Re: 1N3718 tunnel diode testing (475 scope trigger TD)


k1ggi
 

I dont quite see how you managed to exceed Ip with 1k and 2.5V. Could you explain what drive you adjusted?
Until you exceed Ip, the TD is going to look like a low-ohm resistor.
Ed

--- In TekScopes@yahoogroups.com, "cybertheque_museum" <msg.together@...> wrote:

Greetings:

It is difficult to accept that all four tunnel diodes in my recently acquired 475 scope are shorted but that is what the I am seeing with a kludged curve tracer and DMM resistance check. How likely is it that all four are bad? The curve tracer is just a 1kohm resistor from ground to the cathode of the TD under test with the anode driven directly from a -2.5 to +2.5 V triangle wave generator (about 600 ohm output Z) to ground and the X axis of the monitor scope connected between ground and the function generator and the y axis between ground and the high side of the resistor (the monitor scope is not ground isolated so I cannot look directly across the TD junction).

Substituting a convention PN diode and also a Schottky diode for the TD shows the usual knee on the monitor scope. The data for the 1N3718 are:

IsubP = 10 ma
IsubV = 1.3 ma
VsubP = 65 mv
VsubV = 350 mv

I adjusted the drive to cover these ranges. The displayed curve is just a diagonal line with a slope of 1.

Michael

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