[sdiy] CV input op-amp circuit

Harry hbissell at wowway.com
Mon Dec 7 15:36:05 CET 2020

If you can afford and extra trace (to the power supply as one suggested...) you can tie all the input protection shottkies
to a single zener, and still not connect it to the power supply so no load dump is possible. You can set the clamp threshold independently
of the supply voltage.

Tony's suggestion will protect against your supply possibly going overvoltage as a side effect but you need a big wattage zener to stand that
(there may not be series resistance there) 

H^) harry

----- Original Message -----
From: Tony Allgood <oakleysound at gmail.com>
To: Synth DIY <synth-diy at synth-diy.org>
Sent: Mon, 07 Dec 2020 08:24:19 -0500 (EST)
Subject: Re: [sdiy] CV input op-amp circuit

 > It can only absorb the clamping current either momentarily with some 
big decoupling capacitors, or in the steady-state if there is sufficient 
load on the supply.

I have sometimes used a pair of Schottky diodes to the rails on the 
input, along with a suitably rated zener diode across the power rail 
itself. eg. 5V6 on the +5V rail. I reckon if there's enough current 
delivered through the input series resistor to raise the power supply 
voltage via the upwards facing Schottky, the zener should protect any 
devices connected to that rail.

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