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.
Assessment of fractures in endodontically treated teeth restored with and without root canal posts using high-resolution cone beam computed tomography
Background Root fractures are a diagnostic challenge for dentists in endodontic treatment. This study aimed to determine the relationship between the characteristics of tooth fractures and the presence of root canal posts in endodontically treated teeth using high-resolution cone beam computed tomography (CBCT). Material and Methods Fifty high-resolution CBCT scans of endodontically treated teeth with a diagnosis of fracture were obtained, of which 30 were from women and 20 were from men. These scans were acquired with three Veraviewepocs 3D units and one 3D Accuitomo 170 unit, with a 40 × 40-mm field of view and 125 μm voxel size. The variables assessed included the type of fracture, extent of fracture, type of retention, post length, cause of endodontic failure, location of the lesion, and time required to detect the fracture (difficulty score). For data analysis, the chi-squared test, Student’s t-test, and multiple linear regression (α <0.05) were used. Results No association was found between the type of fracture and type of retention or between the type of fracture and its extent (P>0.05). On the other hand, the type of fracture significantly influenced the time required for its detection. Additionally, the most difficult plane for detecting the fracture and the difficulty score were associated, with statistically significant results. Conclusions The type of fracture in endodontically treated teeth was not associated with the type of post used for restoration. All of the CBCT systems used to detect tooth fracture showed the same efficiency. Key words:Cone-Beam CT, Tooth Fracture, Root Canal Post.