Thermistor vs Soft Start - Page 2 - diyAudio
Go Back   Home > Forums > Design & Build > Parts
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, etc.

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 22nd September 2005, 01:51 AM   #11
Arius is offline Arius  United States
diyAudio Member
Join Date: Mar 2004
Location: California
Default Off-Topic

Hey Wes,
Nice to see you lurking around here. I'm "CapJohn" from the forums.

I'm doing the layout for my power amp now. When that's done, I'll work on my soft-start board. Like Richieboy, I find the thermistor method too crude. My goal for soft-start is not only as soft-start but to reduce AC wiring (i.e. no AC wires to multiple devices and from back to front of case). Schematics done, no layout yet.
  Reply With Quote
Old 22nd September 2005, 11:59 AM   #12
diyAudio Member
wes-ninja250's Avatar
Join Date: Feb 2005
Location: Inverary, ON
Chris --

Oh ho, of course! Short out the thermistor with the relay! See attached revision.

The NTC thermistor is critical here, as it allows a smooth voltage rise in the transformer; then when the voltage is high enough, the relay kicks in. Once the relay kicks in, the thermistor is out of the picture; the relay stays on by virtue of it being on. Very appealing in a self-excited sort of way.

I think this circuit would work if tuned properly; one concern I have is if the transformer's output voltage isn't linear during core saturation, the circuit will turn on prematurely.

CapJohn --

Hey, good to see a familiar face! Now you know why I haven't been posting much... to busy building my GainClone! I thought the amp part was going to be tricky; turns out the hard part is the freakin' chassis!! If I tap another freakin' crooked hole, or break another $4 drill bit, I think I'm gonna scream.

My (untested) dislike to the thermistor startup is about the same as Richie's -- I'm concerned that there will be a delay turning on full voltage when the amp has been idle, and that it will add extra noise or choo-choo-ing in the system.

My *like* for the thermistor startup is the symplicity, and zen-like nature: it's on when it needs to be on.

These are the two issues (aside from cost and part count) I tried to address in my circuit.

Attached Images
File Type: gif soft-start-b.gif (7.7 KB, 588 views)
Do daemons dream of electric sleep()?
  Reply With Quote
Old 22nd September 2005, 12:46 PM   #13
anatech is offline anatech  Canada
diyAudio Moderator
anatech's Avatar
Join Date: Jun 2004
Location: Georgetown, On
Now to simplifiy the circuit more and protect from other problems ....
The relay runs off the secondary DC supply. Resistor as required to limit the coil current. The best part is that if you have a short, the secondary voltage may drop enough to drop the relay out. The resistor then acts as a fuse and opens. Of course the relay can be opened with a protection circuit as well.

  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
Soft Start Necessary? dtaylo3 Class D 2 26th December 2008 09:05 AM
B+ soft start Gluca Tubes / Valves 2 3rd September 2007 01:04 PM
Need a soft start? maxpou Solid State 19 18th April 2007 09:23 PM
Soft start & Soft Switch circuit: can anybody help? m.parigi Solid State 95 22nd August 2005 03:32 PM

New To Site? Need Help?

All times are GMT. The time now is 12:04 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