LED light chain QRM killer
I have discovered a strong mains like QRM on 80m band during Xmas season. Based on previous experience I started search
for switched power supply. I found it quickly - small PS supplying chain of LED diodes on about 15m long cable, situated
about 10 meters from my antenna. The PS was in sealed plastic box - so I cut it to get inside. Then I saw this:
Switched power supply without any kind of RF filter, on both input and output! Standard solution for such toys comming
from China (it is funny to read the certifications declared on sticker...).
So as part of my Xmas holiday I started construction of new power supply, to spread peace in electomagnetic spectrum (and among peoples as well).
Here you can see the result. Some points to design. LED's should be supplied by constant current, so the output voltage
should fall down when there is a higher current. It can be achived by resistor in series, but it generates heat.
Better to use reactance (capacitor or inductor). So I joined requirement for higher voltage (around 30V, corresponding
to 10 white LED's connected in series) with constant current requirement - I use small low voltage transformer followed
by voltage tripler, using intentionally low capacitors. The PS gives about 60V without load and falls down to 30V with
80 mA load. Here you can see the circuit diagram. As you see, it is quite simple and I guarante - it generates absolutely
no QRM in shortwave frequency range!
Don't forgot to put the PS into box - dangerous voltage!
Note: I have faced several times already with such kind of QRM - LED lights, halogen bulb lamps with "electronic transformer" etc.
In all cases I throw away the "dedicated electronic" and replace it with something like this, or just simply by old
classic transformer. In this way I am able to keep my house electromagnetic clean, but unfortunatelly I am not able to
spread electromagnetic peace to my neighbours :-(