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I'm trying to come up with a design for controlling a 24VAC water valve with an arduino.

My current design :

enter image description here

I want to use a BT1308W TRIAC controlled by an arduino pin to activate the vale, I'm also using a smbj48ca TVS diode to suppress spike generated by the solenoid when it's de-energized. I was using a similar design using a relay and the arduino was reboting randomly when the solenoid was closed, after adding the TVS diode it's not happening but is the correct use for this diode?

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after adding the TVS diode it's not happening but is the correct use for this diode?

You need a back-to-back (or bidirectional) TVS diode i.e. one rated for AC. At the moment if you apply AC to the terminals (VAC1 and 2) and energize the triac it will short out the AC supply on positive half cycles.

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  • \$\begingroup\$ You are right, the chosen smbj48ca is a bidirectional TVS diode, the symbol was wrong \$\endgroup\$
    – Marc
    Jul 13 '18 at 14:32
  • \$\begingroup\$ Then you should be good to go. \$\endgroup\$
    – Andy aka
    Jul 13 '18 at 14:40
  • \$\begingroup\$ Shouldn't pin 1 of the triac have a connection to the DC part of the circuit as well? \$\endgroup\$
    – Maple
    Jul 13 '18 at 21:45
  • \$\begingroup\$ @Maple yes it should and the OP should make that clear in his circuit hence how could he have proven the original design worked albeit causing EMI issues. Good spot. \$\endgroup\$
    – Andy aka
    Jul 14 '18 at 8:44
  • \$\begingroup\$ Why should the TRIAC have a connection to the DC part of the circuit? A triac is not just sold state relay? \$\endgroup\$
    – Marc
    Jul 20 '18 at 11:07

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