• Proceedings of the KIEE Conference
• /
• 2005.07b
• /
• pp.1503-1505
• /
• 2005

The Cold cathode fluorescent lamp(CCFL) are widely used to illuminate the liquid crystal display(LCD). Ballasts are required for CCFL because the lamp need high starting voltage and behave negative dynamic resistant characteristics in the desired region of operation. Dimming methods of CCFL are used to pulse frequency modulation(PFM) or pulse width modulation(PWM). In this paper, CCFL driving and control circuit is designed by half-bridge type series and parallel resonant inverter that variable frequency modulation method to control the output voltage current. The validity of this study is confirmed from the simulation and experimental results.

• Proceedings of the KIEE Conference
• /
• 2002.07d
• /
• pp.2577-2579
• /
• 2002

In this paper, we describe a CMOS DC-DC converter with a variable output voltage(8-12V @100mA) for a portable battery-operated system applications. The proposed DC-DC converter is used along with a Pulse-Frequency Modulation (PFM) method and consists of a reference circuit, a feedback resistor, a controller, and an internal oscillator. The integrated DC-DC converter with two external passive components(L.C) has been designed and fabricated on a 0.6${\mu}m$ 2-poly, 3-metal CMOS process and could be applied to the Personal Digital Assistants(PDA), Cellular Phone, Laptop Computer, etc.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.15 no.6
• /
• pp.432-440
• /
• 2010

In this paper, a LC series resonant boost converter using a single switch is proposed. The proposed topology contains additional passive elements in the conventional boost converter and performs Zero Voltage Switching(ZVS) without an additional auxiliary switch when a main switch turned on and off. The switch off time of the proposed system determined by LC series resonance, thus a on-time variable Pulse Frequency Modulation(PFM) method is adapted to control output voltage in the proposed converter. Operational modes of the proposed topology are divided with respected to the current conduction paths and then through the theoretical analysis and experimental results, operational modes and characteristics of the proposed converter are verified.

• The Journal of Korean Academy of Prosthodontics
• /
• v.40 no.2
• /
• pp.131-139
• /
• 2002

There have been many studies about marginal discrepancy of single restorations made by various systems and materials. But many of statistical inferences are not definite because of sample size, measurement number, measuring instruments. etc. The purpose of this study was to compare the marginal adaptations of the anterior single restorations made by different systems and to consider more desirable statistical methods in analysing the marginal fit. The in vitro marginal discrepancies of three different all-ceramic crown systems (Celay In-Ceram. Conventional In-Ceram. IPS Empress 2 layering technique) and one control group (PFM) were evaluated and compared. The crowns were made from one extracted maxillary central incisor prepared with a 1mm shoulder margin and $6^{\circ}$ taper walls by milling machine. 10 crowns per each system were fabricated. Measurements or a crown were recorded at 50 points that were randomly selected for marginal gap evaluation. Non-parametric statistical analysis was performed for the results. Within the limits of this study, the following conclusions were drawn: 1 Mean gap dimensions and standard deviations at the marginal opening for the maxillary incisor crowns were $98.2{\pm}40.6{\mu}m$ for PFM, $83.5{\pm}18.7{\mu}m$ for Celay In-Ceram, $104.9{\pm}44.1{\mu}m$ for conventional In-Ceram, and $45.5{\pm}11.5{\mu}m$ for IPS Empress 2 layering technique. The IPS Empress 2 system showed the smallest marginal gap (P<0.05). The marginal openings of the other three groups were not significantly different (P<0.05). 2 The marginal discrepancies found in this study were all within clinically acceptable standards ($100\sim150{\mu}m$). 3. When the variable is so controlled that the system may be the only one, mean value is interpreted to be the marginal discrepancy of a restoration which is made by each system and standard deviation is to be technique-sensitivity of each one. 4. From the standard deviations. the copy-milling technique (Celay/In-Ceram) was not considered to be technique-sensitive in comparison with other methods. 5. Parametric analysis is more reliable than non-parametric one in interpretation of the mean and standard deviation. The sample size of each group has to be more than 30 to use parametric statistics. The level of clinically acceptable marginal fit has not been established. Further studies are needed.

• Tuberculosis and Respiratory Diseases
• /
• v.54 no.4
• /
• pp.386-394
• /
• 2003

Background : ATS(American Thoracic Society) defined new guidelines for COPD(chronic obstructive lung disease) in April 2001, following the results of the global initiative for chronic obstructive lung disease. The most important concept of COPD is an airflow limitation which is not fully reversible compared to bronchial asthma(BA). The criteria for COPD are postbronchodilator $FEV_1$ less than 80% of the predicted value and an $FEV_1$ per FVC ratio less than 70%. The global initiative for asthma(GINA) study defined asthma, which included immune-mediated chronic airway inflammatory airway disease, and found that airflow limitation was wide spread, variable and often completely reversible. Taken together COPD and BA may be combined in airflow limitation. This study was designed to evaluate the prevalence of BA in patients with COPD of moderate to severe airflow limitation. Methods : COPD was diagnosed by symptoms and spirometry according to ATS guidelines. Enrolled subjects were examined for peak flow meters(PFM), sputum eosinophils and eosinophil cationic protein(ECP) levels, serum total IgE with allergy skin prick test, and methacholine bronchial provocation test(MBPT). Results : About 27% of COPD patients with moderate to severe airflow limitation were combined with BA. There was significantly decreased response to PFM in severe COPD. However, there was no significant relationship between BA and COPD according to the degree of severity. The BA combined with COPD group showed significantly high eosinophil counts and ECP level in induced sputum. However, neutrophil counts in induced sputum showed significant elevation in the pure COPD group. Conclusion : Twenty-seven percent of COPD patients with moderate to severe ventilation disorder were combined with BA, but there were no significant differences according to the degree of severity.