ULN2003A DIP package.
Figure 1

How to Use the ULN2003A Darlington transistor Array with Examples

by Lewis Loflin

Here we will explore using the versatile ULN2003A Darlington Transistor array with a typical micro-controller such as Arduino.

The ULN2003A is a high-voltage, high-current Darlington transistor array consisting of seven NPN Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes for switching inductive loads.

The collector-current rating of a single Darlington pair is 500 mA.

The Darlington pairs can be paralleled for higher current capability. Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED and gas discharge), line drivers, and logic buffers.

ULN2003A Darlington transistor amplifier.
Figure 2

Internal diagram of the UNL2003A showing the open-collector Darlington configuration. The ULN2003A has a 2.7K ohm series base resistor for each Darlington pair for operation directly with TTL or 5-V CMOS devices.


ULN2003A Darlington Transistor array internal block diagram.
Figure 3. ULN2003A Darlington Transistor array internal block diagram.


ULN2003A driving a unipolar stepper motor controlled by a PC printer port.
Figure 4. ULN2003A driving a unipolar stepper motor controlled by a PC printer port.


ULN2003A driving 7 24-volt light bulbs.
Figure 5. ULN2003A driving 7 24-volt light bulbs.


ULN2003A driving 4 24-volt relays to control 4 120VAC lamps.
Figure 6. LN2003A driving 4 24-volt relays to control 4 120VAC lamps.


ULN2003A with parallel inputs-outputs driving 2 1-Amp motors.
Figure 7. ULN2003A with parallel inputs-outputs driving 2 1-Amp motors.

I would not recommend using the above circuit. Use an actual transistor driver to handle higher currents. See Driving 2N3055-MJ2955 Power Transistors with Darlington Transistors.


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