A single-switch continuous-conduction-mode boost converter with reduced reverse-recovery and switching losses

A single-switch continuous-conduction-mode boost converter with reduced reverse-recovery and switching losses is proposed. By utilizing the leakage inductances of a pair of coupled inductors and two additional rectifiers, the turn-off rates (di/dt) of the boost output rectifier and the additional rectifiers are slowed down to reduce the reverse-recovery loss. The boost power transistor is also operated under a low-voltage turn-on condition to reduce the switching loss. Experimental results are presented to confirm the theoretical analysis and the performance of the proposed converter.     

Performance evaluation of high-power GaAs Schottky and siliconp-i-n rectifiers in hard- and soft-switching applications

The dynamic switching characteristics of high-power GaAs Schottky and silicon p-i-n rectifiers are studied at various temperatures. Devices were first characterized to measure forward and reverse I-V, C-V, reverse breakdown voltage, and reverse-recovery performance. The same devices were characterized for turn on and turn off in switching circuits designed to study the dynamic switching performances under hard- and soft-switching conditions at different temperatures. Advanced two-dimensional (2-D) mixed device and circuit simulations were used to study the internal plasma dynamics under boundary conditions imposed by the circuit operation. It is shown that for hard-switching applications, GaAs Schottky power rectifiers exhibit significantly reduced switching power losses compared to silicon p-i-n rectifiers. For soft-switching applications, there is not a significant difference in the switching power losses for these two devices. Diode performance at elevated temperatures is measured and simulated, and temperature dependencies of switching and conduction power losses are analyzed     

Modelling and characterization of the reverse recovery of ahigh-power GaAs Schottky diode

The reverse recovery characteristics of high-power GaAs Schottky rectifiers are reported at various temperatures; mixed device and circuit simulations were used to study the internal plasma dynamics during the reverse recovery process. In this approach, semiconductor transport and heat generation and diffusion equations were solved self-consistently using a two-dimensional (2-D) finite element grid structure under boundary conditions imposed by the measurement circuit. The simulation results are shown to be in good agreement with the measured data at temperatures in the range of 25°C to 125°C. These results are compared with the reverse recovery characteristics of a commercial silicon PIN power rectifier under identical conditions and it is shown that carrier depletion is the dominant mechanism causing the reverse recovery in a GaAs Schottky diode. The reverse recovery power loss is negligible in a GaAs Schottky rectifier and is shown to decrease as the case temperature is increased, contrary to the silicon PIN rectifier behaviour     

Silicon carbide PiN and merged PiN Schottky power diode models implemented in the Saber circuit simulator

Dynamic electrothermal circuit simulator models are developed for silicon carbide power diodes. The models accurately describe the temperature dependence of on-state characteristics and reverse-recovery switching waveforms. The models are verified for the temperature dependence of the on-state characteristics, and the di/dt, dv/dt, and temperature dependence of the reverse-recovery characteristics. The model results are presented for 1500 V SiC Merged PiN Schottky (MPS) diodes, 600 V Schottky diodes, and 5000 V SiC PiN diodes. The devices studied have current ratings from 0.25 A to 5 A and have different lifetimes resulting in different switching energy versus on-state voltage trade-offs. The devices are characterized using a previously reported test system specifically designed to emulate a wide range of application conditions by independently controlling the applied diode voltage, forward diode current, di/dt, and dv/dt at turn-off. A behavioral model of the test system is implemented to simulate and validate the models. The models are validated for a wide range of application conditions for which the diode could be used.     

An Alternative Energy Recovery Clamp Circuit for Full-Bridge PWM Converters With Wide Ranges of Input Voltage

A full-bridge dc--dc converter employing a diode rectifier in the output experiences a severe voltage overshoot and oscillation problem across the diode rectifier caused by interaction between junction capacitance of the rectifier diode and leakage inductance of the transformer. The pronounced reverse-recovery current of high-power diodes significantly contributes to these issues by increasing power loss and voltage overshoot. Conventional energy recovery clamping circuits suffer from high voltage overshoot if the converter input voltage is wide. In this paper, a novel energy recovery clamp circuit is proposed to overcome this problem. The proposed circuit requires neither active switches nor lossy components. Therefore, the proposed circuit is very promising in high-voltage and high-power applications. Performance of the proposed circuit is verified both theoretically and experimentally with a 70-kW dc--dc converter.      

