555 pwm circuit not working with small value capacitor

Thread Starter


Joined Jan 11, 2018

Pin 1 to ground
Pin 2 to pin 6
Pin 7 to pin 8 with 10k resistor
Pin 7 to pin 6 with a potentiometers 1 and 2 pins
Pin 8 to 5v
Pin 3 to led with 1k resistor
Pin 4 to pin 8
When i connect a 47uf capacitor (electrolytic) between pin 2 and 1 I get frequency of around 1hz and I am able to change high and low time of led effectively with potentiometer.
But when I connect a 0.1uf capacitor(ceramic) or 1 uf (electrolytic) capacitor to it led just keeps glowing
And i cant control its brightness(pwm) with potentiometer anymore.


Joined Sep 17, 2013
led just keeps glowing
Actually it doesn't. Assuming your pot is 10k, the frequency with the 0.1uF cap will be ~500Hz, which is too fast for the human eye to detect the LED switching off.
With the circuit you have, the change in duty cycle as you twiddle the pot is only 50%, so the average brightness change of the LED will hardly be noticeable, because of the eye's logarithmic response to light levels.
What is your pot resistance?


Joined Sep 17, 2013
If you want a bigger duty cycle adjustment range (~100%) try this circuit :-
Ideally there should be a ~0.1uF cap between pin 5 and ground (pin 1) to reduce possible interference effects.
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Joined Dec 2, 2017
Just to clarify two things.

The circuit as described in the OP is not an actual PWM configuration.

And 500Hz would not be a problem with an actual PWM configuration.