Showing papers on "Buck converter published in 2005"

High efficiency power converter

Abstract: A high efficiency power converter comprises a boost converter for converting an input voltage to a first voltage on a first output, a buck converter for converting the input voltage to a second voltage on a second output, a linear regulator for converting the first voltage to a third voltage on the second output when the second voltage is lower than a first threshold, and a voltage detector for detecting the input voltage for preventing a reverse current flowing from the second output to the buck converter when the input voltage is lower than a second threshold.

High step-up converter with coupled-inductor

Abstract: In this study, a high step-up converter with a coupled-inductor is investigated. In the proposed strategy, a coupled inductor with a lower-voltage-rated switch is used for raising the voltage gain (whether the switch is turned on or turned off). Moreover, a passive regenerative snubber is utilized for absorbing the energy of stray inductance so that the switch duty cycle can be operated under a wide range, and the related voltage gain is higher than other coupled-inductor-based converters. In addition, all devices in this scheme also have voltage-clamped properties and their voltage stresses are relatively smaller than the output voltage. Thus, it can select low-voltage low-conduction-loss devices, and there are no reverse-recovery currents within the diodes in this circuit. Furthermore, the closed-loop control methodology is utilized in the proposed scheme to overcome the voltage drift problem of the power source under the load variations. As a result, the proposed converter topology can promote the voltage gain of a conventional boost converter with a single inductor, and deal with the problem of the leakage inductor and demagnetization of transformer for a coupled-inductor-based converter. Some experimental results via examples of a proton exchange membrane fuel cell (PEMFC) power source and a traditional battery are given to demonstrate the effectiveness of the proposed power conversion strategy.

On the practical design of a sliding mode voltage controlled buck converter

Abstract: This paper presents a simple and systematic approach to the design of a practical sliding mode voltage controller for buck converters operating in continuous conduction mode. Various aspects of the design, including the associated practical problems and the proposed solutions, are detailed. A simple and easy-to-follow design procedure is also described. Experimental results are presented to illustrate the design procedure.

A 233-MHz 80%-87% efficient four-phase DC-DC converter utilizing air-core inductors on package

Abstract: We demonstrate an integrated buck dc-dc converter for multi-V/sub CC/ microprocessors. At nominal conditions, the converter produces a 0.9-V output from a 1.2-V input. The circuit was implemented in a 90-nm CMOS technology. By operating at high switching frequency of 100 to 317 MHz with four-phase topology and fast hysteretic control, we reduced inductor and capacitor sizes by three orders of magnitude compared to previously published dc-dc converters. This eliminated the need for the inductor magnetic core and enabled integration of the output decoupling capacitor on-chip. The converter achieves 80%-87% efficiency and 10% peak-to-peak output noise for a 0.3-A output current and 2.5-nF decoupling capacitance. A forward body bias of 500 mV applied to PMOS transistors in the bridge improves efficiency by 0.5%-1%.

Tapped-inductor buck converter for high-step-down DC-DC conversion

Abstract: The narrow duty cycle in the buck converter limits its application for high-step-down dc-dc conversion. With a simple structure, the tapped-inductor buck converter shows promise for extending the duty cycle. However, the leakage inductance causes a huge turn-off voltage spike across the top switch. Also, the gate drive for the top switch is not simple due to its floating source connection. This paper solves all these problems by modifying the tapped-inductor structure. A simple lossless clamp circuit can effectively clamp the switch turn-off voltage spike and totally recover the leakage energy. Experimental results for 12V-to-1.5V and 48V-to-6V dc-dc conversions show significant improvements in efficiency.

System and method for input current shaping in a power converter

Abstract: A power converter delivers electrical power from an electrical power source to a load according to a plurality of operation modes corresponding to different levels of input voltage or output current. The power converter comprises a power stage for delivering the electrical power from the power source to the load, a switch in the power stage that electrically couples or decouples the load to the power source, and a switch controller coupled to the switch for controlling the on-times and off-times of the switch according to the plurality of operation modes. Each of the operation modes correspond to associated ranges of at least one of an input voltage to the power converter and an output current from the power converter, where the associated ranges are different for each of the operation modes.

