Dropping a few volts ?

In the circuits folder, there is a way to drop a high voltage to a
voltage regulator.

/CIRCUITS/HIGH INPUT VOLTAGE REGULATOR.pdf

it uses a zener diode and a mosfet to drop the voltage to the voltage
regulator.

what if one used a 70 volt zener to a 30 amp mosfet without the
voltage regulator ? would that limit the maximum voltage so we could
use a little higher power supply and stay in the safe range of the
Gecko ?

Assuming a 48V transformer, less 1.2 volt for the rectifier and then
1.414 for the DC voltage, one would expect about 68 volts.

The 70 volt zener would drop to 68V with the 2 volt drop in the
mosfet and therefore the mosfet would add little resistance, but the
drop would also not generate significant heat.

On the surface, it seems that each volt higher would yield one watt
per amp of the power supply. I didn't look at the resistance thru
the mosfet for the additional voltage drop and the heat associated
with no additional drop of the supply voltage.

so, dropping 2 volts at 20 amps would create 40 watts of heat. Not
much considering the benefit.

Dave