The voltage across the DC motor must be step down by
using the DC-DC buck converter in order to reduce the
turning speed of the solar panel to get accurate sun tracking.
Fig. 2 shows the circuit of DC-DC buck converter. M1 is
P12PF06 P-channel MOSFET as the switching element and
M2 is IRF630 N-channel MOSFET as a driver to drive the Pchannel
MOSFET. Since PIC microcontroller cannot produce
a negative voltage to turn on the P-channel MOSFET directly.
Therefore, the N-channel MOSFET is use to turn on the Pchannel
MOSFET. The relationship between the input
voltage and the output voltage of the DC-DC buck converter
are given by