Showing papers on "Buck converter published in 2007"

Buck-Boost Converter for Sensorless Power Optimization of Piezoelectric Energy Harvester

Abstract: This paper presents a comprehensive model for miniature vibration-powered piezoelectric generators and analyses modes of operation and control of a buck-boost converter for the purpose of tracking the generators optimal working points. The model describes the generator's power dependence with the mechanical acceleration and frequency, and helps in the definition of the load behaviour for power optimization. Electrical behaviour of the input of buck-boost converter in discontinuous current mode turns out to be in perfect agreement with the considered optimization criteria with a very simple, sensorless control. Experimental results show that the converter controlled by a very low consumption circuit effectively maximizes the power flow into a 4.8 V rechargeable battery connected to the converter output. The converter's efficiency is above 84% for input voltages between 1.6 and 5.5 V, and for output powers between 200 muW and 1.5 mW. The presented circuit and control can be used as well for power optimization of electromagnetic energy harvesting devices.

Small-Signal Discrete-Time Modeling of Digitally Controlled PWM Converters

Abstract: The letter presents an exact small-signal discrete-time model for digitally controlled pulsewidth modulated (PWM) dc-dc converters operating in constant frequency continuous conduction mode (CCM) with a single effective A/D sampling instant per switching period. The model, which is based on well-known approaches to discrete-time modeling and the standard Z-transform, takes into account sampling, modulator effects and delays in the control loop, and is well suited for direct digital design of digital compensators. The letter presents general results valid for any CCM converter with leading or trailing edge PWM. Specific examples, including approximate closed-form expressions for control-to-output transfer functions are given for buck and boost converters. The model is verified in simulation using an independent system identification approach.

High-efficiency dc/dc voltage converter including capacitive switching pre-converter and up inductive switching post-regulator

Abstract: A DC/DC converter includes a pre-converter stage, which may include a charge pump, and a post-regulator stage, which may include a Buck converter. The duty factor of the post-regulator stage is controlled by a feedback path that extends from the output terminal of the DC/DC converter to an input terminal in the post-regulator stage. The pre-converter steps the input DC voltage up or down by a positive or negative integral or fractional value, and the post-regulator steps the voltage down by a variable amount depending on the duty factor at which the post-regulator is driven. The converter overcomes the problems of noise glitches, poor regulation, and instability, even near unity input-to-output voltage conversion ratios.

Multibit $\Sigma$ – $\Delta$ PWM Digital Controller IC for DC–DC Converters Operating at Switching Frequencies Beyond 10 MHz

Abstract: An integrated digital controller for dc-dc switch-mode power supplies (SMPS) used in portable applications is introduced. The controller has very low power consumption, fast dynamic response, and can operate at programmable constant switching frequencies exceeding 10 MHz. To achieve these characteristics, three novel functional blocks, a digital pulse-width modulator based on second-order sigma-delta concept (Sigma-Delta DPWM), dual-clocking mode compensator, and nonlinear analog-to-digital converter are combined. In steady state, to minimize power consumption, the controller is clocked at a frequency lower than SMPS switching frequency. During transients the clock rate is increased to the switching frequency improving transient response. The controller integrated circuit (IC) is fabricated in a standard 0.18-mum process and tested with a 750-mW buck converter prototype. Experimental results show the controller current consumption of 55 muA/MHz and verify closed-loop operation at programmable switching frequencies up to 12.3 MHz. Simulation results indicating that this architecture can potentially support operation at switching frequencies beyond 100 MHz are also presented.

