Showing papers on "Buck converter published in 2000"

Improved light-load efficiency for synchronous rectifier voltage regulator module

Abstract: DC/DC converter with high efficiency over a wide load range is necessary for many low voltage applications, such as battery supplied systems and micro-processor power supplies-voltage regulator module (VRM). In order to improve the efficiency of low voltage converters, synchronous rectifier technology is widely used. The disadvantage of this technology is low efficiency at light load. This paper proposes a new technology, which utilizes the duty cycle signal, to improve light load efficiency with simple implementation. Since current sensors are not required, high density and high efficiency can be achieved that makes the whole circuit suitable for integration. In the paper, two application examples are given. Experimental results verified that the proposed control schemes significantly improve the efficiency of synchronous rectifier buck converters at light load.

Investigating coupling inductors in the interleaving QSW VRM

Abstract: The multi-channel interleaving quasi-square-wave (QSW) buck converter has been proved to be suitable for the voltage regulator module (VRM) with low voltage, high current and fast transient response. Integrated magnetic is used to reduce the size of the converter and improve efficiency. However, the structure of the integrated magnetic requires precise adjustment. In this paper, analysis shows that a properly designed integrated magnetic can improve the steady-state and dynamic performance without requiring precise adjustment.

Actively clamped bidirectional flyback converter

Abstract: An actively clamped bidirectional flyback converter is proposed. The converter's operation is examined in detail. All switches in the converter have zero-voltage-switching characteristics. A low-frequency behavior model and small-signal transfer functions are derived. It is found that the flow of current is directly under the control of the duty cycle, and that the transformer's leakage inductance has a significant effect on the control characteristic of the converter. It is expected that such bidirectional converters will find wide applications in the interconnection of multiple sources of DC power to a common bus (e.g., in a DC uninterruptible power supply). Simulation and experiment results are also presented.

High efficiency power conditioner employing low voltage DC bus and buck and boost converters

Abstract: A power conditioner interfaces a load to a fuel cell 10 that produces a low voltage that varies with the load. A dc-to-ac inverter 16 operates with a low voltage input provided by a dc bus 14 . When a positive step load change occurs, a low voltage battery 22 provides power equal to the step change until the fuel cell 10 is able to provide enough power to support the entire load. The power from the battery 22 is supplied to the varying dc bus 14 through a boost converter 12 . When very large positive load step changes occur, the battery can feed power to the dc bus through diode D 1 , rather than through the boost converter. Diode D 1 does not need to be used, but its use allows the boost converter to be sized for common load changes rather than for the maximum possible load change (such as might be seen during a faulted output). A buck converter converts the variable voltage on the dc bus 14 to the appropriate float charging voltage of the battery. The buck converter also supplies power for auxiliary equipment when available from the fuel cell. If the fuel cell is unable to provide the auxiliary power (such as during startup or load transients), then the auxiliary power can come directly from the battery.

Switching DC-to-DC converter with discontinuous pulse skipping and continuous operating modes without external sense resistor

Abstract: A switching DC-to-DC converter having at least one power channel including an inductor and a controller which generates at least one power switch control signal for at least one power switch of each power channel. The converter is configured to operate in a continuous mode when the inductor current remains above zero, to enter a discontinuous pulse skipping mode of operation when the inductor current falls to zero (which occurs when the load current is below a threshold value), and to leave the discontinuous pulse skipping mode and resume continuous mode operation when the inductor current rises above zero. The main difference between the continuous and discontinuous pulse skipping modes is that in the continuous mode, a power switch has a duty cycle determined by a feedback signal indicative of the converter's output potential Vout (so that the duty cycle is independent of the current drawn from the converter by the load), and in the discontinuous pulse skipping mode the power switch has a duty cycle which is the longer of a minimum duty cycle and a discontinuous (non-pulse-skipping) mode duty cycle. The discontinuous pulse skipping mode is more efficient than the continuous mode under conditions of low load current. Preferably, the controller includes cycle-skipping circuitry operable in the discontinuous pulse skipping mode and optionally also the continuous mode to cause the power switch to remain off for at least one cycle under the condition that the converter's output potential rises above a threshold. Preferably, the cycle-skipping circuitry includes a comparator which compares an error amplifier output (indicative of the converter output potential) with a threshold potential, and logic circuitry (e.g., an AND gate coupled to the comparator output) which asserts a latch-clearing signal once per switching cycle when the comparator output indicates that the converter's output has risen above the threshold. Other aspects of the invention are a switching controller for use in such a converter and a method for generating power switch control signals for such a converter in a discontinuous pulse skipping mode of operation.