High boost converter using voltage multiplier

Abstract: With the increasing demand for renewable energy, distributed power included in fuel cells have been studied and developed as a future energy source. For this system, a power conversion circuit is necessary to interface the generated power to the utility. In many cases, a high step-up DC/DC converter is needed to boost low input voltage to high voltage output. Conventional methods using cascade DC/DC converters cause extra complexity and higher cost. The conventional topologies to get high output voltage use flyback DC/DC converters. They have the leakage components that cause stress and loss of energy that results in low efficiency. This paper presents a high boost converter with a voltage multiplier and a coupled inductor. The secondary voltage of the coupled inductor is rectified using a voltage multiplier. High boost voltage is obtained with low duty cycle. Theoretical analysis and experimental results verify the proposed solutions using a 300 W prototype.

A comparative evaluation of isolated bi-directional DC/DC converters with wide input and output voltage range

Abstract: The working principles and design equations of four different isolated, bi-directional DC to DC converter topologies (a dual active bridge converter, a series resonant converter and two multiple stage topologies) for a 2 kW bi-directional battery charger that can be operated in a wide input and output voltage range are presented in this paper. The results of a detailed mathematical analysis of the converter topologies as well as digital simulation results are used to select the most efficient topology for this specific converter application, where the two-stage series resonant converter is identified to be the most promising, with up to 90% efficiency at rated power.

A fixed-frequency pulsewidth modulation based quasi-sliding-mode controller for buck converters

Abstract: This paper presents the design and analysis of a fixed-frequency pulsewidth modulation (PWM)-based quasi-sliding-mode voltage controller for buck converters from a circuit design perspective. A practical design approach that aims at systematizing the procedure for the selection of the control parameters is presented. In addition, a simple analog form of the controller for practical realization is provided. The resulting controller exhibits the same structure as a PWM proportional derivative (PD) linear controller, but with an additional component consisting of the instantaneous input voltage and the instantaneous output voltage. Simulation and experimental results show that the performance of the converter agrees with the theoretical design.

Boost Converter with Coupled Inductors and Buck-Boost Type of Active Clamp

Abstract: This paper proposes a boost converter with coupled inductors and buck-boost type of active clamp. In the converter, the active-clamp circuit is used to eliminate voltage spike induced from the trapped energy in leakage inductor of the coupled inductors. The active switch in the converter can still sustain a proper duty ratio when even under high step-up applications, reducing voltage and current stresses significantly. Moreover, since both main and auxiliary switches can be turned on with zero voltage switching, switching loss can be reduced and conversion efficiency therefore can be improved significantly. A 200 W prototype of the proposed boost converter was built from which experiment results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively. It is relatively feasible for applications to fuel cell and battery power conversion

Power budgeting of a multiple-input buck-boost converter

Abstract: The use of a multiple-input buck-boost converter for budgeting power between different energy sources is discussed. It is shown mathematically that the idealized converter can accommodate arbitrary power commands for each input source while maintaining a prescribed output voltage. Power budgeting is demonstrated experimentally for a real converter under various circumstances, including a two-input (solar and line-powered) system. A closed-loop control example involving simultaneous tracking of output voltage and set-point tracking of the solar array shows that an autonomous system is realizable.

Multilevel intelligent universal transformer for medium voltage applications

Abstract: The solid-state transformer allows add-on intelligence to enhance power quality compatibility between source and load. It is desired to demonstrate the benefits gained by the use of such a device. Recent advancement in semiconductor devices and converter topologies facilitated a newly proposed intelligent universal transformer (IUT), which can isolate a disturbance from either source or load. This paper describes the basic circuit and the operating principle for the multilevel converter based IUT and its applications for medium voltages. Various power quality enhancement features are demonstrated with computer simulation for a complete IUT circuit.

