The comparator compares the voltage from the battery and acts as a switch for the voltage regulator circuit. Finally, the battery voltage checker checks the voltage of the battery (as it received from the panel) to determine if the battery needs to charge more.
The circuit is designed to be simple, efficient and reliable by using easily available field replaceable parts. It uses a 12V, 5W solar panel rated from 100 milliamps to 1A and a lead acid or other rechargeable battery that is rated from 500 milliamp hours to 40 amp hours of capacity.
This circuit regulates the voltage flow from the photovoltaic panel to the lead acid battery. It can produce currents up to 150mA. When external pass transistors are added to this circuit, output currents can reach up to 10A. The maximum input voltage to this circuit is 40V (LM723, 2004) with an output voltage adjustable between 2V and 37V. This circuit consists of a series regulator, LM723.
Figure 11 and Figure 12 are the connection diagram and the datasheet circuit (Voltage regulator, 2012) as below: Figure 11: Connection Diagram Figure 12: Datasheet Circuit The basic building blocks of LM723 are: 1 The Reference Voltage Amplifier 2 The Error Amplifier 3 The Series Pass Transistor. The equivalent circuit of LM723 (LM723/LM723C Voltage Regulator, 1994) is shown in Figure 13 as below: Figure 13: Equivalent circuit of LM723. The main components used in the voltage regulator circuit are (Table 1): Table 1: Main components of the voltage regulator circuit Quantity Component Value 1 LM723 - 1 R1 4.87k ? 1 R2 7.15k ? 2 Transistor 2N3055 1 Diode 1N4007 1 VR 10k ? 1 C1 0.1?F 1 C2 500PF Calculations: Following are the calculations for design and operation of the circuit: Output voltage- Vout = Vref x ((R1+R2)/R2) Where R1= 4.87K, R2= 7.15K and Vref= 7.35V from the datasheet. Vout= 7.35 x ((4.87 + 7.15)/7.15) = 12.36V. Figure 14: Output voltage. Current- The current is established from the Darlington transistor pair in the regulator circuit (Q1 and Q2 in Figure 10). Q1 and Q2 (2N3055) are silicon, Epitaxial-Base Planar NPN transistor mounted in a Jedec TO-3 metal case (Charger Circuit for 6V or 12V Car Battery, 2012) and are recommended for use in power switching circuits, series and shunt regulators, output stages and high fidelity amplifiers. Figure 15 shows the Darlington transistor pair: Figure 15: Darlington transistor pair used in voltage regulator circuit. In this circuit, a voltage of 0.7V is applied to the base (B) of the first transistor (TR1) to switch it on. A current of 300 milliamps passes through the first transistor from the collector (C) to the Emitter (E). The emitter of TR1 is connected to the second