why when i use my multimeter on diode test does a Schottky barrier dio
why when i use my multimeter on diode test does a Schottky barrier dio
(OP)
why when i use my multimeter on diode test does a Schottky barrier diode measure only 1v in the reverse direction. forward biased it measures less than 0.2v
and it is for this low forward volt drop that i wanted to use it but was expecting it to measure o/c or 3v as is normally shown on my meter when testing a normal diode?
and it is for this low forward volt drop that i wanted to use it but was expecting it to measure o/c or 3v as is normally shown on my meter when testing a normal diode?





RE: why when i use my multimeter on diode test does a Schottky barrier dio
You know nothing is perfect.. Schottkys have great Vf but horrible reverse leakage current values that can get up to tens of mA. Your multimeter will easily measure something in that direction as it wouldn't with a regular diode.
As you run up the PIV ratings on Schottkys the reverse leakage current plummets down to microamps. But, BUT! if the diode's temperature is raised the leakage will go up rapidly into the mA again.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: why when i use my multimeter on diode test does a Schottky barrier dio
a diode was previously put in series with the drive to prvent this because it appears to fault the drive. as it likes to see a reference of 0-10v. this works but i have found recently that the opperating range of the reference is between about 1v and 3v this makes the volt drop quite critical 0.7v reduced to 0.2v sounds good enough for what i want to achive what do you think will the high leakage current prevent me from achieving what i am tring to?
thanks for the reply
RE: why when i use my multimeter on diode test does a Schottky barrier dio
But to move on, I understand that you want to drop less if you can.
Well the Schottky will definitely do that though often it is more than 0.2, often more like 0.3, or 0.4V. But anyway what will happen is during the reset there may be some leakage out of your drive back to the PLC during its poor behavior moment thru that Schottky. The question is will the current limiting of the diode be enough to prevent whatever is happening to your drive during these negative excursions.
Can you just try it? I suspect it will work fine.
What is the ambient temperature that this Schottky will be at? If it's less than ~35C it will likely work fine. If it is in a hot application you may have to do more. An important number to this all is the current the drive consumes into this 'reference'. Can you measure that? If it is really a small amount then you can add a resistor that limits the leakage more while not effecting the drive's reference. If there is a sizable amount of current then that won't work.
You may also be able to run a diode from your drive 0.0V (ground?) pointing to the reference line. Then when the PLC goes negative the drive will source current from its ground back to the PLC thru the original Schottky rather than having the drive's reference sourcing the current and not liking it.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: why when i use my multimeter on diode test does a Schottky barrier dio
RE: why when i use my multimeter on diode test does a Schottky barrier dio
But, still. That kind of shottky should work quite well.
Gunnar Englund
www.gke.org
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RE: why when i use my multimeter on diode test does a Schottky barrier dio
RE: why when i use my multimeter on diode test does a Schottky barrier dio
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Question: Is it a power shottky you are using? Those have rather high leakage, as smoked says. You should use a small one (same body as a normal 1N4148 etc) for your application. The BAT 42 is a signal shottky - not a power shottky.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: why when i use my multimeter on diode test does a Schottky barrier dio
http:/
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: why when i use my multimeter on diode test does a Schottky barrier dio
The series resistor will create a voltage divider between it and the VFD resistance but it will be constant (10k VFD and 100 ohms series resistor give 99% voltage for example).
Make sure the diode and the PLC output can both handle the current that will flow when at -10V. This is dictated by the added resistor.
Then, you don't need to worry about the series diode drops or reverse leakage current. I hope that makes sense.
RE: why when i use my multimeter on diode test does a Schottky barrier dio
quite like the idea from lionelhutz will try this also as i am interested ion the outcome of both
thanks for your help im learning all the time!
RE: why when i use my multimeter on diode test does a Schottky barrier dio
Perhaps a picture.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: why when i use my multimeter on diode test does a Schottky barrier dio
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this is a bat86 diode seems to fit the low reverse leakage current and low forward volt drop that we have talked about
seem you were right the schotty i have been using has a comparitively high reverse leakage current 7ma at 25c
thanks again
RE: why when i use my multimeter on diode test does a Schottky barrier dio
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: why when i use my multimeter on diode test does a Schottky barrier dio
RE: why when i use my multimeter on diode test does a Schottky barrier dio
In the first picture it probably doesn't have to be a Schottky diode. Something as simple as a 1N4007 would probably work.
RE: why when i use my multimeter on diode test does a Schottky barrier dio
Actually his drive could have the input latching because of the protection diodes inside whatever the input device is. So you probably would want a Schottky in the hopes of your external one conducting before the internal one does. This is because the internal ones are always Schottkys.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com