TECHNICAL FIELD

The present invention relates to an electronic starter in a fluorescent lamp apparatus.

More particularly, the present invention relates to an electronic starter through which a fluorescent lamp can be turned on instantaneously.

BACKGROUND ART

Fig. 1 is a circuit diagram for showing a conventional fluorescent lamp apparatus in which a fluorescent lamp is turned on through a glow starter 1.

In a conventional f_αorescent lamp apparatus as shown i.n Fig. 1, since glow discharge operation is maintained for a considerably long time interval, starting performance is inferior. As a result, darkening with which a fluorescent lamp 2 turns black is caused in fluorescent lamp 2.

In case a low voltage is supplied to the conventional fluorescent lamp apparatus, it takes a long time interval which is needed for turning on fluore ent lamp 2 , or fluorescent lamp 2 will not be turned or.. Further, since spark noise is generated during turn-on operation of fluorescent lamp 2, it exerts harmful influence on household electric appliances and electric communication eguip ent. Further, as the darkening effect becomes widespread, both sides of fluorescent lamp 2 continues to flicker, and starter 1 and a ballast 3 become overheated.

As a result, the lifetime of ballast 3 comes to be shortened and a fire may occur.

DISCLOSURE OF INVENTION

Therefore, it is an object of the present invention

to provide an electronic starter in a fluorescent lamp apparatus for increasing the lifetime of a fluorescent lamp and for instantaneously turning a fluorescent lamp on using semiconductor switch section including power semiconductor device such as a MOS-FET.

It is another object of the present invention to provide an electronic starter in a fluorescent lamp apparatus for turning a fluorescent lamp on at a low voltage. Further, it is another object of the present invention to provide an electronic starter in a fluorescent lamp apparatus for preventing the overheating of a ballast by use of a semiconductor switch section which automatically turns off during flickering effect. In achieving the above objects, an electronic starter in a fluorescent lamp apparatus according to the present invention comprises: a semiconductor switch section for turning on when AC voltage is positively applied through a ballast and filaments; a first semiconductor switch driving section for facilitating current flow between drain and source of the semiconductor switch section; a first switch trigger voltage supplying section for supplying trigger voltage to drive the first semiconductor switch driving section; and a second semiconductor switch driving section for supplying a negative trigger voltage for gate terminal of the semiconductor switch section and so as to turn the semiconductor switch section off when AC voltage is negative.

In an electronic starter in a fluorescent lamp apparatus according to the present invention, since the starter includes semiconductor devices such as a MOS-FET, a fluorescent lamp can be turned on instantaneously and electric power saving can be attained.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and other advantages of the present invention will become more apparent by describing in detail the preferred embodiment of the present invention with reference to the attached drawings, in which:

Fig. 1 is a ircuit diagram for showing a conventional fluorescent lamp apparatus in which a fluorescent lamp is turned on through a glow starter; Fig. 2 is a circuit diagram for showing a circuit of an electronic starter according to an embodiment of the present invention;

Fig. 3(A) is a waveform vs. time graph for showing AC power source voltage Vs according to the present invention;

Fig. 3(B) is a waveform vs. time graph for showing voltage V _L across both output terminals of a fluorescent lamp while starting to turn on a fluorescent lamo according to the present invention; Fig. 3(C) is a waveform vs. time graph for showing preheating current i _L which flows into filaments o* fluorescent lamp while starting to turn on a fluorescent lamp according to the present invention;

Fig. 4 is a waveform vs. time graph for showing voltage VL' across both output terminals of a fluorescent lamp after turning on a fluorescent lamp according to the present invention; and

Fig. 5 is a graph for showing the operation of MOS-FET in a semiconductor switch section according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

A description will be given below in detail to the structure and operations of an electronic starter in a fluorescent lamp apparatus according to an embodiment of the present invention with reference to the accompanying drawings.

