Electronic – What´s the purpose of this diode

circuit-designdiodesflybackrelay

I'm trying to build my own relay board to use with a 3.3V controller. I found the schematic of the board, so I'll try to replicate it. I'm only having trouble understanding what's the purpose of the LL4148 diode parallel to the coils.

Here is the schematic:
enter image description here

Here is a simulation of the circuit. Removing the diode seens to make no difference.

http://bit.do/fgPsz

Best Answer

From the question below:

A diode is put in parallel with a relay coil (with opposite polarity) to prevent damage to other components when the relay is turned off.

This is called a flyback diode.

See also How to choose a flyback diode for a relay?

See also the comment of Kevin White (in my own words):

  • The diode prevents current spikes
  • The problem happens during turn-off