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What is the best way to drive a relay?

swankybarbecue4

I want to use raspberry pi GPIO pins to control a few relays. I was planning to use a 3904 NPN transistor with a 330 ohm resistor on the base of the 3904 and a fly back diode across the coil of the relay (just as shown in the attached image). My questions are: would it be more efficient power consumption wise to drive the relay with an MOSFET or power resister? And will I destroy an NPN 3904 transistor over time if I use it in the circuit shown below? I see people using BC transistors (like a BC 141) instead of an NPN transistor like I described. image

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  • Your circuit should work fine depending on the coil impedance.

    I prefer a MOSFET because they are more efficient - no wasted base current, less load on the digital output, and more voltage across the relay.

    You just need to pick one with enough current capacity and a low enough turn on voltage.

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  • Your circuit should work fine depending on the coil impedance.

    I prefer a MOSFET because they are more efficient - no wasted base current, less load on the digital output, and more voltage across the relay.

    You just need to pick one with enough current capacity and a low enough turn on voltage.

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