A synchronous rectifier PWM (SR-PWM) controller controls a MOSFET in response to the value of a secondary current and the status of a synchronous signal for both discontinuous and continuous operation mode. The secondary current is generated in a secondary circuit and is detected by two threshold-detection terminals of the SR-PWM controller. The SR-PWM controller produces the synchronous signal by detecting a switching signal of the transformer via a detection terminal of the SR-PWM controller. Furthermore, a delay-time is inserted after the MOSFET is turned off and before the next switching cycle starts to ensure a proper operation of the MOSFET. In one embodiment, an equivalent series resistance (ESR) of an output capacitor can be used as a sensor to detect the secondary current. Therefore, no additional current sensor is required.
A synchronous rectification circuit for power converters operable under fixed and/or variable frequencies where no current sense circuit or phase-lock circuit are needed is provided. It has a power switch coupled to a transformer for the rectification. A signal-generation circuit is used for generating a control signal in response to a magnetized voltage of the transformer, a demagnetized voltage of the transformer, and a magnetization period of the transformer. The control signal is coupled to turn on the power switch. The enable period of the control signal is correlated to a demagnetization period of the transformer.
A synchronous rectifying control circuit for utilizing in a forward topology of rectifying circuit. The circuit controls a first current switch and a second current switch provided on both ends of a secondary of a transformer. Two sets of the same of control circuits are utilized to control and adjust respectively the post and future periods of the conductive time and the driving synchronous rectifying switches are extended to replace the conventional of rectifier diodes rectifying method. An improved synchronous rectifying control circuit comprises pulse interruptive protection circuit to prevent the cross-conduction between two current switches and an anti reversing protection circuit to prevent a reverse current from flowing back to the ground.
A synchronous rectification circuit for power converters operable under fixed and/or variable frequencies where no current sense circuit or phase-lock circuit are needed is provided. It has a power switch coupled to a transformer for the rectification. A signal-generation circuit is used for generating a control signal in response to a magnetized voltage of the transformer, a demagnetized voltage of the transformer, and a magnetization period of the transformer. The control signal is coupled to turn on the power switch. The enable period of the control signal is correlated to a demagnetization period of the transformer.
A first drive control signal regenerating circuit outputs an ON timing drive signal at turn-ON of a main switch element, and a second drive control signal regenerating circuit generates an OFF timing drive signal at turn-OFF of the main switch element. A rectifying switch controlling switch element connected between the gate and source of a rectifying switch element is driven by an output of the second drive control signal regenerating circuit. An output of the first drive control signal regenerating circuit connects to the gate of a commutating switch controlling switch element, which connects to one end of an auxiliary winding, the other end thereof being connected to the gate of a commutating switch element. Accordingly, the rectifying switch element is directly controlled from the primary side.
A DC-to-DC converter incorporates a transformer having a primary winding connected to a pair of DC input terminals via an active switch, which turns on and off under the control of a feedback circuit, and a secondary winding connected to a pair of DC output terminals via a synchronous rectifier and a smoothing capacitor. The synchronous rectifier is a parallel connection of a synchronous rectifier switch and a diode. A synchronous rectifier control circuit is connected to the synchronous rectifier switch for causing conduction therethrough while the active switch is off. The synchronous rectifier control circuit comprises a capacitor for determination of the conducting periods of the synchronous rectifier switch, and a logic network for on/off control of the synchronous rectifier switch according to whether the active switch is on or off and whether the capacitor voltage is higher than a predefined threshold or not.
