A red filament style vehicular LED lamp and it's matching little cute box. This I thought was just going to be something very ordinary I Thought this was going to be straightforward resistors or something like that, but it turns out there's a little chip in here and I can zoom down to a degree but there is a limit because this is Tiny actual Azure hold it up to the camera and I shall try and focus on that and take the exposure off a bit. That's going to bring that up and inside you can see a little chip here. Called on Ems117 and I thought that's reasonable enough.

It's going to be a little current regulator. No, it's a voltage regulator. There's a bridge rectifier for polarity correction and a little 22 Ohm resistor. I'm thinking it's time to get this circuit board out and take a look at the circuitry because I think this is a voltage regulator being used as a current regulator? Let's take a closer look at it.

Well, let's find out if we can get this out. First of all, is it a solvent based glue? Is it hot melt glue? but squirt some isopropanol on it? That's out. That's what we want, right. Time to explore further one moment, please and resume.

Oh this. Uh. this caught me out in two ways: I Noticed that one of the filaments here was a bit. Let me just zoom down this.

It was a bit dimmer in the middle. It was almost like there was one LED missing. It wasn't. It turns out that one of these filaments has 10 LEDs in It and the other one has two sections of eight LEDs And so the voltage drop across one of these is about 5 volts and the other one is about three volts.

It makes up a total about eight volts across these filaments. Um, that also means that theoretically one side is twice as bright as the other I Didn't really notice that. notice the thin shim of phosphor in the back. That's purely because some of the blue light from the chips that stimulated phosphor will be coming through.

and it's just to avoid that blue tint. They just re-smear the fuss from the back just to convert that into a slightly orangey red glow too. The current regulation. Well, let's start at the very beginning.

The supply comes in and it goes to this redirect fire. And then you could either Supply AC or DC. If it's AC all the Downs of activists DC then it will just steer it to the appropriate terminal. and uh, only two dials will be used.

Then there's one and this caught me out. Uh, this is a 22 Ohm resistor 2, 2 and a decimal multiplier of zero. So just 22 Ohms that is in series the whole lot. It's just to take some of the dissipation away from this regulator.

Also, maybe to limit the inrush current while it's stabilizing. and but I thought that was a sense resistor. It turns out this stinky little resistor down here is a cent resistor because this is an EMS 1117 which is available in 1.2 volt, 1.8 volt, a 3.3 volt, and 5 volt plus probably some others. But you can also get the adjustable version which is a voltage threshold on it first on its sense pin of 1.25 volt.

So what it's doing here is it's actually measuring that across this 150 ohm resistor. Now notice, this resistor is marked one eight X That's just a industry standard designation and they could have written one five zero and it would have been 15 Ohm. Unfortunately, 1 8X is a secret code. you have to look it up for that standard.

It's disused. for some of these resistors. it would have been easier just to print it on. That's strange how they do that.

Um, and that is more or less of a circuitry covered, right? Tell you what. I'll bring in the schematic and explain it all. Here is the schematic. So here's the incoming: Supply It can be quite a wide voltage range.

because it is current regulated. it goes through a redirect fire which will drop roughly 1.5 volts. The current in this circuitry was what was the current. The circuitry: 82 milliamps 82 milliamps which is the same all the way around the whole circuit.

The first level of current limiting is this: 22 Ohm resistor in the negative reel the current Gaussian, the positive through the LEDs it goes through that double section. LED Package one of the filaments with two times eight LEDs in it in parallel and then it goes through the filament with just 10 on one side so that gives a voltage of about eight volts across that. It then goes to the regulator and that's where it actually measures the voltage across this resistor. This regulator is quite versatile.

It's primarily designed as a voltage regulator where you'd normally you'd have a divider going to the zero volt Rail and going to the input. this and it would basically whatever voltage you set it for. When say you wanted 12 volts out of this, you'd set the voltage divider. so it put roughly 1.25 volts here at the point it reached the correct output voltage.

But in the case of a current regulator which we're using here, it simply has a resistor and the current flowing through resistor causes a potential difference of 1.25 volts across that resistor. and when it senses that across the resistor, then it starts going up in resistance. It regulates the current, it limits it, and in this case, well, I measured 1.24 volts across that. To get that, let me bring in the Kink calculator.

I equals V The voltage dropped 1.24 in this instance, divided by the 15 Ohms gives you your 82 milliamps. Uh, yes, that is right. Likewise I Get caught out I Saw this resistor I thought they'd used a 1.8 volt regulator because by a sheer coincidence, um, the vehicles I are so the current was .082 times that resistance which was 22 ohms equals 1.8 volts. So I thought they had used a 1.8 volt regulator initially and just used as a current regulator.

but Noah is there at the one with the 1.25 volt threshold and that's it. Looks simple was quite tricky to reverse engineer just because the tiny little circuit board and also probing things on both sides. It's always hard holding the probe in place when you're doing that, but that is it. So summary: the current flows, gets rectified, goes through the LEDs goes through this linear regulator which does It will then automatically adjust no matter what the voltage is within a reason.

it will limit the current to that 82 milliamps. and then there's just this resistor here, which is probably just really to take a bit the heat dissipation away from the regulator and that is it. Very clever, very neat. A lot more in the lamp than I was expecting.

It's quite smart. I shall bring in the picture because it's quite a nice picture. It's very colorful just because. Well, I had to use lots of colors to decipher that.

The interesting little thing, it's ceramic filament to smell the LEDs on them and a nice case. And the fact that that uh, it's got the bridge rectifier on it is good because many of these lamps that go into that of their friction fit socket that you can put the lamp in the other way around. Uh, they are polarized so you have to try the lamp in one way and if it doesn't work you take out and put another way. this one because they've gone for a lower voltage.

It's slightly less efficient, but it just means you can put the lamp in either way and it will work first time, so that's quite good. It's quite a neat little lamp.