Using constant switching frequency control in linear-assisted DC-DC switching converters for photovoltaic solar regulators

This article shows the proposal of a linear–assisted converter or linear–&–switching hybrid converter with a constant switching frequency for photovoltaic solar DC-DC regulators. The control loop of the system is based on the current–mode technique. The main disadvantage of a converter with current–mode control is the inherent instability of the loop when switch duty ratios are greater than 0.5. In order to make stable the proposed linear–assisted converter, the article shows the technique based on a slope compensation.Postprint (published version

Linear-assisted DC/DC converters with modified current-mode control applied to photovoltaic solar systems

This article shows the proposal of a current-mode one-cycle control for linear-assisted DC/DC converters. Linearassisted DC/DC converters are structures that allow to take advantages of the two classic alternatives in the design of power supply systems: voltage linear regulators (classic NPN topology or LDO –low dropout–) and switching DC/DC converters. The current-mode one-cycle control technique is proposed in order to obtain the duty cycle of the linear-assisted converter switch. The proposed structure can provide an output with suitable load and line regulations. Thus, the paper shows the design and simulation results of the proposed current-mode one-cycle linear-assisted converter.Postprint (published version

Capacitorless DC–DC regulator as a candidate topology for photovoltaic solar facilities

Postprint (published version

Analysis on Supercapacitor Assisted Low Dropout (SCALDO) Regulators

State-of-the-art electronic systems employ three fundamental techniques for DC-DC converters: (a) switch-mode power supplies (SMPS); (b) linear power supplies; (c) switched capacitor (charge pump) converters. In practical systems, these three techniques are mixed to provide a complex, but elegant, overall solution, with energy efficiency, effective PCB footprint, noise and transient performance to suit different electronic circuit blocks. Switching regulators have relatively high end-to-end efficiency, in the range of 70 to 93%, but can have issues with output noise and EMI/RFI emissions. Switched capacitor converters use a set of capacitors for energy storage and conversion. In general, linear regulators have low efficiencies in the range 30 to 60%. However, they have outstanding output characteristics such as low noise, excellent transient response to load current fluctuations, design simplicity and low cost design which are far superior to SMPS. Given the complex situation in switch-mode converters, low dropout (LDO) regulators were introduced to address the equirements of noise-sensitive and fast transient loads in portable devices. A typical commercial off-the-shelf LDO has its input voltage slightly higher than the desired regulated output for optimal efficiency. The approximate efficiency of a linear regulator, if the power consumed by the control circuits is negligible, can be expressed by the ratio of Vo/Vin. A very low frequency supercapacitor circulation technique can be combined with commercial low dropout regulator ICs to significantly increase the end-to-end efficiency by a multiplication factor in the range of 1.33 to 3, compared to the efficiency of a linear regulator circuit with the same input-output voltages. In this patented supercapacitor-assisted low dropout (SCALDO) regulator technique developed by a research team at the University of Waikato, supercapacitors are used as lossless voltage droppers, and the energy reuse occurs at very low frequencies in the range of less than ten hertz, eliminating RFI/EMI concerns. This SCALDO technique opens up a new approach to design step-down, DC-DC converters suitable for processor power supplies with very high end-to-end efficiency which is closer to the efficiencies of practical switching regulators, while maintaining the superior output specifications of a linear design. Furthermore, it is important to emphasize that the SCALDO technique is not a variation of well-known switched capacitor DC-DC converters. In this thesis, the basic SCALDO concept is further developed to achieve generalised topologies, with the relevant theory that can be applied to a converter with any input-output step-down voltage combination. For these generalised topologies, some important design parameters, such as the number of supercapacitors, switching matrix details and efficiency improvement factors, are derived to form the basis of designing SCALDO regulators. With the availability of commercial LDO ICs with output current ratings up to 10 A, and thin-prole supercapacitors with DC voltage ratings from 2.3 to 5.5 V, several practically useful, medium-current SCALDO prototypes: 12V-to-5V, 5V-to-2V, 5.5V-to-3.3V have been developed. Experimental studies were carried out on these SCALDO prototypes to quantify performance in terms of line regulation, load regulation, efficiency and transient response. In order to accurately predict the performance and associated waveforms of the individual phases (charge, discharge and transition) of the SCALDO regulator, Laplace transform-based theory for supercapacitor circulation is developed, and analytical predictions are compared with experimental measurements for a 12V-to-5V prototype. The analytical results tallied well with the practical waveforms observed in a 12V-to-5V converter, indicating that the SCALDO technique can be generalized to other versatile configurations, and confirming that the simplified assumptions used to describe the circuit elements are reasonable and justifiable. After analysing the performance of several SCALDO prototypes, some practical issues in designing SCALDO regulators have been identified. These relate to power losses and implications for future development of the SCALDO design

Efficient LDO-Assisted DC/DC buck converter for integrated power management system

DC-DC Switching Converters; Voltage Linear Regulators; Linear-Assisted DC-DC Voltage Regulators.Postprint (published version

Supercapacitor assisted low dropout regulators (SCALDO) with reduced switches: A new approach to high efficiency VRM designs

Supercapacitor assisted low dropout (SCALDO) regulator is a new approach to develop high efficiency DC-DC converters with supercapacitors used for energy recovery. One limitation in these topologies is that in some configurations a large number of low-speed switches are required. If the SCALDO technique is adapted to build voltage regulator modules (VRM), it is necessary to reduce number of switches combined with a high current capable LDO. A new topology-variation with less number of switches can be achieved by reconfiguring the original SCALDO and adding an extra LDO to the circuit. The paper presents a summary of some preliminary work, and experimental results for a 2.5V proof of concept-prototype

