- 22 March 2006 -

Second-generation SiC Schottky from Infineon improve switched-mode power supplies

At the APEC (Applied Power Electronics Conference) trade show in Dallas Infineon Technologies AG introduced its second-generation Schottky diodes based on SiC technology.

With the new thinQ!™ 2G family, the company that pioneered SiC Schottky diodes enhances the unsurpassed switching behaviour of its previous generation.

“They enable system cost reductions for switched-mode power supply manufacturers,” said Dr. Gerald Deboy, principal technical marketing, Power Management & Supply at Infineon Technologies. “Reduced switching losses and higher switching frequencies allow the use of smaller, cheaper and fewer passive components and cost-effective transistors. We expect that our second generation will move the entry point for the use of SiC devices to significantly lower power levels.”

Silicon carbide is an ideal material for high-voltage-blocking power semiconductors. It provides a higher Schottky barrier and significantly higher electrical breakdown field strength compared to other Schottky diodes, and a thermal conductivity comparable with that of copper. These characteristics result in low leakage currents, low on-resistance and improved thermal behaviour. While silicon and gallium arsenide Schottky diodes only reach blocking voltages of about 200 to 250 volts, the voltage range of silicon carbide diodes can be extended to more than 1,000 volts, offering new system and topology options to the increasingly growing PFC market.

Unlike conventional silicon PIN diodes, SiC Schottky diodes show an absence of any reverse recovery charge and current during hard commutation. This results in very low switching losses, which is the prerequisite for high-frequency operation. In addition, switching performance is independent of forward current, switching speed and temperature. With the introduction of the second generation of the SiC Schottky diodes, the over-current and over-voltage characteristics are significantly improved through a merged PIN-Schottky structure.

The new SiC diodes have at least double the surge-current capability and improved ruggedness compared to the first generation. This allows them to handle higher start-up inrush and over currents and makes them ideal for PFC (Power Factor Correction) applications in SMPSs (switched-mode power supplies). Unlike other high-voltage SiC Schottky diodes, system designers and power supply manufacturers do not have to oversize the diode for a given application and can use smaller and cheaper diodes, which can result in a 30 to 50% reduction in diode costs and increased application ruggedness.

SiC Schottky diodes are ideal for PFC applications. The PFC market is highly constrained by legal requirements, such as the European EN61000-3-2 standard, which sets the harmonic limits for any off-line application having power consumption over 75W and basically requires the use of PFC. The potential worldwide active PFC device market is forecast (Source: Darnell Group 2006) to grow from approximately 1.2 billion units in 2006 to 2.1 billion units in 2011, a CAGR of 12.3%. There is an increasing need for PFC implementations in a wide spectrum of power supply products in computer, consumer, communications, lighting ballast and industrial applications.

Samples of Infineon's new SiC Schottky diodes are available with blocking voltages of 600 volts (4 A, 5 A, 6 A, 8 A, 2 x 5 A, 2 x 6 A, 2 x 8 A) in a compact TO (Transistor Outline) -220 package and in a TO-252 (D-Pak, MSL3) package. In quantities of 10,000 pieces, the SiC Schottky diode IDT04S60C (4A) is priced at less than Euro 1.50 (US $1.80) per unit.

Boost converters are usually used to achieve active PFC. There are essentially two implementation approaches: DCM (Discontinuous Current Mode) or CCM (Continuous Current Mode). The CCM solution requires an extremely fast diode but offers many advantages, such as significant reduction of the highest occurring currents, which makes it feasible to use smaller passive system components, power switch circuits and simpler EMI filters. SiC Schottky diodes are ideally suited to CCM PFC applications, since they provide the required higher operating voltages compared to other Schottky diodes and do not exhibit reverse recovery and the related high power losses of silicon diodes. This also allows a less expensive MOSFET to be chosen which results in lower system cost. Using Infineon’s SiC Schottky diodes in PFC applications, power designers benefit from higher switching frequencies, reduced size and number of passive components, shrinking or avoiding heat sinks, increased reliability, higher power density and increased efficiency.

Web: http://www.infineon.com/sic