Device description

SPV1002

4/12

Doc ID 018839 Rev 3

3

Device description

A photovoltaic panel consists of a series of PV cells. In optimal conditions, all the cells are

equally irradiated and function at the same current level. However, during normal operation

some cells may become partially shaded or obscured. These shaded cells limit the current

generated by the fully irradiated cells and, in the extreme cases where these cells are totally

obscured, the current flow is blocked.

In this case the shaded cells behave like a load, and the current generated from the fully

irradiated cells produces overvoltages which can reach the breakdown threshold. This

phenomenon, known as a “hot spot”, can cause overheating of the shaded cells and, in

some cases, even permanent damage resulting in current leakage. To prevent hot spots,

therefore, bypass diodes are connected in parallel to the cell strings.

The device described here has the same functionality as a Schottky diode, but with

improved performance. It features very low forward voltage drop and reverse leakage

current. It consists of a power MOSFET transistor which charges a capacitor during the OFF

time, and drives its gate during the ON time using the charge previously stored in the

capacitor. The ON and OFF times are set to reduce the average voltage drop across the

drain and source terminals, resulting in reduced power dissipation.