I was hoping someone could point me towards info for my specific needs, on a budget… It seems all my projects require dimming of some type.
requirements:
-relatively neutral to warm light source (3000-4500k)
-variable dimming (not 3-mode, needs to be user adjustable on the fly)
-battery powered, but would prefer smaller battery instead of longer runtime
-guessing no more than 100-200 lumens is really needed
My big issue is the dimming part. I’ve read about the potential dangers and pitfalls of using a constant current driver and then improperly using a pot, and since I’ll hopefully be wearing this near my forehead at times I do not want it to overheat. I’ve found drivers from $4 up to $25, and without asking I’m sure I’ll order the wrong ones.
My ideas were to get something I’m familiar with like the xp-g or similar no name if it fits the bill. I already have some 14500 and would prefer that over 3 AAA or AA cells, if possible. I’d be up for smaller batteries, but definitely prefer rechargeable. I need them to be safe. Efficiency is a secondary concern (90min vs 60min is not a big deal, I’ll have extra batteries).
As for the dimmer my questions are:
I realize they may not be linear, no big deal, I’d just like the option to slightly increase or decrease the light similar to how older halogen lights
I’m unclear as to the driver required and the order in which the circuit should be (driver~~pot~~>LED?)
I hope I am clear on my questions. Thank you for at least reading this far down.
Most pots are not meant for high currents, so if you want to do that, be sure to get a suitable one.
With a supply voltage of 3.5-5V, there’s no need for a driver, you could just use a power pot plus a normal resistor (to provide a minimum resistance) in series with battery and LED.
Perhaps it has been too long since I learned all this stuff.
Does this seem correct? A driver typically tries to keep light output stable over a variety of voltages as the battery loses juice. A resister is definitely needed or you will fry a high power LED. Like you say, a resistor + pot circuit would simply allow me to adjust the brightness to my liking, but this setup would have the additional hassle of requiring me to constantly update the “knob” if I actually wanted a constant brightness over 10 or 20 minutes. For flashlights this would typically be frustrating, but for my situation it would be decent.
The only downside (upside is the cost) would be that if I labeled my knob 0-10, the actual brightness when I set the knob at 5 would depend on the actual voltage of the battery at the time?
Thank you very much for such a quick reply. This might be less expensive than I thought. I was hoping the $25 drivers would not be needed.
A resistor in series with a current source usually compromises the source compliance voltage and the correct operation of the source. In parallel it reduces the control range of the source.
check out the knob on the back of this headlamp. I had previously thought of simply getting one of these and tearing it down. I was hoping there was somewhere to buy the circuit they use. I’m guessing they don’t use expensive parts to adjust the brightness. Seems these are getting harder to find.
Could I get this and simply replace it with a warmer LED? I realize I probably won’t get the full potential out of the LED.
The sandwich shoppe has some drivers that can take external pots: the Blue Shark and the Shark Bucks with either 1A, 2A, or 3A output.
Several taskled drivers allow external pot inputs. They are not small diameter drivers though, and the ones that do dimming require more voltage than a single li-ion offers.
These drivers have micro controllers and only use the potentiometer as a control input. They have dedicated pads for the pots to be soldered to.
Ahh yes, several luxdrive drivers offer dimming as well: Buckpuck, BoostPuck, BuckBlock, BoostPlus, and FlexBlock. None of these will work on a single Li-ion though.
I suggest using two li-ions (AW IMR 18350’s are great or you can use your 14500’s) and the shoppe’s SharkBuck driver, or the BlueShark driver. The BlueShark is a boost driver and the Vin must be less than the Vout, so with two li-ions you would want to be powering a 3 led string. With the SharkBuck you can use two li-ions and a single led. I also suggest using a triple nichia 219 star with either of these arrangements, or a single 219 if you want an optic that will provide more throw.
I have always considered putting a very small potentiometer in the body of a flashlight and have the shaft attach to the head so that when you turn the head you are dimming the light. A tailswitch could be incorporated if necessary for on/off functionality.
It looks to me like this is an adjustable brightness circuit that would run on 3xAAA or AA. It is used in some of the adjustable brightness LED headlamps. I saw a local Coast HL7 in Home Depot and noticed it does not get that dim, so I’m guessing it doesn’t go down to 5ma (or up to 1000ma, actually). But others may find this useful as well. It is certainly cheaper than ripping open a $40 headlamp. Dealextreme had it for $4 something, but lightscastle had it for $2.62. The part is wy6890 and I haven’t seen much of anything else that is comparable for this price.
And yes, if you are after efficiency this is probably not a good idea. Is there a way just by looking that someone can tell it is PWM or some other way of dimming?
After more and more reading it seems my lumen requirements are quite different than most situations.
Thanks again for all the help. These will probably take a while to get in…
Hi there,
I’m trying to find out how to make a simple infinitly dimmable XP-G2 or XM-L2 T6 in a waterproof housing.
It should be a flooder with a rotary control/switch (for caving ;) What else do i need except the driver above?
BTW: Is there a link to the basics of led practice (emitters, drivers, optics etc.)? I don’t know how to choose
the right items…
Edith: I get no Quote… I mean the wy6890 board at Lightscastle!
Figure out which one is the VOLTAGE potentiometer,Desolder the pot, Put original pot in series with new pot
*Every Driver has different Resistance to voltage ratings. One of mine was a 100Kpot, 20K=25V, 30K=35V. So I bought 10K pot and put original one at 20K and I had the perfect voltage I need without going over voltage. Another one needed a 5K pot to go from 25V to 35V.
Suggestions:
-Use LINEAR pots instead of logarithmic ones.
-I don’t know if anyone will do this but, do not input power to the driver while the pots are not connected in series with the driver because I did this with headphones+music on so I did not hear the capcitor screeching. After a minute or two, it blew up into my eyebrow and i was bleeding all over the place. I am fully healed now, but just be careful.
