Here is a very, very strange thing: I Found being sold second hand on eBay It's one of the many products that popped up during the pandemic and it's a germicidal light, but it's really unusual in the way it actually uses the Gtl3 lamp. Let me push the button here and you'll see the LED starts flashing and after the predetermined delay time, it starts beaming out UVC death rays in all directions. Oh, there it goes. See the traditional startup sort of glow and then ignition of the discharge.

But interestingly, Linda I won't expose myself to this too much. A bit of ozone going on there. Interestingly, just one electrode is gluing and that tells me that this is most likely a DC Supply that's been given to the slab. Uh, so I'll take it out right now.

It's so strange to see the standard vintage germicidal type lamp used in a modern product. Let me grab a screwdriver and we'll take a look inside this. See, there's no no hanging about here. I'm straight into it.

kind of intrigued to see what it's using to generate the supply for the lamp. I Thought at first it might be a little Royer oscillator, but it is running the lamp in DC That suggests to me that because this contains a rechargeable Lithium cylinder, it's fairly a recent product because it's a got a US Oh no, it's got a USB a micro USB port I thought it was I thought it was a USBC for some reason. Anyway, it's rechargeable and uh, I get the feeling that instead of a royal oscillator, the fact it's running in DC Kind of hints that this thing is using just a standard boost circuit with maybe current limiting of some sort. Let's see what we've found when we open it.

Let's make the wrong screwdriver. It's also a completely non-compliant screwdriver. All the health and safety people are screaming because you know it's uh in this relation is Earth Well, I'm seeing I'm seeing a stubborn screw for a start. it's stuffed with otherwise.

I Got three Lithium cells in series. Oh no. I just turned it on. Really, that is not something I was expecting.

It's good. Really, this wasn't serious. A little circuit board at the back there for the USBC Uh, not. USBC the micro USB connector.

Is this really using a boost circuit to charge these? Oh, this is gonna be interesting. This is going to be very interesting. Oh, and each one of these cells has a protection circuit on it. Okay, that's very gooey and sticky.

Yes, it's really, really gooey and sticky, right? Oh, tell you what? Uh, right. Let's not break the connectors off, but let's reverse engineer this one moment. Please, Reverse engineering is complete. Let's explore with that.

Magical Mystery Surprise that they always drop in. Here are the three cells. Each cell has a protection circuit board on it. Turns out that's actually quite a good thing.

And here's a little lamp. It's a standard Gtl3 typically runs about 10 volts, roughly about 300 milliamps or so. It's right about 10 watts, and because they're using one electrode, they are actually just under running it slightly, which is nice. Anyway, on the circuit board, we have two distinct sections.

We have the battery charging ish under the control section. Here's the microcontroller. I've got a single button just for activating it, and then at the bottom, we've got the lamp driver circuitry. here.

there's a little boost converter because it turns out the Lithium cells are actually all just in parallel. So this is a standard 4056 type chip. A couple of steering diodes here Rogue link here: Uh, electrolytic capacitor in the back, the microcontroller, a little mosfet, and that switches on the Bp1808 Um, LED driver that's been used to rather interestingly drive this exotic lamp. Let me show you the back of the circuit board.

There's a capacitor and there's two ground planes. the main ground plane for the circuitry and then a separate ground plane that is Switched for the lamp itself, the lamp driver. Anything else worth mentioning: Two LEDs One is driven by the charge controlled chip. You'll see them on what I'm like laughing uh and the other one the blue one is this very low value 100 ohm resistor.

Uh, over to here for uh, Basically showing that the system is active right? Say well, let's get the schematic and you'll see why I'm going OMG right? So it starts off relatively sensible. Here's the USB input and it goes to the 4056 charge control chip that is a 1K programming resistor to charge these Lithium cells and each Lithium cell has protection and they're all in parallel. Both the USB input has a Hub and the lithium cells have a Schottky Diode feeding the positive rail. which means if you plug it into the USB power supply, you can actually power the lamp directly from the USB power supply.

Or it could be powered from the Lithium cells. And the reason for this diode here is to prevent the USB power supply from going through this diode and then actually going and putting current into the cells. There is a LED and resistor as there typically is just to show when it's finished charging it goes out. Charging is not complete.

Do you know why charge is not complete Because they put a link in here? Let's call it the fu link because uh, they've done that because they thought maybe the current through this diode it's going to be about an amp uh is going to be too much. It's going to cause too much of a voltage drop and it's going to impair the run time or it's going to limit. You know, the operation of the lamp driver. So they just put a link across it.

So now when you plug it in, just ignore the charging circuitry. The current from the USB supplies going through this diode, which is a voltage drop of say, 0.2 upwards. Then it's through this link and just as well. All the Lithium cells are protection structure because otherwise it would overcharge them.

Lovely. So they're going to cut off. the LED will go off first, but it's still charging and then it'll cut off once all the individual protection circuits have kicked in. Lovely.

Uh, so the resistance that's limiting the current through that? Well, it's partly the voltage drop across the start and part of the USB lead and the power supply. There is that electrolytic capacitor. Then we get the microcontroller, which has its own little decoupling capacitor across it. It's got a blue LED via that 100 ohm resistor.

From the positive reel, it's got the button. It's got a mysterious 100K resistor going to pin 2 pin 2 of the microcontroller. Sure what that's for? The usual Pinot applies, And here we've got the pin. One is positive and uh, pin 8 is negative.