A High Efficiency Dual-Mode Buck Converter IC For Portable Applications

Abstract: This paper presents the design of a novel wide output current range dual-mode dc to dc step-down (Buck) switching regulator/converter. The converter can adaptively switch between pulsewidth modulation (PWM) and pulse-frequency modulation (PFM) both with very high conversion efficiency. Under light load condition the converter enters PFM mode. The function of closing internal idle circuits is implemented to save unnecessary switching losses. The converter can be switched to PWM mode when the load current is greater than 100 mA. Soft start operation is designed to eliminate the excess large current at the start up of the regulator. The chip has been fabricated with a TSMC 2P4M 0.35 mum polycide CMOS process. The range of the operation voltage is from 2.7 to 5 V, which is suitable for single-cell lithium-ion battery supply applications. The maximum conversion efficiency is 95% at 50 mA load current. Above 85 % conversion efficiency can be reached for load current from 3 to 460 mA.

An Accurate, Low-Voltage, CMOS Switching Power Supply With Adaptive On-Time Pulse-Frequency Modulation (PFM) Control

Abstract: Integrated switching power supplies with multimode control are gaining popularity in state-of-the-art portable applications like cellular phones, personal digital assistants (PDAs), etc., because of their ability to adapt to various loading conditions and therefore achieve high efficiency over a wide load-current range, which is critical for extended battery life. Constant-frequency, pulsewidth modulated (PWM) switching converters, for instance, have poor light-load efficiencies because of higher switching losses while pulse-frequency modulation (PFM) control in discontinuous-conduction mode (DCM) is more efficient at light loads because the switching frequency and associated switching losses are scaled down with load current. This paper presents the design and integrated circuit prototype results of an 83% power efficient 0.5-V 50-mA CMOS PFM buck (step-down) dc-dc converter with a novel adaptive on-time scheme that generates a 27-mV output ripple voltage from a 1.4- to 4.2-V input supply (battery-compatible range). The output ripple voltage variation and steady-state accuracy of the proposed supply was 5 mV (22-27 mV) and 0.6% whereas its constant on-time counterpart was 45 mV (10-55 mV) and 3.6%, respectively. The proposed control scheme provides an accurate power supply while achieving 2%-10% higher power efficiency than conventional fixed on-time schemes with little circuit complexity added, which is critical during light-loading conditions, where quiescent current plays a pivotal role in determining efficiency and battery-life performance

Voltage Scalable Switched Capacitor DC-DC Converter for Ultra-Low-Power On-Chip Applications

Abstract: This paper presents a voltage scalable switched capacitor (SC) DC-DC converter which employs on-chip charge- transfer capacitors. The DC-DC converter makes use of multiple topologies to achieve scalable voltage generation while minimizing conduction loss and a technique called divide-by-3 switching to minimize the loss due to bottom-plate parasitics. It also uses automatic frequency scaling to reduce switching losses. The converter employs an all digital control which consumes no static power. The voltage scalable SC DC-DC converter with integrated on-chip charge-transfer capacitors was implemented in a 0.18 mum CMOS process and achieves above 70% efficiency over a wide range of load powers from 5 muW to 1 mW, while delivering load voltages from 300 mV to 1.1 V. The active area consumed by the converter is 0.57 mm2.

Power-Factor-Corrected Single-Stage Inductive Charger for Electric Vehicle Batteries

Abstract: A novel power-factor-corrected single-stage alternating current/direct current 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

Consideration of Impedance Matching Techniques for Efficient Piezoelectric Energy Harvesting

Abstract: This study investigates multiple levels of impedance-matching methods for piezoelectric energy harvesting in order to enhance the conversion of mechanical to electrical energy. First, the transduction rate was improved by using a high piezoelectric voltage constant (g) ceramic material having a magnitude of g33 = 40 times 10-3 V m/N. Second, a transducer structure, cymbal, was optimized and fabricated to match the mechanical impedance of vibration source to that of the piezoelectric transducer. The cymbal transducer was found to exhibit ~40 times higher effective strain coefficient than the piezoelectric ceramics. Third, the electrical impedance matching for the energy harvesting circuit was considered to allow the transfer of generated power to a storage media. It was found that, by using the 10-layer ceramics instead of the single layer, the output current can be increased by 10 times, and the output load can be reduced by 40 times. Furthermore, by using the multilayer ceramics the output power was found to increase by 100%. A direct current (DC)-DC buck converter was fabricated to transfer the accumulated electrical energy in a capacitor to a lower output load. The converter was optimized such that it required less than 5 mW for operation.

