“The device works in a simple way: a specific power is dissipated on a transistor while a DS18s20 temperature sensor measures the temperature on the heatsink as close as possible to the transistor,” Raducanu explained in a recent blog post. “The circuit uses a serial connection and is controlled via the terminal. A few preset values are available for the power to be dissipated.”
As noted above, the MCU at the center of the project is Atmel’s ATxmega32A4U, which calculates the thermal resistance of the heatsink, assuming it is hovering at ambient temperature. Meaning, the circuit needs to run until the temperature of the heatsink stabilizes to a new value.
“I am using a small board I designed for another project and another proto board which contains a current sensing resistor and a voltage divider to measure the supply,” he continued. ”A TL431 is used as a 2.5V reference. The circuit uses two supplies, one for the micro which also contains a 3.3V LDO and one for the dissipating transistor.”
According to Raducanu, an IRL540 transistor was chosen as the dissipating element due to its low threshold value.
“This is necessary to allow driving from a 3.3V DAC, considering the voltage drop on the current sensing resistor as well. This was chosen as 0.1 ohm, which corresponds to about 0.25V of drop while dissipating 50W from a 19V supply,” he added.
Raducanu says his open source software package is fairly basic – allowing for a few very simple functions. More specifically, data is relayed via the serial port and can be viewed in a terminal. Generated information includes the supply voltage, current, calculated power, DAC set, temperature and thermal resistance.
So what’s next for the heatsink tester? Well, Raducanu wants a dedicated PCB for the subsequent iteration, along with an LCD, PC app and a case.
Interested in learning more about the Atmel-powered heatsink tester? You can check out the project’s official page here.