Re: Discrete Mosfets/IGBTs mounting techniques ...

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Jan Wagner <jwagner-at-cc.hut.fi> 


On Mon, 16 Feb 2004, Tesla list wrote:
 > Original poster: "Rajesh Seenivasan" <rajeshkvs-at-hotmail-dot-com>
 > I have few discrete power mosfets (TO-247 package) with me. I am planning
 > to design high power inverter for tesla coils.
 > Some mosfets are capable of handling up to 40 Amps. But the problem is how
 > do I mount those power mosfets in a PCB ?
 > Because, even though the mosfets can handle 40 Amps or even higher, the PCB
 > tracks cannot handle that much current ?

If it's 40A_rms then the PCB probably won't handle it as such...

 > Should I have tracks which are several inches wide ?

Basically yes, and you can use a double- or multilayer board for better
layout. A big ground plane is advisable, anyhow.

You may also add further metallisation layers - for example cut and
solder some thicker copper strip onto the PCB tracks. This is the same
copper strip you can buy for transformers. You can also go even heavier
and buy/get some copper plates from a scrapyard and saw them to proper
size, then solder on the PCB. The PCB is still useful as a mechanical
support for the circuit.

Some high power inverters actually use aluminium bars or track "plates"
instead of copper, sometimes these are soldered to the board, sometimes
"nailed" (don't know the proper word - small dents on the aluminium
plate, and then probably ultrasonically bonded to the standard PCB copper
track below, at least, not trivial for DIY)

But adding the extra copper should get you started.

good luck,

  - Jan

--
****************************************************
  Helsinki University of Technology
  Dept. of Electrical and Communications Engineering
  http://www.hut.fi/~jwagner/ - jwagner-at-cc.hut.fi