On-Board Charger (OBC)

Whether a car is a battery electric vehicle (BEV) or plug-in hybrid electric vehicle (PHEV), one critical component is the on-board charger (OBC). This enables the charging of the high-voltage DC battery packs from various electric vehicle service equipment (EVSE) or charging stations. Those range from single-phase Level 1 residential chargers (~3 kW) to multi-phase Level 2 commercial capable of providing up to 22 kW, supporting both 400 and 800 V batteries. Of course Level 3 fast chargers provide a DC voltage direct to the battery, bypassing the OBC. However, a small highly efficient form factor is required to give manufactures the flexibility to place the OBC in different locations in various models.

Block diagram

Highlighted components are Nexperia focus products

Design considerations

  • Designers have multiple options for OBC conversion topologies, including single-phase / multi-phase and uni- / bidirectional 
  • Current batteries are typically 400 V, using 650 V FETs in a bidirectional OBC topology where GaN brings the highest efficiencies (for unidirectional topologies SiC diodes can be used on the secondary side
  • For 800 V batteries, need to go multi-level GaN or high-voltage SiC
  • However OBC topologies are heavily fragmented which may lead to combined 650 / 1200 V device solutions
  • PFC output defines blocking voltage of power semiconductors at DC-DC-Input and battery voltage defines blocking voltage at DC-DC-Output (650 or 1200 V)  
  • Trend towards higher OBC charging power and 800 V batteries for higher class BEV solutions, will require more 1200 V solutions

MOSFET and GaN FET Handbook

Drawing on over 20 years’ of experience, the MOSFET and GaN FET Application Handbook: A Power Design Engineer’s Guide brings together a comprehensive set of learning and reference materials relating to the use of MOSFETs and GaN FETs in real world systems.

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