What Is a DIN Rail Power Supply?

Almost every control cabinet runs its electronics from one low-voltage DC supply. PLCs, sensors, relays, I/O modules, network switches and DIN rail PCs all expect a steady 24 V DC, but the cabinet is fed with mains AC. The DIN rail power supply sits between the two. It clips onto the same TS35 top-hat rail as the equipment it feeds, takes the incoming AC and delivers a regulated DC output on screw or push-in terminals.

Because everything shares that one supply, it is one of the most important parts in the cabinet. If it sags, overheats or fails, every device on the rail goes with it, which is why industrial supplies are built for continuous duty, wide temperatures and electrically noisy plant.

Nearly all DIN rail power supplies are switch-mode designs. The incoming AC is rectified to high-voltage DC, switched at high frequency through a small transformer and rectified again into the output voltage, with a feedback loop holding it steady as the load changes. The transformer gives galvanic isolation between mains and output, so the output is a safety extra-low voltage below 60 V DC that installers can wire like control circuits.

Models above about 75 W usually add active power factor correction, so they draw a cleaner current from the mains and meet the harmonic limits in EN 61000-3-2. Modern 24 V supplies often reach 90% efficiency or more, which matters because every watt lost becomes heat inside a closed cabinet.

The same rail-mounted format covers several jobs:

Datasheets for DIN rail power supplies follow a similar pattern. These are the figures that decide whether a supply suits the cabinet:

Class 2 supplies limit their output to 100 VA, which simplifies wiring rules in the US but caps the load. Ask the manufacturer for the approvals that apply to your market and installation.

A desktop or server computer power supply sits inside the case and produces several rails, mainly 12 V, 5 V and 3.3 V, for the motherboard and drives. A DIN rail power supply produces one output for the whole cabinet. A DIN rail PC takes that single 24 V feed through a terminal block and converts it internally, usually through a wide input such as 9 to 36 V that tolerates dips and surges on the line.

That is also why cabinets standardize on 24 V rather than 12 V: for the same power it draws half the current, so cables run cooler and voltage drop is lower. Our FAQ on 12V vs 24V covers the difference in more detail.

A computer is less forgiving of a supply problem than a relay. A brief dip that a contactor ignores can reset a PC mid-write, so critical cabinets often add a second supply with a redundancy module, use a PC with dual DC inputs, or fit a DC UPS on the computer’s branch. Supercapacitor modules suit sealed cabinets because they need no battery replacement; our page on supercapacitors explains why. Our industrial UPS range includes a supercapacitor DIN rail UPS designed to keep a computer running through supply loss and shut it down cleanly, and the comparison of supercapacitor vs battery UPS sets out the ride-through each gives.

Not every installation starts from mains. On trains the electronics run from the vehicle battery at 24 to 110 V DC, so railway computers take isolated DC inputs directly rather than relying on a cabinet AC supply.

When we configure a DIN rail PC for a project, we check its input range and power figures against the cabinet supply as part of the build.