Sang-kyung Kim

A Low-Cost High-Efficiency CCFL Inverter With New Capacitive Sensing and Control

A new low-cost and efficient cold cathode fluorescent lamp (CCFL) inverter for liquid crystal display (LCD) application is suggested in this paper. The topology of the inverter is derived from modified class E-type resonant electronic ballasts and has a dc-like input current. In addition, a new sensing circuit for lamp current and transformer voltage is proposed. A simple RC-network measures the voltage of a ballasting capacitor in series with the lamp instead of the lamp current itself while the lamp is floated. Utilizing the printed circuit board capacitors for the sensing capacitors and integrating small-valued sensing resistors into a control integrated circuit make the inverter very simple, efficient, and cost-effective. The new sensing circuit can solve many problems that arise when a terminal of the lamp is grounded to sense the lamp current. The control circuits for the prototype experiments are also described in detail. The frequency control scheme with a fixed off-time and a varying on-time was chosen to maintain the operation of zero-voltage switching in the entire dimming range and to reduce the complexity of the control circuits. The control circuits have an analog dimming function using a current control loop, a low frequency pulsewidth modulation dimming, open-lamp protection and voltage regulation, and soft-on/off functions

Voltage-Clamped Class-E Inverter With Harmonic Tuning Network for Magnetron Drive

A passive lossless snubber utilizing harmonic resonance is proposed for the voltage-driven class-E inverter. This snubber reduces the peak resonant voltage stress across the switch in class-E operation by adding the third-order harmonic current into the fundamental resonant part and can be extended to a higher-order network for further reduction. Though the principle is actually equivalent to the class-F operation in RF power amplifiers, it is first tried for the class-E inverter without a current source inductor. A series of analyses is performed to find component values that provide the optimum harmonic condition, and the experimental results from the inverter power supply for driving a magnetron are presented

Detection and regulation of CCFL current and open-lamp voltage while keeping floating condition of the lamp

A new simple balanced circuitry using four printed circuit board trace capacitors effectively detects the cold-cathode fluorescent lamp current and the transformer voltage of the inverter without grounding either side of the lamp. The inverter employing this circuit is free from the problems caused by grounding one side of the lamp, and it provides a stable and wide dimming control as well as an open-lamp voltage regulation with a better efficacy.

P‐40: A Novel Data Driving Method and Circuits for AMOLED Displays

A novel current-mode driving method and driving circuits are proposed for AMOLED displays. The data driving speed in conventional current-mode driving methods is dramatically enhanced by the proposed method and circuits. The proposed method shortens data driving time with feedback of the transient charging current from the parasitic capacitance of an adjacent data line. The current consumption and chip size of the data driver IC are reduced by a half, because one data driving circuit can drive two data lines of a display panel. 10 nA data current can be transferred to the pixel circuit of a display panel with sub-nA accuracy in 15 μsec. The data line parasitic resistance and capacitance are 4 kohm and 20 pF, respectively.

P-45: A Fast Driving Circuit for AMOLED Displays Using Current Feedback

A fast current-mode driving method using current feedback for AMOLED displays is proposed. The proposed driving method dramatically enhanced the driving speed by two negative feedback loops. The loop stability was also guaranteed by the proposed compensation technique and confirmed by simulations. The time to transfer the input current to the pixel current was below 10 usec with sub-nA accuracy for the parasitic loads of 1.5kΩ resistance and 100pF capacitance in data lines.

P-38: Low-Power High-Slew-Rate CMOS Buffer Amplifier for Flat Panel Display Drivers

A new high-slew-rate CMOS buffer amplifier consuming a very small quiescent current is proposed for voltage buffer in flat panel displays. This buffer amplifier recursively copies the output driving current and increases the tail current of the input differential pair during slewing. Since the proposed buffer has a possible slew rate higher than 10 V/μs for a load capacitance of 1 nF almost independently of static currents as low as 1 μA, this buffer amplifier is promising for column driver ICs of flat panel displays.