Pulse duration modulator and pulse duration modulation type switching power source

摘要

A switching transistor is arranged for charging a capacitor in response to a positive going transition of a clock signal. The charging time of the capacitor is determined by controlling the charging current in accordance with an input voltage to a transistor coupled to the capacitor. The pulse width of an output signal is dependent upon the charging time of the capacitor. Using the inventive pulse width modulator, by comparing the voltage of a reference voltage source with a divided voltage obtained through feedback of the output of the pulse width modulator, a switching power source is obtained by simply adding circuitry for converting, rectifying and smoothing the output voltage. A variable range of pulse width of up to 1800 times can be obtained. When the circuit is designed using complementary MOS devices, the operating voltage can be under 1V with a consumption current of less than several . mu.A. When the circuit is integrated, the oscillator of the modulator and the oscillator of the electronic system in which the modulator is used can be easily switched, and the oscillators can be synchronized, resulting in a low noise, miniaturized switching power source.