A kind of auxiliary winding detection method and circuit

Abstract

The invention provides an auxiliary winding detection method and circuit. Based on the existing circuit components, the auxiliary winding clamping topology is more practical without additional cost. Specifically, the detection pin is clamped to the power supply voltage in the excitation stage, thereby The current flowing into the detection pin is proportional to the input voltage to achieve accurate detection of the input voltage; by making the voltage difference between the supply voltage and the detection pin voltage fall on an internal resistor in the degaussing stage, and then transfer the current flowing through the resistor to On the other internal resistor, the sample and hold circuit is used to save the voltage sample on the other internal resistor to realize the accurate detection of the output voltage; by comparing the voltage of the detection pin and the voltage of the power supply pin, the drain voltage of the main switch tube is realized. Detection of the resonance period. Input undervoltage protection, input feedforward, ZVS detection, etc. can be realized based on the input voltage; output overvoltage protection and primary feedback can be realized based on the output voltage; quasi-resonant control can be realized based on the resonance period detection.

Description

technical field [0001] The invention belongs to the field of soft-switching flyback converters, in particular to auxiliary winding voltage detection. Background technique [0002] Active clamp flyback converter is a power converter topology that can realize soft switching of power tubes. Reasonably design the inductance of the transformer excitation inductance, so that the conduction process of the clamp tube continues until there is enough negative excitation current, and then turns off. Zero-voltage turn-on (ZVS, Zero-Voltage-Switch) of the switch. In this way, the turn-on loss of the main switch tube can be eliminated, the overall efficiency of the converter can be improved, and the development of high frequency and high power density of the converter is facilitated. [0003] like figure 1 Shown is the circuit diagram of a typical active clamp flyback converter. In the figure, 101 is the clamping capacitor, 102 (LK) is the leakage inductance, 103 is the power transfor...

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Problems solved by technology

[0006] image 3 The clamping method of the auxiliary winding will not affect the normal power supply of the main control chip, but it will bring difficulties to the detection of important parameters: figure 1 Among them, the rectifier diode 111 of the auxiliary winding power supply circuit is on the high voltage side of the auxiliary winding, and the voltage dividing resistors 115 and 116 of the detection circuit take the ground as the reference potential. When the input voltage VIN is detected in the excitation stage, the anode voltage of the rectifier diode is Simply clamp the 115 / 116 voltage divider, the FA pin, to 0V to convert the input voltage into a current proportional to VIN When the output voltage is detected during the degaussing phase, the FA pin voltage is When detecting the resonance period in the VDS resonance stage, it is only necessary to detect the moment when the FA pin voltage crosses zero; and image 3 Connecting the clamp tube MA to the low-voltage side of the auxiliary winding in series blocks the DC path to the ground. Therefore, the detection of the above three important parameters cannot use the ground as the reference potential. How to accurately detect the three important parameters becomes the auxiliary winding Important Problems in the Use of Clamp Topology

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