Wireless LEDs: Very small inductively powered LEDs

Thread Starter

Ya’akov

Joined Jan 27, 2019
9,237
So here's a curiosity, LEDs that are powered with a the same technology as wireless charging. The special thing is that the are tiny, about 4.5x4.5mm.

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You can see it's a ferrite bobbin coil form with a healthy amount of very high gauge magnet wire topped with a tiny PCB holding an SMD cap and LED.

The power is provided by a small PCB with an XTK-333 wireless power chip. This is a China special, and I didn't have any luck finding a datasheet on it. Some sellers provided application notes schematics for a related chip that I assume is pin compatible but the numbering was different.

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You can see the board is very simple. It's double sided but there are no components on the back, and the only trace is one about a third the size of the board connecting the Vsupply+ to the terminal marked OUT. They must be doing the switching in the low side(?).

The board wants 5V at the input but will operate with somewhat reduced power and switching frequency with less. I did not try to power it with more than the 5V, but it appears to have an LDO (the mystery 6-pin package) so maybe it would be OK.

The seller claims you can place the LEDs 80mm from the coil, and that's not exactly false, but they get quite dim not being exceptionally bright even in the center of the coil. They operate similarly adjacent to the coil, and the are the very brightest, though not be a large margin placed between the output wires.

.IMG_8833.png
The output is about 18V P-P at about 220KHz. I tried making my own loop (a random length, so my results may be influenced by that, and using a function generator to power the lights. I set it to 220KHz, and it worked just fine. However, I found that I could increase the brightness of the LEDs by a subjective ~20% by reducing the frequency to about 204KHz.

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I don't know what I will do with these but they were interesting enough to spend a few dollars on to investigate. Maybe I will find something clever to use them for. I do find the tiny size impressive and I wonder what else might be possible with such a small power receiver.

[EDIT: post-posting proofreading corrections, typos and autocorrect errors\
 
Last edited:

Tonyr1084

Joined Sep 24, 2015
7,957
I remember putting lights at the end of a CB antenna. Wonder if the radiated power from a CB radio would light those LED's. I can envision them pulsating to the modulation of the person speaking "Breaker - Breaker".
 

Thread Starter

Ya’akov

Joined Jan 27, 2019
9,237
I remember putting lights at the end of a CB antenna. Wonder if the radiated power from a CB radio would light those LED's. I can envision them pulsating to the modulation of the person speaking "Breaker - Breaker".
5W on 2m and 70cm (oh, sorry, @Ian0 I meant 700mm) doesn't do anything to them. Of course, the LC network must be resonant at the ~200KHz frequency of the wireless power signal so it might be pretty deaf to 144 or 440MHz and 27MHz would be closer.
 

BillB3857

Joined Feb 28, 2009
2,571
I remember putting lights at the end of a CB antenna. Wonder if the radiated power from a CB radio would light those LED's. I can envision them pulsating to the modulation of the person speaking "Breaker - Breaker".
Going by my foggy memory, there was a mobile CB antenna called the "Lightning Bug" that had a neon light at the tip of the whip.
 
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