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High-Performance DIN Rail Power Supply

By Maurizio di Paolo Emilio for Mouser Electronics

A DIN rail is a metal strip of standard dimensions initially defined in the specifications published by the Deutsches Institut für Normung (DIN) in Germany and subsequently adopted as a European (EN) and international (ISO) standard. Essentially, it is a convenient and fast way to assemble any combination of electrical devices used in many areas of automation.

The ease of assembly and extensive standardization have made the DIN guide increasingly popular among control system manufacturers, thus directing the offer towards a wide choice of components. Among these is a growing range of AC-DC power supplies that are increasingly performing to meet the technical needs of designers.

Introduction

Over the years, industrial applications have employed a variety of control voltages, directing the choice towards DC solutions. DIN-Rail power supplies are generally used in control panels and electrical cabinets to provide standard values of 12V, 24V or 48V DC.

Applications include motors, valves, solenoids or non-linear loads. The shift to 24 V, for example, was motivated by security elements, strongly requested by the programmable logic controllers (PLC). In recent years, DIN rail power supplies have emerged as an ideal solution in this area, taking advantage of the modularity offered by the DIN rail construction.

In industrial applications, there are panels with a removable back plate that allows mounting a DIN rail, representing, in fact, a simple mounting platform for a variety of components, such as relays, terminal blocks, and power supplies. The DIN rail power supply units are easy to use and, above all, easily replaceable in case of problems. In this way, productivity downtime is significantly reduced.

In production, a power loss at the wrong time can result in reduced productivity with costly losses. Many of the features associated with DIN rail supplies are dictated by the quality and reliability of the power supply (Figure 1).

Figure 1: DIN Rail Layout (Source: Recom)

Selecting a DIN rail power supply

The DIN rail is available in various base metals, the most common being steel, aluminum, stainless steel, and copper. Galvanized steel is the most common choice. When selecting a DIN rail with a specific metal composition, you must take several factors into consideration, including electrical cabinet, environment (typically already determined with the selection of the container material), products to be assembled and short-circuit requirements for grounding. The use of dissimilar metals (aluminum casing and steel DIN rail) creates what is called a galvanic cell, which can lead to structural corrosion. Galvanic corrosion causes deterioration of aluminum housing and can cause electrical grounding problems.

In the use of power supplies, the first step is to ensure that the power supply and DIN rails have compatible styles and sizes. Designers benefit from DIN-rail feeders with a slim profile. It is important to choose power supplies that do not require fans or forced air cooling, which would be difficult to install as well as introducing another point of potential failure. It is equally important to consider the operating temperature range to avoid overheating, such as to induce malfunctions or breakdowns. Power supplies must be designed to operate in environments with temperatures above +50 °C.

In some applications, such as test or development systems, the convenience and versatility of an adjustable DC voltage output become essential in many designs. However, many other applications depend on a DC power supply that remains fixed to ensure regular operation. Some LED lighting applications with LED strings in series, work optimally by a constant current source rather than constant voltage. The AC input lines must be kept separate from the DC output pair to minimize noise induction in the DC wiring. In some noise-sensitive applications, it may be advantageous to specify a power supply unit with a fixed switching frequency, for example of 100 kHz. This allows projects to avoid interference with system clock frequencies.

The DIN rail power supply may be subject to electrical errors from the mains or the load. For this reason, it is necessary to implement security functions in the event of an error. Short-circuit, over-voltage, over-temperature, and overload protection are essential for reliable operation. An internal failure in the power supply can cause a change in the output voltage and possibly damage the load. This fault could be due to a short circuit in the wiring, the failure of a passive component or an active device such as a MOSFET. OVP (Overvoltage Protection) is a function that monitors the output concerning an internal reference and short circuits that are emitted if the voltage exceeds the threshold. An example of OVP circuit is called "crowbar" (Figure 2).

Figure 2: Crowbar circuit with overvoltage protection set at 9.1 V (Source: Author)

Adjustments made by digital control have proven to be the most reliable method for voltage adjustments. Designers can take advantage of the features with which digital control allows system optimization. The PMBus defines an open standard digital power management protocol that facilitates communication with a power converter or other device.

