LED Emergency Light with Automatic Battery Cut-of Circuit

The post explains an LED emergency light circuit with sophisticated capabilities such as, over charge battery cut off, day time auto-disable, and need less to say that the circuit switches ON the LEDs instantly when AC mains goes wrong and reverts to charging mode when power is renewed.

The positive thing concerning this circuit is the fact that it includes normal, inexpensive parts which is often very easily obtained from the local market.

Let’s make sure to recognize the circuit working with the aid of the following tips:

IC1 which can be our very own IC555 continues to be set as a comparator. In the course of day time, the light over LDR will keep the LDR resistance low such that the potential at pin #2 of the IC is stored more than 1/3Vcc. This circumstance makes sure that the output of the IC at pin #3 remains at logic high.

The logic high at pin#3 of the IC retains T1 turned on, which accordingly maintains T2 turned OFF.

With T2 shut OFF, the LED array stays inhibited from the ground connectivity thereby the entire white LED array as well remains close off.

One more factor that retains T1 activated and T2 turned OFF, is the voltage from the transformer power supply phase. This work is used via the resistor R9. This actually also signifies that provided that mains AC can be obtained, T2 is limited from carrying out as well as the LEDs are not able to illuminate.

Now guess the mains power to the transformer neglects, and believe that such things happen throughout night or total darkness, pin#3 of IC555 reverts to zero and also there’s no voltage from the power supply, signifies T1 has simply no base bias thereby has got to turn off.

This immediately guides T2 to turn on coupled with the whole LED array also turns ON, offering the needed emergency lighting to the surrounding. Ensure That THE Lighting FROM THE LED Would Not Decrease OVER THE LDR, Which May Activate A Swift Unwanted SWITCHING OF THE LEDS.

The battery charging part contains T3, T4 along with the connected parts. P1 is placed such that it switches ON T3 when the battery voltage actually reaches just above 14 volts. The instance this occurs, T4 switches OFF, cutting of the negative supply to the battery and limiting any more charging of the battery.

Diode D2 helps to ensure that the battery obtains the negative supply during the charging practice only by means of T4 and also offers a standard harmful path to to T2 and the LED array once they perform.

The left side LED implies, mains power ON or existence of day light.

Parts List

R1 = 2M2
R2 = 1M
R3, R4, R5, R9, R6, R7, R8 = 4K7
ALL LED RESISTORS = 330 OHMS
D1, D2, D3 = 1N4007
D4—-D7 = 1N5402
C1 = 1000uF/25V
C2 = 1uF/25V
T1, T3 = BC547
T4, T2 = BD139
Z1, Z2 = 3V/400mW
P1 = 10K PRESET
IC1 = IC 555
TRANSFORMER = 12V, CURRENT = 1/10 OF BATTERY AH
LEDS = WHITE 5mm, OR AS PER CHOICE.
BATTERY = 12V, AH = AS PER LED POWER AND BACK-UP Specifications.

The above circuit could be much less complicated by removing the IC555, and by utilizing just a single PNP transistor rather than two NPN in the battery auto-battery cut of section.

P1 is utilized for changing the ambient light guideline in which the LEDs prevent lighting.

P2 is set such that at 14.6V (across the battery terminals) the base LED turns into very dim, barely noticeable, and at 12.5V it’s brightly lit.

The above circuit may be also combined with a solar panel for getting a programmed charging facility from both the sources that is from the panel during day time and from mains after the sun sets.

Parts List

R1,R2,R3, R4, R5 = 1K
P1 = 470K
P2 = 1K
C1 = 1000uF/25V
D1—D5 = 1N4007
T1 = BC547
T2 = 8050
T3 = TIP127
ALL LED RESISTORS = 330 OHMS
LEDS = WHITE, 5MM
LDR = ANY STANDARD TYPE
TRANSFORMER = 0-12/1AMP