Cost effective electronic load for testing of electronic appliances

Diplomsko delo predstavlja razvoj enosmernega elektronskega bremena, ki je izdelan za bremenjenje tokovno zmogljivejših naprav (preko 10 A). Narejen je z namenom, da se pospeši in olajša proces testiranja naprav v laboratoriju za elektroniko Slovenskega Instituta za kakovost in meroslovje. Glavni del bremena predstavlja regulacijska zanka, ki je sestavljena iz močnostnega tranzistorja, operacijskega ojačevalnika in merilnega senzorja toka. Za merjenje toka je izbran AMR senzor, saj ima, v primeru malo večjih tokov, veliko prednosti pred merilnim uporom, ki ga običajno uporabljamo v podobnih aplikacijah. Regulacijska zanka predstavlja zaprtozančni sistem. Slabost takšnih sistemov je, da so lahko nestabilni. S pomočjo simulacije smo določili fazno varnost sistema in jo nato izboljšali s pravilno izbiro vrednosti komponent, da smo zagotovili stabilnost sistema. Elektronsko breme je sestavljeno iz kontrolnega modula in močnostnega modula. Funkcija kontrolnega modula je, da deluje kot uporabniški vmesnik, ki pošilja nastavitve močnostnim modulom. Ti so namenjeni regulaciji toka in meritvam temperatur, napetosti in bremenilnih tokov. Oba modula sta med seboj povezana preko RS-485 vodila. Preizkus bremena je pokazal, da je močnostni tranzistor sposoben doseči želeno moč 250 W in jo celo preseči. Hkrati so bile izmerjene temperature na hladilniku, ki so tesno povezane s temperaturami tranzistorja. Slabost, ki se je pojavila je, da breme ni sposobno krmiliti štirih MOSFET-ov z eno regulacijsko zanko, zato bo v prihodnosti narejen močnostni modul, kjer bo vsak tranzistor imel svojo regulacijsko zanko. Med izdelavo smo se soočali z nemalo težavami, vendar smo kljub temu uspeli doseči pomemben mejnik na poti do končne verzije elektronskega bremena.The thesis presents the development of a DC electronic load, designed to test higher current devices (over 10 A). It is made in order to speed up and facilitate the process of testing devices in the electronics laboratory of the Slovenian Institute of Quality and Metrology. The main part of the load is the control loop, which consists of a power transistor, an operational amplifier and a current sensor. The AMR sensor is chosen to measure the current because, in the case of slightly higher currents, it has many advantages over the measuring resistor commonly used in similar applications. The control loop is a closed-loop system. The disadvantage of such systems is that they can be unstable. We have used simulation to determine the phase margin of the system and then improved it by choosing the correct values of the components to ensure the stability of the system. The electronic load consists of a control module and a power module. The function of the control module is to act as a user interface that sends settings to the power modules. These are used to regulate the current and to measure temperatures, voltages and load currents. The two modules are interconnected by a RS-485 bus. Load testing has shown that the power transistor is capable of reaching and even exceeding the desired power of 250 W. At the same time, the temperatures at the heatsink were measured and were well corelated with the temperatures of the transistor. The disadvantage that has emerged is that the load is not capable of controlling four MOSFETs with one control loop, so in the future a power module will be made where each transistor will have its own control loop. We faced many difficulties during the development process, but we still managed to reach an important milestone on the way to the final version of the electronic load