| 摘要 |
A double forward DC-to-DC converter with soft-PWM switching provides two voltage pulses to the output low-pass filter within one switching cycle (hence, the name double forward). The double forward DC to DC converter includes a transformer having a single primary winding and a two secondary windings. A main switch, under the control of a PWM control circuit, is connected is series with the primary winding. An auxiliary switch is coupled across with the main switch by way of a resonant capacitor. The resonant capacitor and auxiliary switch are used to automatically reset the transformer core while the main switch is on back to the voltage source connected to the transformer primary. A diode and snubber capacitor is connected across the drain-source terminals for both the main and auxiliary switches for minimizing switching losses. The current mirror used in prior art is abandoned in order to avoid the locked-up mode of operation. The secondary windings of the transformer are connected to a pair of saturable reactors which, in turn, are connected to rectifier diodes in order to eliminate the reverse recovery losses of the rectifier diodes. A freewheeling diode is connected across the secondary winding and cooperates with the saturable reactors to maintain the load current to the secondary windings during the transitions of the main and auxiliary switches.
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