Olegs Tetervenoks

Dimmable LED Drivers Operating in Discontinuous Conduction Mode

Abstract For the modern smart lighting systems one of the most attractive LED advantages is the dimming possibility. Many researchers and engineers from the field of lighting engineering are trying to find compromise between the efficiency of LED dimming process and the ease of its implementation. This paper also presents an attempt to improve LED dimmer parameters. Comparative investigation of the operation of buck LED drivers in continuous conduction mode and discontinuous conduction mode are discussed here. The first section of paper briefly describes the controllability parameters of the converter in both of these modes. The positive impact of discontinuous conduction mode on the controllability parameters as well as the results of the analytical estimation and the results of associated experiments are summarized at the end of the first section. The second section describes the impact of discontinuous conduction mode on the losses of LED dimmer. The analytical estimation of power losses in the main converter components for both operation modes as well as the summary of the experiments to identify distribution of power losses between these components are presented in this section. Finally, the conclusions about using discontinuous conduction mode for dimmable LED lamps as well as guidelines for the choosing of the components with the most appropriate parameters are drawn

Validation of direct current control in LED lamp with non-inverting buck-boost converter

The given paper deals with equipment for smart lighting systems. A hypothesis, that current fed dimmable electrical ballasts with amplitude modulation of light could improve the controllability of such systems, is brought forward. Since there are very few natural current sources it is proposed to use a combination of a voltage source, switch mode voltage-to-current converter and current regulator. The first part can be built as a buck converter, while the regulator is similar to a boost converter. Together this gives a topology known as non-inverting buck-boost converter which, however, in the given case has to be controlled as two modules of “current source” nature. The control rules suitable for such strategy are discussed in the paper. In order to verify the idea a laboratory prototype of such converter has been built and tested. The features of the converter are given in the paper below. The obtained results show that the idea works in general, but certain instability and efficiency problems have to be solved. That is why it was concluded that a more accurate control method for the voltage-to-current source part has to be developed.

Efficiency considerations for non-inverting buck-boost converter operating with direct current control

Amplitude mode LEDs light regulation is most functional when LEDs are supplied from current fed buck drivers, which practical implementation is conjunction of non-inverting buck-boost circuit, extra coil and specific control methods. This report experimentally evaluates the efficiency of drivers versions making focus on their losses and possible electric power savings.

Static losses and controllability of current fed dimmable LED drivers

The paper presents synthesis and comparison of several drivers of original topologies for LED dimming. The work is based on the hypothesis that the direct current control, in contrast to indirect voltage control, is very useful in LED applications where luminous flux is almost proportional to LEDs current. In order to confirm or disprove this hypothesis, several current fed LED ballasts have been synthesized based on corresponding voltage fed converters and known rules of their transformation. The synthesized circuits are mathematically described and experimentally tested. The obtained results show that the approach is useful from the point of view of controllability of LED lamp. Special attention is paid to the estimation of static losses of the LED drivers presented in the given paper. It is concluded that although these parameters are not as good as for voltage fed drivers they remain on an acceptable level. Finally, it is concluded that the current fed step-down driver is advantageous from many points of view and it is worth to work on its further improvement. At the same time, some practical difficulties of implementation of the current fed converters have been detected. This, first of all, regards to the lack of the natural current sources and the risk of their open loop operation. These problems, however, are subject of future works.

Choice of power and control coupling elements for dimmable led driver for smart lighting networks

The studies in the field of smart lighting systems opens new opportunities for energy savings. Such a lighting system is based on LEDs, but the LED drivers are controllable units that allows to change illumination level (provides dimming) in accordance with a given lighting strategy thus the driver is one of the basic elements of a smart lighting system. The power and control coupling elements of non-inverting buck-boost converter based LED driver are considered in this article, but the main attention is paid to the control circuitry in particular the measurement circuitry. In the scope of this article two coupling methods have been studied experimentally: the coupling of analog signal and the coupling of digital signal. Nonlinearity tests as well as the frequency response tests have been carried out. The results of these experiments show, that the approach with the coupling of digital signal has higher frequency response, but the linearity of both methods is similar. The price of digital signal coupling circuitry is higher by approximately 25%. The evaluation of current measurement methods as well as the FET drivers are the subjects for the further studies.

Evaluation of stability of several LED drivers in smart lighting applications

The operation stability and robustness are usually the main criteria for the practically implemented systems. This is especially critical in LED lighting applications, where voltage regulators are used to control current of nonlinear LED load. Also the parameters of the load significantly changes with the temperature change and bin change even for the same brand LEDs. The control system of LED driver must effectively compensate the above mentioned disturbances. In the scope of this article the inherent stability (open-loop frequency response) and the stability of closed loop-system of several converter topologies used in LED lighting applications are analyzed.

The study of microcontroller based embedded system for smart lighting applications

The high power LED driver based on non-inverting buck-boost converter is considered in this paper. The special regulation approach of this converter is described in order to simplify the control strategy. Thus, the implementation of this control strategy in microcontroller based closed loop regulation system allows to increase number of regulation steps (to achieve higher resolution) and to utilize timers of the microcontroller in more efficient way. Also the considerations on the configuration of MOSFET gate driver circuits are given in the paper.

Considerations on practical implementation of control system for switch mode current regulator

The conventional approach in modern LED drivers is the usage of voltage regulators with rapid current feedback (current limit). Previously, the authors hypothesized that the current regulators can provide some advantages compared to the voltage regulators in LED lighting applications. Previous studies were related with theoretical basis and experimental verification of this hypothesis. This paper refers to the several aspects for practical implementation of current regulators. The object of study is non-inverting buck-boost considered as a combination of two stages: constant current source and current regulator. Different approaches for the implementation of control system are considered in this paper and are compared at the end.

Autonomous Power Supply System for Light Sensor of Illumination Measurement Test Bench

Abstract Usually wireless devices require autonomous power supply. They are equipped with radio frequency transceiver modules with relatively high energy consumption especially in data transmission mode. This also means that autonomous power supply of wireless device requires relatively large energy storage. Rechargeable battery in this case is a good solution, but the charging process of a battery takes a long time. In this paper the use of supercapacitor as energy storage for autonomous power supply of wireless node is further elaborated on the example of light sensor for illumination measurement test bench.

Assessment of low cost high power factor electrical ballasts for LED lamps

The rapid development of LED lighting technology as well as increasing demand on new energy efficient lighting devices contribute to the appearance of new companies on the market of solid state lighting. Growing competition enforce these companies to reduce production costs, at the same time keeping the functionality and quality of products at high level. The paper deals with low cost LED driving solutions currently available on the market. They are classified in the scope of the paper. Advantages and drawbacks as well as typical problems of these solutions are discussed.