Study on Mode Transition Instability in PFM/PWM Dual-mode Circuit

Study on Mode Transition Instability in

PFM/PWM Dual-mode Circuit

Study on Mode Transition Instability in PFM/PWM Dual-mode Circuit Zhang Fan Dept. of Electronic Systems Graduate School, Hanyang University Abstract To obtain higher efficiency PFM/PWM dual-mode control is widely used for DC-DC converters. Pulse width modulation (PWM) control shows high conversion efficiency for heavy load range in DC-DC converter. On the other hand, pulse frequency modulation (PFM), according to its effective switching frequency variation proportion to the load, is adopted for high efficiency in light load condition. But some serious jitter in switch control signal is brought out during the mode transition in PFM/PWM dual-mode control. The jitter can cause system instability. In this thesis, a stable mode transition circuit based on Schmitt trigger is designed to solve the problem.

Design of LED System for Acne Vulgaris Treatment Chang-Su Kim

ABSTRACT
* Design of LED System for Acne Vulgaris Treatment Using Pulse Width Modulation Chang-Su Kim Department of Biomedical Engineering, Graduate school, Chungnam National University, Daejeon, Korea
* A thesis submitted to the committee of Graduate School of Biomedical Engineering, Chungnam National University in partial fulfillment of the requirements for the degree of Master of Biomedical Engineering conferred in August, 2012.

PDT(Photodynamic Therapy) is a method that kills cancer cells with photochemical and photobiological actions by vitalizing the substance with light that has special wavelength after injecting a photosensitizer that reacts to particular wavelength into body or putting on the body surface. Based on this, this study designed the LED system that emits light to treatment of acne vulgaris which is one of the dermatological lesions. As a wavelength of LED for treatment of acne vulgaris, the 660nm wavelength was selected because it has an effects on curing papule, pustule and acne vulgaris with inflammatory lesions based on its effect on controlling the formation of sebum, eliminating inflammatory reaction and increase of collagen synthesis. The conventional LED treatment system based on Continuous Wave has a high possibility to cause thermal-destruction of tissues when much heat is generated in living tissues with low energy efficiency. In order to prevent the thermal effects, we designed the Pulse Width Modulation( PWM) circuit specially. The LED system was designed by classifying it into timer module, PWM module and optical delivery part. In order to confirm the energy efficiency of PWM method and thermal reaction of living tissues, the stabled energy output and the stability of living tissues were evaluated by measuring the output energy of LED and surfasse temperature of living tissues in comparison with C.W method. In the results, there was the thermal-destruction in the living tissues with high loss of electric power in case of using C.W in order to get LED energy of 1W intensity and 660nm wavelength for treatment of acne vulgaris. However, the energy efficiency was improved by lowering power consumption of LED through PWM by realizing PWM method. Also there is no thermal destruction phenomenon of living tissues, which is considered that PWM method would be more effective and safer than C.W method in case of treatment of acne vulgaris.
LINK
https://www.mediafire.com/?3bbqxzh9kj3hh2q

A Study on the New Current Sharing Control of PWM Converters in Parallel Operation

ABSTRACT A Study on the New Current Sharing Control of PWM Converters in Parallel Operation By Nam-Ju Park Under the supervision of Prof. Dong-Seok Hyun, Ph.D.
Dept. of Electrical Engineering The Graduate School of Hanyang University

Recently, modern electrical equipment consumes more and more power because they have various functions and complexity in systems. In order to cope with high power consumption, usually PWM converters are operated in parallel instead of using one PWM converter having a big power capability. Parallel operation of PWM converter has many advantages over single operation of PWM converter such as various combination of output voltage, distribution of power, standardization of design, and easiness of heat dissipation. With the increment of power consumption, problems caused by unbalance between PWM converters become severe due to the parasitic components in the converter circuit, which considerably deteriorates the reliability of the system. Hence, it is highly demanded that the currents in each converter should be shared in accordance with the power capability of each converter.
DOWNLOAD LINK
https://www.mediafire.com/?5tuz75ttllvr112

Analysis and Implementation of Switch Mode Power Supplies in MHz Frequency Region Abdul Majid

 

 

Analysis and Implementation of Switch Mode Power Supplies in MHz Frequency Region Abdul Majid © Abdul Majid, 2012 Electronics Design Division, in the Department of Information Technology and Media Mid Sweden University, SE-851 70 Sundsvall
Thesis work for the degree of Licentiate of Technology Sundsvall 2012
LINK ORIGINAL
http://miun.diva-portal.org/smash/get/diva2:543427/FULLTEXT01.pdf

High Frequency (MHz) Planar Transformers for Next Generation Switch Mode Power Supplies Radhika Ambatipudi Mid Sweden University Doctoral Thesis 159 - 2013

High Frequency (MHz) Planar Transformers for
Next Generation Switch Mode Power Supplies
Radhika Ambatipudi
Supervisors
Associate Professor Kent Bertilsson
Professor Bengt Oelmann
Department of Electronics Design
Mid Sweden University, SE-851 70 Sundsvall, Sweden

ABSTRACT
Increasing the power density of power electronic converters while reducing or maintaining the same cost, offers a higher potential to meet the current trend in relation to various power electronic applications. High power density converters can be achieved by increasing the switching frequency, due to which the bulkiest parts, such as transformer, inductors and the capacitor's size in the converter circuit can be drastically reduced. In this regard, highly integrated planar magnetics are considered as an effective approach compared to the conventional wire wound transformers in modern switch mode power supplies (SMPS). However, as the operating frequency of the transformers increase from several hundred kHz to MHz, numerous problems arise such as skin and proximity effects due to the induced eddy currents in the windings, leakage inductance and unbalanced magnetic flux distribution. In addition to this, the core losses which are functional dependent on frequency gets elevated as the operating frequency increases. Therefore, this thesis provides an insight towards the problems related to the high frequency magnetics and proposes a solution with regards to different aspects in relation to designing high power density, energy efficient transformers
LINK
http://miun.diva-portal.org/smash/get/diva2:665725/FULLTEXT01.pdf