Power source for fluorescent lamps and the like

Claim 1

In a high frequency, high voltage power source for a load such as gas discharge lamps, the combination of: an inverter comprising an oscillator circuit and transformer, said transformer having primary, secondary and feedback windings, said oscillator circuit including a transistor having emitter and collector electrodes connected in series with said primary winding across a pair of dc input terminals and having the base and one of said electrodes connected across said feedback winding; an inverter starting circuit including a first resistor and first capacitor connected in series across said dc input terminals, and a breakdown device connected between the junction of said resistor and capacitor and said base, with said capacitor charging through said resistor and discharging through said breakdown device providing a starting current pulse to said transistor; a protection winding on said transformer; a second resistor connected in series at one of said dc input terminals; a thermal circuit breaker for shunting said second resistor; and heating circuit means connected across said protection winding and positioned adjacent said circuit breaker; with said transformer providing an increased output at said protection winding when there is no load at said secondary winding for energizing said heating circuit means and actuating said circuit breaker to the open condition and developing a voltage drop across said second resistor reducing the current in said primary winding and transistor, and with said heating circuit means including a third resistor for heating said circuit breaker and a second breakdown device permitting current flow through said third resistor from said protection winding when the protection winding voltage exceeds a predetermined amount.