Abstract: The power supply, well suited for powering a metal halide lamp, includes a rectifier with an AC input and a DC output. A power transformer has its primary winding connected to the DC output and its secondary winding connected to the lamp. A pulse-width-modulated (PWM) controller is coupled to the primary winding for controlling the flow of power therethrough. A smoothing circuit is connected to the lamp for reducing the rate of change of the current flowing through the lamp. Avoiding filtering of the rectifier output, maintaining a constant pulse width of the PWM controller throughout the period of the AC input power and filtering switching-frequency current components from the input to the rectifier provides a sinusoidal input current to the power supply which is substantially in phase with the input voltage. Such supply has a power factor of over 99%.

Abstract: Disclosed is a DC-powered spark-generating circuit for igniting fuel. Such circuit has two primary windings on a common transformer core and a separate transistor controlling power to each primary winding. Each transistor has a gate and a drain and such gates and drains are "cross-coupled." That is, the gate of the first transistor is coupled to the drain of the second transistor and the drain of the first transistor is coupled to the gate of the second. Also disclosed is a method for spark-igniting fuel. Such method includes applying a voltage across an air gap at a first frequency, establishing an arc across the air gap and maintaining the arc at least until the fuel ignites. Such arc is maintained at a second frequency which different from (and preferably higher than) the first frequency.