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Old 3rd March 2009, 03:58 AM   #81
iko is offline iko  Canada
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Quote:
Originally posted by jwb
As long as we're simulating things, I thought I'd have a look at the improved Jung regulator. The output impedance is nice: below 1mOhm from DC to 4kHz, rising to 25mOhm at 96kHz.

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Hi jwb, I've simulated the Jung regulator in the past, various versions, but never got such good results as you. I tend to never use perfect current sources and such, in an effort to be as close as possible to the real thing (such dreams eh?). Even so, I take my own sim result with a large grain of salt. However, I would be interested to see if your results turn out as good if you replace the perfect current sources with the proper parts. Thanks in advance.
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Old 3rd March 2009, 04:14 AM   #82
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... this is the Jung variation I have tried simulating.
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Old 3rd March 2009, 04:18 AM   #83
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... with not too shabby results.
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Old 3rd March 2009, 04:19 AM   #84
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... output impedance?
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Old 3rd March 2009, 04:52 AM   #85
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ikoflexer: according to your simulator output, I'm sure your version of the Jung is oscillating. Try adding about half an ohm of ESR to C3.

I'm not sure how to model current diodes like Vishay J506. Those are the ones I use in practice. I shall look around for some canned spice models.
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Old 3rd March 2009, 05:05 AM   #86
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Its no good simulating the output load with a sine wave - you need to use a square wave to see how the regulator responds to fast transients. This will let you get an idea of how your loop is compensated and whether it needs tweaking (you won't get the absolutely correct answer from the sim, but the sim will help you understand what is going on in the circuit and where th e best place is to tweak). The last thing needed on a high performance reg whether shunt or series pass is overshoot or ringing on load or line transients.

I'd also look at the behaviour with a squarewave on the input (say 1-2V). this will also help you get a feel for feedthrough mechanisms.

Loop compensation and feedthrough prevention on these high performance regs is the as important as all the effort on low noise design. Don't forget it!


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Old 3rd March 2009, 05:11 AM   #87
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Here's the result with a .5R ESR on the output shunt cap.

As I said, I am pretty sure that the Jung regulator does an extremely good job in practice. My last attempt at a prototype was not very successful, as it oscillated like crazy. I'll probably do it again with some care as far as the layout goes.
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Old 3rd March 2009, 05:13 AM   #88
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Previous result was with the ad820b. The attached one, with an op27c. Surprising.
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Old 3rd March 2009, 05:14 AM   #89
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I'm not sure what you're plotting there. It can't be output impedance! Is it ripple rejection?
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Old 3rd March 2009, 05:25 AM   #90
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Yes, it is ripple rejection. A couple of posts back I plotted output impedance as well, shown as V(out)/-I(I1), with the Y-axis in mohms.

I'd like to mention a little detail which a lot of people may not realize. A humble low-pass filter at the input can make a big difference in practice. The Jung regulator especially might be a good candidate since its psrr curve raises as frequency increases. Here's the psrr plot for the ad820b version, with an LC filter (L=100mH, C=4700u) at the input.

Good night.
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