A soft switching active snubber optimized for IGBT's in singleswitch unity power factor three-phase diode rectifiers

This paper describes a soft switching active snubber for an IGBT operating in a single switch unity power factor three-phase diode rectifier. The soft switching snubber circuit provides zero-voltage turn-off for the main switch. The high turn-off losses of the IGBT due to current tailing are reduced by zero-voltage switching. This allows the circuit to be operated at very high switching frequencies with regulated DC output voltage, high quality input current and unity input power factor. Simulation and experimental results are included     

A comparative evaluation of new silicon carbide diodes and state-of-the-art silicon diodes for power electronic applications

Recent progress in silicon carbide (SiC) material has made it feasible to build power devices of reasonable current density. This paper presents results including a comparison with state-of-the-art silicon diodes. Switching losses for two silicon diodes (a fast diode, 600 V, 50 A, 60 ns Trr), an ultrafast silicon diode (600 V, 50 A, 23 ns Trr), and a 4H-SiC diode (600 V, 50 A) are compared. The effect of diode reverse recovery on the turn-on losses of a fast insulated gate bipolar transistor (IGBT) are studied both at room temperature and at 150 /spl deg/C. At room temperature, SiC diodes allow a reduction of IGBT turn-on losses by 25% compared to ultrafast silicon diodes and by 70% compared to fast silicon diodes. At 150 /spl deg/C junction temperature, SiC diodes allow turn-on loss reductions of 35% and 85% compared to ultrafast and fast silicon diodes, respectively. The silicon and SiC diodes are used in a boost converter with the IGBT to assess the overall effect of SiC diodes on the converter characteristics. Efficiency measurements at light load (100 W) and full load (500 W) are reported. Although SiC diodes exhibit very low switching losses, their high conduction losses due to the high forward drop dominate the overall losses, hence reducing the overall efficiency. Since this is an ongoing development, it is expected that future prototypes will have improved forward characteristics.     

Characteristics of planar n-p junction diodes made bydouble-implantations into 4H-SiC

Double implantation technology consisting of deep-range acceptor followed by shallow-range donor implantation was used to fabricate planar n⁺-p junction diodes in 4H-SiC. Either Al or B was used as the acceptor species and N as the donor species with all implants performed at 700°C and annealed at 1650°C with an AlN encapsulant. The diodes were characterized for their current-voltage (I-V) and capacitance-voltage (C-V) behavior over the temperature range 25°C-400°C, and reverse recovery transient behavior over the temperature range 25°C-200°C. At room temperature, the B-implanted diodes exhibited a reverse leakage current of 5×10^-8 A/cm² at a reverse bias of -20 V and a carrier lifetime of 7.4 ns     

A study of the internal device dynamics of punch-through andnonpunch-through IGBTs under zero-current switching

The effective use of power insulated gate bipolar transistors (IGBTs) requires a good understanding of their internal device physics. This understanding is essential for the optimal interaction among the IGBTs, their snubber elements and the power circuit in which the IGBTs operate. As switching frequencies are pushed to higher values, switching loss reduction becomes an essential part of the design and optimization process. Soft switching techniques such as zero-voltage switching (ZVS) and zero-current switching (ZCS) are widely used for this purpose. This study provides an insight into the internal dynamic behavior of IGBTs under zero-current switching. The latter is accomplished through mixed-mode simulation, providing the necessary insight for the improvement of circuit and device performance. In particular, the authors have analyzed the behavior of the negative current in nonpunch-through (NPT) devices after the first zero-current crossing and the effect of the turn-off delay on the tail current. They have also experimentally characterized punch-through (PT) and NPT IGBTs to confirm the insights provided by the mixed-mode simulation     

Soft switching active snubbers for DC/DC converters

A soft-switching active snubber is proposed to reduce the turn-off losses of the insulated gate bipolar transistor (IGBT) in a buck power converter. The soft-switching snubber provides zero-voltage switching for the IGBT, thereby reducing its high turn-off losses due to the current tailing. The proposed snubber uses an auxiliary switch to discharge the snubber capacitor. This auxiliary switch also operates at zero-voltage and zero-current switching. The size of the auxiliary switch compared to the main switch makes this snubber a good alternative to the conventional snubber or even to passive low-loss snubbers. The use of the soft-switching active snubber permits the IGBT to operate at high frequencies with an improved RBSOA. In the experimental results reported for a 1 kW, 40 kHz prototype, combined switching/snubbing losses are reduced by 36% through the use of the active snubber compared to a conventional RCD snubber. The use of an active snubber allows recovery of part of the energy stored in the snubber capacitor during turn-off. The generic snubber cell for the buck power converter is generalized to support the common nonisolated DC/DC power converters (buck, boost, buck-boost, Cuk, sepic, zeta) as well as isolated DC/DC power converters (forward, flyback, Cuk, and sepic)     

Silicon carbide benefits and advantages for power electronics circuits and systems

Silicon offers multiple advantages to power circuit designers, but at the same time suffers from limitations that are inherent to silicon material properties, such as low bandgap energy, low thermal conductivity, and switching frequency limitations. Wide bandgap semiconductors, such as silicon carbide (SiC) and gallium nitride (GaN), provide larger bandgaps, higher breakdown electric field, and higher thermal conductivity. Power semiconductor devices made with SiC and GaN are capable of higher blocking voltages, higher switching frequencies, and higher junction temperatures than silicon devices. SiC is by far the most advanced material and, hence, is the subject of attention from power electronics and systems designers. This paper looks at the benefits of using SiC in power electronics applications, reviews the current state of the art, and shows how SiC can be a strong and viable candidate for future power electronics and systems applications.