Diotec Semiconductor AG

https://www.diotec.com/

Jul 2, 2026

Beyond Efficiency: Why Rectifier Selection Is Also a Thermal Design Decision

Power electronics designers often focus on switching losses and converter efficiency. Yet one of the most persistent sources of power dissipation in an AC-DC front end is far less conspicuous: the conduction losses of the bridge rectifier.Unlike transient events or overload conditions, these losses occur continuously whenever the converter is operating. They do not trigger protection mechanisms or generate fault messages, but they contribute to the thermal budget throughout the entire operating lifetime of the system.

Small Voltage Differences, Significant Power Savings

In a conventional full-wave bridge rectifier, two diodes conduct during each half cycle of the AC waveform. The forward voltage drop of these diodes therefore has a direct impact on the total power dissipated.

At a load current of 10 A, a standard silicon bridge rectifier with a forward voltage of approximately 1.1 V dissipates around 22 W across the bridge. A low-forward-voltage bridge with a typical forward voltage of 0.9 V reduces this value to approximately 18 W.

A reduction of 4 W may appear modest at first glance. However, this power is dissipated continuously - during every operating hour and in every system deployed in the field.

Heat Affects More Than the Rectifier

The energy saved by reducing the forward voltage does not simply improve the efficiency figure - it also reduces the amount of heat generated on the PCB.

Bridge rectifiers are typically located close to the input stage, where electrolytic capacitors are commonly placed. As a result, the heat generated by the rectifier directly influences the local thermal environment of these neighbouring components.

This interaction is often overlooked because it is not visible in the electrical schematic. Nevertheless, it plays a significant role in the thermal behaviour of the assembled power supply.

Lower Temperature Can Extend Component Lifetime

Electrolytic capacitors are particularly sensitive to operating temperature. Their expected service life decreases significantly as temperature increases. A commonly accepted engineering guideline states that every 10 K increase above the rated operating temperature approximately halves the expected lifetime of an electrolytic capacitor.

Reducing the thermal load generated by the bridge rectifier therefore benefits more than the rectifier itself. Lower local temperatures can contribute to improved reliability and longer operational lifetime of surrounding components, particularly in compact power supply designs.

A System-Level Design Decision

Selecting a bridge rectifier is often viewed primarily as an electrical design choice based on voltage and current ratings. In reality, it is also a thermal design decision.

Lower forward voltage reduces continuous conduction losses, decreases PCB heating, and helps improve the thermal operating conditions of the entire input stage. These effects can simplify thermal management while contributing to higher system reliability over the product lifetime.

Looking Beyond the Schematic

Conduction losses rarely receive the same attention as switching losses because they are neither dynamic nor associated with fault conditions. Nevertheless, they are present during every operating cycle.

When evaluating bridge rectifier technologies, engineers should therefore consider not only electrical performance, but also the thermal impact on the complete system. The consequences of rectifier selection may not be immediately visible in the schematic - but they are always reflected in the temperature distribution across the PCB.