On Thu, Feb 20, 2025 at 05:22 AM, Carlo wrote:
What do you really mean with "DC voltages look wrong" ? .TRAN 60 UIC skips the ITS step, hence there is not a DC solution at all.
What I mean is, what do the steady-state DC voltages look like, and are they correct or incorrect for your circuit?? I was not referring to the INITIAL voltages at the start of the transient simulation.? When the simulation is near 60 seconds and reached steady-state, do the bias voltages look right, or wrong?
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Do you actually mean the average of the voltages on some circuit's nodes ? In this sense, yes, starting from about 50 sec, the (averaged) voltage on heater's pin looks good like the (averaged) current entering it (its sign looks good either !)
I meant the voltages in your circuit, at some or any or all circuit nodes.? Were the FET's gate and source DC (bias) voltages about right, when near 60 seconds?? Or were they wrong?
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There is some feedback from the audio signal into the heater voltage.? Was that intentional?? Or just an undesirable side-effect?? I don't expect it would have very much effect on the heater's temperature (and from there to the triode's characteristics), but it looks undesirable to me.? Should there be filtering?
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.TRAN 60 Startup analysis looks good either.
So, if .TRAN 60 UIC looks bad, but .TRAN 60 Startup looks good, then it should be obvious which one to use and which one to avoid.
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But you added the word "either"!? I don't understand.? Did I misunderstand you?
AFAIK "Start external DC supply voltages at 0V" (Startup) does apply to DC voltage power supply and does not to SINE, PWL, PULSE, EXP sources including subcircuit (SUBCKT) sources. Does it apply to DC current power sources as well ?
Yes, "Startup" applies only to the DC value of independent sources.? I believe "sources" means both voltage and current sources.? (You can try it and see what it does.)
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Note that it does not apply to independent sources inside of subcircuits.? That's why it has the word "external".? I believe LTspice does that because sources inside subcircuits are likely parts of models and how they work, and not the sources that supply power to the circuit.? LTspice wants to start only the main power sources at 0 and then ramp them up, but not modify what's inside the models.
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Andy
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