-1

Is there any other way to reduce the time width of the trigger pulse wave without using 555timer? enter image description here

1 Answers1

6

Your comparator circuit is flawed because of this: -

enter image description here

I've marked a red arrow showing what you have done wrong when using an op-amp with an AC signal source. You are attempting to feed in an input signal that rises 2 volts above and falls 2 volts below 0 volts. That will destroy the op-amp because it's most negative pin (the negative supply rail pin) is at 0 volts.

If you look at the data sheet for the LM358 you will see that you should not take any input lower than 0.3 volts below the negative supply pin.

OK, having said that it doesn't mean that a simulation will burn but, it also won't do anything like what a real circuit can be expected to do. After-all, why should a sim model try and emulate exactly what the real thing does when operated incorrectly? That would be beyond what a simulator is intended for and incur massive math processing overheads just to cater for the inexperienced. Sims are targeted at pro EEs hence you have to use the op-amp within its expected limitations.

So, if you are modeling a circuit in a sim you have to obey the rules for the device and, unfortunately, you are not doing this. I know you want a zero crossing detector but this isn't the way to go about it. The only reason it halfheartedly appears to be (somewhat) working is because the model (the simulation model) is throwing up nonsense results that cannot be relied upon.

You need to start from scratch, rethink your idea and implement a proper circuit (possibly using a window comparator or a regular comparator plus an exclusive or-gate and RC time constant to produce a thin pulse each time the comparator square wave output changes state).

Andy aka
  • 434,556
  • 28
  • 351
  • 777
  • is there any reference material for me to read about the RC time constant, i search up alot of it can't really understand – i suck at programming Jun 16 '20 at 16:00
  • Try looking up first order low pass RC filter. – Andy aka Jun 16 '20 at 16:18
  • uhmm from my understanding first order low pass RC filter work to allow a certain part of frequency to able to pass but from my simulation i see all of the wave is in the same frequency i don't really understand how it able to narrow down the squre wave when its all in the same frequency and i have change to IC to LM741. https://i.stack.imgur.com/lTOkl.png – i suck at programming Jun 16 '20 at 16:41
  • [Reasons not to use a 741](https://electronics.stackexchange.com/questions/304521/reasons-not-to-use-a-741-op-amp). I don't answer questions on circuits that propse to use a 741 other than to give this link. It was designed and built before JFK was killed and before men even got into space. – Andy aka Jun 16 '20 at 16:51
  • ok.. any op amp to recommend i found lm748 seem to meet the requirement but unable to get a simulation got any other op amp recommendation and how the first order low pass RC filter able to narrow the square wave when all the frequency is the same – i suck at programming Jun 16 '20 at 17:57
  • You need to find an op-amp that can handle below the negative rail input signals. There are few (not many and maybe hard to get). But when you do find one you will have a sinewave to square wave circuit and then you need to convert edges to pulses hence what I said about an RC circuit and an exclusive or gate. – Andy aka Jun 17 '20 at 11:26