Showing papers on "Low-dropout regulator published in 2008"

LED Driver With Self-Adaptive Drive Voltage

Abstract: This paper presents an LED driver circuit consisting of multiple linear current regulators and a voltage preregulator with adaptive output voltage. In the proposed driver, the output voltage of the preregulator is always self-adjusted so that the voltage across the linear current regulator of the LED string with the highest voltage drop is kept at the minimum value that is required to maintain the desired string current. Because the linear current regulators in this driver operate with the minimum voltages, the driver efficiency is maximized. The performance of the proposed driver was experimentally verified on a four-string LED setup with eight white LEDs in each string. The measured efficiency improvement of the linear current regulators was approximately 15% compared to the corresponding implementation with a constant preregulator voltage.

Three-Phase Boost-Type Grid-Connected Inverter

Abstract: Alternative energy sources, such as solar energy and fuel cells, are desirable due to their pollution-free property. In order to utilize the present infrastructure of the utility grid for power transmission and distribution, grid-connected DC-to-AC inverters are required for alternative energy source power generation. For many of these applications, the input dc voltage is usually below peak voltage of the output and may vary in a wide range. Thus single-stage buck-type inverters may not be adequate, since they have very limited input voltage range and require the input DC voltage to be higher than the peak of the output voltage. For this reason, two-power-stage topologies, cascaded topologies and multilevel topologies are reported for applications where the input voltage is lower than the peak of the output voltage. Typically, one DC-DC power stage is required to boost the DC voltage in addition to an inverter for DC-AC conversion, which yields increased circuitry complexity. One-stage inverters for low DC voltage to high AC voltage conversion have been reported for non-grid-connected inverters based on the topology of a current source inverter. In this paper, the one-cycle control (OCC) method and the pulse width modulation (PWM) method have been proposed for a three-phase boost-type grid-connected inverter. The inverter features a single power stage that converts dc power to grid-connected ac power by injecting three in phase sinusoidal currents into grids, which may reduce power losses and circuit complexity. The input dc voltage is lower than the peak grid voltage and can vary in a wide range, which greatly suits the power conversion from photovoltaic or fuel cells to grid lines. The DC inductance may be kept low because the average DC current is maintained constant in a switching cycle. With the OCC method, the inverter preserves the advantages of simple circuitry, good stability and fast dynamic response and maximum power point tracking (MPPT) function can be conveniently integrated into the control core. Experiments have been performed with a 1.5-kW laboratory prototype that demonstrated the good performance of the inverter and MPPT function.

Development of Single-Transistor-Control LDO Based on Flipped Voltage Follower for SoC

Abstract: The design issues of a single-transistor-control (STC) low-drop-out (LDO) based on flipped voltage follower is discussed in this paper, in particular the feedback stability at different conditions of output capacitors, equivalent series resistances (ESRs) and load current. Based on the analysis, an STC LDO was implemented in a standard 0.35-mum MOS technology. It is proven experimentally that the LDO provides stable voltage regulation at a variety of output-capacitor/ESR conditions and is also stable in no output capacitor condition. The preset output voltage, minimum unregulated input voltage, maximum output current at a dropout voltage of 200 mV, ground current and active chip area are 1 V, 1.2 V, 50 mA, 95 muA, and 140 mum times 320 mum, respectively. The full-load transient response in the no output capacitor case is faster than a micro second and is about 300 ns.

A 0.9V 0.35 μm Adaptively Biased CMOS LDO Regulator with Fast Transient Response

Abstract: Portable applications often need multiple voltages controlled by a power management IC to power up many functional blocks A switching pre-regulator is usually followed by a low dropout (LDO) regulator to provide a regulated power source for noise-sensitive blocks The LDO regulator has to be stable for all load conditions and frequency compensation is usually needed to stabilize the regulation loop The output voltage droop due to rapid and large load changes could be minimized with a fast regulation loop, such that functional blocks powered by the same LDO regulator would have low crosstalk noise A low-voltage fast transient-response LDO regulator using an inexpensive 035 mum CMOS process is presented in this paper It features a current-efficient adaptively biased regulation scheme using a low-voltage high-speed super current mirror and does not require a compensation capacitor It is stabilized by a low-cost low-ESR ceramic filter capacitor of 1 muF The adaptively biased error amplifier EA drives a small transconductance cell to modulate the output current through a transient-enhanced super current-mirror (SCM)

Dynamic voltage sag correction

Abstract: A voltage sag correction device includes an input terminal adapted to receive a first operating signal having a line-to-neutral voltage. The first operating signal is provided to a load through an output terminal. A regulator module includes a rectifying device adapted to rectify a line-to-line input signal, a storage unit adapted to store energy corresponding to the rectified line-to-line input signal, and an inverter switching device adapted to use the stored energy to generate a correction signal during at least a portion of a voltage sag. An injection transformer in electrical communication with the regulator module is adapted to reduce a voltage of the correction signal. A bypass switch is in a closed position during a normal operating condition such that the injection transformer is bypassed. The bypass switch is in an open position during at least a portion of the voltage sag such that the injection transformer is energized.