A technique for reducing rectifier reverse-recovery-related lossesin high-power boost converters

A circuit technique that reduces the boost power converter losses caused by the reverse-recovery current of the rectifier is described. The losses are reduced by inserting an inductor in the series path of the boost switch and a rectifier to control the di/dt rate of the rectifier during its turn off. The energy from the inductor after the boost switch turn off is returned to the input or delivered to the output via an active snubber     

Circuit topologies for single-phase voltage-doubler boostrectifiers

A new family of single-phase voltage-doubler PWM (pulse width modulated) boost rectifiers is presented. By examining the switching states of several standard single-phase boost rectifier circuits, three characteristic PWM voltage switching patterns are identified: unipolar PWM; bipolar PWM; and phase-adjusted unipolar PWM. From this analysis, an equivalent family of voltage-doubler rectifiers is derived. When high output voltages are required, voltage-doubler rectifiers are shown to be able to generate AC line currents with the lowest current distortion. The circuits presented are examined using circuit simulators and experimental results     

Evaluation of turn-on performance of P-i-N rectifiers and IGBT'sunder zero voltage switching

This paper compares the turn-on performance of two vertical power bipolar devices, viz, P-I-N diode and IGBT, under Zero Voltage Switching (ZVS). Although both the devices are “conductivity modulated” during turn-on, the IGBT carrier dynamics distinctly differ from that of a P-i-N rectifier. It is shown that, for identical drift region parameters, the conductivity modulation in the IGBT is significantly lower compared to that in a P-i-N rectifier mainly because of carrier flow constraints in the IGBT and the inherent bipolar transistor-like carrier distribution in the IGBT. 2-D mixed device and circuit simulations were performed to understand the behavior of the two devices during turn-on under ZVS. The mixed device and circuit simulator was also used to study the effects of variations in the rate of change of current (di/dt) through the device during turn-on, carrier lifetime and temperature on the turn-on behavior of the two bipolar devices under ZVS     

A behavioral circuit simulation model for high-power GaAs Schottky diodes

This paper proposes a physically based behavioral circuit simulation model for high-power GaAs Schottky diodes which is valid over all regions of operation. No conditional statements are needed to define the regions of operation. A new and more accurate method of obtaining depletion capacitance model parameters from the measured capacitance values is proposed. A simple current- and temperature-dependent resistance model is used to model the nonlinear diode resistance as well as contact and packaging resistances. The validity of the model is demonstrated under various DC and transient switching conditions. Simulation results are compared with the experimental data obtained from a 200 V GaAs Schottky diode. The diode model is tested at various temperatures in different test circuits and the simulation results are shown to be in excellent agreement with the measured data under static and dynamic switching conditions. The model can be easily implemented in other circuit simulators.<>     

Operating a three-phase diode rectifier with a low-input currentdistortion using a series-connected dual boost converter

This paper describes a technique for shaping the input current to a three-phase diode rectifier using a two-switch series-connected dual boost converter and a three-phase bidirectional switch circuit. Circuits are described for generating a single voltage DC output, “single DC-rail”, or a dual output DC voltage using center-tapped capacitors, “split DC-rail”. Both rectifier types can be operated with the boost inductors located either on the DC or the AC side of the rectifier. The resultant rectifier circuit configurations have an excellent immunity to the “shoot-through” fault condition and use active switching elements with low per-unit current ratings and low switching losses. These features increase the reliability factor and lower the cost penalty associated with unity fundamental power factor three-phase rectifiers. Test results are presented for the rectifiers using simulation and experimental results     