Fig. 2 is a circuit diagram for showing a circuit of an electronic starter according to an embodiment of the present invention. As shown in Fig. 2, an electronic starter in a fluorescent lamp apparatus according to an embodiment of the present invention comprises a semiconductor switch section 10 turning on when AC voltage is postiviely applied to a ballast 103 and filament Fl; a first semiconductor switch driving section 30 facilitating current flow between drain and source of semiconductor switch section 10; a first switch trigger voltage supplying section 20 supplying trigger voltage for driving first semiconductor switch driving section 30; and a second semiconductor switch driving section 40 supplying a negative trigger voltage for gate terminal of semiconductor switch section 10 so as to turn semiconductor switch section 10 off.

The circuit structure of each of the sections is as follows.

Semiconductor switch section 10 consists of a diode Dl for rectifying positive half wave while voltage of power source is applied, and a MOS-FET Q3 in which the drain terminal is connected to the cathode of diode Dl . First switch trigger voltage supplying section 20 consists of a snap diode D5 for driving first semiconductor switch driving section 30, an electrolytic condenser C2 in which a positive terminal is connected to both the anode of snap diode D5 and the source terminal of semiconductor switch section 10, and resistor R4 connected to a negative terminal of condenser C2.

First semiconductor switch driving section 30 is n kind of double serial amplifier and consists of a resistor R6 to which the trigger voltage is applied from first switch trigger voltage supplying section 20, a condenser C3 with which a time constant is determined, a resistor R5 parallel connected to condenser C3, a resister R7 and a resistor R8 each connected in shunt with resistor R5, a

transistor Ql in which the base is connected to e first terminal of resistor R~ , a transistor Q2 in which the base is connected to the collector of transistor Ql and the collector is connected to the gate of semiconductor switch 10 and the emitter is connected to the source of semiconductor switch 10 and to the emitter of transistor Ql through a resistor R9 and a resistor RIO to which power source voltage Vs is applied.

Second semiconductor switch driving section 40 consists of a diode D2 in which the cathode is connected to a filament Fl while diode D2 is ON with a negative AC voltage, a Zener diode D3 in which the anode is connected to the anode of diode D2 and the cathode is connected in shunt with a resistor Rl and a resistor R2 for drivinq a negative voltage, a condenser Cl connected to a resistor R3 for regulating current and the gate of semiconductor- switch section 10 so as to supply the trigger voltage, a Zener diode D4 pεrallel connected to condenser Cl, resistor Rl connected in shunt with condenser Cl, and Zener diode D4, resistor R2 connected to a negative terminal of electrolytic condenser C2, and resistor R3 connected to a positive terminal of electrolytic condenser C2.

Fig. 3(A) is a waveform vs. time graph for showing AC Power source voltage Vs according to the present invention. Fig. 3(B) is a wave form vs. time graph for showing voltage V _L across both output terminals of a fluorescent lamp while starting to turn on a fluorescent lamp according to the present invention. Fig. 3(C) is a waveform vs. time graph for showing preheating current i _t which flows into filaments of a fluorescent lamp while starting to turn on a fluorescent lamp according to the present invention.

Fig. 4 is a wave form vs. time graph for showing voltage VL' across both output terminals of a fluorescent lamp after turning on a fluorescent lamp according to the present invention. Fig. 5 is a graph for showing the operation of MOS-FET in a semiconductor switch section

according to the present invention.

The rating of AC power source according to the present invention is not restricted to 110V/220V and 50Hz/60Hz. When switch 104 is ON so as to turn on fluorescent lamp 100, voltage V _L across fluorescent lamp 102 has part of voltage waveform in a positive cycle of time interval Tl to T2 which is the starting of operation. At T2, diode D2 is OFF with a reverse bias and diode Dl is ON with a forward bias.

Thus, a positive AC voltage and a negative AC voltage are respectively applied to the drain and the source of MOS-FET Q3 so that semiconductor 10 may turn on and filaments Fl, F2 come to be preheated through resistor R10.

