LM3875 voltage and temp

webby · 11th August 2005, 03:23 PM

Hi all,
I have just built a lm3875 audiosector kit using a dual 25v 300va transformer. Everything is working fine, but i am worried that 36vdc is too much. They get very hot even using a AMD 2000Mhz heatsink!
Is this too much, and what would be the best way to reduce the voltage on this pcb kit?
Many thanks
Ian

chipco3434 · 11th August 2005, 05:22 PM

I run my first GC at +/- 36. If you are using thermal compound on the TF chip and the sinks are very hot there are three options.

1. Reguce the voltage.
2. Turn down the volume.
3. Get a larger sink.

I think that #3 is the answer here.

chipco3434 · 11th August 2005, 05:26 PM

... and by the way. The AMD heatsink is meant to have a fan. That drives the air through those small fins. I believe that you would need a more massive heatsink with larger air spaces for more efficient cooling.

JMO

webby · 11th August 2005, 05:37 PM

thanks chipco!
I think your right about all three points.
I am using thermal greese on the chips, but how hot is ok?
Also the how do i reduce the voltage to say 25vdc?
Thanks
Ian

peranders · 11th August 2005, 07:02 PM

You strive to have less than 60-70 deg C for lifetime reasons.

You may also check with the Excel file how big heatsink you'll need.
http://www.national.com/appinfo/audi...gn_Guide13.xls
http://www.national.com/appinfo/audi...sign_Guide.pdf

Leolabs · 13th August 2005, 01:32 AM

U should check the datasheet of LM3875.

11th August 2005, 03:23 PM	#1
webby diyAudio Member Join Date: Jul 2004 Location: england	LM3875 voltage and temp Hi all, I have just built a lm3875 audiosector kit using a dual 25v 300va transformer. Everything is working fine, but i am worried that 36vdc is too much. They get very hot even using a AMD 2000Mhz heatsink! Is this too much, and what would be the best way to reduce the voltage on this pcb kit? Many thanks Ian

11th August 2005, 07:02 PM	#5
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	You strive to have less than 60-70 deg C for lifetime reasons. You may also check with the Excel file how big heatsink you'll need. http://www.national.com/appinfo/audi...gn_Guide13.xls http://www.national.com/appinfo/audi...sign_Guide.pdf __________________ /Per-Anders (my first name) or P-A as my friends call me

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11th August 2005, 05:22 PM	#2
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	I run my first GC at +/- 36. If you are using thermal compound on the TF chip and the sinks are very hot there are three options. 1. Reguce the voltage. 2. Turn down the volume. 3. Get a larger sink. I think that #3 is the answer here.

11th August 2005, 05:26 PM	#3
chipco3434 diyAudio Member Join Date: Feb 2004 Location: Racine, Wisconsin	... and by the way. The AMD heatsink is meant to have a fan. That drives the air through those small fins. I believe that you would need a more massive heatsink with larger air spaces for more efficient cooling. JMO

11th August 2005, 05:37 PM	#4
webby diyAudio Member Join Date: Jul 2004 Location: england	thanks chipco! I think your right about all three points. I am using thermal greese on the chips, but how hot is ok? Also the how do i reduce the voltage to say 25vdc? Thanks Ian

13th August 2005, 01:32 AM	#6
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	U should check the datasheet of LM3875.

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