[sdiy] Zener issues (again)

[Roman Sowa]

It's not the first time that you write here about counterfreight parts. 
Maybe you should consider changing regular parts source?
1W and 5W zener definitely need different package, so the mistake was 
made on the die level. If it wasn't checked before packaging, it could 
have been some small garage IC maker deep in China forest. Or rice 
field, China does not have much forest I think.

Make one measurement - voltage at the test current shown in datasheet 
that is 49mA for one and 240mA for the other diode. You'll know for sure.
BTW, when I searched for datasheets for them, it showed up about 20 
different brands making those diodes, and I have never heard of any of 
them. That sort of tells you what kind of reliability and repeatability 
to expect.

BTW2, instead of 5.1V zener you can use 5V R-R opamp for clipping 
trapezoids and it will work much more precise, plus free buffering.

Roman

W dniu 2020-11-30 o 06:20, David G Dixon pisze:
> Hello Friends,
> You may recall a few years ago that I built an interpolating scanner 
> with a trapezoid generator for controlling linear VCAs.  The 
> trapezoids were generated with a kind of folding circuit that uses 5.1 
> zener diodes to limit the voltage in a couple of places.  As the 
> incoming CV rises linearly, the circuit output rises sharply from a 
> little less than 0V to 5V, stays there briefly, and then falls sharply 
> back to a little less than 0V as the CV continues to rise.
> So, I built the original circuit with 1N4733 5.1V 1W zener diodes, and 
> it worked perfectly.  Just the other day, I built a very similar 
> circuit for someone, and again used 1N4733s.  However, in this 
> circuit, instead of getting nice well defined trapezoids that peak and 
> ride at 5V, I'm getting narrow peaks that don't quite rise to 5V 
> before falling again.
> I have checked and re-checked (and re-checked, and re-checked) the 
> layout against the schematic, and it is correct.  I went to my 
> simulation, and nothing I did changed the general robustness of the 
> circuit.  However, then I tried replacing the simulated 1N4733 diodes 
> with simulated 1N5338, a 5.1V 5W zener, and -- lo and behold -- the 
> simulation generated wimpy little narrow peaks up to about 4V instead 
> of trapezoids up to 5V.  So, I can only conclude that the 1N4733s that 
> I bought (from Small Bear) are actually 1N5338s in disguise.  I 
> haven't yet desoldered the old zeners and tried them in the new 
> circuit, but I'm going to shortly. I'd bet that this will fix my 
> circuit.  (And, before you ask, I decreased the current-limiting 
> resistors from 4.7k in the original circuit to 3.3k in the new 
> circuit, to no avail -- also, the simulation shows no effect of 
> decreasing these resistors.)
> Has anyone else experienced similar inconsistent behavior with zener 
> diodes?  How likely is it that these 4733s are actually mislabeled 5W 
> zeners?
> Cheers,
> Dave Dixon
>
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