I am trying to generate a sinusoidal PWM signal using analog circuits.
I want to compare my sine wave and triangular wave using an operational amplifier (LM741) which has a rise time of 0.3 µs and slew rate 0.5 V/µs, which will good at 5 kHz theoretically. But I am not getting a good PWM output.
So I first tried to compare the sine wave with a reference voltage (2.2 volt). Sine wave amplitude = 2.5 volt (5 V peak to peak) and frequency 100 Hz and 5 kHz.
- At low frequency (say 100 Hz), the output is good
- At high frequency (say 5 kHz), the output is too bad.
What will be the problem…
If the response is the problem of the comparator, but the slew rate is 0.5 V/µs.
Calculation of slew rate for a sinusoidal signal…
Slew rate= Vm * 2pi * Frequency
= 5 V * 2pi* 5000 Hz = 1570796 volt per second or 0.15 V/µs
Theoretically the slew rate of 0.5 V/µs will be OK for a sinusoidal signal of 5 kHz and 5 volt peak to peak. But in my case the signal is distorted.
Where am I wrong?