Wiring Diagram

Working principle of this circuit is battery voltage compared with the reference voltage. This circuit is constructed by using 741 op-amp ICs. Op-amp is differential amplifier which output will be positive or negative, depends on the difference of input voltages. When the input voltage difference is positive with respect to reference voltage and battery voltage, then the output is positive and the LED will emit light. If negative LED cannot emit light. It is the main principle of battery level indicator. Voltage level indicated by the column of LEDs. For easy of reading LED rearranged in a vertical array.

The top four LEDs indicates the battery voltage is high. Sequentially the lower level indicates the battery voltage is low and bottom four LEDs indicates very low voltage of the battery. So, if the battery voltage continues to decline then LEDs will die in sequence from top to bottom. In this circuit 1mA current is adjusted for reference voltage. Vcc is divided by the total number of resistor for finding the value of resistor R. On the other hand, the resistor value of R1 is calculated by the equation, Component:

1. Op-amp IC 741

2. R = 3kΩ

3. R1 =220kΩ

4.  Diode

Operation:

The voltage drop against the each resistor is 3 volt.

So when the Vin = 0v or less than 3v the output of all op-amp are at

–Vsat . The silicon diodes protect the light emitting diodes against excessive reverse bias voltage.

When Vin is increased to a value 3v to 6v, only the output of op-amp#1 goes positive  to light which indicate “Very Low”.

When Vin is increased to a value 3v and 6v, the output of op-amp#1 and  op-amp#2  are at +Vsat  and goes positive to light which indicate “Low”.

When Vin is increased to a value 6v and 9v, the output of op-amp#1, op-amp#2 and op-amp#3 are at +Vsat  and goes positive to light which indicate “Medium”.

Similarly, when Vin increased to 12v or higher, the output of all op-amps are at +Vsat  and all op-amps output goes positive to emit light of all LEDs which indicate “Full” .

Linear Technology Corporation introduces the LTC4060, an autonomous 1- to 4-cell, 0.4A to 2A linear NiMH and NiCd battery charger. The LTC4060 includes all the functions required for a battery charger circuit. The design is simple and needs only three passive components. The LTC4060 also eliminates the need for a sense resistor and blocking diode, which increases efficiency and lowers the solution cost. This IC is targeted at applications including portable medical equipment, automotive diagnostic systems and industrial/telecom test devices.

•     Complete Fast Charger Controller for Single, 2-, 3- or 4-Series Cell NiMH/NiCd Batteries


•     No Firmware or Microcontroller Required


•     Termination by –?V, Maximum Voltage or Maximum Time


•     No Sense Resistor or Blocking Diode Required


•     Automatic Recharge Keeps Batteries Charged


•     Programmable Fast Charge Current: 0.4A to 2A


•     Accurate Charge Current: ±5% at 2A


•     Fast Charge Current Programmable Beyond 2A with External Sense Resistor


•     Automatic Detection of Battery


•     Precharge for Heavily Discharged Batteries


•     Optional Temperature Qualified Charging


•     Charge and AC Present Status Outputs Can Drive LED


•     Automatic Sleep Mode with Input Supply Removal


•     Negligible Battery Drain in Sleep Mode: <>


•     Manual Shutdown


•     Input Supply Range: 4.5V to 10V


•     Available in 16-Lead DFN and TSSOP Packages

This circuit is IC controlled emergency light. This series of automatic switching-on of the light on mains failure and battery charger with overcharge protection. When mains is absent, the relay RL2 is in deenergised state, feeding battery supply to the inverter section via its N / C contacts and switch S1.

The inverter section comprises IC2 (NE555) which is used in a stable fashion to produce sharp pulses at the rate of 50 Hz for driving the MOSFETs. The output of IC3 is fed to the gate of MOSFET (T4) directly while it is applied to MOSFET (T3) after inversion by gate transistor T2. Thus the power amplifier built around MOSFETs T3 and T4 functions in push-pull mode. The output across the secondary of transformer X2 can easily drive a 230-volt, 20-watt fluorescent tube. In case light is not required to be on during mains failure, simply flip the switch S1 to off position. Battery overcharge preventer circuit is built around IC1 (LM308). Its non-inverting pin is held at a reference voltage of approximately 6.9 volts which is obtained using diode D5 (1N4148) and 6.2-volt zener D6.