Super Regulator, collecting the facts - Page 26 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 31st October 2003, 05:36 PM   #251
jcarr is offline jcarr  United States
diyAudio Member
 
Join Date: Jul 2002
Location: Tokyo, Japan
How are you doing, Fred?

>Deliberately increasing the ESR of capacitor types such as OSCON Black and film caps can also be achieved with a small series resistor.<

I also use this technique a lot, particularly for bypassing/decoupling duties. In my case, the caps are usually some flavor of stacked film, stacked ceramic or OS, while the resistors are typically low-ohmage SMD or leadless packages.

Without the series resistor, at times you can end up with high-frequency high-Q resonances that may lead to a somewhat etched, forward sound. But different situations can give rise to different resonant behavior (or varying sensitivity to the resonances that do occur), so it also pays to experiment on a case-by-case basis.

regards, jonathan carr
__________________
http://www.lyraconnoisseur.com/, http://www.lyraaudio.com
  Reply With Quote
Old 31st October 2003, 05:54 PM   #252
diyAudio Retiree
 
Join Date: Oct 2002
Location: Spain or the pueblo of Los Angeles
Default Thanks

Another treat for Halloween from the other JC. I was wondering how long till you got in on this. Thanks for the very useful information. What a great collection of ideas we've managed to trick out of some of the real audio veterans! Remind me to bring a pocket notepad if I ever go drinking with any of you guys. The forum has really become to place I have long hoped for some really good high end audio design hints.
  Reply With Quote
Old 31st October 2003, 06:06 PM   #253
jcx is online now jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
my point is that there is the possibility of an alternative compensation that allows the use very low esr caps not too "far" from the existing super reg topology/circuit, of course the zero from the esr has to be considered, but i belive my suggestion allows stability with much smaller esr, and allows the "infinite" increase of the Cout that many diy builders tend towards

yes i am finding it hard to find the compensation discussion in the on-line articles i have access to - but then i also have trouble reading off the monitor, maybe time to print it all out...

i should also think anyone here would recognize the "engineering" math; accuracy of calculation beyond the quality of the estimates is pointless, just be sure to round in the conservative direction

i certainly don't mean to badger you on AD's spice modeling, i just wished that OP Amp manufacturers spent an amount of effort on the model proportional to the time their customers end up wasting by using poor models

enjoy your retirement but the name "Walt Jung " will remain associated with Analog Devices in my mind for some time to come
  Reply With Quote
Old 31st October 2003, 06:26 PM   #254
WaltJ is offline WaltJ  United States
diyAudio Member
 
WaltJ's Avatar
 
Join Date: Aug 2003
Location: USA
Default Stability analysis without including ESR?

Quote:
my point is that there is the possibility of an alternative compensation that allows the use very low esr caps not too "far" from the existing super reg topology/circuit, of course the zero from the esr has to be considered, but i belive my suggestion allows stability with much smaller esr, and allows the "infinite" increase of the Cout that many diy builders tend towards
Would you believe that's already been discussed? See article below, page 16, Figure 5 and the associated box.

Pardon me, but I still don't see how anyone could comment on stability without *explicitly* considering the ESR of the very capacitor under discussion.

Quote:
yes i am finding it hard to find the compensation discussion in the on-line articles i have access to - but then i also have trouble reading off the monitor, maybe time to print it all out...
I think I mentioned this one earlier (I could be wrong). I built a website after I was inundated with requests to email the AE 4/2000 article. This article can be retrieved at:

http://home.comcast.net/~walt-jung/w...ed_PN_Regs.pdf

wj
  Reply With Quote
Old 31st October 2003, 06:36 PM   #255
WaltJ is offline WaltJ  United States
diyAudio Member
 
WaltJ's Avatar
 
Join Date: Aug 2003
Location: USA
Quote:
Mr. Jung raises the excellent point that an output capacitors parasitics sold be part of the design process. I believe this topic has come up on the forum in the past as well. The ESR is often given in the capacitor specs and ESL can be estimated by compare the case size of the cap in question with that of a similar cap who's ESL number is characterized.
Fred, I would change "excellent" to necessary, above. Obviously, from the postings by jcx and yours truly, one cannot just hang any old cap on the output of one of these regs. I believe you talked a little while back about using an Oscon on Andy's card? Be careful with that, for the reasons we've been discussing. A small series R of about 0.5 ohm will do wonders tho, and should restore stability.

wj
  Reply With Quote
Old 31st October 2003, 10:09 PM   #256
dimitri is offline dimitri  United States
diyAudio Member
 
dimitri's Avatar
 
Join Date: Oct 2002
Location: retired
Send a message via ICQ to dimitri
Default Invaluable nuggets of information

Yes, yes, Fred, we are watching and listening very carefully with bated breath for the next really good high end audio design hint.

So can be LED used as a voltage reference? Will such reference generate excess noise as compared with the couple of diodes connected in series? Does somebody have a reliable data?
  Reply With Quote
Old 2nd November 2003, 05:13 AM   #257
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
Smile Y'all are going to kill me for this...

I was reading with interest the discussion regarding the current source, and making its value less sensitive to supply voltage. I'm looking at a SPICE simulation of the 90 Volt version posted here: http://www.diyaudio.com/forums/showt...528#post256528 I tried several things. I removed the LED biasing resistor and replaced it with an ideal current source. Then I removed the LED and its biasing resistor completely, replacing the LED with an ideal voltage source. I looked at the voltage transfer function from the unregulated input to the output, that is, the small signal AC line rejection, from 10 Hz to 10 MHz. The result? Absolutely no change whatsoever. Kind of like the old Twighlight Zone episode where the doctor shouts "No change!!!" (sorry, you had to have seen it).