Current bypass for distributed power harvesting systems using dc power sources

Abstract: A converter circuit providing multiple current bypass routes between the output leads to provide reliability in a series connection of several converters. If the converter malfunctions due to component failure, the current bypass routes provide a path for the current that views the malfunctioning converter as substantially a short. Diodes prevent backflow into the power source connected to the converter. Redundancy is provided in the bypass portions of the converter circuit that provides alternate parallel paths in case a defective component in one of the paths opens the circuit along that path. In one example, the converter is implemented as a buck plus boost converter where either the buck or the boost portion or both are operative responsive to a controller controlling the switches of both portions. Most of the converter circuit may be implemented in an integrated circuit.

Autotuning of Digitally Controlled DC–DC Converters Based on Relay Feedback

Abstract: This paper proposes a simple autotuning technique for digitally controlled dc-dc converters. The proposed approach is based on the relay feedback method and introduces perturbations on the output voltage during converter soft-start. By using an iterative procedure, the tuning of proportional-integral-derivative parameters is obtained directly by including the controller in the relay feedback and by adjusting the controller parameters based on the specified phase margin and control loop bandwidth. A nice property of the proposed solution is that output voltage perturbations are introduced while maintaining the relay feedback control on the output voltage. The proposed algorithm is simple, requires small tuning times, and it is compliant with the cost/complexity constraints of integrated digital integrated circuits. Simulation and experimental results of a synchronous buck converter and of a dc-dc boost converter confirm the effectiveness of the proposed solution

Conducted EMI Reduction in Power Converters by Means of Periodic Switching Frequency Modulation

Abstract: Spread spectrum clock generation techniques were originally developed to reduce electromagnetic interference (EMI) in communications and microprocessor systems working in the range of hundreds of megahertz. Nowadays, the switching frequency of power converters has been increasing up to values that make worthy the application of such switching frequency modulation techniques to reduce EMI emissions in power converters. Although random modulations have been applied before to power converters, periodic patterns can provide some advantages. First, theoretical principles of frequency modulation using three periodic patterns for the modulating function are presented. The influence of some important modulation parameters on the EMI reduction is analyzed and some considerations about the EMI filters design are also presented. The effectiveness of such methods in terms of EMI reduction is demonstrated theoretically and confirmed with experimental results obtained from tests carried out on two converters. The first one is a 2.5 W buck converter that can be switched up to 1 MHz and the second one is a 600 W boost converter switching at 40 kHz. In both cases, attenuations obtained in conducted EMI are evaluated. Finally, special attention has been paid to input current and output voltage ripple in order to evaluate possible undesired side-effects produced by this technique.

A Monolithic Current-Mode Buck Converter With Advanced Control and Protection Circuits

Abstract: A monolithic current-mode pulse width modulation (PWM) step-down dc-dc converter with 96.7% peak efficiency and advanced control and protection circuits is presented in this paper. The high efficiency is achieved by "dynamic partial shutdown strategy" which enhances circuit speed with less power consumption. Automatic PWM and "pulse frequency modulation" switching boosts conversion efficiency during light load operation. The modified current sensing circuit and slope compensation circuit simplify the current-mode control circuit and enhance the response speed. A simple high-speed over-current protection circuit is proposed with the modified current sensing circuit. The new on-chip soft-start circuit prevents the power on inrush current without additional off-chip components. The dc-dc converter has been fabricated with a 0.6 mum CMOS process and measured 1.35 mm2 with the controller measured 0.27 mm2. Experimental results show that the novel on-chip soft-start circuit with longer than 1.5 ms soft-start time suppresses the power-on inrush current. This converter can operate at 1.1 MHz with supply voltage from 2.2 to 6.0 V. Measured power efficiency is 88.5-96.7% for 0.9 to 800 mA output current and over 85.5% for 1000 mA output current.

