Synchronous rectification control circuit and method and isolated voltage conversion circuit
A synchronous rectification and control circuit technology, applied in the direction of converting AC power input to DC power output, electrical components, output power conversion devices, etc., can solve problems such as low power supply efficiency, obstruction, and misconduct of synchronous rectification switches
Pending Publication Date: 2020-05-08
杭州必易微电子有限公司
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Problems solved by technology
However, under this control method, if the power supply works in DCM mode (Discontinuous Conduction Mode, discontinuous conduction mode), when the synchronous rectification switch is turned off, the circuit will oscillate, and the parasitic oscillation of the circuit may also cause the synchronous rectification switch body diode conducts, which causes false conduction of the synchronous rectification switch
If the blanking limit is directly imposed on the parasitic oscillation time, the blanking time (Blank time) will hinder the normal turn-on of the synchronous rectification switch in the QR (quasi-resonant mode) and CCM (Continuous Conduction Mode, continuous conduction mode) operating modes , thereby reducing the efficiency of the power
Therefore, the existing synchronous rectification circuit cannot accurately control the conduction of the synchronous rectification switch, and the power supply efficiency is low
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[0064] In order to make the purpose, technical solution and advantages of the present application clearer, the present application will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present application, and are not intended to limit the present application.
[0065] It can be understood that the terms "first", "second" and the like used in this application may be used to describe various elements herein, but these elements are not limited by these terms. These terms are only used to distinguish one element from another element. The term "coupling" or "connection" used in this application includes both direct connection and indirect connection, such as connection through an electrically conductive medium such as metal or through some known active devices and passive devices that can achieve the same function Connection.
[006...
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The invention relates to a synchronous rectification control circuit and method, and an isolated voltage conversion circuit. The method comprises the steps: outputting an effective primary side conduction signal through a detection circuit when the detection circuit detects that a drain-source voltage is in a platform period and the drain-source voltage is continuously greater than a first threshold value in preset time; and after a conduction control circuit receives the effective primary side conduction signal, if the drain-source voltage is smaller than a second threshold value, making a synchronous rectification switch be conducted. The effective primary side conduction signal can represent that the primary side switch is in a conduction state, and a condition that the drain-source voltage is smaller than a second threshold value can represent that a body diode of the synchronous rectification switch is in the conduction state so that a conduction control circuit can accurately judge conduction time of the synchronous rectification switch and control the conduction of the synchronous rectification switch at the conduction time.
Description
technical field [0001] The present application relates to the technical field of synchronous rectification, in particular to a synchronous rectification control circuit and method, and an isolated voltage conversion circuit. Background technique [0002] With the development of electronic technology, synchronous rectification circuits are widely used in occasions requiring high conversion efficiency due to their high conversion efficiency. The synchronous rectification circuit usually refers to receiving the input voltage on the primary side of the transformer, and using a synchronous rectification switch on the secondary side of the transformer to convert the input voltage into the required output voltage. [0003] In the secondary-side synchronous rectification scheme, the turn-on and turn-off of the synchronous rectification switch is usually directly controlled according to the drain-source voltage of the synchronous rectification switch. However, under this control met...
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Login to View More IPC IPC(8): H02M7/217H02M1/08
CPCH02M7/217H02M1/08
Inventor 张波文鹏
Owner 杭州必易微电子有限公司