FEC200 ZZK and ZZT Tests
These test names are synonyms. Both tests measure the impedance in the knee region of zener diodes and express the results Ohms (or K Ohms).
The steady state forcing current (a pulse) is modulated with a 1KHZ sinewave whose amplitude is 10% RMS of the steady state forcing current. The resulting 1KHZ voltage across the zener is then measured, then the Impedance is calculated and reported.
The program needs to know the maximum VZ expected so that it can use an appropriate scale. You can enter this data as in the example below.
- TESTn ZZT 10MA 25V <10R
(use R or KR for limit impedance)
MAXX uses a preset amount of time to stabilize the forcing conditions before turning on the modulation. The number of cycles of modulation is controlled by the SOAK TIME. Usually the default SOAK TIME is appropriate but you can increase it if you wish as follows.
- TESTn ZZT 10MA 25V <10R T24
ZZT, ZZK, and similar test EZT and EZK measure a very small AC voltage riding on a forcing pulse which is typically 1,000 to 10,000 times larger. In addition, the signal is sometimes obscured by noise (particularly in certain parts measured at about 250ľA).
Sometimes the slope of the zener characteristic at low currents is negative.
For these reasons this is sometimes a very difficult test to perform. The circuits used in the FEC200 are chosen to deal with these problems effectively. We have compared our results with a number of competitors' and some in-house bench tests. Our results in the most difficult cases have been very favorable. There are some diodes however that are, shall we say "a challenge." Please feel free to discuss this with us to keep up with the latest developments.
Also it is very important to realize that calibrating this test with a resistor does not necessarily prove that it will read a zener diode correctly.