FEATURE POWER ELECTRONICS DATASHEETS NEEDN’T BE DAUNTING
Jake Moir from Gresham Power Electronics offers some useful tips on how to interpret complex data sheet specifications for power supplies
T
he operating and safety specifications for power supplies
continue to become more complex, adding to the length, level of detail and complexity of data sheets. Nowadays, the data sheet for a product series has to include everything from voltage combinations to mechanical drawings - often for dozens of different models. If you don’t know what you’re looking for, reading one can be a daunting task. Rather than invest in a number of separate devices for different applications, customers are looking to invest in a single power source. This need for interchangeability boils down to simple economics: customers want to do more with fewer devices, which puts pressure on power supply manufacturers to design products that can fit a variety of potential applications. Manufacturers now have to offer power supplies with variable output voltages in addition to offering fixed- voltage devices. Having a variable voltage lets users adjust the power output to their preferred level, allowing the device to be used across more applications. In addition to being interchangeable, power supplies, at the same time, have to meet many specialised requirements. This includes undergoing rigorous, application-specific electrical testing. Consider EN 50155, which outlines the specifications of electronic equipment used in railway applications. This standard requires that power supplies have wider input voltages, including a range of 43 to 160Vdc, as well as pass various tests related to electrical insulation, power surges, ESD, voltage transients and more. The medical industry also has its fair share of tests, most of which are related to EMI, leakage current, immunity and voltage isolation. Tests like the HI pot (high potential) test, which verifies a device’s electrical insulation, are intended to protect patients coming into direct contact with medical equipment. While many of these power supplies were already manufactured to industry standards, manufacturers are now required to list the various tests and results on their data sheets.
24 JULY/AUGUST 2018 | ELECTRONICS
THERMAL MANAGEMENT Many applications demand both wider input ranges, higher power in smaller packages and installation in environments with both high ambient temperatures with limited cooling. In most power supply designs the wide
input can reduce the overall efficiency of the power supply, and it is this efficiency that determines the amount of waste heat produced. In simple terms, the less waste heat, the closer together components can be mounted without exceeding their specifications which in turn reduces the overall power supply size.
Figure 1:
Datasheets are a key source of technical information
manufacturer, especially for the medical and railway industries. Data sheets are required to indicate all new certifications, testing procedures, special model numbers and designations, which adds to their length but provides a lot of useful information for end-users. The medical industry has many standards related to leakage current, EMI resistance and voltage isolation - all of which must be avoided in machines and devices that come into direct contact with patients. In addition, the close proximity of equipment in hospitals increases the risk of noise interference, which could cause medical devices to work incorrectly at a critical time. Safety specifications, particularly ones related to EMI, therefore ensure power supplies pose no risk of interference. Power supplies used in railway
“Data sheets are now required to
indicate all new certifications, testing procedures, special model numbers and designations, which adds to their length but provides a lot of useful information for end-users.”
Originally, power supplies were Original y power suppl es were
mounted one of two ways: PCB mounted with pins or chassis mount with screw terminal connections. But now customers want smaller power supply packages to fit ever-shrinking end products. Manufacturers have responded by providing more mounting and remote placement options, including DIN rail, open-frame and enclosed types, terminal block, surface mount - and more. More options means more drawings. But your options don’t end there. Many certifications listed on data sheets require rigorous testing by the
applications also have their fair share of standards. Consider EN 45545-2, which specifies how materials used on trains must be fire-tested, or EN 50155, which outlines the specifications of electronic equipment used on carriages. EN 50155 also requires power supplies to pass various tests related to electrical insulation, power surges, ESD and voltage transients - all of which are intended to protect the passengers on-board. Additionally, the railway industry requires its own special input voltage range of 43 to 160V, which doesn’t exist for other applications. Because of the increase in safety
specifications and, in many cases, the addition of new products that comply with these standards, data sheets have become longer. While on the one hand, this trend has complicated data sheets, the addition of these details makes data sheets much more useful for customers who require power supplies for medical and railway applications. A datasheet may just be the
beginning of selecting an appropriate power supply for a new product design, replacement for an existing unit or one that has gone out of production.
Gresham
www.greshampower.com T: 01722 413060
/ ELECTRONICS
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