reference

Martin Czech martin.czech at intermetall.de
Thu Nov 11 08:39:34 CET 1999


:::> >   If anyone happens to know of a good source of better than 1% zeners, I'd 
:::> >love to know about them.  Most of them tend to be in the 5% range and 
:::> >I've found only one place carrying 1% zeners.
:::> 
:::> Surely if you need beter than 1%, you shouldn't be using a zener, the
:::> temperature
:::> and load variation is going to be more than this.
:::
:::   Well I like using them as an easy way to limit CV ranges, like say 
:::into a PWM comparator, and want them to have a stable operating point.  
:::Temperature and load variation aren't too much of an issue since they 
:::aren't being turned on most of the time.

I think there are other ways to limit the output of an opamp.
It is a circuit with a bipolar tr. in the feedback path, the voltage
can then be adjusted by resistance ratio/trimmer. If you need 1%
tolerance, the usual series of diodes has too large voltage differences
between the types to hit your wanted voltage.
And  sometimes one doesn't know how far the circuit should go in the
beginning...

I noticed that using less current in the zener circuit (higher feedback
resistor values) causes very soft clamping edges, so you get nonlinear
where you don't want to, and no real limit where you want it.

Of course, without o-p amp or other amplifier, zeners are sometimes the only way.

I think zeners or tunnels (for lower voltages) have a natural wide spread
of tolerance, because doping profiles can not be made with such precision.
>From this point of view 5% is really good.

I guess the 1% types are the "center bin", thus expensive.

m.c.




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