Custom 5 mode LED flashlight 18650 lithium ion

Hi all,


I want to build my own caving light, as the options available are either rubbish or ridiculously expensive. I reckon it won't be too hard to do a better job myself (we'll see). Most of my searching came to threads on this forum, so I'd thought I register to get some advice and help others.


I want 5 modes, approx. outputs: ultra low (moonlight) 6lm, low 60lm, med 150lm, high 400lm and ultra high 1000lm.


Power will be a single 3.7V 18650 lithium ion battery. This provides a good voltage and capacity and is easily available.


So far I've chosen my components and drawn a simple circuit.


Cree XLamp XP-L 10W
3.45 x 3.45 mm | 0.1 - 3A | 47 - 1000lm| ~ 2.65-3.36V


L7135 AMC7135 350mA/2.7-6V Constant Current regulator


Microchip Technology, MIC1557YM5-TR
ww1.microchip.com/downloads/en/DeviceDoc/mic1555.pdf
Low voltage version of the 555 timer chip for PWM control. This is just the first one I saw, I am open to surgestions.


Diodes, transistors, resistors etc as required.


As the battery voltage isn't much higher than the LED voltage a linear regulator seems the best choice, and the L7135 chips are so cheap. I intend to stack 3 or 8 of them for the high and ultra high modes respectively. Others seem to have good results with this, and this method is used in commercial drivers. I know this will result in a slight colour change at the different brightness levels, but looking at the Cree datasheet it's not enough to worry about. Also the LED is more efficient at lower amps; so I may a well take advantage of this.


So for the 7135, I just connect the ground pin to battery negative, VDD to battery positive and connect the LED between battery positive and OUT? Simple enough. For the higher currents I just connect the chips in parallel.


I intend to use PWM to deliver currents less than the 0.35A the 7135 delivers, using a simple 555 timer circuit for the pulse.


The low voltage 555 uses a max current of 300uA. So I intend to use a 9k resistor to prevent damage. 2.7V / 300uA = 9k. I assume the extra current at higher voltages will not be a problem? I'm not sure I read the data sheet correctly (linked above), so if someone could check?


The PWM output will drive the VDD pin of the 7135 via a transistor.


Circuit diagram below. I used the schematic for a regular 555 to aid understanding for those familiar with it. The low power chip looks like it might be slightly different (or the 555 schematic I got off the internet is wrong).


Thanks is advance for any help.

The image link from Google drive didn't work. (Sorry admins I should of read all the Questions/Problems/Suggestions stickys, also resized to less than 800*800.)

Am looking forward to what see what you end up designing and building. Scratch built drivers are problematic, even someone with the electronics knowledge, but as with any challenge, it's all about the satisfaction and pride of seeing what ones hands and mind can produce. Perhaps Semiman or DIWdriver can chime in? Maybe Mattaus?

If you change your mind about building your own driver than take a look at the Mountain DD17m driver series. They make one with pretty much the same settings you outlined and it has a single 7135 for that ultra low moonlight. And they are pretty cheap. Right around $9 IIRC. Keep us posted and welcome to CPF!

I wouldn't say I have that much electronics knowledge really. Educated to UK GCSE level (think the American equivalent would be a high school diploma). Hence why I'm asking if I am on the right track. I made an egg timer using 7 segment displays and a various chips including 555 timers for the coursework. Yes, it's partially the satisfaction and pride if I manage to get it all working. I like to make stuff myself if I can. I have a multi-meter to help with fault finding.

I couldn't find the DD17m driver, however if by Mountain you mean Mountain Electronics then I found other drivers available that are almost what I want. I live in the UK so postage may be expensive (I should probably put my location in my profile).

The problem with any commercial driver I have seen is that the lower modes are just PWM at full current. I would like to take advantage of the better LED efficiencys at lower currents to get the most out of the batteries. Also I want a proper physical switch rather than repeated button presses to change modes. I intend to use a 5+ way turn switch.