6 Volt Automatic Emergency Light BatteryThis circuit is IC controlled emergency light. This series of automatic switching-on of the sunshine on mains failure and battery charger with overcharge protection. When mains is absent, the relay RL2 is in deenergised state, feeding battery offer to the inverter section via its N / C contacts and switch S1.
The inverter section contains IC2 (NE555) that is used in a very stable fashion to supply 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 whereas it's applied to MOSFET (T3) when inversion by gate transistor T2. so the facility amplifier designed 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 needed to be on throughout mains failure, simply flip the switch S1 to off position. Battery overcharge preventer circuit is constructed around IC1 (LM308). Its non-inverting pin is held at a reference voltage of approximately 6.9 volts that is obtained using diode D5 (1N4148) and 6.2-volt zener D6.
The inverting pin of IC1 is connected to the positive terminal of battery. so when mains offer is gift, Comparator IC1 output is high, unless battery voltage exceeds 6.9 volts. therefore the transistor T1 is generally forward biased, that energises relay RL1. in this state the battery remains on charge via the N / O contacts of relays RL1 and current limiting resistor R2. When battery voltage exceeds 6.9 volts (overcharged condition), IC1 output goes low and gets deenergised relay RL1, and so stops more charging of battery. MOSFETs T3 and T4 may be mounted on suitable heat sinks.
