Control circuit for power converter

Abstract

This invention relates to a control circuit of a power converter for detecting the back-relaxation voltage of a transformer of a power converter including a switch, a detecting circuit and a switch circuit, in which, a switch coupling transformer is used in switching transformers and the coupling transformer of the detection circuit is used in detecting the back-relaxation voltage to generate a first signal, a switch circuit generates a control signal based on the first signal to control the switch and regulate the output of the power converter, since the pulse width of the back-relaxation voltage is shortened when the power converter is at light load, the detection circuit generates a bias signal to help detecting the back-relaxation voltage, the bias signal is in inverse ratio with the discharge time of the transformer, in addition to that, the switch circuit generates a blanking signal based on the control signal to guarantee the minimum pulse width of the voltage.

Description

Technical field: [0001] The invention relates to a power converter, in particular to a control circuit of the power converter. Background technique: [0002] According to, power converters are widely used to provide regulated output power today. In consideration of safety, the primary side and the secondary side of the power converter must be isolated, so the power converter is usually provided with a transformer for providing isolation and transferring energy. see figure 1 , is the circuit diagram of a conventional power converter. As shown in the figure, a conventional power converter is provided with a transformer 10, which includes a primary winding N P , primary and secondary side winding N S with an auxiliary winding N AUX , primary side winding N P respectively coupled to an input voltage V IN with a switch 20 . When the switch 20 is turned on, the primary side of the transformer 10 will store energy. Once the switch 20 is turned off, the transformer 10 will r...

AI Technical Summary

Problems solved by technology

[0008] above the flyback voltage V F , which is sent to the voltage detection terminal DET of the controller 25 through a resistor 22, so the controller 25 will generate a detection voltage V DET , and for the voltage detection terminal DET of the controller 25 to detect the flyback voltage V F , but because a parasitic capacitance 23 is coupled to the resistor 22, it will cause a low-pass filter characteristic, resulting in the flyback voltage V F will be filtered

In addition, the power converter will shorten the control signal V G The turn-on time T ON , according to equation (1), it will also shorten the flyback voltage V F The discharge time T DS , which will cause the detection voltage V DET As shown in the second figure, the waveform distortion occurs, so the controller 25 will detect the low-voltage flyback voltage V F

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