Tri-Modal Half-Bridge Converter Topology for Three-Port Interface

Abstract: This letter proposes a novel converter topology that interfaces three power ports: a source, a bidirectional storage port, and an isolated load port. The proposed converter is based on a modified version of the isolated half-bridge converter topology that utilizes three basic modes of operation within a constant-frequency switching cycle to provide two independent control variables. This allows tight control over two of the converter ports, while the third port provides the power balance in the system. The switching sequence ensures a clamping path for the energy of the leakage inductance of the transformer at all times. This energy is further utilized to achieve zero-voltage switching for all primary switches for a wide range of source and load conditions. Basic steady-state analysis of the proposed converter is included, together with a suggested structure for feedback control. Key experimental results are presented that validate the converter operation and confirm its ability to achieve tight independent control over two power processing paths. This topology promises significant savings in component count and losses for power-harvesting systems. The proposed topology and control is particularly relevant to battery-backed power systems sourced by solar or fuel cells

A Multistage Interleaved Synchronous Buck Converter With Integrated Output Filter in 0.18 $\mu$ m SiGe Process

Abstract: The design and analysis of a fully integrated multistage interleaved synchronous buck dc-dc converter with on-chip filter inductor and capacitor is presented. The dc-dc converter is designed and fabricated in 0.18 mum SiGe RF BiCMOS process technology and generates 1.5 V-2.0 V programmable output voltage supporting a maximum output current of 200 mA. High switching frequency of 45 MHz, multiphase interleaved operation, and fast hysteretic controller reduce the filter inductor and capacitor sizes by two orders of magnitude compared to state-of-the-art converters and enable a fully integrated converter. The fully integrated interleaved converter does not require off-chip decoupling and filtering and enables direct battery connection for integrated applications. This design is the first reported fully integrated multistage interleaved, zero voltage switching synchronous buck converter with monolithic output filters. The fully integrated buck regulator achieves 64% efficiency while providing an output current of 200 mA.

Impact of power density maximization on efficiency of dc-dc converter systems

Abstract: The demand for decreasing costs and volume leads to a constantly increasing power density of industrial converter systems. In order to improve the power density further different aspects, like thermal management and electromagnetic effects must be considered in conjunction with the electrical design. Therefore, a comprehensive optimization procedure based on analytical models for minimizing volume of DC-DC converter systems has been developed at the Power Electronic Systems Laboratory of the ETH Zurich. Based on this procedure three converter topologies - a phase shift converter with current doubler and with capacitive output filter and a series-parallel resonant converter - are optimized with respect to power density for a telecom supply (400V/48V). There, the characteristic of the power density, the efficiency and the volume distribution between the components as function of frequency is discussed. For the operating points with maximal power density also the loss distribution is presented. Further more, the sensitivity of the optimum with respect to junction temperature, cooling and core material is investigated. The highest power density is achieved by the series-parallel resonant converter. For a 5 kW supply a density of approximately 12 kW/ltr. and a switching frequency of ca. 130 kHz results.

Design of a 1-MHz LLC Resonant Converter Based on a DSP-Driven SOI Half-Bridge Power MOS Module

