Marius Rangu

Electro-thermal modeling of power LED using SPICE circuit solver

This paper presents a method of multi-domain modeling for power Light Emitting Diodes (LEDs) with the goal of providing the ability for simultaneous simulations of electrical, thermal and optical behavior. This approach enables engineers to have a better insight into LED critical performance parameters in various operating conditions, by considering the main electrical-thermal and optical interactions. Our proposed multi-domain model integrates an electrical model based on typical diode equations, a dynamic thermal model composed of a Cauer type RC network driven by currnet source, and an optical model derived from the forward current and junction temperature variations of the total luminous flux. The presented approach offers three significant advantages over the traditional single-domain modeling: the effects of packaging and board level thermal management can be evaluated in correlation with electrical parameters, the self heating effect of the junction can be analyzed in the time domain, and the variation of luminous flux output can be observed. The model is defined based on SPICE circuit elements and can be used with any conventional SPICE circuit solver, without the need for solver algorithm modification. The inputs necessary for defining the model are based on standard LED measurements and are often specified in the manufacturers datasheets. All the necessary algorithms required to obtain the multi-domain model SPICE code were implemented in Matlab.

SPICE modeling of thermal behavior for passive components

All types of passive components present variations of most parameters as function of the operating temperature. Depending on the component type and thermal management, in a specific application, these parameter variations can sometimes exceed 20% over the entire temperature range, having an important effect on the overall performance of the circuit. These variations in parameter values, although expected, are rarely implemented in the electric simulations because of the lack of temperature dependent electrical models for passive components. This paper presents a method and its software implementation for generating improved SPICE models for passive components, models that describe thermal variations of the main parameters based on manufacturer datasheet information, general package parasitic elements and thermal behavior measurements.

An educational tool for transmission lines animations

Transmission line signal propagation is a mandatory topic of education in high speed electronic packaging. During our didactic activities at “Politehnica” University of Timisoara, we found that our students have difficulties of intuitively perceiving the signal propagation in transmission lines, especially when multiple reflections from impedance discontinuities caused by junctions or unmatched terminations are involved. We considered that the main cause of this problem comes from the inability to visualize the propagation phenomena, which evolves simultaneously in time and space. To cope with this situation, we developed in Matlab a transmission line simulator that produces results in an animated fashion. Based on numerical solving of the Heaviside equations, it is consistent with the physical phenomena and gives the students an intuitively insight of transmission line signal propagation.

A demystifying study of thermal relief pads: Tradeoff between manufacturing and cooling

Thermal relief is a technique used by printed circuit board (PCB) designers to thermally decouple soldering pads from large copper areas, in order to avoid excessive heat transfer from the pads during the soldering process, which would result in late melting or even no melting at all of the soldering alloy. Although from the manufacturing point of view this is a clear and imperative requirement, we found out that many designers deem this technique with precaution because of the possible negative effects on the thermal management of the board. Since thermal relief implies poor thermal coupling between soldering pads and large copper areas, there is a concern that during operation, the heat spreading capability of such large copper areas will not be put at good use, thus localizing the heat at the component terminals. This paper presents the results of our investigation of this problem, based on computational fluid dynamics (CFD) simulations, with the goal to provide a clear answer to this question.

Optimization of a boost switching-mode power supply using electro-thermal modeling and simulation

One of the major drawbacks in the typical design flow of electronic equipment is the lack of synchronization between design stages. Schematic design and thermal management are rarely correlated, although electrical and thermal parameters are very closely linked. Poor thermal design can have severe consequences on the reliability and functionality of the equipment and is often the main cause of component failure. As power density increases on the printed circuit board this problem becomes critical. Our paper presents a method of mixing electrical and thermal simulation with the goal of improving functional parameters and thermal stress behavior. Switching-mode power supply circuits have high power density and are likely to fail due to thermal stress, so as a support application for our method we will use a boost switching-mode power supply designed for automotive use.

An educational tool for crosstalk animations

Crosstalk between coupled transmission lines is a mandatory topic of education in high speed electronic packaging. During our didactic activities at “Politehnica” University of Timisoara, we found out that our students have difficulties of intuitively perceiving the effects of electromagnetic coupling on transmission lines signal propagation, especially when crosstalk coexists with multiple reflections from impedance discontinuities caused by junctions or unmatched terminations. We considered that the main cause of this problem comes from the inability to visualize the propagation and coupling phenomena, which evolves simultaneously in time and space. To cope with this situation, we developed in Matlab a coupled transmission line simulator that produces results in an animated fashion. Based on numerical solving of the coupled transmission lines equations, it is consistent with the physical phenomena and gives the students an intuitively insight of signal propagation in coupled transmission lines.

Sequential sampling time domain reflectometer

Time domain reflectometry (TDR) is a well-known technique used to detect and characterize impedance discontinuities in transmission lines. Usually the application of this technique employs the usage of a step generator to drive one end of the transmission line and a high speed oscilloscope to visualize the signal reflected at various impedance discontinuities points. This paper presents the design and implementation of an USB-based time domain reflectometer which integrates the functions of both equipments and is intended to be a low cost solution for time domain reflectometry. The acquisition technique used is sequential sampling based on integrated delay lines, giving a time step of 250 [ps] at a total acquisition time of about 2.6 [us]. Sequential sampling is successfully used for high speed sampling oscilloscopes [1], [2] and can be implemented using commercially available components. Unlike similar implementations of the method [3], our proposal uses internal delay calibration to eliminate the ghost effect which limits the minimum measurable cable length. Also, by comparison with random sampling TDRs [4], our approach allows an improved control over the acquisition parameters.

A new method for via capacitance control for high speed PCB design

Modern printed circuit board design involves more than just interconnecting components, as complex high speed applications requires special concerns regarding signal integrity and electromagnetic compatibility. In order to fulfill this request, the designer need specialized software tools for modeling and electrical analysis of the physical structure of the board. This paper propose a new design technique aimed to control the capacitances of signal vias, which take advantage of the linear scaling of the electrical and geometrical characteristics of the vias.

Estimation of parasitic elements of multilayer ceramic capacitors

The analysis of decoupling networks for high-speed integrated circuits (IC) used today in most applications, as well as the analysis of the impedance of capacitor networks for most power supplies can prove to be a real challenge for electrical designers today. This paper presents a method of estimating the impedance and equivalent series resistance variation with frequency of multilayer ceramic capacitors and provides a quick solution to an otherwise time consuming approach to analyze the equivalent impedance of various capacitor networks in different applications.

A demystifying study of trace thickening: How does it affect the current carrying capability

Often, the printed circuit boards (PCB) for power applications are manufactured with some traces thickened by a deposit of soldering alloy. The reason for such a design feature comes from the thermal management requirements: as it is believed that this would significantly increase the current carrying capability of the trace. At a first view, such a statement might seem to make sense: thickening the trace would increase the section area of the conductor, thus decreasing its electrical resistance and also the heat dissipation due to Joule effect. On the other hand though, typical soldering alloys have much smaller electrical conductivity than copper, so much of the current will still flow through the copper section of the conductor. Other effects, such as the thermal insulation of the solder mask or the different convection coefficient of the soldering alloy as compared to copper, also affects the thermal dissipation from the trace to the environment. This paper investigates, using computational fluid dynamics (CFD) simulations and experimental measurements, how much the trace thickening actually influences the current carrying capability.