The regulation of power-based products and components is critical for design development and user safety. For decades, the International Electrotechnical Commission (IEC) has dictated how to design information technology equipment and audio/video products for safety. The IEC’s traditional approach to equipment safety has been product-dependent and incident-based, making the previous standards, IEC 60950-1(information and communication technology equipment) and IEC 60065 (audio and video equipment), more reactive and less adaptable to emerging technologies.
A new regulation, IEC 62368-1, became the single default standard on December 20, 2020. Thus, designers no longer can choose to comply with either the information/communication technology standard or the audio/video equipment standard. As the boundaries between information/communications and audio/video technology have blurred, the IEC 62368-1 hazards-based safety engineering standard applies to a broad scope of applications.
The new standard is less product-specific. It focuses on the energy within the equipment and the intended environments. This future-proof approach aims to encourage manufacturers to address known hazards in the design and intended use of the product, whether its application is for industrial or residential use.
Product types covered under IEC 62368-1 compared with products covered by the earlier standards, IEC 60950-1 and IEC 60065. Click for a larger image. (Source: Littelfuse)
Scope and criteria
The scope of the new standard is relatively broad. It includes all previously covered applications under different standards, or not covered at all, addressing electronic equipment up to 600 volts such as point-of-sale, banking, other telecommunication and office equipment, speakers, surveillance cameras, smart home devices, and other audio/video equipment. In addition, the new standard covers internet of things (IoT) devices, laptops, mobile devices, gaming systems, and other battery-powered electronic devices.
Although IEC 62368-1 has been in effect for a few years, designers could choose whether to comply with IEC 60950 or IEC 60065 over IEC 62368-1, depending on the application. Now that choice is no longer possible. The hazard-based approach in IEC 62368-1 takes into consideration a device’s design and its use to determine testing and evaluation criteria. The standard also defines which protection components to consider using within the device. While the evolution of the power-based standards may seem complicated, this new approach allows for improved safety and design flexibility.
AC line protection components help increase product reliability and must comply with specific tests required by IEC 62368-1. It is necessary to decide on the overvoltage category that applies to determine the parameters of some of the tests.
Where the device connects to the electrical grid helps define the overvoltage category. The closer the proximity to the grid, the higher is the category and the hazard. For example, an electric meter on the outside of a house connected by a service wire to a transformer is considered Overvoltage Category IV. The electric breaker Panel inside a home would be in a lower overvoltage category. Personal devices such as PCs, routers, notebooks, tablets, and related power supplies fall within Overvoltage Category II.
Using the Overvoltage Category along with the line voltage, engineers can determine the voltage withstand rating. Power adapters connecting to 120-V outlets have a withstand voltage rating of 1500 V. For adapters connecting to 240-V outlets, the withstand voltage rating increases to 2500 V. This rating is an essential basis for component selection and applicable tests.
The new standard also includes three tests related to varistors and gas discharge tubes (GDTs) for surge protection. The older standards did not have these tests. Varistors exposed to surge events can wear out over time, eventually becoming a hazard themselves. IEC 62368-1 now refers to a varistor as a possible ignition source, thus requiring additional tests.
The varistor overload test (the Annex G.8 portion of the standard) is a stress test that progressively steps up the power in the varistor. The test uses an AC source to apply twice the equipment’s voltage rating through a Resistor to the varistor-under-test. The test starts with high resistance and lowers the resistance until either the varistor fails or a fuse, thermal disconnect, GDT, or other components safely open the circuit.
Required IEC 62368-1 overload and overvoltage tests on safety components with unreliable and reliable earth connections. Click for a larger image. (Source: Littelfuse)
The temporary overvoltage test is similar but defines specific current values and the test duration. In both cases, the varistor cannot cause damage. Engineers can bypass both overvoltage tests by increasing the varistor rating as defined in Table G.10 of IEC 62368-1. However, if a design engineer sizes the varistor to avoid the test, the engineer must select downstream components with higher ratings which add to the product’s cost. The third test, the basic insulation test, evaluates the electric strength of equipment with an unreliable ground bond, most non-industrial plugs. If the ground meets the defined criteria of a reliable ground, this test is not necessary.
Choosing a compliant solution for universal power adapters
Universal power adapters, commonly used in IT equipment, accept a wide range of voltage inputs, such as 90 to 240 VAC. This voltage range allows the product to be used worldwide with a common set of electronics. Safety requirements dictated by IEC 62368-1 require both overcurrent and surge protection.
Selecting the correct fuse is critical to preventing damage from overcurrent events and passing fault testing. When choosing the right fuse, consider the following:
- The fuse should both achieve its purpose within the circuit and remain intact when the circuit is operating normally.
- The fuse must not nuisance trip. It must not open during either normal operations or surge pulse testing. To achieve this, calculate the predicted pulses’ energy and compare it to the fuse’s melting point. By targeting a proper ratio between the two values, engineers can be confident that the fuse will not nuisance trip during predictable pulses.
