2N2646 PN Unijunction Transistor: Datasheet, Pinout and Equivalent

The 2N2646 is a silicon PN Unijunction Transistor that can be used in a variety of industrial applications. The device is commonly used as a triggering device and is not designed to drive high-current loads.

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.

The conductive casing is also connected to a terminal on the 2N2646, making it a three-terminal device. The following is the 2N2646 Pinout diagram of the 2N2646 Unijunction transistor.

2N2646 Pinout

Symbol

2N2646 Symbol

Footprint

2N2646 Footprint

• Low Peak Point Current: 5A (Max)

• Low Emitter Reverse Current:005A (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

• Operating temperature range: -65ºC to +150ºC

• Maximum power dissipation: 300mW

• Passivated Surface for Reliability & Uniformity

• Available as “HR” (high reliability)

• Available as non-RoHS (Sn/Pb plating)

• Timing circuit

• Voltage detector

• SCR firing circuits

• Hobby projects

• Phase control circuit

• Sawtooth wave generator

• Relaxation oscillator

• General-purpose industrial applications

2N2647, 2N4870, 2N4871, 2N1671

The 2N2646 is mostly employed in the design of firing circuits (for Silicon Controlled Rectifiers) rather than amplifier circuits such as transistors. Other applications that demand a guaranteed minimum pulse amplitude, as well as a low emitter leakage current and a low peak point emitter current (trigger current), favor the device. Many low-cost industrial applications use the 2N2646 transistor.

The circuit diagram employing the 2N2646 unijunction transistor is given below. This circuit runs on 9V to 12V DC. A 9V to 12V battery, 2N2646 UJT, LED, 10K and 390 resistors, breadboard, and connecting wires are all needed to make this circuit.

2N2646 Circuit

In this circuit, a 390-ohm resistor is primarily utilized to limit the flow of current via the transistor and LED. The R1 and C1 parameters are mostly responsible for the LED flashing frequency. We can conduct some short experiments using these variables to determine the appropriate LED flashing rate.

We can use any value between 10K and 1M for the resistor 'R1.' In the circuit above, the resistor 'R1' is a 1M potentiometer or variable resistor, while the capacitor 'C1' can be any value between 1uF and 100uF.

When this transistor is turned on, the emitter current is allowed to increase until it is limited by the power supply in the emitter terminal. Because of its negative resistance, this transistor can also be used as an oscillator.

A potential drop occurs when a positive supply is applied to the two base terminals of this transistor. Once the emitter voltage is increased one diode voltage above the voltage where P-type material diffusion occurs, current will flow from the emitter terminal to the base.

As a result of the additional current on the base region, the resistance between the emitter (E) and the base region is reduced, and the UJT's conductivity improves. As a result of the resistance drop, the emitter terminal will connect in forwarding bias, allowing more current to be injected. As a result of the resistance drop, the UJT will be able to operate above negative resistance. As a result, it is extremely useful for oscillators’ circuits.

2N2646 Mechanical Outline

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