Intelligent Load for DC Supplies

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Dr. Varjasi István
Department of Automation and Applied Informatics

Nowadays switch mode power supplies become more popular. These supplies have got many important dynamic parameters near by static parameters, which can be measured by a simple sliding resistance. The reason of the importance of dynamic parameters is, that we usually use other equipment as the load of supply, witch needs constant power for operation (typically PC-s and notebooks). This could be a problem for supply, because the constant power load has a negative resistance at operating point, which reduces the phase reserve of the controlling loop of the supply, and degrades the stability parameters of the supply.

I would like to test dynamic parameters of supplies, but I did not find suitable equipment for my task. Based my experiences I was able to build a fast intelligent supply tester. My goal is to develop and to produce a useful equipment, which could be simulate constant power load for supplies as high frequency range as it possible. Furthermore my equipment also contains HMI and ability of PC-side controlling, and programmable load characteristics. When I define the limits of my intelligent load, I based on the parameters of usually used household and labor installations (eg: PC-supplies and labor-supplies), due to the importance of general use.

I developed a base circuit to try and measure the main semiconductor element of my device, which is a Power mosfet used in linear operation to dissipate the power of supply. After I ran simulations to test the best controller topologies, routing methods and components. The next version of load contains microcontroller, HMI, PC-side communication, own power supply and controlling module. The accuracy of measuring parameters is more than 10 bits against the maximum values at all of measurements. Furthermore my device also contains different protection at software and hardware levels, to avoid the damaging of equipment and tested supply for any wrong end user handling.

Now, my device has PC-side controller where base functions are available. A dynamic operation was tested on oscilloscope by function generator, which I describe in details in my thesis.


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