External power supplies – the classic black bricks that come with so many electronic products these days – are now required to conform to specific energy efficiency requirements. Specifications cover active efficiency – when the power supply is delivering power to the load, and power consumption when there is no load.
When it comes to component power supplies, those built into electronic and electrical equipment, the discussion is a little more complicated. This is because external power supplies are considered as a product in their own right and have easy to understand requirements, but component power supplies are not.
Energy Star requirements apply to the product groups in Table 1. However, each product group may contain several products. For example the product group “imaging equipment” covers digital duplicators, mailing machines, printers, scanners and all-in-ones.
Table1: Energy Star requirements as they apply to product groups.
(Click on table to enlarge)
If we take the case of simple printers, the energy efficiency requirements depend on whether the printing technology is direct thermal transfer, dye sublimation, electrophotography, impact, ink jet, solid ink or thermal transfer. The format (A6, A4, A2 etc.) is also relevant. Therefore the same power supply used in different types of printer will have differing energy efficiency effects. Consider an application involving imaging equipment. There are two ways of demonstrating Energy Star compliance. One is to use the Typical Electricity Consumption (TEC) method, the other is to use the Operational Mode (OM) method.
The TEC approach makes assumptions about how many hours a day the product is in general use, the pattern of use during those hours and the default delay times that the product has before entering a low power mode (sleep). Electricity consumption is measured as accumulated energy used and converted to power by dividing by the test period.
The calculation assumes that there will be two periods of use per day with a low power mode in between, simulating a lunch break. It also assumes that there will be no weekend usage. The TEC value is derived from the various energy measurements taken during active use, sleep mode and auto-off periods. The maximum allowable TEC value is dependant upon the format size, product speed (images per minute) and marking technology.
By contrast, the OM approach is to measure power during the ready, standby and sleep modes and also to measure the default time period until the product enters sleep mode. To be compliant with Energy Star, the product has to meet three criteria:
Default time to entering sleep mode must be less than a given value in minutes, depending on product size format and product speed - images per minute - for imaging equipment, except for mailing machines. For mailing machines the default sleep time delay is only dependant on speed, or mail processed per minute.
Standby power should be less than 1 W for small and standard format products without fax capability or less than 2 W for small and standard format products with fax capability. For large format products and mailing machines there is currently no limit.
Sleep power should be less than a given value according to type of machine, format size and printing technology. There is a base figure for each case and this can be higher if the product has functions beyond the basic print engine. As an example, having a network connection port, memory card reading capability, infrared port, or cordless handset increases the allowable sleep power. The value of additional allowance depends on whether the extra function is active whilst the product is in sleep mode, or inactive. There is also an added figure for the power supply. This is based on its output rating and is 0.05 × (rated power-10).
It can be seen that factors other than the power supply contribute greatly to the energy efficiency rating of the imaging equipment application.
Some products have their own program requirements whereas others are grouped together, such as the copiers and fax machines, mailing machines and printers, scanners and all-in-ones printers/scanners/faxes.
Clearly, as each application and product type needs to meet differing requirements to comply with Energy Star, it is not possible to have component power supplies that can guarantee that all applications can be Energy Star compliant. The functions that the products run whilst in standby or sleep mode, the time taken to enter standby mode and the average energy consumed within a working day must all be taken into account. However, careful selection of power supplies that offer high efficiency throughout their full operating range, from no load to full load, will simplify the design work needed to ensure that the end equipment meets its energy efficiency requirements.
XP Power's ECS45 is an example of a compact power supply that offers a typically operating efficiency of 88 percent and less than 0.3 W power consumption under no load conditions thanks to “green mode” operation. The unit - which has output voltages from 12V to 48V DC – comes in a 3 x 2 x 0.95 inch package and uses a green mode PWM controller chip. The chip provides off-time modulation to continuously lower the switching frequency of the power supply’s flyback converter under light load conditions. This lower switching frequency reduces circuit losses under these circumstances. The chip itself is made in a BiCMOS process to keep start up current to around 14 µA and operating current at 4 mA. The device also provides some of the protection functions in the power supply and ensures constant output power over AC input voltages from 90 to 264 V AC.
Meeting Energy Star or other efficiency requirements for electrical and electronic products is a growing design challenge. Selection of a suitable green mode power supply may not provide the complete answer but it’s a very good start.
About the Author Gary Bocock is Technical Director of XP Power.
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