Protective circuit of synchronous rectification field-effect tube

Abstract

The invention discloses a protective circuit of a synchronous rectification field-effect tube. The protective circuit of the synchronous rectification field-effect tube comprises a protection switch tube, a negative pressure eliminating diode, a speed-up capacitor, a coupling resistance and a grounding resistance. The emitting electrode of the protection switch tube is connected with the source electrode of the synchronous rectification field-effect tube. The collector electrode of the protection switch tube is connected with the grid electrode of the synchronous rectification field-effect tube. The base electrode of the protection switch tube is connected with one end of the speed-up capacitor, the coupling resistance and the grounding resistance. The positive electrode of the negative pressure eliminating diode is connected with the source electrode of the synchronous rectification field-effect tube, and the negative electrode of the negative pressure eliminating diode is connected with the grid electrode of the synchronous rectification field-effect tube. The other end of the speed-up capacitor and the coupling resistance is connected with the positive drain-source voltage end formed by the drain electrode of the synchronous rectification field-effect tube and the secondary electrode of a switch power source. The other end of the grounding resistance is connected with the source electrode of the synchronous rectification field-effect tube and the public ground. The gate-source voltage of the synchronous rectification field-effect tube can be remarkably reduced, and a primary main switch tube and the secondary synchronous rectification field-effect tube of the switch power source can be effectively prevented from generating the simultaneous conduction abnormity.

Description

technical field [0001] The invention relates to a protection circuit, in particular to a protection circuit for a synchronous rectification field effect transistor. Background technique [0002] Most existing switching power supplies use synchronous rectification field effect transistors instead of Schottky transistors on the output side to improve efficiency. However, the control of the synchronous rectification FET is very complicated, such as figure 1 , 2 When the primary main switching tube Q of the switching power supply shown is turned on, the positive drain-source voltage Vds formed on the secondary side of the switching power supply generates a gate-source voltage Vgs through the junction capacitance Cgd and Cgs of the synchronous rectification field effect transistor on the output side, and the gate-source voltage Vgs is generated at the gate When the source voltage Vgs voltage is high enough, the secondary synchronous rectification field effect transistor SR is t...

AI Technical Summary

Problems solved by technology

However, the control of the synchronous rectification FET is very complicated, such as figure 1 , 2 When the primary main switching tube Q of the switching power supply shown is turned on, the positive drain-source voltage Vds formed on the secondary side of the switching power supply generates a gate-source voltage Vgs through the junction capacitance Cgd and Cgs of the synchronous rectification field effect transistor on the output side, and the gate-source voltage Vgs is generated at the gate When the source voltage Vgs voltage is high enough, the secondary synchronous rectification field effect transistor SR is turned on, which often causes the abnormality that the primary main switch Q of the switching power supply and the secondary synchronous rectification field effect transistor SR are turned on at the same time, resulting in damage to the switching power supply

Images