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NPN Darlington power transistor

TIP122 Internal Circuitry

Explore the internal circuitry and functional stages of TIP122.

Inside TIP122

Two NPN stages, common collector and internal discharge resistors.

TIP122 compact two NPN Darlington circuit with common collector and base-emitter shunt resistors.
Original functional drawing based on the manufacturer’s internal schematic. Resistor values are approximate.

Explore the circuit

Select a stage to see its role and connections

First stage

External base current controls the first NPN.

Second stage

The first emitter feeds the second base; the collectors are joined.

Shunt paths

Approximately 8 kΩ and 120 Ω resistors discharge the internal junctions.

Component view