Electro-Thermal Design Part 2: Analog Electronics

by Mike Donnelly
3 September 2020

Electro-Thermal Design Part 2: Analog Electronics

A new thermal model generation capability has recently been provided in Simcenter Flotherm. It will not only improve the accuracy and efficacy of the electro-thermal design process, but will also be easy for electronic circuit designers to use. In this article, which is Part 2 of a series, I’ll focus on an “LED Spotlight” application. This is intended to represent systems that are primarily composed of continuous (non-switching) analog electronics devices.

The electro-thermal dynamics of an LED light with over-temperature detection is shown in the “Live” (interactive) schematic below. In this design, a Vishay NTCLE100 Thermistor is used in a detection circuit to monitor the enclosure temperature. It is used for thermal shut-down protection, to keep the enclosure temperature well below the "Tg" (glass transition temperature) of the spotlight's Nylon 6 polymer lens. This is particularly helpful when operating at higher external ambient temperatures.

The "thermals" of the system are represented by an IEEE Standard VHDL-AMS "Thermal Netlist" model, shown on the far right of the schematic. This model was generated by Simcenter Flotherm for a specific LED Spotlight board layout and enclosure, based on a detailed 3D-CFD analysis. The generated model was directly and easily imported into this electro-thermal schematic, so that it could be simulated in this transient “closed-loop” context. To learn more about generating thermal netlists from the 3D thermal analysis perspective, please see this blog on Simcenter Flotherm 2020.1 by Byron Blackmore.

“Tune” the design for your specifications!

You can make changes to any of the component parameters shown in blue, and run new simulations to see the effect of those changes. For example, increasing the battery voltage will cause more power dissipation in the linear regulator, and therefore faster temperature rise. Increasing r1 decreases the reference (set-point) temperature, so the light turns off at a lower temperature. Increasing r5 reduces the hysteresis band of the thermostat, for faster ON/OFF switching and tighter temperature regulation. Finally, increasing r_isense reduces the LED current and corresponding power dissipation for the LEDs and the linear regulator.

See for yourself!