grounding of leaking PSUs and common ground with rectified mains

Thread Starter


Joined Feb 22, 2023
that title is quite a bit clunky, hope I'll do better job explaining what my problem and requirement is here:

I have a circuit that has two PSUs: one for MOSFET driver chip (PS2); one for Raspberry pi (like) board (PS1).
The driver is driven by the LTV-3120 driver which has it's input opto-isolated.
The driver needs to have common ground with the MOSFET hence GND is connected to the minus terminal (pin 4) of the bridge rectifier. + 100KΩ pull-down resistor between Gate and Source.


function-wise it works, BUT:
PSUs are leaky; a few mA but it leaks 220VAC phase to the it outputs so to NOT to have and operator electro-shocked while connecting sensors to the exposed GPIO pins (J1, J2, J3, J5) I have earth grounded negative terminal of PSU1 (GND1) which solves the issue of electro shocking. I don't think it's an go-forward advisable solution through I know this earth should be screwed on device's chassis.

So, hope you get the idea now and can be helpful with solving the grounds/earth problem now so this can be production ready soon.

Thanks for all suggestions!


Joined Apr 4, 2016
Your PSUs have internal isolation. The bridge rectifier has NO isolation. Pin 4 of the bridge rectifier must not be connected to GND or the GNDPWR (Earth). The circuit as you have drawn it is VERY DANGEROUS.
On most domestic supplies with an RCD (earth leakage circuit breaker) this would instantly trip out.

Thread Starter


Joined Feb 22, 2023
MOSFET's Source must have common ground with it's driver. That be rectifier's pin 4 with PS2 GND. Without this it can't work. GNDPWR as I have in schema is basically neutral line of mains (bad marking, i know, just so we understand each other).

I acknowledge you it's dangerous like this, that's why I'm trying to describe here what I want and gather some opinions on that.

that PSU leaks just a little bit as per spec (0.25mA) which doesn't trip fuse here and I can touch RPI's GPIO without harm when earthened, but still.. I need to get this done properly. please