/diy/ - Do It Yourself

>>1506406
Here you are:
Basically you'll need to define a maximum current and be prepared to always run near that. You'll select a capacitor value such that this current causes its reactance [ X = 1/(2πf*C) ] to be enough to drop the voltage across the rectifier to a volt or so above the 5V/3.3V you need. It's reactive power, so the calculation isn't very straightforward, so I'd just test it in spice (free) until it works as you need it to. The minimum voltage across the rectifier needs to be at least the minimum regulator dropout and appropriate rectifier drop higher than what you want across the ESP. Ensure the dropper cap is not polarised (a film capacitor should do) and can handle the full peak voltage of your mains. Test with a resistor instead of your ESP01 for obvious reasons.

Things to possibly add:
-resistors in parallel with large capacitors to prevent them staying charged up
-thermal fuse on the regulator just in case it gets too hot
-full bridge rectifier for a smaller filter cap

Perhaps look at some of Big Clive's cheaper LED bulb teardowns as they often contain such a power supply for the LEDs, where the capacitor is simply acting as the current limiting resistor. Since the current through a capacitor is 90° out of phase with the voltage, the net power consumed by the capacitor is zero; it simply collects power and feeds it back into the wall again instead of heating up like a resistor does. An inductor can do the same thing, but getting a big enough inductor would take up a lot of room.