Transformerless capacitive coupling of gate signals for seriesoperation of power MOS devices

A reliable configuration for triggering a series string of power metal oxide semiconductor (MOS) devices without the use of transformer coupling is presented. A capacitor is inserted between the gate and ground of each metal oxide semiconductor field effect transistor (MOSFET), except for the bottom MOSFET in the stack. Using a single input voltage signal to trigger the bottom MOSFET, a voltage division across the network of device capacitance and inserted capacitances triggers the entire series stack reliably. Design formulas are presented and simple circuit protection is discussed. Simulation shows reliable operation and experimental verification is presented, Application of the method is applied to series insulated gate bipolar transistors (IGBTs)     

High gain power switching using field controlled thyristors

A technique for high gain power switching using field controlled thyristors is described. This technique uses a MOSFET connected in series with the FCT to control the current flow. The circuit exhibits normally-off behavior and is capable of operation at high voltages. The current through the FCT can be turned on and off by the application of a low voltage gate signal to the MOSFET. Turn-on and turn-off times of less than 1 μs have been observed at a current gain of over 30. The new gating technique offers the advantage of the large operating current density of the FCT even at high breakdown voltages and the high input impedance of the MOS gate used to trigger the device during power switching.     

New zero voltage switching DC converter with flying capacitors

A new soft switching converter is presented for medium power applications. Two full-bridge converters are connected in series at high voltage side in order to limit the voltage stress of power switches at V_in/2. Therefore, power metal–oxide–semiconductor field-effect transistors (MOSFETs) with 600 V voltage rating can be adopted for 1200 V input voltage applications. In order to balance two input split capacitor voltages in every switching cycle, two flying capacitors are connected on the AC side of two full-bridge converters. Phase-shift pulse-width modulation (PS-PWM) is adopted to regulate the output voltage. Based on the resonant behaviour by the output capacitance of MOSFETs and the resonant inductance, active MOSFETs can be turned on under zero voltage switching (ZVS) during the transition interval. Thus, the switching losses of power MOSFETs are reduced. Two full-bridge converters are used in the proposed circuit to share load current and reduce the current stress of passive and active components. The circuit analysis and design example of the prototype circuit are provided in detail and the performance of the proposed converter is verified by the experiments.     

10 kV高重频开关组件设计

设计了一种基于功率金属氧化物半导体场效应晶体管(MOSFET)的高压开关组件。通过串联20只1 kV的RF MOSFET单元电路,获得耐压10 kV以上的高速、高重复频率的开关组件。开展了高压开关组件的结构设计和1 kV的RF MOSFET单元电路设计及散热设计。利用开关组件进行了10 kV脉冲源实验装置设计,测试结果发现脉冲前沿较仿真结果变缓。     

Comparison of -MOSFET lifetime estimates based on GIDL enhancement and transconductance degradation as criteria

A comparison of MOSFET lifetimes based on gate-induced drain leakage (GIDL) enhancement and transconductance degradation as criteria is presented. Analysis of damage mechanisms indicates that degradations related to interface state generation limit the MOSFET lifetime at reduced voltage operations. In conventional gate oxide MOSFETs, GIDL enhancement due to band-to-defect tunneling and transconductance degradation limit the lifetime at reduced voltage. For MOSFETs with reoxidized nitrided gate oxides, our results show that GIDL enhancement due to band-to-defect tunneling is a better reliability monitor than transconductance degradation at low operating voltages.     

A circuit simulation model for high-frequency power MOSFETs

A circuit simulation model suitable for modeling the static and dynamic switching characteristics of high-frequency power MOSFETs is reported. The model parameters were obtained from physical device layout, silicon doping, and measured electrical characteristics of power MOSFETs. Accurate voltage dependencies of the interelectrode capacitances were obtained from extensive two-dimensional device simulations. The voltage dependence of gate-drain capacitance was modeled using an analytic expression. The measured static current-voltage and transient-switching responses under resistive switching conditions are in excellent agreement with simulation results obtained from SPICE. The MOSFET subcircuit model was used to accurately predict the performance of a series-parallel resonant DC-DC converter using a multilevel system simulator     

新型TOPSwitch-GX系列电源的PI设计

TOPSwitch GX系列开关电源芯片内建PWM控制器和高压MOSFET，具有自动复位能力，集成过流，过热保护功能。利用该系列芯片结合PI电源设计软件平台设计了一种小功率多路输出的单端反激式开关电源。试验结果表明，该电源电路结构简单，并且运行可靠，输出电源质量高。     

