EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: L555BAT on April 02, 2021, 08:23:47 am
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Hi, I hope this is posted in the correct place..
I have a lamp which features 3 candle effect LEDs, each powered individually by 3 x 1.5v AAA batteries. I'd like to convert this to something that I can plug into the wall.
I thought that using a spare laptop charger might be useful for a power supply (is it?)
Can anyone advise on how to go about this? What might the circuit diagram look like? I suspect that I need to:
1) Reduce the 19v from the laptop charger to 13.5v (4.5v * 3) - How is best to do this?
2) Wire each of the lights in series in order to supply 4.5v to each of the bulbs. From my limited knowledge the same current will flow through each bulb but the voltage will be divided between the three?
Very much a beginner so wanted to ask your advice on this. Thanks in advance.
Please see the attached images.
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Welcome to the forum.
Those lights have very low power consumption, a laptop charger would be overkill. It would be much easier to wire them in parallel and power them from a 5V USB charger.
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Welcome to the forum.
Those lights have very low power consumption, a laptop charger would be overkill. It would be much easier to wire them in parallel and power them from a 5V USB charger.
Agreed. A diode could be added, to reduce the voltage if you're really paranoid, but 5V will probably be fine..
It's a bad idea to connect anything other than plain LEDs (no flicker effects, flashing, colour changing etc.) in series because the voltage drop will change. The current is probably low enough a dual op-amp and potential divider could theoretically be used, but that's just overcomplicating things.
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Yes, a series diode
(or even two) might be a good idea. Cheap USB chargers tend to head towards 5.25V when lightly loaded. Anything will do within reason, a 1N400x being the most common.
Those candles are designed for normal battery voltage range (they work with NiMh too) so would normally see around 4.8V (fresh alkalines) down to around 3V (discharged cells). An ordinary silicon diode will drop around 0.7V.
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Many thanks for the help, I think I'll go for the 5v USB charger wired in parallel and see how I get on. :-+