This is a Simple Solar Cell Voltage Regulator Circuit Diagram. This device is designed to be a simple, inexpensive ‘comparator’,
intended for use in a solar cell power supply setup where a quick ‘too
low’ or ‘just right’ voltage indicator is needed. The circuit consists
only of one 5V regulator, two transistors, two LEDs, five resistors, two
capacitors, and one small battery. Although a 4-V battery is indicated,
4.5 V (3 alkalines in series) or 3.6 V (3 NiCd cells in series) will
also work.
Solar Cell Voltage Regulator Circuit Diagram
The specifications of voltage regulator IC1 are mainly determined by
the size and number of the solar cells and the current pull of the
equipment connected to the output. Here the low-drop 4805 is suggested
but other regulators may work equally well as long as you observe the
output voltage of the solar cells. Transistors T1 and T2 are
complementary types i.e. one each of the pnp and npn variety.
Although the ubiquitous BC557B (pnp) and BC547B (npn) are indicated,
any small-signal equivalents out of the junk box will probably do. The
values of voltage dividers R1/R6 and R3/R4 may need to be adjusted
according to the type of transistor and its gain, or according to the
desired voltage thresholds. Using the resistor values shown in the
schematic, LED D2 turns on fully when the voltage is just above 5 volts.
LED D1 turns on when the voltage drops below 4.2 volts or so. Between
those two thresholds, there is a sort of no man’s land where both LEDs
are on dimly. A buzzer or other warning device could be connected across
the terminals of LED D1 to give a more substantial warning if the
voltage drops below operating limits. The current consumption of the
circuit is about 20 mA at 5 V, and it decreases with the voltage
supplied by the solar cells.
