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From: gregz <ze...@comcast.net>
Newsgroups: sci.electronics.design
Subject: Re: What's this component?
Date: Sat, 6 Oct 2012 03:09:10 +0000 (UTC)
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Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:
> gregz wrote:
>> 
>> Phil Hobbs <pcdhSpamMeSensel...@electrooptical.net> wrote:
>>> On 10/04/2012 07:03 PM, gregz wrote:
>>>> "tm"<No_one_h...@white-house.gov>  wrote:
>>>>> "Martin Riddle"<martin_...@verizon.net>  wrote in message
>>>>> news:k4ikj9$h87$1@dont-email.me...
>>>>>> 
>>>>>> "tm"<No_one_h...@white-house.gov>  wrote in message> 
>>>>>> news:k4ihfm$21j$1@dont-email.me...
>>>>>>> 
>>>>>>> "Wipf"<w...@ra.msstate.edu>  wrote in message>>
>>>>>>> news:MPG.2ad67594af3d77fd989681@nntp.msstate.edu...
>>>>>>>> In article<k4ia3a$ip...@dont-email.me>, No_one_h...@white-house.gov
>>>>>>>> says...
>>>>>>>>> 
>>>>>>>>> "Wipf"<w...@ra.msstate.edu>  wrote in message
>>>>>>>>> news:MPG.2ad65c8e633299d3989680@nntp.msstate.edu...
>>>>>>>>>> 
>>>>>>>>>> Hi,
>>>>>>>>>> I'm a lurker here and I thought I'd ask for some help.  I have a few
>>>>>>>>>> boards I saved from the trash that appear to be little HV supplies>>>>  >  for a
>>>>>>>>>> mass spectrometer.  I was trying to trace through the circuit and>>>>  >  could
>>>>>>>>>> not figure out what these components were on the (presumably)>>>>  >  multiplier
>>>>>>>>>> part of the circuit. A picture is here
>>>>>>>>>> http://www.flickr.com/photos/dwipf/8051484989/in/photostream
>>>>>>>>>> They look like diodes but don't read as diodes on my multimeter>>>>  >  (maybe
>>>>>>>>>> because they are in circuit). They are marked as 00B or OOB which
>>>>>>>>>> doesn't seem to be any diode code that I can find.
>>>>>>>>>> 
>>>>>>>>>> Any thoughts?
>>>>>>>>>> 
>>>>>>>>>> Thanks
>>>>>>>>>> David
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> It is a HV multiplier. A X3 positive multiplier on the left side and a>>>>  X3
>>>>>>>>> negative multiplier on the right.
>>>>>>>>> 
>>>>>>>>> Look up Cockcroft-Walton multiplier on google for much more detail.
>>>>>>>> 
>>>>>>>> Thanks, I think it is a multiplier but my question is specifically about
>>>>>>>> the "diodes" marked 00B. I couldn't find any info on their specs and, in
>>>>>>>> fact, don't read as diodes using my DMM.
>>>>>>>> 
>>>>>>>> David
>>>>>>> 
>>>>>>> They are high voltage diodes and have a large forward voltage drop.
>>>>>>> Maybe>>  up to 10 volts or so. They are made up of many series diode
>>>>>>> junctions in>>  order to get the high reverse voltage needed.
>>>>>>> 
>>>>>>> Try forward biasing to diode through a current limiting resistor with
>>>>>>>>> maybe 24 volts and 10 k ohms. Measure the forward voltage drop
>>>>>>>>> across the>>  diode. You can do this in circuit.
>>>>>>> 
>>>>>>> Tm
>>>>>>> 
>>>>>> 
>>>>>> if you have a simpson 260, there is enough voltage to get the meter
>>>>>> to>  move a bit  ;)
>>>>>> 
>>>>>> Cheers
>>>>>> 
>>>>>> 
>>>>>> 
>>>>> 
>>>>> Those little diodes don't have very many junctions so you would be right.
>>>>> Some of the>10 kV diodes drop 10 -15 volts (or more) forward. I still
>>>>> use my 260 but you need to be careful. It can do a pretty high current
>>>>> for some solid state devices now days.
>>>> 
>>>> I blew out a large photodiode with a triplet. I was able to see the contact
>>>> wire blown like a fuse.
>>>> 
>>>> Greg
>>> 
>>> Photodiodes are often much more vulnerable than one would expect from
>>> their size, because the epi has to be so thin that transverse voltage
>>> drops give rise to current crowding near the contact.  "Blue enhanced"
>>> ones are worse than the ordinary sort.
>>> 
>>> The best way to measure photodiode polarity is to look for the
>>> photovoltage.  Second best is to measure the photocurrent.
>>> 
>>> Cheers
>>> 
>>> Phil Hobbs
>> 
>> I measured the short circuit on r1 on the triplet. 100 ma.
>> The owner of the diode sort of frowned when I discussed what happened.
>> 
>> Greg
> 
> Oops.  
> 
> Cheers
> 
> Phil Hobbs

I'm glad I never tried that on the 16 X 16 matrix centronix sensor we used.

Greg