PN UJT Transistor 2N2646

The PN UJT Transistor 2N2646 is a classic unijunction transistor (UJT) with one emitter and two base terminals. When the emitter voltage reaches a set fraction of the voltage between the bases, the device switches on sharply, which makes it ideal for simple relaxation oscillators, pulse generators, timers and trigger circuits for SCRs and triacs. It is also a popular part for teaching UJT behaviour in electronics labs.

PN UJT Transistor 2N2646 Specifications

• Type: PN unijunction transistor (UJT)
• Package: TO-18, 3 leads: emitter (E), base 1 (B1) and base 2 (B2)
• Intrinsic standoff ratio (η): 0.56 to 0.75
• Interbase resistance (RBB): 4.7 kΩ to 9.1 kΩ
• Power dissipation: 300 mW
• Interbase voltage: 35 V max
• Emitter current: 50 mA RMS, 2 A peak for short pulses
• Peak point current: 5 µA max; valley current 4 mA min

PN UJT Transistor 2N2646 Applications

• Relaxation oscillators and sawtooth generators
• Pulse generators and simple timers
• Triggering SCRs and triacs in phase control circuits
• LED flashers and tone generators
• Teaching UJT characteristics in university labs

What's in the Box

• 1 × 2N2646 unijunction transistor

Tip: In a basic relaxation oscillator, a resistor and capacitor in series set the emitter voltage, B2 goes to the supply through a small resistor and B1 goes to ground through about 47–100 Ω, where the output pulses appear. The period is roughly R × C × ln(1 / (1 − η)). Check the lead order against the datasheet before soldering.

Orders placed before 14:00 are ready for pickup the same day. Delivery across Lebanon usually takes 1–3 working days.