Help me with this simple LED light circuit?

Thread Starter

PolymerPaladin

Joined Jan 17, 2021
5
Hello everyone,
I’m trying to create a single LED powered by a CR123A battery with a brightness control knob. I’m a noob and I’m learning a lot about this, so please don’t roast me too hard.

I understand that a CR123A is 3V, so that would blow the LED outright.
Do I need to find a dimmer that controls voltage and adds resistance? Ideally I’d like the switch to click on at the LED’s V_min and not go beyond the manufacturer’s recommended ~40mA range.

would this be easier using a AA battery and something that boosts voltage?

I saw some LED dimmers online, but they plug into a LED driver (dunno what that is) and seem to control devices in the 12V range or RC car knobs that still go all the way up to like 8V. Can you customize a voltage knob?

thanks, any help is appreciated and I’m willing to learn
 

DickCappels

Joined Aug 21, 2008
7,426
You can probably do it with an NE555 as a pulse width modulator driving the LED through a resistor or other current limiting device. What can you tell us about the LED, specifically how many volts are normally across it and how current you want to run through it, alternatively, what is the name of the LED's manufacturer and the LED's part number?
 

Thread Starter

PolymerPaladin

Joined Jan 17, 2021
5
You can probably do it with an NE555 as a pulse width modulator driving the LED through a resistor or other current limiting device. What can you tell us about the LED, specifically how many volts are normally across it and how current you want to run through it, alternatively, what is the name of the LED's manufacturer and the LED's part number?
Thanks for the help, the LED is a Chanzon H&PC-59042, just a cheap light off of Amazon. It’s listed as 3.0-3.2V. Just looking at the LED IV curve for white light, it looks like it starts to shine at above 2V and if it exceeds 3.75V it’ll go above the manufacturer’s recommended 50mA.

If I put a logarithmic potentiometer on the circuit would that give me good brightness control?

one big consideration for me is compactness, as I have very little space in this project
 

DickCappels

Joined Aug 21, 2008
7,426
From what you say in your post above, about a 1 K pot connected as a rheostat, not a potential divider might work out for you. No telling whether you will get a more pleasing effect with a log pot or an linear pot. If you have a way of telling, make sure that you don't exceed the pot's wiper current rating.

Something like this:
1610886771169.png

Just curious, why do you want a brightness control?
 

BobTPH

Joined Jun 5, 2013
3,308
You can’t get 40mA out of a CR2032 even into a short circuit.

At 3mA it falls to 2.8V instantly according to the datasheet.

If you put your 3V LED directly across it you will get a max of a couple of mA and it will light well below its maximum brightness.

Bob
 

Thread Starter

PolymerPaladin

Joined Jan 17, 2021
5
CR123A Discharge Curve:
View attachment 228021
Thank you, it sounds like I won’t be able to push beyond 20mA with my 3V battery but I would still be able to dim. I bought a 1k potentiometer, but the site has no information on its max current, is it safe to say 20mA is alright?

I’m trying to have a small LED shine onto the light-collection area of a fiber-optic scope. Ideally the battery and adjustment knob would be mounted to the top rail of the rifle, and be as lightweight/compact as possible because it’ll have to go into a small polymer housing.
 

Thread Starter

PolymerPaladin

Joined Jan 17, 2021
5
An AA battery can supply 25 to 100 mA and is rated at 2500 mAh or more at that current draw (https://data.energizer.com/pdfs/e91.pdf).
A joule thief (https://en.wikipedia.org/wiki/Joule_thief ) is a simply way to boost voltage.

That might be a better solution, if you have space.
Oh wow 2500mAh at 25-100mA? That would be some serious battery life for my use vs the 1500mAh CR123A.

Please help me understand - I have a CR2032 button battery LED flashlight that is rated at 12lumen. What I’m seeing is about the max brightness I’d want for this project. Is there 20mAh of current moving through the LED in this small flashlight? And if so, does that mean my 3V/20mAh CR123A on max current would look something like that?
 

Thread Starter

PolymerPaladin

Joined Jan 17, 2021
5
Oh wow 2500mAh at 25-100mA? That would be some serious battery life for my use vs the 1500mAh CR123A.

Please help me understand - I have a CR2032 button battery LED flashlight that is rated at 12lumen. What I’m seeing is about the max brightness I’d want for this project. Is there 20mAh of current moving through the LED in this small flashlight? And if so, does that mean my 3V/20mAh CR123A on max current would look something like that?
Correction, the small flashlight is x2 CR2016 in a series, which I guess would be 6V. Oof, I’ll have to take a look at what 3V looks like and make sure it’s bright enough for my needs.

if CR123A caps as 3V, then how are they used in high-powered LED flashlights? With a joule-thief?
 
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