UJT (unijunction) (2N2646)
2N2646 unijunction transistor · R_BB ≈ 6.8 kΩ · η ≈ 0.62 · fires when the emitter passes η·V_BB + 0.6 V, then the emitter–B1 path collapses until the current falls below the valley current (≈ 4 mA)
Try it on the benchThe lab drops it on an empty bench and opens its datasheet card.
Typical part: 2N2646 unijunction
Pins
- E (emitter)
- B1 (base 1)
- B2 (base 2)
Ratings and limits
| R_BB | 4.7–9.1 kΩ |
|---|---|
| η | 0.56–0.75 |
| I_P | 5 µA |
| I_V | 4 mA |
How to use it
Relaxation oscillator: a capacitor charges through R until the emitter reaches η·V_BB + 0.6 V, the UJT fires and discharges it into B1. f ≈ 1 ÷ (R·C·ln(1/(1−η))).