Scalability of Quasi-hysteretic FSM-based Digitally Controlled Single-inductor Dual-string Buck LED Driver To Multiple Strings

There has been growing interest in Single-Inductor Multiple-Output (SIMO) DC-DC converters due to its reduced cost and smaller form factor in comparison with using multiple single-output converters. An application for such a SIMO-based switching converter is to drive multiple LED strings in a multi-channel LED display. This paper proposes a quasi-hysteretic FSM-based digitally controlled Single-Inductor Dual-Output (SIDO) buck switching LED Driver operating in Discontinuous Conduction Mode (DCM) and extends it to drive multiple outputs. Based on the time-multiplexing control scheme in DCM, a theoretical upper limit of the total number of outputs in a SIMO buck switching LED driver for various backlight LED current values can be derived analytically. The advantages of the proposed SIMO LED driver include reducing the controller design complexity by eliminating loop compensation, driving more LED strings without limited by the maximum LED current rating, performing digital dimming with no additional switches required, and optimization of local bus voltage to compensate for variability of LED forward voltage (VF) in each individual LED string with smaller power loss. Loosely-binned LEDs with larger VF variation can therefore be used for reduced LED costs.postprin

Single-Inductor, Dual-Input CCM Boost Converter for Multi-Junction PV Energy Harvesting

abstract: This thesis presents a power harvesting system combining energy from sub-cells of multi-junction photovoltaic (MJ-PV) cells. A dual-input, inductor time-sharing boost converter in continuous conduction mode (CCM) is proposed. A hysteresis inductor current regulation in designed to reduce cross regulation caused by inductor-sharing in CCM. A modified hill-climbing algorithm is implemented to achieve maximum power point tracking (MPPT). A dual-path architecture is implemented to provide a regulated 1.8V output. A proposed lossless current sensor monitors transient inductor current and a time-based power monitor is proposed to monitor PV power. The PV input provides power of 65mW. Measured results show that the peak efficiency achieved is around 85%. The power switches and control circuits are implemented in standard 0.18um CMOS process.Dissertation/ThesisMasters Thesis Engineering 201

Control Techniques for DC-DC Buck Converter with Improved Performance

The switched-mode dc-dc converters are some of the most widely used power electronics circuits for its high conversion efficiency and flexible output voltage. These converters used for electronic devices are designed to regulate the output voltage against the changes of the input voltage and load current. This leads to the requirement of more advanced control methods to meet the real demand. Many control methods are developed for the control of dc-dc converters. To obtain a control method that has the best performances under any conditions is always in demand. Conventionally, the dc-dc converters have been controlled by linear voltage mode and current mode control methods. These controllers offer advantages such as fixed switching frequencies and zero steady-state error and gives a better small-signal performance at the designed operating point. But under large parameter and load variation, their performance degrades. Sliding mode (SM) control techniques are well suited to dc-dc converters as they are inherently variable structure systems. These controllers are robust concerning converter parameter variations, load and line disturbances. SM controlled converters generally suffer from switching frequency variation when the input voltage and output load are varied. This complicates the design of the input and output filters. The main objective of this research work is to study different control methods implemented in dc-dc converter namely (linear controllers, hysteresis control, current programmed control, and sliding mode (SM) control). A comparison of the effects of the PWM controllers and the SM control on the dc-dc buck converter response in steady state, under line variations, load variations is performed

Single-inductor, multiple-output buck converter with parallel source transient recovery

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Includes bibliographical references (leaves 65-66).To address the need for multiple regulated voltage supplies in electronic devices, this thesis presents a modeling and design study of a single-inductor, multiple-output (SIMO) DC-DC buck converter with parallel source transient recovery. This converter would provide substantial cost and space savings over traditional options for producing multiple supply voltages. Operating in pseudo-continuous conduction mode (PCCM), it can supply heavy loads while not suffering from cross-regulation problems. The parallel current source circuitry at each output will greatly dampen any voltage spikes that may occur due to sudden load changes, thus improving transient performance. While the entire converter could not be nicely simulated as envisioned, the initial steps and accomplishments outlined in this thesis show definite promise. The proposed converter certainly merits further research, as the problems encountered here most likely stem from implementation and control issues rather than fundamental flaws in the idea.by Charles Jackson King III.M.Eng

Dual-frequency dual-inductor multiple-outputs (DF-DIMO) buck converter topologies with fully-integrated output filters

