing conduction through diode 761 , resistors R210 and R211 to the collector of transistor 774 and on to conductor Z . The voltage generated at the node between resistors R210 and R211 is used to charge the first side of capacitor C120. Capacitor C120 is used to apply a minimum voltage of relatively DC current through diode 762 to the first sides of resistor R212 and R213. The conductive state of transistor 774 during the positive portion of the line cycle causes the emitter of transistor 770 to be pulled low thus turning transistor 770 off. This in turn causes the base and emitter of transistor 772 to reach a relatively equal voltage turning transistor 772 off.

The base of transistor 773 is forward biased during positive portions of line current thus drawing current through resistor R212 which forward biases the base-emitter junction of transistor 771 , This causes transistor 771 to turn on thus conducting current through resistor R213 to the bases of the positive lamp discharge switching transistors Q103a and b . The base voltage at conductor AA increases and decreases during the positive cycle in a substantially sinusoidal manner. The current through switching means Q103 is also substantially sinusoidal during the positive lamp discharge period . The positive lamp discharge period is approximately from 5° until 175° of the 180° positive line half cycle.

During the negative cycle of line current transistor 774 is turned off. This causes a relatively higher voltage to be applied from capacitor C120 through resistor R211 to the rmitter of PNP transistor 770 thus turning it on . When transistor 770 turns on , a relatively higher voltage is applied to the base of transistor 772 as compared to the

emitter thereof thus turning transistor 772 on. Diode 764 and capacitor C121 effectively form a peak detector which is negative in voltage at approximately -4 volts relative to Z . When transistor 772 turns on, this negative voltage is conducted through transistor 772 from emitter to collector and through diode 766 to affirmatively bias the base of the main lamp discharge switching transistors Q103 into a reverse biased condition across the bas.e-emitter junction. This reverse biased condition assures that the transistors are turned off and that positive current cannot be connected to the supply side of lamp 700 during negative lamp discharge periods .

The negative lamp discharge switching control circuitry 670 is constructed and operates in an analogous fashion to the positive circuitry 660 just described . Circuitry 670 includes a transformer 780 which has a primary coil L22 and a secondary coil L23. The first side of coil L22 is connected to neutral conductor N and the second side is connected to the voltage varying conductor M. The first side of coil L23 is connected to the cathode of diode 781 and other components . The second side of coil L23 is connected to conductor Y which is effectively used as the control ground for the negative lamp discharge switching control circuitry 670. The first side of coil L23 is also connected to one side of resistor R224, the other end of which is connected to the base of transistor 794. The base of transistor 794 is also connected to the cathode of diode 783 which has an anode connected to conductor Y. The emitter of transistor 794 is connected to conductor Y. The cathode of diode 781 is connected to one end of resistor R220. The other end of resistor R220 is connected to one end of resistor R221. The other end of resistor R221 is connected to the collector of transistor 794. A first side of capacitor C130 is connected to the node between resistors R220 and R221 and also connected to the anode of diode 782. The cathode of diode 782 is connected to the cathode of diode 781 and to first ends of resistors R220 , R222 and R223. The second side of capacitor C130 is connected to conductor Y. The collector of transistor 794 is also connected to the emitter of PNP transistor 790. The base of transistor 790 is connected to conductor Y and the collector thereof is connected to the base of transistor 792. Resistor R225 extends between the emitter of transistor 792 and the collector of transistor 790. The emitter of transistor 792 is also connected to the first side of capacitor C131 , the other side of which is connected to conductor Y .

