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<DIV><!-- Converted from text/plain format --><FONT color=#0000ff size=2
face=Arial>Hey SDIY Team,</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>As promised, I measured some zeners
with different resistors. Here's what I measured:</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>1N4728 (3.3V) -- 1 diode</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>1N4730 (3.9V) -- 3
diodes</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>1N4731 (4.3V) -- 1 diode</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>1N4732 (4.7V) -- 2
diodes</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>1N4733 (5.1V) -- 2
diodes</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>1N5237 (8.2V) -- 1 diode</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>I used a 15V power supply and the
following 8 resistor values:</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>200R 470R 1k
2.2k 3.3k 4.7k 10k 20k</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>Here are the results, plotted as
zener voltage vs true current (15V minus the measured voltage over the
resistance):</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><IMG border=0 hspace=0 alt="" align=baseline
src="cid:796392106@01072020-066E"></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>As you can see, the spread among the
lower voltage zeners is pretty extreme. None of the 3.9V zeners ever came
up to 3.9V. Nor did the 4.3V zener. I had two different kinds of
4.7V zeners with different markings -- one of them was pretty hopeless and the
other one was quite good (low spread, hit nominal value at low current).
The 5.1V zeners were very good -- almost no spread, and very close to the
nominal voltage at every current. The 8.2V zener was also pretty
good.</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>So, what's the lesson? Again,
measure every zener under the conditions it is to be used to ensure that it will
do what it is supposed to do.</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>Here's the weird part: in the
previous frequency shifter I built (my own unit), I used 3.9V zeners in
the zener bridge, and resulting waveforms are very close to the
desired 10Vpp (about 9.6 or 9.7Vpp -- I can certainly live with
that!). Given how bad the 3.9V zeners performed in tonight's test, I guess
I just got really lucky. Incidentally, those two zeners were ones I had in
my stash, while the ones I measured tonight were all bought from my local
electronics shop yesterday. This leads me to believe that there are "good"
3.9V zeners (like the "good" 5.1V zeners in tonight's test) and there are "bad"
3.9V zeners, and it's just a complete crap-shoot.</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>Cheers,</FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial>Dave Dixon</FONT></DIV></BODY></HTML>