Part of the whole clean-up business also means that I get rid of some of my old junk. Many years ago (2006 actually), on a holiday to Hong Kong, I purchased a set of four Sunshine branded T5 S13582W 13W Ballasts. They were cheap, from a corner variety store, and they seemed to work just fine.
Over time, the plastic covers on these start to crack due to degradation after being exposed to fluorescent light, and the T5 tubes need replacing. The cost of the T5 tubes can be high if you’re only buying a few, and I wasn’t too pleased with the performance of the ballast as it occasionally flickers a bit. They were all instant start, very light, slightly buzzy and now, I’ve started to see similar “plastic body” typed fixtures in lifts and under-table lighting applications.
My curiosity lay in the ballast design – how was it made at the price? It’s definitely electronic (rather than the old iron inductive), but it’s probably not too efficient.
I was going to just throw them out, but then I thought, wouldn’t it be nice to try and take it apart to learn something about it?
Inside the Plastic Tube
I had to cut it up to get access to the insides. Unfortunately, everything was glued together, and bending it provoked the plastic into shattering into shrapnel, so careful cutting managed to liberate the PCB inside.
The PCB itself is very slim – its profile fits within the plastic tube base. It is marked WL17044A. It contains very few variety of components, likely as a compromise to keep supply chain costs low (e.g. all diodes are the same type, all transistors are the same type, there’s a limited number of capacitor values).
The underside reveals how the components are connected, it’s also a single layer PCB on a paper type substrate as you expect of high voltage (and cheap) products. Some of the components caught my eye, so I got some close-up shots of it (also as a chance to test my lens!)
This is a welcome sign, although, at first, I didn’t know what it is. It’s actually a fuse – as a glass capsule. It’s not the standard M205 size or AG3 size soldered down, it’s just a tiny glass capsule, almost the size of an old neon indicator bulb. At least I know if the ballast catastrophically fails, the thing shouldn’t catch fire.
Here, we see the main capacitor – it’s nicely rated at 105 degrees C, but it’s from an unknown brand of Ymin. In the background on the left is a bit of a mystery wrapped inductor marked with 2 and 1.5, and to the right we see a transistor, some greencaps (not green) and a (looks to be) hand-wound toroidal transformer core. None of the transistors have heatsinks either, so I suppose maybe it’s not as inefficient as I had assumed.
Here’s the close-up detail of the colourful windings on the core, made fairly loosely. I suppose that’s a sign of the price.
There is a component marked DB3, which I don’t really know what it is. The body looks like a diode, there are two pins, but it’s got no band at all. It’s probably a diode of some sort, owing to the D-designation.
Tracing the Schematic
Sometimes, I feel like I need to do some mental work – so I undertook the challenge to follow the traces and hand-draw a schematic. To help me, I first made an image where the top side was flipped and overlaid on the bottom so you could see the pads, their interconnections and the components themselves (when not obscured by others).
I then marked off each pad I had “connected” on my hand drawn schematic as I went. Once I had the schematic, it was very absurdly messy, so I redrew one from that which was a bit more logical in its layout.
And there we are! Unfortunately, there may be a few errors that may have crept in from me not being too careful, so don’t use it to build your own! The other thing is that some of the component values aren’t identifiable either.
I don’t really have any idea how to explain its functionality, although I do recognize that it’s a full-bridge rectifier on the input to DC (with L0 being a filter, likely). Then the DC is used to feed the rest of the circuit, which (I suppose) thanks to the way the inductor cores are wound, can self-oscillate. L1 I would presume is to supply the initial start-up peak voltage to ionize the gas, with D8, D9 and C5 helping keep the filament warm while running. That’s all I care to guess about really.
Maybe one day I will completely understand the circuitry, but it did provide some much-needed mental stimulation, on an otherwise “bed-ridden” day.