Supercapacitor assisted LDO (SCALDO) techniquean extra low frequency design approach to high efficiency DC-DC converters and how it compares with the classical switched capacitor converters

Supercapacitor assisted low dropout regulators (SCALDO) were proposed as an alternative design approach to DC-DC converters, where the supercapacitor circulation frequency (switching frequency) is in the order of few Hz to few 10s of Hz, with an output stage based on a low dropout regulator stage. For converters such as 12–5V, 5–3.3V and 5–1.5V, the technique provides efficiency improvement factors of 2, 1.33 and 3 respectively, in compared to linear converters with same input-output combinations. In a 5–1.5V SCALDO regulator, using thin profile supercapacitors in the range of fractional farads to few farads, this translates to an approximate end to end efficiency of near 90%. However, there were concerns that this patented technique is merely a variation of well-known switched capacitor (charge pump) converters. This paper is aimed at providing a broad overview of the capability of SCALDO technique with generalized theory, indicating its capabilities and limitations, and comparing the practical performance with a typical switched capacitor converter of similar current capability

On capacitor–less linear–assisted DC–DC regulators as candidate topology for photovoltaic solar facilities

Linear-assisted DC/DC converters (or linear-switching hybrid DC/DC converters) consist of a voltage linear regulator (classic NPN or nMOS topologies and LDO) connected in parallel with a switching DC/DC converter. They are good candidates for energy processing in photovoltaic solar facilities. In order to control these hybrid structures, different strategies exist, allowing fixing the switching frequency as a function of some parameters of the linear regulator. This article compares two control strategies that, although can be applied to the same circuital structure of linear-assisted converter, are sensibly different. The first one, reported in previous literature, cancels completely the average current through the linear regulator in steady state to achieve a reduction of the losses. Thus the efficiency of the whole system increases and almost equals the one of the standalone switching converter. The proposed approach, in spite of a slightly increment of linear regulator’s losses, reduces the output ripple due to the crossover distortion of linear regulator output stage.Postprint (published version

Cabaran pelajar antarabangsa di Kolej Kediaman UTHM

Setiap pelajar mempunyai pelbagai cabaran tersendiri semasa mereka mengikuti pengajian di peringkat universiti. Cabaran ini terpaksa dilalui oleh mereka dan besar kemungkinan ianya akan mempengaruhi pencapaian akademik pelajar. Oleh sebab itu, kajian ini dilakukan untuk mengenal pasti masalah dominan yang dihadapi oleh pelajar antarabangsa yang tinggal di Kolej Kediaman UTHM. Masalah penyesuaian yang dikaji meliputi akademik, sosial dan peribadi-emosi. Selain itu, kajian ini dijalankan untuk mengenal pasti tahap keselesaan interaksi dalam kalangan pelajar antarabangsa. Perbezaan antara masalah yang dihadapi dengan ciri-ciri demografi juga turut dikaji. Kajian berbentuk tinjauan deskriptif dan inferensi ini menggunakan borang soal selidik sebagai instrumen di mana ia melibatkan 98 orang pelajar antarabangsa yang tinggal di Kolej Kediaman UTHM. Data yang diperoleh telah dianalisis menggunakan pendekatan Rasch Model melalui perisian Winstep versi 3.69. Hasil kajian mendapati (i) masalah penyesuaian sosial dilihat sebagai masalah dominan yang dihadapi oleh pelajar antarabangsa dengan nilai mean measure 0.18 logit; (ii) tahap keselesaan interaksi dalam kalangan pelajar antarabangsa pula berada pada tahap sederhana dengan nilai skor min 2.70; (iii) tiada perbezaan yang signifikan antara masalah penyesuaian akademik dengan CPA; (iv) tiada perbezaan yang signifikan antara masalah penyesuaian sosial dengan CPA; (v) tiada perbezaan yang signifikan antara masalah penyesuaian peribadi-emosi dengan CPA; (vi) tiada perbezaan yang signifikan antara masalah penyesuaian akademik dengan negara; (vii) tiada perbezaan yang signifikan antara masalah penyesuaian sosial dengan negara; (viii) terdapat perbezaan yang signifikan antara masalah penyesuaian peribadi-emosi dengan negara. Diharap maklumat daripada tulisan ini akan memberikan kesedaran dan manfaat bagi semua mengenai isu berkaitan dengan cabaran pelajar antarabangsa untuk kesejahteraan warga dan organisasi

Linear–Assisted DC/DC Converters with Modified Current-Mode Control Applied to Photovoltaic Solar Systems

Los convertidores DC/DC asistidos linealmente (linear-assisted DC/DC converters) son estructuras que permiten aprovechar las ventajas de las dos alternativas clásicas en el diseño de sistemas de alimentación: reguladores de tensión lineales (ya sean éstos con topología clásica NPN o del tipo LDO –baja tensión de dropout–), y convertidores DC/DC conmutados. En este trabajo se muestra la propuesta de un control de un ciclo en modo corriente modificado (modified current-mode one-cycle control technique) para convertidores DC/DC conmutados asistidos linealmente. Se propone esta técnica de control de un ciclo en modo corriente modificado con el fin de obtener el ciclo de trabajo del interruptor del convertidor conmutado. La estructura propuesta puede proporcionar una salida con adecuadas regulaciones de carga y de línea. El trabajo muestra el diseño de las propuestas del regulador DC/DC asistido linealmente, así como los resultados de simulación que validan la propuesta presentada en el artículo.Peer Reviewe