So the circuit is basic. I dont understand why with the base of a standard 2n3700 BJT grounded, the cap is telling me there is 4.37V on it.
The base is hard grounded. There is literally no way for this thing to conduct.
If i take the cap out of the circuit it behaves as expected. It makes me think leakage.
Any one have any ideas?

 

It makes me think leakage.

I would think the same. The figures you see would depend on the accuracy of the BJT simulation model.

 

Your cap is blocking DC. What you are seeing is the collector base junction voltage drop. Once the cap is charged no current will flow through the emitter.

 

Your cap is blocking DC. What you are seeing is the collector base junction voltage drop. Once the cap is charged no current will flow through the emitter.

Its blocking DC in steady state sure.
there is no collector base junction voltage drop. Its in complete cut off

I have fooled around with the initial charge properties of the cap and it seems to work more as expected.

What i am trying to get to work is essentially an RC timer that is triggered by a certain signal at the base of the bjt.
But i cant get the stupid sim to work

 

Any one have any ideas?

It's a nonsensical circuit.

 

What i am trying to get to work is essentially an RC timer that is triggered by a certain signal at the base of the bjt.

You do realize that, once the cap is charged, there is no path to discharge it other than leakage?

But i cant get the stupid sim to work

That's likely because the "stupid sim" normally does a DC operating point analysis to establish the bias conditions before it does the transient analysis.
Try using the uic (Use Initial Conditions) option in the Transient analysis:

 

It's a nonsensical circuit.

yep of course it is!
Funny how you have the ability to say that with no context of the rest of anything.
really productive comment

 

You do realize that, once the cap is charged, there is no path to discharge it other than leakage?
That's likely because the "stupid sim" normally does a DC operating point analysis to establish the bias conditions before it does the transient analysis.
Try using the uic (Use Initial Conditions) option in the Transient analysis:

Yes, its intended as a one shot.

 

yep of course it is!
Funny how you have the ability to say that with no context of the rest of anything.
really productive comment

I didn't feel that stating more of the obvious. The transistor has no DC bias. The simulator is trying to make sense of a circuit that doesn't make sense.

If you don't know how to design circuits, you should tell us what you're trying to do instead of posting nonsense.

 

I didn't feel that stating more of the obvious. The transistor has no DC bias. The simulator is trying to make sense of a circuit that doesn't make sense.

If you don't know how to design circuits, you should tell us what you're trying to do instead of posting nonsense.

You are always such a ray of sunshine! This forum is so lucky to have you!
Its such a travesty that someone would come here to try and learn something and they should only come to this site if they already know EVERYTHING like you! But thanks for calling my work nonsense without having any idea at all what im trying to do!

 

You do realize that, once the cap is charged, there is no path to discharge it other than leakage?
That's likely because the "stupid sim" normally does a DC operating point analysis to establish the bias conditions before it does the transient analysis.
Try using the uic (Use Initial Conditions) option in the Transient analysis:

I dont have that option.
All i have is an option to "skip initial transient bias point"

 

Yes, its intended as a one shot.

Obviously quite literally, since it is once for the foreseeable future.
But how will it be reset if you want to reuse the one-shot another time?

If you want help with your circuits, that's fine, but don't get your shorts in an uproar because we point out you don't have a practical circuit.
So you can tell us exactly what you need the one-shot to do, and we can suggest better circuits, or you can continue to wallow in the circuit you have.

All i have is an option to "skip initial transient bias point"

Same thing.

 

Obviously quite literally, since it is once for the foreseeable future.
But how will it be reset if you want to reuse the one-shot another time?

If you want help with your circuits, that's fine, but don't get your shorts in an uproar because we point out you don't have a practical circuit.
So you can tell us exactly what you need the one-shot to do, and we can suggest better circuits, or you can continue to wallow in the circuit you have.
Same thing.

Just because you dont understand why or how it gets reset does not change the fact that i DONT need it to be reset!
In fact, part of the requirement is that it CANT be reset. The way its reset is the source voltage is removed and this is by intention not a screw up like you are your buddy would suggest.

 

Obviously quite literally, since it is once for the foreseeable future.
But how will it be reset if you want to reuse the one-shot another time?

If you want help with your circuits, that's fine, but don't get your shorts in an uproar because we point out you don't have a practical circuit.
So you can tell us exactly what you need the one-shot to do, and we can suggest better circuits, or you can continue to wallow in the circuit you have.
Same thing.

And by the way, the initial condition option did not change the output

 

Why don’t you explain what you expect to happen when you apply power.

 

Why don’t you explain what you expect to happen when you apply power.

Hi Bob
Thanks for replying
Think I'm just going to go another route.

 

You are always such a ray of sunshine! This forum is so lucky to have you!

Glad you're such a fan of my work that you've read all 15,000 of my posts...

 

yep of course it is!
Funny how you have the ability to say that with no context of the rest of anything.
really productive comment

MOD NOTE: Either report a comment that you take issue with, or ignore it. Snide comebacks are counterproductive.

 

Just because you dont understand why or how it gets reset does not change the fact that i DONT need it to be reset!

So you are saying as a fact, that the circuit will only be turned on once its lifetime?
You'll have to pardon me if I'm skeptical of that.

Your clinging to a clearly badly designed circuit in spite of its deficiencies is interesting.

 

And by the way, the initial condition option did not change the output

Did you define an initial condition for that node?

What simulator are you using?

Using LTSpice and the 2n3904 model (I don't have a 2n3700 model), the default simulation yielded 7.8 mV. But if I put an initial condition of 2 V, the sim starts off at 2 V on that node and stays there. If I start it off at 0 V, it wants to ramp up linearly to about 525 pV at the end of the simulation, but this is clearly a simulation artifact because I get the same result whether the sim runs for 10 ms or 1000000s. If I set the initial condition at -2 V, the voltage decays to about -480 mV, which is about what I would expect.