Mosfet With Middle Pin Missing?

[EpicIntelGamer]

Hi guys!

I was scraping two computer PSU's, just ripping all the parts off and I found something interesting.

There is a ST P10NK60Z N Channel Mosfet mounted to a heatsink and for some reason the middle pin is cut off?

The back of the fet has an insulating pad behind it so they arent using that in place of the pin, what could you use a Mosfet for with a pin missing?

Thanks!

[8086]

A diode

[EpicIntelGamer]

A diode

Wow really?

With what sort of specs?

[8086]

A diode

Wow really?

With what sort of specs?

Well that depends.  Usually not very exciting, with a slightly higher forward voltage than a "normal" diode.

If you look at a symbol for a MOSFET you will usually find the diode in there.

[EpicIntelGamer]

A diode

Wow really?

With what sort of specs?

Well that depends.  Usually not very exciting, with a slightly higher forward voltage than a "normal" diode.

If you look at a symbol for a MOSFET you will usually find the diode in there.

Oh yeah I guess they do. I don't usually look at that little diagram.

What would make them use a mosfet like this instead of a normal diode?

[senso]

Wireless gate control 

[EpicIntelGamer]

Wireless gate control 

0_0 lol

[Andy Watson]

If it was the middle pin it looks like it would have been the drain that was cut off. You wouldn't want to leave the gate floating. Still a bit odd.

[EpicIntelGamer]

If it was the middle pin it looks like it would have been the drain that was cut off. You wouldn't want to leave the gate floating. Still a bit odd.

Yeah its the middle pin and I'm sure I didn't break it off while removing it because I looked at the PCB and there is actually no hole for that middle pin.

Perhaps they needed a diode but had that mosfet sourced for cheap?

[Towz]

maybe a picture of the setup would be useful. All i can think of at the moment is some sort of peak/transient suppresion since it's the Drain that is cut off. This mosfet has built in zener protection between the gate and the source.

[EpicIntelGamer]

maybe a picture of the setup would be useful. All i can think of at the moment is some sort of peak/transient suppresion since it's the Drain that is cut off. This mosfet has built in zener protection between the gate and the source.

I'll grab a picture for you tommorrow, it's pretty late right now.

[amyk]

This mosfet has built in zener protection between the gate and the source.

It's two 30V zeners back-to-back, so maybe that's what they were using it for. Might've been cheaper if the same part was already used in the PSU for switching, than to add another part to the BOM.

[smashedProton]

Wouldn't it be just a low inpeadance connection?  In most packages, the center pin is connected to the case.  Maybe the case on this fet isn't connected to the substrate. 

 I used to cut off the middle pins of a n channel and p channel fets and solder them directly together for an active breaking system I put in by buddys airsoft gun.

[Neilm]

I have seen some packages like this that have two matched diodes in them. The case is common and each leg is one connection to the diode.

Neil

[EpicIntelGamer]

I have seen some packages like this that have two matched diodes in them. The case is common and each leg is one connection to the diode.

Neil

Yeah it has some of those dual doide packages but this is not one of those. This is an N Channel Mosfet (details in the OP) that they cut a leg off of.

[c4757p]

Dear god.... flip it over and trace out that section of the circuit! 

[EpicIntelGamer]

Dear god.... flip it over and trace out that section of the circuit! 

Will do, just a second...

[EpicIntelGamer]

I just tried but really it goes all over the place.

The one side of the mosfet goes over to one side of one of the big filter capacitors on the rectified input.

The other breaks off to multiple locations including some little 8pin IC and then it apparently also goes to the same place as the other side of the mosfet.

[Rufus]

This is silly.

If the drain wasn't connected you are left with gate to source capacitance and wimpy ESD protection diodes as the only accessible components neither of which are useful or require mounting on a heat sink.

How was it fastened to the heat sink? With a screw to make the drain connection I'll bet and the silicon insulator pad was there just for thermal reasons. 

[Psi]

Was it a cheap china powersupply? Might be from a batch of diodes that got wrongly stamped as mosfets.
They could be using them up since they're a surplus/cheap stock of diodes.


This sort of manufacturing mistake happens more often than you know.
Someone at the semiconductor plant sets the machine wrong and before they know it they have 100 reels of diodes marked as mosfets.

[c4757p]

I just tried but really it goes all over the place.

All PCBs do. It's good reverse engineering practice.

[c4757p]

Was it a cheap china powersupply? Might be from a batch of diodes that got wrongly stamped as mosfets.
They could be using them up since they're a surplus/cheap stock of diodes.

Good point. Probe them dammit! You've got to figure these things out for yourself!