What's this component?

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

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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

Reply to
Wipf
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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.

Reply to
tm

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

Reply to
Wipf

I can trace the wiring right through the board in your excellent photo. They HAVE to be the rectifier diodes, but due to the application, they may be multiple stacked dies to get more reverse Voltage. That may defeat your meter.

Jon

Reply to
Jon Elson

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

Reply to
tm

Try something RX 1K or higher to get more voltage. Depends on the meter, some have nine volt batteries on high ohms.

Greg

Reply to
gregz

if you have a simpson 260, there is enough voltage to get the meter to move a bit ;)

Cheers

Reply to
Martin Riddle

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.

Reply to
tm

On a sunny day (Wed, 3 Oct 2012 15:31:13 -0500) it happened Wipf wrote in :

That looks like a voltage multiplier, must be diodes. Some diodes do not simple measure .7 V or as 'diode', some HV diodes are in fact many diodes in series, and would not show any reading, this looks like Ge diodes, if so would read a lot lower and perhaps leak in reverse. Take one out and show us some numbers (I versus U).

Reply to
Jan Panteltje

Multiple-pellet stabistors.

Lord Valve

Reply to
Lord Valve

That is called a "nomenclature".

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Many thanks, 

Don Lancaster                          voice phone: (928)428-4073 
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Reply to
Don Lancaster

I can do that. It sounds like that's the consensus on them. I wasn't aware that HV diodes had such a large Vf. Thanks David

Reply to
Wipf

reverse.

I have posted curves here, the Vf is about 12 V at 20 mA but the curve is non exponential.

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(log)
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(linear)

For comparison, also the 1N4005 diode and a BYV-27-200 Avalance diode also on the board.

Reply to
Wipf

for a

could

multiplier

(maybe

a bit ;)

I blew out a large photodiode with a triplet. I was able to see the contact wire blown like a fuse.

Greg

Reply to
gregz

On a sunny day (Thu, 4 Oct 2012 17:24:38 -0500) it happened Wipf wrote in :

reverse.

Very nce, indeed looks like diodes in series, because of the high value where it starts conducting. The old TV HV diodes (for 4 kV focus, and also 18kV BW), had many small selenium? disks in series in a ceramic tube, I opened one once that was defective, lots of small round disks.

Very nice measurements, reminds me of my student time... :-)

Reply to
Jan Panteltje

could

multiplier

(maybe

a>>>> X3

move a bit ;)

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

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

multiplier

(maybe

a>>>> X3

move a bit ;)

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

Reply to
gregz

supplies>>>> > for a

multiplier

a>>>> X3

about

in

move a bit ;)

Oops.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

supplies>>>> > for a

multiplier

a>>>> X3

about

in

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

Greg

Reply to
gregz

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