Need a cross reference for MOSFETS

[Y2KEDDIE]

I need a good part number for a NF818 and NF840. These are MOSFET's for a switchung power supply.

 

[KrisBlueNZ]

Have you done your due Google diligence?

You're not the only one to ask, but I don't see any answers.

Have you considered replacing the whole board?

 

[Y2KEDDIE]

Have you done your due Google diligence?

You're not the only one to ask, but I don't see any answers.

Have you considered replacing the whole board?

Y

 

[KrisBlueNZ]

O

 

[Y2KEDDIE]

Yes, I tried Google, even tried NT Quick Cross.

Yes I am replacing the entire board, ordered new one this morning..

Still I would like to experiment with the old board.

 

[KrisBlueNZ]

Do you know how those two MOSFETs are used in the circuit?

Do you know if they're opposite polarities?

What package are they?

Start by uploading photos of both sides of the board.

Also post the power rating of the set.

There's not likely to be anything special about those particular part numbers. There are probably suitable general replacement devices available.

 

[Y2KEDDIE]

I traced the Drain connections to the corresponding output pins on the board connector, Pins 10,11,12 are the 5VDC output connections. Pins 2,3,4 are the 12VDC output connections. The filter capacitor correct voltage ratings confirm these outputs.

So CRS101 (NF818) is for the 5V supply, and CRS102 is for the 12V supply. They are a TO-220 package. They are insulated from the heat sink.

The board legend says it is 5VDC@5A and 12VDC@4A. Given the polarities I am assuming these are N-channel MOSFETS.

Vishay Siltronix makes a IFR840, SiHF840 (TO-220), and a SIR818DP (but in a SO-8 package which won't work), Maybe this is a bad cross.

I have little experience with MOSFET's.

Anyway, this is all I have. Could you help me find suitable replacements.

Thank you so much!
Eddie

 

[KrisBlueNZ]

I think they're diodes, not MOSFETs. Are the two end pins connected together, and directly to a pin on the transformer? If so, this should be a suitable replacement: http://www.digikey.com/product-detail/en/STPS20SM60ST/497-12308-ND/2827132

 

[Y2KEDDIE]

Sometimes its hard to see the forest because of the trees! No wonder these fail the MOSFET test! They test fine as back to back diodes. The two outside terminals connect to corresponding transformers. The + supplies are from the cathodes. I feel foolish for missing this, especially after making my diagram.

Thanks for your clever eyes.

 

[KrisBlueNZ]

No problem