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

The stone crystal oscillation circuit adopts CMOS inverting mode to ensure
accurate operation. Because it uses a BCD counter ( IC 2, hi), the maximum oscillation
frequency is 2MHz (requiring 100 times the frequency of 20kHz). Assuming that IC,
The bistable multivibrator IC70 is triggered once every 100 clock pulses output. The reset
function is set by the comparator IC (IC4, 5): once the duty cycle setting value is reached,
the clock pulse count is terminated. , the circuit is reset, so the output of IC ., has
a duty waveform equal to the set value. The resolution is measured in 1% units and is very stable.