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.

TI 8206 BD147C

  • 3
    \$\begingroup\$ "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. \$\endgroup\$ – DSWG Oct 17 '18 at 23:58
  • \$\begingroup\$ 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 \$\endgroup\$ – Anze-- Oct 18 '18 at 0:06
  • \$\begingroup\$ As an aside, 120W dissipation in a TO-220 sounds... optimistic :P \$\endgroup\$ – marcelm Oct 18 '18 at 0:13
  • \$\begingroup\$ 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. \$\endgroup\$ – DSWG Oct 18 '18 at 0:35
  1. Google the part number. I just did, and while I didn't find a data sheet, I did find an NTE cross-reference (for an NPN). This indicates that it's an obsolete consumer part.
  2. Measure each leg against the others with the meter in diode mode.
    1. An NPN will show the base-emitter and base-collector junctions as one diode drop if the base is positive (and if it's a really old transistor you'll learn whether it's silicon or germanium).
    2. A PNP will look like an NPN, only in reverse.
    3. A typical MOSFET will look like an open-circuit from gate to either source or drain. It may look like a diode drop from source to drain (for an N-channel) or from drain to source (for a P-channel) or it may be open, or (if it's depletion mode) it may look like a resistor. If you really think it's a MOSFET you can try putting 10V or so on the suspected gate-source pins and see if the drain-source pins conduct.
    4. A 3-terminal voltage regulator will just look odd
  • \$\begingroup\$ I will follow up with the results, just for record purposes!! \$\endgroup\$ – Anze-- Oct 18 '18 at 1:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.