Transistor inverter circuit for supplying constant current output

Claim 1

In a constant current supply circuit for providing constant current to a load having variable resistance characteristics comprising input means for connecting said circuit to the first and second terminals of a DC power source, a first and second transistor, each of which has a collector, base and emitter element, transformer means having a center-tapped primary winding, a center-tapped feedback winding, an output winding, capacitor means connected across one of said transformer windings, means connecting the center tap of said primary winding over said input means to the first terminal of said source, means connecting the collector elements of said first and second transistors to said primary winding on opposite sides of said center tap, means connecting said base elements to said feedback winding on opposite sides of said center tap, common resistance means connecting the emitter elements of said first and second transistors common to the second terminal on said source, control means for providing a control voltage to the center tap of said feedback winding, and output means including said output winding for deriving an output for said load, said capacitor means and the magnetizing inductance of said transformer means providing at least a part of a tank circuit for effecting operation of said transistors in an oscillatory mode, the circuit components including said common resistance means, the number of turns on said transformer output winding, the number of turns on said center-tapped primary winding, and the number of turns on said feedback winding being of a value to provide a control voltage to the base elements of said transistors which has an amplitude which varies the level of oscillation of the signal output from said transistors by a value to compensate for the changing core loss of the transformer which occurs with changes in the resistance load thereby maintaining the load current constant.