Bill:
You should test your diodes with an OHM Meter that has
a high enough test voltage to overcome the barrier
potential of approx 700mV for a silicon, and about
300mV for a germanium device.
What sort of application are you looking use it for?
For high current/voltage applications, silicon is
pretty much your only choice, as they can be made
with very high PRV (peak reverse voltage), and
higher power rating.
For small-signal use, germanium diodes work best;
they have low barrier potential and lower 'ON'
resistance (sounds like this is what you want).
Used to be, the glass diodes RS used to sell were
a mixture of both types. You can tell the difference
with a DMM that has a 'diode' test range; the DMM
will put enough voltage across the device to foreward
bias it (turn it 'on') and display the apparent
resistance of the device. Germanuim devices will have
a lower apparent resistance.
Another way would be to apply a (low) voltage across
the device with a resistor in series, and measure the
voltage across the device.
Of course, all diodes have some reverse leakage current,
and all diodes exhibit this 'barrier potential' phenomena;
the trick is to find one with a low enough 'on'
resistance that will satisfy your requirements.
I used to get diodes from RS to make crystal sets; in
those days, I found the best ones by wiring it into
the set to test it!
Jeff
On Tue, 22 Feb 2000 16:06:49 -0500 "Bill Sudbrink" <bill_at_chipware.com>
writes:
> Hi,
>
> Once again demonstrating my vast quantities of ignorance...
> I need a diode which completely blocks current in one direction
> and presents as little resistance in the other direction
> as possible. I bought a fist full of little glass ones at
> Radio Shack for 50 cents. On my Ohm meter, they show no
> conductance in one direction and 1400KOhm the other way.
> What do I need to get? RS (which is the only resource I
> have available, I need them like _NOW_) has many different
> kinds of diodes, ranging up to two dollars per pair.
>
> Thanks,
> Bill Sudbrink
>
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Received on Tue Feb 22 2000 - 16:04:35 GMT