how to protect external mcu when applying 2 power sources

Discussion in 'General Electronics Chat' started by ghisbo, Apr 18, 2018.

  1. ghisbo

    Thread Starter New Member

    Apr 18, 2018
    Setup: an external MCU is connected via a DIN Connector (// par lines) to the NTC temp sensor. It applies a voltage of 3.2V over a 2.2K resistor.
    the internal MCU is reading the same value of that voltage over the NTC.
    - When the external MCU is not connected, the internal MCU needs and internal VCC to be applied ( symbol SWITCH)
    - The voltage of the internal VCC is not the same as the external.
    - How can i prevent that the ext MCU get's damaged, or get's false readings.
    - the external MCU can be plugged in or disappear at any time;
    I taught to put a diode in between A and B, but then there is the Forward Voltage drop that will influence the readings.

    Thanks in advance for your attention
  2. danadak

    Distinguished Member

    Mar 10, 2018