Driving circuit and switching power supply circuit

Abstract

The embodiment of the invention discloses a driving circuit and a switching power supply circuit. The driving circuit is applicable to a flyback or forward switching power supply circuit, the turning-on moment of a power switch on the primary side of a transformer of the switching power supply circuit is detected by a high-pass filter, the current working period of the power switch is timed by a slope capacitor, the past working period of the power switch is stored by a maintenance capacitor, and then a synchronous rectified power field effect transistor is turned off through a frequency locking comparator before the power switch is turned on. By means of the driving circuit and the switching power supply circuit, the synchronous rectified power field effect transistor on the secondary side of the transformer of the switching power supply circuit is turned off before the power switch on the primary side of the transformer is turned on, the driving circuit is applicable to the switchingpower supply circuit driven by constant frequency, the condition that the synchronous rectified power field effect transistor is turned off hard is avoided, the efficiency of a switching power supplyis improved, voltage and current stress of the synchronous rectified power field effect transistor is reduced, and the reliability of the system is improved.

Description

technical field [0001] Embodiments of the present invention relate to the technical field of switching power supplies, in particular to a driving circuit and a switching power supply circuit. Background technique [0002] Traditional switching power supplies use diodes for rectification on the output side, but the diodes have a forward voltage drop, so the efficiency of the switching power supply will be limited. Synchronous rectification technology replaces diodes with field-effect transistors, and designs a reasonable circuit to drive the turn-on and turn-off of field-effect transistors, simulating the working characteristics of diodes, and is more forward-opening than diodes, thereby improving the efficiency of switching power supplies. [0003] At present, for the control of the field effect transistor in the switching power supply circuit, the voltage between the drain and the source of the field effect transistor is often detected to judge the required on-off state of ...

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Problems solved by technology

[0005] In view of this, in order to improve the turn-off detection speed and driving speed of the field effect transistor, the embodiment of the present invention provides a driving circuit and a switching power supply circuit, which can solve the problem of insufficient control of the field effect transistor of the switching power supply circuit in the prior art. In time, it causes the instability of the source-drain voltage in the field effect transistor, thereby affecting the technical problem of the power output efficiency of the switching power supply

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