My question in short: Will I damage my Raspberry Pi 4 if I apply (its own) 3,3V onto a GPIO pin that is set to output mode? (With current limiting resistor, of course)

I ask this question because this is what I want to do: enter image description here

  • Ah, let me see. (1) Rpi GPIO High Vh is usually in the range of 2V8 to 3V2 (I forgot the exact numbers, but there is NO officially spec anyway. (2) Suppose now Vh is now 2V8, so voltage across 5k0 is (3V3 - 2V8) ~= 0.5V. Ohm's Law says current flowing into GPIO pins must be 0V5 / 5k0 ~= 0.1mA. (3) I am not sure if current can go into the output buffer. Perhaps it will go into the input buffer which is now disabled, therefore high impedance. Current has no where to go, leaks into a parasitic diode nearby, accumulates enough charge, causes a silicon latch up and subsequent nano explosion. – tlfong01 Aug 31 '19 at 1:20

The answer to your question is - it depends.

With the circuit you have drawn it will be OK.

If the output is HIGH no current will flow;
If the output is LOW 3.3/5 ~ 660µA will flow into the GPIO, which is well within its specifications.

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When the GPIO set to output the impedance of GPIO is low. So if you apply 3.3V through the 5K resistor there will flow current to the GPIO which will be less than 0.1mA . This is very low current and safe for sure. So your schematic should work fine.

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