xarx

modified 10 years ago

Wrong hysteresis

126

01:15:41

Why does the voltage at npn base exhibit hysteresis? Why the graph of current for pnp collector has such a strange shape when the transistor is fully open? Are these simulation artifacts only?

published 10 years ago

rich11292000

10 years ago

Your using this stuff wrong

hurz

10 years ago

Spend a 10kOhm from base to ground will help to not let the npn float. Hope this helps.

xarx

10 years ago

Well, I know that the circuit can be fixed by adding some resistors. But that was not my question. This is a simplified demo circuit only, the problem exhibits itself in a real circuit, but is not so easily visible there.

hurz

10 years ago

Then reality and simulation fits perfectly together! What was your question?

xarx

10 years ago

I should have written "in a real circuit simulation",not a realisation. I was asking about the hysteresis - whether there is realy the hysteresis in this circuit, or whether it is an artefact of the simulator imprecission. I've never heard of h. in transistor behaviour. Please,read my questions again.

hurz

10 years ago

What is a "real circuit simulation"?

xarx

10 years ago

Simulation of a circuit that was constructed by someone else already. But I'd say that you are npt going to answer my question, you are just chatting.

hurz

10 years ago

Because you know already everything and just doing rhetoric questions for nothing. Nobody can help you, help yourself.

thebugger

10 years ago

The collector voltage needs to be higher than the base voltage for it to work correctly. You're driving the base with 1V while having 1V at the collector. Among other ways which can fix this this is the simplest. Just increase the collector voltage to 2V

rich11292000

10 years ago

I answered all three of your questions in the first post. The second post from hurz is a recommendation on how to salvage this circuit. A "simplified demo circuit" is not a full circuit. This can be easily identified by the word "simplified". You also answered your own questions by mentioning "simplified".

xarx

10 years ago

Thank you, thebugger, for the only constructive answer in this thread. Perhaps I simplified the original circuit too much. I'll try to publish the original circuit (it's simple), but will have a hard time to explain what I don't understand about it.

thebugger

10 years ago

This is the simplest solution yet i don't recommend it because the base current is way too high (avg 250mA). You must increase the collector voltage as i said AND add a base current limiting resistor.

xarx

10 years ago

After experimenting with the voltage as suggested, I'm almost sure that the hysteresis is a computational artefact.

hurz

10 years ago

Its the miller capacity of the first bjt.

xarx

10 years ago

That's a good idea. But when I change the AC shape to a more rectangular form, the orange voltage and the green current start jumping. Wouldn't they change gradually if it was the capacitance?

hurz

10 years ago

And the green ramp is caused by oversaturation of input transistor 1V Ube is a little to much, low value of input suppose to 250mV minimal and max 1V.

xarx

10 years ago

I will have to think about what you've said further, currently it's not clear to me. Nevertheless, a big improvement over your previous answers :-). Thanks.

hurz

10 years ago

But the way you make quick statements in your headline while you have to think about simple electronic questions unfortunately did NOT changed!

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