I have no schematic for this. I would like to ask if anyone has any design recommendations.
I would like to build a one shot pulse that is triggered from a rising edge and is capable of driving a power mosfet gate

notes
No negative voltage rail available
No ICs available. Only jelly bean parts.
things im considering.

1. A monostable multivibrator with BJTs
2. A design with a comparator

If anyone has any suggestions, i would be interested in hearing them.

 

A design with a comparator

Is that not an IC?

So what "jelly bean" parts do you have?

 

I would like to build a one shot pulse that is triggered from a rising edge and is capable of driving a power mosfet gate

Tell us what you mean by “one shot”, because in the other thread you used it unconventionally.

 

You need to flesh out your requirements a bit. What input voltages? What output voltages? Just saying that you want to drive a power MOSFET isn't sufficient, since different power MOSFETs have difference drive requirements. Also, a huge difference is whether you are talking about a N-channel MOSFET or a P-channel MOSFET.

How long do you want the delay? Is the goal to delay turning the MOSFET on for some about of time after the rising input edge? Or is it to turn on the MOSFET immediately and keep it on for a certain period of time before turning off again?

What circuits have you looking into? Do a Google search for "transistor one shot" and look through some of the results.

 

So here is what I mean when I say one shot

I need to trigger a circuit with a signal that will rise from -vsat of a comparator and then be pulled high. However it will stay high.The trigger is not a pulse. It’s a transition from low to high
I could make it high to low if needed
When it transitions. I need a pulse to transition from low to high for 1 second then fall back to zero. That’s it
Only want it for one pulse and be done

I can use comparators and bjts caps resistors diodes
No other parts

 

So here is what I mean when I say one shot

I need to trigger a circuit with a signal that will rise from -vsat of a comparator and then be pulled high. However it will stay high.The trigger is not a pulse. It’s a transition from low to high
I could make it high to low if needed
When it transitions. I need a pulse to transition from low to high for 1 second then fall back to zero. That’s it
Only want it for one pulse and be done

I can use comparators and bjts caps resistors diodes
No other parts

That helps, but still need some details.

What is the "high" voltage? 1 V, 5 V, 12 V, 120 V? It makes a difference.

Most transistor circuits are intrinsically inverting, so having the output go low-to-high when the input goes low-to-high will likely involve some additional circuitry. If you can make the input signal transition high-to-low, that will probably make things easier.

What kind of comparators are you able to use? You said earlier that you weren't willing to use any ICs, so do you have a transistor circuit for a comparator that you are planning to use?

Have you gone out and looked at the various transistor-based one-shot circuits that can be found with the simple Google search I suggested?

If so, what questions/issues do you have with whichever one strikes you as a good candidate.

 

That helps, but still need some details.

What is the "high" voltage? 1 V, 5 V, 12 V, 120 V? It makes a difference.

Most transistor circuits are intrinsically inverting, so having the output go low-to-high when the input goes low-to-high will likely involve some additional circuitry. If you can make the input signal transition high-to-low, that will probably make things easier.

What kind of comparators are you able to use? You said earlier that you weren't willing to use any ICs, so do you have a transistor circuit for a comparator that you are planning to use?

Have you gone out and looked at the various transistor-based one-shot circuits that can be found with the simple Google search I suggested?

If so, what questions/issues do you have with whichever one strikes you as a good candidate.

thank you for the reply
I can use a basic comparator ic
The voltage needed should be 12v
I only have 12v to play with and I can use that 12v as a pull up to cause the pulse to go high
As you mentioned , I can make the trigger be active low if needed

I built a near circuit with a d flip flop earlier and I use the latch the to shut the initial pulse off.

I can also use a d flip flop but prefer not to

I have been looking at monostable multivibrator circuits with bjt and also similar with a comparator
My problem is. My trigger will not be a pulse. It’s a rise from low to high or high to low. That has cause problems with the vibrator circuits

I tried to built a monostablr multivibrator with a comparator which is simple enough but like I said my trigger stays high. That circuit seems to want a pulse as a trigger which makes no sense to me. Why build a circuit that outputs a pulse that needs a pulse to trigger it. Unless the goal is a change in period

do you have a suggestion on something to look at on google? Thanks

 

You can turn an edge into a pulse by just using an RC high-pass filter. A diode can be used to clamp the spike on the other edge that would otherwise go outside the supply rails.

