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Let's say I'm trying to control a relay using a microcontroller. This relay requires a 500mA input current which is too large for a microcontroller to drive.

It seems like I could use either a n-MOSFET transistor OR I could use an IC such as a solid state relay control a 500mA input current. But I'm curious, are there pros and cons between each approach? What approach is more common in production circuits?

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  • \$\begingroup\$ Why would you use a 100mA solid state relay if you need to control 500mA? Also why would you use a complex more expensive component for a job that can be done with a cheap simple component? More common is the one that makes most sense in any given situation. \$\endgroup\$
    – Justme
    Jan 16, 2022 at 15:58
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    \$\begingroup\$ What is the load that the relay is controlling? AC? DC? Current? \$\endgroup\$
    – Supa Nova
    Jan 16, 2022 at 16:08
  • \$\begingroup\$ @Justme Sorry that was a typo, just fixed it. Looking at prices on digikey, solid-state relays can be similar to prices to MOSFETs (at least for a small scale purchase). I suppose that idea is that solid state board level relays are pretty easy to understand. \$\endgroup\$
    – Izzo
    Jan 16, 2022 at 16:12
  • \$\begingroup\$ @SupaNova The load relay would be a 12V, 500mA input and 120VAC 10A output. \$\endgroup\$
    – Izzo
    Jan 16, 2022 at 16:12
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    \$\begingroup\$ I’d normally expect to see a mosfet or bjt. \$\endgroup\$
    – Kartman
    Jan 16, 2022 at 16:18

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If you were controlling a DC load and the Load and Arduino can share a common ground reference, then a MOSFET might be practical. However, in your case you want to control 120VAC. That means the AC load needs to be isolated from the DC control signals. You could use a MOSFET and separate power supply to control the existing mechanical relay, or you can purchase a SS relay that can be controlled directly from the Arduino's digital pins. SS relays like that do exist, but they tend to be expensive. Search the usual electronics suppliers. Automation Direct might have better prices. Be very careful to choose one that can be controlled directly by your Arduino.

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