Solar Lead Acid Battery Charger

This circuit is suitable for garden lighting, listening to the radio and playing CDs. A single solar cell that converts solar energy into electrical energy generates an open circuit voltage of about 0.55V, which quickly drops to 0.45V once a load is added.
The 12V lead-acid battery that is used more often as a solar energy storage device cannot be used to directly charge the lead-acid battery with several single solar cells, but a number of cells are connected in series according to the required voltage. The charger should have an output of 13.5-14V.
The figure below shows a simple boost converter circuit, which uses a small number of single solar cells to form a battery assembly to charge the lead-acid battery. The circuit consists of IC1 and a small number of components. IC1 is directly powered by the lead-acid battery, that is, the circuit can still work without the solar cell power supply. Because the current required by the circuit is very small, the lead-acid battery cannot be discharged quickly.
The solar cell is connected to the connector K1. IC1 turns on the field effect tube FET-T1, causing a current to pass through the inductor coil L1. Here, the electrical energy is converted into magnetic energy and stored in the inductor. When the current exceeds a certain value, IC1 turns off the FET. At that moment, the inductor tries to keep the current flowing. This induces a voltage that causes current to flow through D1 and into the battery. This again converts the magnetic energy into electrical energy.
The current through the inductor should not rise too quickly.
IC1 provides a current limiting effect to prevent this from happening. The current through the inductor is transformed into a small voltage across the shunt resistor R1. Once IC1 turns off the FET, this voltage quickly rises to 0.1V.
Resistors R2, P1, and R3 form a voltage divider. The voltage at the sliding point P1 is proportional to the output voltage.
IC1 tries to keep this voltage fixed at 1.5V. Therefore, P1 can be used to adjust the maximum output voltage.