Isolated switching converter and its controller and control method

Abstract

A controller of an isolated switching converter includes an error amplifying circuit, a modulation signal generator, a first comparison circuit, a primary off detection circuit, a secondary logic circuit, an isolation circuit and a primary logic circuit. The error amplifying circuit generates a compensation signal based on the difference between a reference signal and a feedback signal. The first comparison circuit compares the compensation signal with a modulation signal generated by the modulation signal generator and generates a first comparison signal. The primary off detection circuit detects whether the primary switch is off and generates a primary off detection signal. The secondary logic circuit generates a secondary control signal to control the secondary switch based on the first comparison signal and the primary off detection signal. The isolation circuit receives the first comparison signal and generates a synchronous signal electrically isolated from the first comparison signal. The primary logic circuit generates a primary control signal to control the primary switch based on the synchronous signal.

Description

technical field [0001] The present invention relates to an electronic circuit, in particular to an isolated switch converter and its controller and control method. Background technique [0002] Synchronous rectification is a technology that uses power metal-oxide-semiconductor field-effect transistors (MOSFETs) to replace rectifier diodes to reduce losses, and it can greatly improve the efficiency of switching power supplies. The power MOSFET is a voltage-controlled device, and its volt-ampere characteristic is linear when it is turned on. When using a power MOSFET as a rectifier, it is required that its gate voltage must be synchronized with the phase of the rectified voltage. [0003] figure 1 It is the waveform diagram of the existing intelligent synchronous rectification technology, wherein Vds is the drain-source voltage of the secondary switching tube, Isec is the current flowing through the secondary winding, and CTRLS is the control signal of the secondary switchin...

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Problems solved by technology

[0004] The existing intelligent synchronous rectification technology turns off the secondary switching tube after the primary switching tube is turned on. The switching power supply is damaged

Moreover, in the actual circuit, due to the MOSFET's own characteristics and the delay of the control circuit, it takes a while from Vds increasing to greater than -70mV until the secondary switch is turned off, which undoubtedly further increases the possibility of direct connection

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