Ecodesign for switching power supplies

Saving energy - or rather avoiding unnecessary energy consumption - is becoming increasingly prominent given the leading role of electronics and the huge number of electrical equipment used in industry and the household.

In order to apply these requirements to a legal framework, the European Commission published the ‘Ecodesign requirements for no-load condition electric power consumption and average active efficiency of external power supplies’ in the Official Journal L 93 on 7th April 2009.

The limits for external AC/DC power supplies have been established by this regulation at the following, currently applicable values since its publication:

• No-load power consumption (standby): <0.30 W
• Average operating efficiency: > 69.12 %

Switching power supply vs. power transformer

Standard power transformers in the range of 3W output power have an expected standby power of approx. 400mW and an average efficiency of around 50-60%. In light of this, they can hardly meet the requirements of the ecodesign.

Arrow has developed a design concept which replaces 50-60Hz power transformers with switching power supplies.

Switching power supplies like the design concept by Arrow to replace power transformers, which is based on the PWM Controller FSEZ1307MY from Fairchild Semiconductor, offer the following advantages:

• Improved efficiency (~72 %),
• A smaller no-load consumption (<30mW),
• A lower weight
• A wider input voltage range (85-265V)
• An integrated power and voltage regulation

with the same space requirements on the PCB as an EI30 transformer.

It is known that high switching frequencies that are used in switching power supplies create undesired side effects, called electro-magnetic interference (EMI). In the design concept by Arrow, an LC input capacitor and coil filter has been integrated in order to reduce the level of interference. It is recommended to add another X input capacitor in order to ensure that interference levels are reliably reduced below the required limits.

Concerning ‘humming’, in addition to iron and copper losses, it is also recommended to use a high-quality transformer, such as those supplied by Hahn GmbH. Similar, but lower-quality transformers lead to additional losses and interference. Initial financial savings tend to be quickly counteracted by additional expenditure through fault repairs.

Compared to a conventional power transformer with downstream rectification, grading and series regulator, PCB space is saved despite the additional capacitor.

While using a main fuse for the entire system,  the integrated fuse can be cancelled, which further saves PCB space and component price.

Through the primary adjustment of specific resistors, the maximum current or output voltage can be limited or established. As a result, this power supply can be operated in both constant voltage and constant current mode.

Areas of application

Since the design concept by Arrow has been developed for replacing power transformers, there are numerous potential areas of application, such as:

• Battery chargers
• Auxiliary power supplies
• USB chargers
• Flush-mounted supplies
• Industrial controls
• Power supplies for HMI

Download: Solutions Arrow Prototype Report Eco-design