Design Techniques for Thermal Management in Switch Mode Converters

Abstract

Abstract-Thermal management plays a pivotal role in achieving high power densities in converters. Improvement on thermal performance of critical components in printed-circuit board (PCB) assembled switch mode converters is achieved by using design techniques that extend across electromagnetic, geometrical, and thermal-integration technologies. For better use of the already available PCB material, three-dimensional component layout and flexible PCB technology are utilized to gain advantages. A theory to evaluate the thermal-management effectiveness of switch mode converters is introduced based on two new figures of merit, namely thermal-management loss density and thermal-design rating. These two figures of merit quantify the effective use of thermalmanagement material as well as the thermal performance of a converter design. The figure-of-merit criteria allow flexibility so that it can be adjusted to an appropriate design objective. Design objectives include achieving higher power densities or achieving good reliability. The thermal-management-effectiveness theory is applied here to thermally optimize a Flyback converter that has been geometrically integrated. The design technique to adjust the thermal-management effectiveness of integrated switch mode converters to achieve a set objective, by means of the introduced figures of merit, forms the core of the publication, validated by experimental measurements.Index Terms-AC-DC power conversion, design methodology, finite-difference methods (FDMs), optimization methods, printedcircuit board (PCB) assembled power supplies, thermal management, thermal variables control.

Toward the Next Level of PCB Usage in Power Electronic Converters

“…The layout and buildup of the rigid-flex PCB converter shown in Fig. 2 have been governed by a geometrical packaging approach introduced in [18]. This approach seeks to identify mutual-compatible component shapes among the remaining discrete converter components that, due to their operating frequency or energy storage function, remain too large to be integrated into the PCB.…”

“…The 8 Measured using IR thermography. 9 Based on a finite difference method (FDM) estimation approach introduced in [18]. measured surface temperatures and profile of the outer surface are shown in Fig.…”

“…The thermal design rating (TDR PD ) values, shown in Table II, indicate that ≈10% more components operate in a set optimal band at 50% of its optimal temperature in the 3-D PCB converter than was the case in the conventional discrete converter, when applying the predefined power density objective set, as defined in [18]. Sixteen percent of all the converter components operate above 85% of their individual optimal temperatures, indicating that the thermal management is not only keeping the components from thermal destruction but also managing the local component temperatures in such a way that their individual operating temperatures approach their optimal temperatures better, resulting in increased profit from the components performance.…”

“…The 3-D PCB converter excels when the predefined reliability objective set [18] is applied (TDR R ). It has an astounding ≈71% of all its components operating above 85% of their optimal temperature.…”

3D Integration with PCB Technology

“…From a thermal management point of view the integration of thermal functionality into the PCB has resulted in a more uniform temperature distribution along the outer surface of the 3D converter, with a much lower average "hot-spot" temperature (≈ 65 • C) than is the case for the discrete converter with a much higher local temperature of ≈ 125 • C, measured on the power MOSFET switches. The thermal design rating values, shown in Table I, indicate that ≈ 25% more components operate in a set optimal band of 50% of its optimal temperature in the integrated 3D converter than was the case in the conventional discrete converter, when applying the predefined power density objective set, as defined in [30]. 16% of all the converter components are seen to operate in 85% of their individual optimal temperatures, indicating that the thermal management is not only keeping the components from thermal destruction but also managing the local component temperatures in such a way that there individual operating temperatures approach their optimal temperatures better, resulting in increased profit from the components performance.…”