Circuits that shouldn't work...?

In article , Joseph2k wrote: [....]

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You mean like this? I tried it. It works fine. What did you expect me to see?

Well, it *does* show you that you're trying to put 1kA through a 1N4007. It just doesn't tell you that there's anything wrong with doing so. Nor would I want it to. It's up to the user to judge what's reasonable. You can't just switch your brain off and believe everything the simulator tells you.

Perhaps Saber is the simulator for you. That one does have thermal effects in its models. You still can't switch your brain off though...

Jeroen Belleman

In an evolving man-machine system, the man wil get dumber faster than the machine gets smarter. [ by Scott Guthery, SEN Jan 87, p. 20 ]

So you agree with me about what spice will do.

It produces wrong results for me. Of course i can calculate what it should do by hand very easily and test circuits produce the result my hand calcs say it should be. I guess i will have to build up a set of fairly universal PDF's and post it on ABSE. Take me about a week to get around to all that.

You shouldn't, if the diode in the upper leg of the secondary is really missing.

- YD.

It's missing the transformer's wiring resistance, and may be missing its leakage inductance, both of which dramatically affect the charging of C1, and it's missing C1's esr as well.

ohms

should

to

LTspice works very well for me, ive used other simulators too, however you have to remember the results you get are only as precise as the device models, timesteps and lack of parasitic elements etc allow.

you can set many parameters in LTspice wich trade off accuracy for simulation speed.

you can add parasitic elements and problems that some rectifier circuits seem to have will disapear, theres a very good ltspice group on yahoo wich I remember reading about this very thing, although ive never experienced it. its not a problem with the simulation but a problem with what you are trying to get it to simulate, if you could leave out parasitic elements in real life you would probably see all sorts of problems !

certainly start up of high Q oscillators is one area that requires the most attention, for me anyway, but there is a excelent help info for this on the ltspice group.

I wouldnt waste time trying to find and post circuits that dont simulate well, but try and learn how to tune the simulation to get acurate results.

simulation does save a lot of time and wasted components/pcbs etc and does allow you to find a far more optimum solution but does in itself I find take a lot of time sometimes messing about with the parameters and parasitics to get accurate results But within a realistic simulation run time.

its not a substitute for knowledge of electronics in fact it can require a much greater understanding to realise why the results arnt as expected.

If you have a specific problem with a circuit you cant get round with simple advice from the examples/tutorials/educational samples, its best to post the circuit file to the yahoo ltspice grp.

Colin =^.^=

Sorry, I didn't see that.

Did you vet it against bench measurements?

In article , Joseph2k wrote: [....]

My ISP doesn't carry ABSE. Could you post your LTspice schematic here. It is just ASCII text. I'd really like to see what the problem is.

In article , YD wrote: [...]

Diode missing! I don't see no diode missing :)

In article , Winfield Hill wrote: [....]

From my post where I said it worked fine. ==Where (IIRC): == == L1 = 100mH + 2R == L2 = 1mH + 0.1R == K1 = 0.95 == C1 = 1000uF + 0.01R

I don't think I've tried it without the extra resistances in there, but I'll bet it will ring on the capacitances in the diodes etc.

The (IIRC) was because this was more than a year back. The ESR value for the capacitor was just a guess, but the other numbers, I really used[1], were from measuring the transformer.

One problem with bench testing was that the sinewave would start when I closed the switch, not at some determined phase angle. It looked close enough for me to trust the spice stuff on it.

The real circuit had an extra diode in it to isolate the filtered output from a higher current unfiltered output.