Share a good emergency light circuit diagram

This is a circuit diagram for emergency lights, including alarm circuits, to show when your building has no power due to a shutdown or short circuit. When the power to your home/company is shut down for maintenance or shut down due to a short circuit, you may need this circuit to back up your power for temporary use.

When power is restored, the light or siren turns off. The switch provides a "lock-out" feature to extend the operation of the light or siren even when power is restored.

The circuit is permanently plugged into an electrical outlet and the NI-CD battery is trickle charged. In the event of a power outage, the light automatically illuminates. An alarm sounder can be selected instead of illuminating a light.

Components List:

R1____________220K1/4W resistor

R2____________470R1/2W resistor

R3____________390R1/4W resistor

R4______________1K51/4W resistor

R5______________1R1/4W resistor

R6_____________10K1/4W resistor

R7____________330K1/4W resistor

R8____________470R1/4W resistor

R9____________100R1/4W resistor

C1____________330nF400V polyester capacitor

C2_____________10uF63V electrolytic capacitor

C3____________100nF63V polyester capacitor

C4_____________10nF63V polyester capacitor

D1-D5________1N40071000V1A diode

D6______________LED green (any shape)

D7_______________1N414875V150mA diode

Q1, Q3, Q4 ______ BC54745V 100mA NPN transistors

Q2, Q5 BC32745V 800mAPNP transistors

SW1, SW2 ________ SPST switch

SW3____________Single pole double throw switch

LP1____________2.2V or 2.5V250-300mA flashlight bulb

SPKR_______________8 ohm speaker

B1_____________2.5V battery (two AANI-CD rechargeable batteries in series)

PL1____________Male power plug

Circuit Working:

The supply voltage is stepped down to about 12VDC at the terminals of C2 through the reactance of C1 and the diode bridge (D1-D4). This avoids the use of a power transformer.

The trickle charging current for battery B1 is provided by series resistor R3, D5 and green LED D6, which also monitors the presence of main power and correct battery charging.

Q2 and Q3 form a latching pair that starts operating when a power outage occurs. In this case, the Q1 bias becomes positive and therefore this transistor turns on the latching pair.

If SW3 is set as shown in the circuit diagram, the lamp will light up through SW2, which is normally closed; otherwise, the square wave audio generator composed of Q4, Q5 and related components will be started to drive the speaker.

If SW1 is left open, the light or siren continues to operate when main power is restored. They can be disabled by opening the main switch SW2.

If SW1 is closed, restoration of main power terminates lamp or alarm operation by applying a forward bias to the base of Q2.

Note: Close SW2 after the circuit is plugged in.