Glossary · Electrical engineering and control panels
Power supply unit
Also known as: PSU, Switched-mode power supply (SMPS), DC power supply
German: Netzteil
In electrical engineering, a power supply unit is a device that converts electrical energy from one form to another, typically from AC mains voltage to a regulated DC voltage such as 24 V DC, for supplying controllers, sensors and other loads.
- Control panels
In one sentence
A power supply unit converts mains voltage into a regulated DC voltage, such as 24 V DC, for controllers, sensors and loads.
Example
A 24 V DC, 20 A switched-mode power supply unit on the DIN rail feeds the PLC and field devices, with a buffer module bridging short mains interruptions.
How it applies
- Engineering: Size the unit for continuous load plus inrush currents, and check derating at high ambient temperature. Features to consider are power boost for tripping breakers, redundancy modules, DC-OK signals and hold-up time. The output circuit design (for example PELV) must match the protective concept.
- Operation: A DC-OK signal wired to the controller lets the machine report supply problems before devices fail.
- Documentation: List type, rating and output settings in the parts list; if the output voltage is adjustable, document the set value. Maintenance manuals should describe replacement and the check of the output voltage.
Power supply unit vs. UPS
A power supply unit converts voltage but stops when mains fails, apart from a short hold-up time. An Uninterruptible power supply (UPS) contains energy storage to keep loads running during outages.