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I'm using relays that contain a flyback diode internally, so no need to add an external flyback diode. However, I want to provide a place on my PCB to possibly stuff a flyback diode in case I would have to replace the relay with a version that does not have the internal flyback diode.

But I was wondering: suppose the relay has a flyback diode built-in and I still do stuff the external flyback diode so the flyback diodes are put in parallel. Will that do any harm?

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  • \$\begingroup\$ You don't need to actually place the additional diode just because it is in the schematic -- just create an instruction for component placement to leave it out. \$\endgroup\$ – Simon Richter Jul 26 '15 at 12:32
  • \$\begingroup\$ First off, thanks to the guys that have improved the grammar of my question. It's obvious, English is not my native language... :-) \$\endgroup\$ – GeertVc Jul 27 '15 at 11:48
  • \$\begingroup\$ @SimonRichter: yes, that's indeed true and that will be the case too. The "external" diodes will not be stuffed when the relays have the internal flyback diodes. But the real question was if it would harm if you would end up with 2 diodes across the relay. \$\endgroup\$ – GeertVc Jul 27 '15 at 11:51
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Two flyback diodes in parallel do no harm at all. Depending on diode type, either of those diodes takes the load, or both share the load. Two flyback diodes in anti-parallel are a very bad idea, though, because one of those diodes will be conducting when you try to power the coil.

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  • \$\begingroup\$ I don't know what diodes are used internally inside the relays (relays are of type G2RS from Omron, more specific the type G2R-2-SNDI), but I've foreseen 1N4148 in the schematics to possibly put them, if needed. Of course, if I would stuff the external diode, it would be in parallel with the internal one, but in anti-parallel with the coil of the relay. \$\endgroup\$ – GeertVc Jul 27 '15 at 11:56

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