Why does my SMPS show poor regulation? - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Thread Tools Search this Thread
Old 26th July 2010, 05:45 PM   #1
diyAudio Member
Join Date: Nov 2002
Default Why does my SMPS show poor regulation?


I have a PC SMPS (Frontech JIL-2415, 500 Watts) powering a car amp ( Sony XM-504Z, 100Watts RMS ) at home for a sub duty. The SMPS is rated to provide 31 Amps at 12V.

Here is what I found:
1) No load voltage-> 12.1 volts
2) Voltage with amp switched on but no input signal->11.6 volts
3) Voltage with amp fully loaded (about 100 watts) and 20Hz sine played->10.6

Why is the supply sagging so much when the amp is idle? Why is it sagging so much more on load?
Can somebody please explain whats happening?

Audio enthusiast/hobbyist
  Reply With Quote
Old 26th July 2010, 06:22 PM   #2
AP2 is offline AP2  Italy
Join Date: Dec 2009
Location: Italy
the PSU has a normal behavior. because it was developed for continuous load.
then if it is 500w (all voltage) as may 30Amp 12V on output? normally the greatest power is reserved to +5 V.
other reason for the loss of voltage to power is that the other outputs remain unloaded.
(Output circuit has a differential resistance to balance the load across all outputs voltage in relation to the load. (When the load is fixed)

You can (only for test) apply an load at +5V (3-4Amp) when amplifier is in idle and see voltage output.

Last edited by AP2; 26th July 2010 at 06:29 PM.
  Reply With Quote
Old 27th July 2010, 12:10 AM   #3
wwenze is offline wwenze  Singapore
diyAudio Member
Join Date: Mar 2008
That power supply looks like the type that can explode anytime. I reckon the overcurrent protection isn't really working either. And I don't think it has 100W on +12V, regardless of what the label may say.
  Reply With Quote
Old 27th July 2010, 01:05 AM   #4
wwenze is offline wwenze  Singapore
diyAudio Member
Join Date: Mar 2008
Couldn't find a clear picture of the power supply's label. Do try what AP2 has suggested of loading the +5V.
  Reply With Quote
Old 27th July 2010, 03:14 AM   #5
benb is offline benb  United States
diyAudio Member
Join Date: Apr 2010
My understanding is multi-output "PC" SMPS's don't regulate all the outputs - they just regulate ONE output (the highest power, the one that powers the logic on the motherboard, 3.3V or whatever), and the other outputs just follow along. This works well with variations of line voltage, but not with variations in load current. All these voltages are taken off one transformer, and the circuitry can only reasonably regulate one output (the main 5 or 3.3V) for changing load conditions.

At first I was about to agree with others, load down the 5V or main output and see what happens, but on second thought the 12V output is unlikely to be rated for anywhere near 30A.

I did google 500W PC PS and they (the few entries that give current output of each voltage) do have more current on the +12V line than I expected - this one has two 12V outputs, each at 22A:
Newegg.com - Antec earthwatts EA500 500W Continuous Power ATX12V v2.2 80 PLUS Certified Active PFC "Compatible with Core i7/Core i5" Power Supply
This has three 12V outputs, two at 17A and one at 12A:
Black CoolMax 500W Modular Power Supply CU-500B ATX12V EPS12V Supports SATA PCI-E-Best Computer Online Store Houston Buy Discount Prices Texas-Directron.com

It may or may not be a good idea to connect several 12V outputs together to get a single higher-current output. I suspect this will work only because these outputs are not themselves regulated.

Long story short, you're repurposing this supply to do something it wasn't intended to do. It's rather remarkable that it works at all with such a big load on the 12V line and nothing on the others. If you want truly regulated 12V, you need to use a 12V-only output SMPS that will give the current you need.
  Reply With Quote


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
The poor man SMPS mag Power Supplies 5 12th June 2010 10:44 PM
half bridge smps for chip amp voltage regulation question alexclaire Power Supplies 13 8th March 2008 06:39 PM
offline SMPS regulation Pierre Power Supplies 0 12th April 2006 05:25 AM
Show of hands for the Montreal Sound and Image Show (Le Festival Son & Image) alvaius Everything Else 2 28th January 2003 05:48 PM

New To Site? Need Help?

All times are GMT. The time now is 02:54 AM.

vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2