Will 7915 Regulator Handle - 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 18th March 2006, 07:37 PM   #1
diyAudio Member
 
Join Date: Sep 2005
Default Will 7915 Regulator Handle

I am trying to take +-32.6 VDC and get +-15 VDC. I am using ST Microelectronics L7815ACV and L7915ACV regulators. I get +15 VDC with no problem. But the negative regulator gives me 24 VDC.

Looking at the label side of the regulator I have attached the ground to the left leg, the input to the center leg and the output to the right leg. With no other circuitry connected I get -24 VDC from ground to output. I have tried 4 different regulators all with the same result. When I remove power from the supply and the capacitors in the 32.6 VDC sypply discharge, the voltage across the regulator drops to 15 and holds there for a few seconds as though it is trying to regulate.

Is it possible that this regulator will not handle 35 VDC input even though the data sheet says it will? Is there a different regulator I should use? Thanks for any help.
  Reply With Quote
Old 18th March 2006, 07:56 PM   #2
diyAudio Member
 
Join Date: Oct 2004
The 7915 can handle 32.6 volt,I been using 35volts for more than 2years now and they are working fine.

Check wiring

Make you caps are wired properly.
  Reply With Quote
Old 18th March 2006, 11:15 PM   #3
diyAudio Member
 
Join Date: Sep 2005
Default Tried With No Caps

I hooked power directly to the pins of the regulator. -32.5 to the center pin and ground to the left pin. I then measured from ground to the right pin. and got -24 VDC. I even took one regulator that I had removed from the circuit and tried rervsing ground and ouput thinking I was reading the data sheet wrong. But it did not work at all and got very hot in short period.

The positive regulator works fine which is why I am not sure what to do next. I am thinking of trying a different brand.
  Reply With Quote
Old 19th March 2006, 01:14 AM   #4
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
78xx and especially 79xx need a capacitor at the output in order to work stably, and some versions may also need a minimum load (usually a few mA will suffice). In particular do not even try to run a 79xx without at least 10uF output cap, you will get all sorts of nasty effects otherwise. It would be prudent to download a datasheet, they usually include an application schematic, which, you will notice, has at least two caps connected to the regulator. You omit these at your won risk.
  Reply With Quote
Old 19th March 2006, 01:19 AM   #5
diyAudio Member
 
neutron7's Avatar
 
Join Date: Dec 2003
Location: Toronto Canada
i have used a few of these and never had a problem like that. is the output you get actually regualted?

maybe you just have a dry solder joint. look esp on the ground pin. also maybe you got a bad regulator, but i just buy el cheapo chinese ones from ebay and i never even had one of those DOA.
  Reply With Quote
Old 19th March 2006, 08:40 PM   #6
diyAudio Member
 
Join Date: Sep 2005
I added a 10k resistor as a load on the negative supply and that dropped the voltage to -19.6VDC. So I am not getting regulation.
  Reply With Quote
Old 19th March 2006, 10:34 PM   #7
diyAudio Member
 
Join Date: Sep 2005
My problem is solved. The ST Micro version of the 79xx requires a load of 3ma or more to begin to regulate. When I added a load of 5k the voltage dropped to 15.5VDC. What was so misleading is that the 78xx version of the regulator worked fine with no load.

Thanks everyone for your help and suggestions.
  Reply With Quote
Old 20th March 2006, 12:08 AM   #8
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Quote:
Originally posted by LHMAudio
My problem is solved. The ST Micro version of the 79xx requires a load of 3ma or more to begin to regulate. When I added a load of 5k the voltage dropped to 15.5VDC. What was so misleading is that the 78xx version of the regulator worked fine with no load.
Thanks everyone for your help and suggestions.
Well, see my post above
Although it is tempting, one should not compare 78xx and 79xx, internally, they are quite different beasts.
  Reply With Quote
Old 20th March 2006, 04:44 AM   #9
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Quote:
Originally posted by LHMAudio
What was so misleading is that the 78xx version of the regulator worked fine with no load.
79xx and 78xx are not indentical inside depending of that it's hard to make good PNP transistors. It's always a good idea to read datasheets
__________________
/Per-Anders (my first name) or P-A as my friends call me
Super Regulator SSR03 Group buy
  Reply With Quote
Old 20th March 2006, 03:19 PM   #10
diyAudio Member
 
Join Date: Sep 2005
I read through the ST Micro data sheet a number of times looking for an indication of the minimum required current draw and didn't see anything. However, I don't know the meaning of all the speicification abbreviations. Is there a shorthand notation that indicates minimum current draw for regulation?
  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


Similar Threads
Thread Thread Starter Forum Replies Last Post
7815/7915 dual supply hum problem Lenn Art Power Supplies 8 22nd March 2011 09:57 PM
Pin compatible 7815/7915 replacements? i-s Parts 9 26th October 2010 04:05 PM
Can the 338 regulator handle 4 Ohms? amo Chip Amps 42 13th October 2007 04:17 AM
Exploding 7915 diarav Power Supplies 6 11th June 2007 12:21 PM
Can we handle more zen? bertjan Pass Labs 10 31st July 2006 10:04 AM


New To Site? Need Help?

All times are GMT. The time now is 02:04 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