Power Supply Options for Multiple Output Voltage Applications
Jim Dunn, Product Manager, IDEC | September 30, 2014A variety of power supply configurations and designs are available from industrial suppliers. The tried-and-true design of the linear power supply typically has better transient response to load changes, less electrical noise and less ripple than other power supply designs.
However, the design of the switching power supply—with its lower cost, higher efficiency, better hold-up time, smaller size, lighter weight and wider input range—works well in most industrial and machine tool applications.
This article considers switching power supplies and reviews the three basic options when multiple output voltages are required: multiple single-output power supplies, a triple-output power supply or an expandable power supply.
Assembly and packaging equipment suppliers and other end users typically require several DC voltages in their control enclosures and for distribution to field devices. Common voltages include 24V DC for I/O, 5V DC for electronics power and 12V DC for transducers.
A DIN rail-mounted single-output power supply is a popular choice in many industrial applications. Single-output supplies have the widest range of output voltages and currents available. They also typically have the best range of models for DIN mounting and include features such as extreme environment design, peak current ratings and redundant options. However, when additional DC voltages are needed, multiple power supplies must be added at the expense of panel space and higher costs.
A triple-output power supply is an option for multiple voltage applications. These units include only the most frequently used voltage and current combinations, which may not fit the needs of the particular application.
Careful review of the voltage and current options compared to requirements may eliminate a range of available power supplies or start a search for a suitable unit. For example, requiring 24V DC at 10A may be hard to find in a triple output unit. However, if a unit can be found that fits the application, significant hardware cost savings may be found compared to using multiple single-output units.
One option for control system designers requiring multiple voltage outputs is the expandable power supply. These DIN rail-mounted industrial power supplies expand to provide multiple output voltages from a single-output base unit. Expansion modules enable output voltages to be added or branched easily. The base unit is 24V DC only and the expansion modules include 5V DC, 12V DC and 15V DC converters in a variety of combinations and branch terminals, increasing flexibility and functionality.
A variety of mechanical configurations are available for switching power supplies, including encapsulated, PC board mountable, plug-in, chassis based, metal frame, rack mount, bench top and DIN mount. When mounting power supplies in a control panel, DIN rail mounting and panel mounting often are preferred. Rack mounting is also a good option depending on the control enclosure configuration.
Many of the single-output power supplies include built-in DIN mounting capability. However, panel space should be reserved for possible expansion or changing needs. Individual power supplies range from less than 1 inch wide to more than 7 inches wide on high-power units. Required cooling space between power supplies also should be considered when single units are used in multiple output voltage configurations.
The triple output may or may not save panel space depending on its design. These units are typically chassis-based, book-shaped power supplies that usually need brackets to mount to a back or side panel. Many of these units are also open-framed. Although these supplies can be narrow, mounting configurations and wire terminal access should be considered when laying out panels.
The expandable power supply has a slim, compact housing, helping to conserve valuable panel space. These units have a built-in DIN mount capability but also include panel mount or side mount brackets for installation flexibility on back and side panels. In single-output configuration, these 24V DC supplies are available as 5A, 10A and 20A units. Expanding these power supplies to double- or triple-output units saves space, but the current output of the added voltages is limited.
Reviewing power supply catalogs from a selection of suppliers shows many listed specifications are similar with little to distinguish brands. Load regulation, ripple, environmental and safety specifications are all within ranges suitable for a variety of industrial applications.
Most power supplies also have similar features in terms of housing design, visual diagnostic LEDs, finger-safe terminals and automatic input voltage adjustment. Although some suppliers may have their market niche for high inrush loads, medical applications, precision measurement metrology or extreme environments, there’s little overall difference in suitability for most industrial applications.
One of a few notable differences is the range of output voltages available for single-output power supplies. Many of the single-output units have eight or more voltage and current configurations available. This provides wide application flexibility.
Another specification to monitor is efficiency. The newer expandable power supplies offer improved efficiency, up to 93%, when compared to many single-output and triple-output units, which reduces operating costs.
When multiple output voltages are defined at the start of a design, panel space can be reserved to allow installation of multiple single-output power supplies. With three supplies, there is triple the wiring and fusing required. Even so, this remains a flexible option.
Both the triple output and expandable units reduce input power wiring. The expandable power supply is ideal for industrial applications where high power is required and panel space is limited. At 85mm wide, a 20A, 24V DC expandable power supply takes up less space than most 10A power supplies.
Significant overlap exists in the application of single-output, triple-output and expandable power supplies, but there are specific applications that may lend themselves to a particular configuration. Careful consideration of the characteristics of each power supply before specifying can save money, time and panel space.