Electronic Design

Silicon Carbide Promise Turning Into Reality

The electrical properties of silicon carbide (SiC) make it an ideal material for power semiconductors. SiC power semiconductors, which have been under development and discussed at technical conferences for many years, are now a reality for the power electronics industry. The first devices released to the market are SiC Schottky diodes with breakdown voltages up to 600 V, compared to silicon Schottky diodes that have breakdown voltages up to 200 V.

SiC Schottky diodes have essentially no reverse recovery current, and the minimal amount of capacitive current present in turn-off is independent from temperature, forward current, and di/dt. This results in virtually no switching losses for the rectifier and substantially lessens switching losses in the switch. These features enable SiC Schottkys to replace silicon fast-recovery PiN diodes as the boost diode in the power-factor-correction (PFC) stage of switch-mode power supplies, where switching losses are critical. The result is a smaller, more efficient PFC stage and a more efficient power supply.

The development work continues on additional SiC products, which leverage the characteristics of the material and will open up new opportunities for design engineers. Within 12 to 24 months, SiC Schottky diodes with higher breakdown voltages and higher current ratings should be released. The next step would be a Schottky with a 1200-V breakdown voltage. These devices would target applications such as the anti-parallel diode for high-frequency inverters, snubber diodes for high-current IGBT inverters, the boost diode for 480-V input PFC, and high-voltage multipliers.

The initial testing of SiC Schottky diodes as the anti-parallel diode in a 5-hp (horsepower) motor drive shows a reduction in turn-on losses in the silicon IGBT of 30% to 45%. At the same time, the losses in the diode are reduced by up to 80%. Reducing these losses will enable smaller, more efficient motor drives.

Today, 600-V SiC Schottky diodes come in current ratings up to 10 A with a single die and 20 A in a single package. SiC Schottky diodes have a positive temperature coefficient on forward voltage, which makes parallel operation of these devices relatively easy. Higher-current SiC Schottky diodes are being considered both as single- and multiple-die packages as the anti-parallel diode in high-current, high-frequency inverters, as well as in hybrid electric vehicles.

Based on the system designs currently in production with SiC Schottky products and the interest in the future potential products, SiC is becoming widely accepted in the power electronics industry as a device technology for the future.

TAGS: Components
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