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3.7v LED driver Answered

Hi guys how are ya doin? :D

Recently I'm working on the next project, which is about battery powered bicycle led lamp. So in that case I want to use LED driver. Then I've founded this schematic with CMOS 555 timer, who runs more than 5 LEDs in series. Excited by this new found schematic, I bought the parts & connected them like so. Unfortunately, it turns out, it wont work. :/
At 3.7v they won't even light up, but at 5v they start to shine a little bit. I'm wondering do I need to put different transistor (in my case it was PN2222A - that's the one I had and its equivalent to 2N4401)? Or what the problem with this circuit.

I would more than thankful for your help. :D

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Downunder35m

2 months ago

Just use a 5V step up converter and then just the right resistor for your LED's in series to get them the right current and voltage ;)

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JohnSmith-WorkshopDownunder35m

Reply 2 months ago

Thanks for answering.
Is it that easy? I have step up module for power bank, which makes 5v from battery voltage. Do you think it would work?

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Downunder35mJohnSmith-Workshop

Reply 2 months ago

Don't see why I wouldn't but you could also use a cheap power bank to eliminate The problem of control and charging ;)
I give you one more free hint: Superbright LED's :)
A standard LED requires a lot of current to get a really decent brightness and the lifespan is reduced.
But a high brightness LED of 10.000 or more mcd can be used quite well below its max ratings and still produce far more light than a standard LED.
So while you really push hard with 30mA and risk a quick death these superbright LED's are happy to give you more light at 25mA or even below ;)
Red ones need around 1.8 to 2.2V (check the datasheet) so you should be able to use 3 in series on 5V.
And 3 of these strings to make 9 already is quite intense in brightness...
If you need some bright light for the front check flashlights that run on 3 1.5V batteries.
they should contain all you need and can be wired directly to 5V, especially if the battery is located somewhere under the seat ;)