Snubberless voltage sharing of series-connected insulated-gatedevices by a novel gate control strategy

Insulated gate devices, such as metal oxide semiconductor field effect transistors (MOSFETs) or insulated gate bipolar transistors (IGBTs), are increasingly used in high-voltage power converters where a request for fast power switches is growing. Series connection of devices is a viable approach to manage voltages higher than the blocking voltage of the single device. The main problem in such an application is to guarantee the voltage balance across the devices both in steady-state and during switching transients. In this paper, a novel approach is presented, which is used to equalize the voltage sharing during the switching transients. The main advantages of the proposed method consist in avoiding the traditional use of the snubber capacitors, in the output power side, and in working on the gate side. The application of the proposed gate drive technique is firstly discussed and compared with different solutions, hence, validated by experimental tests applied to the control of series connected devices. Finally, a comparison is performed between the transient behaviors of two different configurations: a single switch with high-voltage blocking capability, and in alternative a series of two devices which together ensure the voltage blocking capability of the single switch. The better performances of the latter configuration, working with the proposed control circuit, over the former have been experimentally demonstrated     

1.5 V resistive fuse for image smoothing and segmentation

A 1.5 V resistive fuse for image smoothing and segmentation using bulk-driven MOSFETs is presented. The circuit switches on only if the differential voltage applied across its input terminals is less than a set voltage; it switches off if the differential voltage is higher than the set value. The useful operation range of the circuit is 0.4 V with a supply voltage of 1.5 V and threshold voltages of V_Tn=0.828 V and V_Tp=-0.56 V for n and p channel MOSFETs, respectively     

New series half-bridge converters with the balance input split capacitor voltages

This article presents a new dc/dc converter to perform the main functions of zero voltage switching (ZWS), low converter size, high switching frequency and low-voltage stress. Metal–oxide–semiconductor field-effect transistors (MOSFETs) with high switching frequency are used to reduce the converter size and increase circuit efficiency. To overcome low-voltage stress and high turn-on resistance of MOSFETs, the series half-bridge topology is adopted in the proposed converter. Hence, the low-voltage stress MOSFETs can be used for medium-input voltage applications. The asymmetric pulse-width modulation is used to generate the gating signals and achieve the ZWS. On the secondary side, the parallel connection of two diode rectifiers is adopted to reduce the current rating of passive components. On the primary side, the series connection of two transformers is used to balance two output inductor currents. Two flying capacitors are used to automatically balance the input split capacitor voltages. Finally, experiments with 1000 W rated power are performed to verify the theoretical analysis and the effectiveness of proposed converter.     

High-Voltage Auxiliary Power Supply Using Series-Connected MOSFETs and Floating Self-Driving Technique

This paper deals with high-voltage auxiliary switching-mode power supplies (SMPSs). An overview of the state of the art is given, and a novel solution is proposed. The proposed solution is based on a single-ended flyback or forward topology with the main switch arranged as a series connection of two metal-oxide-semiconductor field-effect transistors (MOSFETs). The bottom MOSFET is driven directly by an ordinary control circuit and gate driver, while the top MOSFET is driven by a floating self-supplied gate driver. The floating gate driver is connected to the input filter capacitors' midpoint. This gate driver plays two roles: driving of the top MOSFET and control of distribution of the blocking voltage among the series-connected MOSFETs, in steady state as well as during commutation. The series connection of lower voltage MOSFETs has two important advantages compared to that of a single high-voltage MOSFET: lower conduction losses and lower cost. When several switches are series connected, each switch supports a fraction of the total blocking voltage, and therefore, each switch can be rated for lower voltage. The total on-state resistance and the cost of such a switch arrangement are lower compared to that of a single switch that supports the full blocking voltage. The proposed SMPS is theoretically analyzed and experimentally verified. The experimental results are presented and discussed.     

