** Updated code for better performance and stability [26 Feb 2015, rev.3]
It has been quite some time since my last post – as often happens, life intervenes and this time just a bit too much hospital time both for myself and one of my kids. Things are good now and normal can resume…
For years I have had this Black&Decker FireStorm FSL18 flashlight, but hardly ever used it due to its anemic light quality. The fixture is powered with an 18v battery pack and uses a KPR18v0.3A bulb putting out 7 candlepower when running at 18 volts. 1 candlepower = 1 lumen. Compared with the brightness of the 12v power LEDs I have been working with lately, the brightness from this incandescent bulb is not much better than a glassed candle.
The trigger for upgrading this flashlight came one day when the wife complained an LED lightbulb had failed in her workshop. I replaced the bulb, but rather than throw it away, I took it down to my workshop to disassemble and identify what had broken. Continue reading
** Schematic diagram corrected and updated **
Update: New post highlighting a ATtiny85 based PWM LED Driver!
In my previous post, I slapped together a quick LED lighting solution for my workbench… but it is truly a hack. What I really want to do is make a simple constant current driver, so the power LEDs can be used in other projects. One of those projects is an LED swimming pool light. It needs to be running at maximum brightness and low cost.
Updated Schematic, correcting op-amp connections
After much digging and testing, I found a simple circuit using a power FET, an OP Amp and 0.5 ohm resistor.
For a while I have been looking to instal LED lighting in my workshop, but every time I go to the DIY center, I look at the price tags and keep on walking. About a month ago, the Electronics Goldmine had a sale on 12V/10W/900 Lumen LEDs. $3 each! 900 lumens is equivalent to a 60 watt incandescent bulb. The datasheet I am using is here.
Once I received the LEDs, a quick test with my powersupply demonstrated them working VERY well, but running them from my bench supply would not do in the long term. A solution had to be found in my parts bin…