High-precision PWM wave generator with duty cycle digitally set in the range of 1% to 99%

High-precision PWM wave generation circuit that can digitally set the duty cycle in the range of 1% to 99%

Function of the circuit

The most commonly used method for generating PWM waves is to use a voltage comparator to compare the signal to be modulated with a linear triangle wave. This circuit can accurately and stably control the duty cycle in the range of 1% to 99% with 1% as the first step. Therefore, it can be used to calibrate and adjust the PWM demodulation circuit or as a signal source for a PWM DA converter.

How the Circuit Works

The quartz crystal oscillator circuit uses C-MOS inverter to ensure accurate operation. Because two BCD counters are used, the highest oscillation frequency is 2MHZ. Assume that IC3 triggers the bistable multi-resonance oscillator IC7 once every 100 clock pulses output. The reset method is to use the comparator IC to set: once the duty cycle setting value is reached, the clock pulse count ends and the circuit is reset, so the output of IC7 has a duty waveform equal to the setting value. The resolution is in units of 1%, and it is very stable.