Super Regulator, collecting the facts - Page 48

jackinnj · 28th February 2007, 12:57 PM

Here's a picture of the negative side regulator -- this is a proto with no silk, and I think I will go to SMT LM337's -- the size can probably shrink by 25% or so -- I've provisioned for the +/- SENSE wires but they are jumpered here:

peranders · 28th February 2007, 02:17 PM

Can't see but have you an emitter follower down to ground from the opamp output? The zener arrangement should create 7-9 volts at the output in order to give supply voltage to the opamp. Have you as a test tried to feed the opamp from the unstablized side (after the LM337)?

jackinnj · 28th February 2007, 04:37 PM

PA -- I found the problem -- the positive connection of the capacitor (C7) connection to the AD825 IN+ was faulty. It won't start if this connection isn't secure.

jackinnj · 28th February 2007, 05:56 PM

here's an a.c. coupled scope-shot of the negative regulator output -- the transistors are MJD45H11 and MMBT5088 -- the trace has been averaged 16X for better clarity -- this is 10.4 millivolts RMS at 1 MHz -- there are no compensation capacitors on the AD825.

Same thing with 300 pF compensation caps (WJ recommended 100pF, but I don't have any SMT 100pf's, drat!)

janneman · 28th February 2007, 06:01 PM

Quote:

Originally posted by jackinnj
here's an a.c. coupled scope-shot of the negative regulator output -- the transistors are MJD45H11 and MMBT5088 -- the trace has been averaged 16X for better clarity -- this is 10.4 millivolts RMS at 1 MHz -- there are no compensation capacitors on the AD825.

Not nice - what's your final output cap? Type, value? I guess you have a prereg - does the prereg show something like this on its output?

Jan Didden

jackinnj · 28th February 2007, 08:47 PM

the oscillation occurs with the LM337 pre-regulator -- the positive SR with no pre-regulator doesn't show any oscillation.

I am using Panasonic FC's 120u/25V.

It isn't apparent from the Audio Elec article of 4/2000 whether WJ performed the same extensive testing on the pre-regulated SR as was the case in the 1995 series. I have to read the series again.

Here's a snapshot of the SR output and the output of the LM337 -- "be some serious modulating going on down there Amos"

WaltJ · 28th February 2007, 09:04 PM

The LM337 requires an output cap for stability, see DS. In the "Improved Positive / Negative Regulator" article of 2000, this is discussed on page 18, and takes the form of C1 and C12 of figs. 1 and 2.

jackinnj · 28th February 2007, 10:13 PM

OK, I put a 120u/25V on the LM337 in put and that seems to have done the trick -- the board was being tested with rather long leads.

jackinnj · 1st March 2007, 06:19 PM

In figure 4 of the AE article from 4/00 there is no bypass on R102 -- 825R from adjust to the output of the SR -- should this also be a.c. coupled to the output?

peranders · 1st March 2007, 06:34 PM

Can you show us how you have made the grounding for all parts. This is very sensitive.

28th February 2007, 02:17 PM	#472
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Can't see but have you an emitter follower down to ground from the opamp output? The zener arrangement should create 7-9 volts at the output in order to give supply voltage to the opamp. Have you as a test tried to feed the opamp from the unstablized side (after the LM337)? __________________ /Per-Anders (my first name) or P-A as my friends call me

28th February 2007, 09:04 PM	#477
WaltJ diyAudio Member Join Date: Aug 2003 Location: USA	lm337 stability requirements The LM337 requires an output cap for stability, see DS. In the "Improved Positive / Negative Regulator" article of 2000, this is discussed on page 18, and takes the form of C1 and C12 of figs. 1 and 2.

1st March 2007, 06:34 PM	#480
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	Can you show us how you have made the grounding for all parts. This is very sensitive. __________________ /Per-Anders (my first name) or P-A as my friends call me

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28th February 2007, 12:57 PM	#471
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	Here's a picture of the negative side regulator -- this is a proto with no silk, and I think I will go to SMT LM337's -- the size can probably shrink by 25% or so -- I've provisioned for the +/- SENSE wires but they are jumpered here:

28th February 2007, 04:37 PM	#473
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	PA -- I found the problem -- the positive connection of the capacitor (C7) connection to the AD825 IN+ was faulty. It won't start if this connection isn't secure.

28th February 2007, 05:56 PM	#474
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	here's an a.c. coupled scope-shot of the negative regulator output -- the transistors are MJD45H11 and MMBT5088 -- the trace has been averaged 16X for better clarity -- this is 10.4 millivolts RMS at 1 MHz -- there are no compensation capacitors on the AD825. Same thing with 300 pF compensation caps (WJ recommended 100pF, but I don't have any SMT 100pf's, drat!)

28th February 2007, 08:47 PM	#476
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	the oscillation occurs with the LM337 pre-regulator -- the positive SR with no pre-regulator doesn't show any oscillation. I am using Panasonic FC's 120u/25V. It isn't apparent from the Audio Elec article of 4/2000 whether WJ performed the same extensive testing on the pre-regulated SR as was the case in the 1995 series. I have to read the series again. Here's a snapshot of the SR output and the output of the LM337 -- "be some serious modulating going on down there Amos"

28th February 2007, 10:13 PM	#478
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	OK, I put a 120u/25V on the LM337 in put and that seems to have done the trick -- the board was being tested with rather long leads.

1st March 2007, 06:19 PM	#479
jackinnj diyAudio Member Join Date: Apr 2002 Location: Llanddewi Brefi, NJ	In figure 4 of the AE article from 4/00 there is no bypass on R102 -- 825R from adjust to the output of the SR -- should this also be a.c. coupled to the output?

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