Paul VK3DIP wrote:
John,
Thanks for the suggestion, I've got a thousand of the things so I have no
problems testing one or two to destruction. However it might take a little
while to rig up a power supply etc., I will give it a go and get back to the
group. No there are no markings at all, not even an indication of a band or
dot to mark the cathode. I too thought they looked like a rf package which
is why I bought them.

I think that the crossbar on the lead marks the cathode. I could be wrong,
of course, in which case it marks the anode.

--
Mike Andrews, W5EGO

Tired old sysadmin

From the looks of the package, Varactor or PIN diode. I think varactors
will have a 0.7 Vf possibly eliminating that, but don't recall PIN diode Vf.
Been too long...Do IR LEDS have that voltage?

Crack some open. There may be multiple die or something.

Steve K9DCI


"Paul VK3DIP" wrote in message
...
Hi all I recently purchased a bag of unmarked supposedly diodes and I am
trying to figure out what they are. The clues so far are normal diode
action on a multimeter (ie conducts one way but not the other) but the
forward voltage is high at about 1.4 - 1.5 volts. The packaging is a
small
square black plastic box with flat axial leads one of which has a small
cross
piece on it. This packaging suggests small signal or at least low power.

If anyone wants to look at the mystery diode it is the top one
in this picture.
http://www.users.bigpond.com/pmcmahon/mysterydiode.jpg
The bottom one is a normal glass 1N914 just for scale.

There is nowhere for the light to come out (or in) so they are not LEDs
which is the only other diode like component I have come across with that
high a forward voltage. Could it be two silicon diodes in series?

Any suggestions or even just identifying the case outline would be
appreciated.

Thanks
Paul VK3DIP

John A,
Spot on we have reverse breakdown at around 15 to 20 volts dependant on
current, this is obviously not a high voltage diode!!!
By the way yes the cross bar is the cathode. All the (known) varactors I
have measure a vf around the 0.6-0.7 volt and so do the PIN's I have, though
I don't have a really extensive collection of either, this is why I had
ruled them out but if you know of other examples then its sounding good.

So so far we know:
Forward Voltage ~ 1.4 -1.5 V
Reverse Voltage Breakdown ~ 15-20V
No Visible or IR light emitted.
Small Signal RF like packaging with cross bar indicating cathode.

So what is left?, 2 series 10V Zeners?

I may have to break one open and get out a microscope yet.

Paul.


"John A" wrote in message
...
Hi Paul,

That sort of "mini-L" packaging is often used for vhf components, e.g.
tuning diodes, hot carrier diodes and PIN diodes - and some of these have
forward volt-drops of more than one volt.

You can investigate that suggestion that it is a high-voltage rectifier by
applying, say, 200v reverse voltage via a 1Mohm resistor and measuring the
breakdown (if any) voltage of the diode, or what current flows. Any of the
other suggestions - including mine - will break down.

Are there definitely no markings?


John A
"Paul VK3DIP" wrote in message
...
Hi all I recently purchased a bag of unmarked supposedly diodes and I am
trying to figure out what they are. The clues so far are normal diode
action on a multimeter (ie conducts one way but not the other) but the
forward voltage is high at about 1.4 - 1.5 volts. The packaging is a
small
square black plastic box with flat axial leads one of which has a small
cross
piece on it. This packaging suggests small signal or at least low power.

If anyone wants to look at the mystery diode it is the top one
in this picture.
http://www.users.bigpond.com/pmcmahon/mysterydiode.jpg
The bottom one is a normal glass 1N914 just for scale.

There is nowhere for the light to come out (or in) so they are not LEDs
which is the only other diode like component I have come across with that
high a forward voltage. Could it be two silicon diodes in series?

Any suggestions or even just identifying the case outline would be
appreciated.

Thanks
Paul VK3DIP

I doubt that it's two series zeners, since it's no trick to make a
single zener with that breakdown voltage.

The only application I know of for series connected diodes with that
sort of breakdown voltage is for high dynamic range mixers. But the
pairs I've seen in a single package have a third pin at the junction so
you can also use them for other applications.

I wonder if it might be a low-C varactor. The very low C ones might
possibly consist of two diodes in series -- the manufacturers don't give
any clues since they don't publish any data on the forward bias
characteristics. The breakdown voltage of low C varactors is in that
ballpark, and the packaging is consistent with that possibility.

Roy Lewallen, W7EL

Paul VK3DIP wrote:
John A,
Spot on we have reverse breakdown at around 15 to 20 volts dependant on
current, this is obviously not a high voltage diode!!!
By the way yes the cross bar is the cathode. All the (known) varactors I
have measure a vf around the 0.6-0.7 volt and so do the PIN's I have, though
I don't have a really extensive collection of either, this is why I had
ruled them out but if you know of other examples then its sounding good.

So so far we know:
Forward Voltage ~ 1.4 -1.5 V
Reverse Voltage Breakdown ~ 15-20V
No Visible or IR light emitted.
Small Signal RF like packaging with cross bar indicating cathode.

So what is left?, 2 series 10V Zeners?

I may have to break one open and get out a microscope yet.

Paul.

Ok,
Both Roy and John A, have effectively suggested series HC Diodes or Low C
Varicaps.
John A has found some data for an older Motorola HC diode the MBD502 that
shows figures for Vf and VBr that are roughly similar in a roughly similar
package. Roy also suggests the possibility of a low capacitance varicap, I
suppose the way to tell would be to measure the capacitance verses reverse
voltage characteristic. If it was something like a MBD502 then the
capacitance would be pretty much constant at a low value, if it is a varicap
it could also have a low ish value but should be varying a bit. Any ideas on
a simple way to do this, I assume my classic multimeter cap range wouldn't
like a DC voltage and a diode across it, and the other simple way I can
think of of known L and a GDO seems a bit messy to measure possibly sub 1pf
values?

By the way just in case anyone else is interested the place I got these from
still says on their web site that they have some 82000 more which they are
selling for $AUS0.0055 each for 1000 minimum which comes to AUS$5.50 for the
1000 see item 31118 at www.rockby.com.au .

Paul VK3DIP



"Roy Lewallen" wrote in message
...
I doubt that it's two series zeners, since it's no trick to make a single
zener with that breakdown voltage.

The only application I know of for series connected diodes with that sort
of breakdown voltage is for high dynamic range mixers. But the pairs I've
seen in a single package have a third pin at the junction so you can also
use them for other applications.

I wonder if it might be a low-C varactor. The very low C ones might
possibly consist of two diodes in series -- the manufacturers don't give
any clues since they don't publish any data on the forward bias
characteristics. The breakdown voltage of low C varactors is in that
ballpark, and the packaging is consistent with that possibility.

Roy Lewallen, W7EL