Synchronous rectification control circuit and flyback switching power supply
A control circuit and synchronous rectification technology, applied in control/regulation systems, high-efficiency power electronic conversion, electrical components, etc., can solve problems such as difficult to avoid parasitic attenuation oscillation misoperation
Pending Publication Date: 2020-12-15
BCD (SHANGHAI) MICRO ELECTRONICS LTD
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Problems solved by technology
Therefore, controlling the rectifier tube M2 according to the amplitude of the voltage at both ends of the secondary winding is difficult to avoid malfunctions caused by parasitic attenuation oscillations
Method used
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[0037] The core of the present invention is to provide a synchronous rectification control circuit and a flyback switching power supply. The method of comparing before and after the volt-second product is used to judge whether the secondary rectifier needs to be opened, so that the secondary rectifier needs to be opened, and the secondary winding When the terminal voltage connected to the rectifier tube is lower than the preset start-up threshold voltage, the rectifier tube is accurately turned on, so as to avoid the phenomenon of mistakenly turning on the secondary side rectifier tube during parasitic attenuation oscillation.
[0038] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments ...
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The invention discloses a synchronous rectification control circuit and a flyback switching power supply. The synchronous rectification control circuit comprises a volt-second integrating circuit, a sampling hold circuit, a comparison circuit and a rectifier tube control circuit. Considering that the volt-second product of the voltages at the two ends of the secondary winding is in a certain rule,the volt-second product value of the voltages at the two ends of the secondary winding excited during normal primary side switch action is maximum, and the volt-second product value of the voltages at the two ends of the secondary winding is gradually reduced during parasitic attenuation oscillation; therefore, whether the secondary side rectifier tube needs to be turned on is judged by adoptinga method of comparing before and after a volt-second product, so that the rectifier tube is accurately turned on when the secondary side rectifier tube needs to be turned on and the voltage of the terminal, connected with the rectifier tube, on the secondary side winding is smaller than the preset starting threshold voltage; therefore, the phenomenon that the secondary rectifier tube is opened bymistake when parasitic attenuation oscillation occurs is avoided.
Description
technical field [0001] The invention relates to the field of switching power supply control, in particular to a synchronous rectification control circuit and a flyback switching power supply. Background technique [0002] The flyback switching power supply controlled by the primary side has gradually become an important electronic component power supply device due to its small size and high efficiency. Generally, a rectifier diode is connected in series at the output end to provide a DC output voltage. With the development of electronic technology, the output voltage required by the load electronic components is getting lower and higher, and the output power is getting higher and higher. Therefore, the forward conduction voltage drop of the rectifier diode has become the main factor limiting the efficiency of the switching power supply. [0003] The commonly used solution at present is to use a rectifier to simulate a diode for rectification, which is the so-called synchrono...
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IPC IPC(8): H02M3/335H02M1/32
CPCH02M3/33592H02M1/32Y02B70/10
Inventor 彭韶华汪虎陈超
Owner BCD (SHANGHAI) MICRO ELECTRONICS LTD