Series SEPIC implementing voltage-lift technique for DC-DC power conversion

Abstract: The voltage-lift technique is an effective method that could be applied in electronic circuit design. A set of positive output DC-DC converters applying series SEPIC implementing voltage-lift techniques is introduced. Compared with the prototype of the SEPIC converter, these converters can perform positive to positive DC-DC voltage increasing conversion with higher voltage transfer gains. They are different from other existing DC-DC step-up converters and possess obvious advantages, mainly including fewer switches, clear conversion processes and a high output voltage with small ripples. Since the proposed converters avoid using transformers and cascade connection, relative simple structures are beneficial to potential practical applications in future. A detailed theoretical analysis for continuous and discontinuous conduction modes is given. Both simulation and experimental results are provided to verify the main characteristics.

Driver that efficiently regulates current in a plurality of LED strings

Abstract: A light-emitting diode (LED) driver according to the present invention consists of a voltage pre-regulator and multiple linear current regulators with an adaptively-controlled drive voltage. In this LED driver, the efficiency maximization is achieved by eliminating the sensing of the voltage drops across the linear regulators, i.e., by removing the external voltage feedback for the adjustment of the output voltage of the pre-regulator. In the LED driver of the present invention, the self-adjustment of drive voltage is achieved by relying on a relatively strong dependence between the gate-to-source and drain-to-source voltages of a current-regulating transistor, e.g., a MOSFET, operating in the linear region. The driver powers all LEDs in a string with a constant current and provides consistent illumination and optimum operating efficiency at low cost over a wide range of input/output voltage and temperature.

High current voltage regulator

Abstract: A linear voltage regulator which includes on its input side an array of switched super capacitors for increasing the overall efficiency between the power source and the load. This apparatus is capable of delivering currents typically from milliamperes to greater than several amperes at very low switching frequencies, hence effectively reducing noise. In addition by using capacitors rather than resistors or transistor devices to drop voltage on the input side, efficiency is enhanced. The array of capacitors is switched by simple analog circuitry or a switching logic with or without a processor subsystem and the capacitors themselves are of the super capacitor type, thus providing very high capacitance, and are effectively series connected during certain phases of operation with the input terminal of the conventional linear voltage regulator portion of the apparatus. Energy stored in the super capacitors during the various phases of operation is reused to improve efficiency.

Power regulation for led strings

Abstract: One embodiment of the invention includes a power regulator system. The system comprises at least one current regulator configured to maintain a substantially constant current flow through each of at least one series connected light emitting diode (LED) string. The system also comprises a power converter configured to generate an output voltage to provide power to the at least one current regulator and the at least one series connected LED string. The system further comprises a voltage regulator configured to determine a voltage that provides power to the at least one current regulator and to adjust the output voltage based on the determined voltage to mitigate power loss due to excessive voltage provided to power the at least one current regulator.

Multiple-Output Dual-Polarity DC/DC Converters and Voltage Regulators

Abstract: A multi-output dual polarity inductive boost converter includes an inductor, a first output node, a second output node, and a switching network, the switching network configured to provide the following modes of circuit operation: a first mode where the positive electrode of the inductor is connected to an input voltage and the negative electrode of the inductor is connected to ground; 2) a second mode the negative electrode of the inductor is connected to ground and the positive electrode of the inductor is connected in sequence to one or more of the fourth and fifth output nodes; and 3) a third mode where the positive electrode of the inductor is connected to the input voltage and the negative electrode of the inductor is connected in sequence to one or more of the first, second and third output nodes.

Boost LED Driver Not Using Output Capacitor and Blocking Diode

Abstract: An LED driver is disclosed that boosts an input voltage to drive any number of LEDs in series. The driver includes a switch-mode current regulator that supplies regulated current pulses to the LEDs. No high voltage output capacitor is used to smooth the current pulses, so the LEDs are turned on any off at the switching frequency. Also, no blocking diode between the switching transistor and the LEDs is used. The cathode of the “bottom” LED in the string is connected to ground via a current sense resistor. In parallel with the sense resistor is connected an RC filter using a small, low voltage filter capacitor. The RC filter provides a substantially smooth feedback voltage for the current regulator to control the duty cycle of the switching transistor so that the feedback voltage matches a reference voltage.

