Buck converter

Summary

A buck converter or step-down converter is a DC-to-DC converter which steps down voltage (while stepping up current) from its input (supply) to its output (load). It is a class of switched-mode power supply. Switching converters (such as buck converters) provide much greater power efficiency as DC-to-DC converters than linear regulators, which are simpler circuits that lower voltages by dissipating power as heat, but do not step up output current. The efficiency of buck converters can be very high, often over 90%, making them useful for tasks such as converting a computer's main supply voltage, which is usually 12 V, down to lower voltages needed by USB, DRAM and the CPU, which are usually 5, 3.3 or 1.8 V. Buck converters typically contain at least two semiconductors (a diode and a transistor, although modern buck converters frequently replace the diode with a second transistor used for synchronous rectification) and at least one energy storage element (a capacitor, induct

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Diabete is a disease which is spreading faster than ever, impacting now a larger population. Patients suffering from this disease need the injection of insulin to control extracellular sugar levels. Pharmaceutical companies developed injector pens to allow patients to inject themself the right amount of drug. But the dosage depends on many parameters as the previous meal, current blood sugar level... and a wrong dosage can lead to health problem e.g., loss of conciousness at short terms and severe diseases like cardiac pathologies at long terms... To prevent these situations, a smart pen cap has been developed at Valtronic Technologies to follow and log the individual injections by measuring the level of drug in the pen, the temperature, and the relative humidity to allow the patient and the medical staff to have an history of the injections and the climatic conditions.Injector pen and smart pen cap have been firstly presented with a non-exhaustive list of different physics which can be used to measure a level of liquid. For need of precision, the capacitance technique is the best technology choice. Therefore, the smart pen cap is based on a capacitive sensor. Different capacitance converter topologies have been compared through a bibliographic study. It appears that the Lock-in converter gives the best sensitivity and Charge Sensitivity Amplifier has the lowest power consumption. A trade-of was to use a capacitance-to-digital-converter. A chip from Analog device has been selected due to its high resolution below the femto-farad level, its simple interface and its availability on the market which allows a fast development and industrialisation. Then, switch and electronic structure are presented. First tests with an empty device have been conducted to find the noise floor, which is below 0.1fF.Subsequently, a study of different electrodes configuration has been performed. Firstly, an analysis on two parallel flat electrodes has been conducted using theoretical and simulation approaches. Then, two semi-cylindrical electrodes have been analysed. A comparison has been made between two theoretical methods which are: considering an infinite number of parallel flat electrodes following the shape of the semi-cylindrical electrodes and the conformal mapping methods. This last method gives coherent results when comparing real measurements and simulation. The device is equipped with semi-cylindrical electrodes which allow for a small package and a good correlation between capacitance and drug level with a convertion slope of 0.5fF/µL. Tests have been performed which give an error of +-1 IU and +-4 IU for large injection (set point equal to 72 IU).Finally, the study of some parasitic effects is presented in the last section. An important effect is the climatic effect which affects the capacitance due to variation of electric permittivity linked to temperature change and water absorption of certain materials as plastics. To compensate for this effect, reference electrodes and a climatic sensor have been implemented. Another important effect comes from the cartridge position in the non-uniform electric field of the smart pen cap. A four electrodes device has been realized to allow a perpendicular rotation of the electric field to obtain a more constant averaged electric field. As a consequence, the position impact of the cartridge has been reduced. Other effects have been considered. The device can detect a minimum injection of 52uL.

EPFL2021

Enhanced-performance integrated Resonant Switched-Capacitor and Buck DC-DC converters for application in extreme radiation and magnetic field environments

