From: jjk439@gmail.com
On Wednesday, October 23, 2013 10:34:04 PM UTC-4, Tom Biasi wrote:
> On 10/23/2013 6:52 PM, jjk wrote:
>
> > On Tuesday, October 22, 2013 11:12:24 AM UTC-4, Tom Biasi wrote:
>
> >> On 10/22/2013 8:59 AM, jjk wrote:
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> >>
>
> >>> On Sunday, October 20, 2013 2:27:14 PM UTC-4, Tom Biasi wrote:
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> >>
>
> >>>> On 10/20/2013 2:04 PM, Fred McKenzie wrote:
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> >>>>
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> >>>>> In article ,
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> >>>>
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> >>>>> jjk wrote:
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> >>>>
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> >>>>>
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> >>>>
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> >>>>>> Zener Diode Dilemma
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> I purchased 50 1N4728 3.3v Fairchild zener diodes and trying to test
them
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> >>>>
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> >>>>>> before installing in a circuit I'm building.
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> The diode test function on my meter shows 0.6v forward biased and .9v
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> >>>>
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> >>>>>> reversed biased. Performing the same tests on a 5.6v zener, I get 0.6v
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> >>>>
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> >>>>>> forward biased and when reversed biased I see the same reading as not
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> >>>>
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> >>>>>> connected to the diode at all - which is what I would expect.
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> Further, I inserted the diodes in a test circuit described below.
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> vcc -> 560 ohm resistor -> milliamp meter -> zener cathode, zener
anode to
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> >>>>
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> >>>>>> ground.
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> When vcc voltage was applied, current was measured as shown below
with the
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> >>>>
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> >>>>>> diode conducting all the time, and I could never get the voltage
across the
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> >>>>
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> >>>>>> zener to reach 3.3v without smoking the resistor.
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> 1.5v 0.1mA
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> >>>>
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> >>>>>> 2.0v 0.6mA
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> >>>>
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> >>>>>> 2.5v 1.1mA
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> >>>>
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> >>>>>> 2.7v 1.5mA
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> >>>>
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> >>>>>> 2.9v 1.7mA
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> >>>>
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> >>>>>> 3.0v 1.8mA
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> All of the 3.3v parts I tested exhibited the same behavior.
Suspecting a bad
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> >>>>
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> >>>>>> lot of diodes I purchased a few 3.3v diodes made by NTE. They all too
exhibit
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> >>>>
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> >>>>>> the same behavior - conducting well before their breakdown voltage.
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> >>>>
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> >>>>>>
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> >>>>
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> >>>>>> Trying the above with a 5.6v zener shows no current flow until the
voltage
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> >>>>
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> >>>>>> across the diode reached the device rated breakdown voltage. I also
put a
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> >>>>
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> >>>>>> scope on the power supply to verify it was stable.
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> >>>>
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> >>>>>
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> >>>>
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> >>>>> JJK-
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> >>>>
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> >>>>>
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> >>>>
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> >>>>> Plotting your Voltage vs current data suggests you may be measuring the
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> >>>>
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> >>>>> forward-bias curve of several diode junctions connected in series. (It
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> >>>>
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> >>>>> looks more like a constant-Voltage curve than constant-current.)
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> >>>>
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> >>>>>
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> >>>>
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> >>>>> The only 3.3 Volt Zener in my collection is a 1N5575A. It checks good
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> >>>>
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> >>>>> as a diode on the diode ranges of a Fluke 8020A multimeter. I did not
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> >>>>
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> >>>>> run your current vs Voltage test, but would expect it to behave as well
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> >>>>
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> >>>>> as your 5.6 Volt test.
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> >>>>
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> >>>>>
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> >>>>
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> >>>>> I wonder if both your source of the 1N4728 diode and NTE, get their
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> >>>>
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> >>>>> diodes from the same factory? There could have been a batch that were
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> >>>>
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> >>>>> mis-labeled, or they could have fallen victim to counterfeit parts.
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> >>>>
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> >>>>>
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> >>>>
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> >>>>> Fred
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> >>>>
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> >>>>>
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> >>>>
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> >>>> The curve is linear until he gets to 2.7 volts then there is a bump
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> >>>>
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> >>>> (reading error?). This looks like a forward conducting diode and the
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> >>>>
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> >>>> readings are across the resistor.
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> >>>
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> >>>
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> >>> Thanks to all who replied.
>
> >>
>
> >>> There is definitely very wrong. I just took delivery of 50 Fairchild
replacement zeners and reran my tests to verify, this time using a 330 ohm
resistor. The results are below for both 3.3v and 5.6v parts. The 5.6v part
works as expected and doesn'
t conduct until the avalanche voltage is approached whereas the 3.3v part is
still exhibiting the wrong behavior. I had to raise vcc to 25v to see 3.3v at
the cathode, then the magic smoke came out of the resistor. :)
>
> >>
>
> >>>
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> >>
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> >>> vcc -> 330 ohm resistor -> milliamp meter -> zener cathode, zener anode
to ground.
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>
> >>> 330 ohm resistor measures 327 ohms
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>
> >>>
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>
> >>> 1N4728A 3.3v 1W Zener diode
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>
> >>>
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>
> >>> Iz
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> >>> vcc (mA) Vzener
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>
> >>> 1.5 0.2 1.42
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> >>
>
> >>> 2.0 0.8 1.72
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> >>> 2.5 1.7 1.91
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> >>> 3.0 2.8 2.05
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> >>> 3.5 4.1 2.16
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> >>> 4.0 5.3 2.24
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> >>> 4.5 6.6 2.3
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> >>> 5.0 8.0 2.37
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> >>
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> >>> 5.5 9.4 2.43
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> >>
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> >>> 6.0 10.8 2.48
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> >>> 7.0 13.6 2.56
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> >>> 8.0 16.5 2.62
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> >>> 9.0 19.4 2.69
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> >>> 10.0 22.4 2.73
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> >>> 20.0 55.2 3.1
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> >>> 25.0 71.3 3.3
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> >>>
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> >>>
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> >>> 1N752 5.6v zener diode
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> >>>
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> >>> Iz
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> >>> vcc (mA) Vzener
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> >>> 1.5 0 1.5
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> >>> ... ... ...
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> >>
>
[continued in next message]
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* Origin: you cannot sedate... all the things you hate (1:229/2)
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