Abstract: An example synchronous rectifier circuit includes a transformer having a primary winding and a secondary winding which are insulated from each other; a main switch provided at a primary side of the circuit, which includes the primary winding; a rectifying FET provided at a secondary side of the circuit, which includes the secondary winding; a commutating FET provided at the secondary side of the circuit; and an auxiliary FET provided between a gate and a source of the rectifying FET. The auxiliary FET has a threshold lower than a threshold of the commutating FET and a gate of the auxiliary FET is connected to a gate of the commutating FET, and a short circuit is produced between the gate and the source of the rectifying FET while the commutating FET is in an on-state.

Abstract: A DC-DC converter circuit for stabilizing the output voltage of the secondary side by correcting the input voltage by using a simple circuit, where no state measurement circuit is necessary at the secondary side. The circuit includes a transformer; a switching circuit including a main switching element which is connected to the primary winding of the transformer in series and has a control terminal for controlling the main switching element, wherein the main switching element is PWM-controlled so as to stabilize an output voltage of the secondary side; a driving circuit for generating PWM driving pulses; and a correction circuit for outputting a voltage whose level is in inverse proportion to an input voltage of the DC-DC converter circuit. An output of the driving circuit is connected to the control terminal of the main switching element and to the correction circuit.

Abstract: There is provided a synchronous rectifier circuit that makes it possible to secure sufficient driving voltage for the rectifier switch regardless of the voltage of the secondary winding. In this synchronous rectifier circuit, the primary winding is insulated from the secondary winding and a rectifier switch is provided on the secondary side. An auxiliary switch, a diode, and an auxiliary winding are also provided on the secondary side. The emitter of the auxiliary switch and the cathode of the diode are connected to the gate of the rectifier switch. One end of the auxiliary winding is connected to the base of the auxiliary switch and the anode of the diode. An end of the secondary winding is collected to the collector of the auxiliary switch. The other end of the auxiliary winding is connected to this one end of the secondary winding.

Abstract: This switching circuit includes a transformer having primary and secondary windings insulated from each other; a voltage-driven switching element which is connected in series to one of the primary and secondary windings and has a control terminal for controlling a switching operation thereof; a drive circuit which has an output connected to the control terminal and drives the main switching element; and an auxiliary winding which is provided in parallel to the primary winding of the transformer and has an output connected to the control terminal via a capacitor with positive feedback.

Abstract: A driving circuit using a novel synchronous rectifier circuit in which reverse current is difficult to produce. The synchronous rectifier circuit includes a transformer having a primary winding and a secondary winding which are insulated with each other; a main switch provided at a primary side of the circuit, which includes the primary winding; a rectifying FET provided at a secondary side of the circuit, which includes the secondary winding; a commutating FET provided at the secondary side of the circuit; and an auxiliary FET provided between a gate and a source of the rectifying FET. The auxiliary FET has a threshold lower than a threshold of the commutating FET and a gate of the auxiliary FET is connected to a gate of the commutating FET, and a short circuit is produced between the gate and the source of the rectifying FET while the commutating FET is in an on-state.

Abstract: A DC-DC converter circuit for stabilizing the output voltage of the secondary side by correcting the input voltage by using a simple circuit, where no state measurement circuit is necessary at the secondary side. The circuit includes a transformer; a switching circuit including a main switching element which is connected to the primary winding of the transformer in series and has a control terminal for controlling the main switching element, wherein the main switching element is PWM-controlled so as to stabilize an output voltage of the secondary side; a driving circuit for generating PWM driving pulses; and a correction circuit for outputting a voltage whose level is in inverse proportion to an input voltage of the DC-DC converter circuit. An output of the driving circuit is connected to the control terminal of the main switching element and to the correction circuit.

Abstract: There is provided a synchronous rectifier circuit that makes it possible to secure sufficient driving voltage for the rectifier switch regardless of the voltage of the secondary winding. In this synchronous rectifier circuit, the primary winding is insulated from the secondary winding and a rectifier switch is provided on the secondary side. An auxiliary switch, a diode, and an auxiliary winding are also provided on the secondary side. The emitter of the auxiliary switch and the cathode of the diode are connected to the gate of the rectifier switch. One end of the auxiliary winding is connected to the base of the auxiliary switch and the anode of the diode. An end of the secondary winding is collected to the collector of the auxiliary switch. The other end of the auxiliary winding is connected to this one end of the secondary winding.

Abstract: This switching circuit includes a transformer 1 having a primary and secondary windings 1A and 1B insulated from each other; a voltage-driven switching element 2 which is connected in series to one of the primary and secondary windings and has a control terminal for controlling switching operation thereof; a drive circuit 3 which has an output connected to the control terminal and drives the main switching element 2; and an auxiliary winding 4 which is provided in parallel to the primary and secondary windings 1A and 1B of the transformer 1 and has an output connected to the control terminal via a capacitor 5 with positive feedback.