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Old 18th December 2012, 08:46 AM   #1
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Default Multiple TDA's sharing heatsink

Hello all.

This is my first post and I would like to start out with a question regarding sharing the same heatsink (large one) for 3 TDA7294 IC. The heatsink will not be connected to ground or any other wires. The box will be made out of wood so no connection to the box either.

Is this ok or should I avoid sharing the same heatsink even if the size should be ok to handle the heat?

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Old 18th December 2012, 09:48 AM   #2
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Do bear in mind two things:-

1. Both ICs MUST be electrically insulated from the heatsink.

2. The heatsink is rated for a single source of heat at its thermal centre. If you mount two ICs away from the centre then the thermal performance of the heatsint will not be as effective - i.e. you will need a bigger heatsink.

As long as you consider both these factors you can mount as many devices to the heatsink as you desire.
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Old 18th December 2012, 10:09 AM   #3
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Although KatieandDad suggested everything , here are my two cents :

I used two TDA2050 ICs together on a heatsink just to test for sometime after first power up.

Since I never play loudly I used a small heat sink ( in the photo below) with mica insulator but they were not sufficient to dissipate the heat.

We need a much bigger heat sink.
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File Type: jpg multiple TDAs on a heat sink.jpg (495.5 KB, 92 views)
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Last edited by csom; 18th December 2012 at 10:12 AM.
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Old 18th December 2012, 10:28 AM   #4
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thanks for the replies.

Why should the ic's be insulated if the heatsink won't touch any other connection? what could occur?
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Old 18th December 2012, 10:46 AM   #5
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The tabs of the IC's are not insulated, so you would effectively be coupling the -Vs via the heatsink. If this is a problem is a different question altogether and can't be answered without more details of the complete setup.
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Old 18th December 2012, 10:51 AM   #6
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Hi Mark.

yes in essence, the tabs will all be connected to the heatsink. Will this be a problem as long as the heatsink won't be connected with any other electrical element?
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Old 18th December 2012, 12:27 PM   #7
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Personal choice: although connecting all V- tabs through the sink is electrically the same as joining them through wires which anyway meet at the PSU, I never liked having a "hot" heatsink, even if inside an amp, at least because it complicates troubleshooting when (didn't say "if" ) one of the chips dies.
Besides, mica+grease added thermal resistance, although looks something good to avoid , is really not that significant.
But others may differ, of course.
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Old 18th December 2012, 12:44 PM   #8
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Quote:
Originally Posted by aadrian View Post
Hi Mark.

yes in essence, the tabs will all be connected to the heatsink. Will this be a problem as long as the heatsink won't be connected with any other electrical element?
Most likely it won't be a problem, but be careful with "live" heatsinks, it bit me in the a** more then once when troubleshooting.. Also take really good care the power supply has an low impedance path to all TDA's (not via the heatsink) otherwise if 1 -Vs connection fails the current will be sourced via the other amps and the heatsink and most likely fry the leads of the other TDA's.
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Old 18th December 2012, 12:51 PM   #9
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all the TDA's are properly powered via sepparate wires directly from the source. the heatsink will not be used for powering purposes.
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