Covering countless safety requirements for SMPS

The second edition of a Standard will improve the safety of a myriad of systems

By Morand Fachot

Low-voltage switch mode power supplies (SMPS) can be found in innumerable applications in IT equipment, vehicles, battery chargers, etc. A second edition of IEC 61204-7, an International Standard addressing safety requirements for SMPS was recently published. This Standard is also available as an Extended version (EXV).

Hypex SMPS Hypex SMPS1200 high-efficiency SMPS specifically designed for Hypex UcD™ sound amplifier modules (Photo: Hypex Electronics BV)

SMPS everywhere…

An SMPS is an electronic circuit that converts power using switching devices that are turned on and off at high frequencies. It has storage components such as inductors or capacitors to supply power when the switching device is in its non-conduction state, according to the IT Education Site Techopedia.

An SMPS transfers power from a DC or AC source (often mains power), to DC loads. It is highly efficient and is widely used in a variety of electronic equipment, including computers and other sensitive equipment requiring stable and efficient power supply.

The IEC 61204 series of Standards covers various aspects of SMPS, such as performance characteristics, electromagnetic compatibility (EMC), supplies and performance and safety requirements for “products that include power electronic converters, with a rated system voltage not exceeding 1 000 V AC or 1 500 V DC.” 

Safety is paramount

IEC 61204-7:2016 concerns safety requirements. This second edition of the Standard cancels and replaces the first edition published in 2006, and constitutes a complete technical revision. It has been prepared by IEC SC 22E: Stabilized power supplies, a Subcommittee of IEC Technical Committee (TC) 22: Power electronic systems and equipment.

This edition includes the following significant technical changes with respect to the previous edition:

  • use of IEC 62477-1:2012, Safety requirements for power electronic converter systems and equipment – Part 1: General, as reference document, instead of IEC 60950-1:2005, Information technology equipment – Safety – Part 1: General requirements.
  • modification of the title by deleting the wording “DC output” and adding “switch mode”.

This Standard specifies requirements to reduce risks of fire, electric shock, thermal, energy and mechanical hazards, except functional safety as defined in the IEC 61508 series of Standards on functional safety.

The objectives of this Standard, which has the status of a product Standard, are to establish a common terminology and basis for the safety requirements of products that contain power electronic converters across several IEC TCs. 

Coverage

IEC 61204-7 lists the various types of hazards, as well as aspects (like functional safety as defined in IEC 61508) and equipment that are not covered, such as motor-generator sets, step-down converters, other types of SMPS and certain types of transformers covered by other IEC Standards.

It also gives details of additional requirements that may be necessary for SMPS intended for certain specific uses. These are listed as “SMPS intended for operation in special environments (for example, extremes of temperature, excessive dust, moisture or vibration (e.g. earthquake zones), flammable gases, and corrosive or explosive atmospheres); SMPS intended to be used in vehicles, on board ships or aircraft, or in tropical countries; and SMPS intended for use where ingress of water is possible.”

This Standard specifies the various provisions necessary to protect against different types of hazards (electric shock, energy hazards, fire and thermal hazards, mechanical hazards, etc.). It also gives details about wiring connections, enclosures and specifies test requirements. 

Standard available as Value Added Product

This Standard is available as an Extended version (EXV), which includes the provisions of the general rules dealt with in IEC 62477-1.

This inclusion allows users to check immediately relevant additions without the need to search for them in IEC 62477-1.

An Extended version is not an official IEC Standard. Only the current versions of the related Standards are to be considered the official documents.

Given the very wide range of equipment and applications using SMPS this second version of IEC 61204-7, with its status of product Standard, and its Extended version in particular, will prove essential for all manufacturers who use SMPS in their products or applications. 

Gallery
Hypex SMPS Hypex SMPS1200 high-efficiency SMPS specifically designed for Hypex UcD™ sound amplifier modules (Photo: Hypex Electronics BV)
Personal computer power supply units use SMPS Personal computer power supply units (PSUs) use SMPS
Universal phone charger Mobile phone chargers use SMPS