Ripple voltage detection method of filer capacitor equivalent series resistor

The invention relates to a ripple voltage detection method of a filer capacitor equivalent series resistor. A ripple voltage detection circuit of the filer capacitor equivalent series resistor is composed of a differential amplifier and an RC series branch, the two ends of the output of a switch power supply circuit are connected with the input of the differential amplifier, the output of the differential amplifier is connected the RC series branch, the measured voltage of a measurement RC branch resistor satisfies the equation (please see the equation in the specification), k is the differential amplifier gain, and v is the ripple voltage of the filter capacitor ESR. Through the proportional relation between detection branch impedance and filter capacitor branch impedance, information of the ripple voltage of the filter capacitor ESR is indirectly extracted, a detection branch only needs the differential amplifier and the RC series branch, few elements are needed, and measurement is convenient and easy; a current sensor is not used, and cost and the size of the switch power supply can be reduced; ripple compensation is conducted by adopting the filter capacitor ESR, and stability of the switch power supply can be improved well.