Zero-voltage-switching multiresonant technique-a novel approach toimprove performance of high-frequency quasi-resonant converters

A novel multiresonant switching concept is proposed to overcome the limitations of high-frequency quasi-resonant converters. A novel family of zero-voltage-switching (ZVS) multiresonant converters is generated. The unique arrangement of the multiresonant network results in absorption of all major parasitic components in the resonant circuit, including transistor output capacitance, diode junction capacitance, and transfer leakage inductance. This allows the new converters to provide favorable switching conditions for all semiconductor devices. Experimental results show that ZVS multiresonant converters are superior to ZVS quasi-resonant converters due to their reduced transistor voltage stress and improved load range and stability     

The influence of source impedance on the electrooptical switching behavior of LED's

Electrooptical switching of LED's is shown to be well described by a very simple equivalent circuit, the decisive elements of which are the diffusion capacitance and the lead inductance. Theory and experimental data indicate that even small lead inductances diminish performance if the LED is driven by a low-impedance source. Using a switched current source instead is likely to give the fastest possible response. The application of a reverse current pulse to the LED will reduce the light-fall time below the value given by the diode time constant. Then the carrier storage time and the light-fall time are found to be identical, thus offering a simple method of determining the latter without use of a photodetector.     

开关电源传导EMI仿真分析

随着电子技术的发展,电磁兼容性的研究越来越受到重视。文章以反激式开关电源为研究对象,分析并建立了MOSFET、变压器等元件的高频模型,利用电容、电感、变压器、MOSFET、功率二极管的高频模型组建了仿真电路。使用OrCAD10．5／PSpice软件模拟仿真,同时对其传导EMI进行了分析并提出了相应的抑制方法,这些工作对开关电源的电磁兼容性设计具有一定的指导作用。     

一种新型软开关BUCK变换器

根据传统硬开关电源引起的不良影响,提出了一种新型软开关BUCK变换器,使得高低桥MOSFET管都能在不管是轻负载或者重负载情况下达到ZVS状态.在连续导电模式（CCM）和高负载电流情况下,上桥MOSFET管开通,下桥MOSFET管侧的二极管在死区时间内导电,这样就造成了上桥MOSFET管的开关损耗.新型软开关BUCK变换器在传统BUCK变换器的基础上加入了电感和电容,在外加电感电容的情况下,在CCM下的死区时间内的电感电流可以有效地从下桥二极管整流到上桥二极管中.根据仿真结果和工作模式分析验证其性能.     

对动态奇异电路的初始值问题的研究

在动态电路的时域分析中,若要解出描述电路的微分方程或状态方程,首先必须知道电路的初始状态。可是对含有纯电容回路和纯电感割集的奇异电路,在“换路”瞬间其初始值有可能发生跃变现象,不能用换路定则来求解。文章对此类电路中的初始值进行了详细的分析。通过深入探讨,给出了奇异电路中电容电压和电感电流初始值的确定方法,并给出了几个应用实例。     

Zero-voltage-switching half-bridge DC-DC converter with modified PWM control method

Asymmetric control scheme is an approach to achieve zero-voltage switching (ZVS) for half-bridge isolated dc-dc converters. However, it is not suited for wide range of input voltage due to the uneven voltage and current components stresses. This paper presents a novel "duty-cycle-shifted pulse-width modulated" (DCS PWM) control scheme for half-bridge isolated dc-dc converters to achieve ZVS operation for one of the two switches without causing the asymmetric penalties in the asymmetric control and without adding additional components. Based on the DCS PWM control scheme, an active-clamp branch comprising an auxiliary switch and a diode is added across the isolation transformer primary winding in the half-bridge converter to achieve ZVS for the other main switch by utilizing energy stored in the transformer leakage inductance. Moreover, the auxiliary switch also operates at ZVS and zero-current switching (ZCS) conditions. Furthermore, during the off-time period, the ringing resulted from the oscillation between the transformer leakage inductance and the junction capacitance of two switches is eliminated owing to the active-clamp branch and DCS PWM control scheme. Hence, switching losses and leakage-inductance-related losses are significantly reduced, which provides the converter with the potential to operate at higher efficiencies and higher switching frequencies. The principle of operation and key features of the proposed DCS PWM control scheme and two ZVS half-bridge topologies are illustrated and experimentally verified.     

