Phase detection control circuit for an electronic ballast

Details Phase detection control circuit for an electronic ballast Phase detection control circuit for an electronic ballast

1998-02-12

1999-12-14

Vu, David H.

Electric lamp and discharge devices: systems

Current and/or voltage regulation

Automatic regulation

315244, 315224, 315194, 315291, 315DIG4, G05F 100

Patent

active

060022140

ABSTRACT:
A circuit for controlling the operating power of a fluorescent lamp by detecting the phase of the lamp resonant circuit current and regulating the phase of the current, thereby regulating the lamp power. In the preferred embodiment of the circuit, the phase of the resonant circuit current is detected using a sense resistor disposed between the low side power transistor of a half-bridge driver and ground, or between the lower voltage lamp filament and ground. The zero-crossings of the resonant circuit current is detected by comparing the voltage across the sense resistor to zero voltage. Using these zero crossings, a phase pulse is generated representing the lamp resonant circuit current as a function of time. This phase pulse is compared to a reference pulse to generate an error signal indicative of the phase difference between the phase pulse and the reference pulse. The frequency of the oscillating half-bridge driver is controlled in accordance with the error signal, such that the lamp power, and hence the brightness, is increased or decreased as necessary to keep the phase of the lamp resonant circuit locked to the phase of the reference pulse.

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