Design of smart power synchronous rectifier

In low-output-voltage DC/DC power converters, power losses due to the conduction of rectifying devices are significant. Using synchronous rectifiers instead of the conventional fast recovery diodes or Schottky diodes is an effective solution to this problem in most topologies. However, for synchronous rectifiers to perform effectively, this requires an external gate drive with proper sensing and timing control circuits. This can increase the complexity and cost in power converter hardware implementation. For the first time, a smart power synchronous rectifier (SPSR), which is a two-terminal MOS rectifier, is designed to overcome this difficulty. The SPSR integrates a simple control unit with a power MOSFET into a smart module to form a self-controlled synchronous rectifier. It has great advantages over the conventional discrete circuit composition, such as integrated gate control, precise timing switching and fast transient response, which are suitable for applications in high-frequency pulsewidth modulation (PWM) power converter circuits     

High-energy pulse-switching characteristics of thyristors

Experiments were conducted to study the high energy, high di/dt pulse-switching characteristics of silicon controlled rectifiers (SCRs) with and without the amplifying gate. High di/dt, high-energy single-shot experiments were first done. Devices without the amplifying gate performed much better than the devices with the amplifying gate. A physical model is presented to describe the role of the amplifying gate in the turn-on process, thereby explaining the differences in the switching characteristics. The turn-on area for the failure of the devices was theoretically estimated and correlated with observations. This allowed calculation of the current density required for failure. Since the failure of these devices under high di/dt conditions was thermal in nature, a simulation using a finite-element method was performed to estimate the temperature rise in the devices. The results from this simulation showed that the temperature rise was significantly higher in the devices with the amplifying gate than in the devices without the amplifying gate. From these results, the safe operating frequencies for all the devices under high di/dt conditions was estimated. These estimates were confirmed by experimentally stressing the devices under high di/dt repetitive operation     

Gallium arsenide Schottky power rectifiers

This paper discusses the development of high-performance gallium arsenide Schottky rectifiers for power switching applications. These diodes are shown to exhibit superior turn-on and turn-off dynamic switching characteristics when compared with silicon p-i-n rectifiers. The theoretical analysis presented in the paper indicates that the gallium arsenide Schottky power rectifier will be attractive for high-frequency power switching circuits operating at 1.00-300 V.     

Large-signal model of picosecond FETs and measurement of the stepresponse

An FET large-signal model is developed for the time-domain computer-aided design (CAD) of ultrafast circuits. Numerical 2-D look-up tables describe the nonlinear parameters; a DC and microwave FET characterization as a function of bias voltage, followed by parameter extraction, completely determines the tables of parameters. The model can be implemented with simulators handling 2-D tables and applied to commercial transistors without a detailed knowledge of the internal structure of the device. The step response of an NEC710 MESFET is measured and compared with the prediction of the model, demonstrating its accuracy in representing switching waveforms and transient phenomena in the range covering tens of picoseconds. The 20-ps switching time of the NEC710 shows that the modeling methodology, measurement, and simulation are adequate for studying picosecond transient phenomena in single transistors     

低压大电流直流开关电源电磁兼容设计研究

文章提出了一种符合EMC要求的低压大电流直流开关电源的设计方法。该方法运用12脉波整流器和ZVS PWM技术来减少主电路的dU/dt(di/dt)和电磁干扰。另外,针对设备特性,在系统设计、PCB板布线、高频变压器工艺和结构设计等方面采用了一些必要的电磁兼容措施。电磁兼容实验验证了这些方法的有效性。     

Evaluation of the ruggedness of power DMOS transistor from electro-thermal simulation of UIS behaviour

High-voltage power MOSFETs have been widely used in switching mode power supply circuits as output drivers for industrial and automotive electronic control systems. However, as the device size is reduced, the energy handling capability is becoming a very important issue to be addressed together with the trade-off between the series on-resistance R_ON and breakdown voltage V_BR. Unclamped inductive switching (UIS) condition represents the circuit switching operation for evaluating the “ruggedness”, which characterizes the device capability to handle high avalanche currents during the applied stress. In this paper we present an experimental method which modifies the standard UIS test and allows extraction of the maximum device temperature after the applied standard stress pulse vanishes. Corresponding analysis and non-destructive prediction of the ruggedness of power DMOSFETs devices supported by advanced 2-D mixed mode electro-thermal device and circuit simulation under UIS conditions using calibrated physical models is provided also. The results of numerical simulation are in a very good correlation with experimental characteristics and contribute to their physical interpretation by identification of the mechanism of heat generation and heat source location and continuous temperature extraction.     

