In this post we will discuss how a transformerless LED emergency lamp can be build using a handful of ordinary components.
I have presented a few number of interesting LED emergency light circuits in this blog, but these mostly include a transformer for charging the associated battery. In this article we discuss a emergency lamp circuit that's free from the usual bulky transformer.
The main features of the proposed automatic transformerless emergency light circuit is though very identical to the earlier designs, the elimination of the transformer makes the design pretty handy.
Because now the circuit becomes very compact, low cost and easy to build.
However, the circuit being completely and directly linked with the AC mains is hugely dangerous to touch in an uncovered position, so it is obvious that the constructor implements all the due safety measures while making it.
How the Circuit Works
Coming back to the circuit idea, transistor T1 being an PNP transistor tends to remains in switched OFF condition as long as AC mains is present across its base emitter.
Actually here the transformer is replaced by the configuration consisting of C1, R1, Z1, D1 and C2.
The above parts constitute a nice little compact transformerless power supply, capable of keeping the transistor switched OFF during mains presence and also trickle charges the associated battery.
The transistor reverts to a biased condition with the help of R2 the moment AC power fails.
The battery power now passes through T1 and lights up the connected LEDs.
The circuit shows a 9 volts battery, however a 6 volt battery may also be incorporated, but then D3 and D4 will need to be completely removed from their positions and replaced by a wire link so that the battery power is able to flow directly through the transistor and the LEDs.
Automatic Emergency Light Circuit Diagram
WARNING - THE CIRCUIT IS NOT ISOLATED FROM AC MAINS, AND THEREFORE IS EXTREMELY DANGEROUS IN POWERED, UNCOVERED POSITION.
R1 = 1M,
R2 = 10K,
C1 = 1uF/400V PPC,
C2 = 470uF/25V,
D1, D2 = 1N4007,
D3, D4 = 1N5402,
Z1 = 12 V/ 1Watt,
LEDs, White, High Efficiency, 5mm