| 摘要 |
An improved switch-mode power supply is disclosed having a direct current power source, a transformer with a primary winding, at least one secondary winding and a core, first and second switching transistors and series with the primary winding of the transformer and drive means for generating signals to switch on the switching transistors to complete a circuit through the direct current power source, the switching transistors and the primary winding. In the improved circuit, a connection is provided through a diode to complete a circuit through the first switching transistor and part of the primary winding on activation of the drive means, drawing energy from a junction between two reservoir capacitors in series. The current from this circuit generates a field in the core of the transformer which is sensed by an auxiliary winding on the transformer connected to the second switching transistor. The signal generated in the auxiliary winding switches on the second switching transistor, allowing a circuit to be completed through both switching transistors and the entire primary winding of the transformer. In a further embodiment of the circuit particularly useful in push-pull converters, third and fourth switching transistors are also provided in series with the primary winding of the transformer to complete a second circuit through the direct current power source, the third and fourth switching transistors and the primary winding. The drive means sends two series of pulse-width modulated drive pulses, the first series switching on the first switching transistor in order to complete a circuit ultimately through the first and second switching transistors and the whole of the primary winding in one direction, and the second series of pulses, 180- out of phase from the first, to switch on the third switching transistor, in order to ultimately complete a circuit through ths third and fourth switching transistors and thQ whole of the primary winding in the opposite direction. A rebalance winding on the core of the transformer and related circuitry are also provided where necessary to replace energy drawn from the junction between the reservoir capacitors to maintain the reservoir capacitors in balance.
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