In the following master thesis, the design and the development process of an electronic load is presented.
The core of the device is an analog electronic circuit, which's analysis and development process is presented within the theoretical chapter. The architecture of the circuit inherently includes a feedback loop, so the badly designed circuit may be unstable. In the several simulations, the impact of the characteristics of the chosen operational amplifiers and the parasitic inductances of the connections between the device and the tested power supply, on stability are presented. With the optimal set of the used components and the redesign of the circuit architecture we achieve that, the final version of the circuit is highly stable with a phase margin of 100° and it is highly immune to the parasitic inductances.
In the next chapter is presented the development process of the sub circuits that, besides the analog electronic circuit, also form the device electronic load. These circuits are used, whether to support the operation of the other blocks or they are used as an interface between a user and the device. The application of the microcontroller is also part of that interface. The application monitors the analog circuit and controls it, according to the status of the circuit and the requirements of the user. The major part of the microcontroller's application is shared into several tasks of the operational system freeRTOS. The rest of the microcontroller's application is implemented within the drivers of the used peripheral units, integrated in the microcontroller. The drivers are implemented so that they with linking and synchronizing of the multiple peripheral units, some functionalities are executed autonomous without CPU time, e.g. sampling of the branch currents and transmitting and receiving of large messages via serial port. The user can control the device via SCPI commands, that are transmitted to the device via provided USB port. The PC application, which supports the transmission of the supported SCPI commands and the reception of the responses was also developed as a part of this master thesis. During the tests of the first prototype of the device, a malfunction in the current measurements was detected. The range of the signal at the output of the measurement circuit was to small, according to the circuit performances. The problem was solved with increasing the gain of the amplifier. After the modification, the circuit works well. The analog circuit is stable, the ripple in the output current is negligible, the output characteristic of the current deviate from the linear characteristic for less than 1 mA in the major part of the output range. Besides that, the device works well, there are a lot of space to improve the device in the next revisions.