- The voltage rating of the fuse must be at least as large as the maximum rating of the power supply or system voltage.
- The fuse should have a maximum fault current rating higher than the maximum available fault current of the location where it will be used. This breaking capacity or interrupt rating determines how much current the fuse can safely interrupt.
- The fuse should fit in available space.
- The fuse must meet required third-party certifications, including UL or IEC requirements.
Use these requirements to identify the best fuse for the application. For example, Littelfuse recommends its 3.15-A fuse in the 215 Series due to a high breaking capacity of 1500 A at 250 VAC.
There are several surge protection technologies available. Safety components include varistors, TVS diodes, protection thyristors, and GDTs.
To determine the best solution for the application, engineers should first consider whether the ground is deemed to be reliable. Many home, office, and commercial spaces have unreliable ground connectors. Examples include wall sockets with a loose earth connector or a damaged ground terminal in the plug. Reliable ground connectors typically exist in industrial applications where the ground is hardwired or the equipment does not function without a good ground connection.
Littelfuse Series TMOV varistors with various disc diameters can withstand peak pulse currents of up to 10 kA and pulse energy levels up to 480 J. (Source: Littelfuse)
For unreliable ground applications, IEC 62368-1 states that when using varistors in the common mode, connections between High and protective earth or between Neutral and protective earth, consider using varistors with a GDT as long as they comply with the Annex G.8 varistor overload test. For varistors used in the differential mode, High-to-Neutral, the varistors must meet all the criteria described in Annex G.8.
To choose the right varistor, the minimum continuous operating voltage should be at least 1.25 times the maximum voltage rating of the equipment. Selecting the varistor’s required surge rating will determine the varistor’s diameter. A GDT should also pass the electric strength test to withstand the necessary voltage for compliance. After selecting a GDT and varistor, the pair must pass the overload and temporary overvoltage tests.
For the universal power adapter example, a 300-V thermally-protected varistor can protect the line-to-line and line-to-neutral connections from voltage transients and lightning while meeting minimum surge requirements. Consider using a 3000-V GDT combined in series with a 300-V varistor in both line-to-ground and neutral-to-ground connections.
Recommended solution for a universal power adapter
Figure 4 shows the two recommended options for overload and surge protection of universal power adapters. Use a fuse and a varistor for differential mode protection for an unreliable ground connection. With a product connecting to a reliable ground, use the fuse-varistor series combination for differential mode line protection and a combination of two varistors with a GDT for common-mode protection.
Littelfuse recommends the components listed below the schematics. These include the TMOV and UltaMov series varistors as well as the CG3 series GDTs.
The TMOV series TMOV14RP300E is a thermally-protected, 14-mm disc diameter varistor rated for 300 VAC. It withstands a 6 kA pulse and pulse energy of 250 J. The UltaMov series V10E300P, recommended for common-mode protection with a GDT, has a 10-mm diameter disc and absorbs a peak current pulse of 3.5 kA.
Littelfuse recommends the CG3 3.3 for use with the V10E300P varistor in common mode connections. CG3 series gas discharge tubes combine high breakdown voltage with a surge current rating of 10 kA.
Recommended overload and surge protection circuit configurations and components for universal power adapters. Click for a larger image. (Source: Littelfuse)
While this is the most common surge protection solution for many electronic applications, designers can also consider other solutions. When comparing technologies, engineers should consider the component’s:
- Clamping voltage, which shows how well the device can protect during a surge event, with lower being better
- Let-through energy during a surge event, again, lower is better
- Leakage current
- Lifetime after multiple surge events
- Size and cost.
IEC 62369-1 provides flexibility for safety requirements
IEC 62369-1 introduces a new way to approach electronics product testing by requiring engineers to consider known hazards and use environments when designing a product. This hazards-based approach aims to keep pace with technological advances while giving product designers more flexibility within the framework.
As manufacturers ensure that their products and components are certified to IEC 62369-1, they can take an approach that uses new, innovative design and construction methods. Partnering with a manufacturer such as Littelfuse or a distributor experienced with the new standard can help designers find the right solutions for safe and effective products.
To learn more, download the Circuit Protection Products Selection Guide, courtesy of Littelfuse, Inc.
IEC 62368-1:2018. Audio/Video, Information and Communication Technology Equipment – Part 1: Safety Requirements. https://webstore.iec.ch/publication/27412 . October 4, 2018.
IEC 60950-1. Information technology equipment – Safety – Part 1: General Requirements. IEC 60950-1:2005 | IEC Webstore . December 8, 2005.
IEC 60065:2014. Audio, video, and similar electronic apparatus – Safety requirements. https://webstore.iec.ch/publication/494 . June 27, 2014.