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QX5252 Solar Light IC

Most electronics amateurs like myself are drawn to the "something for nothing" dark side of circuits via the "Joule Thief", a forgiving and interesting beast that looks a little like this in it's basic form.

By Rowland - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=31765405

I made up some little torches using this circuit with some hand wound ferrite cores (hours of fun watching TV and winding) and my favourite SS8050 as the NPN transistor (seen below in SOT-23 format on a little adapter board).

Bright little light using a "spent" AAA battery

I use this circuit also to grow succulents by harvesting the last of the "flat" batteries that come my way in little grow chambers like this one.

Tiny container with grow lights

A year or so ago I came across a link to a circuit based on the QX5252 chip. This little marvel is used extensively in your typical solar garden light, using a "joule thief" style circuit.

They cost only a couple of cents each, but can easily be used to replace the transistor and some circuitry in the joule thief. You simply add an inductor (I'm exploring through hole radial inductors - no more late night winding) and presto you have a pretty robust circuit.

The next step was to make it stable enough if possible to run a microcontroller (μC) such as my favourite Attiny13. The output from the QX5252 might be good enough for an LED, but in fact the circuit oscillates and fools the human eye into believing that it is a steady light. The resultant signal oscillates too much for the μC.

Brighter minds have since come up with a way of stabilising the signal using the following components.

So now I can have a single AA or AAA NiMH or NiCad rechargeable battery happily running the μC at a much higher voltage using solar panel recharging - with the added bonus of protection built into the QX5252 for low voltage. I am still experimenting with the circuit by changing in and out the following:

1. Other solar light ICs such as the YX805 or YX8018.
2. Size and specs for the inductor (seems around 68μH is about right, a good trade when looking at efficiency vs current)
3. Size and specs for the zener diode (at the moment hovering around 3-5V but still experimenting)
4. Size and specs for the diode shown above as the 1N4007 (at the moment using 1N4148 both in through hole and SMD package format)

I've gone to EasyEDA and JLCPCB for little boards based on this circuit so watch this space for more development for these circuits. I like the idea of wringing a battery dry for both electronic reasons and also for environment reasons. It's my aim to have solar devices all over the house, powered at any voltage DC by the sun.