Users expect high quality, availability, competitive pricing

Despite all the hoopla about ways technology can enhance our lives at home and at work, none of the technology would have reason to exist without ac to dc power supplies. Oh sure, there are batteries, and solar and wind generators, but most technology relies on ac power, and thus the need for ac to dc power supplies.

By Dave Harrold, CONTROL ENGINEERING May 1, 2002
Trends in Power Supplies
  • Universal ac input

  • Power factor correction

  • High efficiency

  • Agency certification

Despite all the hoopla about ways technology can enhance our lives at home and at work, none of the technology would have reason to exist without ac to dc power supplies. Oh sure, there are batteries, and solar and wind generators, but most technology relies on ac power, and thus the need for ac to dc power supplies. Even so, only slightly more than half (51%) of the 210 respondents to a recent Control Engineering and Cahners Research ac to dc power supply survey consider redundancy important or very important.

The three most important and/or very important power supply features or characteristics responders seek are reliability (100%), followed closely by ease of use (92%) and ease of installation (91%). (See ‘Power supply feature/characteristic importance’ graph.)

When it comes time to purchase ac to dc power supplies, responders indicate product quality (99%), availability (97%), and price (96%) as important and/or most important in selecting a manufacturer or supplier.

DIN-rail mounted, standalone, and rack-mounted linear regulated power supplies are most used, followed by a second tier consisting of plug-in linear regulated, miniature with screw terminals, and DIN-rail-mounted unregulated, respectively.

During 2001, 196 respondents spent $3,338,000 (an average of $17,030) on all ac to dc power supplies with rack-mounted liner regulated garnering the lion’s share with $726,400, followed by stand-alone linear regulated at $683,400.

Keep it simple

Though ac to dc power supplies provide the ‘lifeblood’ that keeps technology running, power supply network connectivity isn’t seen as important by Control Engineering survey responders.

In fact, 60% of survey responders indicate simple relay contact outputs are a satisfactory power supply ‘health’ communication method.

Of the 96 survey responders who indicated a preference for power supplies with network connectivity, RS-232, Ethernet TCP/IP, RS-485, DeviceNet, and all Modbus protocols rounded out the top five respectively.

One of the problems with power supply manufacturers ‘keeping it simple’ is that users often don’t know what they want or need until they see it. For example, recent conversations on one web list was discussing the importance and need to monitor power usage on fieldbus segments.

Anyone who’s designed and installed a 4-20 mA loop or fieldbus installation understands the consequences insufficient 24 V dc power has on measurement accuracy and final control device capabilities. Just because users don’t rank such capabilities as important doesn’t mean those same users wouldn’t make good use of hosted intelligence to diagnose and warn of potential power related problems. After all, wouldn’t that be a useful extension of managing assets?

Power supply products

To request info, circle the following numbers or visit . For more manufacturers, visit the Control Engineering Buyer’s Guide at .

Comments? E-mail

Wall-mounted redundancy

Easton,Pa. -Acopian’s redundant power supplies are available in wall or cabinet mounting configurations. Each package contains two identical power supplies with outputs interconnected through a diode switching arrangement, said to detect any fault condition and then isolate the faulty power supply from the system output, passing only the output of the ‘good’ power supply without power interruptions. Relay contacts activate based on failure alarm circuit diagnostics. Acopian

Power for distributed applications

Milwaukee, Wis.- Designed to complement Allen-Bradley’s Flex I/O systems, DIN-rail mounted 1794-PS13 and -PS3 Flex I/O power supplies deliver 24 V dc nominal at 1.3 and 3.0 amps respectively in distributed applications where panel space is premium. The 1794-PS3 provides enough power to operate a full rail of Flex I/O modules or up to six Flex adapters. Rockwell Automation

Flexibility in blocks

Schaumburg, Ill.- Omron’s S8TS block type power supply permits linking of bus connected, DIN-rail-mountable power supplies to meet different power requirements. Four S8TS units can be snapped together to form a system that supplies 5-24 V dc power. When a unit is added to the power-supply block, that unit automatically backs up all other units in the system. Additional dc power security can be connected via stand-by batteries. Omron

6 W per cubic inch

Taunton, Mass.- MK Series high-density switching power supplies provide output power over the range of 40 to 300 W. All models accept universal input from 85 to 265 V ac, provide power densities of up to 6 W per cubic inch, and feature integral power-good LED indicators. Output adjustment potentiometers, operation in temperatures of -10 to 60 °C (14 to 140 °F), overvoltage and short-circuit protection, and integral input line filtering are also included. Sixteen models provide outputs from 5 to 24 V dc. Astrodyne

Active power factor correction

Raleigh, N.C.- C&D Technologies TX1000 is a single-output 1,000 W power supply designed to comply with all relevant international standards. TX1000 incorporates active power factor correction circuitry and has built-in EMI filtering that meets FCC/CISPR Class A standards. TX1000’s input range is 90 to 264 V ac. Available in nine models, TX1000 output range is 5 to 48 V dc. C&D Technologies


Bergenfield, N.J.- KV Series constant voltage/current SCR-controlled, high-voltage power supplies feature 100 to 1,500 V dc output, 0.5% regulated voltage and current, voltage and amperage meters, and hold ripple to 0.5% rms. Four KV Series 1,000 V dc power supplies are available with an output range of 0.5 to 3.0 A. Three additional models offer 1,500 V dc output at 0.5 to 1.5 A. Mid-Eastern Industries

Mini supply, 130 W

San Marcos, Calif.- Taiyo Yuden’s Model ADD130 switching power supply features four outputs and 83% efficiency in a 1.25 x 3.0 x 5.0 in. (3.175 x 7.62 x 12.7 cm) package. ADD130 provides input waveform correction and meets IEC 1000-3-2 harmonic distortion specifications. ADD130 is designed to provide output current sharing among similar units for applications requiring redundancy. Taiyo Yuden

3-phase power supply

Harrisburg, Pa.- Phoenix Contact’s Quint power supply features a wide input range suitable for use in three-phase North American and European machine tool, material handling, and automotive applications. Delivering 20 amps of 24 V dc power, Quint uses standard DIN-rail mounting, provides input power correction, and includes electronic overload and short-circuit protection. Quint has a UL 508 listing and Phoenix Contact spokespersons claim it provides better than 500,000 hours mean time between failures. Phoenix Contact

Small DIN-rail mount

Carlisle, Pa.- Automation Systems offers compact DIN-rail mounted switching power supplies with universal 90 to 264 V ac autoranging input, 1 to 20 amp 24 V dc output, and compliance with UL, CSA, and CE safety and electrical noise requirements. Additional features include power loss alarm, touch-safe enclosures, and front panel LED status indication. Units are also available for applications requiring 5, 12, or 15 V dc output. Automation Systems Interconnect

Power supply suited for Class 1, Div. 2

Irving, Tex.- Entrelec’s 5 to 48 V dc switching power supplies feature UL 1604 approval for use in Class 1, Div.2, Groups A, B, C, and D hazardous locations. All models can operate in the 0 to 55 °C (32 to 131 °F) temperature range, and provide universal ac input rangeability, fused inputs, and a maximum peak-to-peak ripple of less than 300 mV. ABB Entrelec

Gary Mintchell, Control Engineering , senior editor, also contributed.