As gate-to-source voltage VGS is zero, the current flowing from the drain to the source is not enough to preheat filaments Fl, F2. Part of the current passing through semiconductor switch portion 10 preheats filaments Fl, F2 through resistor R10. The remainder of the current flows into electrolytic condenser C2 of first switch trigger voltage supplying section 20. A half-wave -rectified positive voltage is rectified with double voltage and charged in electrolytic condenser C2 so that the remainder of the current turns snap diode D5 on and is discharged through resistor R4. Then, discharging of electrolytic condenser C2 is partial and charging of electrolytic condenser C2 tries to continue until fluorescent lamp 102 turns on. The trigger voltage is supplied for first semiconductor driving section 30 through snap diode D5 and applied to the base of transistor Ql. Then, the base of transistor Ql is forward biased according to the respective setup of values for timing condenser C3 and resistor R5, and transistor Ql turns on as the collector current flows when the base-to-emitter voltage is not less than a threshold voltage. As the collector current of transistor Ql increases, most of the collector voltage is

applied to resistor R7 so that transistor Ql turns off.

Since the base of transistor Q2 is biased with the collector-to-emitter voltage and the voltage applied to resistor R9 with turning transistor Ql off, the transistor Q2 turns on. As transistor Q2 turns on, the current flows into the collector of transistor Q2.

With continuing increase in the collector current and consequent saturation in the collector-to-emitter voltage, most of the voltage is applied to resistor R5. Then, cut-off in the collector current will result in turning transistor Q2 off.

With turning transistor Q2 off collector-to-emitter voltage VCE is established, -producing an increase of collector-to-emitter voltage VCE with amplifying operation. The double serial-amplifier constituting an essential part in first semiconductor switch drivinq section 30, is not subject to the characteristics of frequency restriction so that the double serial-amplifier is able to amplify DC voltage. As shown in Fig. 5, MOS-FET Q3 operates in a depletion mode when gate-to-source voltage VGS is equal to zero.

When to the gate terminal of semiconductor switch section 10 is applied collector-to-emitter voltage VCE of transistor Q2 corresponding to a double-amplified voltage of a base bias-voltage of transistor Ql, MOS-FET Q3 operates in an enhancement mode such that the gate of MOS-FET Q3 is supplied with a positive trigger voltage from first semiconductor switch driving section 30. A - with enhancement mode operation of MOS-FET Q3, channel width between drain and source becomes increased and the magnitude of current is increased, so that enough preheating current is supplied for a path consisting of switch 104, ballast 103, filament Fl, diode Dl, drain-to-source of MOS-FET Q3, resistor R10 and filament F2.

The aforementioned operation is possible because the value of drain current ID of MOS-FET Q3 is given by the formula

when filament F2 starts to be preheated, the voltage across fluorescent lamp 102 is egual to zero, so that all power source voltage Vs is applied to ballast 103.

As shown in Fig. 3(C), prior T2 the preheating current flowing though filaments Fl, F2 start to be supplied slower than AC power source voltage Vs due to an inductance of ballast 103. The preheating current flowinα through filaments Fl, F2 has a maximum value for predetermined time interval, starting from the time a positive gate voltage reaches maximum value, and decreases gradually with a decrease in the trigger voltaqe until Tl when a positive half period of AC power source voltaqe V3 terminates.

A negative half period of power source voltage Vs starts from T3, and then diode Dl becomes OFF with the power source voltage Vs negative, first switch trigger voltage supplying section 20 becomes OFF with snap diode D5 reversed-biased. With first switch trigger voltage supplying section 20 OFF, first semiconductor switch driving section 30 ceases to supply pulse for the gate terminal of MOS-FET Q3. At T3 semiconductor switch section 10 doesn't turn on fluorescent lamp 102 but continues to preheat fluorescent lamp 102 such that semiconductor switch section 10 continues to operate even though the gate-to-source voltage becomes zero T3 to T4 second semiconductor switch driving section 40 operates.

Thus, diode D2 conducts with forward bias, Zener diode D3 sustains a Zener voltage with reversed bias when voltage as much as Zener voltage is applied to Zener diode D3. Resistors Rl, R2 divide a negative voltage. When condenser Cl parallel connected to Zener diode D4 supplies a Zener voltage for Zener diode D4, a trigger voltage is applied to the gate terminal of semiconductor switch section 10 so as to begin to decrease the channel width gradually.