Symmetrical multilevel converters with two quadrant DC-DC feeding

Abstract: In the technology sector of power electronics and control, the multilevel converter technology is still a rather new research area, but the application possibilities in the field of power drives and energy will demand more solutions with this promising technology. In the future, more converter systems will be realized with the multilevel topology. Up to now, multilevel converters have only been used in very particular applications, mainly due to the high costs and complexity of the multilevel converter system. The high costs are due to the fact that the latest technology on semiconductors, magnetic material for inductor and transformer cores and control system technology had to be used. But nowadays new developments in the fields of power semiconductors such as the IGBT, IGCT and perhaps in the future SiC switches as well as improvements of the performance of magnetic cores used in medium frequency transformers will favor the multilevel converters for many other application fields. It can be noted that the industrial trend is moving away from heavy and bulky passive components towards power converter systems using more and more semiconductor elements controlled by powerful processor systems integrating intelligent multi-task control algorithms. The presented work is a contribution to the large field of multilevel converters. It shows a certain kind of multilevel converter in a single phase and a three-phase configuration, called the series-connected four-quadrant converters (SCFQ). The two specialties of the presented converter type are a) that all the multilevel converter steps are fed by an identical DC voltage and b) that every multilevel converter step is realized with an individual AC-DC converter or four-quadrant converter. This type of multilevel converter is called multilevel converter with symmetrical feeding. In this work, a general theoretical development has been done for the use of this multilevel converter type. A special type of DC-DC converter is presented, in order to feed the individual four-quadrant converters of the multilevel converter with a constant DC voltage. All the developments and methods used are based on mathematical expressions. Various simulations using the latest software simulation tools are accomplished and are used to study different cases. The feasibility of the developments is underlined with a series of experimental results with all types of the used converters, which have been realized in the framework of this thesis. The main application for the multilevel converter presented in this work is the frontend power converter in locomotives. Instead of using a heavy low-frequency transformer to reduce the high-voltage from the catenary to a supportable voltage for the semiconductors, a multilevel converter concept is used. The multilevel converter is directly coupled to the catenary. There are many advantages compared to the existing solutions. In the same context, a novel solution of a multilevel converter has been developed for a locomotive usable on different power lines. The converter allows not only the operation on the high AC voltage power line (15kV), but also can be coupled to a medium-voltage DC power line (3kV). Three different configuration types of the locomotive converter have been developed and tested in a complex simulation environment. Besides the locomotive application, there are many more interesting applications for the symmetrical multilevel converter, e.g. in the fields of energy transmission (FACTS, static VAR compensators, electronic high-voltage transformers, etc.) and industrial drives. But certainly in the future with the availability of cheap semiconductors adapted to the needs of the multilevel converter, even more applications in lower power fields will be realized.

Buck or boost power converter

Abstract: A buck or boost (BOB) power converter circuit. A buck converter is cascaded with a boost converter to form a buck or boost circuit ( 20 ). The BOB converter is controlled by a controller ( 26 ) such that only the buck or boost converter is operating at any given time. A reference signal V ref can be applied to the controller ( 26 ) such that the output voltage from the converter closely tracks the reference signal. Positive and negative ramp signals are generated and an error feedback signal is compared with the ramp signals to control the output in accord with V ref . This is useful in application of the output voltage as the power supply to an RF Power Amplifier ( 16 ) so that the reference signal can represent the envelope of a signal to be transmitted and the RF PA ( 16 ) can operate at high efficiency.

Power converter mode transistioning method and apparatus

Abstract: A method and apparatus are provided for transitioning a power converter between a switched mode of operation and a linear regulator mode of operation. The power converter operates according to one or more intermediate modes of operation in which the switched mode and linear regulator modes cooperate to produce a shared power converter output. The power converter transitions between the various modes of operation in response to changes in circuit parametric conditions as defined by a series of state transition diagrams. Power converter output voltage is maintained in regulation during all modes of operation and transitions therebetween. The method and apparatus includes an integrated device that may be operated as a switch or a variable resistance device.

