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My old 1-channel relay driver circuit works (lemmy.ml)
submitted 3 days ago by to c/askelectronics@discuss.tchncs.de
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so i have shared the it's schematic and board design with the eevblog.com community and they said "that this module will not work and the relay contacts and board tracks can't handle high current" I improved and made the board anyway and tested it with inductive and resistive loads and it works without a problem huh

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[–] 8 points 3 days ago* (4 children)

(squints)

Looks fine up to about 6 amps I reckon, judging from the size of that relay. Not a huge high power coil on that so a simple npn transistor switching the coil to ground would be fine. Got a diode across the coil to catch the back-EMF, looks like all the basics are covered .Would only bother adding extra solder to the tracks for the relay contacts if I was doing it but that's neither here nor there.

Dunno what those eevblog folks are on about 🤷

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  • [–] [S] 1 point 3 days ago* (2 children)

    I already added solder to the relay contact tracks to increase it's thickness

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  • [–] 2 points 2 days ago (1 child)

    Looks fine. Mayyyyyyybe the 1k resistor is a little high, depends on the gain of the transistor. 5 volts would feed it with 5mA on its base, which might not be enough to fully switch it on. However, as it's only driving the relatively high resistance coil in the relay it's nothing to worry about if it works.

    If you were driving it with 3.3V, I'd probably swap that transistor out for a Darlington pair to make sure the gain is high enough to fully switch on at that kind of drive voltage. You can get Darlington pairs in the same pinout as normal transistors so it would be a straight swap on the board.

    Having said all that, if it's working in your application, leave it. 🤷

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