Abstract: In this paper, the design of a 1-MHz LLC resonant converter prototype is presented. Aiming to provide an integrated solution of the resonant converter, a half-bridge (HB) power metal oxide semiconductor (MOS) module employing silicon-on-insulator technology has been designed. Such a technology, which is suitable for high-voltage and high-frequency applications, allows enabling HB power MOSFET modules operating up to 3MHz with a rated voltage of 400V. The power device integrates the driving stages of the high-side and low-side switch along with a latch circuit used to implement over-voltage/over-current protection. The module has been designed to be driven by a digital signal processor device, which has been adopted to perform frequency modulation of the resonant converter. By this way, output voltage regulation against variations from light- to full-loaded conditions has been achieved. The issues related to the transformer design of the LLC resonant converter are discussed, too. Owing to the high switching frequency experienced by the converter, 3F4 ferrite cores have been selected for their low magnetic power losses between 0.5 and 3 MHz and core temperatures up to 120degC. The resonant converter has been designed to operate in an input voltage range of 300-400V with an output voltage of 12V and a maximum output power of 120W. Within these design specifications, a performance analysis of the LLC converter has been conducted, comparing the results obtained at the switching frequencies of 500kHz and 1MHz. A suitable model of the LLC resonant converter has been developed to aid the prototype design.

Interleaved Zero-Current-Transition Buck Converter

Abstract: This paper introduces interleaved zero-current-transition (ZCT) converters where two sets of switches are operating out-of-phase and share the load power equally. Turn-on transitions at zero current and a significant reduction of the losses associated with diode reverse recovery are accomplished through addition of two small inductors. This paper describes a 30-kW (300 V/100 A) interleaved ZCT buck converter operating at 32-kHz effective switching frequency. Losses and efficiency of the experimental prototype compare favorably against the standard and interleaved hard-switched buck converters. Constant frequency operation with low switching losses and low output current ripple is very well suited for the realization of dc power supplies in plasma processes.

DC–DC Power Converters

Abstract: DC–DC power converters employ switched-mode circuitry to change dc voltages and currents with efficiencies approaching 100% Basic converter circuits can reduce the voltage (buck converter), increase the voltage (boost converter) or both (buck-boost, Cuk, and SEPIC converters) Transformer-isolated circuits include the bridge, forward, and flyback converters Loss mechanisms include conduction loss arising from resistances or forward voltage drops of the power components, and switching loss generated during the transistor and diode switching transitions Synchronous rectifiers can be employed to reduce the significant conduction loss caused by diode forward voltage drops in low-voltage applications The discontinuous conduction mode may arise when the inductor current is sufficiently small, which causes the output voltage to be strongly load-dependent Voltage-mode control employs pulse-width modulation to regulate the converter output voltage or other quantities through variation of the transistor duty cycle Another popular technique is current-mode control, in which a circuit eauses the peak transistor current to follow a control reference signal Averaging methods are commonly employed to model the dynamics and efficiency of dc–dc power converters The state-space averaging method leads to an equivalent circuit model that predicts the converter small-signal transfer functions The circuit averaging technique is easily applied to simulate the converter transfer functions, in both continuous and discontinuous conduction modes, using computer programs such as SPICE 1 Introduction 2 Converter Circuit Topologies 3 Analysis of Converter Waveforms 4 Transformer Isolation 5 Switch Implementation 6 Discontinuous Conduction Mode 7 Current-Mode Control 8 DC-DC Converter Modeling Keywords: pulse-width modulation; voltage-mode control; buck converter; boost converter; buck-boost converter; state-space averaging method

A Current Fed Two-Inductor Boost Converter With an Integrated Magnetic Structure and Passive Lossless Snubbers for Photovoltaic Module Integrated Converter Applications

Abstract: In this paper, a photovoltaic (PV) module integrated converter is implemented with a current fed two-inductor boost converter cascaded with a line frequency unfolder. The current source is a sinusoidally modulated two-phase buck converter with an interphase transformer. The boost cell operates at a fixed duty ratio and has an integrated magnetic structure. The two inductors and the transformer are integrated into one magnetic core. Passive lossless snubbers are employed to recover the energy trapped in the transformer leakage inductance and to minimize the switching losses. The two-inductor boost converter output interfaces with the mains via an unfolding stage, where the MOSFETs are driven by the PV gate drivers. Experimental results are provided for a 100-W converter developing a single phase 240-V 50-Hz output

