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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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  • Hi Merrick,

     

    I see you've copied a diagram from some website, but if that website didn't help explain or provide you with some confidence that the circuit was a suitable way of doing things, then it isn't a very good website to use for learning. You're better off grabbing a couple of beginner books, because they will cover this. Please see the information (in the body of the post, and in the comments section) here: I Want to Do Electronics!  Where do I start?

     

    It will be far quicker than trying to explain the behaviour of a NPN transistor, or a MOSFET, or a power resistor. Also, you should just try it (with low voltage) to experiment with it. If you want to see example circuits connected to GPIO, check out this link, it has a relay circuit too, and you'll see it is similar to what you've shown in the diagram.

    Raspberry Pi GPIO Explained

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  • Hi Merrick,

     

    I see you've copied a diagram from some website, but if that website didn't help explain or provide you with some confidence that the circuit was a suitable way of doing things, then it isn't a very good website to use for learning. You're better off grabbing a couple of beginner books, because they will cover this. Please see the information (in the body of the post, and in the comments section) here: I Want to Do Electronics!  Where do I start?

     

    It will be far quicker than trying to explain the behaviour of a NPN transistor, or a MOSFET, or a power resistor. Also, you should just try it (with low voltage) to experiment with it. If you want to see example circuits connected to GPIO, check out this link, it has a relay circuit too, and you'll see it is similar to what you've shown in the diagram.

    Raspberry Pi GPIO Explained

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