The first side of capacitor C131 is connected to one end of resistor R226 and the other end of that resistor is connected to the anode of diode 784. The cathode of diode 784 is connected to the first side of coil L23. The collector of transistor 792 is connected to the base of transistor 791 and to the anode of diode 785 and cathode of diode 786. The cathode of diode 785 is connected to the emitter of PNP transistor 793. The base of transistor 793 is connected via resistor R227 to the first side of coil L23. Resistor R229 is connected between the base of transistor 793 and conductor Y . The collector transistor 793 is connected to conductor Y . The collector of transistor 791 is connected to a second side of resistor R223. The emitter of transistor 791 is connected to the bases - of negative lamp discharge transistors Q104 , the anode of diode 786 , and one side of resistor R228. The other side of resistor R228 is connected to conductor Y . A capacitor C132 is connected between the bases of the negative lamp discharge switching transistors 104a and b and conductor Y . Conductor BB represents the negative lamp discharge switching control circuitry output signal to the negative lamp discharge switching means Q104.

In operation the negative lamp discharge switching control circuitry 670 generates a relatively more positive voltage at the first end of coil L23 during the negative cycle portions of the incoming line current . The circuit otherwise operates in the manner described above with respect to positive circuit 660 except that it is of opposite polarity and out of phase in operation because of the opposite relationship between primary and secondary coils L22 and L23 of transformer 780. This results in the base conductor BB being forward biased in a substantially sinusoidal fashion during the negative portion of the incoming line alternating current cycle . It also results in a reverse bias on the base-emitter junction of transistors Q104a and b during the positive cjrcle portions of the incoming line current .

Control circuits 660 and 670 provide for asynchronous operation of the positive and negative lamp discharge switching means Q103 and 104. In the preferred embodiment as shown the positive lamp discharge switching transistors Q103 are conductive during the positive portion of the AC line cycle . The negative lamp discharge switching transistors Q104 are biased into a conductive mode during the negative portion of the incoming line AC current . Although this in-phase relationship is preferred in the embodiment as shown and described , it is

alternatively possible to operate the lamp discharge transistors partially out of phase or directly out of phase with the incoming line alternating current cycles . However , the positive and negative lamp discharge switching means Q103 and Q104 must be operated asynchronously or otherwise be adapted to prevent application of the positive and negative currents to lamp 700 at the same time.

Fig. 3 also shows small power supply subcircuit 680 which includes a resistor R230 which is connected to the second end of coil L23 . The other end of resistor R230 is connected to the anode of diode 767 and to the cathode of diode 768. The cathode of diode 767 is connected to one side of capacitor C123 and to one end of resistor R231. The other side of capacitor C123 is connected to conductor Z . The other end of resistor R231 is connected to conductor T and to one end of resistor R232. The other end of resistor R232 is connected to conductor Z. Conductor T is communicated to the modulation circuitry shown in Fig. 4A.

In operation diode 767 allows positive current to flow therethrough and charge capacitor C123. This provides a substantially DC voltage riding on the alternating voltage defined by conductor Z. Conductor T provides a substantially constant +4 volt level over the alternating voltage existing on conductor Z which is connected to the supply side of lamp 700. The +4 volts of conductor T ^" with respect to conductor Z defines the target voltage differential used in the control of the positive pulse width modulator described below . Circuit 680 also includes a negative power supply using diode 768 which has the cathode thereof connected to resistor R230 and the anode thereof connected to one side of capacitor C124. The other side of capacitor C124 is connected to conductor Z. The anode of diode 768 is also connected to one end of resistor R.233. The other end of resistor R233 is connected to conductor U and to one end of resistor R234. The other end of resistor R234 is connected to conductor Z. This portion of the power supply circuitry 680 generates a voltage of approximately -4 volts at conductor U with respect to the alternating voltage existing on conductor Z. The voltage on conductor U is utilized in the negative modulator driving circuitry 632 described belov; with respect to Fig. 5 A. The circuitry generating the voltage at conductor U functions in substantially the same manner as that described above with respect to the generator of the voltage on conductor T

