A switching power circuit having a power factor improving circuit for a composite resonance type converter, wherein a switching pulse is fed back from a tertiary winding, which is coiled around an insulating converter transformer, via a series resonance capacitor. And a rectified current is turned on and off by a fast recovery diode in accordance with the feedback output, hence achieving power factor improvement. In this structure, a smoothing capacitor is charged with the resonance current even during an off-period of the fast recovery diode due to the resonance of a series resonance circuit including the series resonance capacitor. This circuit configuration eliminates the necessity of selection of a higher withstand voltage relative to the primary-side smoothing capacitor by suppressing rise of the DC input voltage in a no-load state.

A circuit for supplying AC voltage and current to a gaseous discharge lamp upon the application of DC voltage and current, the circuit comprising: a transformer including a first and a second primary windings; a first capacitance means, coupled across the primary windings to define a resonant circuit; a start-up current source coupled to a drive terminal; first and second transistors coupled to the drive terminal; at least one drive winding coupled on one end to the drive terminal and coupled on the other end to the base of one of the transistors; and first and second current-blocking devices, in one embodiment a diode and in another embodiment a transistor, each current-blocking device configured so as to block a current from flowing into the emitter element of one of the transistors. Additionally, the circuit comprises a means for establishing a constant current flow between the base terminals of the transistors, sufficient to maintain the circuit in an oscillating mode, the means having a linear inductor, a resistor and at least one diode. In another embodiment, the circuit has one drive winding coupled to the base element of the first transistor switching means, and a parallel combination of a second capacitance means and a second resistor means coupled to the base element of the second transistor switching means.

A pre-converter is connected with AC power line voltage and provides DC rail voltage to a current-fed self-oscillating FET bridge inverter ballast. The inverter is loaded by way of a parallel-tuned L-C circuit connected across the bridge inverter's output, thereby providing a sinusoidal AC output voltage thereat. Each of several instant-start fluorescent lamps is connected via a current-limiting capacitor across the bridge inverter's output. The magnitude of the DC supply voltage is so chosen as to cause the magnitude of the AC output voltage to be such as to effectuate proper instant-starting of the fluorescent lamps. Each of the four FET's is driven by a sinusoidal AC voltage derived directly from a positive feedback winding on the tank-inductor of the L-C circuit. To enhance circuit efficiency, the absolute magnitude of the DC rail voltage is controlled to be just higher than the peak absolute magnitude of the AC power line voltage.

A circuit for supplying AC voltage and current to a gaseous discharge lamp upon the application of DC voltage and current, the circuit comprising: a transformer including a first and a second primary windings; a first capacitance means, coupled across the primary windings to define a resonant circuit; a start-up current source coupled to a drive terminal; first and second transistors coupled to the drive terminal; at least one drive winding coupled on one end to the drive terminal and coupled on the other end to the base of one of the transistors; and first and second current-blocking devices, in one embodiment a diode and in another embodiment a transistor, each current-blocking device configured so as to block a current from flowing into the emitter element of one of the transistors. Additionally, the circuit comprises a means for establishing a constant current flow between the base terminals of the transistors, sufficient to maintain the circuit in an oscillating mode, the means having a linear inductor, a resistor and at least one diode. In another embodiment, the circuit has one drive winding coupled to the base element of the first transistor switching means, and a parallel combination of a second capacitance means and a second resistor means coupled to the base element of the second transistor switching means.

In an electrical circuit for feeding a fluorescent lamp, a serial resonant circuit is comprised of a first coil of a feedback-transformer, a resonant inductor, a coupling condenser, a first lamp cathode, a resonant condenser, and a first coil of an isolating transformer, this serial resonant circuit being connected between the output of an inverted rectifier, connected to a voltage supply source and one terminal of said voltage supply source, with a second coil of the isolating transformer being connected in parallel with the second lamp cathode. If the coils of the isolating transformer have the same number of loops, this connection of the second lamp cathode ensures that the same heating current will flow through both lamp cathodes, so that these will be heated equally. The parallel circuit of the second lamp cathode with the second coil of the isolating transformer is connected through a resistance with a terminal of the supply voltage. The lamp current flows through this resistor, thus the voltage across the resistor is proportional to the actual current of the lamp and it can therefore be transmitted to the main circuit which regulates the lamp current.