Integrated bi-directional converter for plug-in hybrid electric vehicles

Abstract: This invention relates to a power module for a plug-in hybrid electric vehicle including an integrated converter having a rectifier changing AC to DC, a DC/DC converter changing from a first voltage to a second voltage, and a battery storing electrical energy. The integrated converter operates in three modes 1) AC plug-in charging mode, 2) boost mode supplying power from the battery to the electrical bus and 3) buck mode supplying power from the electrical bus to the battery. The integrated converter utilizes the same single inductor during each of the three operating modes to reduce cost and weight of the system.

The Tapped-Inductor Boost Converter

Abstract: In many emerging applications it is required a high boosting gain; in the literature has been proposed many topologies to make this possible, since the traditional dc-dc boost converter can not make the very high boosting function by itself. In this paper a different approach to obtain the high boosting gain is proposed: the tapped-inductor boost converter. This converter has few components and high efficiency, and also operates in a simple way. Analysis and experimental results are presented.

Analysis of Inductor Current Sharing in Nonisolated and Isolated Multiphase dc–dc Converters

Abstract: Current sharing among inductors is an important issue in both isolated and nonisolated dc-dc converters. In this paper, average current sharing is in-depth modeled and analyzed for both interleaved multiphase buck converters and isolated current-doubler dc-dc converters. The features and comparison of various current-sharing techniques used in isolated and nonisolated dc-dc converters are presented, and the corresponding design guidelines are provided based on the theoretical analysis. The analysis reveals that the state-of-the-art current-sharing technique for multiphase buck converters cannot be directly applied to isolated current-doubler rectifier (CDR) dc-dc converters to achieve balanced inductor currents. Passive and active current-sharing methods are proposed for isolated current-doubler dc-dc converters to balance two inductor currents. Experimental results are presented to verify the modeling analysis and the proposed current-sharing techniques for CDRs in isolated dc-dc converters.

LCL-T Resonant Converter With Clamp Diodes: A Novel Constant-Current Power Supply With Inherent Constant-Voltage Limit

Abstract: The LCL-T resonant converter behaves as a constant-current (CC) source when operated at the resonant frequency. The output voltage of a CC power supply increases linearly with the load resistance. Therefore, a constant-voltage (CV) limit must be incorporated in the converter for its use in practical applications wherein the open-load condition is commonly experienced by a CC power supply, such as in an arc welding power supply. A novel LCL-T resonant converter with clamp diodes is proposed in this paper, which has built-in CC-CV characteristics. Since the CC-CV characteristics are inherent to the converter, and complex feedback control is not required, the proposed converter is rugged and reliable. The principle of operation of the converter is explained. Experimental results on a 500-W prototype are presented to demonstrate the inherent CC-CV behavior of the converter. Simple extensions of the topology featuring variable CV limits are described

A New Resonant Gate Drive Circuit for Synchronous Buck Converter

Abstract: This paper proposes a new resonant gate drive circuit for driving both the control metal oxide semiconductor field effect transistor (MOSFET) and synchronous MOSFET in a synchronous buck converter. The circuit can recover more than 70% of the conventional gate drive loss. More importantly, the driving circuit can also reduce the switching loss. It charges and discharges the gate of MOSFET at a constant current during switching interval. Other advantages of the proposed circuit include better noise immunity for dv/dt turn on, less sensitive to parasitic track inductance. The experimental prototype shows that the loss reduction is 10% of the output power for 12 V input, 1.5 V/15 A output with switching frequency of 1 MHz.