except that diode 768 is oppositely oriented in order to pass the negative portion of the alternating current generated in coil L21 thereby leading to the -4 volt supply voltage at conductor U versus the +4 volts supply voltage on conductor T. Figs . 4 A and 4B show the drive circuitry for controlling operation of the positive modulator transistor 621. The inputs to this system include the signal T which is the target +4 differential voltage generated by circuitry 680 with respect to the lamp supply terminal. Inputs also include signal P which is generated at the node between inductor 661 and current sense resistor R202. Final input is signal Q which is generated on the other side of resistor R202. Resistor R202 is shown in Fig. 2 and the voltage drop thereacross is indicative of the amount of current which is being passed through inductor 661. The outputs from the system are the HH signal and II signal which are connected to the gate and source terminals of transistor 621 to control its pulse modulation operation . In general the circuitry of Figs . 4A and 4B are referenced to Q which is the voltage at the lower voltage end of current sense resistor R202.

Fig. 4A shows the +4 volt power supply conductor T with respect to conductor Z being connected to the circuit at one end of resistor R250 and to an anode of diode 801. The second end of resistor 250 is connected to resistor R251. The cathode of diode 801 is connected to the other side of resistor R251 which is also connected to a third resistor R252. The second end of resistor R252 is connected to resistor R253. The second end of resistor R252 is also connected to the anode of diode 802 and cathode of diode 803 as well as to the inverting input (-) of operational amplifier A5 and one end of feedback resistor R254. The second end of resistor R254 is connected to the output of operational amplifier A5. The second end of resistor R253 is connected to conductor Q which is functioning substantially as a referenced ground and to the cathode of diode 802 and the anode of diode 803. The inverting or plus (+) input of operational amplifier A5 is connected to one end of resistor R255 with the opposite end of resistor R255 being connected to conductor Q . The resistors R250 , R251 , R252 and R253 are connected between the

T conductor and Q conductor to form suitable voltage drops therebetween . Diode 801 is connected to provide protection against

excessive swing in the operational amplifier A5. Diodes 802 and 803 similarly limit the swing of the minus input of that operational amplifier.

The error signal generator 623 also includes operational amplifier A6 which is connected to function as a current sensing comparator. The inverting input of operational amplifier A6 is connected to the Q conductor via input resistor R258. The noninverting input is connected to conductor P via input resistor R259. Thus the inputs to this operational amplifier are connected across the current sensing resistor R202 shown in Fig. 2. The inverting input of operational amplifier A6 is also connected to one end of resistor R260 and one end of feedback resistor R261. The other end of resistor R260 is connected to conductor EE which supplies an approximately +0.7 volt reference with respect to conductor Q. The opposite end of feedback resistor R261 is connected to the output of amplifier A6. Amplifier A6 is also connected to conductor FF which is a +5 volt supply with respect to conductor Q, and is generated in pulse width modulator chip 860 shown in Fig. 4B . Operational amplifier A6 is also connected at another power connection to an approximately -4.3 volt power supply generated in conductor 816 by a 3.6 volt zener diode 809 connected in series with diode 815 to conductor Q.

The output of current sensing comparator A6 is connected to the cathode of diode 808 and the anode thereof is connected to a first end of resistor R263. The opposite end of resistor R263 is connected to the cathode of diode 818, the base of transistor 807 , and a first end of resistor R264. The anode of diode 818 is connected to conductor Q . The other end of resistor R264 is connected to the cathode of zener diode 809 and the cathode of diode 815. The anode of diode 815 is connected to conductor Q . The collector of transistor 807 is connected to the cathode of diode 815. The output of amplifier A5 is connected to ends of resistors R256 and R257. The other end of resistor R257 is connected to the cathode of diode 804 and to the anode of diode 805. The cathode of diode 804 is connected to the base of NPN transistor 806. The base of NPN transistor 806 is also connected to resistor R262. The opposite end of resistor R262 is connected to the +0.7 volt power supply line EE from power supply circuitry 817. The collector of transistor 806 is also tied to the +0.7 volt supply EE. The emitter of transistor 806 is connected to the second end of resistor R256. Resistor R256 and the emitters of

transistors 806 and 807 are connected to the noninverting input of operational amplifier A8 via resistor R269. A capacitor C140 is connected between the emitter of transistors 806 and 807 and conductor Q to suppress high frequency noise . The signal generated at the node marked 819 connected to the second end of resistor R256 and the emitters of the transistors 806 and 807 defines the output from the inner signal generator 623. This output , is received by the integrator circuitry 624.

