NMOS on Bat +

[bigkahoonaa]

I built the circuit in my http://www.fieldlines.com/story/2008/2/26/72614/0725">last diary, and I'm still waiting for a decent wind to test things out.  Isn't that always the case?  20 to 30 + winds when you're getting things ready, and then it's like you're in the eye of a hurricane.

At first I didn't think that having separate grounds for battery and generator would be a problem.  I was thinking of using batteries as the power source for MOSFETs but now I realize that I can't (at least with my limited understanding of electrickery).  MOSFET ground should go to generator ground, and if a use the battery as a source, then MOSFET ground also has to go to battery ground.  Oops.  So, I'm looking at putting the MOSFET on the battery + terminal.

From looking at different chips to drive MOSFETs in a buck converter, I've noticed that almost all use a capacitor which I think is used as MOSFET return.  I'm not explaining this very well, and a picture is worth a 1000 words:

C1 is the cap is talking about.  The SwCADIII simulation(here) seems to show that it could work.  Anyone try something like this?

Big

[commanda]

It's called a charge pump. When Q1 is off, C1 charges up via D1. When the fet starts to conduct, the gate supply voltage will always be more positive than Q1 source by the voltage stored in C1. So when the fet is fully on, V-DS = zero, and the gate voltage will be V(C1) greater than genny voltage.

This is why we normally common the positives, and put the N-channel fet between battery -ve and generator round. Then the Gate voltage switches between zero and Vbatt.

Amanda

[commanda]

Sorry, Typo.

This is why we normally common the positives, and put the N-channel fet between battery -ve and generator Ground.

[bigkahoonaa]

Hi Commanda :

So it's a charge pump.  I've noticed in the simulation that the poor old diode D1 could see genny voltage + Vcc.  I think I understand it better now.  Thanks.

The circuit in my previous diary has common positive, and the N-channel mosfets are between battery -ve and generator ground.  I'm using a wall wart as power source for the fets, but I'd like to use the battery as fet power source.