generated in the circuitry 30 and supplied to the gate g of the scr to control the firing thereof since the fire pulse generating circuitry 30 is completely disassociated from the fire sensitivity control circuitry i e npn transistors q2 and q3 the circuitry 30 is not limited to any specific type of circuitry e g npn transistors and the type and variety of circuitry which can be used to trigger the scr is greatly enhanced referring to fig3 an scr circuit similar to that illustrated in fig2 is disclosed however in this circuit the fire sensitivity control circuitry is attached to the base of a pnp transistor q101 the emitter of which is connected to the anode a of the scr and the collector of which is connected to the base of transistor q100 further a fire pulse generator is connected to an external gate g which is connected to the base of the transistor q1 in the scr thus while the fire sensitivity control circuitry is practically limited to pnp type transistors to interface with transistor q101 the fire pulse generator is not limited to any specific type of transistors or semiconductor devices it will of course be understood by those skilled in the art that the transistors q2 q3 and q101 will generally be switching transistors which normally operate in one of two modes when the switching transistor is conducting it provides a very low impedance and when the switching transistor is non conducting it provides a very high impedance.