I. What is an On-Board Charger (OBC)?
Serving as a critical bridge connecting the power grid to the vehicle's traction battery, the On-Board Charger (OBC) is responsible for converting Alternating Current (AC)—sourced from home outlets or public charging stations—into Direct Current (DC) to charge the high-voltage battery pack.
II. Electrical Risks Facing the OBC
| Risk Category | Main Sources | Impact Path | Typical Consequences |
| Surge / Lightning-Induced Surge | Grid switching operations, lightning-induced surges, industrial power grid fluctuations | Conducted from AC input side into rectifier and PFC stages | Rectifier bridge breakdown, power MOSFET damage, PFC stage failure |
| Electrostatic Discharge (ESD) | Charging gun interface, AC input port, chassis coupling paths | Coupled through interfaces or enclosure into control and communication circuits | Control IC malfunction, communication errors (CAN/PLC), reset or system crash |
| Common-Mode Transient Interference (CMTI) | High dv/dt switching in SiC / GaN systems, ground bounce noise | Coupled into control and gate drive circuits via parasitic capacitance | False triggering, gate drive malfunction, reduced system stability |
| Insulation & Breakdown Risks | 800V high-voltage platforms, insufficient PCB creepage distance, inadequate device voltage rating, surge energy accumulation | Weak insulation points between high-voltage and low-voltage domains | Dielectric breakdown due to insufficient creepage distance, device failure, system shutdown |
III. Why is the OBC a "High-Risk Node" in the EV Power System?
In an Electric Vehicle (EV), the On-Board Charger (OBC) connects directly to both the AC power grid (220V / 380V) and the vehicle's high-voltage battery system (400V / 800V). This means the OBC is simultaneously exposed to:
Surge transients from the power grid side
High-voltage switching interference from the vehicle side
Coupled effects from external lightning strikes and ESD
Consequently, the OBC constitutes one of the most vulnerable and sensitive links within the EMC (Electromagnetic Compatibility) chain.
IV. Core Protection Strategy for OBCs: A Multi-Stage Energy Dissipation Architecture
Referencing a typical OBC architecture (as illustrated), the primary points requiring protection include:
- L1/L2/L3 Input Terminals
- AC/DC Conversion Stage
- High-Voltage DC Link
- Battery-Side Control Interface
The protection strategy follows a specific sequence: first, dissipate high-energy transients; second, clamp the voltage levels; and finally, provide fine-grained protection for the integrated circuits (ICs).
V. Analysis of Semiware's Protection Solutions ((MOV + GDT Coordinated Protection))
| Section | Device | Role / Position | Key Functions | Advantages / Design Notes |
| Primary Protection Stage | GDT (Gas Discharge Tube) | AC input front end | Absorbs kA-level surge current; Diverts lightning energy directly to ground; Reduces stress on downstream components. | Extremely high surge handling capability; Ultra-low leakage current; Long service life; Key selection focus: 8/20 µs & 10/350 µs surge performance, low capacitance, high repetitive surge endurance. |
| Secondary Protection Stage | MOV (Metal Oxide Varistor) | L-N / L-G / DC side | Fast overvoltage clamping; Limits residual surge voltage after GDT conduction; Protects rectifier and PFC stages. | Fast response (ns level); Cost-effective; Easy to integrate; Selection focus: voltage rating matched to 400V / 800V systems, energy absorption (J-level), low leakage preferred. |
In this solution:
- The MOV (Metal Oxide Varistor) is responsible for rapidly clamping voltage transients, thereby protecting the downstream rectifier bridge and PFC (Power Factor Correction) circuits;
- The GDT (Gas Discharge Tube) is responsible for dissipating high-magnitude currents and providing isolation against DC bias voltages;
- By combining these two components, the solution achieves a synergistic protection effect where the combined result is greater than the sum of its parts—effectively demonstrating that "1 + 1 > 2."
VI. Design Recommendations
| Topic | Key Requirements | Engineering Considerations |
| MOV Selection | System voltage compatibility (400V / 800V) | Must match system voltage level; Prioritize energy rating (Joule level); Lower leakage current improves efficiency and thermal stability. |
| GDT Selection | High surge robustness & EMI compatibility | Must support 8/20 µs and 10/350 µs surge waveforms; Low capacitance to avoid EMI impact; High repetitive surge capability ensures long-term reliability. |
| PCB Layout Design | Minimize parasitic effects and improve surge discharge efficiency | Place GDT as close as possible to AC input terminal; Ensure MOV and GDT form the shortest possible discharge loop; Avoid routing high dv/dt paths near control/communication circuits to reduce coupling risk. |
Conclusion
The On-Board Charger (OBC) serves as the core component for energy replenishment in electric vehicles. Given the complexities and variability of power grid environments, implementing a scientifically sound circuit protection design is of paramount importance.
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Should you encounter any issues during your OBC design process, please feel free to contact us for technical support or sample testing services. Leveraging our extensive experience in industry applications, we will provide you with highly reliable and customized protection solutions.
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