On the High-Speed Turn-Off of a Power Transistor by a Small Saturable Core

An effective method for reducing the size and weight of the switching dc-dc converter is to increase the switching frequency. To accomplish this with no deterioration in efficiency, it is necessary to suppress the switching loss per cycle by shortening the switching time. An efficient dc-dc converter operating at the megahertz region is presented. The turn-off time is shortened by using the current feedback and the core saturation. The turn-off mechanism is analyzed with the equivalent circuits. As a result, it is found that the excess carrier in the base region is discharged quickly by the large reverse base current, which flows when the energy stored in the base-emitter capacitance of the power transistor is transferred to the saturated inductance of the core with high frequency oscillation.     

Nonlinear Analysis of the Schottky-Barrier Mixer Diode

The waveshape of the local-oscillator voltage component that exists across the nonlinear junction of a Shottky-barrier diode is a fundamental determinant of mixer performance. This waveshape significantly differs from that of the total local-oscillator voltage impressed across the diode terminals since it is influenced by parasitic, particularly spreading resistance and contact inductance, which exist in series with the junction. The junction-voltage waveshapes resulting from a 9.375-GHz sinusoidal local-oscillator generator voltage are computed for three common equivalent-circuit models of the diode. In the first model the diode is represented by a nonlinear conductance in series with a fixed spreading resistance. The second model includes the nonlinear capacitance associated with the junction, and the third additionally includes the contact inductance. In each case, the junction-voltage waveshape is significantly nonsinusoidal. It is shown that the contact inductance can induce a peak inverse junction voltage that greatly exceeds the peak voltage impressed across the diode terminals. This parasitic reactance thus can have an important bearing on the burnout properties of the mixer diode.     

Analysis and optimization of a nondissipative LC turn-offsnubber

A nondissipative LC turn-off snubber is used to reduce the voltage stress on a switching transistor, which is caused by the energy stored in the transformer leakage inductance. A detailed analysis of the fundamental characteristics of a buck-boost converter with an LC snubber is given, clarifying the effect of the snubber capacitance. In particular, it is found that the transformer current increases with the snubber capacitance, the transistor surge voltage and power loss are evaluated, and the optimum value of the snubber capacitance is derived. The most effective value of the snubber inductance is also discussed     

Effect of Diode Parameters on Reflection-Type Phase Shifters (Short Papers)

This short paper describes effects of series inductance, shunt capacitance, and resistances associated with p-i-n diodes on the performance of reflection-type digital phase shifters using a shorted transmission line behind a shunt-mounted diode. It is found that the shunt capacitance is the most dominant reactance influencing the phase shift and it increases the phase-shift value. The series inductance reduces the phase-shift value. Expressions for phase shift in various cases are presented.     

Voltage Regulator Optimization Using Multiwinding Coupled Inductors and Extended Duty Ratio Mechanisms

This paper examines design optimization of voltage regulators (VRs) for microprocessor applications. Optimality of competing VR topologies, such as conventional (Conv) buck, coupled inductor, and extended duty ratio converters, is examined using efficiency norms and a new cost-per-watt metric to compare the amount of output capacitance (which is strongly correlated to the VR cost) to the efficiency. Coupled inductors provide a higher steady-state inductance than transient inductance. Lower transient inductance allows for smaller output capacitance. However, lower output capacitance requires a higher switching frequency and thus yields greater switching losses and lower efficiency. Extended duty ratio mechanisms reduce the switching voltage, and hence, reduce switching losses and increase efficiency. Experimental data are provided that the coupled inductor extended duty ratio converter has the same average efficiency, has higher light-load efficiency, and uses one-third of the output capacitance as the Conv multiphase buck converter. Hence, the combination of multiwinding coupled inductors and extended duty ratio mechanisms is shown to be the optimal VR configuration. The optimality concepts contributed in this paper resolve the ambiguity between VR cost and efficiency, and are essential for selecting the best solution among several competing VR designs.      

Cutoff frequency of microwave coaxial multimode limiter

Broad-band microwave diode limiters are realized in a coaxial low-pass filter structure. It is shown here that there is a cutoff frequency of the coaxial limiter above which the limiter will not function as a limiter. The cutoff frequency depends on diode package inductance, package capacitance, and the capacitances of the coaxial structure used to realize the limiter.     

