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ULN2803 Relay Driver: Datasheet, Specification, Circuit

  • Contents

What is ULN2803?

The ULN2803 is a relay driver. The ULN2803 is a relay driver with a Darlington transistor array that can operate at high voltages and currents. The Darlington pairs are connected in a parallel configuration to increase current capability. The component contains eight NPN Darlington pairs with high-voltage outputs and common-cathode clamp diodes that are directly related to switching inductive loads. Each Darlington pair has a collector-current rating of around 500 mA.

This blog provides you with a basic overview of the ULN2803 transistor, including its pin descriptions, functions and specifications, alternative products, etc., to help you quickly understand what ULN2803 is. We will be glad to find that this blog can be useful for people loving electronic components.

Catalog

ULN2803 Pinout

ULN2803 Circuit

ULN2803 Applications

ULN2803 Features

ULN2803 Advantage

ULN2803 Package

ULN2803 Parameters

ULN2803 Equivalents

Where to use ULN2803

ULN2803 Manufacturer

How is ULN2803 Working

Component Datasheet

FAQ


ULN2803 Pinout

ULN2803 Relay Driver Pinout

Pin Number

Description

BASE CONNECTIONS for DARLINGTON ARRAYs

1

1B-Base of 1st Transistor

2

2B- Base of 2nd Transistor

3

3B- Base of 3rd Transistor

4

4B- Base of 4th Transistor

5

5B- Base of 5th Transistor

6

6B- Base of 6th Transistor

7

7B- Base of 7th Transistor

8

8B- Base of 8th Transistor

SHARED TERMINALS

9

GND- Emitter of all Transistor s

10

COM- Common cathode (Negative) node for flyback diodes. 

COLLECTOR CONNECTIONS for DARLINGTON ARRAYs

11

8C-Collector of 8th Transistor

12

7C-Collector of 7th Transistor

13

6C-Collector of 6th Transistor

14

5C-Collector of 5th Transistor

15

4C-Collector of 4th Transistor

16

3C-Collector of 3rd Transistor

17

2C-Collector of 2nd Transistor

18

1C-Collector of 1st Transistor


ULN2803 Circuit

ULN2803 Circuit

ULN2803 Circuit 1

ULN2803 Circuit

ULN2803 Circuit 2


ULN2803 Applications

ULN2803 is widely used in the following applications:

  • Hammer drivers
  • Display drivers
  • Logic Buffers
  • Gas & LED discharger
  • Logic buffers
  • Relay drivers
  • Lamp drivers
  • Line drivers

ULN2803 Features

The specifications, as well as features of ULN2803, are as follow:

  • The allowed maximum voltage between emitter & collector for each and every Darlington transistor is 50 volts.
  • The maximum current that is allowed to flow through the collector of every Darlington pair is 500 mA.
  • Between the emitter and base of the Darlington pair, the maximum voltage that is allowed is 30 volts.
  • In each Darlington pair, a fly-back diode is present and the maximum current that is allowed to pass through that is 500 mA.
  • The rise time is 130 ns.
  • Typically, the fall time is 20micro-second.
  • The operating temperature of ULN2803 lies in the range of -65°C – 150°C.
  • In order to operate this chip, no additional power is needed.

ULN2803 Advantage

ULN2803 chip

ULN2803 Chip

ULN2803 is a high-voltage, high-current transistor array IC, especially for microcontrollers that need to drive high-power loads. The IC consists of eight NPN Darlington-connected transistors and a common clamp diode to switch the load connected to the output. This IC is widely used to drive high loads, such as lamps, relays, motors, etc. Its rated current is usually 50v / 500mA.


ULN2803 Package

Here we take ULN2803A as an example to introduce ULN2803 package.

ULN2803 Package


ULN2803 Parameters

Drivers per package

8

Switching voltage (Max) (V)

50O

utput voltage (Max) (V)

50

Peak output current (mA)

500

Delay time (Typ) (ns)

130

Input compatibility

CMOS, TTL

Vol @ lowest spec current (Typ) (mV)

900

Iout/ch (Max) (mA)

500

Iout_off (Typ) (uA)

50

Rating

Catalog

 


ULN2803 Equivalents

There are no PIN-to-PIN replacements for ULN2803 but there are similar functioning ICs like ULN2003, ULN2004. You can remodel eight Darligngton Transistors or eight MOSFETs to substitute for ULN2803.


Where to use ULN2803

The ULN2803 chip can be used in the following cases:

  • To control the inductive loads those are making use of the logic obtained by the control unit. In ULN2803, the Darlington array act as separate 8 individual switches and thus can be turned off and on as desired. Each set of these Darlington pair is capable of driving high power loads that use logic from the control unit.
  • If you are willing to drive multiple loads, then this chip can be used as it is capable of driving eight loads at a time. However, the MOSFETs, as well as transistors that are being used in this chip, will suffice and also placing eight loads at the same time will be a cumbersome job but this chip is widely used in order to replace the bulk switching devices.
  • This chip can also be used for programmable load sharing. if we are having one low power load as well as one high power load then multiple arrays can be connected in parallel in order to drive the high power load.

ULN2803 Manufacturer

TI Logo

Texas Instruments Inc. (TI)  is an American technology company that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally. Its headquarters are in Dallas, Texas, United States. TI is one of the top ten semiconductor companies worldwide, based on sales volume. Texas Instruments's focus is on developing analog chips and embedded processors, which accounts for more than 80% of their revenue. TI also produces TI digital light processing (DLP) technology and education technology products including calculators, microcontrollers and multi-core processors. To date, TI has more than 43,000 patents worldwide.


How is ULN2803 Working

The ULN2803 IC consists of eight NPN Darlington pair which provides the proper current amplification required by the loads. We all know that the transistors are used to amplify the current but here Darlington transistor pairs are used inside the IC to make the required amplification.

A Darlignton pair is two transistors that act as a single transistor providing high current gain. In this pair the current amplified by the first transistor is further amplified by the next transistor providing high current to the output terminal.

When no base voltage is applied that when is no signal is given to the input pins of the IC , there will be no base current and transistor remains in off state. When high logic is fed to the input both the transistors begin to conduct providing a path to ground for the external load that the output is connected. Thus when an input is applied corresponding output pin drops down to zero there by enabling the load connected to complete its path.


Component Datasheet

ULN2803A Datasheet


FAQ

  • What is ULN2803?

ULN2803 is a high-voltage and high-current Darlington transistor array and is mainly used as a relay driver with an ability to handle 8 relays at a time.It comes with a collector-emitter voltage around 50 V and input voltage residing at 30 V.

  • What is the use of ULN2803 in driving a relay?

Explanation: We need a ULN2803 for driving a relay because the relay coil requires 10mA or more current to be energized. If microcontroller pins are not able to provide sufficient current to drive relays then we need ULN2803 for driving relays.

  • How do you use ULN2803?

ULN2803 is a High voltage, high current Transistor Array IC used especially with Microcontrollers where we need to drive high power loads. Thic IC consists of a eight NPN Darlington connected transistors with common Clamp diodes for switching the loads connected to the output.

 

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