The 80 cents inverter from AliExpress

Oh wow, it took me a long time to get started writing this. I've been quite busy, though mostly busy doing absolutely nothing of value.

The inverter in question is a device I bought on AliExpress already under the presumption that it was going to be fake. What surprised me was that not only was it not fake, it was not even the worst one out of the lot.

The claimed specs are as follows:

Voltage 220V
Wattage 40W
Frequency High frequency current

I'll get this out of the way first: No, this is not 40W. The energy it delivers before the voltage drops unusably low is about 20W. And yes, the voltage does drop. There is no feedback on this thing.

That "High frequency current" is also a bit weird. But in the end, it just means the inverter runs at several kilohertz (>40kHz - you can't hear it). That means measuring the voltage can be a bit "exhausting".

How does it work

After a bit of searching, I found that this circuit is actually a Royer Oscillator, a simple two-transistor oscillator with a capacitor and inductor. My first guess that it was fake seemed to be mostly unfounded. I had based it on the price and the weird design of the PCB, along with the fact that what looks like the AC output is actually one part AC out and another part the rectified DC output. A diode being across the AC out, which seemed to be the case, would almost certainly have caused a fire instead of an AC voltage output.

Do I like it?

Hell yeah I do! 80 cents for a working voltage step up module is really quite insane. I currently mostly use these as a power supply for tinkering with vacuum tubes.
Unlike the 150W and 300W ones, this can drive LED bulbs too: they use a step down converter that relies on properties of sine waves.