Schottky diodes start to motor
Schottky barrier diodes (SBDs) operating at 200 V and with low leakage current are being increasingly used for hybrid and full electric powertrains and inverters (writes Nick Flaherty).
There is currently a strong effort towards mechanical integration in 48 V hybrid drive systems, by combining the motor and peripheral circuits in a single module. This requires highly efficient and high-voltage SBDs capable of stable operation at high temperatures, as well as devices that operate at 200 V.
The latest SBDs have these characteristics, enabling them to replace fast recovery diodes (FRDs) and rectifier diodes, which consume more power. The higher efficiency of SBDs means they are expected to replace conventional rectifier diodes and FRDs in automotive power supplies that are exposed to high temperature.
However, one drawback is that they have higher power losses at higher operating temperatures, which can lead to thermal runaway.
The RBxx8 series from Rohm, for example, therefore uses a barrier metal that is optimised for high temperatures and which significantly improves the IR leakage characteristic – the most important challenge when using SBDs in automotive power supplies. That ensures safe operation at high temperatures in automotive and industrial applications, and eliminates the possibility of thermal runaway.
The SBDs have 11% better forward voltage than conventional FRDs, reducing the power losses and allowing smaller package designs as less heat is generated. Rohm is currently developing medium-power packages, and plans to decrease the mounting area by as much as 71% by replacing 5.9 x 6.9 mm FRDs with 2.5 x 4.7 mm products.