This is a design circuit for an emergency light is a battery-backed lighting device that comes on automatically when a building experiences a power outage. This is the figure of the circuit;
If AC supply is present, the alternating voltage is passed through diode D1. D1 behaves as a half wave rectifier and lets only positive voltage to pass on. When AC supply goes off, capacitor C1 discharges through R3. Due to this discharging of C1, voltage across C1 decreases gradually.
Part:
R1, R2 _____200k – 1W
R3 ________100k – 1/2W
R4 ________100k – 1/2W
D1 ________IN4004
C1 ________0.1mF – 50V
T1 ________BC148B
T2 ________SL100
Dry cell battery 1.5V
Bulb 3V
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