Acetylene Diodes

[Prudhomb]

Just looking to get smarter here. What is the purpose of the red diode in combo with the. BS170? Is this some sort of clipping before the opamp?

 

[fig]

It's an over-charge/static protector. You can use a zener or 1N4148 as well.

 

[Prudhomb]

It's an over-charge/static protector. You can use a zener or 1N4148 as well.

Thanks. I’ve not seen this in any of the other circuits I built

 

[fig]

It's common practice with a MOSFET (from what I have read).

 

[Chuck D. Bones]

It's ESD protection. MOSFET gates are easily damaged by static. Any MOSFET that has a short path from the gate to a jack should be protected. A 1N4148 does not provide adequate protection. A zener rated for 13V or lower is preferred, but LEDs also work because their reverse breakdown voltage is under 10V.