Semiconductor devices across EV power conversion stages

Written by

Irina Kulkarni

Power Semiconductors Editor

19 Oct 20267 min read

An electric vehicle moves energy through several conversion stages before it reaches the wheels or the vehicle’s auxiliary loads. Understanding these EV power conversion stages and semiconductor devices helps engineers connect each circuit’s function to its voltage, current, switching, and thermal requirements.

How EV power conversion stages work together

The high-voltage battery stores energy as DC. During driving, a traction inverter converts that DC into controlled AC for the motor. During charging from an AC supply, the onboard charger converts incoming AC into DC suitable for charging the battery. A separate DC-DC converter typically supplies lower-voltage vehicle systems from the high-voltage bus.

These stages do different jobs, but they share a common purpose: regulate the flow of electrical energy. Power electronics in an EV control voltage and current so that energy is delivered in the form and at the level each load requires. In the traction system, that means controlling motor torque and speed. In charging, it means managing power transfer to the battery. In auxiliary conversion, it means supplying vehicle loads while separating their voltage requirements from the traction battery.

Switches and rectifiers are central to this process. A semiconductor switch turns on and off under control to shape current or voltage. A rectifier conducts current in the required direction, converting AC to DC or providing a path for current in a switching circuit. Their roles depend on the circuit topology and operating mode; they are not interchangeable in every design.

A system-level view also helps when evaluating high-voltage SiC diodes. A diode’s role in a particular converter depends on the circuit, operating conditions, and electrical requirements—not simply on the fact that the vehicle has a high-voltage battery.

Semiconductor devices in the traction power stage

The traction inverter is the power stage between the battery and the electric motor. It uses controlled semiconductor switches to convert the battery’s DC into a sequence of AC currents. By controlling the switching pattern, the inverter regulates the motor’s electrical output and therefore its torque and speed.

The switch must withstand the voltage across it when it is off and carry current when it is on. Switching frequency and operating conditions affect switching losses, while conduction losses depend on current and the device’s conduction characteristics. Both contribute to heat that the thermal design must remove.

During regenerative braking, the motor operates as a generator. Energy flows from the motor back through the inverter toward the battery. The inverter’s switching devices manage this reverse power flow, while diodes or other rectifying paths can conduct current as part of the circuit’s operation. The exact current paths depend on the inverter design and control strategy.

For an EV power electronics design, device choice cannot be made from a voltage rating alone. Engineers also need to account for current, switching behavior, package, cooling, transient conditions, and the required operating margin. Our guide to EV component selection discusses how to organize those criteria when comparing candidate devices.

Power conversion during onboard charging

An onboard charger (OBC) converts AC from a charging source into DC for the vehicle battery. Its power stage needs to manage the incoming voltage and current, then control the DC output in coordination with the battery-charging system. Circuit designs vary, so there is no single switch or rectifier arrangement that applies to every OBC.

Rectifiers provide AC-to-DC conversion, while controlled switches regulate energy transfer through the charger’s conversion stages. Depending on the design, the charger may also include power-factor correction and an isolated DC-DC stage. Those functions shape how the input current is drawn and how energy is transferred to the battery.

The semiconductor requirements follow from the charger’s input and output conditions, switching frequency, power level, thermal path, and package constraints. Comparing devices for an OBC therefore means looking beyond a headline voltage or current rating to the operating conditions and losses in the intended circuit. For a closer look at switch selection, see our guide to power electronics MOSFETs.

Auxiliary converters for vehicle electrical loads

The high-voltage battery is designed to supply the traction system, but many vehicle loads require lower-voltage power. A DC-DC converter transfers energy from the high-voltage bus to a lower-voltage electrical system. Its output supports auxiliary functions such as control electronics, lighting, and other vehicle loads.

This converter has its own design constraints. The input voltage range must suit the high-voltage bus, while the output must remain within the requirements of the connected loads. Engineers also consider output-current demand, transient response, isolation requirements where applicable, switching losses, and heat removal.

Auxiliary conversion should not be treated as a minor version of the traction inverter. Its power level and load profile may be different, and its design priorities can differ too. The right semiconductor depends on the converter topology and the voltage, current, switching, package, and thermal conditions it must meet.

Choose semiconductor devices for each conversion stage

Device selection starts with the stage and its electrical operating envelope. Silicon MOSFETs, SiC MOSFETs, and diodes each have distinct roles and tradeoffs; no material or device category is automatically the right choice for every EV converter.

Silicon MOSFETs may be considered where their ratings and switching characteristics fit the design. SiC MOSFETs are often evaluated in higher-voltage or high-efficiency conversion designs, but suitability still depends on the specific circuit and operating conditions. Diodes may provide rectification or freewheeling paths, with the required voltage, current, recovery behavior, and thermal performance shaped by their position in the circuit.

For each candidate, check:

• Voltage rating against the bus voltage and expected transients, with appropriate design margin.
• Current capability under the actual conduction and switching conditions.
• On-state and switching losses, which contribute to device temperature and cooling demand.
• Switching behavior and the effect of the device on converter efficiency and electromagnetic design.
• Package, mounting, isolation, and thermal-interface requirements.
• Datasheet conditions, including how ratings and thermal parameters are specified.

The same device specification can have different implications in different stages. A traction inverter may face demanding motor-current and transient conditions; an OBC is governed by its AC input, charging output, and converter topology; an auxiliary converter must satisfy its lower-voltage output and load profile. Compare devices against the stage’s real requirements rather than selecting from a generic EV component list.

Use stage requirements to guide device selection

The useful starting point for selecting EV power semiconductors is a defined conversion stage, not a material preference. Map the voltage range, current profile, switching conditions, transient requirements, package constraints, and thermal path for the traction inverter, onboard charger, or auxiliary converter.

Then compare candidate devices using their datasheets and the circuit’s operating conditions. This approach makes tradeoffs visible: a device that meets a voltage requirement may still be unsuitable if its package, losses, or thermal performance do not fit the design. For engineers assessing EV power conversion stages and semiconductor devices, stage-by-stage requirements provide a clearer basis for evaluating silicon switches, SiC devices, and rectifiers.

About the author

Irina Kulkarni

Power Semiconductors Editor

Irina Kulkarni writes about power semiconductor technologies and their role in efficient power conversion. She has a background in electrical engineering and experience evaluating silicon carbide devices for high-voltage applications. Her coverage includes SiC diodes, MOSFETs, device selection, and practical design considerations for engineers working on EV, renewable energy, and data centre systems. She aims to make technical guidance precise, useful, and grounded in real design trade-offs.

SiC diode selectionSiC MOSFET applicationsHigh-voltage power conversionDevice thermal and switching performanceEV and renewable energy power systems