OBC Power Class Comparison: 3.3 kW vs 6.6 kW vs 11 kW vs 22 kW for Electric Vehicles

This article focuses on the AC grid interface and OBC power class selection. Battery voltage architecture (400 V, 800 V, 800 V+) and HV-HV DC/DC converter topology are related design dimensions covered separately. Grid specifications referenced are IEC 61851 (Europe) and SAE J1772 (North America); other regional standards apply, notably GB/T in China.

This article focuses on the AC grid interface and OBC power class selection. Battery voltage architecture (400 V, 800 V, 800 V+) and HV-HV DC/DC converter topology are related design dimensions covered separately. Grid specifications referenced are IEC 61851 (Europe) and SAE J1772 (North America); other regional standards apply, notably GB/T in China.

Example: a 22 kW OBC on a 7.4 kW home wallbox charges at 7.4 kW, not 22 kW. The OBC rating is a ceiling the vehicle can use — not the speed it always achieves.

Key point: charge speed = the lower of OBC rated power and available infrastructure power.

AC charging levels are defined by infrastructure standards — IEC 61851 in Europe, SAE J1772 in North America — in terms of voltage and maximum current. The OBC is the vehicle-side converter that converts AC grid power to regulated DC via two stages: a Power Factor Correction (PFC) stage on the AC side, and an isolated DC/DC conversion stage that adjusts the output voltage to match the battery voltage level and state of charge. Its power rating is a design choice made within the ceiling those standards permit.

All OBC power classes — from 3.3 kW to 22 kW — require an isolated DC/DC conversion stage. Liquid cooling is standard for high-power OBCs and is also common in PHEV OBC designs; a small number of low-power or special-use-case designs use air cooling.

OBC power class at a glance

How to choose your OBC

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  • B6/B8 three-phase PFC topology strongly preferred; bridgeless totem-pole PFC applies only to 3 × single-phase configurations
  • 1200 V switches can be used
  •  CoolSiC™ MOSFET (1200 V) is the dominant switch choice for PFC and DC/DC stage — targeting above 96% efficiency
  • Single-Stage Converter as new trend and alternative to classic two-stage converters for flat, compact designs and lower costs
  • Thermal management is one of the dominant design constraints; power density a critical challenge
  •  Liquid cooling architecture and power density targets should be defined at the architecture stage to prevent costly late-stage redesign
  •  Gate drivers: EiceDRIVER™ for SiC MOSFETs | EiceDRIVER™ for xEV applications
Hardware profile
Hardware profile
Hardware profile
Hardware profile
  • B6/B8 three-phase PFC topology strongly preferred; bridgeless totem-pole PFC applies only to 3 × single-phase configurations
  • 1200 V switches can be used
  •  CoolSiC™ MOSFET (1200 V) is the dominant switch choice for PFC and DC/DC stage — targeting above 96% efficiency
  • Single-Stage Converter as new trend and alternative to classic two-stage converters for flat, compact designs and lower costs
  • Thermal management is one of the dominant design constraints; power density a critical challenge
  •  Liquid cooling architecture and power density targets should be defined at the architecture stage to prevent costly late-stage redesign
  •  Gate drivers: EiceDRIVER™ for SiC MOSFETs | EiceDRIVER™ for xEV applications

How OBC power class affects topology, semiconductors, and thermal design

Choosing an OBC power class is not only a performance decision. It determines the power converter topology, semiconductor technology, thermal design, and regulatory compliance scope — all of which affect engineering timelines and system cost.

A single-phase OBC (3.3 kW or 6.6 kW) cannot be scaled to 11 kW or 22 kW simply by adding more switches. Moving to three-phase requires a fundamental change in converter architecture.

OBC power class is the primary filter in semiconductor selection.

Power losses scale with current squared. Key consequences:

  • A 22 kW OBC does not have twice the thermal challenge of an 11 kW design
  • Packaging density and thermal interface materials require careful engineering from the start
  • Liquid cooling architecture and power density targets should be defined at the architecture stage to prevent costly late-stage redesign

Moving to 11 kW or 22 kW adds compliance requirements:

  • IEC 61851-1 Mode 3: AC charging via dedicated infrastructure (applies across all power levels using dedicated EV supply equipment)
  • IEC 61000-3-12: Harmonic current limits for equipment drawing >16 A per phase (single-phase high-power OBCs fall under IEC 61000-3-2/3-4)
  • Bidirectional (V2G/V2H) designs: additional grid feedback certification required in some markets — applicable across all OBC power classes. See: Bi-directional on-board charging (OBC)

Plan for extended compliance timelines when specifying 11 kW or 22 kW OBCs.

A single-phase OBC (3.3 kW or 6.6 kW) cannot be scaled to 11 kW or 22 kW simply by adding more switches. Moving to three-phase requires a fundamental change in converter architecture.

