Well maybe the 'father and mother' diodes only apply in my line of work. I work in the radio communications division so we deal with crossover platforms and crystals and that sort of thing every day. So I will try to explain these and although I'm not the best at explaining this maybe it will help you understand what they are and their uses.
So here goes.....
If you have a DC circuit from battery to unit device its not a problem at 12v. You can use a normal diode and that why it doesn't drain the battery when the machine is not in use for several days. Now these come into play when you have a DC unit, aka desk mic or tape recorder, on an AC circuit like a 120v wall plug system. (Well sort of but I will explain as this goes on) So the desk mic or tape recorder must have DC to operate at its given value and if AC is what it gets the circuits will fail or not function. Now a father diode will go between the unit of DC control and the AC source, it will not have a pot put it can be physically adjusted to control the power flow to the unit and then that couples to a mother diode that converts it to DC through another circuit that is usually connected to a strip terminal. So it goes from 120v AC to 48v DC in this example, since most industrial tape machines and desk mic typically run on 48v DC systems. It makes it an easy pathway when you can't run DC wiring through a build due to interference it would cause with the machines in the area.
I hope this makes it easier to understand.