Avtech AVR-EB4-B, Инструкция по эксплуатации

Страница: 26 / 83

words, the I
REVERSE
/
IFORWARD
ratio is irrelevant). The capacitance may be so small that it
becomes impossible to obtain the full -4 Amps of reverse current.
Normally, the forward and reverse amplitudes should be set near the maximum values
(+100V, -200V). Performance may degrade if the amplitudes are set lower than 10% of
the maximum values.
AMPLITUDE ACCURACY
Due to the variations in V
F
and R
DIODE-FORWARD
and R
DIODE-REVERSE
as a function of operating
conditions, the AMP1 and AMP2 settings should not be relied upon for any degree of
accuracy . Instead the voltage at the OUT terminal on the test jig should be monitored
with a calibrated oscilloscope. As mentioned above, I
DUT
= V / 5Ω.
It is particularly important that the oscilloscope's parasitic DC offset be properly nulled.
A non-zero offset can introduce significant errors in calculating I
REVERSE
/ I
FORWARD
, leading
to errors in the measured recovery time.
R
A
and R
B
can be measured directly on the test jig (with the test jig disconnected) to
determine calibrated relationships, if desired. R
C
is provided by the user, and can be
calibrated as required.
INCORRECT ORIENTATION
The instrument and the DUT will not be damaged if the diode is installed with the
incorrect orientation (i.e., with the anode and cathode reversed). However, incorrect
waveforms will be generated,
CABLE LENGTHS
The test jig is connected to the mainframe using two cables:
1) A 2-meter-long DB-9 control cable
2) A coaxial cable.
The length of the coaxial cable affects the measured waveform slightly. The cable
length should be chosen based on the type of diode that will be tested.
Normally, the 60 cm / 2 foot-long coaxial cable should be used, except when
reflections are observed on the output waveform.
However, diodes with extremely short recovery times (< 10 ns), like ultra-fast Schottky
diodes, or diodes with “step recovery” or “hard switching” characteristics, may generate
noticeable reflections after the end of the reverse transient. If these reflections overlap
with the transient itself, a longer cable should be used. This will increase the period of
26