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EMI reduced commutation of HID lamps

IP.com Disclosure Number: IPCOM000019942D
Publication Date: 2003-Oct-13
Document File: 2 page(s) / 15K

Publishing Venue

The IP.com Prior Art Database

Abstract

ID611396, ID611397 and ID611398

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ID611396, ID611397, ID611398

EMI reduced commutation of HID lamps

    HID lamps are often supplied with a square wave shaped AC current. When the polarity of the lamp current is changed the lamp extinguishes and has to be reignited. Often the lamp reignites and subsequently extinguishes a couple of times during a few microseconds before the lamp operation becomes stable once more after reignition.

    This behavior causes EMI (radio interference). To prevent this radio interference the following possibilities exist.

    The first possibility is illustrated in Fig. 1. Fig. 1 shows a ballast circuit with a lamp La connected to it. The ballast circuit comprises a bridge circuit with a load circuit comprising an inductor (Lignition) and a capacitor Cextra connected to it. By choosing the value of the capacitor comparatively large, the current through the inductor has increased to a relatively large value when the voltage across the capacitor Cextra and thus across the lamp is high enough to reignite the lamp. Because of the high inductor current and the large amount of charge on the capacitor, the "take over" of the lamp is good and only one reignition voltage peak is generated reducing EMI. A drawback of the use of such a large capacitor is that it is very difficult to ignite the lamp for the first time. This drawback can be overcome by switching the capacitor Cextra out of the circuit during first ignition of the lamp or by igniting the lamp for the first time making use of re...