Rafal Kasikowski, Design Engineer – Power Specialist, TT Electronics
External power supplies (EPSs) are contained in a separate housing from the devices they are powering and contribute substantially to total global electricity consumption. As governments strive to address their ongoing environmental responsibilities, resolving the inefficiencies of power conversion has become a pivotal requirement across the globe.
As governments and consumers become more aware of the environmental impact of today’s lifestyles and electrically powered devices, a number of new, often parallel, regulations concerning the energy conservation for EPSs have been drawn up. These regulations aim to ensure a high average energy efficiency and minimum no-load power consumption for EPSs. In the United States, the Department of Energy (DOE) has prepared a set of new regulations (Level VI standards) that went into effect in early 2016, and the EU followed with the European Union’s Code of Conduct (CoC) standards (Tier 1 and Tier 2) . The European initiative is voluntary and has not come into force, but specifications remain likely to become binding in the EU in the near future. Designers of external power supplies must track the latest developments to ensure that their products are compliant with current regulations in different regions of the world.
How do Level VI standards decrease energy consumption?
The DOE’s Level VI regulations define two performance criteria: no-load power consumption and minimum average efficiency limits in active mode (measured at 25%, 50%, 75% and full load), and cover the following range of products:
· Single-voltage external AC-DC power supply, basic-voltage (output voltage ≥6 V)
· Single-voltage external AC-DC power supply, low-voltage (output voltage below 6 V)
· Single-voltage external AC-AC power supply, basic-voltage (output voltage ≥6 V)
· Single-voltage external AC-AC power supply, low-voltage (output voltage below 6 V)
· Multiple-voltage external power supply
The table above gives the minimum average efficiency thresholds and the maximum standby power EPSs falling into the above classes.
The DOE Level VI legislation is tougher to meet than the previously applicable regulations, and adds a new category of multiple-voltage external power supply and a new output power level threshold of 250W. In the table, a multiple-voltage EPS is defined as ‘an external power supply that is designed to convert line voltage AC input into more than one simultaneous lower-voltage output’, and theln(Pout) designation refers to a natural logarithm of an output power. The DOE ruling differentiates between direct operation (an external power supply that can operate a consumer product that is not a battery charger without the assistance of a battery) and indirect operation EPSs. The majority of EPSs falling into the direct operation category (see ) will comply with the above table.
The EU Code of Conduct (CoC) on External Power Supplies
In the EU, the European Commission Joint Research Centre created new energy conservation standards in order to encourage manufacturers to develop products of low environmental impact. Similar to the DOE’s regulations, the new European scheme aims to minimise the energy consumption of external power supplies both under no-load and load conditions. The proposed regulations, thus far voluntary and still under revision, were arranged in two sets of requirements, Tier 1 and Tier 2. The Tier 1 provisions are effectively
comparable to the DOE’s Level VI rulings, although certain differences exist. In the proposed document, a new 10% measure is implemented in addition to the four-point average efficiency in active mode. In addition, there is no separation of direct and indirect EPSs, and high-power EPSs (Pout > 250 W)are not a subject of the regulations. The CoC for Tier 2 is more ambitious and stringent, and raises requirements to above the DOE’s Level VI and the CoC’s Tier 1 for both no-load power consumption and the minimum average.
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Figure 2: CoC Tier 1 and Tier 2 Energy Efficiency Criteria for Active Mode, Basic-Voltage, >/= 6V
What should EPS designers do?
Although only the DOE’s Level VI specifications, among the ones discussed herein, became mandatory, and neither the CoC Tier 1 nor Tier 2 requirements have as yet come into force, power supply design engineers and manufacturers should be prepared and start planning for the inevitable changes needed to meet key performance criteria.
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Figure 3: CoC Tier 1 and Tier 2 Energy Efficiency Criteria for Active Mode, Basic-Voltage, < 6V
TT Electronics is taking a proactive approach to our environmental responsibilitiesand investing in R&D at our power research and design centre in Norwich, UK, to engineer a number of products that meet and surpass the latest and most stringent standards. This, although challenging, can be achieved with the implementation of latest technologies and topologies with inherently higher efficiencies and low standby power features. However, addressing the new standby and efficiency requirements of power supplies should not impact power quality and the technology must be carefully considered for the application. Switching regulators equipped with frequency-reducing features to boost the light-load efficiencies may worsen the output voltage parameters affecting an end user or, in a worst-case scenario, render the product unsuitable for certain applications if the burst mode is within audible frequency range.
It is widely recognised that our way of life today has adverse environmental effects, and these effects are on the increase. The new EPS efficiency standards legislation is being imposed to counteract these effects, aiming to cut energy consumption and reduce CO2 emissions. This will save money and/or allow redirection of the saved kilowatts into different applications. There is a growing understanding of the benefits of this course of action among EPS designers and manufacturers as they pledge to deliver products compliant with quickly evolving legislation. The development and production of energy-efficient EPSs is also a way to differentiate newer eco-friendly EPSs from the older alternatives, and thus increase market share.