diodesmosfettransistorszener
Does anyone know if its possible to wire up a MOSFET transistor as a zener diode? I have been happily making normal diodes from my MOSFETs by shorting the gate and the source
simulate this circuit – Schematic created using CircuitLab
But now I need a zener diode for a voltage regulator an am struggling to come up with anything! Any ideas would be great…
That is a fairly husky Zener diode. The test current shown in the datasheet is 45 mA. You are only allowing 2.5 mA, which is apparently not enough to get over the diode's "knee".
To be more accurate, in a typical power U-mosfet structure in use today [aka trench mosfet], this body diode is a PIN diode:
Image from this textbook.
Best Answer
This works: -
simulate this circuit – Schematic created using CircuitLab
As the drain voltage rises from 0V D1 is not conducting until it reaches its zener voltage (simplistic words). Then a gate-source voltage starts to develop as the drain voltage rises further. At some point (maybe 1V - 4V higher than the zener voltage) the drain starts conducting current and therefore keeping the drain voltage about constant.