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Old 8th March 2019, 02:19 PM   #1611
jan.didden is offline jan.didden  Europe
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Assuming D2 is in series with output of opamp, and the opamp output is at 1.18V, the regulator seemd to work OK, but there's an issue with the pass transistor or the input voltage. The opamp tries to pull base current to increase Vout, but can't go lower than 1.18V. Just an educated guess.

And again, measurements at the opamp pins and the pass transistor pins are much more telling.

Jan
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Old 8th March 2019, 03:56 PM   #1612
powermike145 is offline powermike145  United States
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Mr. Didden, thanks for the quick responses! Iíll take those measurements and report back.
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Old 8th March 2019, 07:27 PM   #1613
powermike145 is offline powermike145  United States
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D2 Zener diode is in series and has the correct orientation. Picture of the board is attached below. I took the following measurements with a 34.2V board input. All measurements are referenced to POS return:

U1 - IN: 7.86V
U1 + IN: 7.25V
U1 out: 1.11V
Q1 E: 12.5V
Q1 B: 13.1V
Q1 C: 34.1V
Q2 C: 13.1V
Q2 E: 32.0V
Q2 B: 31.4V

I also took a few more measurements with different input voltages. The super reg output stayed constant at 12.5V. Unfortunately, I took the wrong reading for the non inverted opamp input-so I don't have it-but here is the rest.

32.7V input:
U1 - IN: 7.86V
U1 + IN: ??? (I can go back into work and measure if needed)
U1 out: 1.1V
Q1 E: 12.5V
Q1 B: 13.4V
Q1 C: 32.6V
Q2 C: 13.1V
Q2 E: 30.1V
Q2 B: 30.0V

28.0V input:
U1 - IN: 7.86V
U1 + IN: ??? (I can go back into work and measure if needed)
U1 out: 1.1V
Q1 E: 12.5V
Q1 B: 13.1V
Q1 C: 28.2V
Q2 C: 13.0V
Q2 E: 26.3V
Q2 B: 25.7V

25.4V input:
U1 - IN: 7.86V
U1 + IN: ??? (I can go back into work and measure if needed)
U1 out: 1.1V
Q1 E: 12.5V
Q1 B: 13.1V
Q1 C: 25.4V
Q2 C: 13.0V
Q2 E: 23.6V
Q2 B: 23.0V

From your last post, I guess having over 600mV difference in opamp input is not good. Since I increased R5 from 4.99k to 8.25k(to keep D5's forward current=2mA) and R6/7 from 1k each, to 2k and 4.99k respectively; maybe these increased resistances are the issue? If so, I could lower the R6/7 divider to something like 1k and 2.5k, but not sure what to do about R5. Do you think changing the resistors is the right place to start? Thanks again for all the help!
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File Type: jpg 24v SupReg.jpg (669.2 KB, 332 views)
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Old 8th March 2019, 07:42 PM   #1614
jan.didden is offline jan.didden  Europe
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U1 - IN: 7.86V
U1 + IN: 7.25V
U1 out: 1.11V

So the output voltage divided down by the two resistors comes out to 7.86. Because that's higher than 7.25, the output of the opamp is slammed to ground.

You have an issue with those two resistors that divide down the Vout to -inp. The ratio should be (24-6.9) on top and 6.9 at the bottom. Check that.

Jan
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Old 8th March 2019, 11:41 PM   #1615
powermike145 is offline powermike145  United States
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Of course! I had R6/7 reversed. I had the right values to give 24V (2K and 4.99K), just stuffed on the board wrong. I swapped them and now have 24.5V steady output.

Mr. Didden, thanks again for all the help! If I every make it back to Belgium, I owe you a beer or two. Maybe an Orval or Rochefort 10? My favorites.
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Old 9th March 2019, 06:54 AM   #1616
jan.didden is offline jan.didden  Europe
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Beer is good ;-)

But seriously, these regulators are a simple circuit. You only need to know ohm's law and opamps. 99.9% of the issues can be diagnosed easily from looking at the opamp inputs and output.

If the -inp is higher than the +inp and Vo is too low, there's a problem with the feedback divider. It is that feedback divider that sets Vo, everything else is secondary. The only thing the opamp does is move its output to try to make -inp and +inp equal; it has no idea what a 'regulator' is. So if the opamp output is slammed to gnd or Vo, it is trying but not getting there.

Jan
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Cable: a potential source of trouble interconnecting two other potential sources of trouble - Erik Margan
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Last edited by jan.didden; 9th March 2019 at 06:56 AM.
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Old 25th March 2019, 07:48 PM   #1617
ApolloZhang is offline ApolloZhang  Europe
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Managed to finish the last 60 Pages or so, must admit that, Jan, you really have my respect, for repeating the same contents over the years, again and again...

Back to the topic.

Just read Erno Borbelys latest All Fet Super Reg, it seems that Mr. Borbely basically made an error amp out of Jfets, the rest is pretty the same as other Shunt regs.

It occured to me that, why not just build a single stage error amp? So heres some crude simulation in LTSpice:
捕获.PNG

Regulator.asc

PSRR in HF seems okay, but strange phase shift?
Point in using a single stage error amp is to minimize noise in this part, since one can use bjts with low Rbe to achieve even lower noise than ops like ad797, IMO....

Last edited by ApolloZhang; 25th March 2019 at 07:51 PM.
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Old 25th March 2019, 08:15 PM   #1618
Mark Johnson is offline Mark Johnson  United States
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Super Regulator
Output impedance is inversely proportional to error amplifier gain. To get SuperRegulator class output impedance you need LOTS of error amplifier gain. Among your design choices are (a) use an error amplifier topology with two gain stages; (b) duplicate the 140 dB gain that Scott Wurcer got from a single gain stage {folded cascode} using monolithic matching tricks; (c) positive feedback.
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Old 25th March 2019, 08:42 PM   #1619
ApolloZhang is offline ApolloZhang  Europe
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Quote:
Originally Posted by Mark Johnson View Post
Output impedance is inversely proportional to error amplifier gain. To get SuperRegulator class output impedance you need LOTS of error amplifier gain. Among your design choices are (a) use an error amplifier topology with two gain stages; (b) duplicate the 140 dB gain that Scott Wurcer got from a single gain stage {folded cascode} using monolithic matching tricks; (c) positive feedback.
Oops, getting 140dB of gain with discrete elements sounds pretty impossible, not to mention that most Op-Amps have OLG lower than 130dB...So the ad797 stays the best error amp for a SuperReg?
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Old 25th March 2019, 08:55 PM   #1620
jan.didden is offline jan.didden  Europe
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AD797 is very good but you need to be very diligent in wiring and general layout to avoid instability in this application.

I've had best results with the AD825 in pretty much any situation, clean, stable and dependable.

Jan
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