The present invention relates to a pulse width modulation switching direct voltage circuit. The PWM circuit comprises a first passive device, a second passive device and a third passive device connected in series between a power supply and a ground such that the first passive device is connected to the second passive device and the second passive device is connected to the third passive device, and a fourth passive device which is connected in-parallel between an output end and a point between the first passive device and the second passive device, wherein the rated value of the fourth passive device is at least three times more than the rated value of the first passive device. Herewith, the voltage-cycle relationship of the PWM circuit becomes linear. Under such a state, the PWM circuit is enabled with good work efficiency.