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Relay Driver IC ULN2003 Circuit Diagram



Normally when we are designing electronic circuits applied resistances are being controlled (on,off) by applying  micro-controller blocks.To chive it the electronic circuits need relays,working as controlled switch mechanism e.g different types of relays are used for various electronic circuits.Relay controls the load resistance which depends upon the electric signals received from micro-controller or some other controlled circuits.Relay depends upon the continuously supplied electric power,it activates itself when its got driven or when it  get the control signals and then the loads can be switched on,off.So,basically we should be  aware about the RDC(relay driver circuits).

RDC(relay driver circuits):

The circuit which is used to drive a relay can be named as a RDC  and also it can be implemented  by the use of different ICs(integrated circuits).these are relays are required to driven to activate or to turn it on.that’s why some specific driver-circuit is required for relay to switch to on or off(according to the needs).RDC is easy to realize by the use of various ICs.e.g (uln-2OO3)(cs-11O7)(max-4896)(fan-3250)(a-255O….

The above mentioned discussion allows us to know about RDC with the use of (uln-2OO3).before going for a deep talk about RDC we  must know about integrated circuit (uln-2OO3).

RD integrated circuit (uln-2OO3):

The integrated circuit (uln 2003) is darling-ton transistor array  used when the very high voltage or very high current takes place.different types of RD integrated circuits are available like high-side-toggle-switch,bipolar n.p.n transistor,DT, (uln-2OO3)d integrated circuit diagram of the pins of  integrated circuit  above has sixteen pins .The integrated circuit (uln-2OO3a).

Relay driver provide a more efficient method for enabling a eight relays. for this purpose, we use seven relays by using the relay driver circuit. it’s more perfect solution to solve difficult task in easy way & we use ULN 2003 and ULN 2008 relay driver circuits. this circuit to give many interfaces by using relay driver circuit ULN 2003 and relay driver also use to construct a clamp diodes.

The program that can be used for turning the relays ON and OFF is given below with delay time of one second.


void main()


TRISD = 0x00;    //PORT D is made as output



PORTD.R1 = 1;  //Relay 1 turns ON

PORTD.R2 = 1;  //Relay 2 turns ON

PORTD.R3 = 1;  //Relay 3 turns ON

PORTD.R4 = 1;  //Relay 4 turns ON

PORTD.R5 = 1;  //Relay 5 turns ON

PORTD.R6 = 1;  //Relay 6 turns ON

PORTD.R7 = 1;  //Relay 7 turns ON…and so on.

Delay_ms(1000); // 1 second Delay

PORTD.R1 = 0;  //Relay 1 turns OFF

PORTD.R2 = 0;  //Relay 2 turns OFF

PORTD.R3 = 0;  //Relay 3 turns OFF

PORTD.R4 = 0;  //Relay 4 turns OFF

PORTD.R5 = 0;  //Relay 5 turns OFF

PORTD.R6 = 0;  //Relay 6 turns OFF

PORTD.R7 = 0;  //Relay 7 turns OFF

Delay_ms(1000); //1 second Delay




Micro-controller send the signals to the relay , this signals are used to manipulation or perform the the action of relay (no and off ). This type of the operation are used for connecting or disconnect the load from the relay.

How to used relay is circuit?

if you understand the working of the relay. now i will tell you who to use relay in circuit with real time example. Assumed that we that four different power supplies like main power supply, generator power supply, solar power supply, and last invert-er power supply. we need if anyone of this can fail then automatically switch to any other power supply at the end on lack of power supply. in this project we are use 8051 family micro-controller to interrupt this. this micro-controller have four different type of switches for each power supply. Thus, the absence or failure of specific power source can be represented by pressing a particular switch or key.


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