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Old 24th February 2014, 07:26 PM   #211
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Quote:
Originally Posted by eddyvb View Post
Hi Jan, standby current is 100mA, 'on' is 440mA @18V.
I've put a lm317 circuit in front of the super reg. Maybe I can do something between the 2 reg's..
ps: great superreg pcb quality!
A simple solution would be to have a resistor and an LED on the input of the reg for standby indication.
Then in series with the prereg you do a small resistor that drops about 0.6V at 300mA, and use the resistor between E and B of a transistor, using the C to drive another resistor with current into the same LED. That will give you extra luminosity on the LED when load exceeds 300mA.

Jan
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Old 27th February 2014, 01:20 AM   #212
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Quote:
Originally Posted by Mark Johnson View Post
To increase the maximum output current, modify the design.

One possible design mod would be to substitute a high current depletion mode MOSFET + plenty big heatsink, for the series pass transistor. Perhaps something like the IXTP3N100.

Another possible design modification would be a 2-transistor replacement for the D44H11. You could consider a Complementary Feedback Pair ("Sziklai Pair"), a Darlington pair, or a depletion MOSFET-BJT pair. The Supertex DN4250 depletion MOSFET that Walt Jung advocates, might be an especially good choice.

A third possible design modification would be to use the Jung/Didden SuperRegulator with a conventional PNP (on big heatsink) current booster. The SuperReg supplies the first 75mA and the PNP supplies all the rest. Chose R1 = (VBE / 75mA) in the generalized schematic below.

In each case, your designer would want to verify that the modified circuit was unconditionally stable, and that its regulation characteristics (output impedance, line regulation, load regulation, noise, etc) remained excellent.

Click the image to open in full size.
Hi Mark

I am interested in trying the 1st and the 3rd suggestions.
However, before I plug a MOSFET into the regulator,
I need some clarification and advice.

Q1. Most MOSFETs have capacitance in the range of nF,
will it cause instability to the opamp as it has to drive a large capacitive load?

Q2. I have looked up some information from some MOSFETs datasheet,
in particular, I focus on parameters like max I, Vgs, Rds, Tr, Pdis and various Cs.
I look for low Tr, Vgs and large Pdis. Are there any other important parameter that I missed? (IXTP3N100 looks pretty good to me, what about IRLZ24N or IRF530N, I have plenty 530s at home)

Q3. I am confused that whether I need and n-channel or a p-channel MOSFET?
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Old 27th February 2014, 03:42 AM   #213
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BTW, it seems that IXTP3N100 is enhanced mode, rather than depletion mode.
Does it matter?
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Old 27th February 2014, 11:47 AM   #214
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The Jung/Didden Super Regulator is a sophisticated, high performance, marginally stable circuit that is prone to oscillation, even when constructed by expert designers who have lots of experience. I recommend that you DON'T try to modify it unless you really know what you're doing.

If you can duplicate jackinnj's simulated Bode plot of the unmodified Super Regulator (in post#177), then you might have a chance of succeeding. If not, I recommend you don't attempt to modify the SR. It won't work and you'll be unhappy.
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Old 27th February 2014, 11:56 AM   #215
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I think Mark's warning is appropriate. Although I would probably not agree to 'marginal stability', the design is highly optimized for very high performance. For example, replacing the output electrolytic with a boutique film cap will modify the loop gain and can induce oscillations.
I have build dozens of these circuits with no problems, but some of the changes discussed above are quite drastic and you are on your own on those.

If there is enough interest, I could develop a high-current version....

Jan
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Old 27th February 2014, 01:14 PM   #216
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Mark & Jan

Thank you for the cautious advice.

I need some time to figure out and work on the subcircuit and models in LTSpice.
I will start from here and plug in the necessary components:

http://www.diyaudio.com/forums/blogs...regulator.html
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Old 27th February 2014, 02:07 PM   #217
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Just plug AD797-15V model from AD into the asc.

Need to made an update to the MOSFETs model in LTSpice.
Attached Images
File Type: jpg AD797-MOSFET.jpg (156.6 KB, 413 views)

Last edited by B&W_arthur; 27th February 2014 at 02:08 PM. Reason: post pic
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Old 28th February 2014, 10:07 AM   #218
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Sorry for posting a wrong plot.

I re-ran the simulation (some resistor values in RJM's blog are different from Jung's 2000 article). I plugged the values show in the article into the schematic. It seems that there is something wrong around 1~2kHz if AD797 is used. For some MOSFETs, simulation cannot be run with AD797.

If replaced by OPA134, the plot looks more stable but the performance at low frequency is ...
Attached Images
File Type: jpg AD797-MOSFET-revised.jpg (161.0 KB, 382 views)

Last edited by B&W_arthur; 28th February 2014 at 10:11 AM. Reason: more info
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Old 28th February 2014, 02:02 PM   #219
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Here are some plots of the Jung Regulator with AD797:

Click the image to open in full size.

and

Click the image to open in full size.

The Z-out graph is the best i was able to measure in the very low end. Impedance in the vicinity of a micro-Ohm is not easy to measure.
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Old 1st March 2014, 10:16 AM   #220
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Quote:
Originally Posted by B&W_arthur View Post
Sorry for posting a wrong plot.

I re-ran the simulation (some resistor values in RJM's blog are different from Jung's 2000 article). I plugged the values show in the article into the schematic. It seems that there is something wrong around 1~2kHz if AD797 is used. For some MOSFETs, simulation cannot be run with AD797.

If replaced by OPA134, the plot looks more stable but the performance at low frequency is ...
The 797 is a somewhat different opamp from 'the others'. For one thing, it has an internal neutralisation loop based, iirc, on positive feedback. I don't know how accurate this is reflected in the spice model.
I do remember that the 797 was harder to stabilise in a practical superreg and both Walt and I eventually recommended other opamps for the design.

Jan
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