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I'll guess that the main use for this tube will be in window displays or theming. It provides a nice splash of vibrantly coloured light.
The construction is different to what I was expecting. The tube opened easily, but kinda self-destructed in the process. I'm guessing the LED strip is glued on with a custom jig.
The driver chip is very minimalist, but I wonder if linear regulators are going to be the standard from now on.
In hindsight, the live connection being repeated at one end may be due to the design possibly being for use in retrofit tubes with a feed at both ends. The LED PCB would then have an extra power track on it. Those tubes have lost favour due to posing a shock risk to maintenance operatives putting them into live fixtures.
I got this tube from this UK eBay listing:-
They do 2', 4' and 5' versions. I ordered the shortest, partly because it was less likely to get destroyed in the post.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.

It's a purple led light. Stick and this one came from ebay. It seems possible to come from a relatively reputable-ish seller, but i'm not really sure it's very hard to tell these days. Let's plug it in and test it, so i'll bring up the hoppy and as with these terminals, i show, since it comes with bare leads anyway, i shall just stuff them into the hoppy.

That's prospect clue, i'm not really sure if this, if it's appropriate, for it to come out without a plug in the end or not, i'm not sure what this intended application is to me. This is something that be used in display lighting, but if it's being sold as decorative lighting, it should relive the plug. It does come with two metal clips for mounting it onto the surface. So, let's plug this in and we'll see what power it's drawn.

The hobby says 9.8 watts and it's very bright. It is girishly blind. It looks very, very even the illumination illumination illuminated until you turn it around, and you see that big dark stripe running up this side, which has been kind of swamped out. It's not as bad on the camera as it looks in real life right here.

Let's unplug this and we'll take it apart. So i'll put the hobby out of the way - and this is where this is the second of these sticks, because i thought the end was going to be glued on with plastic solvent and decide to give it just preemptively. Before making a video earlier on, i thought i'll give it a squeeze and see if i can get it off and uh it suddenly twisted and the strip detached the full length inside. Let me show you here is the other tube, so the end twisted off it was just held on by silicon.

The reason i thought it might be. The plastic summed is because i've taken apart some the past that were held on by plastic solvent and they were very hard to get off. So once i take the other end off in the same way, by just twisting the uh, the strip of leds inside is just loose. I shall put that tube out of the way, first of all i'll just point out that there's not a way slot.

I was kind of thinking, there's going to be a little guide, groove in here that the leds slipped into, but it's actually physically glued onto the side of the tube, and it's come off so cleanly that it makes me wonder if just thermal stresses would actually break This bond not really sure once i've taken that off. It reveals the circuit board inside because there's a little driver. Let me see if i can get this is actually molded in this could be tricky. This could be very messy.

This could be very destructive right. So uh, what's the best bet here, i shall uh try and get this out this power supply. Although it is to be honest, it's just one of those standard generic supplies, but i do feel i need to get out, so i shall try and get it out. One moment please, it is out it turns out that when this has been molded in they've, uh left plane to length of water to solder that on and then the whole thing's just been stuck in with glue.

But wait till you see this. I've never seen one as simple as this. It is the most minimalist driver ever i'm just going to go and take a picture of this and show you so minimalist. Let's explore the chip is a kp 107 90wp made by kiwi.

Their website is terrible. It just leads loads of links leading to random error messages and uh. The one retailer i've found that did say claimed have a data sheet, wanted you to type in your phone number and they'd. Send you a confirmation text message? No, i don't think so.

I don't want spammed with sales calls from china. Thank you very much. So this chip is interesting. It's a buck regulator, it's a bug, regulator with built-in bridge rectifier.

So it's basically one chip, a resistor for sensing, a couple of capacitors, an inductor and that's your entire power supply the components i've drawn in on here. This is the our what's the other side, which is basically the inductor and two capacitors. That is all that's on the other side. Uh.

The best way to describe this. To be honest, is i've tried worked out what's actually inside it, so i shall zoom down on it, because this is the best way to actually show you zoom down on a drawing right. The live and neutral come in and they go to an internal direct fire and come straight out in the pins. It's almost like a bridge right far on that end, with positive going along here and negative going along here.

There is that big fat capacitor provides smoothing of that dc. There's an integrated mosfet and the leds. It's a standard buck regulator. You get leds in parallel with a one microfarad capacitor for to prevent ripple and then there's a inductor, and this little module in here turns a mosfet on guess.

