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Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
Hi, I've got a question, so I thought I'd better ask: I'm planning to build Steve Ward's mini SSTC, and since the circuit is nice and compact, I decided to make a box out of perforated aluminum sheet (Imagine a sheet of aluminum which looks like sterotypical cheese ie. full of holes) and using the entire box as a heatsink for the MOSFETs and housing for the circuitry, then mounting the coil on top. And then a thought came to me, why not ground the casing as well, since it's metal.
Now, here's the question: Would RF grounding the case be bad? Because I've got this little voice at the back of my head nagging me that I'm going to kill the MOSFETs that way. (Ps. I'm using a counterpoise, if it matters.) Or should I ground the casing to the earth wire of the house system, or not at all?
Registered Member #123
Joined: Fri Feb 10 2006, 12:58PM
Location:
Posts: 162
Hi There, It all depends if you FETs are isolated from their metal casing or if collector is tied to it. If isolated all should be fine. if not then it must float and the 2 fets must be on seperate heatsinks. although you could use sil pads and ignore all i have just said Cheers Colin I hate it when my answers become questions about the answer
Registered Member #567
Joined: Tue Mar 06 2007, 10:55AM
Location: Singapore
Posts: 147
Well, they'll be IRFP460's in a TO247, so that's not entirely isolated.
But as I understand it, the entire casing, should it be hooked to the RF ground, will be floating at a semi-high voltage, correct? Won't that be able to arc over even a silicon pad?
Registered Member #180
Joined: Thu Feb 16 2006, 02:12AM
Location: Ontario, Canada
Posts: 187
If it's ground it shouldn't be at any potential. But I guess if you wan't to be totally safe just ground it to your house wire, that'll make things easy. Like colin said don't forget to insulate the FETs with a silicone pad. Oh and I'm not totally sure on this one but I think if you happen to get a primary secondary flash over, your FETs will be toast.
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Grounded casing?
