[sdiy] Zener diode knee sharpness differences?

Neil Johnson neil.johnson71 at gmail.com
Tue Jun 24 11:48:46 CEST 2014


Mattias Rickardsson wrote:
> I'm using SMT zener diodes from Diodes Inc, and I have noticed that
> some of them have a zener knee that is significantly less sharp. The
> zener voltage at the 5 mA test current in the datasheet is correct -
> but before that zener voltage is reached, the knee has a more rounded
> shape.
> As a result of this, when these rounded-knee zeners are used as a
> resonance limiter in a VCF, acting well below the 5 mA test current,
> they limit the resonance to a much lower signal level, and the filter
> acts and sounds very different.
> Is it expected that the zener knee can vary a lot in its shape from
> unit to unit, or should it be seen as a defect?

It is not unexpected.  As you say, the zener diodes are characterised
at a current of 5mA.  That is the minimum current that the
manufacturer guarantees correct operation.  Below that level and
performance is not guaranteed, so they can behave exactly as you are


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