LT Spice opamp a liittle weird

Submit your question to the LTspice List... I have no clue as to how Mikey's UniversalOpamp2 is supposed to work. ...Jim Thompson

Where's that?

I have no clue as to how

I use it a lot, and it seems to work fine, but the current limit is really weird. If you ground the output, you get the limit that you specify. But the current limit declines as the output moves toward the rails; not ever super close to the rails.

UOP2 is not mentioned in the LT Spice help. And not mentioned much anywhere else.

E-mail Helmut Sennewald and ask how to join... I can't remember how it's done since Yahoo @#$%'d up everything. ...Jim Thompson

Got a 2Amp OpAmp handy ?>:-} ...Jim Thompson

I'm actually using a TCA0372, which is a dual 1-amp part. But I set the current limit to 1 amp in the UniversalOpamp2 model, and it limited way below 1 amp.

The OnSemi data sheet says that it will output 1 amp, but doesn't say what the typ current limit is. Must be more. The cartoon schematic in the data sheet doesn't show any current limiting!

So UniversalOpamp2 is fuzzy, and TCA0372 is fuzzy. Situation normal.

Sure thing--I have a couple of dozen LM675s in my drawer cabinet.

Cheers

Phil Hobbs

LT1210, with model in LSspice.

RL

LT spice on Yahoo groups... but it now fills up my gmail account.

George H.

Subscribe to the _digest_, I get one or two a day, easy to follow. ...Jim Thompson

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Thinking outside the box... producing elegant solutions.

"It is not in doing what you like, but in liking what you do that is the secret of happiness." -James Barrie

The schematic is impossible (PNP in upper output pair), not fixed in dozens of revs, and still there in r11. Candidate for Bad Circuits.

But it is a great amp, and dirt cheap. I've used 3300 so far, no problems.

That's what I like about electronics. We use physics, math, control theory, simulation, data sheets, app notes, professional advice... and you can't trust any of them.

Larkin's question was posted by me into the yahoo group earlier today. After three attempts two of my posts eventually showed up on the mail list. Yahoo's group web page is too FUBAR for me to see my own posts there. YMMV.

Here's a copy-and-paste of the only response from the LTSpice yahoo group thus far:

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Don asked questions about the UniversalOpamp2 in LTspice.

True ... but there is a little bit to be found on the example schematic at ...\examples\Educational\UniversalOpamp2.asc where it shows the four available versions or levels.

It does indeed. It is not related to or caused by the "ilimit=2" parameter which h as a hard limit at 2 amps. It seems to be going into soft limiting beginning somew here around 0.5 amps. It also depends on whether the load is resistive or inductiv e; and the limiting is not at the peak of either the voltage or the current. (It's almost like a slew rate limit of the output current?)

I'd recommend posing this question to Mike Engelhardt himself. Send your question and schematic to the address shown in Help > About LTspice.

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As noted earlier, yahoo's group web page is FUBAR for me. So, another subscriber needs to obtain Engelhardt's email addy.

Thank you,

I gave up trying to post via the web. Fortunately you can do it easily via E-mail reply from the Digest E-mail.

Mike Engelhardt ...Jim Thompson

John, I like to roll my own simple opamps in SPICE, for custom fT and slew rate. Ignore other niceties: multiple poles, time delays, supply-rail saturation.

Use controlled-source elements: a G element provides the gain-node error current, a cap to ground sets fT. Add an E element with G=1 for the output, finish with a series output resistor for open-loop Zout. If you want current limiting, add an output sense resistor and npn + pnp current-limit BJTs with their collectors back to the gain-node.

If you must have supply-rail limiting, add two diodes from gain-node to appropriately-set voltage sources. If you need better, accurate slew rate, etc. etc, then go ahead and make a Boyle macromodel, see LTC's AN48.

Snork!

I sometimes use "e" as an opamp, with or without adding a single-pole rolloff. Doesn't need power supplies! But UniversalOpamp2 has slew rate, e and i noise, offset, bandwidth, current limiting, rail swing (which may be squirreley), bias currents, all that. I often use it as-is, or maybe tweak one or two parameters. That's easier than using an LTC part, unless you're familiar with it already.

Helmut Sennewald, the LTSpice yahoo group guru, recently posted:

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The UniversalOpamps2 from LTspice cannot be used for high current applications without a modification. I have reduced Ron in its switch-model from 10Ohm to 1Ohm.

Right-mouse-click on the placed symbol to lower "Switch_Ron" to get even more current.

You can download an example which I made 2012.

UniversalOpamps2power_test.zip

I will check later whether the UniversalOpamp2 model has changed since that time.

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In regards to electronics being an amalgamation of many things, it turns out that my job description is gestalting generalist.

A generalist knows more and more about less and less until until eventually he knows nothing about everything. A specialist knows more and more about less and less until eventually he knows everything about nothing.

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BTW Win, TIA for the circuit boards that you are sending me.

Thank you,

The current model doesn't include a visible Switch_Ron parameter. I added one and it didn't complain, but it seemed to have no effect.

I'm not registered with Yahoo.

Try this link instead:

Thank you,