PURPOSE:To eliminate unintentional ON of a transistor by forming a resonator by a tank circuit consisting of the secondary winding of an output transformer and a tank capacitor, and providing an attenuator for attenuating a ringing surge generated in the transformer. CONSTITUTION:When an AC power source is turned ON, a base current flows through a bias resistor 38 to a transistor 32 with increase in the output of a full-wave rectifier 2. When the transistor 32 is turned ON, an inverter 3 is oscillated by the resonance of the inductance of a feedback loop from the collector of the transistor 32 through the primary winding 31P, feedback winding 31F, a resistor 36 and a capacitor 35 to the base and the secondary winding 31S with a capacitor 33. Thus, a high-frequency output is generated in the winding 31S of an output transformer 31. A resistor 36 inserted into the feedback circuit prevents the excess effect of a ringing surge across the base and the emitter of the transistor 32 to prevent it from again becoming ON.
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