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Ideal diode circuit confusion

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kernels:
Hi guys,

I built the circuit below last night as part of an ideal diode experiment and am confused about the result I'm getting. The bit that confuses me is that the circuit works, when I apply 20V to the gates of the two N-Channel mosfets, I get 10V across the load resistor, take away the 20V gate drive and I get 0V across the load resistor.

What I don't understand is where the two sources are referenced to, does it have something to do with the gate-source capacitance ? or maybe the body diode?

hermitengineer:
The MOSFETs in your diagram have the gate relative to the source, so that's the reference they use.  When your gate voltage is 20V, VGS on the left transistor is +10V (20V-10V).  VGS on the right MOSFET is 20V (20V-0V) initially, but once current flows, VGS on the right also drops to +10V since it's passing the left MOSFET's current now.

When you turn off the +20V, VGS left is -10V and it turns off.  VGS on the right is 0V, so it also turns off.

The diodes don't really figure into this circuit because both MOSFETs are either on or off at the same time, and the diodes block each other's current flow when the MOSFETs are off.

kernels:
But the 10V is on the drain of the left mosfet, not on the source, the two sources are tied together without any other connection.

langwadt:

--- Quote from: kernels on January 21, 2020, 12:18:43 am ---But the 10V is on the drain of the left mosfet, not on the source, the two sources are tied together without any other connection.

--- End quote ---

cosider what happens when you look at the right mosfet as a diode and then when the left mosfet turns on

kernels:
Ahhhhhh  I see, initially the left side mosfet source just sees ground through a diode (and load), so it can turn on, which then puts 10V on the sources and allows the other one to turn on too, thanks langwadt!

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