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Old 12th January 2010, 03:04 PM   #1
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Default Power Supply Bode plot - a "how to" video

Frederick Dostal of National Semi did this last December, I just found the link when cleaning up some stuff left over from Christmas:

Measure power-supply loop transfer | Test & Measurement World

You can get a PDF of the article on the EDN website:

Measure power-supply loop transfer - 2008-09-01 06:00:00 | Test & Measurement World
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Old 12th January 2010, 04:59 PM   #2
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Originally Posted by jackinnj View Post
Frederick Dostal of National Semi did this last December, I just found the link when cleaning up some stuff left over from Christmas:

Measure power-supply loop transfer | Test & Measurement World

You can get a PDF of the article on the EDN website:

Measure power-supply loop transfer - 2008-09-01 06:00:00 | Test & Measurement World
Nice. BTW, is this Frederic Dostal's calling name 'Jiri'? I have a great opamp book by one Jiri Dostal, at the time residing in Eastern Europe. Frederick's accent sounds like he came from there, too.

jd
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Old 12th January 2010, 06:22 PM   #3
luka is offline luka  Slovenia
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I have already posted this...
but thanks again
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Old 12th January 2010, 06:43 PM   #4
syn08 is offline syn08  Canada
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Here's more on the same topic:

http://cp.literature.agilent.com/lit...989-6304EN.pdf

It's not difficult to adapt this to use only an oscilloscope and a signal generator.
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Old 12th January 2010, 06:57 PM   #5
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Good luck reading the phase lead/lag between the two signals on an o'scope with any degree of precision. Of course, if you just want to know if the margin is big enough, this method should be fine. But to generate bode plots like the one shown in the article, one needs a network analyzer or gain/phase analyzer. I've considered building my own using the AD8302, but have yet to do so. Its dynamic range is a bit limited compared to full-blown test equipment, but it should be good enough to verify phase and gain margin.

BTW: For measuring phase margin on op-amp circuits, I usually implement an inverting amplifier and measure the voltage at the inverting input of the op-amp vs the input voltage to the complete amp. Basically, I'm measuring the error voltage of the feedback system. The resulting gain/phase plot is the inverse of the loop gain.

~Tom
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Old 12th January 2010, 07:30 PM   #6
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Quote:
Originally Posted by tomchr View Post
Good luck reading the phase lead/lag between the two signals on an o'scope with any degree of precision. Of course, if you just want to know if the margin is big enough, this method should be fine. But to generate bode plots like the one shown in the article, one needs a network analyzer or gain/phase analyzer. I've considered building my own using the AD8302, but have yet to do so. Its dynamic range is a bit limited compared to full-blown test equipment, but it should be good enough to verify phase and gain margin.
~Tom
I searched "Bode Plot" before posting and didn't see that it had already been put up.

The Intersil "Phasemeter" works pretty well -- looks to be the same principle as my HP Phase-Gain meter -- you take the sine wave, amplify it to clipping, run through a high speed comparator and integrate the difference. You need a pretty decent looking sine wave, however. One with a lot of noise, a lot of harmonics doesn't do it.
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Old 25th February 2012, 10:11 PM   #7
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More Bode Plot tutorials on Omicron-Lab's website: OMICRON Lab "Smart Measurement Solutions": Video Tutorials
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