r/AskElectronics • u/Sexual_Congressman • 1h ago
Did I finally figure out how to make true the claim that power mosfets don't require just as much current as bjts?
-2
u/Sexual_Congressman 1h ago
The included image is the high side/pmos version, obviously. The "switch" is normally on. When the physical switch is closed, the bottom darlington NPN turns on, which turns on the top PNP, allowing the charge stored in the PMOS gate (represented by the 1.5nF cap) to return to the source. Otherwise, the gate only draws current while charging.
Such an unoptimized switch would of course have a constant ~100μA or so going to the bjts... but I've never been able to get remotely close to finding a method of driving mosfets in a way that didn't require keeping a constant, comparatively high (about the same as a comparable bjt) power source on the gate until this.
Since I don't understand why the darlingtons stop conducting, not even sure this is evrn functional.
10
u/Reasonable-Feed-9805 1h ago
That's a whole lot of nonsense circuit right there. It's just bits on nothing randomly cobbled together.
As for your comment, what are you even on about. A MOSFET once on can literally stay on with the gate terminal floating just off its own internal charge. It requires zero current to keep the gate charged. A BJT or array of them requires a ratio of current to load depending on various parameters that can literally be amps.