In general, while designing electronics projects the loads are controlled switched ON or OFF using microcontroller block. But, for this purpose the circuit requires relays, acting as controlled switches for different circuits different types of relays are used. Depending on the signals received from the microcontroller or other control circuits the relay controls the load. The relay consists of continuous power supply and whenever it gets driven or gets control signal then the relay gets activated and loads can be turned ON or OFF. But, primarily we must know what is a relay driver circuit. The circuit used for driving a relay can be termed as a relay driver circuit and it can be designed using various integrated circuits.

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Pin Number. Pin Name. Input 1 to Input 7. Ground Reference Voltage 0V. Used as test pin or Voltage suppresser pin optional to use. Output 1 to Output 7. Respective outputs of seven input pins. So if you have anything that anything more than 5V 80mA to work, then this IC would be the right choice for you. It has seven Darlington Pairs inside, where each can drive loads up to 50V and mA. Adding to that we can a ground and Common pin. The ground pin, as usual is grounded and the usage of Common pin is optional.

It might be surprising to note that this IC does not have any Vcc power pin; this is because the power required for the transistors to work will be drawn from the input pin itself.

In the circuit consider the LED to be the loads and the logic pins blue colour as the pins connected to the Digital circuit or Microcontroller like Arduino. Notice that the Positive pin of the LED is connected to the positive load voltage and the negative pin is connected to the output pin of the IC. This is because when the input pin of the IC gets high the respective output pin will get connected to ground.

So when the negative terminal of the LED is grounded it completes the circuit and thus glows. The loads connected to the output pin can be maximum of 50C and mA each.

However you can run higher current loads buy combining two or more output pins to gather. The COM pin is connected to ground through a switch, this connection is optional. It can be used a test switch, meaning when this pin is grounded all the output pins will be grounded. Subscribe to stay updated with industry's latest Electronics components and news. Component Datasheet. ULN datasheet. Tags Motor Driver. Get Our Weekly Newsletter!


Relay Driver Circuit using IC ULN2003

It features common-cathode flyback diodes for switching inductive loads. A Darlington transistor also known as Darlington pair achieves very high current amplification by connecting two bipolar transistors in direct DC coupling so the current amplified by the first transistor is amplified further by the second one. The resultant current gain is the product of those of the two component transistors:. The seven Darlington pairs in ULN can operate independently except the common cathode diodes that connect to their respective collectors. The ULN is known for its high-current, high-voltage capacity. The drivers can be paralleled for even higher current output.



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