Abstract: A saturating inductor or transformer is used to shape input current flowing into an alternating current (AC) to direct current (DC) power supply to correct the power factor for the supply. If a saturable inductor is used, it is connected to feed current into the power supply and a capacitor is connected across the input of the power supply. The capacitor precharges the saturable inductor to a point just short of saturation during a preliminary portion of each sinusoidal half cycle of the input AC power. For steady state operation, this is the point at which current will start to flow into the AC to DC power supply and the inductor will saturate. Since the inductance falls in accordance with a permeance curve characteristic of material used to construct the inductor, the current will continue to flow at the same or an increasing level despite the declining voltage level of the AC input power.

Abstract: A solid state ballast includes a pulse width modulation (PWM) circuit to maintain substantially constant power to a discharge lamp over its lifetime. The PWM circuit is powered from a high voltage (HV) DC source and is referenced to the source voltage level. Lamp power is maintained substantially constant provided the HVDC source maintains at least a normal lamp operating voltage level and is operated at a reducing power levels as the HVDC source voltage drops below the normal lamp operating level. Lamp operating power can also be controlled by selecting the PWM reference voltage level. For initial power-up, a bootstrap power supply is provided to power solid state circuitry of the ballast from the HVDC source. The bootstrap power supply is shut-down by operation of a primary low voltage power supply or if operated for more than a few seconds. A lamp is driven through a capacitor which is charged to a high voltage for lamp ignition.