The 2N2646 is a UJT transistor (Unijunction transistor) comes in three terminal and available in TO-18 packaging. This article describes the 2N2646 Transistor pinout, equivalent transistor and additional information’s regarding this transistors which is helpful for all electronic technicians.
What is 2N2646 UJT Transistor?
The 2N2646 is a unijunction transistors. This three terminal transistor is different from normal BJT transistors. The regular transistors are using for switching and signal amplification. But this UJT transistors are using only for switching applications like turn On or OFF.
2N2646 UJT Transistor Pinout
| Pin / Terminal | Name | Function |
|---|---|---|
| 1 | Emitter (E) | Emitter terminal is used to trigger the UJT into conduction. |
| 2 | Base 1 (B1) | Lower end of the internal base bar it is commonly used as the reference/output terminal. |
| 3 | Base 2 (B2) | Upper end of the internal base bar is normally connected toward the positive supply. |
Specifications of 2N2646 Transistor
- Total Power Dissipation is 300 mW
- Max Emitter-Base 2 Voltage is 30 V
- Max Inter-base Voltage (B2B1) is 35 V
- Peak Emitter Current us 2 A
- Static Inter-base Resistance is 4.7 kฮฉ to 9.1 kฮฉ.
Internal Structure and Working of UJT Transistor
In this 2N2646 transistor a uniform N-type silicon bar with Base 1 and Base 2 at its end. When in normal condition supply voltage is applied across the base it acts like a resistor and voltage across the bar is evenly distributed.
Working of 2N2646 Transistor
The emitter pin is act as the Trigger voltage injector. The emitter voltage is lower than the standoff voltage the internal PN junction blocks the voltage. This will cause the UJT to completely OFF state. Once the emitter voltage is raised and the PN junction reaches the forward biased, once is completely forward biased and charge moves across the PN junction. Internal resistance decreased and current passing through it.
Equivalent UJT Transistor as Replacement
The direct replacement options are 2N2647, 2N4870 and 2N4871. You can use 2N1671 but the packaging is different, it is available in TO-5 packaging.
Applications
- Used in thyristor trigger circuit. In high power switches like SCR and triac based circuit control heavy Ac loads but it requires sudden pulse of gate current to work perfectly.
- Timing and Delay Circuits.
- Bistable Switching & Sensing.
