VOLTAGE COMPENSATED FIRING CIRCUIT

A firing circuit for firing a number of controlled rectifiers in which there are a number of slave controlled rectifiers, each of which is associated with a storage capacitor for firing the slave controlled rectifier upon discharge of the storage capacitors. A master controlled rectifier is connected in circuit with the storage capacitors for discharging the storage capacitors to fire the slave controlled rectifiers upon firing of the master controlled rectifier. There is a timing circuit including a programmable unijunction transistor which conducts when its anode voltage exceeds its gate voltage by more than its junction voltage drop. The gate of the programmable unijunction transistor has a selectively variable connection to a voltage divider circuit, which, in turn, is connected in circuit across the pulsating potential source. A first Zener diode is connected in circuit across the pulsating potential source and a resistance-capacitance circuit is connected across the Zener diode. The anode of the programmable unijunction transistor is connected to the charging circuit. The gate of the master controlled rectifier is connected to the cathode of the programmable unijunction transistor for firing the master controlled rectifier, and thus the slave controlled rectifiers, upon conduction of the unijunction transistor. The voltage divider circuit, in one form includes a second Zener diode, having a lower regulating voltage than the first Zener diode, for providing a regulated voltage to the programmable unijunction gate. In another version, the voltage divider circuit is connected to the first Zener diode through a dropping resistance for providing the gate of the programmable unijunction transistor with a regulated voltage.