Operating a power converter at optimal efficiency

Abstract: A power converter control system is provided which combines a pulse train regulation control technique with a pulse train optimization technique, to control the output level of the power converter, while maintaining optimal performance for other power converter parameters. The power converter control system describe herein provides versatility not previously available in power converter control systems by providing features such as quasi-resonant mode control, discontinuous mode control, and/or power factor correction. A pulse optimizer adjusts or customizes, for example, the ON time, duty cycle or frequency of pulse train pulses output by a pulse generator. The adjusted pulses are gated by a pulse rate controller to selectively actuate a power switch, thereby regulating the output power level and optimize the overall performance of the power converter.

A comparative investigation on the use of random modulation schemes for DC/DC converters

Abstract: A comparative investigation on the use of random modulation schemes for DC/DC power converters is presented. The modulation schemes under consideration include randomized pulse position modulation, randomized pulsewidth modulation (PWM) and randomized carrier-frequency modulation with fixed and variable duty cycle. The paper emphasizes the suitability and applicability of each scheme in DC/DC power converters. Issues addressed include the effectiveness of randomness level on spreading the dominating frequencies that normally exist in constant-frequency PWM schemes, and the low-frequency power spectral density (PSD) of each scheme. The validity of the analyses is confirmed experimentally by using a DC/DC buck converter operating in the continuous conduction mode. The PSD of the output under each scheme is presented and compared.

Power-factor-corrected single-stage inductive charger for electric-vehicle batteries

Abstract: A novel power-factor-corrected single-stage AC-DC converter for inductive charging of electric vehicle batteries is introduced. The resonant converter uses the current-source characteristic of the series-parallel topology to provide power factor correction over a wide output power range from zero to full load. Some design guidelines for this converter are outlined. An approximate small-signal model of the converter is also presented Experimental results verify the operation of the new converter.

Negative impedance stabilizing controls for PWM DC-DC converters using feedback linearization techniques

Abstract: Power electronic converters, when tightly regulated, have constant power sink characteristics at their inputs. This is a destabilizing effect, which is known as negative impedance instability, for the DC/DC converters feeding these loads in a multi-converter power electronic system. In this paper, necessary and sufficient conditions of stability for PWM DC/DC converters with constant power and conventional constant voltage loads are expressed. A nonlinear robust stabilizing controller based on feedback linearization techniques is proposed. Furthermore, the stability of the proposed controller for the Buck converter using the second theorem of Lyapunov is verified.

High-power-density MHz-switching monolithic DC-DC converter with thin-film inductor

Abstract: In this paper, we report the newly developed DC-DC converter IC termed monolithic DC-DC converter, in which a thin-film inductor and power IC are integrated, and describe the micro DC-DC converter module utilizing this IC. The thin-film inductor used in the monolithic DC-DC converter was fabricated by RF sputtering, photosensitive polyimide lithography and electro-plating onto the power IC. The micro DC-DC converter module using the monolithic DC-DC converter achieved power density of 5.6 W/cm/sup 3/ at output power of 1 W and maximum efficiency of 83.3% at switching frequency of 3 MHz.

Topology and control method for power factor correction

Abstract: In a power factor corrected AC-to-DC power supply system, a DC-to-DC power converter is coupled to the output of an AC-to-DC power converter in order to produce a regulated DC output signal from a rectified AC input signal. The AC-to-DC power converter and the DC-to-DC power converter each includes a switch for controlling the operation of their respective power converter. The AC-to-DC converter includes an inductor. The system provides power factor correction for minimizing harmonic distortion by including a controller that receives the regulated DC output voltage as a feedback signal, and in response, produces a series of drive pulses having predetermined constant duty cycle. These pulses are simultaneously fed to each switch, to operate the respective converters alternately between ON and OFF states. When the AC-to-DC converter is driven by a fixed duty cycle of the series of pulses, power factor correction is improved since the current flowing through the inductor is substantially proportional to the waveform of the rectified AC input signal. By preselecting the value of the inductor, the AC-to-DC converter is operable in a discontinuous mode when the instantaneous rectified AC input signal is low and in a continuous mode when the instantaneous rectified AC input signal is high.

Interconnection of a photovoltaic panels array to a single-phase utility line from a static conversion system

Abstract: This paper presents the analysis of a static conversion system for treatment of the solar energy from photovoltaic panels. This system is interconnected with the mains power supply, contributing to the generation of the electrical energy. The power structure is composed of a current-fed push-pull converter, a buck converter, and a current inverter. The main features of the system are: simple control strategy, robustness, lower harmonic distortion of the current and natural isolation. The principle of operation, design procedure and experimental results are presented.

