The invention provides a power supply circuit and a PWM circuit capable of performing PWM control within the range of 0-100% working ratio and capable of high-speed response, including: a DC-DC conversion circuit, which is connected in series to the power input terminal 1 and the reference potential input terminal The PMOS (QP1) and NMOS (QN1) between 2 are respectively turned on alternately with the PWM signal, so as to obtain the DC output voltage controlled by the PWM as the output; the error amplifier 40, which performs the DC output voltage and the reference voltage compare, and then output an error voltage; and the PWM circuit 30, which performs PWM control within the range of 0-100% duty ratio according to the error output of the error amplifier 40, wherein, the PWM circuit 30 adopts the first and the second half cycles of interleaving Divide-by-two clock pulses generate triangular wave signals with alternate half periods through the charge and discharge circuits used to generate the triangular waves, and use the triangular wave signals as the first and second PWM signals, which are converted by the first and second Schmitt trigger circuits After they are mixed, a PWM signal is generated.