Limiting in-rush current at start up. - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Solid State Talk all about solid state amplification.

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 7th September 2002, 07:51 AM   #1
diyAudio Member
Join Date: May 2002
Default Limiting in-rush current at start up.

I am in UK (240v AC) and am designing a power amp psu with a 560va torroidal transformer with 30v secondaries and 40,000uf smoothing caps. What value current limiting device (thermistor)would I need to limit the inrush current at switch on, but not limit the amps peak output( approx 100w into 8ohms) Thank you.
  Reply With Quote
Old 7th September 2002, 09:22 AM   #2
diyAudio Member
supernet's Avatar
Join Date: Dec 2001
Location: Europe
Elektor magazine got one soft start circuit in their previous issues. It got four 10 ohm series resistors and relay to bypass them after some time.

I am using this circuit to power 1500VA toroid and works fine.

  Reply With Quote
Old 11th September 2002, 07:34 AM   #3
diyAudio Member
Join Date: Sep 2002
Location: south yorkshire, UK
for a 560va transformer I wouldn't bother unless the psu caps are huuuge .....

I've been using a 650va toroidal psu for years ( about the last 15 or so ) without any failures of fuses or psu components ( use slow-blow fuses, or they _will_ fail....)

if it really worries you , or you have a massive cap bank, or very expensive caps , have a look at this site. they have a number of ideas:


  Reply With Quote
Old 11th September 2002, 07:42 AM   #4
diyAudio Member
Join Date: Sep 2002
Location: south yorkshire, UK
...another point , you specify a power output of 100W into 8R.

with a 560va tranformer and 40,000 uF caps you should never reach a point where any thermistor is going to affect the voltage rails. even with a really inefficient amp design the full-power current draw is never going to reach the point where it exceeds the rating of the tranny.

you can probably get away with using thermistors in each rail to the caps , this'll halve the loading on each and still keep the initial charging current down.

the magnetic inrush current won't be too bad for a 560va toroidal transformer.

  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
12V DC/DC for amplifier. Current limiting? Pierre Power Supplies 22 1st May 2007 11:46 AM
Is this in-rush current? woodturner-fran Power Supplies 6 11th September 2006 11:58 PM
how to calculate in rush current limit circuit demons_wing Chip Amps 5 26th November 2005 05:57 AM

New To Site? Need Help?

All times are GMT. The time now is 04:42 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