High-efficiency DC/DC converter with high voltage gain

Abstract: A high-efficiency converter with high voltage gain applied to a step-up power conversion is presented In the proposed strategy, a high magnetising current charges the primary winding of the coupled inductor, and the clamped capacitor is discharged to the auxiliary capacitor when the switch is turned on In contrast, the magnetising current flows continuously to boost the voltage in the secondary winding of the coupled inductor, and the voltages across the secondary winding of the coupled inductor, the clamped capacitor and the auxiliary capacitor are connected in series to charge the output circuit Thus, the related voltage gain is higher than in conventional converter circuits Moreover, this scheme has soft-switching and voltage-clamped properties, ie the switch is turned on under zero-current switching and its sustainable voltage is comparatively lower than the output voltage, so that it can select low-voltage low-conduction-loss devices and there are no reverse-recovery currents within the diodes in this circuit In addition, closed-loop control methodology is utilised in the proposed scheme to overcome the voltage drift problem of the power source under the load variations As a result, the proposed converter topology can promote the voltage gain for a conventional boost converter with a single inductor, and deal with the problem of the leakage inductor and demagnetisation of the transformer for a coupled-inductor-based converter Some experimental results via examples of a proton exchange membrane fuel cell power source and a traditional battery are given to demonstrate the effectiveness of the proposed power conversion strategy

Single-phase Z-source PWM AC-AC converters

Abstract: The letter proposes a new family of simple topologies of single-phase PWM ac-ac converters with a minimal number of switches: voltage-fed Z-source converter and current-fed Z-source converter. By PWM duty-ratio control, they become "solid-state transformers" with a continuously variable turns ratio. All the proposed ac-ac converters in this paper employ only two switches. Compared to the existing PWM ac-ac converter circuits, they have unique features: providing a larger range of output ac voltage with buck-boost, reversing or maintaining phase angle, reducing in-rush and harmonic current, and improving reliability. The operating principle and control method of the proposed topologies are presented. Analysis, simulation, and experimental results are given using the voltage-fed Z-source ac-ac converter as an example. The analysis can be easily extended to other converters of the proposed family. The proposed converters could be used in voltage regulation, power regulation, and so on.

A novel winding-coupled buck converter for high-frequency, high-step-down DC-DC conversion

Abstract: This paper analyzes the fundamental limitations of the buck converter for high-frequency, high-step-down dc-dc conversion. Further modification with additional coupled windings in the buck converter yields a novel topology, which significantly improves the efficiency without compromising the transient response. An integrated magnetic structure is proposed for these windings so that the same magnetic cores used in the buck converter can be used here as well. Furthermore, it is easy to implement a lossless clamp circuit to limit the device voltage stress and to recover inductor leakage energy. This new topology is applied for a 12V-to-1.5V/25A voltage regulator module (VRM) design. At a switching frequency of 2MHz, over 80% full-load efficiency is achieved, which is 8% higher than that of the conventional buck converter.

Magnetics on silicon: an enabling technology for power supply on chip

Abstract: Data from the ITRS2003 roadmap for 2010 predicts voltages for microprocessors in hand-held electronics will decrease to 0.8V with current and power increasing to 4A and 3W, respectively. Consequently, low power converters will move to multimegahertz frequencies with a resulting reduction in capacitor and inductor values by factors of 5 and 20, respectively. Values required at 10 MHz, for a low power buck converter, are estimated at 130 nH and 0.6 uF, compatible with the integration of magnetics onto silicon and the concept of power supply-on-chip (PSOC). A review of magnetics-on-silicon shows that inductance values of 20 to 40nH/mm/sup 2/ can be achieved for winding resistances less than 1/spl Omega/. A 1-/spl mu/H inductance can be achieved at 5 MHz with dc resistance of 1/spl Omega/ and a Q of four. Thin film magnetic materials, compatible with semiconductor processing, offer power loss density that is lower than ferrite by a factor of 5 at 10 MHz. Other data reported includes, lowest dc resistance values of 120 m/spl Omega/ for an inductance of 120 nH; highest Q of 15 for an inductance of 350 nH and a current of 1 A for a 1- /spl mu/H inductor. Future technology challenges include reducing losses using high resistivity, laminated magnetic materials, and increasing current carrying capability using high aspect-ratio, electroplated copper conductors. Compatible technologies are available in the power switch, control, and packaging space. Integrated capacitor technology is still a long-term challenge with maximum reported values of 400 nF/cm/sup 2/.

