Koninklijke Philips Corporation N.V.

Philips Electronics North America Corporation

Feng-Kang Hu

Yimin Chen

Yongping Xia

Sreeraman Venkitasubrahmanian

Nicolaas Hendrik Mario Pol

Clint Mason

Zhenggang Yang

Jaap Schlejen

A self-oscillating bridge circuit comprises a start circuit for rendering one of the switches conductive for the first time at the start of operation. The start circuit is configured in such a way that it does not influence the switching of the bridge switches during stationary operation.

Circuit arrangement including DC-AC converter having a dependable start circuit

In an electronic ballast for operating a discharge lamp at a high frequency, a single feedback and a double pump feedback are implemented in a combined way. The resulting electronic ballast combines the advantageous of a simple topology with favorable properties with respect to power factor, THD, efficacy, crest factor of the lamp current and EMI restrain.

Circuit arrangement

A ballast for a gas discharge lamp includes a detection circuit which detects an operating state of the lamp in which the lamp current for the column discharge of one polarity is different from the lamp current for the column discharge of the other polarity by detecting the DC component of the voltage across the discharge lamp. The detection circuit includes (i) a device coupled such that a DC voltage is imposed there across when the lamp current is different for the column discharge according to one polarity verses the other polarity, and (ii) a sensing circuit for sensing the DC voltage across the device. The device may be a capacitive device, and in a particularly inexpensive implementation, is a DC blocking capacitor or a ballast capacitor. The sense circuit senses when the DC voltage across the device exceeds a threshold value, which may corresponds to fully-rectified state of the lamp or more favorably, to a lesser state of imbalance. In another embodiment, the variance in the DC voltage across the lamp is detected at the midpoint of a bridge inverter. A control circuit changes the output of the ballasting circuit when the DC voltage exceeds the threshold value to turn off the lamp or to recurrently cycle the lamp on and off to signal the user that the lamp needs to be changed.

Lamp ballast with lamp rectification detection circuitry

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Palos Verdes Estates, CA, United States of America

Feng-Kang Hu