The error signal generator 623 operates by sensing the voltage drop across resistor R202 of Fig. 2 using this as an indicator of the amount of current flowing from inductor 661. Under normal operating conditions during positive lamp discharge periods the comparator A6 has minimal effect on the error signal from amplifier A5 at node 819. powever during startup and negative lamp discharge periods the output from comparator A6 operates to limit the swing on error signal node 819 thus reducing the amount of current pulsed through the modulator . Operational amplifier A5 in general produces an error signal output which fluctuates plus or minus to 0 volts relative to conductor Q . The output of A5 is dependent upon the voltage drop across diode 642 , the positive lamp discharge switching means Q103 , and resistors 204 , all shown in Fig. 2. Transistors 806 and 807 operate in an inverting mode of operation to limit the range of the error signal at node 819 to ±0.7 volts relative to conductor Q. The error signal is then communicated to integrator circuitry 624. Integrator circuitry 624 includes operational amplifiers A7 and A8.

As explained above , the output from error signal generator 623 is received at the noninverting input of operational amplifier A8. The inverting input to amplifier A8 is connected to the output from operational amplifier A7 via resistor R268 . The inverting input of operational amplifier A8 is also connected to the output thereof via feedback resistor R270. The inputs to amplifier A7 include signal Q at the noninverting input via resistor R266. The inverting input to operational amplifier A7 is connected to the output thereof via a feedback loop and resistor R267. The inverting input of amplifier A7 is also connected via resistor R265 to the output of amplifier A8. The output of operational amplifier A8 is connected to resistor R271 at the first end thereof. The second end of resistor R271 forms the integrator output

and is connected to one side of high frequency filter capacitor C141. The other side of capacitor C141 is connected to conductor Q .

Fig. 4A also shows a power supply section 817. Power from the alternating current line is received through conductor M which is connected to one side of coupling capacitor C142. The other side of capacitor C142 is connected to resistor R281. The other end of resistor 281 is connected to the anode of diode 811 and the cathode of diode 810. The anode of diode 810 is connected to capacitor C152 which has its other side connected to conductor Q. The anode of diode 810 is also connected to the -anode of zener diode 809 via resistor R280. The alternating current passed across capacitor C142 is selectively divided with negative charge collecting on capacitor C152 and positive charge collecting on capacitor C143. Diode 815 and zener diode 809 limit the charge on capacitor C152 to produce the -4.3 volt signal referenced to conductor Q.

The positive charge stored on capacitor C143 is connected to conductor LL which provides an approximately +17 volt signal with respect to conductor Q. Resistor R282 is connected between conductor LL and the cathode of zener diode 812. Capacitor C144 is connected from the cathode of zener diode 812 across to conductor Q . Zener diode 812 allows an approximately +12.1 volt signal to be generated on conductor MM. Capacitor C144 serves to stabilize the voltage generated at that node and on conductor MM. The anode of zener diode 812 is connected to the first end of resistor R283. The second end of resistor R283 is connected to the first end of resistor R284 which has its second end connected to conductor Q . The anode of zener diode 812 is connected to the anode of diode 813. The cathode of diode 813 is connected to the anode of diode 814 which has its cathode connected to conductor EE in order to generate the EE signal which is approximately +0.7 volt with respect to conductor Q. The conductor marked GG communicates a biasing signal to the base of transistor 821 shown in Fig.- 4B . This turns transistor 823 on which draws current from the approximately +5 volt supply FF through resistors R296 and R297 and transistor 821 to conductor Q . The node between resistors R296 and R297 is connected to a comparator 863 which forms a subcircuit within the pulse width modulator chip 860. The capacitor C147 is connected between the same input node and conductor Q . Function of transistor 821 is to provide a soft startup

procedure for the pulse width modulator chip so that initial transient voltage fluctuations occurring during initiation of power to circuitry 600 does not cause damage within the chip .

