Power switching circuit for a pulsed laser

Abstract

A power switching circuit for providing variable pulse width drive signals for a laser in response to pulsed control signals. The power switching circuit includes a transformer circuit and a power transistor output circuit. The transformer circuit comprises a first pair of primary windings coupled to input terminals through a switch and an associated pair of secondary windings coupled to the output circuit to apply switching signals thereto. The transformer circuit further includes a second pair of primary windings coupled through a resistor to the input terminals with a polarity opposite that of the first pair. Control signals having a pulse width and repetition rate associated therewith are applied to the switch. During inter pulse intervals the voltage applied to the second pair of primary windings biases the transformer into saturation in a direction opposite to that of the first pair. The transistor output circuit includes three power transistors arranged in parallel with their bases coupled to the transformer circuit secondary windings and their collectors coupled to the laser tube cathode. A clamping circuit including a diode and capacitor is coupled to the collector emitter output of the transistors in close proximity thereto to protect the transistor output circuit from the effects of line inductance when the high current laser drive signal to the cathode is suddenly terminated by the action of the power switching circuit.