1N5817 Schottky Diode, 5V1 Zener Diode and a 470uH radial inductor
A few blogs ago I wrote about using a QX5252 solar light IC to run lights on minimal current from a single rechargeable AA NiMH battery. I had many such devices strewn all over the house and was haphazardly monitoring their efficiency over the last few months. Some lights were finished after about an hour, whilst others soldiered on with varied success through the night, depending it seems on the components chosen for the circuit (and the generation of the code running the whole show).
In the original design and in consultation with many sources, including the datasheet of the QX5252, I had chosen a 5V1 zener, a 1N4007 diode and a low value (e.g. 47uH) inductor as per the following circuit diagram.
It was clear from long term observations that a couple of outstanding devices were able to take up minimal solar energy during the day and shine all night and beyond with little signs of flagging. I grabbed these superior devices and looked closely at the values that I had chosen for some of the more critical components.
The zener was 5V1 as tested, but in the long lasting lights it seems that I had chosen a low forward voltage drop Schottky diode 1N5817 in place of the 1N4148, which in turn had replaced the 1N4007 from the original circuit. Amazingly the inductor was a hefty 470uH. That is significantly above the highest recommended inductance in the datasheet which tops out at 330uH to give a limited current of only 11mA.
Having seen how efficient the circuit was at lighting a 1W LED to prevent the night stumbles, I started wondering if it was good enough to supply an ATTiny13a full of "candley goodness" as per a recent blog post.
Under normal circumstances I would have said not - but in this case the ATTiny13a could be running at a miserly 128kHz (so only ~400μA required by the actual microcontroller). Also recently I re-wrote the candley code using hyper efficient AVR assembler with hopefully not too many wasted cycles.
As well, the super-duper LEDs I use seem to require far less than their stated 60mA - which makes sense as they are cycling up and down with PWM taking out much of the required power - and fair enough too as they are "candle" night lights, not search lights!
I took the poor performing lights and stripped off their inductors, zeners and diodes and replaced them with a 5V1 zener, 1n5817 Schottky and 470uH radial inductor to match the observed super lights. Then I burnt the bootloader to 128kHz and replaced the C-code with assembler all with a handy in-situ programmer.
What a revelation - all "candles" are now burning all night on minimum daylight - recharging the single AA NiMH battery with just a few murky ergs fighting their way through the thick clouds down here in Tasmania. Lovely!
No comments:
Post a Comment