Fig. 4B also shows that the integrator output signal on conductor CC is communicated to the pulse width modulator chip 860 via resistor R294 to a first error amplifier 861 existing within the pulse width modulator chip . The noninverting input of error amplifier 861 is connected not only to resistor R294 but to one end of resistor R293. The opposite end of resistor R293 is connected to the approximately +5 volt power supply conductor FF. Conductor FF is also connected to resistor R292 at the first end thereof. The second end of resistor R292 is connected to the inverting input of internal error amplifier 861. Resistor R290 is connected between conductor Q and the inverting input of amplifier 861. The inverting input of amplifier 861 is also connected to a first end of resistor R291. The second end of resistor R291 is connected to the output of second error amplifier 862 and to a first side of capacitor C146. The other side of capacitor C146 is connected to capacitor C145 which is also connected to a power pin driving the first error amplifier 861. The opposite side capacitor C145 is connected to conductor Q.

Pulse width modulator chip 860 functions in the typical manner by receiving the output signal CC from integrator 624 and processing it through error amplifier 861 which is communicated to a digital logic section 865 within the chip . An oscillator 864 within chip 860 provides a triangle wave function which is advantageously set to 100 KHz as determined by the values of capacitor C148 and resistor R298 which are connected between chip 860 and control ground .

The pulse width modulator chip internal logic 865 drives internal push-pull transistors 866 and 867. Transistors 866 and 867 are connected with the emitters thereof connected to conductor Q . The bases of transistors 866 and 867 are connected to logic unit 865 , and the collectors thereof are connected to pins which conduct output signals from chip 860. The collector output from transistor 866 is connected to the base of transistor 832 , the cathode of a constant current diode 830 , and the cathode of diode 831. The anode of constant current diode 830 is connected to the approximately +17 volt supply provided on conductor LL with respect to conductor Q . Conductor LL is also connected to the collector of transistor 832 supply driving current

thereto which is controllably conducted from the emitter. Diode 831 is connected with the cathode to the collector of transistor 866 and the anode to the emitter of transistor 832. Diode 833 is connected with its anode to the emitter and its cathode to the base of transistor 832. The emitter of transistor 832 is also connected to one side of a coupling capacitor C150. The other side of coupling capacitor C150 is connected to the first end of primary coil L30 of a transformer 880. The opposite or second end of coil L30 is connected to the emitter of transistor 842. The base of transistor 842 is connected to the collector of the second push pull transistor 867. The constant current diode 840 is connected with the cathode thereof to the base of transistor 842 and the anode thereof connected to conductor LL. Diode 841 is connected with the cathode thereof to the collector of transistor 867 and the anode thereof connected to the emitter of transistor 842. Diode 843 is connected with the anode thereof connected to the emitter of transistor 842 and the cathode connected to conductor LL.

The pulse width modulator chip operates with the push pull transistors 866 and 867 switching at the desired modulation frequency such as 100 KHz. This causes pulses of current to flow through primary coil L30 which induce pulses of current in the secondary coil L31 of transformer 880.

Secondary coil L31 is connected with the first end thereof connected to the anodes of diodes 851 and 852 and the cathode of diode 855. The second end of coil L31 is connected to the anodes of diodes 853 and 854 and to the cathode of diode 856. The anodes of diodes 855 and 856 are connected to conductor II which as shown on Fig. 2 is connected to the source of the positive modulation transistor 621. The cathodes of diode 851 is connected to the emitter of PNP transistor 859 and to resistor R299. The opposite end of resistor R299 is connected to the gate of modulation transistor 621. The collector of transistor 859 is connected to the source of transistor 621. The base of transistor 859 is connected to the cathodes of diodes 852 and 854. The base is also connected to the anode of constant current diode 857 which has its cathode connected to the source of transistor 621. Capacitor C151 is connected between the gate and source of transistor 621.