Active damping control of a high-power PWM current-source rectifier for line-current THD reduction

The use of active damping to reduce the total harmonic distortion (THD) of the line current for medium-voltage (2.3-7.2 kV) high-power pulsewidth-modulation (PWM) current-source rectifiers is investigated. The rectifier requires an LC filter connected at its input terminals, which constitutes an LC resonant mode. The lightly damped LC filter is prone to series and parallel resonances when tuned to a system harmonic either from the utility or from the PWM rectifier. These issues are traditionally addressed at the design stage by properly choosing the filter resonant frequency. This approach may result in a limited performance since the LC resonant frequency is a function of the power system impedance, which usually varies with power system operating conditions. In this paper, an active damping control method is proposed for the reduction in line current THD of high-power current-source rectifiers operating at a switching frequency of only 540 Hz. Two types of LC resonances are investigated: the parallel resonance excited by harmonic currents drawn by the rectifier and the series resonance caused by harmonic pollution in the source voltage. It is demonstrated through simulation and experiments that the proposed active damping control can effectively reduce the line-current THD caused by both parallel and series resonances.     

Physical modeling of the power VDMOST for computer-aided design ofintegrated circuit

This paper presents a methodology for physical modeling of the vertical double-diffused MOS transistor (VDMOST) for power-integrated-circuit (PIC) design. The circuit model comprises the regional models derived from basic semiconductor equations. The unique features of the VDMOST such as quasi-saturation, nonlinear inter-electrode capacitances, reverse-recovery current, and temperature dependencies are accurately modeled based on device simulations. The composite model is implemented in Saber and SPICE2G.6 source code. It is verified against steady-state and capacitance-voltage measurements on test devices. A parameter extraction routine is developed, and a system that links ICCAP and Saber is set up that performs measurement, simulation, and parameter extraction. The application of the described model in computer-aided design (CAD) is demonstrated for several power-electronic circuits     

Techniques for minimizing the input current distortion ofcurrent-controlled single-phase boost rectifiers

Techniques for minimizing the input current distortion of current-controlled single-phase boost rectifiers are described. The switching patterns of several boost rectifiers are examined to identify the nature of their input current waveforms. This analysis is used to examine the low-frequency current distortion levels, and hence the power quality, associated with the rectifiers. A PWM (pulse width modulation) strategy that selectively switches between positive unipolar PWM and negative unipolar PWM, called phase-adjusted unipolar PWM, is shown to produce the lowest current distortion levels. A novel two-switch asymmetrical half-bridge rectifier is presented that draws an input current at a unity fundamental power factor and with the same low distortion as obtained with the four-switch H-bridge rectifier. The operation of the various rectifiers is examined with reference to theoretical predictions, circuit simulations, and experimental results. This analysis is used to compare the performances of the various rectifier switching patterns     

Utilization of an active-clamp circuit to achieve soft switching inflyback converters

Flyback derived power convertor topologies are attractive because of their relative simplicity when compared with other topologies used in low power applications. Incorporation of active-clamp circuitry into the flyback topology serves to recycle transformer leakage energy while minimizing switch voltage stress. The addition of the active-clamp circuit also provides a mechanism for achieving zero-voltage-switching (ZVS) of both the primary and auxiliary switches. ZVS also limits the turn-off di/dt of the output rectifier, reducing rectifier switching losses, and switching noise due to diode reverse recovery. This paper analyzes the behavior of the ZVS active-clamp flyback operating with unidirectional magnetizing current and presents design equations based on this analysis. Experimental results are then given for a 500 W prototype circuit illustrating the soft-switching characteristics and improved efficiency of the power converter. Results from the application of the active-clamp circuit as a low-loss turn-off snubber for IGBT switches is also presented