Why are SiC devices not yet replacing IGBTs?
The production process and technology of silicon carbide (SiC) devices have become increasingly mature, and the biggest obstacle to market promotion is cost. This includes the cost of R&D and production costs as well as the drive capacitor resistance in the entire circuit after the SiC device is replaced by the IGBT. Unless the manufacturer pushes, it does reduce costs and improve performance. After all, adopting new things will cost a lot. Affected by manufacturing costs and product yield, the main reason for hindering the large-scale entry of SiC products into the market is that it is expensive, generally about 10 times that of similar Si products. Although in the future, with the improvement of technology and cost, the replacement of IGBT by silicon carbide (SiC) device is inevitable silicon carbide (SiC) device, and its performance may be very powerful, but it can become a big trend not only in performance but also in cost and reliability. Multiple guarantees on reliability.
The application advantages of silicon carbide devices are obvious
High efficiency, high reliability: SiC BJT products enable high efficiency, current density and reliability, and can operate at high temperatures smoothly. In addition, SiC BJT has excellent temperature stability, and its characteristics at high temperatures do not differ from those at room temperature. SiC BJT actually has the advantages of all IGBTs and solves all bottlenecks in the design of IGBTs. Since IGBT is voltage driven, SiC BJT Is current driven, design engineers use SiC BJT replaces IGBTs, which may not be accustomed at first, but device suppliers, such as Fairchild, generally provide reference designs to help engineers design drive lines. In the future, after the introduction of dedicated driver chips in this area, SiC will be used. BJT will be more simplified.
Low loss, lowering costs
The Vce of SiC BJT is reduced by 47%, Eon is reduced by 60%, and Eoff is reduced by 67%. SiC BJT offers the lowest conduction loss on the market, with Ron less than 2.2 milliohms per square centimeter at room temperature. SiC BJT provides the smallest total loss, including driver losses. SiC BJT is the most efficient 1200V power transfer switch ever, SiC BJT achieves a higher switching frequency with lower conduction and switching losses than IGBTs (30-50%), enabling up to 40% output power boost in systems of the same size. 2KW booster circuit from 400V to 800V, when realized with silicon IGBT, can only achieve 25KHz switching frequency, and need to use 5 film capacitors, and use SiC When BJT is realized, not only the switching frequency can be 72KHz, but also only two film capacitors are needed. The size and inductance of the heat sink are reduced by one-third, and a smaller inductor can be used, thereby greatly saving the total BOM cost of the system. .
Improve the switching frequency of the power supply to achieve high frequency
The biggest disadvantage of the traditional IGBT is that the switching speed is slow and the operating frequency is low. When it is turned off, a current tail will cause a high turn-off loss. SiC The BJT switch speed is fast and no IGBT turn-off is the current tail, so the switching loss is very low. Under the same rated withstand voltage, the conduction internal resistance of SiC BJT is also higher than the VCE(sat) of IGBT. Come low, which can reduce conduction losses. SiC The best application for BJT is a power supply design with more than 3000W power. Many of these power supplies use IGBTs as switching devices to optimize cost and efficiency. Design engineer if using SiC BJT replaces the IGBT, which makes it easy to greatly increase the power switching frequency, thereby reducing the size of the product and improving the conversion efficiency. Due to the increase in frequency, the inductance and the number of capacitors required for the peripheral circuits can also be reduced in design to help save costs. SiC on the other hand BJT's switching speed is very fast, and it can be switched in <20nS, which is even faster than MOSFET, so it can also be used to replace MOSFET. Compared with bipolar IGBT devices, SiC BJT has a lower conduction internal resistance, which can further reduce conduction loss. SiC BJT's high temperature stability and low leakage are beyond IGBTs and MOSFETs. In addition, its internal resistance is a positive temperature coefficient change, which is easy to use in parallel for high-power power supply design.
