Re: [CAD_CAM_EDM_DRO] Dropping a few volts ?

turbulatordude wrote:

>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 ?
>
>

You have to protect the gate of the MOSFET with some other Zeners, as
it must never exceed about 15 V + or - of the Source terminal. Otherwise,
this is a very good idea, up to a point. Almost all MOSFETs have a
parasitic diode that will allow power to flow from the drive to the bulk
supply, if that condition arises.

>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.
>
>

Well, I don't see the great advantage to dropping 2 volts. 68 V is just
fine
for the Gecko, especially if you have big motors and want the maximum
speed.

Jon