NOTE: Some updates are at the end of the article.

Recently I purchased a couple of Solar powered LED garden path lights at the local Dollar Tree store for $1 each. Ever since I read TalkingElectronics.com‘s writeup on converting such garden lights into 5-volt solar power supplies, I have wanted to tinker with one. The one dollar light intrigued me because it was so amazing that one could be sold for that price. The one-dollar LED garden path light reduced the parts count and that is probably a big part of their ability to sell it so cheaply. I reverse engineered the circuit. It matches, quite closely, the example circuit for the Shiningic YX8018 specification sheet. My reverse engineered schematic is shown below: The Shiningic YX8018 specification sheet does not show the internal schematic of the YX8018 integrated circuit. However, the YX8018 contains an approximately 200 KHz gated oscillator that  drives an open drain NMOS switch to ultimately boost the battery’s 1.2 volts to, typically, three volts in order to power a three volt white LED – a sort of a joule thief. A joule thief is a minimalist Armstrong oscillator voltage booster. It would function similarly to the circuits shown by TalkingElectronics.com‘s writeup on the older type of garden lights that use discrete components. The YX8018 only runs the oscillator when it detects that the solar panel is in the dark. When the solar panel is producing power the YX8018 turns off  the oscillator and the battery is charged.

Analog Devices did a nice article on the YX8018 device. They drew The YX8018 internals based upon their analysis, which is shown below. Below the Analog Devices’s YX8018 illustration is one from Pete’s QBASIC website for the QX5252, another similar, if not identical IC. There are others, as well, that appear to be functionally equivalent if not, in some cases,  identical chips. For example, YX8019, JD1803, ANA608, ANA618, YX802, YX803, YX805, YX806, JD228, JD318 and F1-4S597.

yx8018-internals

All manufacturer datasheets refer to the 4-pin package as a TO-94 package, yet the only TO-94 JEDEC package that I can find is for the threaded bolt thyristor. To me, it is a 4-pin SIP package. I have no clue as to why the Chinese refer to this as a TO-94 package.

I  did a Rube Goldberg conversion of one of these lamps into a solar 5-volt power supply, similar to what was described by TalkingElectronics.com‘s writeup. I have had an ultimate plan to use one of these to power an Arduino (really an ATmel ATtiny84 or 85) in a remote installation but I suspect that current limitations may preclude this. I may try a 3.3-Volt converter suspecting that it will yield a little more current but I still doubt that the current will be enough to do anything meaningful. Posted research by Radio-GHE’s website hints that I’ll never get anything more than a few milliamps. My circuit modifications are shown in the schematic below:

Modified Lamp Circuit

Conversion to 5V Power Supply

As you can see from the photo above, my circuit yields 5.1 Volts. I did a load test, of sorts. Using two meters, I measured the voltage while simultaneously measuring the current through a 10k-ohm potentiometer that served as a load. Adjusting the potentiometer I found that the circuit provided .424 ma at 4-volts (yes, 4/10s of a milliamp!). This was rather disappointing – only 0.001696 Watts! The load resistance was 9.4kΩ I am abandoning any thought of using these lights for anything other than their intended purpose – illuminating a single LED. However, these lights are interesting little packages of rather clever engineering. [NOTE: I have learned that dropping the inductor down to around 33uH will provide usable current – in the order of 22-26mA.]

UPDATES:

  • Check out THIS-POST for some interesting information on this chip.
  • Reader “Peter” posted a good comment and referenced a blog named “Tom’s Projects” wherein he describes his successfully modified a similar garden light to power a thermometer with Morse code output on an LED as well as providing the 3.3V supply for its ATtiny25 controller. I assume that Peter and Tom are actually the same person. In any case, he has successfully achieved my objective, at least at the 3.3V level. His series of three posts are excellent and I encourage you to read them. They are Part1, Part2 and Part3.
  • An anonymous commenter to “Tom’s Projects”  references a good Russian article about how to make a YX8018  stabilized power supply. The Google translation version is at THIS-LINK or the original Russian version is HERE.
  • An excellent article on the YX8018 operation is at wiki.analog.com.