In a feedback circuit of a power supply, an electrical level of an output voltage is stabilized corresponding to changes of an electrical level of a pulse width modulation signal, and effects, which are caused by spikes, on passive elements are decreased to a lowest degree. The electrical level of the output voltage is stabilized by storing a voltage corresponding to a low-to-high electrical level of the PWM signal with a capacitor, by discharging the stored voltage with a high-to-low electrical level of said PWM signal, and by regulating a discharging path of the stored voltage with a diode, which is not conducted. The abovementioned disposition may be utilized on various power-consuming devices, a duty cycle of each of which is controlled with a PWM signal, for stabilizing output voltages of said power-consuming devices, and for reducing effects, which are caused by spikes, on passive elements inside said power-consuming devices.