Where did you find that circuit? A little context for it might be useful.Steve
I can't find the source.
3. Why is a high value of 470uF used? I searched and found that many power supply decoupling capacitors are less than 100uF for my application where the supply is only about 12 V DC.
Can anybody explain the use for the diode? If the power source is connected in wrong polarity, the diode can't do anything but burn out.
My guess is reverse polarity protection.