replace adjustable regulator with fixed? - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

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
Reply
 
Thread Tools Search this Thread
Old 17th September 2012, 11:29 AM   #11
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
Doubtful it's continuous unless there are some heatsinking secrets to tell, but the current-limit curves do show it possible to pull a couple of amps through the regulator.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 17th September 2012, 11:54 AM   #12
diyAudio Member
 
Join Date: Feb 2009
the heatsinks has little to do with the current passing through it.
but more the voltagedrop. if one run 25V in and 12V out. you will need some "big sinks" to pull any current. but with 15V in and 12V out, thats a whole other story.
lets say 1A current. at 25V in. thats 13W dissipation. at 15Vin its only 3W.
  Reply With Quote
Old 18th September 2012, 01:49 AM   #13
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
I'll agree, but there is much to do with junction temperature (via the in-out differential, ie power dissipated in the reg, ie Tj), so heatsinking is quite relevant. There's current limiting and thermal shutdown to consider, so AndrewT is correct - it's treading into no-man's land.
Attached Images
File Type: png peakamp.png (7.2 KB, 98 views)
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine

Last edited by sofaspud; 18th September 2012 at 01:50 AM. Reason: forgot the pic
  Reply With Quote
Old 18th September 2012, 02:12 AM   #14
diyAudio Member
 
Join Date: Feb 2009
there is. but the difference between 1A and 2A is kids candy.
the difference from 3Vdrop to13-18V drop is a much bigger issue.
all diveces reach a maximum. but the main reason that a regulator fails, is voltage drop(dissipation). not the current that it draws.
  Reply With Quote
Old 18th September 2012, 02:15 AM   #15
diyAudio Member
 
Join Date: Feb 2009
lets say a worst case. LM317 with 35V in and 5V out. at 1A. hell. thats 30W dissipation
not a easy task for a to-220die
  Reply With Quote
Old 18th September 2012, 08:57 AM   #16
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Audio
What pre regulation do you have for the implementation you have described in post7?

How much does the Vin vary?
How much could Vin vary for worst case operation?

Does Vin, with some ripple, drop low enough for regulator drop out to occur?
__________________
regards Andrew T.
  Reply With Quote
Old 18th September 2012, 09:32 AM   #17
diyAudio Member
 
Join Date: Feb 2009
Vin is pretty darn stable.
worst case operation? do you think of in regards to heatsink?
  Reply With Quote
Old 18th September 2012, 10:27 AM   #18
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Well, guess what, I disagree with "pretty darn stable".

For 15Vdc @ 2Adc, I'd use 230:12Vac, 100VA transformer operating from 240Vac, feeding a bridge rectifier and 4u7F of smoothing.

Apply a -6% mains voltage variation. i.e. 225.6Vac for a check on whether regulator drop out occurs.
Input to regulator becomes a worst case low of about 14.8Vdc +-200mV of ripple. Giving a Vin from 14.6Vdc to 15Vdc.

Now apply a +6% mains voltage variation, i.e. 254.4Vac. to check for maximum Pd.
Input to regulator becomes a worst case high of about 16.72Vdc +-200mV of ripple.

For a 2A output the transformer is running at 50% o maximum continuous output and the regulator Pd varies from ~5.6W to ~9.4W

That is not "pretty darn stable".

The questioner should do something along the same lines as I have shown and insert his own data to arrive at his operational Pd and how much it can vary for his/her mains voltage variation.
__________________
regards Andrew T.
  Reply With Quote
Old 19th September 2012, 02:23 PM   #19
diyAudio Member
 
Join Date: Feb 2009
i don't know about you. but over here i have never had more then about 2-3% variation on mains.
  Reply With Quote
Old 19th September 2012, 02:56 PM   #20
diyAudio Member
 
jackinnj's Avatar
 
Join Date: Apr 2002
Location: Llanddewi Brefi, NJ
Quote:
Originally Posted by AudioSan View Post
i don't know about you. but over here i have never had more then about 2-3% variation on mains.
Over here the line voltage can dip into the mid 90's and run as high as 128 during the summer == i had our electric company put a data logger on the main panel.

We had a competitor whose a.c. power was cut in the summer of 2007 -- their thermal curing ovens were powered by natural gas and didn't cut out quickly enough during the initial stage of a brownout -- what a mess!

If it's a low voltage application, I would try replacing the LM317 with one of the fixed voltage regulators in the LT1963A series -- there are 4 fixed voltage choices.
  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
push pull adjustable fixed bias hpupo Tubes / Valves 3 14th June 2011 03:25 AM
How to replace trimmer pot with fixed resistor? kptseng Solid State 9 8th August 2008 04:29 PM
Adjustable Fixed Grid Bias dsavitsk Tubes / Valves 5 4th December 2007 03:58 PM
Adjustable power supply to replace volume control Leolabs Solid State 8 11th July 2007 04:43 PM


New To Site? Need Help?

All times are GMT. The time now is 08:29 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