Switching LEDs using ULN2803

David's picture

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Joined: Aug 08, 2020

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Switching LEDs using ULN2803
August 8, 2020 - 6:32pm

Hi new member here and hoping somone can answer what is probably a simple question to the experienced. I am making a model project and am lightng LEDs using a nano and a ULN2803 transistor array. I am using high brightness LEDs and want to drive them at around 25mA.

At 5v and using a 68ohm resistor i get 26mA running the LED direct. Now when I connect into the circuit with the nano and ULN2803 the LED is only getting 17mA. I assume this is due to the internal resistance of the ULN chip. Will I run into any problems if I just reduce the resistor so I achieve my 25mA.

Many thanks for any advice

Dave

Sourav Gupta's picture

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Joined: Feb 12, 2018

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The Darlington pairs are rated for 500mA 50V output. It wouldn't be a problem but the 2803 will heat up.

David's picture

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Joined: Aug 08, 2020

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Thanks

I will be running 3 LEDs in parralel with their own resistor from each output pin across all 8 outputs so 600mA total. I have read that a MOSFET would be more efficient in this application, what would be a suitable logic level MOSFET array that would drop right in instead of the 2803?

Sourav Gupta's picture

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Joined: Feb 12, 2018

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It will not cause problem because each individual Darlington pairs have maximum current of 500mA, 50 V.  TPL7407L is a 7-channel Mosfet array equivalent to it, speced with 600mA drain current, 40V.