LED driver with fast open circuit protection, short circuit compensation, and rapid brightness control response

Abstract: An LED driver drives one or more strings of series-connected LEDs. A feedback voltage at a sense resistor is detected by an op amp, and the op amp controls the conductivity of a MOSFET in series with the LEDs to regulate the peak current. The MOSFET is also controlled by a PWM brightness control signal to turn the LEDs on and off at the PWM duty cycle. A boost regulator provides an output voltage to the string of LEDs. A divided voltage at the end of the string of LEDs is regulated by the boost controller to keep the divided voltage constant. When an LED becomes an open circuit, the boost regulator controller is immediately decoupled from the regulator's switching transistor. If an LED shorts, the boost regulator reduces its output voltage, and the duty cycle of the brightness control signal is automatically increased.

Multimode voltage regulator circuit

Abstract: A multimode voltage regulator circuit includes a linear regulator sub-circuit configured to supply current to a load in a low-current mode, responsive to a first control signal from a first control path, as well as a switching regulator sub-circuit configured to supply current to the load in a high-current mode, responsive to a second control signal from a second control path. The circuit further comprises a shared error amplifier configured to generate an error signal based on the difference between a reference voltage and a feedback signal coupled from the load, and a switch configured to selectively route the error signal to the first control path in the low-current mode and to the second control path in the high-current mode.

Phase locked loop circuit having regulator

Abstract: Embodiments of present invention provide a circuit including a voltage regulator, a phase frequency detector, a charge pump, a low pass filter a control-voltage generating circuit and a voltage controlled oscillator. In a first mode of operation the voltage controlled oscillator produces an output clock in accordance with a control voltage produced from the control-voltage generating circuit and the output voltage of the voltage regulator. In a second mode of operation, the voltage controlled oscillator produces an output clock in accordance with a control voltage from the low pass filter and the output voltage of the voltage regulator.

A novel LED driver with adaptive drive voltage

Abstract: This paper presents an LED driver circuit consisting of a voltage pre-regulator and multiple linear current regulators with an adaptively-controlled supply voltage. The proposed driver circuit powers all LEDs in a string with a constant current and provides consistent illumination and optimal operating efficiency at low cost. The performance of the proposed driver was verified experimentally.

Digital double-loop output voltage regulation

Abstract: A switched mode voltage regulator has a digital control system that includes dual digital control loops. The voltage regulator comprises at least one power switch adapted to convey power between respective input and output terminals of the voltage regulator and a digital controller adapted to control operation of the power switches responsive to an output of the voltage regulator. The digital controller further comprises dual digital control loops in which a first control loop provides high speed with lower regulation accuracy and a second control loop has high accuracy with lower speed. Thus, the digital control system provides the advantages of both high speed and high regulation accuracy.

A 10 MHz Bandwidth, 2 mV Ripple PA Regulator for CDMA Transmitters

Abstract: A combined class-AB and switch-mode regulator based supply modulator with a master-slave architecture achieving wide bandwidth and low ripple is presented. Low frequency content of the envelope waveform is provided by a synchronous-rectifier based switch-mode power supply while high frequency content is provided by a rail-to-rail class-AB amplifier. A wide range, low loss output current sensing circuit is used at the class-AB amplifier output, canceling the ripple due to switch-mode power supply and extending overall modulator bandwidth. The proposed regulator is designed and fabricated on a 0.35 mum CMOS process. The combined regulator achieves a maximum efficiency of 82% and an IMD3 of 65 dBc at 10 MHz for 16 dBm output power. The regulator achieves a frequency range up to 10 MHz with less than 0.2% envelope tracking error, making this PA regulator suitable for CDMA applications.

Battery charging systems and methods with adjustable current limit

Abstract: Embodiments of the present invention include techniques for charging a battery using a regulator In one embodiment, the present invention includes an electronic circuit comprising a regulator having an input coupled to a power source for receiving a voltage and a current and an output for providing an output current, an input voltage detection circuit coupled to the power source, and an adjustable current limit circuit for controlling the input or output current of the regulator, wherein input voltage detection circuit monitors the voltage from the power source and the adjustable current limit circuit changes the input or output current of the regulator to optimize the power drawn from power source

A Low-Supply-Voltage CMOS Sub-Bandgap Reference

Abstract: A low-power (21 muW ) bandgap reference source that is operable from a nominal supply voltage of 1.4 V is described. The circuit provides an output voltage equal to the bandgap voltage having a low output resistance and allows resistive loading. It does not use resistors or operational amplifiers. Thus, the design is suitable for fabrication in any digital CMOS technology. The circuit uses a current conveyor and current mirrors to convert the proportional to absolute temperature voltage into a current using a MOSFET. The current is converted back to a voltage by using the functional inverse of the FET v-i characteristics. This makes the voltage gain linear and temperature independent. The absence of back-gate bias is the reason for achieving the low supply voltage of operation. Simulation results using the transistor models for the 0.18-mum TSMC process show that the voltage-variation over the temperature range 0 to 100degC is <1 mV.

