Hi everyone,

I need to control 3 stepper motors with s7-1214C DC/DC/DC . I used motion control instructions and the simulation worked good.

The drivers of the motors needs a 5V/8-15mA input signals. Is it a good solution to use resistors to reduce the PLC's 24V output voltage to 5V?

Hello!

    You could use step down converters (known also as Buck converters). Or some simple transistor logic (adequate transistor bipolar or FET) with base/gate voltage at 24V and Vce(collector emitter voltage) or Vds (drain source voltage) connected at a 5V power supply. I think you can find a lot of examples more detailed. It's the equivalent of using interface relays let's say.

    Buck converters are relatively cheap and easy to use (having just input and output connections) but they are switching power supplies and I'm not sure how it will affect the control of your stepper (I don't know if you want to make micro-stepping or just a simple control). I don't think they can be an option if you need fast switching. On the other hand transistors are faster (check the datasheet for switching frequency and choose the desired ones). 

    Sure, you can use voltage dividers (with resistors) but the output voltage will not be a stable 5 V as in theory. You will need to stabilize it with a voltage follower (an amplifier with very high input impedance, meaning it sucks ideally 0 A current ). Google it, voltage divider with voltage follower and you will get a lot of results.

      I would personally go with the divider and the follower or with transistors as are both fast,  reliable and relatively cheap. Just make some calculations on power dissipation on your resistors and choose adequate values (so they don't overheat).

Hope it helps, Mihai.

Hello Dhafar,

I wouldn't use resistors to reduce the voltage.

The best way is to use a solid state relay to trancduce the voltage.

e.g. from Phoenix Contact.

Solid-state relay module - PLC-OPT- 24DC/TTL - 2900363

You need then also a DC/DC converter from 24 to 5 V DC

eg. also from Phoenix Contact

DC/DC converters - MINI-PS- 12- 24DC/ 5-15DC/2 - 2320018

Then you should have no problems with your interface at the stepper.

regards
CaOd

Hi there,

I used 2 Res 2k7 paralel  for control my step driver(5V-8V). It worked fine.

Thanks