Power Electronics Components

Advanced architectures and topologies need to be accompanied by superior power electronics components, including power semiconductor devices, magnetic components and capacitors.

With the recent developments in wide bandgap semiconductor devices, silicon carbide (SiC) JFET and power MOSFET have become two candidates for commercialization after SiC Schottky diodes. Featuring high blocking voltage, high workable temperature and low on-state resistance, SiC switches have shown great potential to substitute conventional Si switches in high power, high voltage, high frequency, and high density (H4) applications. CPES has been working with device manufacturers such as SiCED and CREE to evaluate the performance of these new devices, and investigate their possibility of utilization in H4 converters.

Extensive efforts have been made in CPES on the characterizations, testing, and modeling of both SiC JFET and SiC MOSFET. In the absence of manufacturer datasheet, both static and dynamic characterizations have been performed on SiC MOSFET to get a full picture of the device’s overall performance, whose results show a blocking capability of more than twice whereas a reduction in on-resistance of more than five times compared to conventional high voltage Si MOSFET. High temperature characterizations have also shown the superiority of SiC MOSFET being workable under higher junction temperature and more insensitive in its main characteristics like on-resistance. Preliminary switching tests, on the other hand, have exhibited much higher switching speed and lower switching loss of the new device compared to Si IGBTs with similar voltage ratings.

Generic modeling process for the new SiC MOSFET has also been developing in CPES to incorporate the device model in circuit simulations which can greatly ease the design of high speed gate driver circuit for the new device.

Similar work has been conducted on SiC JFET as well. As a normally-on device, more care has been paid to the fast and secure driving of the device. Ultra-fast gate drive circuit using the RCD network and zero gate resistance has been designed and is now tested in a phase-leg configuration. Same JFETs have also been applied in an actual converter system under regular switching speed achieving much higher power density.

Other than Trench and Lateral MOSFETs, CPES has investigated different switch structures since 1997, such as CPES’ lateral trench and JFET, and monolithic integration approach for high-frequency, high-density POL applications. With a good understanding of switching behavior of power MOSFET under practical scenario, CPES has been developing elaborate analytical loss model for POL applications with proven accuracy. Contrasting with traditional FOM (Figure of Merits), new FOM equations, taking into account other key factors missed before by new loss model, have been developed for more accurate device evaluation and selection.

Magnetic components and its integration is another essential part. CPES has been investigating new high-frequency magnetic materials suitable for high-frequency applications in the multi-Mhz frequency range. To characterize the behavior of magnetic components and to optimal design, high-frequency modeling, together with finite element analysis, is widely executed for high-frequency, high-current transformer/inductor designs.

With the increased popularity of portable electronics, improved integrated solutions are desired to improve low-power DC/DC converter technology. With the state-of-the-art designs, the bulky magnetic components are a major barrier for integrating a DC/DC converter into a single chip. The 3D integrated solution that uses a low-profile inductor as the substrate is one possible method to integrate the magnetic component with the active component. Previously, the embedded winding with vertical flux is the conventional way to make low profile inductor. With this vertical flux structure, the inductance density will suffer when the core thickness is very thin. In order to solve this problem, CPES proposed low profile inductor structure with lateral flux pattern, which can have large inductance density even with very thin core thickness. A planar inductor based on LTCC technology was developed for a single-phase buck converter operating at a switching frequency exceeding 1 MHz. The inductor was experimentally verified on a prototype buck converter. The performance of the LTCC inductor in the buck converter surpassed that of commercial surface-mount power inductors of a similar value. In addition, the thick film–based LTCC inductor also outperformed the power handling capability of the on-chip inductors designed to operate at similar circuit conditions by a factor greater than ten.

To further improve the performance and reduce the size of the inductor, different magnetic structures and flux pattern inside the core, as well as the flux coupling, are being investigated.

Related CPES Research Volumes:

1.  Power Devices and their Applications (Volume III)
2.  Power Electronics Components and Circuit Modeling and Analysis (Volume VI)
3.  Low Voltage Power Conversion and Distributed Power Systems (Volume IX)
4.  Advanced Soft-Switching Techniques, Device and Circuit Applications (Volume XI)