GB1299024A - Interruptor circuit - Google Patents

Abstract

1299024 Converting STANDARD TELEPHONES & CABLES Ltd 3 May 1971 12674/71 Heading H2F [Also in Division H3] In an inverter or chopper, a main transistor 1 has positive feedback via a transformer 2 so as to ensure rapid saturation when turned on and has a controllable impedance device, such as transistor 28, connected across two more windings of transformer 2 and arranged to present a low impedance when it is desired to turn off transistor 1, thus rapidly discharging stored carriers. As described, a positive-going half cycle of a square wave at 4 turns off transistors 21 and 28 so that the voltage induced in winding 24 of a ferrite-cored transformer 2 turns on the main transistor 1, initiating current in a load circuit 31, 32. Transistor 1 rapidly becomes saturated because of positive feedback via windings 23 and 24. Terminal 35 is biased negatively with respect to 36 during this time. The next half cycle of the input at 4 turns on transistors 21 and 28 thus, short-circuiting windings 25 and 26 and removing the input to transistor 1. The average value of current in transistor 1 may be controlled by pulse-width modulation of the input at 4. Modifications.-A further transistor 1 may be included if the circuit is to chop the output of an A.C. source. Two switching circuits as shown may be employed as an inverter.