New-Tech Magazine - Europe | January Digital edition

Figure 1. The Level VI minimum average efficiency requirement is significantly higher than in previous specifications

Table 1. Summary of no-load and dynamic efficiency targets for Level VI marking protocol

smartphones, tablets, printers, Internet hubs, routers, and IoT gateways. Given the expectation for explosive growth in IoT applications, the Level VI specification for external power supplies could be seen as providing valuable protection for the environment against the effects of the large numbers of IoT gateways soon to be connected to the power grid. CUI began introducing Level VI products to its EPS range in late 2014, to address the new regulation. EPS manufacturers typically adjust their product portfolios to meet the highest mandatory standard, which enables OEM customers to maximize operational efficiency and eliminate supply-chain errors by shipping a common power supply type with products destined for multiple export markets. The Level VI protocol is significantly more complex than its predecessors, and defines five categories of adapters including, for the first time, units rated over 250 W. Table 1 lists the specified no- load power and average efficiency for all categories covered. Typical IoT gateways are unlikely to require a 250 W or multi-output adapter, but could be designed for use with a single-voltage AC/DC supply of above 6V or a sub-6V low-voltage supply in the under-1W or 1W-49W category. Figure 1 compares the minimum average efficiency specifications for Level VI single-voltage (output > 6V) power adapters against the Level III, Level IV and Level V specifications. The limit is significantly higher for units in the 0.5W-5W range that will likely power a large proportion of

IoT gateway devices. Depending on the application the gateway may be designed to make use of sleep modes, taking advantage of the lower no-load power consumption of the Level VI specification. Other applications may require the gateway to be active more or less continuously. Meeting Level VI by Design The new Level VI specifications present tough challenges to power supply designers. Compared with CUI’s Level V power supplies, the Level VI units incorporate changes to almost every aspect of the primary and secondary- side circuitry. These have included designing-in the latest control ICs that support enhanced light-load operating modes: in normal operation the new controllers operate at the same 65 kHz switching frequency used in the Level V products, but change to 22 kHz at light- load and no-load to reduce power loss and improve efficiency. The capacitor and resistor values in the secondary feedback circuit have also been re-optimized to mitigate the effects of increased ripple and noise at lower switching frequencies. The control IC also takes advantage of new technologies to reduce quiescent power, which contributes further towards meeting the tougher maximum limits on no-load power consumption. Changes in the secondary-side circuitry of low-voltage/high-current Level VI power supplies include adopting synchronous rectification using MOSFETs and a dedicated control IC, in place of simple

diode rectification. Other component changes include re-optimized resistance values, and the use of increased wire gauges to reduce internal power dissipation. Moreover, newer MOSFETs with lower on-state resistance help to raise efficiency at heavier loads. On the other hand, the main power circuitry is arranged in much the same way as the previous Level V units. Units rated below 120 W use CUI’s established flyback design, while adapters over 120 W use LLC resonant topology. It is worth noting that the increased average efficiency of the Level VI power supplies also helps to reduce the typical working temperature thereby boosting reliability. This can be a particularly important advantage in IoT applications, where equipment often is required to operate for long periods in the field with little or no maintenance. Improvements for IoT and Environment The US Environmental Protection Agency (EPA) has said the regulations imposed on external power supplies over the last decade have already cut CO2 emissions by more than 24 million tons per year and saved households $2.5 billion annually. The US Department of Energy now believes enforcing Level VI will save around 47 million tons of CO2. Manufacturers of equipment such as IoT gateways need to keep abreast of the latest standards applicable to power supplies and energy.

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