Impact of the gate driver voltage on temperature sensitive electrical parameters for condition monitoring of SiC power MOSFETs

Condition monitoring using temperature sensitive electrical parameters (TSEPs) is widely recognized as an enabler for health management of power modules. The on-state resistance/forward voltage of MOSFETs, IGBTs and diodes has already been identified as TSEPs by several researchers. However, for SiC MOSFETs, the temperature sensitivity of on-state voltage/resistance varies depending on the device and is generally not as high as in silicon devices. Recently the turn-on current switching rate has been identified as a TSEP in SiC MOSFETs, but its temperature sensitivity was shown to be significantly affected by the gate resistance. Hence, an important consideration regarding the use of TSEPs for health monitoring is how the gate driver can be used for improving the temperature sensitivity of determined electrical parameters and implementing more effective condition monitoring strategies. This paper characterizes the impact of the gate driver voltage on the temperature sensitivity of the on-state resistance and current switching rate of SiC power MOSFETs. It is shown that the temperature sensitivity of the switching rate in SiC MOSFETs increases if the devices are driven at lower gate voltages. It is also shown, that depending on the SiC MOSFET technology, reducing the gate drive voltage can increase the temperature sensitivity of the on-state resistance. Hence, using an intelligent gate driver with the capability of customizing occasional switching pulses for junction temperature sensing using TSEPs, it would be possible to implement condition monitoring more effectively for SiC power devices.     

A reverse-voltage protection circuit for MOSFET power switches

When MOSFET is used as a power switch, it is essential to prevent reverse current flow through the parasitic body diodes under reverse voltage condition. A new built-in reverse voltage protection circuit for MOSFETs has been developed. In this design, an area-efficient circuit is used to automatically select the proper well bias voltage to prevent reverse current under the reverse-voltage condition. This built-in reverse protection circuit has been successfully implemented in a high-side power switch application using a 0.6-μm CMOS process. The die area of the protection circuit is only 2.63% of that of a MOSFET. The latch-up immunity is greater than +12 V and -10 V in voltage triggering mode, and greater than ±500 mA in current triggering mode. The protection circuit is not in series with the MOSFET switch, so that the full output swing and high power efficiency are achieved     

Current-source parallel-resonant DC/AC inverter with transformer

This paper gives the theory and experimental results for a current-source parallel-resonant inverter with a transformer used to change voltage levels and provide isolation. The analysis is performed in the frequency domain using Fourier series techniques to predict output power, efficiency, DC-to-AC voltage transfer function, and component voltage and current stresses. The inverter consists of two switches, a large choke inductor, a transformer, and a parallel-resonant circuit. The magnetizing inductance of the transformer is used as the inductance of the parallel-resonant circuit, thereby requiring one less component. Each switch consists of a MOSFET in series with a diode. The MOSFETs have their sources grounded so there is no need for a complicated gate-drive circuit. An inverter was designed and constructed. The DC input voltage was 156 V and the output voltage was a sine wave with a peak value of 224 V at an operating frequency of 50 kHz. The output power at full load was 100 W     

Dynamic Voltage Equalization for Series-Connected Ultracapacitors in EV/HEV Applications

Energy-storage systems (ESSs) play an important role in electric vehicle (EV) and hybrid EV (HEV) applications. In the system, an ultracapacitor is preferred for high power buffer and regenerative braking energy storage because it has the advantages of high power density, long life cycles, and high efficiency. While in the high-voltage application, the ultracapacitors are employed in series, and the voltage unbalance issue must be taken care of. This paper presents a novel circuit for equalizing a series ultracapacitor stack, which is based on a dc-dc converter. The proposed voltage-equalization circuit derives energy from the series ultracapacitor stack and transfers them to the weakest ultracapacitor cell. The equalizer balances the whole stack by sequentially compensating the weak ultracapacitor cells. Unlike previous methods for battery-storage systems, which include complex circuit detecting and comparing the voltages of capacitor cells, the novel equalizer can realize autonomic voltage equalization without voltage detection and comparison, and it is more efficient with the soft switching method, which is a benefit for high-power applications in EV/HEV. The simulation and experiment results validate the feasibility of the proposed equalization circuits.     

