Constant current signal generator having transistor burnout protection device

Claim 1

A SIGNAL GENERATOR FOR PROVIDING A CONSTANT CURRENT OUTPUT TO AN ELECTRICAL LOAD HAVING DIFFERENT IMPEDANCE CONDITIONS COMPRISING IN COMBINATION, AN OSCILLATOR FOR PRODUCING AN ALTERNATING CURRENT OUTPUT, AMPLIFIER MEANS COUPLED TO SAID OSCILLATOR FOR INCREASING THE MAGNITUDE OF SAID OSCILLATOR OUTPUT, A TRANSFORMER FOR COUPLING SAID AMPLIFIER MEANS TO SAID ELECTRICAL LOAD, SWITCHING MEANS ELECTRICALLY CONNECTED ACROSS THE PRIMARY WINDING OF SAID TRANSFORMER FOR CONDUCTING CURRENT AND REMOVING THE OPERATING BIAS VOLTAGE FROM SAID AMPLIFIER MEANS WHENEVER SAID ELECTRICAL LOAD BECOMES OPEN CIRCUITED, AND SENSING MEANS RESPONSIVE TO THE CURRENT COUPLED TO SAID ELECTRICAL LOAD FOR FEEDING BACK A SIGNAL PROPORTIONAL TO THE DIFFERENCE BETWEEN THE AMPLITUDE OF THE CURRENT COUPLED TO SAID ELECTRICAL LOAD AND THE AMPLITUDE OF SAID CONSTANT CURRENT TO THE OSCILLATOR WITH SUCH POLARITY AS TO CONTROL SAID OSCILLATOR ALTERNATING CURRENT OUTPUT IN SUCH MANNER AS TO MAINTAIN A SUBSTANTIALLY CONSTANT CURRENT TO SAID ELECTRICAL LOAD.