| 摘要 |
A pulse-width modulator (103) controls a switching transistor (Q1). The switching transistor is coupled to a primary winding (W1) of a chopper transformer (T). The switching transistor and the primary winding are referenced to a nonisolated ground conductor. To initiate a standby mode of operation, a first on/off control signal (ON/OFF) that is referenced to an isolated ground conductor disables a horizontal oscillator (37) that is energized from a secondary winding (W4) of the chopper transformer and that is also referenced to the isolated ground conductor. As a result, a decrease loading (iS4) of circuit elements that are referenced to the isolated ground occurs. In the standby mode, current pulses in the primary winding (iP1) are produced at a substantially higher frequency than in normal operation. A frequency detector (31) referenced to the nonisolated ground generates a second on/off control signal (V13) that is referenced to the nonisolated ground in accordance with the frequency of the current pulses in the chopper transformer. In this way, the second on/off control signal is generated without the need for an additional isolation element other than the chopper transformer. <IMAGE> |
