Power supply via USB or 2 position plug


Power supply to the ACE PLC is provided via a two position pluggable connector, included with the ACE unit.

All ACEs shipped today are compatible from 5 to 24 VDC.

The ACE can be powered on via:

  • its USB port (except ACEs with analog outputs)
  • or its 2 position pluggable connector

You can plug both (USB and Power plug) at the same time.

PLCs are reverse voltage protected.
Input power goes through a switching regulator to regulate to 5 VDC.  Alternately, 5V from the USB passed through a diode to the same point.  The 5V is then regulated to 3.3 V, which is what the internal circuitry runs on.

All digitals inputs/outputs are compatible from 5 to 28 VDC whatever the ACE

5 to 24 VDC version

ACE with a blue ace of spade close to
the product reference written in blue

5 VDC version

ACE with the product reference
written in black


To connect power, insert the +VDC and the ground connections from a power supply into the plug, as shown in the figure below. When plugged into the PLC’s power connector socket, the +VDC connection is to the right, closest to the PLC corner.


TTL level

If the ACE PLC is connected to USB, it is advisable to supply the PLC with an external 5V power supply at the same time, otherwise the PLC is supplied with 3.8V (there are 2 diodes in series) and there may be detection problems for the 0-5V TTL levels.

Possible problems

The pre-regulator in the PLC regulates a voltage (from 5.1 to 28 VDC) to 5V. It is then down regulated to 3.3V, which all circuits use. The USB power supply goes through a diode, to the same 3.3V regulator.

Program stop/loss or damaged PLC: A high voltage spike can occur on the power supply input, or in the digital output circuit. When you start a program in Run mode, there is a bit set in the EEPROM that tells the PLC to restart after a power failure. This bit could have been cleared for various reasons.

Also remember that if you leave the ACE running in debug mode, after powering down, it will not restart.

Read more about 24V power supply and electrical noise

Extract from the documentation “System Design for Control of Electrical Noise” from Allen-Bradley