PULSE WIDTH MODULATOR AND PULSE WIDTH MODULATION TYPE SWITCHING POWER SOURCE

摘要

PURPOSE: To provide a low-operation-voltage, low-current-consumption, low-noise and small-sized switching power source under fine pulse width control with specific circuit constitution. ;CONSTITUTION: When the output OSC CLK of an oscillator is Low, a PMOS transistor(TR) 21 short-circuits a capacitor 24 with low impedance and discharges it, so the voltage (1) of the capacitor 24 becomes VDD. The moment the CLK goes up to High in this state, the TR 21 turns OFF and a TR 22 turns ON; when the gate voltage of an NMOS TR 23 exceeds a threshold voltage, the drain current of the TR passes through the NMOS TR 22 to start charging the capacitor 24. When the capacitor 24 is charged until its voltage exceeds the threshold voltage of a PMOS TR 25, the TR 25 turns ON, its output (2) goes up to H, and the output (3) of an inverter 27 goes down to L. Then (2) and (39) are inputted and the output (3) of a NOR circuit 28 becomes the output of the modulator.;COPYRIGHT: (C)1996,JPO