Control circuit and flyback switching power supply system

Abstract

The embodiment of the present invention provides a control circuit and a flyback switching power supply system, the control circuit is used to control the conduction of the synchronous rectifier in the switching power supply system, including: VD terminal, input secondary side winding of the switching power supply system Voltage; Gate terminal, connected to the gate of the synchronous rectifier; and a charging current module, a diode, a first transistor, a capacitor and a second transistor connected between the VD terminal and the Gate terminal; one terminal of the charging current module is connected to the VD terminal , the other end is connected to the anode of the diode; the cathode of the diode is connected to the drain of the first transistor, one end of the capacitor, and the gate of the second transistor; the gate of the first transistor receives POR, the source is grounded; the other end of the capacitor is grounded ; The drain of the second transistor is connected to the Gate terminal, and the source is grounded; when the POR is low, the second transistor is turned on. According to the above technical solution, the peak voltage at the Gate terminal can be suppressed, and accidental conduction of the synchronous rectifier can be avoided.

Description

technical field [0001] The invention belongs to the field of integrated circuits, and in particular relates to a control circuit and a flyback switching power supply system. Background technique [0002] With the continuous improvement of power efficiency standards, synchronous rectification control circuits have been more and more widely used in switching power supply systems. Compared with the traditional switching power supply system, the synchronous rectification control circuit can effectively improve the power density, improve the conversion efficiency, reduce the temperature rise, and also increase the complexity of the power supply system to a certain extent. Considering the cost of the entire power supply system, the synchronous rectification control circuit usually directly detects the voltage of the secondary winding of the transformer to determine whether the synchronous rectification MOS transistor is turned on or not. [0003] However, there is a parasitic cap...

AI Technical Summary

Problems solved by technology

[0003] However, there is a parasitic capacitance C between the Gate-Drain (gate-drain) of the synchronous rectification Metal-Oxide-Semiconductor (MOS) transistor. gd , under the action of this parasitic capacitance, the voltage of the secondary side winding will be coupled at the Gate terminal of the synchronous rectification MOS tube to generate a peak voltage

[0004] Since the turn-on threshold voltage of the synchronous rectification MOS transistor is usually small, the peak voltage is usually higher than the turn-on threshold voltage of the synchronous rectification MOS transistor, so it may lead to false conduction of the synchronous rectification MOS transistor, which may lead to lower overall efficiency. , device damage, etc., bringing a series of safety issues

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