Application of diodes in the bridge rectifier arrangement.
Application of the quad opamp IC LM324 as comparator.
Nowadays maintenance-free lead-acid batteries are common in vehicles, inverters, and UPS systems. If the battery is left in a poor state of charge, its useful life is shortened. The Lead Acid Battery Charger cum Voltage Analyser is capable of replenishing the charge in a battery within 6-8 hours and checking the battery voltage before charging starts (since overcharging may damage the battery). The circuit gives an audio-visual indication of the battery voltage level and also warns about the critical voltage level at which the battery requires immediate charging.
No. of ICs used: 1
The power supply circuit of the Lead Acid Battery Charger cum Voltage Analyser consists of a standard step-down 12V AC (2-amp) transformer and a bridge rectifier comprising of four diodes (D1 through D4). A capacitor (C1) smooths the AC ripples to provide a clean DC for charging the battery.
The heart of the circuit is the quad op-amp LM324 (IC1) that has four separate op-amps (A through D) with differential inputs. Each op-amp has been used as a comparator in the Battery Charger circuit. A push-to-on Switch (S2) is provided in the circuit, which when pressed momentarily checks the battery voltage level before charging the battery.
The non-inverting terminals of op-amps A, B, C and D are connected to the positive supply rail via a potential divider chain comprising of resistors (R1 through R5). Thus the voltage applied to any non-inverting input is the ratio of the resistance between that non-inverting terminal and ground to the total resistance (R1+R2+R3+R4+R5). The resistor chain provides a positive voltage of above 5V to the non-inverting inputs of all op-amps when battery voltage is 12.5V or more. A reference voltage of 5V is applied to the inverting inputs of op-amps via a 5V zener diode (ZD1). When the circuit is connected to the battery and the push-to-on switch (S2) is pressed (with S1 open), the battery voltage is sampled by the analyser circuit. If the supply voltage sample applied to the non-inverting input of an op-amp exceeds the reference voltage applied to the inverting inputs, the output of the op-amp goes high and the LED connected at its output lights up.
The different levels of battery voltages are indicated by LED1 through LED4. All the LEDs remain lit when the battery is fully charged (above 12.5V). The buzzer connected to the output of IC1 also sounds (when S2 is pressed with S1 kept open) as long as the voltage of battery is above 9.8V. If the voltage level goes below 9.8V, the buzzer goes off, which indicates that it’s time to replace the battery.
