Application Note

HV Isolation in Electric Vehicles

Reliable Insulation Detection for 800V Architectures.

The Shift to 800V Fast Charging

High-voltage fast charging has become the preferred choice for the automotive industry to reduce charging times and increase efficiency. In 2019, Porsche’s Taycan was the first to introduce an 800V high-voltage electrical architecture, supporting 350kW charging.

Since 2021, major international giants like Hyundai and Kia, along with domestic leaders such as BYD, Great Wall, GAC, and Xiaopeng, have launched 800V platforms. This high-voltage capability is now a key differentiator in the EV market.

The Challenge: Isolation & Safety

Unlike conventional internal combustion vehicles, hybrid and electric vehicles are composed of complex high-voltage electrical modules. Automotive safety standards require a continuous Internal Insulation Detection System to ensure the chassis is fully isolated from the high-voltage battery.

To ensure this detection system functions correctly, it must switch or disconnect from the high-voltage bus with absolute reliability. This requires a switching component with high isolation voltage, low leakage, and long life.

Why Dry Reed Relays?

Although solid-state switches exist, MiRelay Dry Reed Relays offer distinct advantages for isolation detection:

Linear Capacitance: Unlike semiconductors, reed relays do not change capacitance with temperature.
Pico-Ampere Leakage: Ensures accurate measurement of isolation resistance.
Fast Switching: Up to 1ms response time.
Reliability: No internal wear components, ensuring millions of operations.