OBC power class is the primary filter in semiconductor selection.

Power losses scale with current squared. Key consequences:

  • A 22 kW OBC does not have twice the thermal challenge of an 11 kW design
  • Packaging density and thermal interface materials require careful engineering from the start
  • Liquid cooling architecture and power density targets should be defined at the architecture stage to prevent costly late-stage redesign

Moving to 11 kW or 22 kW adds compliance requirements:

  • IEC 61851-1 Mode 3: AC charging via dedicated infrastructure (applies across all power levels using dedicated EV supply equipment)
  • IEC 61000-3-12: Harmonic current limits for equipment drawing >16 A per phase (single-phase high-power OBCs fall under IEC 61000-3-2/3-4)
  • Bidirectional (V2G/V2H) designs: additional grid feedback certification required in some markets — applicable across all OBC power classes. See: Bi-directional on-board charging (OBC)

Plan for extended compliance timelines when specifying 11 kW or 22 kW OBCs.

Common misconceptions about EV charging levels and OBC power ratings

Fact: Level 2 defines a voltage tier (230–400 V AC), not a fixed power level. A Level 2 circuit can deliver anywhere from 3.3 kW to 22 kW depending on the circuit breaker rating and the OBC power rating installed in the vehicle. An 11 kW OBC on a 7.4 kW Level 2 wallbox charges at 7.4 kW. "Level 2" describes the infrastructure; the OBC determines how much of that power is used.

Fact: Charge speed equals the lower of OBC rated power and available infrastructure power. A 22 kW OBC on a 7.4 kW wallbox charges at 7.4 kW; on a 22 kW three-phase supply it charges at 22 kW. The OBC power rating is a ceiling, not a fixed operating point.

Fact: These are fundamentally different architectures. With AC charging, the AC-to-DC conversion happens inside the vehicle via the onboard charger, and power is limited to up to 22 kW via a Type 2 (IEC 62196) connector. With DC fast charging, conversion happens inside the station — bypassing the OBC entirely — delivering 50 kW to 400 kW directly to the battery via CCS, CHAdeMO, or GB/T.

Frequently asked questions

An EV charging level and an onboard charger (OBC) power rating describe two different things: the charging level defines what the infrastructure can supply; the OBC power rating defines what the vehicle can accept. Charging levels — standardised by IEC 61851 in Europe and SAE J1772 in North America — specify the voltage tier and maximum current the supply equipment delivers. The OBC power rating is a vehicle-side design choice: the converter inside the car that converts AC grid power to regulated DC for the battery. A vehicle with a 22 kW OBC plugged into a 7.4 kW wallbox charges at 7.4 kW. The OBC sets the ceiling; the infrastructure determines how much of that ceiling is reached.

No. A 22 kW onboard charger can only draw as much power as the supply equipment allows. Charge speed equals the lower of two values: the OBC's rated power and the available infrastructure power. On a 7.4 kW home wallbox, the 22 kW OBC is limited to 7.4 kW — charging a 60 kWh battery in approximately 8 hours rather than the 3 hours it would achieve on a 22 kW three-phase supply. The OBC rating is a capability ceiling, not a fixed operating point. Full 22 kW throughput requires a three-phase 400 V / 32 A installation, typical in fleet depot and high-end residential settings.

The step from a 6.6 kW to an 11 kW onboard charger is a fundamental architecture change, not a component upgrade. A 6.6 kW OBC runs on a single-phase AC supply and uses a single-phase PFC topology — typically a bridgeless totem-pole stage. An 11 kW OBC requires a three-phase 400 V supply and a three-phase PFC topology such as a B6/B8 configuration or Vienna rectifier, which involves a completely different converter architecture. Semiconductor selection also shifts: at 6.6 kW, silicon MOSFETs remain competitive, though CoolSiC™ MOSFET starts to win on system efficiency. At 11 kW, 1200 V CoolSiC™ MOSFETs are the dominant choice, driven by the above-96% efficiency targets that three-phase designs demand.

Yes — OBC power class is the primary filter in semiconductor selection. At 3.3 kW, silicon MOSFETs and TRENCHSTOP™ IGBTs are cost-competitive because switching frequency requirements are modest. At 6.6 kW, CoolSiC™ MOSFET begins to win on total system efficiency depending on volume. At 11 kW and 22 kW, CoolSiC™ MOSFET (1200 V) is the preferred choice: higher switching frequency, lower switching losses, and reduced heat dissipation make SiC the enabling technology for meeting the above-96% efficiency targets and power density requirements of three-phase OBC designs.

Which OBC power class for your vehicle segment

From 3.3 kW single-phase to 22 kW three-phase OBCs, Infineon's CoolSiC™ MOSFET and CoolGaN™ families cover the full OBC power range — with EiceDRIVER™ gate driver ICs and reference designs for each topology.

 

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