2N2646 Uni Junction Transistor & Its Working

• N2646 is a general-purpose silicon PN Unijunction Transistor that is designed for general-purpose industrial applications.
• This transistor is made out of n-type semiconductors, with the length of the p-type material controlled to help fix the intrinsic standoff ratio parameter. Emitter, base, and collector are the three terminals on a typical 2n2646 UJT.

Pin Configuration

Working

1. When the Emitter is Open

• When the voltage VBB is applied with the emitter open, a potential gradient is established along the n-type silicon bar.
• The voltage V1 (between emitter and B1) establishes a reverse bias on the PN-junction.
• Emitter current is cut off, but a small leakage current flows from B2 to emitter due to minority charge carriers.

• Thus, the device is said to be in an OFF state.

2. With Emitter at Positive Potential

• When a positive voltage is applied at the emitter terminal, the PN-junction will remain reverse biased till the input voltage is less than V1.
• The PN-junction becomes forward-biased when the input voltage at the emitter exceeds V1.
• Under this condition, holes are supplied from the p-type region into the n-type bar, due to this saturation of charge carriers occur.
• The emitter current is limited by the emitter power supply because of this saturation.

• Now, the device is conducting, hence said to be in ON state.

Characteristics of 2N2646 Uni Junction Transistor

• Low Peak Point Current: 5mA (Max).
• Low Emitter Reverse Current:005mA (Typ).
• Maximum voltage between two bases (VB2B1): 35V.
• Maximum emitters reverse voltage (VB2E): 30V.
• Maximum RMS emitter current (Ie): 50mA.
• Maximum peak emitter current (Ie): 2A.

Applications of 2N2646 Uni Junction Transistor

• Timing circuit.
• Voltage detector.
• Phase control circuit.
• General-purpose industrial applications.