I am just starting with Arduino and my first project consists in switching a LED light with Arduino.

I know a relay must be use to control AC high voltage device (i.e. 240V), however, as my LED seems to be powered by DC 7V voltage (7V - 0.43A written on the power supply which is integrated within the outlet, so I can only access the low voltage wire), I am wondering how to control such a device.

Do I still need a relay or the Arduino can handle this on its own?

  • Do you have the LED datasheet?
    – CrossRoads
    Sep 20, 2019 at 12:14
  • 1
    It's the Jansjo lamp from Ikea. I copy below what's written on the outlet: MODEL: KMV-070-030-GS-3, PRI: 220-240V~50/60Hz 0.05A, SEC: 7V_-- 0.43A 3W SELV
    – floflo29
    Sep 20, 2019 at 12:26
  • 1
    Look into MOSFET as a switch
    – chrisl
    Sep 20, 2019 at 12:40
  • You could probably run the Arduino from that same 7V supply. Negating the need for a separate adapter.
    – Gerben
    Sep 20, 2019 at 12:48
  • 1
    I have just found a relay (SRD-05VDC-SL-C) which can handle 10A/30V DC devices so I will start with this.
    – floflo29
    Sep 20, 2019 at 13:46

2 Answers 2


Use a power MOSFET transistor. This one from Sparkfun is an example: https://www.sparkfun.com/products/10213

If you use a relay you will probably need transistor and a separate power supply to drive the relay coils anyway, and will also need a flyback diode to protect the control circuit of the relay from the "back EMF" of the relay coils.

DO NOT try to drive relay coils directly from an Arduino digital pin. It will almost certainly fry the Arduino pin, and might destroy the entire Arduino.

A MOSFET transistor like the one I linked can be controlled directly from an Arduino GPIO line, and can switch DC loads of up to 60V and 30A.

  • Why would I need an extra power supply while the SRD-05VDC-SL-C relay can be driven with 5V, as output by the Arduino?
    – floflo29
    Sep 20, 2019 at 14:39
  • You can drive the control line of a relay like that with 5V, but it needs a 5V supply to drive the relay coils. It may be within the current limits of the Arudino's 5V line, but it might also cause the 5V line to bounce around as the relay energizes and de-energizes.
    – Duncan C
    Sep 20, 2019 at 15:19

No You can easily achieve this by using a NPN Transistor....


simulate this circuit – Schematic created using CircuitLab

You can use BC548 NPN transistor for this is..

But make sure that ground of both emitter and arduino should be same....

  • This transistor is a poor recommendation because the Collector Current — Continuous for the BC548 is only 100mA, yet the LED load could be up to 430mA.
    – VE7JRO
    Sep 21, 2019 at 20:00

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