I recently had the job of fixing my sons yard light.
Hadn't really investigated the circuits before, it uses an interesting 1.4v IC XD5252, eliminates the need for a photo-cell for daylight detection.
The integrated circuit does several things. It charges the 1.2 volt battery during the day, using power from the 1.7 volt solar cell. It detects when the solar cell is in the dark, and starts up the circuit inside that boosts the 1.2 volts from the battery to over 3 volts, and sends that to the LED.
The current to the LED is decided on the value of the μh inductor.
A couple of modifications can be made for more or brighter LEDS.

 

In the parts-reduction Olympics, that is a serious contender for the gold.

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Most of my solar garden lights that use the QX5252F IC use an 82uH inductor for one bright LED light.
At the IC output of some garden lights I added a series 1N5817 Schottky diode feeding a 0.1uF filter capacitor to drive a colors-changing LED.

 

It's been 10 years since these chips just ruined my hobby of tearing down solar lights to reverse the drive. It used to take two transistors some resistors and some caps to drive the step up inductor. Now just one boring chip.

Two years back I found a guy on EBay who was buying cheap solar lights, cutting them into components, and selling the pieces. Hey, for 5 bucks I could get 10 driver boards with LEDs, but I just couldn't buy the shopping cart. I noticed his NY address was comming up as somewhere in Europe. I messaged him, he thanked me as he had no orders in 2 weeks during his busy season, and flipped me a double bunch of these.

 

Cheap solar garden lights used to use a solar panel and LDR with plastic covers that soon got sunburned.
They used a poor quality N-CAD battery cell that leaked and rusted away soon.

2 years ago a better quality solar garden light was sold for $1.00 at Walmart. It used a QX5252F IC, a solar panel with a glass cover, no LDR and a Ni-MH battery that did not rust but it had a low capacity. The cheap LED had steel leads that rusted away in a few months. It was easy to replace the battery and LED with better ones.

 

I wonder if the same 5252 IC is used in torches? I have an el cheapo multi-LED torch which runs from a single AA alkaline cell, but I haven't taken it apart to check the circuit.

 

I have datasheets for the 5252 and 2 other voltage stepup ICs. Some of my solar garden lights use other ICs that do not have datasheets.
Some even have an unmarked Black Blob On Board.

 

This is one I just picked up from the dollar store has a Yx8018.

 

Here is a list of many YX IC specs:

 

I have been asked to repair some of these by various friends and relatives. The common failure modes have been rust, battery failure, corrosion, and solar cell failure. Rust can be sanded away, battery or solar cell failure ends the work because a replacement battery costs more than a replacement solar light.

 

The Walmart solar garden lights were sold for $1.00 each. The AAA Ni-MH battery had a rust-proof material (stainless steel?) but a labelled capacity of only 300mAh that was actually about 100mAh or less. I replaced it with an Energizer 800mAh AAA Ni-MH cell.
The garden light was so cheap that the garbage battery in it was free. Nobody in China puts a good quality battery cell in a solar garden light.

 

The Menards lites sold for $3.95, and they rusted almost before the plastic parts broke. Qualities vary quite a bit.

 

Approximately ALL solar garden lights are cheap crap. I have three in one garden that I particularly like as they have a colored pattern housing, just look pretty without pretending they can cast and appreciable light.

These have worked for me for at least 5 or 6 years so far as I rebuild the guts as needed. Once I even grafted on a fresh solar panel.

 

I have been asked to repair some of these by various friends and relatives. The common failure modes have been rust, battery failure, corrosion, and solar cell failure. Rust can be sanded away, battery or solar cell failure ends the work because a replacement battery costs more than a replacement solar light.

In many cases the originals can be quite expensive, e.g. Ceramic or metalic ornamental objects, so cannibalizing a cheapo from the Dollar $tore makes sense, the components are generally identical.
Which is what I did in this case!

 

One way to deter future ingress of moisture etc, is to spray the interior with WD-40, also seal covers etc with white lithium grease.