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I am using the below AC electromagnet to switch on/off a pneumatic system. (It is a pneumatic actuator. I think that is what it is called.)

The issue is, when I turn off (disconnect the switch) the coil generates a big negative voltage spike in my nearby PCB electronics and cables and messes up with my LCD screen and buttons (they get randomly pushed.)

Except for having to remake my PCB to be EMI-proofed, which is costly, can I use two Zener diodes back to back to create a 'fly-back diode' for the AC current? What other techniques there are?

Pneumatic actuator: The pneumatic actuator

The initial schematic:

schematic

simulate this circuit – Schematic created using CircuitLab

The one I am thinking of implementing:

schematic

simulate this circuit

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    \$\begingroup\$ Does this answer your question, perhaps? electronics.stackexchange.com/questions/171974/… \$\endgroup\$ – tanto Feb 11 at 22:00
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    \$\begingroup\$ a 400V sidac might be a better part for this application, or a small triac used as a sidac. \$\endgroup\$ – Jasen Feb 11 at 22:38
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    \$\begingroup\$ Your idea should work. 10A is a little overkill though. The valve says it's 10VA, so closer to 43mA. 1A or 2A diodes should work just fine. Also, you could chose a little lower voltage, maybe 350V, but that's not critical. \$\endgroup\$ – Aaron Feb 12 at 0:03
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    \$\begingroup\$ Looks like there’s a varistor there already. \$\endgroup\$ – Kartman Feb 12 at 1:09
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    \$\begingroup\$ @andrewmorton I got your point. Thanks for link. \$\endgroup\$ – user263983 Feb 17 at 12:05
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The flyback diodes were too expensive to buy, and we had no other varistors here for these voltages required. So we ended up changing the AC valve with a DC one of 24V.

But the alternatives of using a higher value varistor or back to back zener diodes, would also work.

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