I would like to do something like this application note: http://www.onsemi.com/pub/Collateral/AND9093-D.PDF
And I'm using this transistor: https://www.fairchildsemi.com/datasheets/FD/FDS5670.pdf
For me Vin = 20 V, and I apply 5 V on the gate. Load = 22k
But it's like the MOS is always open. That's I don't understand, Vgs > Vth, so why is it always open? And what I should do for make it work?
Thanks edit: Add schematic, sorry I forgot it