I use an AQH3213 Opto-Isolater. When I use 3.3V on the 'dc motor side', everything works fine and it 'turns off and on in an interval of 1 second'. But when I use 5V, it's always on....

Do you have any suggestions what I do wrong?

The simple test code is correct, because it works with 3.3V; so must be a curcuit problem I guess.


  • 1
    \$\begingroup\$ You have supplied what appears to be a Fritzing wiring diagram. We prefer schematic diagrams so we understand the schema, the part numbers and the pin functions. See if you can generate the schematic and upload that instead. Add links to datasheets for components used. \$\endgroup\$ – Transistor Nov 18 '18 at 15:27

The AQH3213 is an optically isolated triac device for controlling AC loads. It should not be used on DC loads because the triac, once properly "fired" will remain on all the time until power is removed.

The reason it "appears" to work correctly at the lower DC voltage is that the triac will act as an on-off device if the current taken by load is below the threshold-latching level. Once above the threshold level it will remain permanently activated unless power is removed or cycled (as when used in an AC application).

  • \$\begingroup\$ Ah thank you very much! Do you have an alternative for me for DC? Can't find fitting ICs adhoc... \$\endgroup\$ – dessi Nov 18 '18 at 20:02
  • \$\begingroup\$ Try looking for an optically driven MOSFET - I believe panasonic also make those and these have pretty low impedances and are more suitable. Else, decide that a regular opto driving a regular N channel MOSFET is a good ploy. Else, do you really need an optical isolation in your circuit. \$\endgroup\$ – Andy aka Nov 18 '18 at 21:16

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