POWER
Evaluating single-stage OBC topologies for next-generation EVs
As consumers demand faster charging, longer ranges and more cost- effective EVs, the role of the on-board charger (OBC) in the battery lifecycle has never been more critical. By Betty Guo, staff channel marketing Specialist, Renesas
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raditionally, EVs use a two-stage OBC architecture because it separates grid- side power quality control from battery-side isolation and regulation. The front-stage power factor correction (PFC) rectifier shapes the AC input and produces high-voltage DC, while the rear-stage isolated DC/DC converter provides galvanic isolation and conditions the voltage for safe battery charging. However, as 800V platforms become mainstream and power ratings climb to 11kW and beyond, limitations including bulk, inefficiency and cost have become increasingly apparent.
The two-stage OBC: A mature but constrained design
The two-stage OBC is the industry’s workhorse. Its front-stage PFC converts AC grid power into a stable DC bus voltage while achieving a power factor above 0.99 and total harmonic distortion below five per cent, helping the system comply with international grid standards. Interleaved totem-pole PFC topologies using silicon carbide (SiC) or gallium nitride (GaN) devices are common
because they offer high efficiency, although they require dedicated boost inductors and DC-link capacitors.
The isolated DC/DC stage then converts the DC bus voltage to the level required by the traction battery—typically approximately 500V to 900V for an 800V system—while providing galvanic isolation. LLC resonant converters are widely used for high efficiency, while dual active bridge topologies support bidirectional operation for Vehicle-to-Everything (V2X) applications.
Although mature, this architecture involves duplicated power devices, magnetic components and control circuits, increasing size, weight and bill-of-materials cost. Efficiency losses also accumulate: if each stage achieves 97 per cent efficiency, total system efficiency falls to approximately 94.1 per cent. Bulky electrolytic DC-link capacitors create an additional reliability bottleneck, with a typical lifespan of five to eight years. Large inductors, capacitors and separate thermal- management requirements also restrict power density, making it difficult to meet the compact packaging requirements of modern EVs.
The introduction of single-stage OBC DC/DC
Two-Stage Converter
Single-stage OBC DC/DC converters address these limitations by integrating PFC and isolated DC/DC conversion into one
power-conversion stage. This eliminates the intermediate DC bus and several associated components.
Matrix converter-based designs use bidirectional GaN switches to reduce DC- link energy storage significantly, enabling very high power density but requiring advanced control algorithms. Wide-bandgap semiconductors are key enablers of this architecture. SiC and GaN devices support higher switching frequencies—with GaN operating at frequencies of up to 900kHz— while reducing switching losses and allowing the use of smaller magnetic components.
Advantages of single-stage OBC DC/DC converters
Single-stage converters can deliver important improvements in efficiency, size, cost and functionality, helping address the requirements of next-generation EV platforms.
Unprecedented power density Eliminating the DC-link capacitor, boost inductor and other redundant components
Power Grid 24 SEPTEMBER 2026 | ELECTRONICS FOR ENGINEERS
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