Giacomo Ripamonti

DC-DC converters based on Application Specific Integrated Circuits (ASICs) have been developed in this doctoral work for the High-Luminosity Large Hadron Collider (HL-LHC) experiments at CERN. They step down the voltage from a 2.5 V line and supply a load current up to 3 A. The main focus has been the miniaturization of the converters while maintaining high efficiency, together with the improvement of the dynamic performance and the minimization of the impact of substrate parasitic devices. These are challenges that industry and research are facing to power modern microprocessors, with the aim of minimizing the system volume, cost and power consumption, while guaranteeing good regulation performance. Miniaturization is a key requirement for application in the HL-LHC experiments, since any added material is detrimental for the physics performance. In addition, the converters must be tolerant to a high magnetic field (up to 4 T) and to ultra-high levels of radiation. Tolerance to the magnetic field is achieved by employing air-core inductors (which are the bulkiest components on the board), while radiation-hard ASICs have been designed in this work in a commercial 130 nm CMOS technology by extensively applying hardening by design techniques. Converters using two different architectures have been designed: a buck converter, which had been identified in a previous work as a good option to achieve high efficiency and low mass, and a Resonant Switched-Capacitor (ReSC) converter, which can further increase the power density while keeping high efficiency. A novel dual-edge pulse width modulator for the buck converter that has improved dynamic performance compared to conventional solutions has been designed and implemented. Its small-signal response has been modeled, and the model has been validated by measurements. In addition, this thesis proposes an integrated system that monitors in real-time the voltage stress experienced by the devices of the buck converter and adjusts its operation accordingly, in order to guarantee the required reliability, while maximizing the efficiency. The main building block of this system has been designed and has proved to be fully functional. A substrate-currents-aware characterization method that allows the evaluation of the impact of substrate parasitic devices on the circuit performance and reliability has been also devised, and it has been applied to select the best floor-plan for the buck converter. A novel control scheme that optimizes the efficiency of the ReSC converter for the whole load current range by adopting different operation modes has been proposed and implemented. This thesis reports the steady-state analysis of each mode and a small-signal model for one of them. The buck converter uses a 100 nH inductor, and the last prototype shows a peak efficiency of 88.4% for the 2.5 V-to-1.2 V conversion. It complies with the radiation specifications, and mass production will soon start. The designed prototype ReSC converter employs a 12 nH inductor, and its area occupancy and thickness are respectively 20% and 55% lower than the buck. Its efficiency is larger than that of the buck converter in a range of conversion ratios and load currents, reaching a peak efficiency of 91.4% for the 2.5 V-to-1.2 V conversion. Radiation tests have highlighted that the converter complies with Total Ionizing Dose specifications. By introducing a few improvements, a future prototype could be close to production readiness.

EPFL2020

Etude formelle pour la synthèse de convertisseurs multiniveaux asymétriques

Jean-Sébastien Mariéthoz

The multilevel converters allow generating a voltage waveform whose magnitude and quality are higher than those of conventional converters. They are devoted to medium and high-voltage, high-switching-frequency applications. Among the series connected cell inverters, the symmetrical multilevel inverters are made of identical cells, which topology is generally the H-bridge inverter. This dissertation deals with asymmetrical multilevel converters, which combine high-voltage cells — made of low conduction loss switches — with low-voltage cells — made of low switching loss switches. The different cells play different roles. The goal is to design a converter that has both better energetic efficiency and higher resolution with the same number of cells. This dissertation develops a set of tools that allows synthesizing an asymmetrical multilevel converter. It develops the cell combination rules, which allow defining several cell association classes. The inverter step uniformity condition determines the finesse that can be reached. The optimized modulation condition allows to reduce the highvoltage cell switching frequency without changing the low-voltage cell switching frequency. This property is essential to derive benefit from combining switches of different characteristics. The power balance condition determine how to control the power sharing between the cells. These association classes are different for the single-phase converters and the three-phase converters — without neutral wire. They allow to select a configuration suitable for a given application. Furthermore, several ways that allow improving the inverter resolution are investigated. The modulation is essential to associate a high-quality signal (which will really be delivered to the load by means of the inverter levels) to the reference signal (which should ideally be applied to the load). The modulator evaluation methods are assessed. An approach—based on the modulated signal decomposition in elementary frames—is proposed. The main modulator drawbacks are highlighted. A modulator—which arrange the frames in order—allows to reduce the modulated signal distortion and number of transitions. The specific control methods that allow to minimize the inverter number of switchings are developed. The active power cell supply implies several conversion stages, which decrease the converter energetic efficiency. Some solutions that allow to reduce these losses are proposed. Finally, this dissertation attempts to determine, which are the more interesting solutions, depending on the application.

EPFL2005