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I'm hoping that someone will be able to help me. I'm looking to produce a power interrupt for testing. I'm looking to have 28V DC input flowing to an output which I can hook up to a load and then switch on and off using an Arduino. I'm thinking of using an NPN high current transistor, I have built the box and code which runs fine. The issue I am having is the pin output on pin 13 doesn't have enough current to switch the transistor, can anyone recommend a transistor that would be able to take the high current and be switched by the Arduino? If you would like a schematic to help you understand it I can provide one!

Thanks for reading, Lewis enter image description here

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  • Define "high current" - also how is the transistor wired?
    – Majenko ♦
    Oct 28 '16 at 21:29
  • Around 4A, see photo above for wiring of transistor
    – Lewis
    Oct 28 '16 at 22:12
  • For high side switch I would use PNP not NPN, and switch it using an NPN. To be more specific I would use a P-channel MOSFET and switch it using an N-channel MOSFET or NPN transistor. Google "MOSFET High Side Switch" and you will find many circuits.
    – Majenko ♦
    Oct 28 '16 at 22:13
  • Here is one example: electronics.stackexchange.com/questions/42030/…
    – Majenko ♦
    Oct 28 '16 at 22:15
  • Your current circuit will only apply around 4.3v to the load (assuming a 5v Arduino PSU). Can you switch the ground side rather than the 28v side? Circuitry will be far simpler.
    – kiwiron
    Oct 29 '16 at 7:14
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If you did manage to switch the transistor on, It would only output 4.3V, the rest would be dissipated in the transistor. If you managed to switch 4A this would dissipate 96W - and the transistor would melt.

A MOSFET would be a better option and could be easily switched by the Arduino. (I regularly switch 10A using a MOSFET and Arduino.)

This assumes you can put the MOSFET in the negative lead. If not you should use a P-Channel MOSFET, but you need a more complex circuit to drive it.

Have you considered using a relay module?

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  • Thanks for the answer! So I'd be able to use the MOSFET in this configuration and get the Arduino to switch it. I did look at using a relay but I didn't think that the Arduino would be able to switch it, this would be a simpler solution though, any relays that you could recommend ?
    – Lewis
    Oct 29 '16 at 15:50
  • Could I use this relay ? uk.rs-online.com/web/p/solid-state-relays/6996632
    – Lewis
    Oct 29 '16 at 16:01
  • Or this transistor? uk.rs-online.com/web/p/mosfet-transistors/5411720
    – Lewis
    Oct 29 '16 at 16:03
  • @Lewis, that SSR is rated at 4 A max. Look for an 8 to 10 A rated SSR or electromechanical relay to handle your 4 A load. The P mosfet is ok except its V_GS is limited to ±20 V, hence the gate must be above 8 V if the source or drain is at 28 V. Anyhow, to definitely turn the P mosfet off, you need to have the gate above 26 V, and to definitely turn it on, below 24 V (assuming V+ = 28 V). The Arduino's pin 13 is (Vcc+0.5 V) max, too low to drive the P mosfet's gate without using an intermediate N-fet or NPN or some diode network.
    – James Waldby - jwpat7
    Oct 29 '16 at 18:50
  • Thanks for all your help guys, my knowledge is still getting there, thanks for being patient. So this relay would be able to be controlled by the Arduino due to its low control voltage? @jwpat7
    – Lewis
    Oct 29 '16 at 19:54

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