Why can't SiC devices replace IGBT?
The production process and technology of silicon carbide (SiC) devices are becoming more and more mature. At present, the biggest obstacle to market promotion is the cost. Including research and development and production costs, and the cost of driving capacitors and resistors in the whole circuit after silicon carbide devices replace IGBT in application. Unless the manufacturer pushes it, and it can really reduce the cost and improve the performance. After all, it will cost a lot to adopt new things. Due to the influence of manufacturing cost and product yield, the main reason hindering SiC products from entering the market on a large scale at present is the high price, which is generally about 10 times that of similar Si products. Although it is inevitable that silicon carbide (SiC) devices will replace IGBT with technological progress and cost reduction in the future, and the performance may be very strong, it is not only the performance, but also the cost and reliability that can really become the general trend.
The application advantages of silicon carbide devices are obvious.
High efficiency, high reliability: SiC BJT products can achieve high efficiency, high current density and high reliability, and can work smoothly at high temperature. In addition, SiC BJT has excellent temperature stability, and its working characteristics at high temperature are no different from those at normal temperature. In fact, SiC BJT has all the advantages of IGBT and solves all the bottlenecks in IGBT design. As IGBT is driven by voltage and SiC BJT is driven by current, design engineers may not be used to replacing IGBT with SiC BJT at first, but device suppliers such as Fairchild Semiconductor generally provide reference designs to help engineers design driving circuits. With the introduction of special driver chips in the future, it will be easier to use SiC BJT.
Low loss and cost reduction: Vce of SiC BJT is reduced by 47%, Eon by 60% and Eoff by 67%. SiC BJT can provide the lowest conduction loss in the market, and Ron is less than 2.2 milliohms at room temperature. SiC BJT can provide the minimum total loss, including driver loss. Silicon carbide BJT is the most efficient 1200 volt power transfer switch in history. SiC BJT achieves a higher switching frequency, and its conduction and switching losses are lower than those of IGBT (30-50%), so the output power can be increased by up to 40% in the same size system. The 2KW boost circuit from 400V to 800V can only reach the switching frequency of 25KHz when realized by silicon IGBT, and it needs five thin film capacitors. However, when using SiC BJT, the switching frequency can reach 72KHz, and only two thin film capacitors are needed, which reduces the size of the heat sink and inductor by one third, that is, smaller inductors can be used, thus greatly saving the total BOM cost of the system.
Improve the switching frequency of power supply to achieve high frequency: The biggest disadvantage of traditional IGBT is its slow switching speed and low working frequency. When it is turned off, a current tail will lead to turn-off loss. The switching speed of SiC BJT is fast, and there is no IGBT turning off as the current tail, so the switching loss is very low. Under the same rated withstand voltage, the on-resistance of SiC BJT is lower than VCE(sat) of IGBT, which can reduce the on-loss of SiC BJT.
The best application of SiC BJT is the design of power supply with more than 3000W power. Many of these power supplies use IGBT as switching equipment to optimize cost and efficiency. If the design engineer replaces IGBT with SiC BJT, it is easy to greatly increase the switching frequency of the power supply, thus reducing the product volume and improving the conversion efficiency. With the increase of frequency, the number of inductors and capacitors required by peripheral circuits can also be reduced in design, which helps to save costs. On the other hand, the switching speed of SiC BJT is very fast, and it can complete the switching action in less than 20nS, even faster than MOSFET, so it can also be used to replace MOSFET. Compared with bipolar IGBT devices, silicon carbide BJT has lower on resistance, which can further reduce the conduction loss. The high temperature stability and low leakage current of silicon carbide BJT have surpassed that of IGBT and MOSFET. In addition, its internal resistance changes with the positive temperature coefficient, so it can be easily connected in parallel for the design of high-power power supply.
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