PURPOSE: To eliminate unnecessary losses by connecting a Zener diode for setting applied maximum voltage connected in series with a transistor (TR) of the pre-stage and a diode for blocking reverse flow of control signal to eliminate the need for a current disabling the control.
CONSTITUTION: When a control signal is applied between terminal 13 and 12, a collector current equivalent to a hFE multiple of a CD current amplification factor of the base current flows. When a TR12 is at an active region, the base current of a TR11 is applied via the Zener diode CD and the TR11 is operated so that the collector current equivalent to hFE times is equal to the collector current of the TR12. In this case, the level of the diode CD12 reaches a potential of reverse blocking and a base current of the TR11 from a terminal 13 is not applied. When the TR12 is in the saturated region, the base current of the TR11 is fed to the TR11 from the terminal 13. When it is necessary to decrease the collector-emitter voltage of the TR11, the diode CD11 is cut off by increasing a drive signal through the diode CD12 and the collector current is made depending on the level of the terminal 13.
KAWAKAMI YOUICHI
NAKAJIMA HIROSHI
OSABE RIYOUJI
TOSHIBA KK