Simple voltage regulator get crazy... and so am I - 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 17th August 2009, 05:43 PM   #1
diyAudio Member
 
Malefoda's Avatar
 
Join Date: Jun 2006
Send a message via MSN to Malefoda
Angry Simple voltage regulator get crazy... and so am I

Hi folks,
Maybe I deserve to be treated as an idiot but I can't figure it out.

Take a TX, some schottkys, a 2200/35V Rubycon ZL to smooth that.
Then I have 17V.
Well that is too much for the numerous LM317@5V after (heat!).

So i fitted, just after the cap, a A7810 from TI, followed by a 2200/16 ZL.
With output leg in air it's 10V, when soldered with the cap... madness, my DMM can't auto-scale, it happened once that I saw 10V for few seconds but also that the TX started to humm...

I just don't understand, did I over rated the later cap? I think it is better with, else there will be nothing between my 7810 and many 7805 at 10/20 cm away... help!!!! When I see a 4700F after a 7805 in my CDP I don't understand why that stupid thing goes wrong...

Matthieu wich is used to have troubles only with simple things...
__________________
QED T260, Thorens TD-318, Marantz CD-43, TK2050, JBL 4313B & MJK's OB: music!
  Reply With Quote
Old 17th August 2009, 06:27 PM   #2
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Default Re: Simple voltage regulator get crazy... and so am I

Quote:
Originally posted by Malefoda
Hi folks,
Maybe I deserve to be treated as an idiot but I can't figure it out.

Take a TX, some schottkys, a 2200/35V Rubycon ZL to smooth that.
Then I have 17V.
Well that is too much for the numerous LM317@5V after (heat!).

So i fitted, just after the cap, a A7810 from TI, followed by a 2200/16 ZL.
With output leg in air it's 10V, when soldered with the cap... madness, my DMM can't auto-scale, it happened once that I saw 10V for few seconds but also that the TX started to humm...

I just don't understand, did I over rated the later cap? I think it is better with, else there will be nothing between my 7810 and many 7805 at 10/20 cm away... help!!!! When I see a 4700F after a 7805 in my CDP I don't understand why that stupid thing goes wrong...

Matthieu wich is used to have troubles only with simple things...

Two possibilities I can think of: the 7810 is oscillating, or it is connected the wrong way around. Did you connect the ground pin of the 7810 to the samr ground as the caps? How long is the wire between caps and 7810?
But if you could post a circuit diagram it may jump out at you/us.
I know, the circuit should be easy to visualize, but then if it was so easy it would work, right?

Edit: any chance that the last cap is the wrong way around? That would explain the tx hum and the 10V when unloaded. It would also explain the multimeter going crazy: the cyclic current limiting of the 7810 causes the Vout to fly all over the place.

jd
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 17th August 2009, 07:33 PM   #3
Khron is offline Khron  Romania
diyAudio Member
 
Join Date: Jul 2005
Location: Finland
Send a message via AIM to Khron Send a message via MSN to Khron Send a message via Yahoo to Khron
The 7810 oscillating is still a possibility. The ZL is a low-ESR series, and linear regs don't really get along with low-ESR caps on the outputs.

You could try and see what happens with a smaller cap after the 7810, or at least with a non-low-ESR cap.
  Reply With Quote
Old 17th August 2009, 07:49 PM   #4
diyAudio Member
 
Malefoda's Avatar
 
Join Date: Jun 2006
Send a message via MSN to Malefoda
Thanks gentlemen,

the cap is on a test board with the 7810, maybe 3mm after And yes I've checked many times and can say it's the right wiring.
I will try the same but a LM317 and/or a 220/50 ZL. In datasheets they say a 0.1 or 1F is recommended in most cases before the filter cap if it's far away (what does "far-away" stands for in mm???) and after (I have loads of Wima's MKS if needed...). But what in the case of "bewteen" pre-reg 7810 and regs LM317?

Matthieu
__________________
QED T260, Thorens TD-318, Marantz CD-43, TK2050, JBL 4313B & MJK's OB: music!
  Reply With Quote
Old 17th August 2009, 07:55 PM   #5
Khron is offline Khron  Romania
diyAudio Member
 
Join Date: Jul 2005
Location: Finland
Send a message via AIM to Khron Send a message via MSN to Khron Send a message via Yahoo to Khron
Once again, even if only as a test, try a non-ZL cap, if you have any, at hand At least to see if that's the problem or not.
  Reply With Quote
Old 17th August 2009, 08:31 PM   #6
diyAudio Member
 
Malefoda's Avatar
 
Join Date: Jun 2006
Send a message via MSN to Malefoda
Unfortunately my testboard will not survive that I guess...(bended cap legs to make links...) anyway it's faulty.
Until this answer I read on Internet many opinions... like input//filter cap (same in my case) smaller or as big as the output (2200//2200F), lack of tiny caps (1/0.1) around or such...
In fact I'm also concerned by the best solution, AFAIK LM317/Low ESR in audio (CDP) do better than 7810/Non-Low ESR? If the 7810 is a part of the problem I may remove it
I'll tell you what I've found tomorrow, no light at the work table right now.
Matthieu
__________________
QED T260, Thorens TD-318, Marantz CD-43, TK2050, JBL 4313B & MJK's OB: music!
  Reply With Quote
Old 17th August 2009, 11:01 PM   #7
Matt BH is online now Matt BH  United Kingdom
diyAudio Member
 
Join Date: Jul 2009
Location: Cheltenham
I have had a few 7810s oscillate like mad before. Is it an old one? I find the older 7810 and 7809 to be particularly troublesome. I guess they just fool a standard 5V one by floating the ground pin with a few PN junctions, a sure way to make them unstable. The newer ones seem fine however (better, more accurate trimming of an actual 10V reg).

The 78/79 series of regs are very variable from manufacturer/manufacturer and batch to batch. So try another if you have one and or lose/lower the 2200uF cap. Or if you want to keep it, first try the circuit without it, then add some R in series with it untill it is OK.

Cheers Matt.
  Reply With Quote
Old 18th August 2009, 12:08 AM   #8
kevinkr is offline kevinkr  United States
diyAudio Moderator
 
kevinkr's Avatar
 
Join Date: Sep 2004
Location: Boston, Massachusetts
Blog Entries: 6
Probably a stupid question but what are you using for a heat sink on the regulator? Also most LM317 are not happy if the load current is significantly less than 10mA which you can usually cater to by setting the reference current to 10mA. (121 ohm resistor)

In terms of mm if the supply cap is within 50mm of the regulator there generally should not be a problem.

The 317 generally works fine with 30V supplies and can be operated at much higher voltages provided that the differential across it does not exceed about 35V. (I've used them in 300V supplies - similar to the Maida without problems, I believe something SY does to this day.)
__________________
"Extraordinary claims require extraordinary evidence." - Carl Sagan
  Reply With Quote
Old 18th August 2009, 03:14 AM   #9
iko is offline iko  Canada
diyAudio Moderator
 
iko's Avatar
 
Join Date: May 2008
Location: Toronto
Humming transformer? Sounds like a short to me. Try a light bulb in series with the transformer primary. If it lights up, it's a positive.
  Reply With Quote
Old 18th August 2009, 08:56 AM   #10
diyAudio Member
 
Join Date: May 2008
I would second the comment on heat. Is the regulator a TO-220 package? If it is, these are suitable for current up to 1A, which should be fine for your application. You could push it even higher with suitable heat sinking.

If it is in a TO-92 package, it will be unsuitable for your application, as the heat generated will cause it to become unstable after a few seconds of operation.
  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 12:59 PM.


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