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Strange circuit behaviour through SPICE

Hi all, I've done some poweramp circuits and wanted to check them in SPICE. I'm using Multisim ver.10. I was curious about the circuit's openloop gain and bandwidth and ran an "AC Analysis" in the simulation menu. I made the closedloop gain many times more the amount of openloop gain. The result indicates that I should have problem with "Nyquist stability". In other words, the openloop gain hasn't dropped below zero when the phase shift has reached 180 degrees. The real circuit operates fine, with no indications of instabilty. Dominant pole compensation is used. Is there a chance that SPICE has a problem in simulating such circuits, or am I doing something wrong?

Reply to
powerampfreak
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"powerampfreak" schrieb im Newsbeitrag news: snipped-for-privacy@i12g2000prf.googlegroups.com...

Hello,

If you use the amplifier with a gain setting of 10 for example, you should look for the phase at 20dB open loop gain.

Best regards, Helmut

Reply to
Helmut Sennewald

Or adapt my PSpice LoopGain function (available on my website) to Multisim, and get it exact.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
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Reply to
Jim Thompson

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