Scientific 5000 Series, Руководство пользователя

Страница: 257 / 360

APPENDIX F
MODEL 5000 SERIES MANUAL
Version 1.23
13-17
Figure 13-5 Holding Current Characteristic
V
D
, R
L
, I
GT
and I
H
are entries made in the test program, the initial current is
determined by V
D
and R
L
. The gate current is pulsed and then removed. V
D
is
lowered until I
AK
reaches the I
H
value entered or until the thyristor drops out. The test
passes if the thyristor stays on (fails to drop out).
In the test conditions specified by G.E. for this method, it is recommended that V
D
not
be reduced below 6 volts. This condition requires that R
L
be a value that will
maintain V
D
above 6 volts at the lowest expected holding current.
The reason for this condition is that the holding current will vary somewhat as the
load line is varied. This effect is most significant at lower values of V
AK
. This can be
seen by visualizing a vertical load line (R
L
= 0) and reducing V
AK
until the vertical line
is tangent to the thyristor characteristic. The holding current is highest under this
condition.
The holding current then does vary somewhat with anode load; but then, anode loads
vary with applications. It may be important in some cases to test holding current with
the anode load used in a specific application. It is possible to do this with the 5000
Series tester.
If the anode load for a specific application is not known, use an R
L
that gives a V
D
of
approximately 6 volts for the minimum expected holding current. It is recommended
that the V
D
entry for this condition in the 5000 Series Tester be at least 24 volts. This
assures sufficient initial current to cause the device to latch.
MOSFET V
GSF
and V
GSR
Tests
CAUTION: In holding tests, initial current is limited
only by R
L
. Use a value sufficiently high to limit the
initial current to no more than 6 amps.