Overview

An electric vehicle (EV) on-board charger (OBC) is directly connected to both the AC power grid (220V/380V) and the vehicle’s high-voltage DC battery (400V/800V) during operation. It is susceptible to threats such as lightning surges, switching transients, and electrostatic discharge (ESD), necessitating a robust surge protection design.

1. AC Input Protection (Grid Interface Side)

Primary threats:

Lightning surges, grid voltage spikes, and power-frequency transient overvoltages.

Common protection components:

  • Fuses: Provide overcurrent protection, preventing sustained short circuits in the event that a surge damages other components.
  • Common-mode/differential-mode inductors + X/Y capacitors: Filter out high-frequency interference and improve electromagnetic interference (EMI) suppression.
  • Metal-oxide varistors (MOVs): Absorb lightning surges; common types include 14D/20D models with ratings of 470V–820V (depending on the grid voltage level).
  • Gas discharge tubes (GDTs): Serve as the first line of defense against high-energy lightning surges by shunting current to the ground.
  • Thermistors (NTC/PTC): Suppress inrush current during power-up, protecting the rectifier bridge.
  • Rectification and PFC Circuit Protection

2. Rectification and PFC Circuit Protection

Primary threats:

High dv/dt (rapid voltage change) and inductive flyback surges.

Common protection components:

  • TVS diodes: Protect the gates and drain-source junctions of power switching devices (MOSFETs/IGBTs) from transient overvoltages.
  • RC snubber circuits: Absorb voltage spikes across switching devices and rectifier bridges.
  • Diode reverse protection: Suppress surges caused by inductive flyback.

3. DC/DC Conversion and Output Protection (High-Voltage Battery Interface Side)

Primary threats:

Surges fed back from the battery side and inductive switching spikes.

Common circuit protection components:

  • High-voltage TVS diodes: Protect the OBC output port (e.g., the SM8S series, capable of withstanding 600W–1500W surges). TVS diodes in parallel with the drain-source terminals of power MOSFETs/IGBTs: Provide rapid clamping of voltage spikes.
  • Fuses at the battery interface: Prevent overcurrent into the battery in the event of an OBC (On-Board Charger) failure.

4. Protection for Communication and Control Interfaces (CAN / LIN / Signal Lines)

Primary threats:

Electrostatic Discharge (ESD) and lightning-induced surges.

Commonly used protection components:

  • Low-capacitance ESD diode arrays: Protect CAN/LIN signals to prevent communication interruptions.
  • Common-mode chokes: Filter out common-mode noise.

Semiware Recommended Protection Circuit Solutions

Summary

Surge protection for On-Board Chargers (OBCs) typically employs a multi-stage protection scheme:

  • Input side: GDT + MOV + EMI filtering + Fuse
  • Power stage: TVS + Snubber circuit
  • Output side: High-voltage TVS + Fuse
  • Communication ports: ESD suppressors + Common-mode chokes
  • This approach ensures comprehensive protection against lightning-induced surges, power-frequency transient overvoltages, and electrostatic discharge.

Learn More

The above information outlines the surge protection solutions recommended by Semiware for EV On-Board Chargers. For further details, please contact our engineers or explore our available reference designs at https://en.semiware.com/applications/on-board-charger/.