After Zener diode D4 is triggered, electric charges

in condenser Cl are completely discharged. As a result, as shown in Fig. 5, MOS-FET Q3 of semiconductor switch section 10 operates in an depletion mode when the value of gate-to-source voltage VGS reaches a cut-off voltage. When the value of gate-to-source voltage VGS becomes cut-off voltage VGS(off), semiconductor switch section ]0 turns off, so that the preheating current flowing through filaments Fl, F2 is cut off at T4 (as shown in Fig. 3 (C)). Then, as shown in Fig. 3(B), as the preheatinq current is instantaneously cut off at T4, from T4 to T , counter electromotive force is generated due to choke coil of ballast 103, and ιigh voltage pulse voltaqe Ldi/dt is generated.

T4 to Tl ' turning fluorescent lamp 102 on is implemented with the resultant voltage adding high voltage pulse voltage Ldi/dt to power source voltage Vs.

As described above, preheating and turn-on operations are repeated every half cycle, and fluorescent lamp 102 turns on after filaments Fl, F2 are fully preheated. As shown in Fig. 4, after fluorescent lamp 102 turns on, voltage across both end terminals VL' becomes decreased, and current flows through filaments Fl, F2 and fluorescent material within fluorescent lamp 102,. so that all operations of the electronic starter of the present invention ceases with a small current less than a sustaining current.

Consequently, in an electronic starter according to the present invention, since turning fluorescent lamp 102 on is implemented with the resultant voltage adding high voltage pulse voltage Ldi/dt to power source voltage VS, turning fluorescent lamp 102 on is implemented instantaneously as compared with a conventional fluorescent lamp apparatus using glow starter, and the life span of fluorescent lamp 100 can be increased owing to the instantaneous turn-on operation. Further, since the magnitude of preheating current is small and the time necessary to apply a high voltage is short, electric power necessary to turn on fluorescent lamp 102 can be

considerably saved.

Further, in an electronic starter according to the present invention, in case the darkening effect in fluorescent lamp 102 is widespread or flickering effect continues to cause both ends of fluorescent lamp to flicker without turning fluorescent lamp 102 on after making several attempt for turn-on operation and MOS-FFT Q3 begins to be heated due to above flickering effect, the value of drain-to source inner resistance increases, therby producing a gradual decrease in the drain-to-source current. As a part of current is discharged from filament Fl directly to filament F2 through fluorescent material, the role of first switch triggering voltage supplying section 20 becomes gradually inactive after a predetermined time elapses, so that zero becomes the sustaining current necessary to bias the base of transistor Ql in first semiconductor switch driving section 30 and first semiconductor switch driving section 30 is automatically off. Accordingly, as the current follows through MOS-FET Q3 becomes less than a sustaining current, MOS-FET Q3 is OFF, and stops preheating and hiσh voltage pulse functions stop so as to prevent overheatinα.

Consequently, in an electronic starter according to the present invention, when Ac power source voltage Vs is positive, a trigger voltage is applied to the σate terminal of semiconductor switch section 10 using characteristics of MOS-FET Q3 through first semiconductor switch driving section 30, facilitating flow of drain-to-source current, so as to fully preheat filaments Fl, F2. When AC power source voltage VS is negative cycle voltage, filaments Fl, F2 are fully preheated by operating second semiconductor switch driving section 40. Then, filament Fl, F2 are continuously preheated and the preheating current is cut off instantaneously, producing high voltage pulse Ldi/dt in ballast 103, so that fluorescent lamp 102 can be instaneously turned on by the resultant voltage adding the high voltage pulse Ldi/dt to power source voltage Vs.

In the above, the present invention is described based on the preferred embodiment of the present invention, out it should be apparent to those ordinarily skilled in the art that various modifications and change can be added without departing from the scope of tlv present invention which is limited only by the appended claims.