Lenian He

A Low-dropout Regulator with Unconditional Stability and Low Quiescent Current

An unconditionally stable low-dropout regulator (LDO) with ultra low quiescent current is presented. By using frequency compensation of dynamic miller on the LDOs structure, the proposed LDOs stability is independent of the load or off-chip capacitor. The LDO works at a low quiescent current of approximately 4 muA. Low quiescent current is due to a precision CMOS current reference, which operates in subthreshold region and generates 30 nA bias current. The current reference has max-to-min fluctuation of less than 2.5% over a temperature range of -40 degC to 150 degC. The proposed LDO has been implemented in a 0.5-mum CMOS technology. The experimental results revealed that the LDO provides a full load transient response of less than 50 mus setting time and less than 75 mV overshoots and undershoots. Moreover, the dropout voltage is 170 mV at 150 mA loading, and quiescent current is 4.17 muA when output current is 150 mA

High-precision constant current controller for primary-side feedback LED drivers

This paper presents a novel constant current LED controller with primary-side feedback control method for flyback topology. The method is proposed based on sampling input peak current and secondary-side electric information detected by an extra auxiliary winding. Eliminating opto-isolator, the controller can still regulated the output current precisely by designing special sample circuit and compensating signal propagation delay. A prototype with 7 LEDs has been built to verify the control method. The experiments results meet the design requirements of 3% current regulation in a wide range of input ac voltage from 85 V to 265 V.

A linear constant current LED driver with no off-chip inductor or capacitor

This paper presents a linear constant current LED driver with no off-chip inductor or capacitor. The proposed circuit consists of a main controller and constant current sources to drive the LED array. An improved control method is used for lighting the LED array step by step, shaping the output current in proportion to the input voltage. Each constant current source has functions of temperature compensation and over voltage protection. A prototype of a 7×7 LED array has been built to verify the control method. The chip is designed and implemented by using CSMCs 1 μm 700V process. The post-layout simulation results indicate that under the 220V|rms 50Hz utility voltage, the system can realize a high power factor of 99.76% and a maximum power conversion efficiency of 90.68%.

A Current-Mode DC-DC Buck Converter with High Stability Independent of Load and Supply Voltage

A current-mode DC-DC buck converter with high stability independent of load and supply voltage is presented. The loop gains expression of the current-mode converter is derived by employing an advanced model of current-mode control converter. After analyzing the loop gains expression, which illustrates the method of selecting suitable frequency compensation for control-loop, and a novel pole-zero tracking frequency compensation is proposed. Based on theoretic analysis, a DC-DC buck converter which has high stability independent of load and supply voltage is designed with 0.5 mum-CMOS technology. The simulated results revealed that stability of the converter is independent of load current and input voltage. Moreover, the converter provides a full load transient response of less than 5 mus setting time and less than 30 mV overshoots and undershoots

A primary side feedback control for flyback LED driver with no output voltage feedback resistors

A constant average output current flyback LED driver without auxiliary windings, opto-couplers or output voltage feedback resistors is proposed. A novel on-chip feedback method through parasitic capacitor of the power MOS to detect demagnetizing time of the magnetizing inductor is used in the driver. The proposed scheme reduces the cost and improves the compaction of flyback LED drivers. The driver possesses over output voltage protection and short circuit protection on the basis of the demagnetizing time detection method. The system simulation results for a typical application show the functions of the LED driver meet the specification. Moreover, the demagnetizing time error was detected to be less than 0.6% and the average output current error is 4.43% at the worst case.

A novel bias circuit design in low power LCD driver

The traditional bias circuit in an LCD driver, by means of resistors dividing a voltage, consumes power continuously as it works. Based on the properties of liquid crystals with a large parasitic capacitance and resulting in a large time constant during charge and discharge, a novel bias circuit using dynamic resistors is proposed in this paper. The new bias circuit has been applied in a 32/spl times/4 LCD driver. The power dissipation in the biasing circuitry part could be reduced by about 36/spl times/ to more than 100/spl times/.

A 14-bit column-parallel two-step SA ADC with on-chip scaled reference voltages self-calibration for CMOS image sensor

This paper presents a 14-bit column-parallel successive approximation analog-to-digital converter (SA ADC) for CMOS image sensor. The proposed SA ADC utilizes a 7-bit charge redistribution capacitor digital-to-analog converter (CDAC) with four column shared reference voltages to significantly reduce the area and power consumption. An on-chip self-calibration scheme is employed to calibrate the two scaled reference voltages. The calibration technique is free from comparator offset and convenient to implement. Simulation shows that the error of the scaled reference voltages after calibration is less than 0.21 LSB. The proposed SA ADC is implemented in 0.18-μm CMOS technology and achieves a DNL of +0.33/-0.33 LSB and INL of +0.39/-0.33 LSB while consumes 191 μW at a sampling rate of 600 KS/s.

Multi-mode control strategy for primary-side regulation system

A multi-mode control strategy for primary-side regulation (PSR) system is presented. The idea uses four mode control strategy to improve the efficiency under variety load conditions. In addition, the usual peak current control mode is replaced by voltage control mode under standby condition. By this way, the pulse width of drive signal can be reduced regardless of the leading edge blanking time in the peak current control mode when the power switch turns on. Thus the standby power can be reduced when the system switching frequency remains the same as conventional system. The prototype is achieved by using CSMC 700V BCD technology. The experiment results show that the average efficiency is improved about 3.6% comparing with conventional system and the standby power is less than 10mW under different conditions.

A linear constant current LED driver without off-chip inductor and capacitor

A linear constant current light-emitting diode (LED) driver without off-chip inductor and capacitor is presented in this paper. The proposed driver consists of one resistor, one diode bridge and one controller integrated circuits (IC). The controller IC employs four LED strings and sequences their conduction to shape the output current in proportion to the input voltage. The controller IC was designed and implemented by using HHNEC 1μm 700V process. The experimental results show that high PF of 97.93% and efficiency of 90.41% under the input voltage of 220V|rms utility voltage were obtained.

An electrolytic-capacitorless and inductorless AC direct LED driver with power compensation

In this paper, a novel system for driving LEDs directly from AC supply without the use of electrolytic capacitors and inductors is proposed. The system includes a power compensation module, enabling the output power of LED approximately constant if there is a fluctuation in input voltage. Unlike the conventional LED drivers, the proposed LED driver only employs one rectifier, one controller IC, four LED strings and a few chip resistors and capacitors. The four LED strings will automatically conduct according to the level of input voltage, thus creating a step-shaped input current proportional to the sinusoidal voltage waveform. By this means, high power factor is achieved. The controller IC is designed by using CSMCs 0.8-μm 650V process. Simulation results show that the LED driver has a high power factor of 97.46% and efficiency of 90.64% under the 220V|rms utility input voltage.