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142 CHAPTER 4 Performance of MPPT Techniques of Photovoltaic Systems

2.3.2 Sensors and Driver Circuits
2.3.2.1 Power Supply Circuits
The voltage and current sensing circuits and switch driver circuit requires þ5V dc
power to operate. The required dc power has 0 V ground. The source of power can be
either the PV cells directly or any other power source like mains ac power or a bat-
tery power. For experimental purpose, ac power has been used for sensing; the
switch driver circuits are as shown in Fig. 4.24.
The ac power is first transformed to 12 V ac using a step-down transformer, and
then the 12 V ac is rectified using a full-diode bridge rectifier circuit. The output
from the rectifier circuit is regulated by the lowedrop-out voltage regulator
LD1585C. The LD1585C has a maximum of 1.2 V voltage drop (drop between input
voltage and output voltage) at full load current of 5 A. The output from the ac recti-
fier is about þ9 V while the regulated output voltage from LD1585C is þ5 V, which
keeps a margin of þ4 V drop between the input and output, this grants a þ5 V stable
regulated voltage even at the full load current of the LD1585C. The LD1585C output
voltage can be adjusted using the resistor R54 (V out ¼ 1.25*(1 þ R54/R53)). The
regulator has a fast response to load current requirements, which makes it suitable
to supply fast switching circuits. For more information about LD1585C features
and usage requirements, refer to the device datasheet.

2.3.2.2 Boost Switch Driver Circuit
The boost switch (either MOSFET or IGBT) may require a low-resistance and high-
power driver to enable it switch on/off while passing a large amount of boost current
through it. The FPGA outputs can only supply a current up-to 24 mA at 3.3 V. If the
boost switch sinks more current than this amount from the FPGA, then the FPGA
output buffer may damage. The circuit here provides a high-power buffer to
FPGA output before driving the boost switch gate as shown in Fig. 4.25. The circuit
also shifts up the driving level from 3.3 Vat FPGA output to 5 Vat switch gate. This
grants more reliable operations, especially at high boost currents and fast switching
frequencies.
The device used here is MCP14E5-XP, which is a high-speed/high-power MOS-
FET driver with output enable signal. The device has two inputs and two outputs, the
first output has the same polarity as the first input and the second output has the
inverted polarity of the second input. Connecting the two inputs together will pro-
duce two outputs with one of them having the same polarity as the input and the sec-
ond output having an inverted polarity than the input. The device has a peak output
current of 4 A.

2.3.2.3 PV Voltage-Sensing Circuit
The PV voltage has to be sensed and passed to the fuzzy control algorithm by using a
PV voltage sensing circuit in Fig. 4.26. The PV voltage is first scaled down to an
acceptable voltage level to be fed to analog to digital converter circuits (ADCs).
The scaling is achieved by a simple two-resistor voltage divider BOOST_RDIV3
and BOOST_RDIV4. The voltage drops on BOOST_RDIV4 must not exceed the