The thesis describes the development of the new revision of the power supply for the portable display, presents the problems with electromagnetic interferences and suggested solutions. The new revision is an update of the existing power supply for portable display. The updated power supply will be used to power all of the electronics inside the portable display. The power supply can be connected to an external DC power adapter or directly to the output power connector of a computer manufactured by Dewesoft for field applications.
The need for a new revision of the power supply arose due to the distrubances, that appeared as horizontal moving lines on the screen. Because we wanted to research the cause of the distrubances, we tried to upgrade the existing power supply to solve the issue. The search for the problem started right at the power supply schematic, where our attention was brought to the short circuit between input and output contacts of the filter. The absence of the filter suggested that the common mode noise might be worth pursuing. Therefore, we designed a new filter and determined the component values with the help of the simulation tool LTspice. However, even though the filter was replaced with the new one, the problem still persisted. Therefore we focused to the ground loops and after ground loop elimination a clean image appeared on the screen. We performed immunity tests which were not initially successfull. We added an RC circuit between the shield and housing which improved the immunity to a satisfactory level. Finally, we applied all the modifications into a new revision of the power supply.
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