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ATare.1
ATare.1
Visitor II
October 4, 2020
Question

Reverse Power flow for LD39050 regulator, what will it affect

  • October 4, 2020
  • 1 reply
  • 543 views

Hello everyone,

I have a question, and i hope someone can help me,

I am currently building a circuit which contains 2 source of power;

1- main source (3V CR2 battery)

2- auxiliary source (5V USB in case of emergency)

taking into consideration that all the circuit is 3v tolerant, i needed to add a regulator when using emergency power (LD39050PU33R),

the question is if circuit is operation from battery and the regulator is having reverse power flow (3v input from battery and the vout pin) however the regulator is disabled,

How that will affect the circuit and how can take the necessary design actions if needed?

Thank you

This topic has been closed for replies.

1 reply

Peter BENSCH
Peter BENSCH
ST Technical Moderator
October 5, 2020

If I understand correctly, the supply voltage of your system is 3V while the LD39050 supplies this 3V from the USB 5V?

If this is your setup, there are two potential problems:

  • battery only, which causes reverse current from the battery to the input of the regulator
  • 5V from USB, which would (via the regulator) drive current into the battery, which could be dangerous

You can use two Schottky diodes: one from the regulator output, the 2nd from the battery, the cathodes of which are connected together to your system. Set the regulator's output voltage slightly higher than the maximum battery voltage to ensure that the regulator is powering your system instead of the battery.

Does it answer your question?

/Peter

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