Simple 12v adjustable help - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Power Supplies

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 16th November 2012, 04:41 AM   #11
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
The circuit is like this.
Change the transistor according to the load current required. May be heatsinked also.

Add a small capacitor(optional) from base to negative.

Gajanan Phadte
Attached Images
File Type: jpg vary DC.JPG (12.5 KB, 74 views)

Last edited by gmphadte; 16th November 2012 at 04:53 AM.
  Reply With Quote
Old 16th November 2012, 04:54 AM   #12
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
Scale the transistor for the current required and add a capacitor(optional) from base to negative.
  Reply With Quote
Old 17th November 2012, 01:04 AM   #13
diyAudio Member
 
Join Date: Feb 2011
I just came across this circuit here (scroll down to Simple Adjustable Voltage Source):

Telephone In-Use Relay, LM317 Regulators, Lithium Charger

And this sounds perfect

Now my questions are, how many amps could this simple npn pnp circuit provide? Also just how much heat will it produce?

I only have the small clip on heatsinks that I can put on it although I could possible place it on the larger heatsink in the power supply and possibly even next to the slow running 80mm intake fan if needed?

I think I will go this route as it's simple and cheap just need to know how many amps I can get in this circuit and how well I need to cool it

If possible I would like to be able to supply up to 5a so if different parts are needed in this same circuit please do let me know although I could live with 2a output
  Reply With Quote
Old 19th November 2012, 05:38 AM   #14
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
Power dissipation across the MJE2955 should not exceed its rating. Not exceeding the junction temperature of the device is important.

Gajanan Phadte
  Reply With Quote
Old 19th November 2012, 10:55 AM   #15
MarianB is offline MarianB  Romania
diyAudio Member
 
MarianB's Avatar
 
Join Date: Jul 2011
Location: Romania
Send a message via Yahoo to MarianB
I never use theese so called voltage regulators, they have no tollerance what so ever to the variations of the imput voltage cus they have no stable Vreff, so any change in the voltage at it's imput translates in a similar change at the output, that is no regulator, just a worthless follower.

The simplest way you can get a voltage regulator is with LM317 but it needs that minimum voltage difference to work, another way would be with a fixed Vref, let say a 5,1V zenner and an error amplifier, transistor differencial or OA, they have the advantage of less voltage drop across them and a verry fine voltage setting but they are sort of more complex. If you are interested i can provide a schematic that u can use.
__________________
Trance Session Live by Dj Marik
  Reply With Quote
Old 20th November 2012, 06:05 PM   #16
diyAudio Member
 
Join Date: Feb 2011
Quote:
Originally Posted by MarianB View Post
I never use theese so called voltage regulators, they have no tollerance what so ever to the variations of the imput voltage cus they have no stable Vreff, so any change in the voltage at it's imput translates in a similar change at the output, that is no regulator, just a worthless follower.

The simplest way you can get a voltage regulator is with LM317 but it needs that minimum voltage difference to work, another way would be with a fixed Vref, let say a 5,1V zenner and an error amplifier, transistor differencial or OA, they have the advantage of less voltage drop across them and a verry fine voltage setting but they are sort of more complex. If you are interested i can provide a schematic that u can use.
As ive said before my input is from a pc power supply's 12v so the 12v is extremely regulated already and shouldn't fluctuate at all unless I put maybe 30A on it, using a simple circuit and only pulling 5a it shouldn't fluctuate, maybe .1 of a volt max

I will go with the simple circuit I posted above and will share my results when its all up and running
  Reply With Quote
Old 20th November 2012, 07:34 PM   #17
MarianB is offline MarianB  Romania
diyAudio Member
 
MarianB's Avatar
 
Join Date: Jul 2011
Location: Romania
Send a message via Yahoo to MarianB
Quote:
Originally Posted by liamstears View Post
As ive said before my input is from a pc power supply's 12v so the 12v is extremely regulated...
Actually the outputs of a ATX power supply are well regulated only when they are equally charged, that is the 2 main outputs, +5 and +12V, they both need the same load current for theyr voltages to be stable. You cand try it yourself, charge the 5v with 5 amps and 12V with 1 amp, you will see what i mean.
__________________
Trance Session Live by Dj Marik
  Reply With Quote
Old 21st November 2012, 06:49 AM   #18
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
Quote:
Originally Posted by MarianB View Post
I never use theese so called voltage regulators, they have no tollerance what so ever to the variations of the imput voltage cus they have no stable Vreff, so any change in the voltage at it's imput translates in a similar change at the output, that is no regulator, just a worthless follower.

The simplest way you can get a voltage regulator is with LM317 but it needs that minimum voltage difference to work, another way would be with a fixed Vref, let say a 5,1V zenner and an error amplifier, transistor differencial or OA, they have the advantage of less voltage drop across them and a verry fine voltage setting but they are sort of more complex. If you are interested i can provide a schematic that u can use.
U have to read the posts properly. They r not voltage regulators at all. It is a voltage varying circuit connected to a regulated supply.

Enjoy

Gajanan Phadte
  Reply With Quote
Old 21st November 2012, 08:24 AM   #19
MarianB is offline MarianB  Romania
diyAudio Member
 
MarianB's Avatar
 
Join Date: Jul 2011
Location: Romania
Send a message via Yahoo to MarianB
Quote:
Originally Posted by gmphadte View Post
U have to read the posts properly...
Do i? i sayd so called voltage regulators, ofcourse i know what they are, and getting stuck on sematics helps nowone, from my point of view they remain simple followers, worthless in voltage regulation/setting/variating, or anything else you wanna call it. And as i sayd the outputs on a ATX supply is only well regulated on some conditions so i would not use this for anything, there are other ways much more stable and efficient.
__________________
Trance Session Live by Dj Marik
  Reply With Quote
Old 23rd November 2012, 09:44 AM   #20
diyAudio Member
 
Join Date: Jul 2003
Location: Dona paula, Goa
You surely need to read more. Start with the datasheet of 317.

Enjoy
  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
simple adjustable voltage regulator? AKHeathen Equipment & Tools 7 2nd July 2012 01:23 PM
Simple 12v gain stage dublin78 Solid State 10 14th April 2008 04:37 PM
Simple 12V SMPS for small powered devices EWorkshop1708 Power Supplies 16 13th April 2008 11:46 PM
Simple 12v Smps johnyp Power Supplies 13 10th July 2006 02:45 PM
Simple 12V DC Power Supply for a Beginner? Llamas Everything Else 1 23rd August 2003 02:23 PM


New To Site? Need Help?

All times are GMT. The time now is 05:08 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