I noticed on the Krankosaurus schematic that there is a zener diode between the drain and the 1M to ground on the first MOSFET stage, but not in subsequent stages. I am assuming that this diode, like the LED in the MOSFET stage of the ROG Peppermill, protects and stabilizes the MOSFET. Is this protection only necessary in the FIRST MOSFET stage of a circuit? If so...why do subsequent stages not require it?
Don't have the schem handy, but it's not really needed anyway. That diode AFAIK protects the (incredibly high Z) drain (edit: 'scuse me, Gate, is what that should say) from any transients on the input. These are mostly caused by static electricity while plugging in/out, and can be very high voltage (remember pulling sparks running over a wool carpet in polysomething socks?). Although it can't really supply any current, static electricity is more than capable of destroying the innards of a MOSfet.
The diode protects from this.
The circuitry before the other stages secures those stages from any accidental transients caused by plugging in/out, so those aren't in need of that particular protection.
That's the way I understand it, I'm sure someone more knowledgeable will chime in if I get something wrong or leave anything out ;P
You got it, Mike.
I worry a little about that "between drain and gate". Generally protection zeners are between gate and source or gate and ground. But I don't have the schemo, either.
Good point - I completely failed to register it was the *drain* he was talking about - I thought he referred to a zener gate-ground...reading well combined with some actual cogitation appears to be a challenge. See, I even substituted "drain" where I actually should have said gate... Ahem. :-[ Mordechai - Are you sure it's the *drain* or could you be referring to the gate and source (which I think you are)?
Sorry, you're right...the SOURCE and the GATE. Identical to where the LED goes in the first stage of the Peppermill (it is connected from the source to the 1M that also goes to the gate).
Makes sense now, so again, thanks very much.