Marian Vladescu

Power LED efficiency in relation to operating temperature

In this paper there are presented investigations regarding power IR LED efficiency in relation to operating temperature in order to define the reference values and conditions for using such devices for realizing long range proximity sensors, especially for applications in the automotive domain. The previous experiments done regarding the power LED used for infrared sources emphasize the optical power dependency to temperature. The new experiments were designed for measuring optical power and temperatures of LED heat sink and case, respectively of star and square type circuit boards (thermally conductive insulated metal substrate - IMS), at different points in the same time, for different values of LED driving current and various ambient temperatures, in order to make a correlation between LED efficiency and temperature. The results obtained and presented in this paper will be used further as references for designing an anticollision warning system with applications into automotive domain. Keywords: Power

Working temperatures influence over the solder joints properties

It is an actual trend for electronic equipment to be used into growing range of working temperatures and at high level of the mechanical stress. As example, for the domains exempted by RoHS 2 EU Directive (it became law from January 2013) like aerospace, the standard maximum working temperature is 398.15K (125°C). The results of the comparative investigations regarding electrical and mechanical properties of the Lead/Lead-free solder joints function of working temperature and soldering thermal profile are presented in the paper. The experiments were designed based on previous work [1,2] having as starting point the “Homologous Temperature” concept [1,3,4], in order to respond to constrains imposed by the qualification processes of lead-free solder alloys for usage into exempted domains according to the RoHS 2 EU Directive [5,6].

Power LEDs operating temperature measurement using the protection reverse diode

Determination of the junction temperature of power LEDs is a great challenge. Indirect calculation of the junction temperature can be done by calculations, starting from the temperatures that could be measured with thermocouples in the accessible points and taking into consideration the thermal resistances of the materials included in the LED structure and in the mounting PCB used as heatsink. In this paper the authors proposed to use as temperature sensor the protection diode embedded in most of the power LED structures.

Programmable pulsed current driver for high power LEDs applications

To obtain maximum performance from a LED, it must be driven with a constant current. The maximum continuous current allowed is limited by the thermal characteristics of the package, but often the die supports higher peak currents. By driving the LED with high current pulses, the optical flux is greatly increased and more distant objects can be illuminated. This paper describes the design of such a driver and the results obtained from driving high power LEDs.

Electrical conductivity of inkjet printed silver tracks

The work aims to assess the conductivity of Silver tracks printed using a state-of-the-art PixDro LP50 inkjet printer which has the capability to print conductive tracks with width as low as 50μm. The conductivity of tracks with different dimensions is measured using a Keithley measurement setup. The equivalent resistivity depends on the material, printing technology and geometrical dimensions. Profile measurements indicate a track thickness of around 300nm. The optimal printing resolution appears to be 450dpi, ensuring conductivity for all selected track widths from 50μm to 400μm. This paper analyses the influence of the layout on the electrical properties with a focus on determining the minimum metal quantity necessary to have tracks with good conductivity.

Implementation of an omnidirectional surveillance system based on 360-degree panoramic vision

The omnidirectional vision can be achieved by using a convex mirror placed in front of a camera. In this way, the camera acquires a panoramic image that covers 360o of the surrounding environment. This concept has been the aim of many researchers and has had various setups so far, using different mirror profiles, camera models and type of lens. Our target was to implement a robust surveillance system, for indoor and outdoor use, day and night vision capable, which could be easily integrated in the IP environment. Both hardware and software for the image processing have been developed in order to achieve our goal.

Automated platform for determination of LEDs spatial radiation pattern

Nowadays technologies lead to remarkable properties of the light-emitting diodes (LEDs), making them attractive for more and more applications, such as: interior and exterior lighting, outdoor LED panels, traffic signals, automotive (tail and brake lights, backlighting in dashboard and switches), backlighting of display panels, LCD displays, symbols on switches, keyboards, graphic boards and measuring scales. Usually, LEDs are small light sources consisting of a chip placed into a package, which may bring additional optics to this encapsulated ensemble, resulting in a less or more complex spatial distribution of the light intensity, with particular radiation patterns. This paper presents an automated platform designed to allow a quick and accurate determination of the spatial radiation patterns of LEDs encapsulated in various packages. Keywords: LED, luminous

Test and measurement procedures for RFID systems

The necessity of having instruments for analyzing the quality of signal received by the reader from the transponder is more and more important in order to evaluate the performance parameters of RFID systems. In this paper we review the existing test procedures and transponder simulators that proved their utility in the development of SLRM1000 RFID system. We propose a new measurement device and procedure that produce 2D maps of the quality of the received signal as the position of the transponder is varied across the antenna.

Automated Platform for Characterization of RFID Reader Antennas

RFID systems have evolved from simple ones to complex equipment, but one of the most important components in their structure is the antenna. The overall system performance is highly depending on quality of the communication between antenna and transponders, so it is very important to characterize it with high accuracy. This paper presents an automated platform for antenna characterization based on automatic exploration of the usable area of antenna, using a transponder positioned on X and Y coordinates with two stepper motors and the associated mechanics.

VPS control module EMC modeling and evaluation

The present paper is the result of studies, experiments, modeling and simulation regarding electromagnetic compatibility (EMC) of an electronic module able to control and vary the power requirements of a Vapor Phase Soldering (VPS) machine in order to obtain the desired thermal profile. The original electronic solution has been designed to obtain very low radiated electromagnetic emission during operation by switching the power device when the AC main is zero-crossing. Electromagnetic compatibility (EMC) performance and field effects have been analyzed using 3D EM simulation software, REMCOM XFdtd by considering the VPS process control module the source of radiations. EMC evaluations of the electronic module regarding conducted and radiated emissions have been done in laboratory in order to validate the modeling and simulations results. In order to complete the design for excellence (DFX) activities in case of new products development processes the authors intend to develop a design methodology which will include modeling and EM simulation for optimum electromagnetic compatibility within the Vapor Phase Soldering system.