A Simple Single-Sensor MPPT Solution

Abstract: Maximum power point trackers (MPPTs) are used to ensure optimal utilization of solar cells. The implementation essentially involves sensing input current and voltage. An MPPT algorithm uses this information to maximize power drawn from the solar cells. Understandably, such realization is costly. Current state of the art allows replacing one of the sensors by complicated computations. In the present work, an empirical observation is used to develop a strategy, which employs a single voltage sensor and carries out simple computations for a buck converter-based MPPT

Active-Clamping ZVS Flyback Converter Employing Two Transformers

Abstract: This paper presents a two-transformer active-clamping zero-voltage-switching (ZVS) flyback converter, which is mainly composed of two active-clamping flyback converters. By utilizing two separate transformers, the proposed converter allows a low-profile design to be readily implemented while retaining the merits of a conventional single-transformer topology. The presented two-transformer active-clamping ZVS flyback converter can approximately share the total load current between two secondaries. Therefore, the transformer copper loss and the rectifier diode conduction loss can be decreased. Detailed analysis and design of this new two-transformer active-clamping ZVS flyback converter are described. Experimental results are recorded for a prototype converter with an ac input voltage ranging from 85 to 135 V, an output voltage of 24 V and an output current of 8 A, operating at a switching frequency of 180 kHz.

High-Efficiency Active-Clamp Forward Converter With Transient Current Build-Up (TCB) ZVS Technique

Abstract: In this paper, an active-clamp forward converter with transient current build-up zero-voltage switching (ZVS) technique is proposed. The proposed converter is suitable for the low-voltage and high-current applications. The structure of the proposed converter is the same as that of the conventional active-clamp forward converter. However, since it controls the secondary synchronous switch to build up the primary current during the very short period of time, the ZVS operation is easily achieved without any additional conduction losses of magnetizing current in the transformer and clamp circuit. Furthermore, there are no additional circuits required for the ZVS operation of power switches. Therefore, the proposed converter can achieve the high efficiency and low electromagnetic-interference noise resulting from the soft switching without any additional conduction losses and shows the high power density resulting from the high efficiency and no additional components added. The operational principle and design example are presented. Experimental results demonstrate that the proposed converter can achieve an excellent ZVS performance throughout all load conditions and a significant improvement in the efficiency for the 100-W (5 V, 20 A) prototype converter

Characterization of $Cdv/dt$ Induced Power Loss in Synchronous Buck DC–DC Converters

Abstract: Good understanding of power loss in a high frequency synchronous buck converter is important for design optimization of both discrete and system level. Most of the power losses are relatively easy to quantify. The exception is the power loss associated with Cdv/dt induced turn on of the low-side metal oxide semiconductor field effect transistor (synchronous rectifier). This paper characterizes the Cdv/dt induced power loss in two ways. First, detailed device characterization, in-circuit testing, and modeling are used for a comparative loss calculation. This method offers detailed loss breakdown but requires specialized test equipment and is rather complicated and time consuming. A simple method is then introduced to accurately quantify the Cdv/dt loss. With this method, the Cdv/dt induced power loss on synchronous buck converters at different operation conditions can be readily assessed. The impacts of Cdv/dt induced loss on different applications are addressed. Finally, the design tradeoffs at both discrete and system levels are discussed.

Limit-Cycle Oscillations Based Auto-Tuning System for Digitally Controlled DC–DC Power Supplies

Abstract: This paper introduces a new method and system for parameter extraction and automated controller adjustment, suitable for low power digitally controlled DC-DC switch-mode power supplies (SMPS). The system allows closed-loop calibration throughout regular converter operation. During a short-lasting test phase, SMPS parameters, such as output capacitance and load, are estimated by examining the amplitude and frequency of intentionally introduced limit cycle oscillations in duty ratio control variable as well as from its steady state value. Accordingly, a digital compensator is automatically constructed to provide fast dynamic response and good output voltage regulation. In addition, the load estimation data are used for improving efficiency of a converter having segmented transistors. It is performed through a selection of driving sequence resulting in minimized sum of switching and conduction losses. The effectiveness of the system is demonstrated on an experimental 400 kHz, 9 V-to-3.3 V, 10 W, digitally controlled synchronous buck converter.