That's really common now. I'm going to expect to go to pin four if it was like a pick or something like that, but it's not. And it's got the button that pulls one of the pins to the zero volt reel for input and then it's got a 2K7 resistor on its own to the mosfet, which then switches the lamp driver section. So far, so good.

Well, they're not very good because of the fuel link. not to worry, that is an exciting feature and the diodes there, but they just put the link there as well. it's just they they put the link option in and then build it with a link. Very strange.

They have contemporary Lithium cells. Here is the switched lamp. driver circuitry. very interesting because it's using a Bp1808.

Uh, Drive Chip Here that is a boost circuit that boosts the voltage up and then has current sensing so it can actually drive normally LEDs They should normally LEDs down here. So the supply comes in the coupling capacitor. There is a 10 mega Henry inductor and that inductor is pulsed to the zero volt reel. Well, Initially the chip gets its powered through the diode here presumably or it may get it from there, but it has a it drives its own power supply which is down here Vdd pins so it generates its own Supply from whatever it can take and it's got a little capacitor.

There's also a dim input for presumably positive modulates and output, but they've tied that high via 1K resistor, which is reasonable enough. It's not even shown in the data sheet, but they've done it. There is also a comparator capacitor here for the current voltage sensing inside. When the unit is running, it switches this end of the inductor to the zero volt reel to ground, and when it does so, this ends up positive.

This end is pulled down to negative. It's much like a garden light boost circuit, so it turns on And then it turns off and it's built up in magnetic field in here. Then as the field collapses, this end goes negative. This angle is positive and that then adds to the supply voltage and goes through the Stout and charges up this capacitor.

There is an over voltage protect circuit here which has a potential divider 100K resistor and a 6.2 key resistor 6200 ohms and its threshold voltage is 1.2 volts I Did a very rough calculation I'll let you guys do the more accurate calculation. Uh, potential divider 100K 6.2 Okay, and it's aiming to reach up to 1.2 volts. At that point, the chip will cut off because if you unscrew the lamp from this, the voltage would shoot up quite high and it's just basically open circuit protection to stop the voltage going too high. Uh, the boosted voltage charges this capacitor and it also goes through the load via a current sense resistor 0.75 ohms.

There is an input for current sense which is set to 0.2 volts, 200 millivolts to 100 millivolts or 0.2 volt. And based in that 0.75 volt resistor, it's measuring the voltage across it. Here, that's going to be about 266 milliamps going through the load, which is the Gtl3 lamp. I've drawn it like this I Don't know if this actual way to draw these.

Uh, because it's such an exotic lamp. What we have here is a heater filament in a V-shape inside here and the heater filament has thermionic emission coating at both ends. Normal, it's designed to run off AC but the running off DC Here it is mercury vapor inside and what happens initially is that the heating element in here that the filament heats up and you see it glow orange initially and then this emissive coating drops in volts across it. And because it's now emitting electrons, you get a Mercury discharge glow and that bypasses effectively the filament.

Some current will still flow through the filament, but a lot of current is flowing through the mercury vapor at the sides. and this is a UVO glass or quartz glass designed to pass wavelengths in the UVC region 254 nanometer and I Believe this one is passing 184 nanometer. so very high Purity glass and that's producing a slight width of ozone. Not an awful lot of ozone.

these are these were originally used as germicidal lamps inside laundry equipment in the old days. Um, but they're used I Looked up at some data on this and one said it's used for uh, curing needles. That's wrong, it's not. You don't use UVC for Pure Nails although it will put out other wavelengths as well.

so this is very odd. It's an unusual Arrangement here that they've used an LED Drive Chip with current regulation boost circuitry to actually drive a really old style, um, vintage ultraviolet lamp. Very peculiar and that is it. I Mean the only real what are something about this is that mysterious Fu link there that just basically bypasses that diode.

It's so strange if you look at the circuit board here. um, where are we? There Is the diode? Uh, the the battery supply. These are all in parallel would normally feed onto the common positive rail, but there's the little Ro link that they've used to link that diode out but left the diode in, which seems very bit of an oversight from the Chinese manufacturing perspective. You know they do not like spending money on excess components, but it's an exotic Uh unit.

There is information: these batteries. Is it 10? 20? I'm trying to read the last number. it's covered in sticky tape. Uh, 10 20 35 So, uh, 35 millimeter long, 10 millimeter thick, 20 millimeter wide, presumably.

And it does the protection chip and then the Dw01 and its mosfet. so that is at least going to compensate. It means that instead of charging up to 4.2 volts, it's going to charge up to 4.25 before it cuts off. But other than that, you know they're really just using this as a end of charge indicator because of what they've done there.

Yeah, but it's interesting. Quite a novel. Little late it is doing that rather bizarre thing that the the lamp when it's screwed in here with this little lid on the top. uh, the only place light can get out is, uh, just little slots all around it.

so they aren't possibly relying it for ozone blue level ozone because it's blocking the majority of the UVC light actually came out of it. Would have been better if just had a very simple wireframe over the top of it, but that is what they've done. Maybe they just designed it just to cash in the pandemic and that's the lamp they could get. But interesting stuff.

A very intriguing and smart looking little light with just very slightly Shady circuitry, but nicely designed nonetheless.