design of charger

example of circuit

The circuit uses a 12 volt solar panel and a variable voltage regulator IC LM 317. The solar panel consists of solar cells each rated at 1.2 volts. 12 volt DC is available from the panel to charge the battery. Charging current passes through D1 to the voltage regulator IC LM 317. By adjusting its Adjust pin, output voltage and current can be regulated.

VR is placed between the adjust pin and ground to provide an output voltage of 9 volts to the battery. Resistor R3 Restrict the charging current and diode D2 prevents discharge of current from the battery. Transistor T1 and Zener diode ZD act as a cut off switch when the battery is full. Normally T1 is off and battery gets charging current.

When the terminal voltage of the battery rises above 6.8 volts, Zener conducts and provides base current to T1. It then turns on grounding the output of LM 317 to stop charging.

block diagram

Solar panel	·         Output: 5.5V/40mA. Received energy from sunlight and can produce electricity from a range of frequency light.
Voltage comparator (LM339)	·         Convert analog signal to digital signal as convert from the energy to electricity. Because solar panel voltage is lower than battery voltage, simple boost converter will be sufficient. It is also to compare two analog signals and produce a one bit digital signal.
Battery	·         1000 - 1300 mA-hrs. Battery charger used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.
Voltage/Current sense circuit	·         Sense circuit measures panel and battery voltage and current. Accurate measurement is required for microcontroller (PIC16877A) tracking
Load control and monitoring	·         Overload protection. It also disconnects the load if the battery is depleted
System power supply	·         Regulated 3.3V power supply. Most of the system components are powered by 3.3V
PIC16877A, microcontroller	·         Microcontroller that implements MPPT algorithm, controls voltage comparator and displays system information at LCD.
LCD, System information display	·         Shows current system state on the LCD display. Solar panel power, level of battery charge, load power and other information.