Electrostatic Discharge

Table 2 – EN 61000-4-2 Test Levels.
Medical device designers must pay particular attention to electrostatic discharge (ESD) issues. The IEC 61000-4-2 standard defines four standard levels of ESD protection, using two different testing methodologies shown in Table 2: contact discharge and air discharge for cases where contact discharge testing is not possible.

Designers should perform an engineering analysis to ensure that there would not be a significant unit cost increase in order for the power supply design to be compliant with the more stringent standard.

From a power supply design perspective, designing a product to comply with the IEC 61000-4-2 ESD requirements can be a challenge at the higher discharge voltages. This becomes even more challenging with a Class II AC input (two wire, no-earth ground conductor). When the ESD discharge is applied to the output or signal pin, the voltage is developed across various isolating barriers and capacitors. This occurs because the AC mains are virtually grounded at some point, so applied ESD voltage appears between the point where the charge is applied and earth ground.

Without careful consideration of the various discharge paths within the power supply, unexpected arcing and damage to the power supply can occur. Testing to the standard and providing a test report is some assurance that the product will perform well within the confines of the specification.

Conclusion

The evolving market trends and regulatory climate for medical device design can present daunting challenges on many levels, just a few of which we’ve addressed here. Other important aspects include RFI and wireless considerations, risk management, and regional differences, as well as issues relating to various types of devices and where they will be used. In all of these cases, starting the design with a power supply that addresses known requirements will give any design an edge for speeding development and meeting overall regulatory goals. Choosing a vendor with a depth of medical regulatory experience can further simplify the design process and ensure the smoothest path to market.

This article was written by Cochise Mapa, Director, Global Product Management, and Lorenzo Cividino, Director, Field Technical Support, SL Power Electronics, Ventura, CA. For more information, Click Here.