Power Supplies

DRL100-24-1 / C2 is a DIN Rail power supply with 88W power and 24V output voltage realized by TDK-Lambda. The power supply meets the requirements of class 2 of the NEC (National Electric Code) of the United States in accordance with UL310, thus making them usable in building automation systems and safety systems that require restrictions on the amount of available output current, in order to avoid damage to the wiring even in fault conditions.

All DRL models work with a range of input voltages ranging from 85 to 264VAC and can withstand a peak of 300VAC for five seconds. The no-load energy consumption is less than 0.5W, and the efficiency is 90% at full load with a 230VAC input. The DRL series has a Class II construction (double insulation) and 3,000VAC input-to-output isolation. All models are convection-cooled and classified for operation at ambient temperatures from -20 to + 71 °C (Figure 3).

Figure 3: DRL100 TDK-Lambda power supply (Source: TDK-Lambda)

Technological advances require more automation and control, minimizing the size of the control system without compromising reliability. XP Power offers the new DSR range of DIN rail AC-DC power supplies suitable for industrial systems (ICE) and IT equipment. These versatile power supplies provide reliable power with a peak load capacity of 150% with an ultra-slim and compact design of only 32 mm for 75W and 120W models, and 45mm for 240W models. These models can be used in building control applications (Figure 4).

Figure 4: DIN rail power supply by XP Power (Source: XP Power)

The RECOM RACG100 and RACG150 power supplies offer a compact structure with 100W or 150W continuous power without cooling, available for single-phase or 2-phase and three-phase power supply environments. The RACG100 series modules provide 100W output continuously and are provided with protection measures against short-circuit and overload. The 150W continuous output modules of the RACG150 series also have additional protection measures against overvoltage and overheating (Figure 5).

Figure 5: DIN rail power supply by Recom (Source: Recom)

Traco Power offers its product line of the TIB family of DIN rail power supplies covering 80 ~ 480 watts of continuous power with high efficiency of 90% to 94% and a slim design. The TIB-EX product line offers ATEX certification and combines the most efficient circuit topology with an optimized cost/performance ratio for industrial applications (Figure 6). The TIB 240-EX of 240 W is suitable for harsh environments and dangerous locations, the reduced heat dissipation of the product allows a full load operating temperature range of -40 °C to + 60 °C (operation up to + 70 °C with 20% reduction).

Figure 6: TIB-EX from Traco Power (Source: Traco Power)

CUI has developed a series of DIN rail feeders with 3 to 240 W. The models are characterized by high efficiency up to 92%, a universal input voltage range and output voltages from 3.3 to 48 Vdc (Figure 7). Other features include active power factor correction and 150% peak load capacity, depending on the model. An adequate power factor in the AC / DC power supplies serves to increase efficiency. The problem is solely because the alternating voltage at the input must be rectified and leveled.

The solution consists of adopting a circuit that allows reducing the harmonics to a minimum. Instead of connecting the capacitor directly to the rectifier, a pulse-width modulator is connected in an intermediate position. The modulator generates several current pulses synchronized with the input voltage and adjusts the charging current so that it approaches the sinusoidal waveform. A suitable PFC circuit can bring the power factor to "0.95", as a minimum, and at the same time reduce the harmonics to a minimum.

Figure 7: CUI DIN rail power supply (Source: CUI)

Conclusion

Power Supply is a vital aspect of production and automation. Companies lose billions of dollars due to power outages. Enabling company and factory structures with robust, efficient, and easy-to-manage solutions supported by a digital control, allows safeguarding the production process. Today's industrial power systems are often modular, allowing scalable development for smart-facility operations.

Maurizio Di Paolo Emilio holds a Ph.D. in Physics and is a telecommunication engineer and journalist. He has worked on various international projects in the field of gravitational wave research. Working as a software/hardware developer in the data acquisition system, he participated as the designer of the thermal compensation system (TCS) for the optical system used in the Virgo/Ligo Experiment (an experiment for detection of the gravitational wave that achieved the 2017 Nobel Prize in Physics). Actually, he collaborates with University of L'Aquila and INFN to design devices for radiobiological and microscopy applications and new data acquisition and control systems for space applications. Moreover he works in the software/hardware engineering field as editor and technical writer. He is the author of several books published by Springer, as well as numerous scientific and technical publications on electronics design.