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want to know a value of transistor

Discussion in 'General Electronics Discussion' started by jay_3189, Sep 24, 2013.

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  1. jay_3189


    Sep 19, 2013
    I want to control a 6 solenoid valves(Operates at 24DCV and 0.5A) with the use of 6 relays connected to an Arduino's 6 pins via 6 BJT(NPN) Transistor.

    The Arduino output pin is 5V and can source 40mA maximum.

    I would like to use a relay to switch the valve on and off.

    So, suggest me that which transistor is better to use here and value of resistor that I have to put between arduino and transistor.
    and DC voltage for relay to operate.
  2. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    Aug 27, 2013
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    Do you want to use the transistor to turn the valve on and off, or do you want to use a transistor to switch a relay to switch the valve?

    It's hard to point you to an appropriate transistor. To switch a relay, a BC548 or a 2N2222 might both be acceptable. What value base resistor? Possibly between 120 ohms and 1k depending on the load and the gain of the transistor. Also don't forget a diode across the load if it is inductive.

    The voltage for a relay is the rated voltage. If you've got a 5V supply, you would probably choose a 5V relay (a relay with a 5V coil, the contacts are rated for the maximum load they can switch)
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