Controller Output diode

[macbahi]

Hi!!

I read the recirculating diode across the relay coil is optional.

Please how can I know if my controller has some output with this option. 

What documentation please.

Thank you very much

with best regards

[acmall]

The diode being optional is mentioned on page 4 of this document, although it does not specify any particular controller type.

https://assets.danfoss.com/documents/53526/BC152886483485en-000501.pdf

[G30RG3]

As far as I read this, the "optional diode" is external.  There are internal diodes and they are always present.

[FluidPowerTom]

Some relays can be ordered with built-in internal diodes.  I would check the relay to see if it indicates a diode on the diagram on the relay.  Otherwise you'll want to verify with the part number.  Same goes for valve coils.

However, modern microcontrollers such as PLUS1 generally do not require you to use valve coils or relays that have the diode.  That's really only needed now when you're controlling the coil with a PLC or a mechanical switch.