LED Emergency Light With Transformerless Power Supply

This circuit diagram uses 230 volts power supply without a transformer to light a combination of 36 SMD or DIP LEDs. Since this circuit is not isolated from 230 volts AC by a transformer there is danger of electric shock while testing and therefore utmost care needs to be taken. Alternately a 12 volt and at least 500 mA DC adapter can be used across the zener diode as a substitute for the transformer-less power supply.

When the power supply is ON the battery will be charging and the LEDs will be OFF. When power supply turns OFF the LEDs will light through the battery supply. Various 12v batteries  from around 2Ah to 7.2Ah can be used.

Additionally the a 12v supply from a solar panel of about 320mA and above can also be used. But the two supplies have to be connected through DPDT switch. The center terminal will go to +ve of battery. One of the other terminal will connect to solar panel output +ve and the third will connect to ac/dc adapter output +ve. All three -ve join together. Since the voltage of solar panel varies with intensity of sun light it is necessary to connect a 1N5402 diode between +ve of solar panel and +ve of battery to prevent reverse current flowing from battery into solar panel.

If a 12v battery of more than 2Ah is used it is necessary to increase the value of R2 to 10k or 15k or even more to prevent battery draining through it.




Parts List

All resistors are 1/4 watt, 5%,

R1 = 1M

R2 = 1K,

R3---R14 = 56 Ohms

C1 = 2uF/400V PP Capacitor

Also C1 = 2 nos 1uF/400V PP
Capacitors connected in parallel
1uF/400V same as 105/400V
C2 = 100uF/ 25V

D1, D2 = 1N4007,

D3, D4 = 1N5402

T1 = TIP127

Z1 = 15V 1 watt Zener diode

Battery = 12V/2AH or more

LEDs = SMD, 3V white, 20 mA
















Since this circuit diagram does not have battery overcharging protection it is advisable to connect a 13v Zener diode across battery terminals.


A 12v 7.2Ah battery can be used to light up to 100 LEDs.

When the circuit is powered the voltage across base and emitter should be around 0v.

When input ac power fails then there should be small voltage across base and emitter. This is required for current to flow from emitter to collector from battery into the LEDs.

Depending on the Ah capacity of battery used the value of R2 has to be increased till LEDs are fully OFF when ac supply is ON.


*The voltage supplied to charge battery should always be higher than the rated battery voltage.


*** The above circuit can be used to charge batteries of different voltages by changing the value of C1 capacitor and the value of Z1 zener diode.


To protect from starting surge currents a thermistor can be connected in series with the 230v input supply.
Example:





OTHER SIMILAR CIRCUITS:



 





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