Always verify with the datasheet — TO-92 pinouts in particular vary wildly between part numbers.
TO-92 (viewing flat face)
| Part | Pin 1 | Pin 2 | Pin 3 | Notes |
|---|---|---|---|---|
| 2N3904 (NPN) | E | B | C | EBC order |
| 2N3906 (PNP) | E | B | C | EBC order |
| 2N2222A | E | B | C | EBC |
| 2N2907A | E | B | C | EBC |
| BC547 / BC337 | C | B | E | CBE (European ordering!) |
| BC557 / BC327 | C | B | E | CBE |
| 2N7000 (N-MOSFET) | S | G | D | SGD |
| BS170 (N-MOSFET) | S | G | D | SGD |
| TIP120 (NPN Darlington, TO-220) | B | C | E | BCE |
TO-220 / TO-247 (leaded tab)
| BJT 2N3055 / MJE3055 | Pin 1 B, Pin 2 C (tab), Pin 3 E |
|---|---|
| N-MOSFET IRF540 etc. | Pin 1 G, Pin 2 D (tab), Pin 3 S |
| P-MOSFET IRF9540 | Pin 1 G, Pin 2 D (tab), Pin 3 S |
| LM317 / LM7805 | Pin 1 ADJ/IN, Pin 2 OUT (tab), Pin 3 IN/OUT — check each! |
SOT-23 (top view, markings visible)
| BJT (MMBT3904 etc.) | Pin 1 B, Pin 2 E, Pin 3 C |
|---|---|
| MOSFET | Pin 1 G, Pin 2 S, Pin 3 D |
Notes
- US transistors often use EBC (2N3904 family). European BC-series often use CBE. Swapping them may appear to work but with catastrophically wrong gain.
- The metal tab on TO-220/TO-247 is almost always internally connected to the middle pin (drain/collector).
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