A converter circuit and technique for increasing the output efficiency of a variable power source

Abstract: The present invention provides a converter circuit (300) and accompanying switch mode power conversion (315) technique to efficiently capture the power generated from a solar cell array (210) that would normally have been lost, for example, under reduced incident solar radiation. In an embodiment of the invention, the converter circuit generates an output current from the solar cell power source using a switch mode power converter. A control loop is closed around the input voltage to the converter circuit and not around the output voltage. The output voltage is allowed to float, being clamped by the loading conditions. If the outputs from multiple units are tied together, the currents will sum. If the output(s) are connected to a battery (220), the battery's potential will clamp the voltage during charge. This technique allows all solar cells in an array that are producing power and connected in parallel to work at their peak efficiency.

EMI reduction in switched power converters using frequency Modulation techniques

Abstract: Frequency-modulation techniques have been used to reduce electromagnetic interference (EMI) produced by the clock of digital systems working in the range of hundreds of megahertz. The working principle consists of modulating the original constant clock frequency in order to spread the energy of each single harmonic into a certain frequency band, thus reducing the peak amplitude of EMI at harmonic frequencies. Nowadays, the switching frequency of power converters has increased up to values that make interesting the application of such techniques to reduce EMI emissions due to switching of power circuits. This paper presents the theoretical principles of frequency modulation using deterministic profiles for the modulating function. It shows the effectiveness of such methods in terms of EMI reduction for different modulation profiles and other parameters. The method is compared with other methods using random modulation. Tests carried out on a buck converter are presented for experimental validation of the method. A short discussion on optimal modulation profiles and parameters is also included.

Power tracking for nonlinear PV sources with coupled inductor SEPIC converter

Abstract: The photovoltaic (PV) generator exhibits a nonlinear i-v characteristic and its maximum power (MP) point varies with solar insolation. In this paper, a V2-based MP point tracking (MPPT) scheme is developed using a buck-boost transformation topology. Although several buck-boost transformation topologies are available we have considered here a coupled inductor SEPIC converter for experimentation. To achieve almost ripple-free array current we have used ripple steering phenomena with the help of integrated inductor. This integrated inductor not only reduces the magnetic core requirements but also improves converter performance. Mathematical models are formulated and tracking algorithm is evolved. A combined PV system simulation model is developed in the SIMULINK. For a given solar insolation, the tracking algorithm changes the duty ratio of the converter such that the solar cell array (SCA) voltage equals the voltage corresponding to the MP point. This is done by the tracking algorithm, which mainly computes the power proportional to square of terminal voltage and changes the duty ratio of the converter so that this power is maximum. The proposed algorithm is implemented in real-time with the help of Analog Device ADMC-401 DSP evaluation module. The tracking program is developed to perform experimental investigations using analog-to-digital converter (ADC) interrupt. Using this processor we are able to track the MP within 200 ms. The proposed peak power tracking effectiveness is demonstrated through simulation and experimental results.

