I read that a capacitive dropper supply, like those found in some LED light bulbs, has issues like inconsistent brightness, flickering, and voltage fluctuations.


Is the following correct?

The flicker isn't caused by the cap. Fluctuations on the secondary are due to all the following:

• fluctuations of the primary (mains)
• fluctuations in the load
• mains frequency

In other words, it's a non-regulated output.

 

The particular circuit shown will flicker at 60 Hz as the current path alternates between the two LEDs

 

Though if the LEDs are close enough together (or are in some way diffused) it will appear to flicker at 120 Hz (assuming you are on a 60 Hz main) as one LED will be on during one half cycle and the other will be on during the other half cycle.

If you only use one LED (instead of having two that are antiparallel) you will almost certainly exceed the reverse breakdown voltage of the LED (which is typically something in the ~5 V to ~7 V range), so keep both of them there. Having said that, the high impedance of the capacitor might limit the current to a non-destructive level.

 

A note that capacitive droppers, as with any non-isolated circuit connected to the mains or any power source >50V, is inherently dangerous. Unless you have experience designing and constructing such circuits it is ill-advised to attempt it. And never use a low voltage breadboard when experimenting with such circuits. The danger is proportional to the voltage, so in places were the wall power is 240V, it is an even more foolhardy thing to do.

If you really must do experiments with CD circuits, acquire a high quality transformer with a 10:1 ratio (e,g,: 120V on the primary producing 12V at the secondary), mount it in an enclosure with a suitable line cord and output terminals, and use the stepped down AC output as a “scale model” of the mains.

 

Usually the circuit enclosed within an LED bulb assembly is adequately inaccessible to all except the very most determined folks. I know, because I have done it. BUT not with power applied.