presented by:
GANGADHAR YADAV

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Automatic Emergency Light
AIM:-
To design the circuit of AUTOMATIC EMERGENCY LIGHT
INTRODUCTION:-
This is automatic emergency light used in night at emergency time when the power cut or off by some region. This emergency light takes 230V AC and it converts it in 12V DC and charge the battery which is used in this circuit. The power of the battery is used that time when the power is cut off or we need to use it. This light is used mostly in villages because there is the lack of electricity is provided.
In this circuit I use BD 140 transistor the advantage of this emergency light is that if we Use this emergency light in a room no other light source is required but in other emergency light we use another light source when the power is available.
BLOCK DIAGRAM
BLOCK DISCRIPTION
First the power supply is given 230 through the step down transformer, the transformer convert it into 12V 1A but it is not gives dc so rectifier is used in it to convert it into dc. For filter the signals in the circuit a capacitor is used on it which filter the signals and convert it into pure DC. It also charged the battery when the power is given in the circuit. A transistor is used to maintain the power supply regularly and the control units (Zener diode) it maintain the zener voltage and also used it as a switch in reverse biased condition after that battery is the second power supplier which charged first and give backup power when the main power is cut off.
CIRCUIT DIAGRAM
CIRCUIT DESCRIPTION
This is the circuit diagram of low cost emergency light based on white LED. The white led provides very bright light which turns on when the mains supply is not there. The circuit has an automatic charger which stops charging when the battery is fully charged. Here 230v is converted into 12v using step down transformer. Bridge rectifier is used to convert AC input to DC supply. Capacitor is used to filter the input AC supply. When the main supply is ON the charged capacitor voltage is much greater than the battery voltage which keeps the transistor T1 & T2 in reversed biased. As soon as the main supply fails or removed the capacitor voltage becomes lesser as compared to battery voltage. This puts both transistor T1 and T2 in forward biased and the LEDs will glow with the battery voltage.
Uses
1. Convert 120V-230V Ac into 12V Dc and charge the battery.
2. Use in that places where the power doesn’t supply properly.
Advantages
 Saves fuel.
 Pollution free.
 Easy to use.
 Very low cost under Rs(200-300)
 Easy to install anywhere.
Disadvantages
 It can be used only for short period.
 Delectated circuit.
IMPLEMENTATION
This project is useful to us. It is used in emergency.
Capacitors
Function
Capacitors store electric charge. They are used with resistors in timing circuits because it takes time for a capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of charge. They are also used in filter circuits because capacitors easily pass AC (changing) signals but they block DC (constant) signals.
Capacitance
This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to show the smaller values.
Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):
• µ means 10-6 (millionth), so 1000000µF = 1F
• n means 10-9 (thousand-millionth), so 1000nF = 1µF
• p means 10-12 (million-millionth), so 1000pF = 1nF
Capacitor values can be very difficult to find because there are many types of capacitor with different labelling systems!
There are many types of capacitor but they can be split into two groups, polarised and unpolarised. Each group has its own circuit symbol.
Electrolytic Capacitors
Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their leads will be marked + or -. They are not damaged by heat when soldering.
There are two designs of electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand upright on the circuit board.
It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum for most battery circuits.
Tantalum Bead Capacitors
Tantalum bead capacitors are polarised and have low voltage ratings like electrolytic capacitors. They are expensive but very small, so they are used where a large capacitance is needed in a small size.
Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. However older ones use a colour-code system which has two stripes (for the two digits) and a spot of colour for the number of zeros to give the value in µF. The standard colour code is used, but for the spot, grey is used to mean × 0.01 and white means × 0.1 so that values of less than 10µF can be shown. A third colour stripe near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink 35V). The positive (+) lead is to the right when the spot is facing you: 'when the spot is in sight, the positive is to the right'.
For example: blue, grey, black spot means 68µF
For example: blue, grey, white spot means 6.8µF
For example: blue, grey, grey spot means 0.68µF
Unpolarised capacitors (small values, up to 1µF)