12.8 Synchronized floating current mirror for maximum LED utilization in multiple-string linear LED drivers
High-voltage linear drivers for multiple-string LEDs have been widely used in general lighting due to their low cost, simplicity, low electromagnetic interference (EMI), and high reliability. However, in conventional multiple-string LED drivers, the LED strings are turned on and off sequentially depending on the magnitude of input voltage (VIN) in order to achieve high power factor (PF) and low total harmonic distortion (THD) [1-3]. The turn-on duty cycles of each string in a four-string LED driver are roughly 80, 60, 40 and 20% respectively, given that VLEDs are identical. Due to its low duty cycle operation, the total brightness is reduced and the brightness of each LED string becomes uneven. This problem becomes more noticeable in long bar-type or surface-type lamps when a triac dimmer is applied. This low utilization of LEDs is a major drawback of multi-string LED drivers. One approach to increase turn-on duty cycle uses diodes and capacitors in each LED string to sustain voltage when VIN is not enough [4]. The problem is that it requires large capacitors due to long turn-off time. Another method is to change the parallel/serial connection of LED strings to match the total voltage drop of LEDs to VIN [5]. Due to its high voltage operation, it is very challenging to make an appropriate, low-cost, and simple solution for all VIN ranges. In order to overcome these problems, a floating current mirror (FCM) IC fabricated in an 85V 0.18um BCDMOS process is presented. As long as VIN is higher than the minimum required LED voltage, FCM enables to turn on all LED strings for all VIN ranges not by using large capacitors, but by modifying only the functional aspects of LED connections. In addition, this approach also prevents EMI problems by keeping an appropriate di/dt during commutation.
A High-Efficiency Linear LED Driver With Concave Current Control for Low-Power Application
This paper presents a linear light-emitting diode (LED) driver with concave current control method for low-power applications. In order to achieve a high efficiency of the linear LED driver, control methods with three different current shapes, namely, traditional flat current shape, convex current shape, and the proposed concave current shape, have been discussed and compared via theoretical analyses, numerical simulations, and experiments in this paper. It is concluded that the proposed concave current control method has the highest efficiency among these three methods for universal input voltage conditions. The operation principles and design considerations of the control method have been provided. It is verified by the experimental results that the proposed concave current control method has a 10% efficiency improvement when compared with the flat and convex current control methods. Furthermore in order to limit the peak current of the concave current for practical considerations, a revised cut-top current control method is presented by adding a limited current. Both simulation and experimental results show that a 37% reduction of the peak current is obtained for the cut-top current control method. On the other hand, a 5% improvement of the efficiency can be achieved by the revised cut-top current than flat and convex current control methods.
Parboiled rice effluent: A wastewater niche for microalgae and cyanobacteria with growth coupled to comprehensive remediation and phosphorus biofertilization
Abstract The potential of microalgae and cyanobacteria for bioremediation of wastewater by nutrient uptake combined with simultaneous biomass production is a well recognized perception of today's world. The present study illustrates the treatment of a highly polluted wastewater generated during parboiling of paddy in rice mill industries, widely operational in developing countries where rice is the staple food crop, with the help of microalgal and cyanobacterial isolates capable of growing at high rates in parboiled rice mill effluent (RME). This endeavor leads to comprehensive bioremediation of the said effluent and subsequent use of the harvested biomass as slow release phosphorus biofertilizers and the treated effluent for crop irrigation. The RME-acclimatized algal consortium demonstrated highest growth in terms of fresh weight and greatest remediation efficiency at the end of 36 days' treatment of RME, with 93.9% phosphorus and 100% ammonia-nitrogen removal, 98.7%, 91.6% and 93.5% reduction in biological oxygen demand, chemical oxygen demand and total dissolved solid, respectively, and an increment of 186 ± 0.3 mg L − 1 dissolved oxygen, bringing down the pollutants level well below the discharge limits suggested by Central Pollution Control Board, India. Additionally, microalgae in the consortium aggregated in clumps spontaneously in presence of the filaments of Phormidium sp. facilitating easy harvest. The RME-acclimatized algal consortium demonstrated highest accumulation of polyphosphate (poly-P) (0.76 ± 0.01% of dry weight) as well as highest release of phosphorus in non-sterile soil emphasizing the essential role of soil phosphorus solubilizing organisms to leach soluble phosphorus from the insoluble poly-P present in the biomass. The rice seedlings watered with treated RME also showed improved growth effect on shoot height and leaf width. The study results establish the suitability of RME as an excellent growth media for microalgae and cyanobacteria.