Self-oscillating power supply

Abstract

A self-oscillating circuit particularly adapted for driving the deflection yoke of a cathode ray tube (CRT) or a high voltage pulse transformer is disclosed. The circuit includes an NPN transistor, to the collector of which is coupled a direct voltage source and a first inductance and to the base of which is coupled a second, grounded inductance. Following transistor turn-on, the collector current ramps up in storing energy in the first inductance. With the transistor base drive removed, a voltage spike appears on the transistor's collector to which is coupled a grounded capacitor. The LC network comprised of the first inductance and the grounded capacitance attempts to resonate, with the collector voltage clamped by the transistor collector-base junction. The energy stored in the first inductance flows via the grounded voltage source and the collector-base junction of the forward biased transistor into the second inductance until the energy stored in the first inductance has been reduced to the point where the transistor's collector-base junction is no longer forward biased. Continued current flow through the second inductance to the transistor's base turns the transistor on, causing current to be reversed in the first inductance in repeating the cycle as energy is again stored therein. Transistor base drive stops when the energy in the second inductance is depleted. The values of a resistance in series with the second inductance and the aforementioned capacitance determine the circuit's oscillatory period.