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Examining safety standards for transformer design

Posted: 06 Aug 2014  Print Version  Bookmark and Share

Keywords:flyback power supply  safety standards  inductors  electromagnetic interference  telecommunication 

When designing an offline flyback power supply, integrating the IC with the other components can be overwhelming. Integrating the transformer properly is more than finding the turns-ratio to match with your input and output(s). I thought a Flyback transformer is just transferring energy across a safety isolation barrier. I guess there is more to understand. Not knowing the safety standards will usually mean more iterations than necessary when working with a transformer manufacturer. Not knowing the safety standards can lead to unwanted surprises of non-conformance at the qualifying labs and sending a product back to design phase rather than qualification before mass production.

Understanding the requirements that govern transformer design and manufacturing will shorten design cycles to finished products using Fairchild parts in Power Supply WebDesigner (PSW). Just knowing the safety standards required for your design will be enough to allow Wurth Electronics Midcom to design the right part the first time over 90% of the time.

Knowing safety standard required during product definition or design definition will ensure unnecessary design iteration and cost. Below you will find the most common standards used in the industry to define the safety requirements of offline transformers. Wurth Electronics Midcom is very familiar with these standards and typically knowing which standard you are trying to meet and the insulation type is enough to get you what you need.

Which transformer safety standard to use is not always so clear for the designer of electronics. Typically the standards to be met for a product are based on the equipment type to be designed and the markets that the equipment is targeting. Product Marketing as well as Safety Engineers with in a company are best equipped to choose which standards apply.

In order to make your search easier, we have listed a number of the more common standards that are referred to by electronics manufacturers that apply to their equipment. We have attempted to take the scope and a brief description of these standards from the standards themselves. While the descriptions have been pulled directly from the standards, they have been paraphrased for readability and are not in any way a substitute for the actual standard. The gain here is to compile the scopes of the most typical standards that are used into one document to let you easily identify which standard might apply. From there you can purchase the standard for further review.

Standards
EN 50470-1 AC Electricity metering equipment
This standard provides the general requirements for class B and C Metering equipment. The scope of this European standard applies to newly manufactured watt-hour meters intended for residential, commercial and light industrial use, for use in 50Hz electrical networks.

The standard applies to electromechanical or static watt-hour meters for both indoor and outdoor application. The standard applies to the active energy metering part and not to other functional elements, like maximum demand indicators, electronic tariff registers, time switches, ripple control receivers, data communication interfaces, etc. that are enclosed in the meter case.

EN 60935 Fixed inductors for electromagnetic interference suppression
This International Standard applies to inductors designed for electromagnetic interference suppression for use with electronic or electrical equipment and machines and is restricted to inductors for which safety tests are appropriate.

Inductors within the scope of this standard may also be used to protect from electrical noise and voltage or current transients coming from either the supply or from other parts of the apparatus.

EN 61347-2-13 LED module lamp control gear for both AC and DC applications
This standard applies to LED control modules that are designed to provide constant voltage or current at SELV or SELV equivalent or higher voltages. As defined the lamp control modules are one or more components between the supply and lamps which may serve to transform the supply voltage, limit the current of the lamps to the required value, provide starting voltage and preheating current, prevent cold starting, correct power factor or reduce radio frequency.

As defined in the standard the lamp control modules shall be designed and constructed that in normal use they operate without danger to the user or surroundings. Where luminaire enclosure for protection against electric shock are not used, they must be sufficiently protected against accidental contact with live parts.

IEC 60335-1 Safety for household and similar electrical appliances
This International Standard deals with the safety of electrical appliances for household and similar purposes with rated voltage not more than 250 V for single-phase appliances and 480 V for other appliances.

This standard also applies to battery-operated appliances and other DC supplied appliances. Other appliances not intended for normal household use but which nevertheless may be a source of danger to the public, such as appliances used by laymen in shops, in light industry and on farms, are within the scope of this standard. Examples of such appliances are catering equipment, cleaning appliances for commercial use, and appliances for hairdressers.

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