The output from integrator circuit 624 is conducted by conductor CC which is communicated to the pulse width modulator and its associated interface componentry as shown in Fig. 4B . Conductor FF

carries a relatively fixed 5 volt voltage supply relative to conductor Q. This voltage supply passes through resistor R292 and R290 to conductor to generate a relatively fixed +2. 5 volts to the minus input of the operational amplifier 861 within pulse width modulator 860. In a similar fashion the +5 volt voltage supply connected to conductor FF conducts current through resistor R293 and resistor R295 to conductor Q . This also tends to generate the same +2. 5 volt signal at the plus input of operational amplifier 861 with respect to the voltage on conductor Q. The integrated signal on conductor CC passes through resistor R294 to vary the input at the plus terminal of operational amplifier 861. This causes the output of amplifier 861 to vary and control the logic section 865 of the pulse width modulator . The logic section 865 controls the operation of push pull transistors 866 and 867 so that only one of the transistors is conductive at any particular time . Operational amplifier 862 is biased into an inoperative condition and performs no useful function in this circuit . Comparator 863 turns the logic section 865 on after an appropriate initial start up period is defined by the soft start circuitry described hereinabove .

When logic circuitry 865 turns first push pull transistor 866 on , it effectively connects the conductor Q to the base of transistor 832. This causes transistor 832 to turn off. At the same time transistor 867 is turned off which allows the regulated current flow through constant current diode 840 to be applied to the base of transistor 842 which turns transistor 842 on to conduct current from the +17 volt conductor LL through transistor 842 to the first coil L30 of transformer 880. The current path passes through coil L30, capacitor C150 and diode 831 and down through transistor 866 to conductor Q . The conduction of current through transistors 842 and 866 produces a relatively negative voltage at the dot or first end of the secondary coil L31. Accordingly, the second end of coil L31 is relatively more positive which generates current flow through diodes 853 and 854. Current flow through diodes 853 and 854 causes the base and emitter of transistor 859 to be at approximately the same voltage thus turning transistor 859 off. This allows positive current through diode 853 to pass through resistor R299 to the gate of transistor switch 621 thereby turning it on . The constant current diode 857 maintains the source of transistor 621 at a diode drop lower voltage than the gate thus assuring conduction through transistor 621 when a pulse is received .

In the opposite situation when second push pull transistor 867 is conductive , this causes transistor 842 to be turned off. When transistor 867 is turned on , then transistor 866 is turned off according to the logic of 865. When transistor 866 turns off, it causes the base of transistor 832 to rise in voltage towards conductor LL at +17 volts thus turning transistor 832 on to conduct positive current from conductor LL which is capacitively coupled across the capacitor C150 to generate a relatively more positive voltage at the first or dotted end of primary coil L30 which in turn induces a relatively positive voltage at the first or dotted end of secondary coil L31.

The gate of transistor 621 is forwardly biased with respect to the source when current is conducted either through push pull transistors 866 or 867. When the push pull transistors switch , there is a drop in current through coil L30. The charge ^stored on capacitor C151 thus discharges through resistor R299 and raises the emitter of transistor 859 higher in voltage than the base which is discharged through the constant current diode 857. This causes transistor 859 to turn on which causes the gate and source to be connected together thus turning the modulator transistor 621 off. Power is modulated by transistor 621 by controlling the duty cycle during which transistors 866 and 867 are both off, thus increasing or decreasing the current with decreasing or increasing off time, respectively, per cycle of the push-pull transistors 866 and 867.

