Does a PLC power supply need to be an isolated power supply?

[aneves]

Hi,

I am wondering what is to be gained in having an isolated 24vols to 5volts power supply to power the microcontroller in a PLC. Utilizing an isolated power supply forces all IO to use isolation to communicate with the microcontroller. Not using an isolated power supply to the microcontroller could save a lot of glue logic.

Any comments that might help me steer in the right direction.

Regards,

Alfredo

 

[Prototyp_V1.0]

It causes less strict requirement for earth fault protection (the wall plug included).

 

[aneves]

We manufacture a small PLC that is powered by 24 volts and we use a small isolated DC-DC converter to provide power to the microcontroller. Since now the microcontroller is in an isolated power domain we have to use digital isolators between the microcontroller IOs and the external IO (24 volts). This introduces extra cost (isolated DC-DC, digital isolators, etc). I have been wondering what problems we would have if we just used a simple 24V to 5V regulator and forgot all the isolation stuff, especially concerning noise and ground loop type problems. Would we have a less reliable system?