# Discriminate MOS from BJT easily

I have a transistor for which no datasheet is available

the transistor is supposed to be NPN (which implies BJT).

(BD247C-Transistor-NPN, 100V 25A, 120W in TO220)

how can I find out easily if it's a MOS or if it's a BJT?

I have a Digital multi meter and a +5,+12V power supply.

• "NPN" in the name is a dead giveaway, as BJTs can either be on NPN or PNP topology. MOS as you say, or MOSFETs, are either N-Channel or P-Channel topology. – DSWG Oct 17 '18 at 23:58
• You are right! But NPN is not printed on the casing!! It's just an info from the seller, which might have confused NPN with N-Channel – Anze-- Oct 18 '18 at 0:06
• As an aside, 120W dissipation in a TO-220 sounds... optimistic :P – marcelm Oct 18 '18 at 0:13
• Anze--, okay, in a more general sense it would be a very hard process to "check" which it is. You would need a bench power supply, a variety of resistors, the ability to reverse-polary the setup (in order to check for PNP/P-Channel versions), a multimeter, and be willing to potentially blow up a few. On top of that, without the datasheet, it would be impossible to know the maximum ratings, $V_{gs(th)}$ if it is a MOSFET, and other information you really need in order to properly (and safely!) use it in a design. So your question is something that should never really be asked. – DSWG Oct 18 '18 at 0:35