A constant-frequency method for improving light-load efficiency in synchronous buck converters

Abstract: The low-voltage synchronous rectifier buck topology suffers from low efficiency at light loads due to dissipation that does not scale with load current In this paper we present a method for improving light-load efficiency in synchronous buck converters by reducing gate drive losses We propose a new gate drive technique whereby the gate voltage swing dynamically scales with load current such that gate drive loss is traded for conduction loss Since conduction losses scale with the square of load current, an optimal gate swing exists that, at light loads, is shown to be less than the supply voltage Using this method we obtain a 625% increase in converter efficiency at a load current of 10 mA and operating at a constant switching frequency of 2 MHz

Dynamic hysteresis band control of the buck converter with fast transient response

Abstract: A dynamic hysteresis control of the buck converter for achieving high slew-rate response to disturbances is proposed. The hysteresis band is derived from the output capacitor current that predicts the output voltage magnitude after a hypothesized switching action. Four switching criteria are formulated to dictate the state of the main switch. The output voltage can revert to the steady state in two switching actions after a large-signal disturbance. The technique is verified with the experimental results of a 50 W buck converter.

A family of high power density unregulated bus converters

Abstract: This paper begins by reviewing current bus converters and exploring their limitations. Next, a family of inductor-less bus converters is proposed to overcome the limitations. In the new bus converters, magnetizing current is used to achieve zero-voltage-switching (ZVS) turn-on for all switches. The resonant concept is used to achieve nearly zero-current-switching (ZCS) turn-off for the primary switches and no body diode loss for the synchronous rectifiers (SRs). Meanwhile, the self-driven method can be easily applied to save drive loss of SRs. Based on these concepts, a full-bridge bus converter is built in the quarter-brick size to verify the analysis. The experimental results indicate that it can achieve 95.5% efficiency at 500-W, 12-V/45-A output. Compared with industry products, this topology can dramatically increase the power density. These concepts are also applied to nonisolated dc/dc converters. As an example, a resonant Buck converter is proposed and experimentally demonstrated.

A matrix converter based micro-turbine distributed generation system

Abstract: This paper investigates the use of an AC-AC matrix converter, as an alternative to AC-DC-AC converter system, to interface a high-speed micro-turbine generator (MTG) to a utility grid as a distributed generation unit. A new switching strategy and a control mechanism for the converter are presented. Based on time-domain simulations in the PSCAD/EMTDC environment, the dynamic behavior of a micro-turbine generation system, including the dynamic models of the micro-turbine (thermodynamics), generator, matrix converter, converter control and micro-turbine control, is studied. The studies conclude that a matrix converter is technically a viable option to interface a MTG to a utility grid.

An integrated CMOS current-sensing circuit for low-Voltage current-mode buck regulator

Abstract: An integrated current-sensing circuit for low-voltage buck regulator is presented. The minimum achievable supply voltage of the proposed current-sensing circuit is 1.2 V implemented in a CMOS technology with V/sub TH/=0.85 V, and the current-sensing accuracy is higher than 94%. With the developed current-sensing circuit, a buck regulator, which is able to operate at a 1.2-V supply, is implemented. A maximum output current of 120 mA and power-conversion efficiency higher than 89% are achieved.

An improved boost converter with coupled inductors and buck-boost type of active clamp

Abstract: This paper proposes an improved boost converter with coupled inductors and buck-boost type of active-clamp feature, PWM control and zero-voltage switching in both main and auxiliary switches. In the converter, the active-clamp circuit is used to eliminate voltage spike induced from the leakage inductor of the coupled inductors. The active switch of the converter can still sustain a proper duty cycle when it operates with a high step-up voltage ratio, reducing voltage stress significantly. A set of passive-clamping circuit is adopted to eliminate undesired resonance between leakage inductor of the coupled inductors and stray capacitor of the boost diode, recovering trapped energy. Thus, conversion efficiency can be improved significantly. A 200 W prototype of the proposed boost converter was built from which experimental results have shown that efficiency can reach as high as 92% and surge can be suppressed effectively.

