Output C

COM

E

3 k

2 .7 k

Input B

7.2 k

Copyright © 2016, Texas Instruments Incorporated

10

ULN2003B

SLRS064B – JUNE 2014 – REVISED AUGUST 2016

www.ti.com

Product Folder Links: ULN2003B

Submit Documentation Feedback

Copyright © 2014–2016, Texas Instruments Incorporated

8 Detailed Description

8.1 Overview

This standard device has proven ubiquity and versatility across a wide range of applications. This is due to it's

integration of 7 Darlington transistors that are capable of sinking up to 500 mA and wide GPIO range capability.

The ULN2003B comprises seven high voltage, high current NPN Darlington transistor pairs. All units feature a

common emitter and open collector outputs. To maximize their effectiveness, these units contain suppression

diodes for inductive loads. The ULN2003B has a series base resistor to each Darlington pair, thus allowing

operation directly with TTL or CMOS operating at supply voltages of 5 V or 3.3 V. The ULN2003B offers

solutions to a great many interface needs, including solenoids, relays, lamps, small motors, and LEDs.

Applications requiring sink currents beyond the capability of a single output may be accommodated by paralleling

the outputs.

This device can operate over a wide temperature range (–40°C to +105°C).

8.2 Functional Block Diagram

All resistor values shown are nominal.

Figure 22. Schematic (Each Driver)

8.3 Feature Description

Each channel of ULN2003B consists of Darlington connected NPN transistors. This connection creates the effect

of a single transistor with a very high current gain. This beta can be high at certain currents see Figure 5.

The GPIO voltage is converted to base current through the 2.7-kΩ resistor connected between the input and

base of the pre-driver Darlington NPN. The 7.2-kΩ and 3-kΩ resistors connected between the base and emitter

of each respective NPN act as pull-downs and suppress the amount of leakage that may occur from the input.

The diodes connected between the output and COM pin is used to suppress the kick-back voltage from an

inductive load that is excited when the NPN drivers are turned off (stop sinking) and the stored energy in the

coils causes a reverse current to flow into the coil supply through the kick-back diode.

In normal operation the diodes on base and collector pins to emitter will be reversed biased. If these diode are

forward biased, internal parasitic NPN transistors will draw (a nearly equal) current from other (nearby) device

pins.