| 摘要 |
An improved high intensity discharge ("HID") ignition circuit for a ballast uses a gapped transformer with a capacitor placed across the secondary thereof. The ballast includes a DC source, a down converter, a commutator, and the ignition circuit. The output of the commutator is supplied to the secondary winding of the gapped transformer and the lamp, which are connected in series. The lamp is an HID lamp such as, for example, a metal halide lamp, high pressure sodium lamp, high pressure mercury lamp, or a metal vapor lamp. Power is furnished to the lamp over a cable. Ignition of the lamp is handled by the ignition circuit, which in addition to the secondary winding and the capacitor includes an inductor, the primary winding of the gapped transformer, two SIDACs, and the parallel combination of a resistor and a capacitor, all connected in series between the output of the down converter. The design parameters of the gapped transformer are selected so that the gapped transformer does not saturate at full load current. The capacitor across the secondary of the gapped transformer adjusts the resonance frequency of the secondary circuit for shaping the ignition pulse so that the ignition pulse specification of the HID lamp is met throughout the full range of load conditions for which the ballast is intended, including varying load capacitance as affected by length of the cable.
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