Many applications require isolation of hazardous voltages to comply with international safety standards. To ensure the safety of equipment and operators, these standards often require isolation components (such as digital isolators or optocouplers) to withstand high voltage surges above 10 kV (peak). Therefore, testing the isolator surge performance is a necessary part of developing a safe, reliable device.
Standards published by the International Electrotechnical Commission (IEC) and VDE (Verband der Elektrotechnik) regulate the system-level and component-level applications of isolation technology in systems such as medical, industrial, consumer, and automotive. To ensure the safety of personnel and equipment in the event of high voltage surges, these standards specify different surge ratings depending on the level of isolation required for the specific application.
There are three common types of isolation: functional isolation, basic isolation, and enhanced isolation. Functional isolation has only a small number of safety requirements, as it is generally only used where isolation of the ground reference voltage is required to ensure proper operation of the circuit. It can be seen that security and surge performance are not the main considerations for functional isolation.
However, safety is a primary consideration for basic isolation and enhanced isolation, so surge levels are key to determining isolation quality. Basic isolation protects end-users from electric shock. Enhanced isolation is a separate isolation system that provides protection equivalent to two redundant single or basic isolation systems. Medical and industrial applications generally require enhanced isolation to protect patients and end users from fatal shocks. VDE's enhanced isolation standard for digital isolators is VDE 0884-10, which specifies a minimum surge voltage (VIOSM) rating of 10 kV and specifies operating voltage (VIORM) and withstand voltage (VISO).
The surge voltage rating of a digital isolator specifies the impact resistance after being subjected to a continuous transient high voltage pulse. Figure 1 shows the timing characteristics of a surge waveform in accordance with IEC 61000-4-5.
Figure 1. Surge voltage waveform
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