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How is my 3.3V rail feeding back to my 5V rail??
▲ 9 r/AskElectronics

How is my 3.3V rail feeding back to my 5V rail??

The board is a dot-matrix control board (7-rowsx10-columns) with can communication interface

it has 3 voltage rails:

  1. +24V input goes to a MC34063 buck ic
  2. +5V from the buck converter
  3. +3.3V from an AMS1117 regulator

in this test setup I'm feeding the board a 3.3V from an stlink just to program the board but I noticed that there is also a voltage appearing on the +5V rail when measuring I get about 2.5V

I disconnected the stlink and measured the resistance between the 5v and 3.3v rail and go about 7kohm resistance

on the board I have:

  1. stm32f103c8t6
  2. ULN2003 darlington array IC to drive the dot matrix rows
  3. MCP2551 ic for CAN communication

I'm suspecting the ULN2003 to be the reason for this because I'm connecting it's Vcc to +5V

what could be the reason for this?
could this create problems down the line??

EDIT: You can find the shematic in the link below

https://imgur.com/a/87KbhPC

u/AmbassadorBorn8285 — 3 days ago
▲ 2 r/EngineeringStudents

Recommend me books like the ones in the picture please.

I'm looking for books on technical topics that don't contain a lot of heavy calculations or math that requires extensive outside research. I’m fine with a few equations here and there, but I’d like something I can read while at work or on the bus.

I am primarily interested in Electrical Engineering (any field), as well as Computer Science. However, if you know of any books in other engineering fields that are a good read, please share them!

Thank you in advance.

u/AmbassadorBorn8285 — 9 days ago