Patent ID: 8638042
Filing Date: 2014-01-28
Classification: H05B,Y02B

Abstract:
1. A lamp ballast comprising: a buck inverter circuit having a pair of high frequency switching elements and a pair of low frequency switching elements arranged in a full bridge configuration between positive and negative rails of the ballast; a capacitor and an inductor coupled in series between a first node between the low frequency switching elements and a second node between the high frequency switching elements; a lamp igniting circuit at least coupled between the first node and a first lamp output terminal, a second lamp output terminal being coupled to a third node between the capacitor and the inductor; and a control circuit having inputs coupled to the second node, the third node and the negative rail, and effective to turn on and off the switching elements based on an inverter operation, the control circuit further effective during an open circuit operation to regulate a low frequency square wave voltage generated across the first and second output terminals to be less than an input DC voltage from the positive rail, wherein the buck inverter operates in either of a critical discontinuous mode or a discontinuous mode during an open circuit operation.