Skip to datasheet
Eight-channel Darlington driver

ULN2803A Internal Circuitry

Explore the internal circuitry and functional stages of ULN2803A.

Package view

Inside ULN2803A

One Darlington channel, repeated eight times inside the package.

An internal 2.7 kilohm input resistor drives two NPN transistors. Their collectors share the output, the second emitter returns to pin 9, and the clamp diode cathode connects to COM pin 10.
Representative channel inside the IC. Small bias resistors are omitted for clarity; see the manufacturer equivalent circuit.

Explore the circuit

Select a stage to see its role and connections

Input drive

A 2.7 kΩ resistor limits base drive from the logic input.

Two-transistor gain

The first emitter drives the second base; both collectors form one output sink.

Clamp return

The diode anode is at the collector and its cathode is at COM pin 10.

Component view