Sunday, November 4, 2012

Hardware Design 0.1.3

This evening I posted an update to the hardware design, resulting on feedback I have received over the past week.  Major changes include adding a FET driver to the Field circuit  replacing the original NPN - Pull Up.  By doing so, I expect on/off transitions in the FETs to be much quicker during PWM control of the Field (Esp during  the Turn OFF transition where previously the 4.7K pull-up would be the limiting factor).

I also corrected a major design error around the I2C bus extension power supply.  The original simple Resistor / Zener did not take into account loads placed by the pull-up resistors and just would not have worked.  A new 9v LDO regulator takes its place.

And finally  I have decided to be a Lemming and stick with the High Side field control.  I still can not find justification of why but am so bothered as to how almost universally every example of alternator control devices I can find drive the High Side.  There MUST be a reason, and though a low-side driver does make more sense from a FET driver standpoint, I can not shake the obvious direction the industry has taken - even I have have no clue why.

So, high side it is.

Going to let this sit for a bit longer as I posted the project to another website this evening.  After a week will look to get the PCBs and parts ordered.  Want them to be at our mail-drop for our trip in December.

Then the REAL fun begins!

No comments:

Post a Comment