| 摘要 |
A switching power supply has first and second switching elements that are alternately turned on to cause an alternating current to flow through a primary winding of a transformer. The alternating current flowing through the primary winding induces voltages respectively across first and second secondary windings of the transformer. Synchronous rectifying transistors are turned on by the voltages induced across the first and second secondary windings, causing a current to flow alternately through the first and second secondary windings. Either one of the first and second switching elements is turned on while the other is being turned off, except for short off-times in which both the first and second switching elements are prevented from being turned on. As a result, when currents flow through the first and second secondary windings, the synchronous rectifying transistors are turned on. Therefore, no current flows through internal parasitic diodes of the synchronous rectifying transistors, and hence any loss caused thereby is very small.
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