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Old 7th June 2010, 01:35 PM   #1
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Default Cooling/heatsink option

Dear,

I have a cooling question.

I carefully read a lot on this forum about amplifier PCB layout and grounding. Especially forum member Eva's general advice was a eye opener.

In order to keep power high currents and small signal currents separate, I was thinking of mounting the power transistor in the middle of a PCB. Then on the bottom I will put the whole rectifier circuit (bridge + elco's). This way the power is very close to the transistor pins. On the top of this PCB I add the small signal parts including the VAS enz.

If you mount the transistors in the middle you need a way to conduct the heat to the main heat-sink. I've see in the Hypex modules they do this with a aluminum bar. I was wondering if I do the same for a class A/B amplifiers would such a aluminum bar (10mm. thick) be enough to transfer the heat to the heat-sink?

I want to place a 1mm. bar in the middle of the PCB. Mount the transistors on this bar and then mount the whole PCB on the heat-sink by connecting this bar to the heat-sink.

Like this: http://www.hypex.nl/pics/products/UcD700HG.jpg

With kind regards,
Bas
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Old 7th June 2010, 03:41 PM   #2
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there is a big chance that this is not working .... things to consider is one how much heat this small part can take and second how fast ( and /or even more importand ) this metal part can transfer the heat to "another" heatsink

best option could be to leave a hall on the top of the pcb and use this to drive a screw through to attach the semi directly to a proper heat sink

can be tricky if you have more than one pair of semis even more tricky if electro's are on board( too heavy ) and also let us not forget the VBE multiplier


regards sakis
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Old 7th June 2010, 06:21 PM   #3
Variac is offline Variac  United States
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Quote:
Originally Posted by Sebastiaan View Post

I want to place a 1mm. bar in the middle of the PCB.
Like this: http://www.hypex.nl/pics/products/UcD700HG.jpg

With kind regards,
Bas
You meant 10mm as you mentioned earlier in your post, right? Copper has best heat transfer.
You would need more than just the end of the bar attached to the heatsink I believe, you would want a lot of contact area between the bar and sink, smooth surfaces, thermal grease.

Last edited by Variac; 7th June 2010 at 06:24 PM.
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Old 7th June 2010, 08:55 PM   #4
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I a msure there are much better ways than putting the transistor in the middle of the PCB.
I have designed loads of pcb's and always managed to get the power and output close to the output transistors. Start by doing it on a piece of paper then transfer to a pcb.

Simple solutions are always the best.
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Old 7th June 2010, 08:56 PM   #5
jcx is online now jcx  United States
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bringing in power supply to the output devices without coupling to/"contaminating" signal gnd is a fine idea

but low emission cable/power bus topology and spacing the rectification and bulk capacitors away from the amplifier electronics is the more often recommended approach

physical spacing is a cheap form of interfering magnetic field attenuation since magnetic fields sources are all are dipole the field falls as the cube of the distance

the large packages of power rectifiers, bulk capacitors will result in their wiring having unavoidable loop areas so moving sensitive signal circuitry a larger distance from these components is a good idea

segmented "star" gnd principles, twisted pairs or star quad cable, multilayer/interleaved power/gnd pcb trace/planes and attention to geometry and relative loop areas/orientation can control the problems very well without requiring gymnastics for your heatsink location

Last edited by jcx; 7th June 2010 at 09:15 PM.
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