On a slightly different subject, there's been some discussion of the load capacitor and its effect on stability. For the 90 Volt reg, I decided to post a plot of the simulated voltage transfer function from the base of the PNP emitter follower connected to the op-amp output to the output of the regulator itself. As I mentioned before, the load capacitor is 100 uF with a series inductance of 30 nH and a series resistance of 0.25 Ohms. This gives a series resonant frequency of about 93 kHz. Note also that the ESR of the cap is of the same order of magnitude as the open-loop output impedance of the pass element. You can clearly see that the cap interacting with the pass transistor gives the circuit the behavior of a very low-Q notch filter, but with high-end rolloff. That filter has phase lead above the 93 kHz center frequency, which helps the stability situation somewhat. The solid curve is the magnitude and the dotted curve is the phase. For this circuit, you don't want the unity loop gain frequency to be much above 3 MHz or so.
Attached Images
File Type: gif regpasselements.gif (16.3 KB, 1189 views)
  Reply With Quote
Old 2nd November 2003, 08:53 AM   #258
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Andy,

I have two remarks on this very interesting post, if I may.

Firstly, the fact that you can find no difference in the line rejection when changing the input cs configuration. I find that VERY strange. I would accept something counter-intuitive, because such often are the ways of mother Nature, but no change? Really?

On the transfer function curves, I note that the dip of the magnitude is just 8dB or so. Although it does diminish the curative effects of the control loop in that area, 8dB is not dramatic.
Is it too much to ask to run the same simulation but now with an output cap of 1uF, 5nH and .01 Ohms?

Jan Didden
  Reply With Quote
Old 2nd November 2003, 02:07 PM   #259
WaltJ is offline WaltJ  United States
diyAudio Member
 
WaltJ's Avatar
 
Join Date: Aug 2003
Location: USA
Quote:
Andy, I have two remarks on this very interesting post, if I may. Firstly, the fact that you can find no difference in the line rejection when changing the input cs configuration. I find that VERY strange. I would accept something counter-intuitive, because such often are the ways of mother Nature, but no change? Really?
Hi Andy. I tend to agree with Jan here. As a SW EE, surely you must have been bitten somewhere along the way by a SPICE blind spot?

I suggest backing up and looking at it with a DC sweep, to get the basic feel of what the different topologies do, then go on to the AC. They should be readily differentiated.

Some more general comments on your ckt (which I hope will be helpful).

1) The noise of the high voltage level shifting zeners will be horrendous relative to the Isource noise. I would suggest moving the C3 100uF bypass cap to other side of R7, to make a LP filter that works against 300 ohms vis-a-vis the low dynamic Z of the zeners.

2) Note that this will also have another positive effect, that of attenuating the AC components of the Isource noise. In fact the lower the Z seen at the Isource output, the better off will be everything.

3) You alluded to the Pd of the TL431. Yes, at 30V, it is an issue! Here's a suggestion for you. Couldn't this be helped by dropping the terminal voltage downward? The OP37 op amp (and others) don't require a full 30V to operate. 15V should do fine, and will help the Pd of the 431 by a factor of 2x.

I would think that the relative Z of the Zobel network R17-C5 would have a dramatic effect on phase/gain, in the regions you are targeting.

Hope this is helpful.

wj
  Reply With Quote
Old 2nd November 2003, 04:43 PM   #260
andy_c is offline andy_c  United States
Banned
 
Join Date: Apr 2003
Hi guys,

Regarding the simulated line rejection results, please note that I'm not making the claim that these are some kind of ironclad results. It's really just to say, "This is what I found". I'm going to try some more things and see what shakes out. I did have to use a .NODESET directive to get the DC analysis to converge. I need to figure out how to get LTSpice to report the DC operating points it found for the AC analysis.

Walt was right about the Zobel network affecting the results, though it is a bit subtle. The plots without the Zobel network (not shown) show slightly less phase shift at 10 MHz - about -37.5 degrees lag instead of -45 degrees, and -8.0 dB of gain. I found that reducing the Zobel network series capacitance by a factor of 10 still killed the 50 MHz parasitic just fine. That should kill the extra phase lag from this contribution.

Per Jan's request, I've shown a plot with a load capacitor of 1 uF, having a series resistance of .01 Ohm and a series inductance of 5 nH. The attenuation at the notch is 33.3 dB, which would correspond to an output impedance of the pass transistor of 0.45 Ohms if it were purely resistive. This is consistent with the 61 mA operating current from the DC current source load. The behavior with the 100 uF cap with 0.25 Ohm ESR is also consistent with that value of pass transistor output impedance. I think this plot shows pretty clearly that a low ESR cap is not good. The notch can be so deep that it forces the loop gain magnitude to unity at a frequency below the notch where the phase is lagging considerably.

I would expect the D44H11's to do better here than the MJE15030 I'm using, because of their higher ft. I have done some checking of the simulated ft of the MJE15030 model vs the data sheet curves. They agree well with the data sheets. Those results are shown here http://www.diyaudio.com/forums/showt...533#post245533 Note that I incorrectly wrote "IKF" in that post when I should have written "ITF", which Christer later caught. Maybe I could get one of the mods to edit this.

I did the plot below by replacing the 100 uF cap with the 1uF cap. I'm now beginning to wonder whether Jan wanted this or to add it in parallel with the 100 uF cap. The Zobel network has been removed for this simulation.
Attached Images
File Type: gif regpasselements2.gif (13.9 KB, 1070 views)
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



New To Site? Need Help?

All times are GMT. The time now is 03:54 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2