IC ULN 2803 Pinout & Working

Introduction

IC ULN2803 consists of octal high voltage, high current darlington transistor arrays. The eight NPN Darlington connected transistors in this family of arrays are ideally suited for interfacing between low logic level digital circuitry (such as TTL, CMOS or PMOS/NMOS) and the higher current/voltage requirements of lamps, relays, printer hammers or other similar loads for a broad range of computer, industrial, and consumer applications.

Features
  • Eight Darlingtons with Common Emitter.
  • Open–collector outputs.
  • Free wheeling clamp diodes for transient suppression.
  • Output Current to 500 mA.
  • Output Voltage to 50 V.
  • Inputs pinned opposite outputs to simplify board layout.

Pinout


ULN2803 Pinout

Working


The ULN 2803 IC consists of eight NPN Darlington connected transistors (often called a Darlington pair). Darlington pair consists of two bipolar transistors such that the current amplified by the first is amplified further by the second to get a high current gain β or hFE. The figure shown below is one of the eight Darlington pairs of ULN 2803 IC.


ULN 2803 Internal Darlington Pair

Now 2 cases arise:-

Case 1: When IN is 0 volts.


Q1 and Q2 both will not conduct as there is no base current provided to them. Thus, nothing will appear at the output (OUT).

Case 2: When IN is 5 volts.


Input current will increase and both transistors Q1 and Q2 will begin to conduct. Now, input current of Q2 is combination of input current and emitter current of Q1, so Q2 will conduct more than Q1 resulting in higher current gain which is very much required to meet the higher current requirements of devices like motors, relays etc. Output current flows through Q2 providing a path (sink) to ground for the external circuit that the output is applied to. Thus, when a 5V input is applied to any of the input pins (1 to 8), output voltage at corresponding output pin (11 to 18) drops down to zero providing GND for the external circuit. Thus, the external circuit gets grounded at one end while it is provided +Vcc at its other end. So, the circuit gets completed and starts operating.


DataSheet
  • Download ULN2803 datasheet- Link 1
  • Download ULN2803 datasheet- Link 2

11 comments:

Anonymous said...

Thanks! I was searching all day to find info on inpout/output. Because of the inverters in the datasheet i thought it would sink when 0v was appliet

vamsijv said...

I want to light a group of leds using 8051 microcontroller via a 3*8decoder ..i need an led driver circuit after decoder to drive the leds. can ULN2803 be used?
is it a source driver or sink driver?
i mean does it source current or sink?

Jaspreet Singh Kaleka said...

@vamsijv

ULN2803 can be used for driving the LEDs.
ULN2803 sinks the current.

raviteja said...

thank for ur reply.. how can i use ULN 2803 IC as source driver? please give pictorial representation of tht ckt.? and whts the use of that COMMON pin??

vamsijv said...

thank for ur reply.. how can i use ULN 2803 IC as source driver? please give pictorial representation of tht ckt.? and whts the use of that COMMON pin??

Jaspreet Singh Kaleka said...

@vamsijv

Connect cathode of an LED to the ULN's output pin and apply appropriate +ve voltage to the input pin of ULN and anode of LED.

Note: ULN2803 IC cannot provide +ve voltage to drive the LED directly due to its internal circuit. We need to use the above given method to drive an LED.

ULN2803 can be damaged if high reverse voltages are introduced at its output pins. To prevent this we apply +ve voltage to the COMMON pin.

Anonymous said...

Just curious, is there a different component that could source in the same way?

krishna priya said...

how to test atmel at89s51 working? give me in pictorial representation.

Er.Daljit Singh said...

why led is blinking on clear and off when set..??

Er.Daljit Singh said...

thanx sir ur topic helps me lot....

j m said...

thanks for such precious info..

my question is
can uln2803 ic increase the pulse of 0.35 volt to 3-5 volt for ttl circuit?
and if yes, then how?