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Seoul, South Korea

Choi J.,Institute of Microelectronics, Singapore | Han H.-S.,Silicon Mitus | Lee K.,Korea Advanced Institute of Science and Technology
IEEE Transactions on Power Electronics | Year: 2015

A light-emitting diode (LED) driver compatible with fluorescent lamp (FL) ballasts is presented for a lamp-only replacement without rewiring the existing lamp fixture. Ballasts have a common function to regulate the lamp current, despite widely different circuit topologies. In this paper, magnetic and electronic ballasts are modeled as nonideal current sources and a current-sourced boost converter, which is derived from the duality, is adopted for the power conversion from ballasts. A rectifier circuit with capacitor filaments is proposed to interface the converter with the four-wire output of the ballast. A digital controller emulates the high-voltage discharge of the FL and operates adaptively with various ballasts. A prototype 20- W LED driver for retrofitting T8 36-W FL is evaluated with both magnetic and electronic ballasts. In addition to wide compatibility, accurate regulation of the LED current within 0.6% error and high driver efficiency over 89.7% are obtained. © 1986-2012 IEEE. Source

Kim J.,Pohang University of Science and Technology | Jeong I.,Pohang University of Science and Technology | Lee K.,Silicon Mitus | Nam K.,Pohang University of Science and Technology
IEEE Transactions on Power Electronics | Year: 2014

The dc-link voltage fluctuation problem is more serious for an inverter system which utilizes a single phase ac source. As an effort to reduce the dc-link capacitance, there is a tendency to make torque oscillate in synchronism with the input power. Then, the fluctuating motor power matches the converter power. The key idea is to enforce current oscillation along a constant torque line which only affects the reactive power of the motor. In other words, the proposed method uses the motor as inductive energy storage by controlling the motor flux by the reactive current component. Analytic method for obtaining the current bounds was derived. Also, a practical recursive algorithm was proposed. Simulation and experimental results support the effectiveness of the proposed method. © 2014 IEEE. Source

Hong S.-I.,Hanyang University | Han J.-W.,Hanyang University | Kim D.-H.,Silicon Mitus | Kwon O.-K.,Hanyang University
Digest of Technical Papers - IEEE International Solid-State Circuits Conference | Year: 2010

Light-emitting diodes (LEDs) are used as an alternative to the cold cathode fluorescent lamp (CCFL) for LCD backlight units (BLU) for their lower power consumption, wider color gamut, and better dimming capability, in addition to being mercury-free [1, 2]. Recently, various studies have focused on low-power solutions using LED BLUs in a multi-channel LED configuration [1-3]. While these methods effectively reduce power consumption of LED drivers with the phase-shifted backlight driving method [1], the transient response of the LED forward current is limited by the transient response of the boost converter in the LED driver IC. This makes it difficult to obtain a higher PWM dimming frequency than 1kHz in the LED BLU. In addition, the slow transition time of the LED current limits the minimum duty cycle and PWM dimming resolution. These problems generate audible noise and negatively affect the contrast ratio and power consumption of LCDs. To overcome these problems, we use an adaptive boost voltage with a double-loop control method. Here, the transient response of the LED current depends only on the transient response of the current regulator, which is significantly faster than that of the boost converter. ©2010 IEEE. Source

Hong S.W.,Silicon Mitus | Kim H.J.,Konkuk University | Park J.-S.,Konkuk University | Pu Y.G.,Konkuk University | And 3 more authors.
IEEE Transactions on Power Electronics | Year: 2011

This paper presents a low-profile low-cost (LLC) resonant controller IC for LED backlight units fully operating at the secondary side. The integrated dimming circuitry is proposed to improve the dynamic current control characteristics and the LED current density for the brightness modulation of a large screen liquid crystal display. A dual-slope clock generator, including a soft start, is proposed in order to overcome the frequency error due to the undershoot found in conventional approaches. In addition, a new dead-time generator is proposed in order to implement an accurate dead time independent of the output frequency of the clock generator. Protection circuits, such as a under voltage lock out, thermal shut down, open LED detector, and shorted LED detector, have been implemented in order to improve the reliability of the controller IC. The chip is fabricated using 0.35 μm bipolar CMOS DMOS decimal technology; the die size is 2mm × 2mm. The frequency of the clock generator ranges from 50 to 500kHz; the dead time ranges from 50 ns to 2.2 μs. The efficiency of the LED driving circuit is 91%. The current consumption of the LLC resonant controller IC is 40mA for a 100kHz operation frequency using a 15V supply voltage. © 2011 IEEE. Source

Huh Y.,Silicon Mitus
2011 Proceedings of Technical Papers: IEEE Asian Solid-State Circuits Conference 2011, A-SSCC 2011 | Year: 2011

Mobile devices such as smartphones have two major restrictions from the standpoint of design: thermal dissipation and the supply of battery power. Thermal dissipation restricts power consumption of AP (Application Processor), which additionally limits computational performance. Battery usage time is also determined by power consumption of the mobile device. Due to these reasons, power management to improve efficiency of electric power usage becomes a very crucial part of mobile product design. In this paper, we look into power management from two different hierarchical aspects: power management techniques at the processor design level and PMIC (Power Management IC) at the power analog circuit level. Particularly, PMIC in the smartphone is expanding its role to a multi-function solution chip from the traditional function of power conversion and distribution. Future direction of PMIC and engineering challenges will be also discussed. © 2011 IEEE. Source

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