AC-DC Emergency Lamp. Utility Gadgets.11

Once I purchased a China make AC-DC LED emergency lamp for Rs.70. I wonder ,how they are selling the device cheaply. Due to curiosity, I opened the case of thelamp. So simple circuit that cost only Rs.20, a small 6 volt battery and LEDs. This is the reason why they are selling the device at low cost. Reliability? Sometimes it will last years, otherwise few days. That depends on the use and conditions. Most of the China make devices use tranformerless power supply which can damage when spikes appear in the mains lines. Any way, simplicity and low cost can be considered. I have drawn the diagram and constructed one sample. It is still working. Let us see the circuit.

1. A 105 K 250 volt AC capacitor is dropping the 230volt AC to low volt AC.

2. Bleeder resistor R1 is used to remove the stored current from the capacitor. See without this resistor, the voltage in the capacitor can be as high as 400 volts and will be present many days in the capacitor. So it can give a shock if the plug is touched. The resistor will bleed the current immediately at power off.

3. D1 through D4 rectifies the low AC to DC and capacitor C2 makes the DC ripple free.

4. Around 20 volts DC with a current of 100 mA will be available from 105 K (1uF) capacitor. In capacitor power supply, as a rule there will be 100 mA current per uF of capacitor.

5. Remaining part is simple. Switch S1 is two way. When it is placed to one end, current passes through D5 to charge the battery and to light LEDs. If the switch is in the other position, Lamp turns off.

6. When the mains power is off, D5 reverse biases and D6 forward biases. LEDs light using the battery power.

Caution: This circuit uses high volt AC directly. So it can give a lethal shock if touched. Switch on the power only after enclosing the circuit  in a plastic case. Do not trouble shoot, solder or test while it is connected to AC.

Always use footwear while doing work in AC circuits. Use a sleeved AC tester for screwing and unscrewing the screws. An ELCB connected switch box is ideal in work place.


4 thoughts on “AC-DC Emergency Lamp. Utility Gadgets.11

  1. reghuthalikuzhy 28 Oct 2012 / 8:59 pm

    you are repeating the power supply hazard unnecessarily. Please bear in mind the people related with the field is more or less vigilant. Do not consider this as an insultation

    • D.Mohankumar 28 Oct 2012 / 10:51 pm

      That I know. There are requests regarding the simple power supply circuit designs because plenty of china make gadgets are available and people want to how it is working because they are using them. In every AC circuit, there will be a caution notice regarding the shock hazard. Only experienced persons will handle AC circuits. Anyway thanks for the comment

    • Binoy Manithara 30 Oct 2012 / 4:56 pm

      hey mr reghuthalikuzhy, keep in mind that there are lots of people even now wonder how the transformerless power supply works ,only due to mohankumar sir ‘s repeated posting i came across what this transformerless power supply is . If you think these are unnecessary then i think you have a place next to einstein , so please go and invent another low cost power supply and go for patents , you should go and create another website where you will even never use a word like “is” 2 times, also why the letter “U” is repeated in your name two times ?? its so disgusting for me to see that the letter “H” is repeated 3 times , the letter “U” for 2 times in your name , next time pls dont repeat it.This is not a place for showing your knowledge , this is a place where including me a lots of people who want to enrich their knowledge.This is not a place for so called “HI FI” guys.dont think as a insult .thank you

      • D.Mohankumar 30 Oct 2012 / 7:33 pm

        Dear Binoy
        The most attracted topic of the present days is energy conservation, use of alternate ways to reduce cost of electronics equipments etc. You know, I bought a White LED in 2006 for Rs. 90 and now it is Rs.1 by the introduction of china products in the market. Transformer less power supply is every where now. What about Mobile charger, What about LCD TV and what about a Computer. No transformer is there. What is its reason. Two things. Transformer is bulky and there will be severe power loss due to heat. Then regarding shock hazard. Even an LKG student knows that it is not safe to touch a plug point. So people knows how to handle electricity and only who knows that will construct an AC circuit. If we are using battery only, how can we use an AC adapter without fear. I am posting the same aspect in different forms because there are lot of space for changing the design even if the basic aspect remains same. I have one critic abroad. When I publish a circuit, immediately he copy that image and post it in his website with harassing comments. Fortunately, he is giving link to my website. So I have an advantage. My site traffic increases and more and more people subscribe the updates.Every person has his own views and it is better to take it in a good spirit. But I will not moderate such harassing and insulting comments in my pages because it is not the space for popularity.

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