Low-dropout voltage regulator for stabilizing LEDs drives in dimmable group current sinks
The well-developed constant current sink (CCSK) supplied from a constant voltage source (CVS) has been widely qualified for driving group-parallel strings of power LEDs. This approach takes advantage of current balancing between multiple parallel strings of the LEDs for producing uniform luminous output. However, the drain-to-source voltage vds of the driver MOSFET may move into triode region when the sink current increases since the change of the forward voltage of the string LEDs and the voltage drop on source resistor cannot be compensated with the CVS. In this paper, a low-dropout controlled voltage regulator (LDCVR) is proposed to adaptively well bias the string LEDs and to prevent the sink MOSFETs from working in triode region when dimming for high luminous needs. An experimental to design approach is adopted in design considerations to facilitate the control means between CCSKs and LDCVR so as to stabilize the luminous output uniform with low conduction loss in the sink MOSFETs.
Design and Analysis of an Adaptively Biased Low-Dropout Regulator Using Enhanced Current Mirror Buffer
This paper presents an adaptively biased low-dropout regulator using an enhanced current mirror (ECM) buffer for effectively driving the gate of the PMOS power transistor. The proposed ECM buffer offers very low output impedance, which pushes out the pole at the gate of the PMOS power transistor to improve the stability. At the same time, it offers a symmetric pull-up/down slew rate to enhance the speed of the buffer, whenever the regulator is under large signal operation during the load transient. Moreover, the ECM buffer is modified to develop the regulator topology without introducing an error amplifier as a separate independent stage. It helps to minimize the overall quiescent current consumption at low-load condition and makes frequency compensation easier. Finally, the speed of the adaptive bias loop is increased by avoiding the highly capacitive gate node of the PMOS power transistor. A comprehensive small-signal analysis of the proposed regulator is also carried out for a clear understanding of the stability of each loop considering the interaction of the other loop. The regulator is implemented in a 0.18-μm CMOS technology with a quiescent current of 900 nA. A maximum transient output voltage variation of 2.1% is observed with Co = 470 nF.
Geomagnetic micropulsations due to the motion of ocean waves
When sea waves move in the magnetic field of the earth, electric currents are generated in the water volume. These currents give rise to a small magnetic field which perturbs the earth's field. For plane trochoidal waves, this perturbing field decays exponentially with altitude and lies in a vertical plane which is oriented in the direction of wave propagation. The magnitude of the perturbing field also depends upon the magnitude and dip angle of the earth's field, and upon the height, wavelength, and propagation direction of the sea waves. For north-south waves, sea state 5, and an altitude of 100 feet, the perturbation is of the order of 0.1 gamma.