IS29.4 - Beyond the Plug: Meeting Product Safety Under IEC 60335-1 and Minimizing Standby Power Consumption

This presentation explores how to ensure electrical safety in household appliances by effectively discharging X-capacitors, while also complying with emerging energy efficiency regulations.

X-capacitors, used in appliance power supplies to reduce EMI by filtering AC line noise, can retain hazardous voltages even after the appliance is unplugged. This residual voltage poses an electric shock risk, particularly if users touch the plug prongs. To mitigate this danger, the IEC 60335-1 standard requires that the capacitor voltage falls below 34 V within 1 second of disconnection.

Traditionally, this requirement is met using bleed resistors, which safely discharge the capacitor. However, this method presents a challenge as the capacitance increases, lower resistance is needed for faster discharge, which in turn increases standby power consumption. The EU’s upcoming Commission Regulation (EU) 2023/826 caps off-mode power consumption at 300 mW, meaning that systems with X-capacitance over roughly 1.8 µF can easily exceed this limit if passive discharge resistors are used alone.

To address this, the presentation proposes a more energy-efficient solution: a switched self-powered discharge circuit. This circuit detects when the appliance is unplugged and rapidly activates discharge FETs, allowing the capacitor to discharge safely through higher resistance paths only when needed. This design enables compliance with both safety and low power consumption requirements, reducing power consumption to less than 5 mW.

The presentation also compares IEC 60335-1 (appliance safety, prescriptive) and IEC 62368-1 (ICT/AV equipment, hazard-based) standards, highlighting different user protection criteria and testing conditions. It also tackles the additional test requirements when using a switched self-powered discharge circuit to meet compliance for both IEC 60335-1 and IEC 62368-2 standards.

In conclusion, this session is targeted at power electronics professionals and design engineers working on household appliance compliance. It offers practical insights into meeting stringent IEC 60335-1 capacitor discharge requirements while avoiding excessive standby energy loss, ensuring both safety and regulatory compliance in modern appliance design.