Air cooling and the thermal resistance.

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- overgeo
  
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posted
17 years ago

Tue, Jul 25, 2006 3:43 PM

HI i'm designing an inverter, the characteristics are, DC bus voltage

300V, Irms 30A, pwm frequency 100Hz, and a maximum junction temperature of 80=BAC, I have used this igbt calculator

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and i get 160 Watts of power losses and a resistance for the disipator of 0.117 =BAC/w, are these results more o less correct?, i have chosen this igbt IRG4PSC71UD, in the datasheet says that maximum power dissipation at Tc =3D 100=BAC is 140W, the igbt will be able to dissipate my power losses?

I have looked for disipators but i haven't seen disipators with this thermal resistance so the solution i'm gonna use is a disipator with air cooling, and i would like to know how is the diminution of the thermal resistance of a disipator using air cooling?, and finally if someone has some suggestions about the use of air cooling please tell me, thanks in advance, and sorry if my english sounds a little bad, i'm spanish.

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- bill.sloman
  
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posted
17 years ago

Tue, Jul 25, 2006 4:29 PM

Have a look at the Farnell catalogue or the Martson web-site

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Farnell carry a couple of Marston heatsinks that can offer around

0=2E1C/W thermal resistances to ambient when coupled to a 120mm fan.

It is difficult to mount a single dissipating device on such a heat sink without having as much thermal resistance from the device to the heatsik as you get from heatsink to ambient - carbon fibre cloth is good, but it is also electrically conductive.

--=20 Bill Sloman, Nijmegen

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- Nico Coesel
  
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posted
17 years ago

Tue, Jul 25, 2006 6:30 PM

No, that power rating is based on a die kept at 25 degrees with a magic cooler (read 'magic' as: it doesn't exist in the real world). It is a number to use in calculations.

Another thing to worry about is thermal dynamics since you are working with pulsed signals. Try to read some about it, you'll see the amount of power a device can dissipate is much less than its rated capacity.

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posted
17 years ago

Wed, Jul 26, 2006 8:57 AM

snipped-for-privacy@ieee.org ha escrito:

tm

te

Hi thanks for your answer, i will use a disipator of that page or something similar that i'll find in my country. I will keep in mind that the resistance device heatsink will be as bigger as the heatsink ambient, thanks.

Nico Coesel ha escrito:

ipate

Hi thanks for your answer, i have been look for info about power dissipation

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.pdf) and you're right the specifications are not very real, but i didn't found anything related with power dissipations and pulsed signals the only thing that i found was the thermal response.

The solution to this problem that i have thought is to change the igbt or paralelling, i think the easiest is to change the igbt, i was looking to the products of international rectifier, and the IGBT with the biggest dissipation is this IRGPS60B120KD, the datasheet says that Pd at 25=BA is 600W and at 100=BAC 240W, do you think that this will be suitable for my case?. In addition i have seen the modules (SKM75GB123), but i will like prefer to use a discrete igbt, thanks again for your help.