The 2N4870 is a unijunction transistor (UJT) manufactured by Central Semiconductor Corp. UJTs are three-terminal semiconductor devices exhibiting a negative resistance characteristic, making them suitable for oscillator, timer, and triggering circuit applications. The 2N4870 is specifically designed for pulse and timing circuits, and is often used in relaxation oscillators, triggering circuits for SCRs and TRIACs, and voltage sensors.

Applications:

• Relaxation oscillators
• Triggering circuits for SCRs and TRIACs
• Voltage sensors
• Timing circuits
• Pulse generators

Features:

• Peak-Point Emitter Current (IEP): 2 μA (maximum)
• Emitter Reverse Current (IRB2): 5 μA (maximum)
• Interbase Resistance (RBB): 4.7 kΩ to 9.1 kΩ
• Intrinsic Standoff Ratio (η): 0.68 to 0.82
• Valley Point Voltage (VV): 3V (typical)
• Package: TO-18

Benefits:

• Simple oscillator circuits: Can be used to create simple and cost-effective oscillator circuits.
• Precise timing: Allows for accurate and repeatable timing functions.
• Reliable triggering: Provides reliable triggering signals for SCRs and TRIACs in power control applications.
• Low power consumption: Suitable for low-power applications.
• Compact size: TO-18 package allows for integration into space-constrained designs.

Additional Details:

The 2N4870 UJT operates by exhibiting a negative resistance characteristic once the voltage at the emitter reaches a specific threshold, causing it to switch into a low-resistance state. The intrinsic standoff ratio (η) is a critical parameter that determines the firing voltage of the UJT. The interbase resistance (RBB) is the resistance between the two base terminals. When using the 2N4870, it's essential to consider the operating voltage, frequency, and temperature to ensure proper and reliable performance. The device is commonly used in basic electronic circuits for generating timing signals and pulses.