Adaptive zero current sense apparatus and method for a switching regulator

Abstract: A switching regulator includes a low-side switch having a body diode. During the low-side switch is on, a zero-current sense circuit monitors the inductor current of the switching regulator and triggers a signal to turn off the low-side switch when the inductor current falls down to a zero-current threshold, to prevent reverse inductor current from the output terminal of the switching regulator. A body-diode turn-on time controller monitors the turn-on time of the body diode and adjusts the zero-current threshold according thereto, and the turn-on time of the body diode can be reduced to an optimal interval subsequently. The self-adjustable zero-current threshold is adaptive according to the application conditions, such as the inductor size, input voltage and output voltage of the switching regulator.

Voltage regulator having fast response to abrupt load transients

Abstract: A voltage regulator includes an undervoltage detector having a charge transistor smaller than an output transistor of the voltage regulator, providing a detection path for fast response, compensating undervoltage without large control current when loading changes from light to heavy.

High efficiency quasi-parallel Voltage Regulators

Abstract: High efficiency voltage regulators (VR) are desired for battery life extension and energy saving. In this paper, a novel quasi-parallel VR architecture is proposed. Its working principle and small signal model are illustrated in detail. The proposed VR takes advantage of the high-efficiency, fast-transient unregulated converter and relies on it to deliver most of the output power, while uses low power Buck type converter to achieve voltage regulation. The simulation and preliminary experimental results demonstrate that the proposed VR can achieve 4%-5% higher efficiency than state-of-the-art multi-phase buck VR and it can eliminate all the output bulk capacitors with 600k Hz switching frequency.

Low voltage charge pump with regulation

Abstract: Techniques of providing a low output voltage, high current capability charge pump are given. The charge pump has multiple capacitors along with switching circuitry. In an initialization phase, the first plate of each of the capacitors is connected to receive a regulator voltage and the second plate of each capacitor is connected to ground. In a transfer phase, the capacitors are connected in series, where, for each capacitor after the first, the second plate is connected to the first plate of the preceding capacitor in the series. The output voltage of the pump is from the first plate of the last capacitor in the series. Regulation circuitry generates the regulator voltage from a reference voltage to have a value responsive to the output voltage level of the pump.

A new method for voltage and frequency control of stand-alone self-excited induction generator using PWM converter with variable DC link voltage

Abstract: Three-phase self-excited induction generators (SEIG) play an important rule in renewable energy sources such as wind and hydraulic energy. Their main disadvantage is poor voltage and frequency regulation under varying load and speed. This paper introduces a new and simple method for voltage and frequency control of three-phase unregulated speed induction generators in the islanding mode. The method uses a constant voltage constant frequency (CVCF) PWM converter without regulating the DC capacitor voltage. The capacitor voltage is left changing with the loading conditions and the AC side voltage is regulated by controlling the modulation index. This eliminates the need of an auxiliary switch in the DC side which reduces the cost and also reduces the high frequency current components flowing in the DC capacitor and that increases its life time. The proposed technique is tested under step changes in load and prime mover speed. The proposed technique gives the same response as the old technique but without the use of DC side switch.

Analysis and Design of Voltage Regulator With Adaptive FET Modulation Scheme and Improved Efficiency

Abstract: This paper presents a load adaptive voltage regulator that achieves high efficiency extended to light and heavy load regions. The presented method is named as adaptive field effect transistor modulation (AFM) since multiple field effect transistors (FETs) with different characteristics (different sizes) are applied in parallel such that the number of driven FETs and their respective gate driving voltage are adaptive to load current. The capability of adaptive modulation of FETs' parasitic charges and resistances along with adaptive gate driving voltage allows the optimization of equivalent FET characteristics over a wide load range. Moreover, the AFM operation under load dynamic conditions is studied and a scheme is proposed. The AFM operates at a fixed switching frequency for almost the entire load range. Therefore, it has no impact on the operation and the dynamic performance of a conventional buck VR, and it is easy to implement. In this paper, the concept, design and theoretical analysis of the AFM are discussed and verified experimentally. Even though the simulation and experimental works design example given in this paper is for lower power and low voltage converter with discrete components for demonstration purposes, the AFM may have better improvement in higher power and/or higher voltage applications and in integrated voltage regulators.

