Patent ID: 8009448

Claim:
A forward-flyback DC/DC converter, comprising: an isolated transformer having a primary winding, a first secondary winding and a second secondary winding, wherein the two secondary windings are connected in series to form a center-tapped configuration and their common node is grounded; a main switch; an output capacitor having a positive terminal and a negative terminal; an output load; a forward sub-circuit having an output and comprising: an output inductor operating in discontinuous conduction mode; the first secondary winding transmitting input energy to the output inductor, the output capacitor and the output load via the transformer when the main switch is turned on; a first diode forwardly transmitting a secondary side current to the output when the main switch is turned on; and a second diode providing flywheeling function to transmit energy stored in the output inductor to the output when the main switch is turned off; a flyback sub-circuit operating in continuous conduction mode and comprising: the second secondary winding providing magnetic reset of the transformer when the main switch is turned off; and a third diode having an anode connected to the second secondary winding in series and a cathode connected to the positive terminal of the output capacitor to directly transmit magnetic reset energy of the transformer to the output; and an active-clamp circuit clamping voltage spike of the main switch and engaging in magnetic reset of the transformer when the main switch is turned off.