Dimmer Circuit Simulation Problem

Thread Starter


Joined Nov 4, 2020
Hi I am trying to make a dimmer circuit with proteus. But it is not working according to our calculations. I am very new both in proteus and also learning about OP-AMPs. So I am not understanding what's wrong with the schematics. Both the current and voltage is showing zero.

Here is the handwritten version of the circuit and we need to simulate it.


Here is the proteus version


Here I am sharing the schematics file if you need in case https://drive.google.com/file/d/1_s-Pi9OePqi4SvDcLtxsLL5XfQTVm9BG/view?usp=sharing.

Can you please help me to complete the simulation? That would be a great help! Thanks in advance.


Joined Jan 8, 2017
Also you effectively have no input to to pin 2 of U1 as the output of RV1 is floating with respect to the rest of the circuit. In your hand drawn circuit the voltage on pin 2 can be set to between zero volts and + 4.2 volts with respect to to ground. For it to work correctly when the input is close to zero volts you will probably need a negative supply to U1 as a 741 is a VERY OLD design of op amp. You could use a more modern op amp that works with its input's close close to it's negative supply rail. I have just noticed that you have a sine wave input on pin 3 of the op amp so this pin will go negative to - 1.414 x the RMS amplitude of the sine wave. So even with an op amp that can work with it's inputs close to the negative rail you woud need a negative supply to the op amp.

Last edited:


Joined Aug 7, 2020
This circuit should have a comparator, not an op-amp.
V1 should have a DC offset of half the supply voltage.
D1 serves no useful purpose (apart from sending the output of the 741 into current limit)


Joined Jun 17, 2011
Its always a good idea to use some decoupling C on inputs and Vcc rails. Why is there AC on pin 3 ? If the purpose is to dim a lamp then I would expect to see no waveforms. As mentioned Zener not required. if pin 6 goes above zener voltage the you will exceed the op amp output rating and this could destroy the chip. Personally id start again with a handful of components and some breadboard and make google your friend. You could also simplify the circuit by using a Fet to drive the lamp and have the voltage divider feed the gate and thus doing away with the opamp. I cant help but feel im missing something :)


Joined Mar 14, 2008
You can mess with that circuit as much as you like but, as noted, the ancient 741 cannot operate properly down to its negative rail voltage (which you have as ground).
It must have a negative supply voltage as well as the positive.

Do you not understand that?
led dimmer.gifPerhaps this will give you some new ideas.
The 555 is there to develop the sawtooth wave that is used as one input to the Op-Amp comparator. The voltage divider changes the other input as you turn the potentiometer.