Schematic Questions

[Kasmodean]

Hi everyone,

I was looking at the schematic for the Cougar controller board Rev2a and the 1000 AMP Mosfet board Rev5A. Reason for looking is I try to understand what I am building before putting soldier to components. I am a mechanical engineer with a limited amount of electric knowledge and I have a few questions. I would appreciate anyones help.

In the "12V Conttrol Supply Input and Filtering" section
1) Where does DC_DC_12V+ IN connect? Between resistor and cap?
2) What is the reason for diode on negative 12V? Does this raises control ground to the diode forward voltage. Is this component really needed?
3) What is the reason for the choke on DC line?

In the "Isolated DC-DC Converter" section
4) EC4A02H pins don't match internal connections. Is this an Error?
5) I see multiple 15V Lines on the power board, are these from multiple EC4A02H chips? If not, why does this 15V supply need to be isolated? It isn't next to any high voltages.
6) Why is the EC4A02H Vout- tied to Control_GND? Doesn't this remove the point of isolation? Is Control_GND suppose to be 15V GND?

In the "Driver Circuit" section
7) Where does Driver output signal go? I don't see it reference anywhere else.

In the "Hardware Overcurrent/Undervoltage Trip" section
8) Why not implement this logic in the microcontroller? A redundant fail safe is case of microcontroller failure?

Mosfet board
9) What is purpose of IXD604 circuit with the transformer and diodes? It looks like a it is the basic components of an isolated DC-DC converter circuit. Why not just buy an IC like EC4A02H?
10) Is C7 backward on the schematic?
11) What is the purpose of the ATTiny25? Is it just to provide pulses for the IXD604 to convert DC to AC? If so, why not just buy an IC like EC4A02H?
12) The BOM says four line filters are used, how do I connect them to the IXD604 circuit? In series?
13) I don't see a part number for the line filter in the BOM. I can use anyone I want?
14) What is the purpose of opposing zener diode D21 & D22, D23 & D24, Etc.? Why not just a resistor?

I know that is a lot of questions, but any help is welcome.