In multi-core DSPs, there is a need for multiple independent power supplies to power the digital cores. Each power supply needs to have fast dynamic response and must support a wide range of output voltage with up to hundreds of mA load current. In this dissertation, the key performance metrics in power converter design are introduced, the advantages and dis-advantages of the conventional power converter topology are analyzed and a new Dual-Frequency Dual-Inductor Multiple-Output (DF-DIMO) buck converter topology is presented to improve the limitations of the conventional topologies. The proposed topology employs a dual-phase 20-MHz current-mode-controlled input stage to reduce the inductance required per phase to only 200 nH, and a 4-output 100-MHz comparator-controlled fully-integrated output stage to reduce the capacitance required per output to 10 nF. To enable each output to handle up to 250-mA load with less than 40-mV voltage ripple, a 3rd-order bond-wire-based notch filter is employed at each output for voltage ripple suppression. Additionally, the proposed design employs dynamic output re-ordering to enhance dynamic and cross-regulation performance, interleaved pulse-skipping to enhance light-load efficiency, and high-gain local output feedback to enhance DC load Regulation. Targeting multi-core DSPs, the proposed design is implemented in standard 65-nm CMOS technology with 1.8-V input, and outputs in the range of 0.6–1.2 V with a total load of 1 A. It achieves a peak efficiency of 74%, less than 40-mV output voltage ripple, 0.5-V/70-ns Dynamic Voltage Scaling (DVS), and settling time of less than 85 ns for 125-mA all with no cross regulations

State Separate Modular Modeling Methodology of Multioutput DC-DC Converters

Conventional modeling and simulation of n -output dc-dc converters requires (n+1) × (n+1) matrix computations. This approach increases the modeling approach's complexity and increases the design and simulation time required for the modeling process. A state separate modeling methodology is proposed where each state of the dc-dc converter is considered separately and combined with the help of a multiplexer. The proposed modeling approach is modular and thus improves the scalability to multiple outputs. The proposed methodology aids the designer in designing and modeling multioutput dc-dc converters faster, enabling fast prototyping. The proposed model outperforms the existing mathematical models in terms of computation time. The output voltage variation to duty cycles has a root mean square error in between 0.08 and 0.22 V

An ultra-low power voltage regulator system for wireless sensor networks powered by energy harvesting

A DC-DC converter is an important power management module as it converts one DC voltage level to another suitable for powering a desired electronic system. It also stabilizes the output voltage when fluctuations appear in the power supplies. For those wireless sensor networks (WSNs) powered by energy harvesting, the DC-DC converter is usually a linear regulator and it resides at the last stage of the whole energy harvesting system just before the empowering sensor node. Due to the low power densities of energy sources, one may have to limit the quiescent current of the linear regulator in the sub-uA regime. This severe restriction on quiescent current could greatly compromise other performance aspects, especially the transient response. This dissertation reports a voltage regulator system topology which utilizes the sensor node state information to achieve ultra-low power consumption. The regulator system is composed of two regulators with different current driving abilities and quiescent current consumptions. The key idea is to switch between the two regulators depending on the sensor state. Since the "right" regulator is used at the "right" time, the average quiescent current of the regulator system is minimized, and the trade-off between low quiescent current and fast transient response has been eliminated. In order to minimize the average quiescent current of the system, nano-ampere reference current design is studied, and the proposed reference current circuit is shown (theoretically and experimentally) to reduce the supply voltage dependence by 5X. The regulator system has been fabricated and tested using an ON Semiconductor 0.5 μm process. It has been verified through experiments that the proposed system reduces the quiescent current by 3X over the state-of-the-art in the literature; and, more importantly, it achieves low quiescent current, low dropout voltage, and fast transient response with small output voltage variation all at the same time. The thesis further presents data on the application of energy harvesting system deriving energies from various RF signals to power a commercial off-shelf wireless sensor node

Battery-sourced switched-inductor multiple-output CMOS power-supply systems

Wireless microsystems add intelligence to larger systems by sensing, processing and transmitting information which can ultimately save energy and resources. Each function has their own power profile and supply level to maximize performance and save energy since they are powered by a small battery. Also, due to its small size, the battery has limited energy and therefore the power-supply system cannot consume much power. Switched-inductor converters are efficient across wide operating conditions but one fundamental challenge is integration because miniaturized dc-dc converters cannot afford to accommodate more than one off-chip power inductor. The objective of this research is to explore, develop, analyze, prototype, test, and evaluate how one switched inductor can derive power from a small battery to supply, regulate, and respond to several independent outputs reliably and accurately. Managing and stabilizing the feedback loops that supply several outputs at different voltages under diverse and dynamic loading conditions with one CMOS chip and one inductor is also challenging. Plus, since a single inductor cannot supply all outputs at once, steady-state ripples and load dumps produce cross-regulation effects that are difficult to manage and suppress. Additionally, as the battery depletes the power-supply system must be able to regulate both buck and boost voltages. The presented system can efficiently generate buck and boost voltages with the fastest response time while having a low silicon area consumption per output in a low-cost technology which can reduce the overall size and cost of the system.Ph.D