A forward DC/DC converter using semi-synchronous MOSFET rectifiers with a peak detector and a pulse transformer. In another example edge triggered circuits and active clamps are used. The gate driving signal for one MOSFET is derived from the secondary of the input power transformer, but the second MOSFET gate is driven from a combination of the secondary of the input power transformer and the pulse transformer. The second MOSFET remains on during the core reset and dead time periods thereby providing a low voltage current path for the load current.

A current flowing through a reactor flows through a resistor, which generates a voltage in accordance with the value of the current. As the voltage generated by the resistor is greater than or equal to the threshold of a transistor, the transistor is in an on state. As the current flowing through the reactor decreases and the voltage generated by the resistor becomes lower than the threshold of the transistor, the transistor turns off and an NMOS turns on. Accordingly, the gate voltage of an NMOS is decreased by a diode, ensuring that the NMOS is turned off before the current flowing through the secondary winding of a transformer becomes zero.

A flyback converter has a primary side including a main switch and a control device and a delay circuit. The converter has a secondary side including a drive circuit controlling a rectifying switch. The drive circuit has a first part including a first transistor, a first discharge diode and an on-node and a second part including a second transistor, a second discharge diode and an off-node. The control device is connected to the drive circuit via at least one drive capacitor to the on- and off-nodes. The control device issues drive pulses to the main switch through the delay circuit and to the drive circuit. The drive circuit has a first mode of operation in a flyback phase, which is triggered when the main switch is turned off and the rectifying switch is rendered conducting. A second mode of operation is a forward phase, which is triggered when the main switch is turned on and the rectifying switch is rendered non-conducting. The flyback converter includes few components and the main switch is efficiently prevented from conducting simultaneously with the rectifying switch.

A synchronous rectifying circuit for a flyback converter includes a synchronous rectifying element (Q.sub.2) coupled to the secondary winding (N.sub.2) of a transformer (T) and performing a synchronous rectifying operation according to an on/off operation of the synchronous rectifying element; an auxiliary inductance circuit (L.sub.3) coupled to the secondary winding (N.sub.2) of the transformer (T) and having an energy discharge time period shorter than that of the secondary winding (N.sub.2); and a control element (Q.sub.3) for turning the synchronous rectifying element (Q.sub.2) off in response to the detection of termination of the energy discharge of the auxiliary inductance circuit (L.sub.3).

The invention concerns a direct energy-transfer converter of the AC/AC or DC/DC type, including a self-regulated synchronous rectifier, in which the rectifier switches are controlled through one or more transformer windings. The converter includes a primary stage with at least one primary winding of a transformer and at least one controlled switch, with a secondary stage having at least one secondary winding (10) of the transformer, and a synchronous rectifier (1) with at least a first switch (20) which is self-regulated and conducting during the conducting phase of the controlled switch of the primary stage, known as the direct energy-transfer stage, and at least one secondary switch (30) which is self-regulated and conducting during the non-conducting phase of the controlled switch of the primary stage, known as the freewheel phase, and an output filter (5). Said converter also includes the means (CTC1) to render conducting said second switch (30) independently of the voltage at the terminals of the secondary winding (10) during said freewheel phase.