ROG Omega & Zener Protection?

[davent]

In various Mosfet boosters and Mosfet HV regulators i've built there has always been zener protection for the Mosfet. I may finally get around to building an Omega but the schematic shows no such protection of the Mosfet. In this case, totally unnecessary or a good idea to add a zener, I'm inclined to put one in but just curious.

Thanks,
dave

[Muthauzem]

Can you provide a link to a schematic that shows the Zener protection?

If you look at the datasheet for most of the mosfets (BS170 and 2n7000, included), you will see that there's already an internal diode between source and drain. There's a possibility that those schematics just showed that. But I'm really not sure.

[davent]

They're all external zeners, for the boosters 9v1 to be specific. Boosters i was thinking of, AMZ Mosfet Booster and Zvex's SHO. (BS170 Mosfets)

http://www.muzique.com/schem/mosfet.htm
http://www.zvex.com/module_instructions.pdf

An example of HV regulator would be the VVR.

http://tinyurl.com/cspez8k

dave

[slacker]

In things like the Mosfet booster the Zener is to protect the mosfet from signals greater than 9 volts or negative voltages. In the Omega the output of Q1 can only be between 0 and 9 Volts so there's no need for the Zener. I don't know for sure,  but It might still be worth putting it in to protect it from static.

[davent]

Thanks Ian, that also clears up my puzzlement with why in schematics for say... the Box of Rocks, only the first Mosfet has the gate protection zener.

Take care
dave

[Muthauzem]

A zener diode is connected from the transistor's gate to source in order to protect it from static charges or over-voltage inputs. If the transistor chosen has an internal zener protection, D1 could be deleted.

Quote from the first link...

Yeah, they are not what I thought they were at first. I don't think they are needed, in the sence that the effect will work without it. Those capacitors and resistors at the input will already attenuate most of a static discharge from the input jack (which will be, even though very eventually, the main source of static charges, in a enclosed circuit with proper shielding).
But then again, you can never be too safe and since it's a simple and cheap protection, I would add it anyway.