How to generate PWM using 555 timer where the duty cycle is controlled by the op amp using ntc

by nb_0201
October 19, 2021

Try to vary the voltage at pin 5, CONTROL, of the 555 to dramatically influence the timing (and so, the frequency).

Look for "Police Siren" in "50 555 circuits" by Collin Mitchel, for an example. (

by vanderghast
October 19, 2021

I have made the circuit but the duty cycle of the pwm is not being varied due to the constant output of op amp. I used a ntc for op amp to work after a certain temperature. But after that temperature the wave is not changing after increasing temperature further.

by nb_0201
October 20, 2021

I need to specifically use op amp and NTC

by nb_0201
October 20, 2021

You are probably saturating your OpAmp output, which then acts line an on/off (digital) output. Have you tried to reduce the amplification, with appropriate standard negative feedback?

by vanderghast
October 20, 2021

Thank You so much for all the help. It's done!

by nb_0201
October 21, 2021

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