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.
Implementação de um Módulo IoT para controle de luminárias LED baseado em espelho de corrente com chaveamento de ramos
The paradigm of Internet of Things has assumed prominence for specific and global solutions in the most varied systems, having as main element the information flowing between the different processes. One area susceptible to the Internet of Things is Lighting. Today there is a shortage of solution in Smart Lamps. Therefore, the purpose of this article is to propose a solution that integrates the concept of Internet of Things and lighting converging into smart lamps. This solution will use concepts related to transistor circuits responsible for current control in LED luminaires as well as the User Datagram Protocol and Transmission Control Protocol that are responsible for the system communication rules. The implementation of this module will be able to make LED luminaires, which are currently passive elements in buildings, into luminaires that offer the user remote lighting control possibilities. Resumo: O paradigma de comunicação Internet das Coisas assumiu destaque para soluções específicas e globais nos mais variados sistemas, tendo como elemento principal a informação fluindo entre os diferentes processos. Uma área susceptível à aplicação de Internet das Coisas é a iluminação. Atualmente existe uma carência de soluções em luminárias inteligentes. Por isso, o objetivo deste artigo é propor uma solução que integre o conceito de Internet das Coisas e iluminação para a convergência em iluminação inteligente. Essa solução utilizará de conceitos relacionados a circuitos transistorizados responsáveis pelo controle de corrente em luminárias LEDs assim como o User Datagram Protocol e Transmission Control Protocol que são responsáveis pelas regras de comunicação do sistema. A implementação desse módulo será capaz de tornar as luminárias LEDs, que atualmente são elementos passivos em edifícios, em luminárias que disponibilizam ao usuário possibilidades de controle de iluminação de forma remota.
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 CSMC's 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%.