LM3875 voltage and temp

[webby]

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]

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]

... 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]

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]

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/audio/files/Overture_Design_Guide13.xls
http://www.national.com/appinfo/audio/files/Using_Overture_Design_Guide.pdf

 

[Leolabs]

U should check the datasheet of LM3875.