Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

LM317/LM337 accuracy
LM317/LM337 accuracy
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 24th May 2007, 01:58 PM   #1
Stuey is offline Stuey  Australia
diyAudio Member
 
Join Date: Mar 2006
Location: Perth, Western Australia
Default LM317/LM337 accuracy

Hi,

I built a simple power supply as per the one on Nuuk's website which has a 50VA 18-0-18 transformer, 4700uF smoothing caps and a series of paralleled polypropylene bypass caps before the above regulators. It's built on stripboard.

http://myweb.tiscali.co.uk/nuukspot/...nclonepre.html

The idea was to have a two stage reg in which this first stage would put out ~+-21V and the second stage reg to +-15V.

However, after carefully building the (simple) first stage, the damn thing was putting out -22.2V and +21.8. The unloaded DC voltage before the regs was a steady 27.7V both sides.

I'm using 220R and 3K6 1% metal film resistors to set the voltage.

I checked the resistors' values by disconnecting one end - they were within spec. I then bought two new LM regs, and replaced these and the resistors after matching the new resistors with my meter.

Now the voltage is -21.5V and +22.0V...

I'm fairly sure the regs are proper ONsemi devices.

Any tips on what could be the issue? I know it's hard over the net, but I'm stumped. I've even checked for minor current leakage around the regs through rosin between tracks - there's nothing wrong.

Cheers

Stuey
  Reply With Quote
Old 24th May 2007, 02:04 PM   #2
Christer is offline Christer  Sweden
diyAudio Member
 
Join Date: Sep 2002
Location: Sweden
The internal voltage reference of the regulators have a tolerance of almost +/- 5 %. LT makes a version with +/- 1 % tolerance, if I remember correctly. However, it is cheaper and simpler to just adjust the resistor values so you get the desired voltage.
  Reply With Quote
Old 24th May 2007, 02:17 PM   #3
zacster is offline zacster  United States
diyAudio Member
 
Join Date: Dec 2003
Location: NYC
If you use a pot to set the resistance, you can get the voltage perfect and it will hold steady.

And the bear is a white polar bear at the north pole.
  Reply With Quote
Old 24th May 2007, 02:21 PM   #4
peranders is offline peranders  Sweden
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
LM317/LM337 accuracy
Notice also that an absolute voltage isn't necessary, only a stable and noise free one.
__________________
/Per-Anders (my first name) or P-A as my friends call me
Group buy: DCT03 DC trap for big toroidal transformers. Sign up for interest HERE. 41 pcb's in interest.
  Reply With Quote
Old 24th May 2007, 02:39 PM   #5
Stuey is offline Stuey  Australia
diyAudio Member
 
Join Date: Mar 2006
Location: Perth, Western Australia
Ahhh, thanks. Three replies giving the three possible answers I'd thought about...!

I just assumed that they'd give the same voltage out if the Vin was equal side to side.

Thanks people.

Cheers

Stu
  Reply With Quote
Old 24th May 2007, 02:42 PM   #6
richie00boy is offline richie00boy  United Kingdom
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
LM317/LM337 accuracy
Also that the +ve and -ve regs have different Iadj so by using larger than the datasheet recommended 120R you increase the error due to the voltage developed due to this current.

But don't worry, as said a bit either way won't matter.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
  Reply With Quote
Old 25th May 2007, 08:31 AM   #7
Stuey is offline Stuey  Australia
diyAudio Member
 
Join Date: Mar 2006
Location: Perth, Western Australia
Thanks for that additional info Richie.
  Reply With Quote

Reply


LM317/LM337 accuracyHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Another look at the LM317 and LM337 regulators jbau Power Supplies 417 28th June 2017 02:43 AM
Regulated PS w/ LM317 & LM337's oldfatbubba Chip Amps 36 21st October 2013 03:44 PM
Equation for LM317 and LM337 +-15v vdi_nenna Power Supplies 11 14th May 2007 12:34 PM


New To Site? Need Help?

All times are GMT. The time now is 03:49 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki