Looking for the Right AC/DC Supply in High-Reliable Industrial Applications
The electronic devices within factory automation applications are often subject to some of the most stringent standards in order to comply with various functional safety requirements. To ensure the safety of the operator and the surrounding environment, as well as the smooth operations of the facility, all devices within these systems are scrutinized. Many off-the-shelf AC/DC power supplies may not be sufficient as they may not have adequate protection from overvoltage transients, noise from external systems, and other protection mechanisms in place to ensure the reliable operation of the component. Power supplies within these applications must also be rugged to withstand common environmental and mechanical stressors such as vibration and shock. The ambient temperature could negatively impact the device’s performance, so steps must also be taken to prevent premature failures due to high/low temperatures and variable relative humidity. This article dives into the various factors to consider when selecting a power supply for high-reliable industrial and robotics applications and how P-Duke’s TBF500 500W full brick AC/DC power supplies are designed for these rugged environments.
AC/DC power supplies in industrial automation
There are many examples where a regulated DC supply is required from an AC input in industrial automation. Motor drives and other motor control systems will require these power supplies to turn on DC motors and, in some cases, control their speed. For example, in an industrial pump, the liquid is processed at variable speeds. At startup, a motor causes a large inrush current that can cause voltage dips in the supply line and damage other equipment or may force a reset of the system. These drives often use contactors and motor starting units to isolate and protect other electronics. More often than not, motor starting units, contactors, relays, and variable speed drives require a regulated 24 VDC voltage. Programmable logic controllers (PLCs), human-machine interfaces (HMIs), sensors (e.g., pressure, liquid level, temperature/ humidity), and actuators (e.g., valve terminals) also often convert the line voltage to 24 VDC to operate. These systems are scattered throughout industrial automation systems universally, making the parts they comprise (i.e., the AC/DC power supply) important to maintain operations. For these systems to operate smoothly, safely, and have a long field life, the power supplies must also be of high quality in terms of standards compliance, ruggedization, and internal safety features.
The P-DUKE TBF500 is a 500W full-encapsulated, full-brick package power supply mounted on the system chassis to dissipate heat for high-temperature applications. With a universal input range from 85 to 264 VAC, the TBF500 can take standard AC supplies (120 VAC, 230 VAC, or 240 VAC) and output 12, 15, 24, 28, 48, and 54 DC voltages to supply. With its various features, the TBF500 is well-suited for some of the use cases cited earlier.
Overvoltage category (OVC) III
Factory and building automation applications increasingly call for overvoltage category III (OVC III) levels. These categories are listed in a number of international safety standards. The one most often cited is the IEC 60664-1 standard that focuses on insulation requirements (i.e., creepage and clearance distances) for low-voltage systems. Others include IEC/EN/UL 62368-1 information technology safety standard, IEC/UL 61010-1 for the safety of equipment used in test and measurement (T&M) environments, UL 508 for the safety of industrial control equipment, and more (e.g., IEC 60364 and EN 50110).
The OVC level will vary based on where a specific piece of electrical equipment is installed. Depending on its location, it may have to withstand different levels of transient overvoltages from factors such as lightning or unstable grid variations. Table 1 and Table 2 list the transient voltages tolerated for different OVC levels at varying nominal voltages, as well as the location of equipment with various OVC ratings.
As shown in Table 2, distribution-level circuits and industrial equipment with a permanent connection to the fixed installation, such as motor control systems, distribution panels, and load centers, can be used safely with an OVC III level. The P-DUKE TBF500 is rated at OVC III and protects both equipment and operators. Note only a few additional components are needed to comply with the EN/IEC 50032, Class B, inrush current limiter function, and OVC III (overvoltage category) (Figure 1)
This supply can be used in, for example, the digital output modules within safety PLCs that take the relatively weak signals of a logical processing of an automation program and convert them into stronger signals with current and voltage levels capable of driving output devices (e.g., solenoids in valves, stepper motors, relays, indicating lights, coils, alarms, mechanical brakes, etc.). These often use an external power source as the digital output modules contain control devices (e.g., optocouplers, diodes, triacs, etc.) with larger power/current levels (relative to the digital input module/internal microprocessor) as shown in Figure 2.
Extending beyond this, any safety instrument systems (SISs) in industrial facilities must often guarantee a safety instrument level (SIL). To do this, every component within the system must be assessed for its reliability or probability of failure (PFD). So, both mechanical and electrical components must be analyzed for potential issues that can occur during their field life. For electrical equipment, this often boils down to system redundancies, various standards compliance such as the level of insulation coordination (i.e., OVC category), and the over-dimensioning of electrical devices such that the rated current/voltage is much higher than the operating current/voltage.
The IEC/UL/EN 62368-1 Safety Approval
The TBF00 also has the IEC/UL/EN 62368-1 safety approval. The 62368-1 safety standard can be applied to both consumer and enterprise technology in audio/video (A/V) and information communication technology (ICT) that is based on the hazard-based safety engineering (HBSE) approach. This approach considers the type of energy source of the equipment (e.g., Class 1, 2, or 3), determines the appropriate safeguards to prevent damage to personnel or property, and tests the effectiveness of the safeguards. Internal and external power supplies within industrial equipment may have to comply with these regulations, especially if the system they use falls under A/V or IT equipment (e.g., webcam, routers, microphones, sound cards, video capture cards, etc.).
Electromagnetic compliance (EMC)
There are many sources of noise within industrial facilities. UPS equipment, for example, can generate non-sinusoidal waveforms that carry harmonics and noise that nearby equipment can conduct. This can (and often does) interfere with the operation of the electronic equipment. Large rotating components can generate power supply fluctuations and cause unwanted EMI. More and more power supplies are incorporating fast-switching devices such as SiC power MOSFETs that can generate EMI if not properly filtered out. It is critical that EMI is dealt with at the device level to maintain plant operation. Power supplies must comply with EMC standards. The TBF500 is tested in accordance with various conditions within the EN/IEC 55032 or EN 61000 standards, as shown in Table 3. Note the EMI of the TBF500 can be additionally reduced when connecting four screw bolts to the shield plane.
Outside of compliance with various safety standards, the power supply itself should have a number of protection features in place to prevent faults. The TBF500 includes over-current protection, short-circuit protection (SCP), over temperature protection (OTP), and output overvoltage protection. For OCP, the TBF500 will shut down when the current exceeds the power supply’s specified limit. After a short period of time, the power supply will restart and, if the overcurrent is still present, will shut down once more―hence the term “hiccup mode.” The SCP uses a similar automatic recovery mode where the power supply will shut down in the presence of a short circuit and restart intermittently until the short circuit is resolved. An internal thermistor will trigger the OTP feature and cause the power supply to enter hiccup mode until the temperature issue is resolved. The output overvoltage protection uses latch mode, where a manual restart is required after an overvoltage is detected. All of these features safeguard the device against power supply variations and failures.
An inrush current limiter function can also be implemented with additional equipment to protect the power supply from the inrush current that often occurs when starting a motor (Refer to Figure 1). This is particularly useful in industrial settings with components that exhibit a low impedance upon turn-on, causing a surge in current, this is also known as inrush current. This inrush current can be seen within circuits containing capacitors rapidly discharging or, more commonly, with motors that at startup that speed up to meet their specified horsepower at startup. Motors are used in so many plant processes and systems (e.g., pulleys, conveyors, belts, robotics, etc.), so it is often important to ensure a connected circuit is not damaged from the potential inrush current.
Environmental and mechanical ruggedization
Safety and regulatory compliance are critical in industrial automation applications that call for high reliability. Another layer of consideration must also be put into the environmental and mechanical resistance that a power supply exhibits. There are instances where the device may be exposed to consistent vibrations and even mechanical shock. Environmental stressors such as exposure to high (and low) temperatures, temperature cycling, and exposure to high relative humidities might also have to be taken into consideration. For more niche use cases, there is also the potential exposure to harsh chemicals in industrial facilities (e.g., salt atmosphere, explosive atmosphere, hydraulic fluid, engine oil, etc.). There are instances where devices will require protection from these potential outcomes.
One of the classic standards that deal with testing against various environmental stressors is the MIL-STD-810F US military standard (Table 4). The TBF500 is tested in accordance with the MIL-STD-810F standard for operating altitude (5000m or 16,400’), thermal shock, mechanical shock, and vibration. It can also operate at a relative humidity as high as 95%.
This level of ruggedization requires a special design and unique construction. In order to qualify to perform in factories or facilities that operate at high altitudes, for instance, larger clearance and creepage distances are required to limit the risk of high voltage arcing. This is more likely to occur at higher altitudes since the atmosphere is thinner and is, therefore, a less effective insulator. The air is also less effective at removing heat from the PCB, potentially causing thermal management issues. This must all be considered when designing a power supply for higher altitudes.
Thermal management and package size
Both thermal management and package size are often linked when it comes to power supplies. The power density and efficiency of the supply itself are important in reducing the overall size of the solution. The TBF500 supplies are fully encapsulated with 500W of power in a compact brick package (4.2”x 2.4”x 0.5”). The device operates with an efficiency of up to 93% and a low 0.6W power consumption at no load. Its 0.5” or 12.7mm height allows the power supply to be readily installed in spaces with limited profiles. The full-encapsulated form factor, together with baseplate cooling, is an effective countermeasure to heat generation, allowing this AC/DC power supply to handle rugged applications in demanding environments from -40 °C to 105 °C with derating (Figure 3).
The module can also be paralleled with an optional current share function allowing for a maximum of three modules to increase the output power up to 1275W (Figure 4). Note each module should not exceed 85% of the maximum output power.
The TBF500 has been tested and certified according to many standards, making it more optimal for high-reliability applications such as factory automation. The OVC III level of insulation combined with its IEC/UL/EN 62368-1 safety approval and EMC ensures the device will operate within the guidelines of industrial and enterprise-level safety standards. The power supply has also been tested for environmental and mechanical reliability, an important factor in harsh industrial environments. The highly efficient, power dense modules can also be connected in parallel to scale up power and open up the TBF500 to industrial applications higher up the power spectrum.