Phase-shifted dual-bridge DC/DC converter with wide-range ZVS and zero circulating current

Abstract: Disclosed is a family of new DC/DC converters and a new control method. The converter comprises two bridge inverters, two full-wave rectification circuits and a current-doubler filter. Each inverter is able to generate a symmetrical and isolated AC output voltage. Phase-shift control is employed to control the phase difference between the two bridge inverters. By shifting the phase, the converter changes the two inverters' output voltage overlapping area to regulate its output voltage. The bridge inverters always operate at 50% duty cycle, like an open loop Bus Converter, to achieve wide-range zero voltage switching and eliminate circulating current for normal operation. For low output voltage regulation and soft start, Pulse Width Modulation (PWM) control is used. The converters and the control method improve power conversion efficiency, maximize magnetic component utilization, reduce semiconductor stress and decrease EMI emission.

A CMOS Low Noise, Chopper Stabilized Low-Dropout Regulator With Current-Mode Feedback Error Amplifier

Abstract: Low 1/f noise, low-dropout (LDO) regulators are becoming critical for the supply regulation of deep-submicron analog baseband and RF system-on-chip designs. A low-noise, high accuracy LDO regulator (LN-LDO) utilizing a chopper stabilized error amplifier is presented. In order to achieve fast response during load transients, a current-mode feedback amplifier (CFA) is designed as a second stage driving the regulation FET. In order to reduce clock feed-through and 1/f noise accumulation at the chopping frequency, a first-order digital SigmaDelta noise-shaper is used for chopping clock spectral spreading. With up to 1 MHz noise-shaped modulation clock, the LN-LDO achieves a noise spectral density of 32 nV/radic(Hz) and a PSR of 38 dB at 100 kHz. The proposed LDO is shown to reduce the phase noise of an integrated 32 MHz temperature compensated crystal oscillator (TCXO) at 10 kHz offset by 15 dB. Due to reduced 1/f noise requirements, the error amplifier silicon area is reduced by 75%, and the overall regulator area is reduced by 50% with respect to an equivalent noise static regulator. The current-mode feedback second stage buffer reduces regulator settling time by 60% in comparison to an equivalent power consumption voltage mode buffer, achieving 0.6 mus settling time for a 25-mA load step. The LN-LDO is designed and fabricated on a 0.25 mum CMOS process with five layers of metal, occupying 0.88 mm2.

Controlling current through serial LEDs using a low voltage transistor when using a high voltage driver

Abstract: Various circuits are described herein where a series transistor used to control current through a string of LEDs, driven by a high voltage, is not subjected to the high voltage when the transistor is turned off pursuant to a PWM signal. To avoid the transistor experiencing the high voltage, the HV regulator is disabled shortly before the transistor is turned off and is enabled shortly after the transistor has turned back on. Control circuits for controlling the regulator and transistor include delay circuits and/or voltage sensing circuits to ensure that the transistor is always on prior to the voltage regulator being enabled pursuant to the incoming PWM signal, and the voltage regulator is always disabled when the first transistor is off pursuant to the incoming PWM signal.

Limiting primary peak charge to control output current of a flyback converter

Abstract: A controller IC adjusts the on time and cycle time of current flowing through the primary inductor of a flyback converter to generate a constant output current and constant output voltage. A desired output current limit is achieved even with an inductor whose inductance varies from the stated magnitude. A transconductance current is generated from a voltage across an emitter resistor and is then integrated to generate an integrated-current voltage. An inductor switch is turned on by an oscillator signal and turned off at the earlier of when the integrated-current voltage reaches a charge limit voltage during constant current mode or when the emitter resistor voltage reaches an error voltage during constant voltage mode. Current is output independently of the primary inductance by varying the current limit voltage inversely proportionally to the input voltage and by adjusting the cycle time so that it varies inversely proportionally to the output voltage.

System and method for improving inductor current sensing accuracy of a DC/DC voltage regulator

Abstract: The DC/DC voltage converter comprises at least one switching transistor. An inductor is connected to the at least one switching transistor. A pulse width modulation circuit generates control signals to at least one switching transistor responsive to a current control signal. A current sensor connected in parallel with the inductor senses current passing through the inductor. The sensor comprises a resistor and an NTC capacitor connected in series with the resistor. Circuitry for monitoring the voltage across the NTC capacitor generates the current control signal responsive to the monitored voltage.