There is something I don't understand with protection diodes. I am talking about a series diode between the + and the load of the circuit to prevent damaging components when there is a wrong polarity on the supply, like this :
Normally the current through the diode grows exponentially with its voltage accross, with a forward voltage of 0.7 V (for example).
I understand that if there was no load, then there would be 12 V accross the diode, resulting in a very large amount of current which would quickly destroy it.
But when there is a load, and that the circuit is working properly :
- Why is the voltage across the diode always 0.7 V ? I understand that all diodes have a forward voltage due to their depletion area, but I don't understand why if I supply the diode with a load behind, the voltage across the diode will always be 0.7 V and across the load 11.3 V. What sets this value ? Why not something else ?
- If the load needs a current of 10 mA or a current of 1 A, then the current through the diode will be 10 mA or 1 A, and given its characteristic curve the voltage across the diode will be very different. It seems like a contradiction to the above point.
There is clearly something I am missing there, hope you could enlighten me. :)