Development of a switched-capacitor DC-DC converter with bidirectional power flow

Abstract: This brief presents a switched-capacitor dc-dc converter that offers features of voltage step-down, voltage step-up, and bidirectional power flow. Concept of energy transfer is achieved by using two current-controlled bidirectional converter cells, which operate in antiphase. Good regulation capability and continuous input current waveform are other substantial advantages that facilitate practical realization and reduce electromagnetic interference with other circuits and supply networks. State-space averaging technique is applied to study the static and dynamic characteristics. A 20-W, 5-V-9-V prototype has been built and has an overall efficiency of over 80% in all operations.

High power factor rectifier based on buck converter operating in discontinuous capacitor voltage mode

Abstract: The buck converter with LC input filter operating in discontinuous capacitor voltage mode has inherent power factor correction properties and continuous input current. The paper presents a detailed analysis of the converter operating in this mode, leading to design criteria. Finally, experimental results for a 48 V/sub dc//100 W converter are presented.

Analysis and optimization of synchronous buck converter at high slew-rate load current transients

Abstract: Analytical equations are derived for a power supply system at high slew-rate load current transients. The analyzed model includes a synchronous buck converter, controller, output capacitor and supply bus parasitics. The impacts of system parameters on output voltage transient response are studied. An optimization procedure for power supply system design is suggested. Finally, influence of controller limitations on transient response characteristics is evaluated. Analytically derived waveforms are in good agreement with measurements.

Multiple voltage output buck converter with a single inductor

Abstract: A low cost, multiple output buck converter is provided using a single inductor, a single pulse width modulator integrated circuit, and two MOSFETs plus one additional MOSFET and capacitor for each voltage output.

Isolated interleaved-phase-shift-PWM DC-DC ZVS converters

Abstract: This paper presents a new isolated DC-DC zero-voltage-switching (ZVS) converter, which is composed of two half-bridge converters associated in series operating at constant frequency. The converter can be seen as an alternative to the ZVS-phase-shift full-bridge DC-DC converter for high-voltage applications. The paper proposes a new command strategy, named interleaved phase shift, which allows equalization of the input capacitor voltage, where each capacitor shares one-quarter of the total input voltage. Due to phase-shift modulation, the current is equally shared among main switches, reducing the converter conduction losses, when compared with conventional pulsewidth modulation. Furthermore, the input capacitors voltage oscillations are reduced due to load variations, as well as due to input DC-bus 120 Hz ripple. Just as with a ZVS-phase-shift full-bridge converter, the proposed converter achieves ZVS in a wide load range, as a function of the transformer leakage inductance. The paper describes the analysis, operating principles, and design procedure for the proposed converter. Experimental results from a 1.5 kW prototype converter operating at 100 kHz with isolated 60 V/25 A output are presented to validate the theoretical analysis and to demonstrate the performance of the proposed converter.

An improved ZVT PWM boost converter

Abstract: This paper proposes an improved ZVT-PWM boost converter. The main switch of the conventional ZVT-PWM converter is always switched at zero voltage. But the auxiliary switch is turned-off with switching loss due to hard switching condition. Therefore, the proposed converter reduces the turn-off switching loss of the auxiliary switch by using an additional circuit. All of the losses for the switches are minimized, and high power density system can be realized.

Ultra-capacitor based dynamically regulated charge pump power converter

Abstract: A charge pump power converter efficiently provides electrical power by dynamically controlling a switch matrix of the charge pump that includes a flying ultra-capacitor C U F . Instead of open-loop oscillator-based control, a dynamic controller provides power upon demand by sensing the output voltage and changing the operating frequency of the charge pump in response. Moreover, this closed-loop dynamic control intrinsically voltage regulates the output voltage of the charge pump power converter without the inefficient addition of a step-down voltage regulator, downstream of the power converter. In addition, this closed-loop dynamic control allows for maintaining a desired output voltage even with variations in the input voltage. Further efficiency is achieved by controlling the charging and discharging of the flying ultra-capacitor C U F , both in rate of current change and in voltage ripple.

Analysis of utility interactive photovoltaic generation system using a single power static inverter

Abstract: This paper presents the analysis of a static conversion system for treatment of the solar energy from photovoltaic panels. This system is interconnected with the mains power supply, contributing to the generation of the electrical energy. The power structure is composed of a current-fed push-pull converter, a buck converter, and a current inverter. The main features of the system are: simple control strategy, robustness, lower harmonic distortion of the current and natural isolation. The principle of operation, design procedure and experimental results are presented.

