Samsung Electronics Co., Ltd.

Maeng-ho Seo

Nak-choon Choi

A feedback control system of ballast which has function to detect the number of lamp and is applied to an integrated circuit to control the ballast for a fluorescent lamp etc, and provides the ballast with the feedback control system which can detect the number of lamp, control ballast continuously by means of the n-lamp detector and soft start controller which produce the compensated current from the feedback current and direct link voltage. Therefore, the feedback control system can control the ballast accurately according to the load change such as the change of input voltage, number of lamp.

Preheat current control circuit based upon the number of lamps detected

Switching loss in push-pull switching transistors in a resonant inverter or the like, is minimized by assuring the switching of each of the transistors into conduction occurs when the voltage across its principal conduction path is zero-valued, or substantially so. This is done responsive to sensing the flow of forward currents through clamp diodes connected across the principal conduction paths of each of the transistors. This sensing is done so as to avoid the need for an additional coupling transformer. More particularly, the current flow to or from either of the terminals of the primary direct voltage supply, which current flow is in a first direction when either of the switching transistors is conductive and is in a second direction opposite to the first direction when the clamp diodes are conductive, is sensed for determining the times when the switching transistors are to begin to be conditioned for conduction. The switching transistors begin to be conditioned for conduction when the current flow is in the second direction.

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Seoul, South Korea

Maeng-ho Seo