It's mosfet that then pulls that pin to the zero volt rail but passes the current through the sent. Resistor 2.15 ohm very specific value, um the initially, as it builds up magnetic field that resists the current flow, so the current's flowing through the leds it's building up magnetic field. This end is effectively positive. That end is negative.

It reaches a point as the current increases that the voltage across this resistor is sensed, and it turns the mosfet off when it turns the mosfet off the field collapses. This goes negative. This goes positive and it finds a way back through this diode inside which i presume is in there. I could have measured that uh back to the positive rail, and that means it's very efficient.

It's basically utilizing utilize, the inductor when it's both building up magnetic field and collapsing the magnetic field. I want to know if that diode's in there now that this was just a guess: here's the circuit board, here's a meter, let's set it to diode and continuity. Is it going to be a schottky diode if there is a diode or is it going to be a standard diode shortcut will be around about 0.2.3 volts standard it'll be 0.6 0.6. It's a standard silicon diode in there, so they really have just integrated all the semiconductor aspects of a switching of a buck regulator into just that little tiny chip there - that's quite impressive um other things worth of note here: yeah this, the i'll zoom back out again For this, so you can actually see.

Oh, incidentally, i show three leds here: the strip contains 40 leds wired as 20 parallel pairs of just two in parallel, but then 20 sets those two in series, so the combined voltage is about 60 volts across this chip. This strip and uh the leds, are being run about quarter watt each. I suppose that's reasonable enough. It's not that bad um yeah so that that's the leds.

What was i going to look at there? I remember. I thought it a bit odd, these four pins here. One of which is connected to live uh, i get the feeling this design has been repurposed and that this is probably designed to work with a fluorescent, fitting type tube, where the led replacements, where they have live and neutral coming from one end and going back along Uh, the positive and negative - i could be wrong here. Maybe a bit of filtering other end is filtering circuit board, other end passes live neutral along and then it comes back as the dc to the leds, in which case this circuit board would have been slightly bigger.

This pad would have been separate and it would have been neutral and it would have gone back along here and over to there. That's just a guess, though, but that is it, there's not really much else to say it's an interesting light. It's quite vibrant! Oh, the leds are worthy of note uh. They are very strange looking because to get that purple, they're, basically a blue chip and if you actually look at the led hold on i'll just emulate that here.

If you look at the led inside, you see the usual little s of like the clear coating with the metal pads inside the little chip mounted on it and then the pad there with a little wire bond onto the top of it. But the actual phosphor. To make it purple, it's just speckled very coarsely, with dots of red phosphor when you look at it, it just looks like basically particles of phosphor, just splattered throughout the gel. It just looks like slightly off clear gel, but the end result is that vibrant purple color it's quite neat, but that is it it's one of the simplest buck regulators.

I've seen. I guess it is probably optimized for modern, uh replacement, fluorescent tubes, but in this case well it is being used effectively. Is that it's being used as an illuminated led baton, but pretty neat interesting construction?.

12 thoughts on “Purple led tube with neat driver”
  1. Avataaar/Circle Created with python_avatars Leroy says:

    Looks like a light saber that driver circuit is nice

  2. Avataaar/Circle Created with python_avatars Glitter Fart says:

    the more i watch your videos the less i like them

  3. Avataaar/Circle Created with python_avatars D Hristov says:


  4. Avataaar/Circle Created with python_avatars Todd Sharp says:

    FYI – there are services online that give you a temporary throwaway phone number that can receive SMS online. They come in handy!

  5. Avataaar/Circle Created with python_avatars devttyUSB0 says:

    Very nice, that driver circuit!

  6. Avataaar/Circle Created with python_avatars Silverfoxwolfen says:

    'This could be very destructive'… that's why we are here and of course 'one moment please' 😀

  7. Avataaar/Circle Created with python_avatars DC Allan says:

    The tube is something I could use but not the LED strip. I have looked for just the tube but not found any yet. Very simple electronics. 2x👍

  8. Avataaar/Circle Created with python_avatars Dave Seddon says:

    Why has it got that squiggly wiggly track to pin 1?

  9. Avataaar/Circle Created with python_avatars Rocco Rizzo says:

    How hot does it get?

  10. Avataaar/Circle Created with python_avatars Howling Wolven says:

    purple’s nice!

  11. Avataaar/Circle Created with python_avatars AMDRADEONRUBY says:

    The purple tube looks nice

  12. Avataaar/Circle Created with python_avatars deathlydarkness says:

    This video is far less moist.

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