I need to build a setup, using one 18650 to power up an XM-L LED with dimming control. It is not in a flashlight setup and I just need to build this thing for some special purposes.
By the way I am also looking at this variable resistor sold in Aliexpress as it does possibly work for my setup, but it says 10k ohm? Which is 10,000 ohm?!
The 12-24V is likely the V-in, so it must be a buckdriver, with the dimming done by PWM, a single li-ion then will not power it (too much overhead voltage needed). I am a bit worried about the amperage, it can be read as .8A (800mA) which is what I suspect, or 8A (as also claimed in the dx-description) which is not nice for an XM-L even when on copper.
The pictured dimmer won't work for one LiPo cell. It is designed for the LED tapes/strings which also integrate current limit resistors.
You said your application is not a flshlight, but that doesn't mean you can't use a driver meant for a flashlight. Unless you really need a knob to adjust the dimming.
djozz, thanks and if that is the case perhaps I should pass it and look for the others. 8A will almost kill the XM-L instantly I think lol.
hank, thanks and I just read the description at mouser, but according to their datasheet the resistance is very high, which is ranging from 500 to 100k ohm. Looks like it is not suitable for a single 18650 application or did I miss something?
Crux, sorry I should have mentioned that yes I need to control the dimming by turning a knob, so this kind of dimmer/potentiometer came into my mind. This is for my research project to study on knob turning application, and I plan to connect the knob turning operation to some indicator (output), says a LED or display. It’s a bit difficult to go into details for what I am going to use it for here, anyway I can either look for a different rotational resistor or think of a complete different setup. Any idea?
allan d, yeah as the other members have mentioned this dimmer looks like it’s for higher power application, no luck on this.
Appreciate for all the explanations and feedbacks guys, and please keep them coming.
I’d just use a standard 7135 based driver with an Arduino or similar product. An Arduion can easily take an analog input (potentiometer w/ knob) and output a PWM signal. Hookup the PWM wire to the Vdd pin on the AMC7135’s and you’re done.
If you don’t have an Arduino I still think that might be a good option for your project. You could pickup a Pro Micro clone for <$10 and just use a micro-USB cable and the free software to program it. I can’t find a pre-made sketch right now but there must be some around or it would be really easy to write using the tools they provide.
I gave you an inadequate link for Mouser, but their search tool lets you specify exactly what you’re looking for — but what I find there for 0.5 Ohms isn’t cheap. Neverrmindddd….
Controlling the brightness of an LED a power LED using only a potentiometer (setup as a variable resistor) is a bad idea, I recommend against that. There are good reasons that you don’t find us doing that in flashlights.
too much power for a normal potentiometer, must use very expensive ones (assuming they exist?) We’re talking about 0-2W or something for an XM-L or XM-L2 on a single Li-Ion.
it’s not constant current or constant voltage or constant anything. LED temperature, pot temperature, and other factors will allow drive current to change significantly.
other stuff I can’t think of right now Like I said, there are good reasons we don’t just throw a potentiometer in a flashlight, I just can’t be bothered to come up with them.
This is a photo of a DX’s customer who opened up the case of the dimmer showed that there is a ME555 generates PWM signal to an operational LM358 IC to control a 15N03L FET switcher.
I planned to go to a local electronics shop and ask about these variable resistor, but ended up did not go there yet due to something else. So is it okay to use these variable resistors with some generic LED like those 5mm LED?
2 & 3. I still don’t really get that why constant current/voltage is so important in this kind of setup. It’s ok if you don’t feel like to explain.
Microa,
This kind of dimmer uses PWM to control the current? So is it suitable for my single 18650 + XM-L setup? Or is it only suitable for AC current?
Yes, OK for 5mm but you must add the normal limiting resistor in series w/ the variable resistor. Use a calculator such as this one: http://led.linear1.org/1led.wiz
LED brightness is determined in large part by current, voltage isn’t so important as long as your input voltage is close to the LED’s Vf (I was just making a point that there is no regulation). Constant current gives mostly constant brightness. LEDs are pretty delicate, you can’t just give them too much current/voltage or they will die.
This dimmer is designed for LED stripe application which was specified the input DC voltage from 12 to 24V. I thought this dimmer is not suitable for a single cell usage.
