Ordinary silicon diodes used in switched-mode power supplies lose up to 1% efficiency by not turning off immediately, but now STMicroelectronics is among the first companies to introduce silicon carbide (SiC) diodes that save this energy normally lost during switching.
The STPSC806D and STPSC1006D SiC Schottky diodes are especially useful in converters for solar power systems, where every fractional efficiency percentage is valuable. Power supplies for servers and telecom systems, which are operational round the clock, will also benefit from the cumulative savings of this apparently small improvement in efficiency. These diodes can also be used in motor controllers, which are deployed in large numbers worldwide, thereby saving the environmental impact of many thousands of Watts of generated energy.
Moreover, by saving the energy normally dissipated as heat by the silicon diode, the new SiC technology enables engineers to consider a lower maximum current rating for the diode. This allows smaller components to be used without sacrificing usable power. In high-power applications where heatsinks are normally used, these can also be made smaller leading to more compact power supplies delivering higher power density.
A further benefit for switched-mode power supply designers is that SiC diodes allow higher switching frequencies, which enable other components such as filtering capacitors and inductors to become smaller and less expensive, and consume less power.
SiC technology is able to deliver these benefits because no reverse recovery charge accumulates during the diode’s normal conduction period. When a conventional bipolar silicon diode is turned off, this charge must be dispelled by recombination between groups of charge carriers close to the diode junction. The current flowing during this recombination period is called the reverse recovery current. This undesired current, when combined with the voltage across associated semiconductor power switches, generates heat that will be dissipated by the switches. By eliminating this reverse recovery charge, SiC Schottky diodes have much lower switching losses across the board, leading to higher efficiency and lower heat dissipation.
The 8 A rated STPSC806D and 10 A STPSC1006D, for 600 V applications, are available in the TO-220AC package.
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