The automotive environment is one of the most severe environments for electronics. Today’s EV chargers designs proliferate with sensitive electronics, including electronic controls, infotainment, sensing, battery packs, battery management, electric vehicle point, and on-board chargers. In addition to the heat, voltage transients, and electromagnetic interference (EMI) in the automotive environment, the on-board charger must interface with the AC power grid, requiring protection from AC line disturbances for reliable operation.
Today’s component manufacturers offer multiple devices for safeguarding electronic circuits. Due to the connection to the grid, on-board charger protection from voltage surges using unique components is essential.
A unique solution combines a SIDACtor and a Varistor (SMD or THT), reaching a low clamping voltage under a high surge pulse. The SIDACtor+MOV combination enables automotive engineers to optimize the selection and therefore, the cost of the power semiconductors in the design. These parts are needed to convert the AC voltage into the DC voltage to charge the vehicle’s on-board battery charging.
Figure 1. On-Board Charger Block Diagram
The On-Board Charger (OBC) is at risk during EV charging due to exposure to overvoltage events that may occur on the power grid. The design must protect the power semiconductors from overvoltage transients because voltages above their maximum limits can damage them. To extend the EV’s reliability and lifetime, engineers must address increasing surge current requirements and lower maximum clamping voltage in their designs.
Example sources of transient voltage surges include the following:
Switching of capacitive loads
Switching of low voltage systems and resonant circuits
Short circuits resulting from construction, traffic accidents, or storms
Triggered fuses and overvoltage protection.
Figure 2. Recommended Circuit For Differential And Common Mode Transient Voltage Circuit Protection Using MOVs And A GDT.
A 20mm MOV is preferred for better reliability and protection. The 20mm MOV handles 45 pulses of 6kV/3kA surge current, which is much more robust than the 14mm MOV. The 14mm disc can only handle around 14 surges over its lifetime.
Figure 3. Clamping Performance Of The Little lnfuse V14P385AUTO MOV Under 2kV And 4kV Surges. The Clamping Voltage Exceeds 1000V.
Example selection determination
Level 1 Charger—120VAC, single-phase circuit: The expected ambient temperature is 100°C.
To learn more about using SIDACt or Protection Thyristors in electric vehicles, download the How to Select the Optimum Transient Surge Protection for EV On-Board Chargers application note, courtesy of Little fuse, Inc.
Post time: Jan-18-2024