Synchronous rectification device and control method thereof

Abstract

A synchronous rectification device comprises a synchronous rectification tube, a drive control circuit, a Vcc capacitor and a charging circuit for charging a grid electrode of the synchronous rectification tube. The Vcc capacitor is charged through the charging circuit by means of reverse voltage applied to the synchronous rectification device, and when the voltage of the Vcc capacitor is detectedto rise to the upper limit value Vcc_H of the Vcc capacitor, charging of the Vcc capacitor is stopped; and when the Vcc voltage is detected to be reduced to a lower limit value Vcc L, starting to charge the Vcc capacitor is carried out, so that a switching tube of the charging circuit works in an intermittent and complete conduction state. By controlling the upper limit and the lower limit of theVcc voltage, the charging circuit is promoted to work intermittently, and the power consumption of the power supply circuit is greatly reduced; in a standby state, when the working frequency is lower, the current consumption of the Vcc end is extremely low, the working intermittent time of the charging circuit is longer, the power consumption is further reduced, and the heating and standby powerconsumption is reduced.

Description

technical field [0001] The invention relates to the technical field of switching power supplies, in particular to a power supply technology of a synchronous rectification device and a control method thereof. Background technique [0002] A diode is a commonly used rectifying device. It is turned on when a forward voltage is applied, and the current flows forward, while it is turned off when a reverse voltage is applied, and the reverse current is blocked. Because the diode has an inherent conduction when it is turned on The greater the current, the greater the voltage drop. The loss of a diode is usually described as the current multiplied by the conduction voltage drop. Therefore, as the current flowing through the diode increases, its loss also increases. Resulting in a reduction in switching power supply efficiency. In order to solve the problem of rectification diode loss, power semiconductor devices, such as MOS tubes, can be used to replace diode rectification, that i...

AI Technical Summary

Problems solved by technology

[0002] A diode is a commonly used rectifying device. It is turned on when a forward voltage is applied, and the current flows forward, while it is turned off when a reverse voltage is applied, and the reverse current is blocked. Because the diode has an inherent conduction when it is turned on The greater the current, the greater the voltage drop. The loss of a diode is usually described as the current multiplied by the conduction voltage drop. Therefore, as the current flowing through the diode increases, its loss also increases. Causes a reduction in switching power supply efficiency

The schematic diagram of the charging circuit is shown in figure 1 As shown, including charging MOS tubes, voltage regulator tubes, etc., the basic principle is to use the reverse voltage generated by the secondary side rectifier to supply power to the control circuit through the switching action of the primary side of the isolation topology, and the voltage regulator tube connected to the gate of the charging MOS tube Clamp the Vcc voltage. During normal operation, when the difference between the Vcc voltage and the gate voltage of the charging MOS tube is less than the turn-on threshold of the auxiliary transistor, stop charging Vcc, so the Vcc voltage is clamped to a certain voltage value by the voltage regulator tube. In practical applications, when the circuit reaches a steady state, the auxiliary transistor works in a non-completely conducting state, similar to a linear regulator, and there will be current flowing through the auxiliary transistor in each cycle, resulting in a huge power loss, resulting in Problems of heat generation, low efficiency and large standby power consumption

Images