The Whats and Hows of DIN Rail Power Supplies

Din rail supplies

The adapter feeding direct current from the mains supply to your laptop is an example of a switched-mode power supply (SMPS). This is a power supply unit (PSU) that uses some kinds of switching devices to convert AC output into usable DC. It is the type of power supply used for many electronic devices because of its efficiency, high power density, relative low cost and compact dimensions. 

SMPS have also become the standardised form of power supply in many industrial and commercial applications. Here they also benefit from their compact footprint allowing them to be set along DIN rails. A DIN rail PSU is extensively used in controlling and monitoring power supply in industrial automation processes, in mechanical engineering, the process industry, in logistics, the automotive industry and more. It shields industrial equipment and circuitry from overcurrent, overloads and short-circuiting as well as inverse and reverse voltage. High heat levels and power loss are also brought to a minimum.  

What is a DIN Rail Power Supply?  

A DIN rail PSU converts input AC to a higher frequency using rectifier and inverter electronics and then quickly switches power between the load and onboard inductors and capacitors. The voltage is converted by a transformer, which because of the high frequencies involved can assume a more compact size. In short, a DIN rail PSU converts an unstabilised input voltage into a regulated output voltage. It gets its name from the 35mm tall metallic DIN mounting found in the cabinets, distribution boxes and machines in a myriad of industrial applications. As a standardised mount, DIN rails are also used to house other electrical components, like circuit breakers, relays, motor controllers and terminal blocks. The system allows for easy and quick installation of componentry, using less space and simplified wiring in a centralised unit.  


Parts of a DIN Rail SMPS 

A typical DIN rail switched-mode power supply consists of several parts. An input filter, consisting of a combination of inductors and capacitors, removes any damaging voltage inconsistencies from the mains supply, as well as electromagnetic interference. The filtered AC input then passes through a bridge rectifier, which converts it to DC. Power factor correction (PFC) is used to reduce power losses, together with harmonics that can result in interference to other equipment connected to the same power source. Next, the switcher uses power transistors to switch a DC voltage at very high frequencies and the transformer converts the power supply from one voltage to another, with the process being controlled by an SMPS controller. Output filtering is done with capacitors and inductors.  

Benefits of a DIN Rail PSU 

DIN rail PSUs offer a higher level of conversion efficiency than other types of power supplies, notably linear and unswitched PSUs. They are easy to install along a DIN rail, needing no tools. Din rails PSUs also allow for easy wiring between the mains and the load via screw or spring clamp terminals.  

Another area where they excel is reliability. Most types used today have no mechanical parts, like fans involved in reducing heat, but instead deploy convection cooling. This minimises the risk of premature failure typical of mechanical componentry. In addition, safety circuitry protects internal components and connected equipment from damage.  

Then, there’s the compact size. This means stacking in smaller spaces to reduce overall system size. And lastly, universality with UPS power supplies being able to take various mains voltage, meaning the same unit can be used in grids across the globe. 

Factors to Consider when Buying and Installing a DIN PSU 


Power Supply Phase and Type of Input/Output 

Power supplies can be configured for single or three-phase supplies. Also, the type of input, AC or DC, and the output voltage, current and number of ports vary among different DIN rail PSU models. A single-phase power supply will have one input port for the live, neutral and earth wires. By comparison, a three-phase unit has three live ports, along with the neutral and earth. In addition, DC to DC converters can deliver various vDC outputs, ranging from 5 to 48 vDC. Currents also vary. Units with multiple output ports allow more than one dc-power device to be connected at the same time. 

Working Environment 

Temperature extremes and humidity levels can affect the efficiency of the power supply. Optimal ambient operating temperatures range between -25°c and +70°C. Also, lower levels of dust and vibration will mean a more efficient power supply. 


DIN rail PSUs are small, though some are smaller than others. Dimensions matter in large-scale operations, and selecting a unit in the correct dimensions as well as placement need to be taken into account.  

Efficiency and Lifetime 


Many DIN rail PSUs come in at 90-95 percent efficiency. Efficiency affects overall lifetime of the units and are affected by the working environment as well as heat levels generated in power supply conversion. An efficient unit will stay cool even when at full load.  

Standards and Certifications 

Always use DIN power supplies that have been tested and certified for the relevant application.