The negative modulator drive circuitry 632 is shown in Figs . 5 A and 5B . In general the circuitry construction is the same as that shown in Figs. 4A and B and as described above , except with respect to certain polarity changes which will be described below and the fact that the inputs and outputs from the circuit are connected into the general electronic ballast circuit 600 with respect to the negative channel rather than to the positive channel. The inputs to the negative error signal generator is via conductor U which generates a -4 volt supply relative to the lamp supply terminal 700a. Diode 901 is used in lieu of diode 801 with diode 901 connected with the cathode thereof connected to conductor U and the anode thereof connected between resistors R251' and R252' . Resistor R252' has its opposite end connected to the plus input of operational amplifier A5\ Resistor R253' is connected from the plus input of operational amplifier A5' to the conductor R. Diodes 902 and 903 are connected in parallel between the plus input of operational

amplifier A5' and conductor R in opposite orientation . Feedback resistor R254' is connected from the output of amplifier A5' to the plus input.

Conductors R and S are connected at opposite ends of the negative current sense resistor R203 shown in Fig. 2. Conductor S is connected to the minus input of operational amplifier A6' using input resistor R259' . The plus input of operational amplifier A6' is connected to conductor R via input resistor R258' .

Remaining portions of negative modulator drive circuit 632 are the same as described above with respect to positive modulator drive circuitry 622 with the added prime to indicate usage in the negative channel. The outputs from the pulse width modulator chip 860' and its coupling circuitry result in signals on conductors JJ and KK which are connected to the gate and source of negative modulating transistor 631 , respectively.

The operation of negative modulating drive circuitry is substantially the same as described above with respect to the positive modulating drive circuitry 622 with proper consideration given to the opposite polarity . Table VI below presents preferred values of resistance , inductance and capacitance for resistors , inductors and capacitors useful in a preferred form of circuit 600.

TABLE VI

RESISTORS

R200 , R201 150K ohms

R202 , R203 0. 1 If

R204A , B 0. 47 fl

R205A , B 0. 47 II

R206 , R207 470K II

R210 82 It

R211 2. 2K It

R212 680 11

R213 20 It

R214 3. 3K II

R215 10K It

R216 220 1!

R217 3. 3K It

R218 270 II

R219 220 11

R220 82 II

R221 2.2K "

R222 680

R223 20

R224 3. 3K "

R225 10 K

R226 220

R227 3. 3K "

R228 270

R229 220

R250 R250' 1. 5M "

R251 R251* 1. 5M ^" "

R252 R252' l 1 o ~muirv.

R253 R253' 47K

R254 R254 ¹ 560K

R255 R255' 47K

R256 R256' 12K

R257 R257' 13K

R258 R258' 10K

R259 R259' 10K

R260 R260' 330K

R261 R261' 3. 6 "

R262 R262' 3. 3K "

R263 R263' 2. 2K "

R264 R264' 3. 3K "

R265 R265* 470K

R266 R266' 240K

R267 R267' 470K

R268 R268' 470K

R269 R269' 240K

R270 R270' 470K

R271 R271' 18K

R280 R280' 68

R281 R281' 33

R282 R282 ^τ 330

R283 R283' 1. 6K "

R284 R284* 1. 6K "

R290 R290' 100K

R291 R291' 47K

R292 R292' 100K

R293 R293' 100K

R294 R294' 47K

R295 R295' 100K

R296 R296' 33K

R297 R297' 10K

R298 R298' 33K

R299 R299' 33

CAPACITORS

C100 , C101 560 microfarads

C102 , C103 3

C104 , C105 0.02

C108 , C109 5

C123 47

C124 47 It

C140, C140' 0.02 If

C141, C141' 0.1 11

C142, C142' 1 11

C143, C143' 330 11

C144, C144' 47 It

C145, C145' 0.1 11

C146, C146* 0.01 II

C147, C147' 0.47 II

C148, C148' 220 picofarads

C149, C149* 0.47 microfarads

C150, C150' 0.1 II

C151, C151' 0.002 it e 1 In TUTl.PT 1 υ noxvu c

661, 662 700 microhenries

Industrial Applicability

The inventive apparatuses and methods described herein are useful for powering electrical discharge lamps.