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Author Topic: minict curve tracer, zener diodes, etc  (Read 5147 times)

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Offline cncjerryTopic starter

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minict curve tracer, zener diodes, etc
« on: November 08, 2016, 07:46:28 pm »
I picked up the April 2015 QST and found an article written by Veikko, N7VK about a mini curve tracer and decided to build it.  It took some learning as I haven't touched the 8051 in a while but with a little help from Veikko, I got it running.  First, I am amazed that more people haven't built this curve tracer.  Veikko wrote almost 6k lines of code on the PC application side and overall it works very well.  I've been using it to explore various active components and plan to use it to check for leaky FETs in HP volt meters I am repairing.

In playing around with it I found something that I've never noticed about zener diodes.  First, they aren't that accurate, around 5%.  Second, as you can see in the attached trace, the knee varied between zener voltages with the lower values having a smoother knee vs the higher values.   I checked several packs of the cheap eBay specials and they track very closely.

The trace on the left is for a 2.2V and the right, 6.8V.  The little circle on the 6.8V trace shows the zener voltage at 7.004V and the 2.2V trace is actually 2.275.  Both of these voltages compare closely to a test circuit I made.

Is this typical?

Thanks.

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Offline Kleinstein

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Re: minict curve tracer, zener diodes, etc
« Reply #1 on: November 08, 2016, 08:07:55 pm »
The behavior of the zeners is normal. The low voltage one are not that good. At about 6-7 V they are usually best (sharpest knee) and get less good at higher voltages.
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Offline Johnny10

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Re: minict curve tracer, zener diodes, etc
« Reply #2 on: November 08, 2016, 08:09:29 pm »
I have a couple or 3 or wait a minute 4 curve tracers.

Are you showing the forward and the reverse voltage?
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Offline cncjerryTopic starter

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Re: minict curve tracer, zener diodes, etc
« Reply #3 on: November 08, 2016, 09:05:56 pm »
yes, forward and that little drop off the left of the curve is -.644V.

I have two tracers, this one I just built and one of those cheap ones built on a transformer that attaches to the XY display on a scope.  This one will do the AC sweep at 60hz (like the transformer type using the DAC on the 8051.
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Offline cncjerryTopic starter

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Re: minict curve tracer, zener diodes, etc
« Reply #4 on: November 08, 2016, 09:53:09 pm »
The first attachment is another trace using a 9.1V zener and a negative starting voltage that shows the reverse voltage of -.777V and current of 6.122ma.  You can see where the two plots overlap (reference in red, current in green and overlap in yellow).

The minict Veikko designed is somewhat limited in current to less than 20ma and voltage of about 10V, maybe as high as 14V depending on where you calibrate it.  You can always add higher voltage transistor amps as well as a voltage divider to the base circuit.

The second file is a trace of a 2n3904 transistor.  I haven't checked the accuracy off this sweep yet.  I ran it using a script file Veikko supplied.  That is one of the more interesting features of his code.  You can generate a script file almost automatically and then edit it, etc.

« Last Edit: November 08, 2016, 09:57:39 pm by cncjerry »
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Offline Johnny10

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Re: minict curve tracer, zener diodes, etc
« Reply #5 on: November 08, 2016, 09:57:36 pm »
Ok,

Two pics..
First with curved knee is normal .633 diode drop at .2volts per division
Second is 22 V Zener at 10 volts per division and a little parallax error from iphone.


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Offline Messtechniker

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Re: minict curve tracer, zener diodes, etc
« Reply #6 on: November 08, 2016, 10:21:33 pm »
Quote from: cncjerry on November 08, 2016, 07:46:28 pm

The trace on the left is for a 2.2V and the right, 6.8V.  The little circle on the 6.8V trace shows the zener voltage at 7.004V and the 2.2V trace is actually 2.275.  Both of these voltages compare closely to a test circuit I made.

Is this typical?

Yes.
Voltages below about 5.7 V --> Zener effect.
Voltages above about 5.7 V --> avalanche  breakdown effect

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Offline Johnny10

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Re: minict curve tracer, zener diodes, etc
« Reply #7 on: November 08, 2016, 11:41:58 pm »
Looks like a pretty interesting curve tracer.
I will have to read the download.
Yes your results seem about right.
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Offline edavid

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Re: minict curve tracer, zener diodes, etc
« Reply #8 on: November 08, 2016, 11:59:07 pm »
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Offline kermitfrog

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Re: minict curve tracer, zener diodes, etc
« Reply #9 on: February 23, 2018, 02:06:53 am »
I read the QST article and had considered building one, but couldn't find any indication on where to get the software. Is it still availble on the ARRL site? Do you have a link?
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Offline Wimberleytech

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Re: minict curve tracer, zener diodes, etc
« Reply #10 on: February 23, 2018, 02:14:08 am »
Love the 575.  I am always thinking I should get one...just because.
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Offline Johnny10

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Re: minict curve tracer, zener diodes, etc
« Reply #11 on: February 23, 2018, 02:27:15 am »
Get the 400V version.

And you could probably build a tube curve tracer test jig for it also.

That is going to be a project in the future.
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Offline danadak

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Re: minict curve tracer, zener diodes, etc
« Reply #12 on: February 23, 2018, 11:03:18 am »
kermitfrog, I looked author up in qrz.com call sign database, FCC
shows his address as -

KANTO, VEIKKO A
3355 W Lobo Rd
TUCSON, AZ 85742

If you can get it please post it on this thread.

Regards, Dana.
« Last Edit: February 23, 2018, 11:10:22 am by danadak »
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Offline RolandK

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Re: minict curve tracer, zener diodes, etc
« Reply #13 on: September 12, 2019, 07:00:57 am »
The complete description of the minict can be found in this thread:
https://www.eevblog.com/forum/projects/curve-tracer-designs/msg2139304/#msg2139304
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Offline mikerj

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Re: minict curve tracer, zener diodes, etc
« Reply #14 on: September 12, 2019, 11:38:25 am »
The (minimal) homepage for the project seems to have moved to http://kc4zvw.shell.freeshells.org/project5.html
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