Hello!
I am designing an embedded system that would be normally powered from an AC to DC power supply (MYRRA 47152).
The 5V output of this supply will be regulated down to 3.3V by an LDO regulator (MCP1825ST-3302E/DB).
When I want to program the MCU, I don't want to actually use high ac voltage to power it, but rather supply 3.3V from an external regulator.
My question is, does the regulator care if it has 3.3V applied between its output and ground while its input is not active (i.e. disconnected or 0V).
To better explain the situation there's a schematic:

So can the regulator get damaged from this voltage?

 

hi 128,
The usual method is to connect a diode in parallel, so the Vreg will have only 0.7v reverse voltage, when the Vout exceeds the Vin.
E

 

hi 128,
The usual method is to connect a diode in parallel, so the Vreg will have only 0.7v reverse voltage, when the Vout exceeds the Vin.
E

Thank you! I always wondered what is the purpose of this diode and now I understand. This looks like a great method for my application.

 

hi,
In most Vreg circuits, where large Vin and Vout caps are used, at power Off the Vout can exceed Vin, so the diode is fitted to prevent reverse voltage damage to the Vreg.
E