Modify Transformerless Power Supplies

Question

Based on this article:
https://hackaday.com/2017/04/04/the-shocking-truth-about-transformerless-power-supplies/

I have some rf wireless plug outless which use transformerless power supply.

I would like to build in an ESP32 (3.3v) in it. I don't know currently what output the transformerless powersupply in these produce but I seen some 24V relays so I have to check.

My questions are:

1, Regardless that it is not safe to connect an ESP32 through the mains as the article explains, is the output of a TPS fine grain enough to power an ESP?

2, In the article it states: "excess current is shunted to ground when the load draws less than the 25 milliamps", an ESP32 power consumption is between 100-250 mA (using wifi) why does it matter how much my load drains?
For example let's assume that this circuit I wan't to modify would output 3.3V to the board, would I still need to modify it if my load is different?

3, Is there some online calculator for TPSes where I can put in my load value and desired voltages and it will calculate what cap and resistor(s) will I need?

Thanks

Dorian · Answer

Here is an online calculator for TPS in various configurations.

Play with the values and you will see that for 250mA load you will need a non polarised capacitor with a value over 4.7uf at 400V. At a quick search the capacitor I found is 25/25/35mm in volume and costs 3$.

The TPS will have a low efficiency and your project very hard to debug.

Please follow Wesley's and Indraneel's  advice and use a phone USB charger or something similar, some simple chargers can be tricked to output 3,3V It will be not only cheaper but also smaller , safer and will heat less.

Modify Transformerless Power Supplies

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