Simple Solar Cell Voltage Regulator Circuit Diagram

Description

This apparatus is conceived as a straightforward, cost-effective ‘comparator’, intended for application within a photovoltaic system where a rapid ‘too low’ or ‘perfectly adequate’ voltage signal is required. The circuit comprises a single 5V controller, two transistors, two light-emitting diodes, five resistors, two capacitors, and a small battery. While a 4-V battery is indicated, 4.5 V (3 alkaline cells in series) or 3.6 V (3 NiCd cells in series) are also suitable.

The characteristics of the voltage regulator IC1 are primarily dictated by the dimensions and quantity of the photovoltaic cells, along with the current draw of the devices connected to the output. The low-drop 4805 is recommended here, but other regulators can function equally well as long as the output voltage of the solar cells is carefully monitored. Transistors T1 and T2 are of complementary nature, meaning one is a PNP and the other an NPN type.

Circuit Diagram:

Frequently used BC557B (pnp) and BC547B (npn) transistors are shown, but any small-signal equivalents salvaged from a ‘junk box’ will likely suffice. The values of voltage dividers R1/R6 and R3/R4 may need alteration based on the particular transistor and its amplification factor, or according to the desired voltage levels. Utilizing the resistor values depicted in the schematic, LED D2 illuminates completely when the voltage surpasses 5 volts.

LED D1 activates when the voltage decreases below approximately 4.2 volts. Between these two limits, there exists a transitional zone where both LEDs glow dimly. A buzzer or alternative alerting device could be connected across the terminals of LED D1 to provide a more pronounced indication if the voltage drops below operational limits. The current consumption of the circuit is approximately 20 mA at 5 V, and this reduces as supplied by the photovoltaic cells.

Integrated Circuits Details

The 4805 is a three-terminal positive-voltage regulator IC. This integrated circuit is designed to maintain a constant output voltage despite variations in input voltage or load current. It’s a widely used component in various electronic circuits. It consists of a Zener diode, a transistor, and resistors, all working together to regulate the voltage. It is suitable for a broad range of applications, including powering sensitive electronic circuits and providing stable voltage supplies. [simg=4805_ic.jpg]

The BC557B is a commonly used small-signal NPN transistor. It's a bipolar junction transistor (BJT) designed for general-purpose switching and amplification applications. BC547B is a complementary PNP transistor. These transistors are frequently used in comparator circuits and other applications where a complementary pair of transistors is required. [simg=bc557b_ic.jpg] [simg=bc547b_ic.jpg]