A power supply circuit includes first and second current sources, first and second switches, first and second comparators, a latch, a driver, first to the third resistors, a first
capacitor, and first and second electric switches, wherein the grounding of the first
current source is realized through the first switch and the first
resistor, the first switch is controlled by a PWM
signal, the grounding of the second
current source is realized by the first
capacitor, the first
comparator is used to compare the
voltage at the node between the first switch and the first
resistor with the
voltage of the first
capacitor, the grounding of the second capacitor is also realized by the second switch, the second switch is controlled by a reverse PWM
signal, the first
comparator is connected with the driver through the latch to control the driver for PWM low level
signal output, the second and third resistors are connected in series between a
voltage output end and the grounding, the second
comparator is used to compare the voltage at the node between the second and third resistors with a reference voltage, and the second comparator is connected the driver through the latch to control the driver for PWM high level signal output. The invention improves the
system stability.