Static Performance of 20 A, 1200 V 4H-SiC Power MOSFETs at Temperatures of −187°C to 300°C

Silicon carbide (4H-SiC) power metal–oxide–semiconductor field-effect transistors (MOSFETs) have been attracting tremendous attention for high-power applications at a wide range of operating temperatures, owing to their normally-off characteristics, high-speed switching operation, avalanche capability, and low on-resistance. To optimize performance of 4H-SiC MOSFETs for various applications at different temperatures, it is important to understand the mechanisms of temperature dependence of the key parameters, such as on-resistance, threshold voltage, and metal–oxide–semiconductor (MOS) channel mobility. We report on the temperature dependence of the on-resistance of 20 A, 1200 V 4H-SiC power MOSFETs for temperatures ranging from −187°C to 300°C. The MOSFET showed normally-off characteristics throughout the entire experimental temperature range. Different temperature dependences of the total on-resistance in different temperature regimes have been observed. Due to the poor MOS channel mobility and the low free carrier concentration in the inversion channel of the 4H-SiC MOSFET, the MOS channel resistance is the dominant part of the total on-resistance. This was also found to be true in a 4H-SiC long-channel lateral MOSFET.     

Zero-voltage DC/DC converter with asymmetric pulse-width modulation for DC micro-grid system

This paper presents a zero-voltage switching DC/DC converter for DC micro-grid system applications. The proposed circuit includes three half-bridge circuit cells connected in primary-series and secondary-parallel in order to lessen the voltage rating of power switches and current rating of rectifier diodes. Thus, low voltage stress of power MOSFETs can be adopted for high-voltage input applications with high switching frequency operation. In order to achieve low switching losses and high circuit efficiency, asymmetric pulse-width modulation is used to turn on power switches at zero voltage. Flying capacitors are used between each circuit cell to automatically balance input split voltages. Therefore, the voltage stress of each power switch is limited at V_in/3. Finally, a prototype is constructed and experiments are provided to demonstrate the circuit performance.     

Efficient resonant power conversion

The DC analysis of a series-resonant converter operating above resonant frequency is presented. The results are used to analyze the current form factor and its effect on the efficiency. The selection of the switching frequency to maximize the efficiency is considered. The derived expressions are generalized and can be applied to calculations in any of the switching modes for a series-resonant circuit. For switching frequencies higher than the resonant frequency, an area of more efficient operation is indicated which will aid in the design of this class of converters and power supplies. It is pointed out that (especially for power MOSFETs where ohmic losses dominate) it is more attractive to select switching frequencies that are higher than the resonant frequency because of the possibility of nondissipative snubbers. Slowing down the rise of the gate voltage and, hence, the slow decrease of ON resistance during turn-on is also not a drawback to high-frequency switching. Because of this safer operation, the standard intrinsic diode of the power MOSFET could be used at high frequencies instead of the more expensive FREDFET     

采用分段式自适应PWM/PFM调制的Buck型DC-DC转换器设计北大核心

为了在轻重负载条件下获得更高的转换效率，采用分段式结构和导通电阻更小的NMOS作为输入级，并采用PWM/PFM双调制方式，设计了一种Buck型DC-DC转换器。为解决PWM/PFM调制信号切换问题，采用零电流检测方式进行切换。利用断续导通模式(DCM)和连续导通模式(CCM)下端NMOS管导通时电感电压的不同，检测下端NMOS在导通时电感电压大于零的周期。当电感电压大于零的周期大于2时，则处于DCM模式并自动采用PFM调制模式，关闭一部分功率管以减小开关频率和功率管寄生电容，优化轻载效率；反之则处于CCM模式并采用PWM调制。仿真结果表明，在负载电流10～1 000 mA范围内，该电路可以在两种调制模式平稳切换，在800 mA时峰值效率可提升到96%以上。     

Study and implementation of a low conduction loss zero-current resonant switch

Zero-current (ZC) resonant switches allow one to reduce the switching losses in high-frequency DC/DC switched mode power supplies. ZC resonant switches can be either unidirectional (half-wave) or bidirectional (full-wave). If a conventional power MOSFET is chosen to implement the ZC resonant switch, the turn-on of the slow intrinsic diode has to be avoided. This is usually done with a fast blocking diode, which is connected in series with the MOSFET. Furthermore, an antiparallel fast diode is added when a FW ZC resonant switch is required. The conduction losses are relevant in this implementation, owing to the threshold voltage and to the series resistances of the two diodes. In this paper, a low-conduction-loss FW ZC resonant switch has been proposed. Its implementation is based on a power MOSFET and a single antiparallel Schottky diode. The possibility of an implementation with a power MOSFET alone is also discussed. A control circuit suitable for the proposed ZC resonant switch has been described. The experimental results obtained from a ZCS-QR buck converter are discussed.<>