EDIT: Fix typo.

 

You can turn an edge into a pulse but just using an RC high-pass filter. A diode can be used to clamp the spike on the other edge that would otherwise go outside the supply rails.

So are you suggesting the comparator approach and turning my rising edge into a pulse to trigger it with a high pass filter?
Appreciate your input very much

 

I'm just saying that if a problem that you are having is that you have a signal that transitions from one level to another and you need a pulse at that edge instead, that a high pass filter will produce that pulse.

 

Presuming this to related to your other thread, you need a schmitt trigger followed by a differentiator (high pass filter) triggering a monostable multivibrator.

 

Presuming this to related to your other thread, you need a schmitt trigger followed by a differentiator (high pass filter) triggering a monostable multivibrator.

Isn’t the high pass going to need an inductor?
sense I have a comparator, isn’t there any easy way to make the vibrator with it?

 

No, a capacitor and resistor is all that is needed. Look up RC high pass filter. It blocks the DC value and provides a short pulse on fast transitions. Inductors pass low frequencies and block high ones.

It is not really a high pass filter anyway, the cutoff frequency is not relevant, it is a differentiator, i.e. responds to changes in level.

I think this project might be beyond you.

If you would tell us what you are trying to do, we could probably offer a simpler solution. An RC timer for 5 seconds is not a good choice.

 

No, a capacitor and resistor is all that is needed. Look up RC high pass filter. It blocks the DC value and provides a short pulse on fast transitions. Inductors pass low frequencies and block high ones.

It is not really a high pass filter anyway, the cutoff frequency is not relevant, it is a differentiator, i.e. responds to changes in level.

I think this project might be beyond you.

If you would tell us what you are trying to do, we could probably offer a simpler solution. An RC timer for 5 seconds is not a good choice.

beyond me? You should be a motivational speaeKe!
it’s beyond me because I have not looked at a high pass passive circuit in 20 years and need to refresh some thing? Yea ok dude

feel free to not replyto anything I ask in the future

 

You can use this simple circuit:

ADDED:

Why is this preferable over a simple rc circuit

Because simple RC circuit does not generate good shaped pulse
exactly in time, defined by R4 and C1 values, but this circuit does.
Also, as you said, circuit "needed fast slew on the output".

It still requires 100uf

Feel free to modify circuit for your needs, for example -
decrease capacitance of C1:

 

You can use this simple circuit:
View attachment 302375

thank you
It still requires 100uf
Why is this preferable over a simple rc circuit

 

beyond me? You should be a motivational speaeKe!

Nope, I am a very poor liar.

feel free to not reply to anything I ask in the future

I will feel free to reply or not to anything I want. You can block me if you don’t like my posts.

 

Nope, I am a very poor liar.

I will feel free to reply or not to anything I want. You can block me if you don’t like my posts.

you are extremely rude
I guess being human is “beyond you”

 

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MOD NOTE: Enough! Both of you.

If you don't like the way that you are being treated in a thread that is not yours, then simply ignore the thread. At the very least, ignore the posts you don't like. If you feel something more is warranted, then the something more is to report the member to the moderation staff. If the thread IS yours, then either ask the other person, politely, to cool down their behavior or report the post and request, as the thread starter, that the other person be banned from replying to your thread thread. In either case, stop engaging in tit-for-tat personal exchanges or you can both find yourself being banned.

I have done nothing wrong
I have asked for help and repeatably told my work is nonsense and simple circuits are beyond my skill level
I am tired of being internet bullied when all I have done is come to an electronics forum for assistance with electronics and repeatedly thank folks for trying yo help

I’m tired of being told I’m not worthy just because I came to a help forum asking for
Help