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MOSFET (How to determine correct orientation)

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Newbie level 5
Aug 9, 2009
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I am assembling a board which uses some IRFD110 MOSFETs but I don't know which way round to insert them. The PCB shows the components with a semi-circular cutout on one end, like many components, but the component itself has no such indicator. The MOSFETs are 4-pin devices with 2 pins linked, but that is not indicated on the PCB. How do I determine which way to orientate the MOSFETs?

You can see it's datasheet and found pins detail. It's a N-Chanel mosfet if it's single in circuit. Definitely pin(S) connected to ground. You wold found GND in board.

There's no pin number assignment in the datasheet, so marked pin 1 has been arbitrarily assigned by the circuit designer. The schematic should clarify if pin 1 is at the gate or drain. It should be also quite easy to identify the shorted drain pins on the PCB.

A NC pin is together Drain pin. So presumably it will not connect in circuit. It will simple to found.

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The datasheet VERY clearly shows which pin is which.

But not showing pin numbers.

The pcb shows pin numbers but the datasheets don't. Then ask the designer of the pcb and tell him he is an idiot.

If this is a kit, you are probably not the first person to have this problem.

Do a Google, or Google Image search for the name of the kit.
It may even turn up a picture of the board, or link to some Forum where this problem has been discussed.
Its a long shot, but luck may be on your side.


The pcb shows pin numbers but the datasheets don't. Then ask the designer of the pcb and tell him he is an idiot.

Yes and no.

1) in a pcb layout system the packages are often designed for general use - not related to a specific device
2) there are pin numbering recommendations like IPC-7351
3) maybe the datasheet of the same device from another manufacturer shows pin numbers.

Pin numbering is more a recommendation. You can not rely on it, at least not as "common knowledge". Only with a specific manufacturer and a specific device with its specific datasheet.

All cross reference is critical


I looked at the datasheets from about 6 semiconductor manufacturers. Most simply copied the photo in the oldest datasheet that has no pin numbering.
I think the end with the semi-circular cutout shown on the pcb is the two drain pins connected together. The pcb probably also connects the drain pins together.
In Google I found a project posted by a student that had a pcb with two lines at the drain pins end of the IRFD110.

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