Controller arrangement for boost converter systems sourced from solar photovoltaic arrays or other maximum power sources

Abstract: Conventional power converter systems, such as boost converters, derive their input from sources that may be considered to have negligible output impedances. As such, the use of quite simple conventional control algorithms suffice to give acceptable performance. When the output impedance of the source to such a converter is no longer negligible, and moreover if the source has a markedly nonlinear output impedance, the simple conventional algorithms will no longer be adequate to satisfy the control requirements of the converter. The effect of driving such a converter from a type of source, for example a photovoltaic array which has a point of maximum power delivery within the operating range is discussed, as is the impact that the use of such a source has upon the control requirements of the converter. A novel control arrangement, which includes a complete embedded maximum power tracker, is then presented together with results validating the proposed controller.

A quadratic buck converter with lossless commutation

Abstract: High switching frequency associated with soft commutation techniques is a new trend in switching converters. Following this trend, the authors present a buck pulsewidth modulation converter, where the DC voltage conversion ratio has a quadratic dependence on duty cycle, providing a large step-down. By introducing two resonant networks, soft switching is attained, providing highly efficient operating conditions for a wide load range at high switching frequency. Contrary to most of the converters that apply soft-switching techniques, the switches presented are not subjected to high switch voltage or current stresses and, consequently, present low conduction losses. The authors present, for this converter, the principle of operation, theoretical analysis, relevant equations and simulation and experimental results.

Controlling a DC-DC converter by using the power MOSFET as a voltage controlled resistor

Abstract: Most converter designs assume that a closed power switch has zero volts across it. In general, this is a valid assumption that reduces the design complexity. However the fact that a power switch does have a finite resistance means that there will be a nonzero voltage across it during its on time. This voltage can be taken advantage of. This paper proposes a simple control technique that utilizes the variable resistance of the power MOSFET in a dc-dc converter. This is the first switched mode power supply that uses the power switch in more than two states or operating points. It is also the first switched mode power supply that uses the power switch as a variable control device as well as a power device. A 48-5-V 20-W forward converter is implemented to confirm the theory and demonstrate its practicality. The proposed technique provides self oscillation, self overload protection, zero voltage switching (ZVS), input voltage feedforward, and a reduced component count and cost.

Modeling average current mode control [of power convertors]

Abstract: An averaged small signal model is presented which predicts some of the previously reported phenomena and offers new insights with analytical expressions useful for design. Detailed analysis is given for the buck converter topology with the boost and buck-boost results also provided. The modulator gain, for a first order approximation, is shown to be constant as in voltage mode control. Guidelines are presented to optimize the design of the current loop and control-to-output transfer functions are given which are necessary to compensate the voltage loop. Experimental data is provided, in the case of the buck converter, to develop and verify the model.

Converter and inductor design for fast-response microprocessor power delivery

Abstract: The fundamental constraints for fast-response buck converters for applications such as microprocessor power delivery are analyzed, with an emphasis on the role of the inductor. Optimum values of ripple ratio, and thus inductor value, are calculated. Based on this analysis, microfabricated inductor designs are analyzed, and an inductor design is proposed with predicted performance including power density of 158 W/cm/sup 2/ and 95% efficiency for an 8 MHz, 3.6 V to 1.1 V converter.

Use of a priori information in the identification of global nonlinear models-a case study using a buck converter

Abstract: This paper investigates some issues related to grey-box identification. In particular it is discussed how a priori information about the system static nonlinearity can be incorporated into the model. Also, it is shown that in some applications involving nonlinear systems, there must be a tradeoff between the accuracy of the estimated model static nonlinearity and the quality of forecasts. These concepts are applied in the identification of a real DC-DC buck converter operating in continuous mode. Improvement in model global stability was achieved by using simple a priori information that takes into account the steady-state voltage relation of the converter. Models that are valid over a wide operating range are included. Such models are compact and can be estimated directly from data obtained from the converter.

Microwave power amplifiers with digitally-controlled power supply voltage for high efficiency and high linearity

Abstract: A power amplifier architecture is presented which comprises a basic amplifier with an efficient, high modulation bandwidth DC-DC converter. The amplifier and the DC-DC converter are controlled by a digital signal processor that provides input signal pre-distortion, supply voltage optimization and equalization. Experimental results at 950 MHz showed ACPR values acceptable for IS-95 CDMA handset applications. With variable power supply, the overall efficiency improved by a factor of 1.4/spl times/ (when averaged over representative conditions of usage).