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 28th January 2012, 11:33 AM   #1
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
Default HEATSINK QUESTION

I am working in one application where one amplifier class AB will be placed in a specific housing outputs will be 1943 5200 power supply will be 35+35 volts and the duty will be casual low listening probably something like 10-15W at the very maximum
Bias for the amplifier will be no more than 70 ma ( rough calculation i can even go lower )

Problem is that the heatsink will be one aluminum size 35cm x45 cm 2mm thick

do you think that i might get away with it ?
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 28th January 2012, 11:37 AM   #2
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
As a rule of thumb that's not going to be enough.

Your application wont need a big heatsink but it will still get quite warm.

You are trying to dissipate 70V x 0.07A under no load = 5W.

For reliability try to keep the output transistors below 65 Degrees C - they can run far hotter.

Lets take a lovely summer day where the air temperature is 35 Degrees (I wish).

The heatsink calculation is Tj = Ta + ( Tjc + Tcs + Tsa)P

P is the power being dissipated - 5W in this case.

Tjc can be gained from the transistor data sheet but is nominally in the order of 1.5

Tcs is down to the mica washer and is generally about 0.3

Tsa is the figure that we are after - Transfer of Heatsink to Air

Tj is the maximum temperature that we want the transistor to reach (as stated 65 Degrees)

Ta is the maximum air temperature (as stated 35 Degrees)

Transposing the formula that gives us ((Tj-Ta)/P)-Tjc-Tjs = Tsa

Or ( ((65-35)/5)-1.5-0.3 = 4.2 Degrees C/Watt

Now if you do a bit of homework you can see what sort of heatsink you would need to meet this requirement.

This is with NO SIGNAL applied.

You will need to increase the figures when the amp is at FULL SWING.

Last edited by KatieandDad; 28th January 2012 at 11:52 AM.
  Reply With Quote
Old 28th January 2012, 11:38 AM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
15W from a 50W amplifier will just about hit the worst case heat dump from the transistors to the heatsink.

If you had said "normal music" levels of 1/2W to 2W, then I would point you to using the Pq as the heatsink load. From there you could estimate the Tc of the devices.
But at 10W to 15W for domestic listening the heat load is going to be far greater than Pq.
__________________
regards Andrew T.
  Reply With Quote
Old 28th January 2012, 11:51 AM   #4
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
ok got it will make some tests and see how far i can go
Due to the nature of the application i have to go like that ...one think i can change though is the thickness of the metal from 2mm to 3mm any comments on that ?

also the shape of the aluminum is not flat ...its something like a W ...with the transistors located in the inner sides of the W ( i am trying to say that obviously a V or W shaped piece of metal will be more effective than a flat one

Will also post pictures as we speak
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 28th January 2012, 11:59 AM   #5
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
The thickness of the plate will make little difference.

It is how much alluminium is available to dissipate heat to the air around it.

Hence the design of heatsinks.

If you are limited in space available then you might have to consider forced cooling. (Fans - Water - Peltier )
  Reply With Quote
Old 28th January 2012, 12:07 PM   #6
diyAudio Member
 
KatieandDad's Avatar
 
Join Date: Nov 2011
Location: UK
Have a read of these articles.

DIY Heatsink

http://sound.westhost.com/heatsinks.htm

Last edited by KatieandDad; 28th January 2012 at 12:09 PM.
  Reply With Quote
Old 28th January 2012, 12:56 PM   #7
diyAudio Member
 
Join Date: Feb 2008
Location: Jackson,michigan
Here are a few online Heatsink Calculators that I think you may find useful,



Heat Sink Calculator

- heatsink design tools

Heatsink Surface Area Calculator.

enjoy !!!

jer
  Reply With Quote
Old 28th January 2012, 03:14 PM   #8
diyAudio Member
 
Michael Chua's Avatar
 
Join Date: Jul 2006
Location: Calais, ME
Quote:
Originally Posted by sakis View Post
I am working in one application where one amplifier class AB will be placed in a specific housing.....
One option is to forced fan cool the heatsink. A 40x40mm 12V case fan may fit into your housing.

Another possibility is to use the housing as heatsink, provided it's possible.
__________________
AmpsLab.com
  Reply With Quote
Old 28th January 2012, 05:33 PM   #9
diyAudio Member
 
east electronics's Avatar
 
Join Date: Jan 2006
Location: Athens GREECE
hey Michael !!!!

always very good to see you ...i will e mail you pictures ( if you have the time to see )

kind regards
sakis
__________________
SERVICE ΕΝΙΣΧΥΤΩΝ ΚΑΙ ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr
  Reply With Quote
Old 28th January 2012, 09:26 PM   #10
diyAudio Member
 
Michael Chua's Avatar
 
Join Date: Jul 2006
Location: Calais, ME
Hello sakis

Look forward to your mail.
__________________
AmpsLab.com
  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
Heatsink question Apogee Pass Labs 195 23rd July 2008 08:07 PM
heatsink question? xdissent Solid State 13 18th June 2004 02:44 AM
Heatsink question kheldar Chip Amps 8 30th January 2004 02:50 PM
heatsink question tpenguin Solid State 3 23rd December 2003 09:47 PM
yet another heatsink question BrianGT Pass Labs 3 19th September 2002 07:55 PM


New To Site? Need Help?

All times are GMT. The time now is 02:46 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