Criteria for wide-band radial switch design

This paper presents criteria for the design of radial switches, such as can be used in electronically steered circular array antennas for satellite communications mobile terminals. The choice of the switching circuit and diode used in each channel is discussed and the required inductance for the diode shunt capacitance compensation for lower insertion loss is given. Analytical formulas are derived for the general case of an ideal transmission-line switch to show the dependence of the return-loss bandwidth on the choices of the line impedance. Important optimization criteria for lower insertion loss and increased bandwidth are drawn. The criteria have been used to guide the design of economical L-band microstrip switches for use in INMARSAT/MSAT antenna arrays, using low-cost printed-circuits and surface-mount plastic-encapsulated p-i-n diodes. Implementation results for insertion loss, reflection coefficient, and isolation between channels are reported     

Conduction power loss in MOSFET synchronous rectifier withparallel-connected Schottky barrier diode

The conduction power loss in an MOSFET synchronous rectifier with a parallel-connected Schottky barrier diode (SBD) was investigated. It was found that the parasitic inductance between the MOSFET and SBD has a large effect on the conduction power loss. This parasitic inductance creates a current that is shared by the two devices for a certain period and increases the conduction power loss. If conventional devices are used for under 1 MHz switching, the advantage of the low on-resistance MOSFET will almost be lost. To reduce the conduction loss for 10 MHz switching, the parasitic inductance must be a subnanohenley     

Microwave Diode Cartridge Impedance

In any application of a semiconductor microwave diode, the impedance of the diode cartridge plays a very important role. Two commonly made assumptions, which are quite erroneous, are that 1) the impedance of the diode cartridge consists simply of a shunt capacitance and whisker inductance, and 2) the metal-to-semiconductor junction at microwave frequencies behaves approximately as it does at 10 mc. In this paper it is shown that the impedance of the diode cartridge at microwave frequencies can be measured accurately by substituting a carbon die for the semiconductor.     

Design considerations of step recovery diodes with the aid of numerical large-signal analysis

Switching behavior of the step recovery diode (SRD) is studied through exact large-signal analysis. Two numerical methods are presented. One is suitable for steady-state and slow-transient calculations, while the other is based on a principle given by Scharfetter and Gummel, being appropriate for fast-transient calculation. Criteria for each method are described in terms of space and time intervals. A variety of doping profiles is generated by seven parameters, to determine the influence of each parameter on switching response. The normally defined transition time for current falloff from 90 to 10 percent consists of a physical transition phase and the phase of the CR time constant, which is defined as the product of junction capacitance and series resistance. The former is minimized by a narrow region of light doping, or by an abrupt profile, whereas the latter is minimized by a wide region of light doping, thus making a compromise necessary. Under the assumption of improved device fabrication technology, operation with low external impedance will allow total transition time to decrease to about one-half or one-third of today's standard sample. As was pointed out by Moll et al., a small amount of series inductance is desirable for fast transition.     

A novel method of high speed frequency shift keying modulation in mm waves

To place a high speed switching diode in the cavity of the mm wave scillator has the behavior equivalent to an inductive post. The on-and-off switching of the diode will give rise to the change of inductance, hence the change of parameters of the cavity, and the osaillating frequency. In this article, the basic principle and the measured result are given. It is found that this is an efficient method in high speed frequency shift keying (FSK) modulation for a mm wave transmitter in communication.     

Unified AC model for the resonant tunneling diode

A physics-based model is shown to yield the small-signal equivalent circuit of the resonant tunneling diode (RTD) including an analytic expression for both the quantum inductance and capacitance. This model unifies previous models by Brown et al. for quantum inductance and by Lake and Yang for quantum capacitance, and extends the RTD SPICE model of Broekaert. The equivalent circuit has been fit to both current-voltage and microwave S-parameter measurements of AlAs-InGaAs-InAs-InGaAs-AlAs RTDs from 45 MHz to 30 GHz and over biases from 0 to 0.81 V. Good agreement between the model and measurement is shown.     

关于谐振电路中能量问题的讨论

在谐振电路中,一般学生会认为电源所提供的能量全部被电阻所吸收,能量的互换只是发生在电感和电容之间.本文以RL与C并联谐振电路为例,给出了电路谐振时电感和电容中所储存的总能量随时间的变化规律,其电感和电容所储存的总能量并不是恒定值,因此认为谐振电路中,能量的互换只是发生在电感和电容之间的观念是错误的.     

基于MSP430单片机的智能阻抗测量仪设计

为了智能小巧高灵敏度地测量电阻、电感和电容,基于MSP430单片机控制、FPGA数字信号处理,设计了一个智能化的LRC（电感、电阻、电容）测量系统,实现了系统使用较少模拟器件,可以实现对电阻、电感、电容元件的自动识别。自动切换档位和测试频率以保证测量精度,具有良好的显示界面,测量范围广,体积小等特点。