On-Board Charger Rectifier Design: PFC and DC-DC, Two Different Mindsets

An on-board charger normally separates AC-input power-factor correction from isolated battery charging. Rectifier selection starts with the voltage and current seen in a specific circuit position. The input bridge, a boost diode, a synchronous switch, a traction-battery output, and a low-voltage auxiliary rail are different duties.

Last updated: October 16, 2026

Map the two conversion stages before selecting a diode

Draw the AC input, input rectification where used, PFC bus, isolation stage, and battery connection. Record normal and fault voltages, current direction, commutation, and protection for each semiconductor position. Bidirectional or totem-pole designs may use controlled switches where a conventional design uses diodes.

TI's PMP22650 reference design provides an example using totem-pole PFC and a full-bridge CLLLC stage with synchronous rectification. Its topology illustrates why an OBC component list cannot be inferred from the charger’s headline power alone.

Select the PFC blocking and commutation capability

A conventional boost PFC diode blocks the DC bus when the boost switch conducts. Its voltage rating must cover the actual bus and switching overshoot with the project’s required margin. Read recovery or capacitive behavior at the relevant current, voltage, temperature, and slew rate. A forward-drop comparison alone misses the interaction with the boost switch.

The application’s measured stress and the component’s guaranteed limits must be compared under compatible conditions. Treat the input bridge and the boost diode separately: their waveforms and switching requirements differ.

Keep high-voltage charging and low-voltage auxiliary conversion separate

An on-board charger’s isolated output may charge a high-voltage traction battery. It must not automatically be treated as a low-voltage, high-current auxiliary rail. Draw the transformer, rectification or synchronous-switching network, battery range, and reverse-blocking paths before choosing a voltage class.

In TI's PFC design comparison for on-board chargers, example boost stages with roughly 380–400 V output use suitably rated high-voltage rectification components. A 200 V or 250 V device is not suitable for a position that must block the full 400 V bus. Such a device can only be considered in a different, explicitly lower-voltage circuit position after its complete stress envelope has been established.

Allocate loss using the actual circuit waveforms

Estimate conduction loss from the device voltage-current behavior over the conducting intervals. Assess recovery, capacitive, switching, and drive loss in the positions where they occur. Avoid charging the same commutation energy to both the diode and switch and then adding it twice to the system budget.

Document whether each result describes one die, one leg, one stage, or the complete charger. Link each loss estimate to the thermal reference and mounting arrangement used for that device. The rectifier thermal guide develops the heat-flow calculation.

Validate the operating corners and qualification scope

Check input and battery-voltage extremes, load range, startup, shutdown, repeated events, and the temperature condition required by the project. Retain efficiency, waveform, EMI, protection, and thermal results with the component ordering codes and document revisions.

Device qualification and quality-system certificates have specific scopes. Neither a component’s voltage label nor a generic automotive description approves the complete charger. Confirm the required component evidence and system validation separately.