Overview
TOKYO─Toshiba Corporation (TOKYO: 6502) has demonstrated the world’s first successful fabrication of high-performance circuits with analog–digital integration on a single chip driver integrated circuit (IC) for controlling next-generation power semiconductors (*1). The developed IC detects the voltage and current status of power semiconductors at ultra-high speeds of 2 µs or less, and fine control reduces noise generated by power semiconductors by up to 51%. Theoretical calculations also confirm that power loss when driving the motor can be reduced by 25% compared with equivalent noise reduction by conventional methods. In the event of a short circuit or other malfunction, the power semiconductor can be immediately protected to prevent damage to it.
This is a technology that maximizes the performance of next-generation power semiconductors. It will contribute to the realization of a carbon-neutral society by assisting in miniaturization, high efficiency, and high reliability of the motor drive circuits and DC–AC converters used in electric vehicles, industrial equipment, smart power grids, and so on.
Background of the development
Power semiconductors control voltages and currents. They are used to drive motors in many applications, and for DC–AC power conversion. To realize a carbon-neutral society, it is vital to improve the efficiency and reduce the size of power semiconductors and power converters. Furthermore, the power semiconductor market continues to expand every year, and the global market for driver ICs for controlling power semiconductors has grown from approximately 140 billion yen in 2017 to approximately 180 billion yen in 2021, and this trend is expected to continue in the future (*2).
Currently, devices such as insulated gate bipolar transistors (IGBT) (*3) and silicon metal–oxide–semiconductor field-effect transistors (Si-MOSFET) (*4) are typically used for power semiconductors. Further improving efficiency will require reducing the power loss that occurs during power conversion, so the development of next-generation power semiconductors with low loss characteristics such as silicon carbide MOSFET (SiC-MOSFET) (*5) is progressing. Next-generation power semiconductors will reduce power loss in power conversion, achieve high efficiency, and facilitate heat dissipation, thereby enabling reductions in both size and weight. However, when these devices are controlled using conventional circuit methods, power loss reductions come at the expense of increased noise. Furthermore, heat dissipation paths shrink, so in the unlikely event of a short circuit or other fault, the temperature will instantly rise, making it easier for semiconductor elements to break.
There has been research on technologies for reducing noise in next-generation power semiconductors by improving control methods, but flexibility in reducing noise has been problematic because the optimum method for doing so differs according to the voltage and current state of the power semiconductor element. In addition, conventional methods require system designers to implement fault detection and protection functions for short circuits and the like via a microcomputer, and the inherent delay can result in damage to the element.
Features of the technology
Toshiba has thus addressed this problem by developing the world’s first high-performance single-chip gate driver IC with mixed analog and digital circuits. Conventionally, realizing high functionality like that provided by this IC required configurations using many individual semiconductor components such as signal converters, memories, operation circuits, and amplifier circuits. However, mounting analog and digital circuits together, allows for the use of an analog circuit to detect voltage and current in power semiconductor elements as well as a digital circuit to select a control method based on the detection results, thereby realizing optimum control by a single chip without many parts. The developed semiconductor also has memory for storing control methods, and during control, a resolution enhancement circuit combining low-speed digital and high-speed analog circuits realizes appropriately fine control by using analog circuits only for those parts requiring high-speed control.
Toshiba has also developed an analog waveform preprocessing technology that extracts only those features required for control and fault detection from the high-speed voltage and current waveforms of power semiconductors, allowing fault detection with a low-speed analog-to-digital converter. There is thus no need to pass through a microcomputer, allowing immediate detection of short circuits and other faults.
This IC can also be realized by low-cost complementary metal–oxide–semiconductor (CMOS) (*6) process technologies that are compatible with existing fabrication equipment. Using this IC, the company succeeded in controlling a 1.2-kV SiC-MOSFET power semiconductor and reducing its surge voltage, a major cause of noise generation, by 51% with no increase in power loss. Using conventional methods for an equivalent surge reduction would increase loss when driving the motor, but theoretical calculations clearly show that using this IC can reduce power loss by 25%. The IC also succeeded in fault state detection at speeds as low as 2 µs without using a microcomputer. These features are expected to maximize the performance of next-generation power semiconductors.
Figure 2: Noise reduction effect when controlling a SiC-MOSFET power semiconductor and the results of high-speed fault detection.
Future developments
The Toshiba Group will aim for practical use of the developed IC by 2025. Power electronics is a market of focus for the Toshiba Group, which will continue to develop technologies related to this IC. The group will promote the application of next-generation power semiconductors to various power conversion systems, thereby contributing to the reduction of CO2 emissions through higher efficiency of power semiconductors, and the realization of a carbon-neutral society.
*1: This technology was presented at the 2021 IEEE Energy Conversion Congress and Exposition, an international IEEE conference held online from October 10–14, 2021.
*3: IGBT: A bipolar transistor with a MOSFET built into the base.
*4: Si-MOSFET: A type of transistor better suited to low-power, high-speed operations compared with IGBTs.
*5: SiC-MOSFET: A power semiconductor using a new material, SiC.
*6: CMOS: A type of semiconductor circuit used in personal computers and many other electronic devices.