[sdiy] Zener clipping Was : ...that 1K resistor on the output

[Harry Bissell]

Depends...

In any case you need a series limiting resistance. You can use schottky diodes to clamp the input to
+.3V above the rail and -.3V below, most ICs are ok with this from a survival standpoint, althought they
might not function properly...  This voltage is quite well defined.

Downside of this, if these clamps are active they can pass current onto your power supply rails, maybe even trying
to power a circuit that is 'off' and causing a latch up (bad).

Back to back zeners shunt the voltage through themselves and the series resistance... so no current can flow into the power supply.

Downside is, the range of voltages is limited by available zeners, and their tolerance.  If you were trying to clamp to (lets say)
+/- 5V, you'd need a 4.3V zenrer (plue the .7 volts that the other zener contributes). With 5% or 10% tolerances, you may not get
accurate enough results. If they are too high, you pass an overvoltage, too low and you conduct some current in normal cases.

I usually prefer the zeners for clamping, I trust the method more than the shottky dioes to the supply rails.  Zeners are quite robust !

H^) harry


----- Original Message -----
From: Mark Rivera <marr at lumin.us>
To: SDIY List <synth-diy at dropmix.xs4all.nl>
Sent: Fri, 28 Jan 2011 10:29:15 -0500 (EST)
Subject: [sdiy] Zener clipping Was : ...that 1K resistor on the output

> If I'm using Zener/clipping diodes on Inputs/Outputs

Is a pair of zeners the preferred method for limiting a bipolar input
to a given voltage range?
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-- 
Harry Bissell & Nora Abdullah 4eva