Friday, November 2, 2012

Type A or Type B Field Control?

There are two ways to drive an alternators field:  Ground one side and feed the other +12v via the regulator, or tie one side to the battery and have the regulator manage the field by grounding the other.  This past week I have posted the current draft design onto a couple of web sites asking for peer-review, and one of the points that came up was:  Grounding FETs are cheaper and better than the  High Side approach I currently have designed in.

It is true.  N Channels are better then P Channels...  And cheaper to boot!

I have been spending the past few days looking to find a valid reason to select High Side vs. Low Side, and am stumped.  From a FET standpoint, the Low Side makes the most sense   However - almost without exception - all external regulators I can find, and even most all of the IC's used by companies alternator companies for their internal regulators control the field from the High Side.

 FET design leads one to Low, but everyone does High....  Why is that?

So, going to let is sit for the weekend.  See if some other folks can give insight into this.  And lacking any direction, I just might take the Lemming Approach and stay with High Side....


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