An OBC is a power device where the power grid (AC), the vehicle's high-voltage battery (DC 300–800V), and the vehicle's 12V low-voltage ECU converge. The surge sources are from the power grid side, the vehicle's high-voltage side, and the vehicle's low-voltage side, with completely different energy levels, waveforms, and damage paths. This can cause power device breakdown, insulation breakdown, control chip damage, overall device failure, and high-voltage safety hazards.

I. Three Major Surge Sources and Waveform Standards

  1. AC Grid Surge (Most Severe, Highest Energy)

Scenery Occurrence:

  • Indirect lightning-induced surges (outdoor charging piles, lightning coupling in residential power distribution);
  • Switching of large inductive loads on the power grid (transformers, reactive power compensation capacitors);
  • Power grid short circuits, fuse tripping, neutral wire disconnection causing overvoltage rise.

Standard Waveform (GB/T 17626.5 / IEC 61000-4-5)

  • Open Circuit Voltage: 1.2/50μs; Short Circuit Current: 8/20μs;
  • Standard vehicle-mounted OBC AC port requirements: ±2kV (Level 3), outdoor fast charging OBC requires ±4kV (Level 4);
  • Common mode (L-PE/N-PE) and differential mode (L-N) must withstand high-energy surges; single pulse energy can reach hundreds of joules.

Intrusion Path

AC Input → EMI Filter → PFC Pre-stage Rectifier Bridge → PFC MOS/Diode → DC Bus Capacitor → Rear-stage DC-DC → Power Battery.

  1. On-board High-Voltage DC-Side Surge (Transient High-Voltage Circuit Inside the Vehicle)

Scenarios

  • High-voltage contactor engagement/disengagement, pre-charge circuit operation;
  • Battery pack internal BMS relay disconnection, motor controller start/stop coupling;
  • Long cable inductance + bus capacitor form LC oscillation high-voltage spikes;
  • Grid surges are conducted to the high-voltage DC bus via AC/DC coupling.

Standard Basis

ISO TS 7637-4 (New Energy High-Voltage Transients), surge spikes can reach 2~3 times the nominal voltage (800V platform instantaneous impact 1600–2400V).

Risk Characteristics

Large-capacity film capacitors on the DC bus, SiC MOS, and high-frequency transformer primary windings are the main targets of damage.

  1. Vehicle-mounted 12V Low-voltage Control Side Surge (Control Board, CAN/LIN Communication)

Scenarios:

  • Vehicle 12V loads: Compressor, water pump, wiper motor power failure back EMF;
  • ISO 7637-2 pulse 1/2/3a/3b negative high-voltage transient (-100V~-150V);
  • High-voltage surges are coupled to low-voltage control ground through isolation capacitors and PCB distributed capacitance;
  • CAN bus cable inductively coupled surges.

Hazard Characteristics:

Low energy, high-speed steep edge; does not burn out power transistors, but directly damages the MCU, driver IC, CAN transceiver, and operational amplifier, resulting in system blackout, uncontrolled charging, and communication loss.

II. Four Core Risks Caused by Surges

Permanent Damage to Components (Hardware Failure)

  • Semiconductors: Breakdown of MOS, SiC, diodes, driver ICs, and CAN chips;
  • Passive Components: Short circuits in safety capacitors, bus capacitors, and inductor turns; varistors exploding;
  • PCB: Creepage breakdown between high-voltage and low-voltage traces; copper foil burning.

Functional Safety Risks (Vehicle Failure, Battery Risk)

  • Surges causing sampling distortion → uncontrolled output voltage, overcharging of the power battery, bulging, and thermal runaway;
  • High- and low-voltage insulation breakdown → vehicle insulation fault alarm, high-voltage interlock disconnection, vehicle breakdown;
  • Control chip malfunction → charging cannot be stopped, continuous high current damages the wiring harness.

EMC / Regulatory Failure Risks

National standards GB/T 18487.1 and GB/T 17626.5 mandate surge immunity. Without graded protection, the following risks may occur:

  • Surge test shutdowns and hardware damage (Class D/E, failure);
  • Excessive common-mode surge leakage current, leading to false alarms in insulation monitoring;

Long-term reliability degradation (latent aging);

  • MOV varistors experience increasing leakage current year by year, with accelerated aging at high temperatures;
  • Film capacitors suffer internal micro-breakdowns, resulting in gradual capacitance decay;
  • Transformer insulation suffers cumulative damage, leading to decreased insulation resistance after long-term use.

III. Surge Protection Solutions from Semiware

Surge Risks and Solutions for OBC Electric Vehicle On-board Chargers-Protection Devices-TVS Diodes-ESD Protection devices-Gas Discharge Tube-Thyristor-Pled Protectors-Mov

Learn More

For more details on OBC on-board charger surge protection solutions, please visit: https://en.semiware.com/applications/on-board-charger/