Analysis of Double Step-Down Two-Phase Buck Converter for VRM

Abstract: A novel two-phase buck converter suitable to apply the power supplies for MPU is proposed Compared to conventional two-phase buck converter, the proposed converter essentially has double step-down ratio as Eo/Ei = D/2 and high efficiency is realized by reducing the switching loss of the switching elements In addition the current ripple of the output smoothing capacitor is improved to the same value as that of conventional four-phase buck converter Moreover the current unbalance between two inductors in each phase is removed automatically without any current sensing means The above fine characteristics are simply achieved an additional capacitor

Three-level buck converter for envelope tracking in RF power amplifiers

Abstract: This paper proposes a three-level buck converter for efficient wide-bandwidth envelope tracking in RF power amplifiers (RFPA). The focus is on low-power battery-operated systems, and the goal is to enable practical implementation of the envelope elimination and restoration (EER) technique, which theoretically allows realization of a highly linear, highly efficient RFPA for non-constant envelope modulations. In terms of ripple, switching frequency and bandwidth tradeoffs, it is shown that the three-level buck converter is similar to the two-phase configuration, while employing a single inductor in the power stage. Additionally, a digital control technique for regulation of the flying capacitor voltage is proposed to ensure signal tracking fidelity. Experimental results show the improved performance of a three-level buck converter prototype as regards efficiency and ripple rejection for the illustrative case of tracking the envelope of a two-tone test signal

Portable hybrid applications for AC/DC load sharing

Abstract: Portable hybrid applications for AC/DC load sharing includes circuitry for simultaneously using at least one of external AC, internal DC power and/or external DC power. The apparatus also includes an input power receptacle for receiving at least one of AC power and external DC power. A power router inside the apparatus routes at least one of AC power, internal DC power, and external DC power to provide power for an application. An apparatus for providing DC to DC conversion includes a tip and a DC to D C whip connected to the tip. A male plug is connected to the second end of the whip. A buck converter within the male plug converts DC power to a DC power level associated With the whip and transmits the converted DC power along the DC to DC whip to the tip. Alternatively, an internal DC source provides internal DC power.

A planar inductor using Mn-Zn ferrite/polyimide composite thick film for low-Voltage and large-current DC-DC converter

Abstract: A new planar inductor using a composite magnetic core for low voltage and large current dc-dc converter has been developed The composite material consisted of a 40% volume fraction of Mn-Zn ferrite particle with a mean diameter of 10 /spl mu/m and polyimide matrix The composite magnetic core exhibited a low relative permeability of 6 The fabricated planar inductor with a size of 15/spl times/15/spl times/14 mm consisted of an inner two-turn copper square spiral coil, a top 350-/spl mu/m-thick composite magnetic core and a bottom 1-mm-thick Ni-Zn ferrite substrate The inductor had a dc coil resistance of 15 m/spl Omega/ and an inductance of 140 nH The degradation of inductance was below 4% at a superimposed dc current of 10 A A synchronous rectifier type buck converter with a switching frequency of 1 MHz, an input voltage of 5 V, and an output voltage of 1 V was constituted using a planar inductor, and exhibited a maximum conversion efficiency of 80% at 4 A

Open-loop power-stage transfer functions relevant to current-mode control of boost PWM converter operating in CCM

Abstract: This paper presents the analysis of open-loop power-stage dynamics relevant to current-mode control for a boost pulsewidth-modulated (PWM) dc-dc converter operating in continuous-conduction mode (CCM). The transfer functions from input voltage to inductor current, from duty cycle to inductor current, and from output current to inductor current are derived. The delay from the MOSFET gate drive to the duty cycle is modeled using a first-order Pade/spl acute/ approximation. The derivations are performed using an averaged linear small-signal circuit model of the boost converter for CCM. The transfer functions can be used in modeling the complete boost PWM converter when current-mode control is used. The theory was in excellent agreement with the experimental results, enforcing the validity of the transfer functions derived.