A while ago, i made a video about an inductive device for powering leds wirelessly. Basically speaking of the coil, when you put an led near it lit up, oh i'll show you the led lighting up. There's the led lit up on that tiny little coil there. This appears to be the original intended application for these.

This is just a novel use that they found for it. Let me just put this out the way and we'll take a look at this. So this little tiny coil down here, i'm going to zoom down a bit because it really is very, very tiny but i'll show you a scaled-up picture of it. In a moment.

It's a energy transfer coil for charging batteries. So, as i bring this little circuit board, the matching circuit board up to you'll see that the leds on this butchered usb stick light as soon as i come within the vicinity of it and the data with this the label. Here it translates to uh power supply. Five to six volt output, five volts, the output is not five volts.

The output is four volts in the button suggesting this is designed for recharging lithium cells. It also says if it is larger than 2 millimeters, it will be damaged if you use it close up. Does this mean you're not supposed to go close right up hard like this, but you're actually supposed to be at least a fair distance away? I guess that's what it is, but it does it's not a huge range uh measuring the output of this uh. It starts putting output and at increasing current as you bring it closer at round about six millimeters, that's roughly quarter of an inch before it starts doing it, so it is designed for very parallel placement through thin plastic cases, since i did know that uh someone's going To ask: will it power the coil? It will power my little uh butchered, led that isn't a tuned circuit, but will not power any of the other wireless leds because they are a tuned circuit and that's what this relies on.

So since these are tiny, let's cut straight to the chase and grab the pitch of the circuit boards, i shall put this out the way and turn the power supply off. So i shall shove those over there and i shall bring in exhibit number one exhibit number one is almost exactly the same circuit i'm gon na have to zoom out now it's almost exactly the same circuit as the uh. The large coil was designed for exciting leds, but instead of using an external coil, it's got the coil integrated onto the circuit board and the diameter of these modules is approximately 20 millimeters diameter. That's about three-quarters of an inch.

So what we have on here, we've got the xkt 001, which is basically speaking, it's an oscillator that you program with two resistors and then it drives a mosfet. In this case, it's a matched mosfet xkt r1 and that then drives this coil with a capacitor across it that forms a tuned circuit. So the incoming supply is this: decoupling capacitor these two resistors program, a frequency in that driving the more spec, but then that then pulses the coil at a fixed frequency. The coil to get the maximum number of turns it starts off down here.

Spirals outwards to the edge goes through the plated hole, spirals backwards to the middle in the same direction and then ducks back through onto the other side of that capacitor exhibit number two, the receiver and this uh. I did not find a data sheet. I have had to kind of reverse engineer it based on what it is as such, but we have the tuned coil again again, it's the coil winding its way out to the outside ducking through here and winding. Its way back to the inside, coming back through here goes through tuned, the capacitor across it to create tuned circuit.

There is a shortcut diode that then leads to another capacitor which provides a sort of unregulated supply, and that's then used via this resistor to provide a power supply to this chip, but it also provides the solid supply to the chip, the chip, i'm guessing. It's a linear regulator, then regulates it down based on these resistors here, which form a sort of divider that's used for sensing and the output then has a 3k resistance. Here's the led just to show it's working and then out through a shock you die to whatever you're charging. That is it it's a very straightforward, looking circuit, all the magic is done in these chips.

Let me bring in the schematic for your delight, so i'll zoom down this here is the transmitter. The five volts comes in, they say five to six volts. Has a decoupling capacitor to provide a local reservoir for stability of the circuit. Here is the xkt001 oscillator chip or clock generating chip, and it has a 200k resistor and a 10k resistor.

The choice of resistor sets the frequency output to this mosfet and i'm pretty sure, it's a 50 50 square wave. This mosfet is dedicated to the task. Xkt r1 - i don't know if that's just it's optimized for fast, switching or designed to be comfortable with being in sears with coils, but the coil has a capacitor across it, and this is the transmitter. Call that's spiraled around outside that circuit board and in its passive state.

This circuit draws 24 milliamps um, which equates to about just over 10th of a watt. So it's not that bad. When i had the circuit right up close to it, it went up to about 100 milliamps, but that may have been affected by the resistor and series of these leds, or it might just be its maximum of its ability of energy. To couple the receiver is a bit more complicated.

This is what i think it does, because i've deduced it based on the components connected to the pins and what i believe the function is here is the receiver coil, with its tuning capacitor across it forming the resonant tune circuit, the lc network. It goes through the shortcut diode and it charges up this capacitor and uh offload that charged up to about 9 volts. When i had this across it, it went down to about 6.3 volt 35 volts. It goes through this device and the chip.

I should have actually written with. That is. What is that hold on? Where is i've just dropped? I i know i've, not. Let's write it now x, k t dash r, two very cryptic, so it goes through the r2 chip, and i reckon this is a linear.

Current regulated output, i don't think there's any fancy. Switching going on and the output then goes via this shortcut diode to the batteries or whatever you're look powering with this. There is the led from that side with the 3k resistor i'm guessing the diode. Is there purely to stop it? The batteries back discharge into this lighting that led powering these this little resistive divider, which is very high value and possibly losses in the chip itself, but um.

So that means the voltage here will have to be just about 0.2 volts higher than this uh than the desired voltage to allow for the drop across the shortcut diode on the output. There's always this also, this resistive divider 680k and a one mega ohm resistor, which is quite high, and that goes to the sense input and i'm guessing that by varying the value of these resistors, you can then set the output voltage from that. If it is a linear regulator, i guess maybe it's got internal thermal protection if it was ever to get that much of you know if you were to short circuit the output or something like that, assuming it can transfer that much energy across at 5, volts and 100 milliamps, that's literally, i mean that's tiny, um, that's a minute amount of power, so it's not really going to be dramatic. 500 milliwatts half a watt, although that could be quite hot for that chip.

But this is just speculation again. If i ever find the data sheet, i'm pretty expect much expected to be this so sense: coil, rectifier, capacitor, voltage regulator with feedback, resistors and an led and then the output. That is it. So it's quite an interesting set of little circuit boards.

I got them from aliexpress um. I can't really immediately think of many applications. Charging of batteries note that the wires that they come with the transmitter comes with fairly thick wires because it's drawing quite high current pulses. The receiver comes with very, very thin wires, but then they're not real.

It's not dealing with a lot of current, it's just designed to build into your own device, but this could be useful. It could be useful for um just wireless charging, where you want something to be kept waterproof or you just want to be able to put it down and have it charged, or maybe just an ornament that you just want to be placed. The ornament on the table and it sort of powers the ornament, but it does have to be an intimate contact so quite interesting. Little circuit boards,.