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Old 19th January 2004, 06:38 AM   #1
azira is offline azira  United States
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Default Zen Heatsink Question

This weekend I built a Zen using a +24-volt rail. It turns out no parts had to be changed and the bias can still remain at 2-amps.

I'm using an IRFP9140 for the CCS and a IRFP450 for the amplifier. The Datasheet and searches suggest they should be more than capable for a Zen.

So... first I prototyped it with a breadboard for the low current circuitry and aligator clips for the high current stuff. I put the IRFP9140 on a small heatsink like a PCB mount one for maybe a high dissapation voltage regulator. And I put the IRPF450 on another heatsink. This one is aluminum about 4"x5" with 7 1/2" fins on it.

On this setup, the CCS heatsink heated up pretty good but the other one was less than luke warm. I could touch either one no problem.

So confident that everything was grand, I decided to move the CCS onto the same heatsink as the driver and wired everything on perf-board.

Now, after less than a minute, the heatsink gets quite hot. I can still touch it but not for very long. The 0R33 bias resistor voltage is holding steady at .68 Volts (2.06 A) and my wiring looks right.

I think this is just a case of "not enough heatsink" but my prototype didn't get this hot.... even on the smaller heatsink. Comments?
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Danny
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Old 19th January 2004, 09:55 AM   #2
Mad_K is offline Mad_K  Norway
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What's the 'C/W rating of your heatsink?

And how is it placed (standing on a table, or...)?
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Old 19th January 2004, 04:25 PM   #3
azira is offline azira  United States
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The reason why I'm not using the specified transistors or the specified rail voltage from the Zen "manuscript" is that I picked up what I found at the local surplus store.
The IRFP450's weren't priced and they gave them to me for $.25, so I cleaned them out and then decided later what to do with them...

Anyway, in short, I don't know because it was in a box of misc heatsinks and looked convenient for mounting stuff... it was one of the bigger ones they had. It's placed sort of on it's side so that the channels between the fins go upwards.
I'm using Sil-pads for mounting, since the heatsink gets so hot I guess they are working ok.
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Old 19th January 2004, 05:59 PM   #4
Mad_K is offline Mad_K  Norway
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if you can touch the heatsink (if only briefly) you're ok
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Old 19th January 2004, 09:23 PM   #5
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If you can touch the heatsink for a long time - the temperature is below 40-50C.

I running PenZen V4 with unknown C/W heatsink, and obtained near 80C of the FETS (directly on the FET's body).
This is not a problem, becouse IRFP150 are rated up to 175C (crystal temp.) that ~ 120C on the body.

In my professional activity, I offen use MOSFETS at the 100-130C on their body without any problems.
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Old 19th January 2004, 09:32 PM   #6
azira is offline azira  United States
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Well.... I DID buy a new DVM this weekend because it has Temp and hFE testing on it.... I guess it's time to just measure it and see how hot it really is getting on there.

thanks for the info...
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Old 20th January 2004, 02:34 AM   #7
azira is offline azira  United States
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Well.... I put a thermocouple on it this evening. It hit 100 deg-C in about 10 minutes with no input signal since that'll dissapate the most heat and looked like it would still climb. The Thermocouple was taped onto the HS right against the body of the CCS transistor.

I'll take that as I need a bigger heatsink and that it would seem just about any heatsink I use is going to get pretty damn warm...
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Old 20th January 2004, 02:50 AM   #8
moe29 is offline moe29  United States
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the ZEN does run hot!

when you think you have enough heatsink, double it.
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Old 20th January 2004, 08:38 AM   #9
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"when you think you have enough heatsink, double it."

Or - use a fan !

I use 4.5" fan, that originally is 230V, but I run it from 115V (half of the primaty of the main trafo) and I don't hear any sound from it.
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