Power MOSFET Substitution

[PerroGrande]

This is a bit OT, sorry.  It isn't musical, but it is electronic and I wanted to get the opinions of the gurus on here...

I recently ended up working on a Plasma display.   I'm working a bit blind, but after searching on the internet extensively, I found a technician's manual for a similar model that uses some of the same boards that the PDP I have uses. 

After some troubleshooting, one of the key voltages that is used for the Sustain Drive circuit is dead (a smoked resistor started me in the direction of this discovery). So instead of 158 volts, I've got zero.  This causes the protection circuitry to engage and shut down the unit (probably a good thing).

Anyway -- the resistor smoked because one side of it is at 175V and the other side is (erroneously) grounded -- via either a smoked power MOSFET (or two, or three, or four) or a shorted electrolytic cap.  The power MOSFET used in this circuit is a 2SK3652 -- a serious piece of MOSFET indeed (continuous Id of 50A, peak to 200A, 230V Vdss max)...

Problem:  This MOSFET (2SK3652) doesn't seem to be readily available through my normal channels (although the data sheet is easy to find).

However, the Fairchild FDA2712 is available for under 6 bucks each at Mouser.  It *looks* to be an equal to superior replacement (it even uses the same form-factor), and is indicated for PDP use according to the datasheet.

Does this MOSFET (FDA2712) look like a reasonable replacement for the original 2SK3652 ? 

Thanks!

[R.G.]

It does, but with two caveats: (1) the Fairchild device has about 1/8th the avalanche energy of the Panasonic, 245mJ instead of 2200mJ for the Panasonic and (2) the Ciss is about twice as big for the Fairchild device.

The avalanche energy will be important if and only if the circuit it's in lets the transistor eat some of the flyback energy of the inductance - if any - that it drives. The Ciss will be important if the circuit is speed critical.

That is, there's no good way to tell without knowing the circuit operation.

One of Keen's Laws says that having any device that works now better than having the perfect device someday and a piece of not-too-useful sculpture until the perfect one comes along.

[PerroGrande]

Thanks R.G.

Unfortunately, I don't know the complete circuit details.  The manual I found isn't complete with schematics -- just some snippets and block diagrams.  The troubleshooting section is mostly calibration of a working unit - repair is via board-swap.  The do show some waveforms, though, so perhaps I can use that to get a sense of the speed of switching required and guesstimate if Ciss is going to cause problems.   The avalanche energy could be an issue -- I just don't know the theory of PDP well enough to know if it "looks" like an inductor to the bank of 4 MOSFET based switches that are on this board.  Looking at some of the current ratings and the internal traces / heatsinks / etc, I can understand why plasma displays get hot, though!

I like your "Law" -- and I do have the luxury of being in a no-lose situation.  The only place that repairs this brand has quoted my employer a price that is essentially the same as a new plasma display.  If I can get this thing working, great -- if not, they're going to spring for a new panel anyway.  I'm going to give it a try and see how it works out.

Thanks again!