MERCURY
SWITCH
S1
MUR8100E, MUR880E
+VDD
IL
40 mH COIL
VD
ID
IL
DUT
t0
BVDUT
ID
VDD
t1
t2
t
Figure 6. Test Circuit
Figure 7. Current−Voltage Waveforms
The unclamped inductive switching circuit shown in
Figure 6 was used to demonstrate the controlled avalanche
capability of the new “E’’ series Ultrafast rectifiers. A
mercury switch was used instead of an electronic switch to
simulate a noisy environment when the switch was being
opened.
When S1 is closed at t0 the current in the inductor IL ramps
up linearly; and energy is stored in the coil. At t1 the switch
is opened and the voltage across the diode under test begins
to rise rapidly, due to di/dt effects, when this induced voltage
reaches the breakdown voltage of the diode, it is clamped at
BVDUT and the diode begins to conduct the full load current
which now starts to decay linearly through the diode, and
goes to zero at t2.
By solving the loop equation at the point in time when S1
is opened; and calculating the energy that is transferred to
the diode it can be shown that the total energy transferred is
equal to the energy stored in the inductor plus a finite amount
of energy from the VDD power supply while the diode is in
breakdown (from t1 to t2) minus any losses due to finite
component resistances. Assuming the component resistive
elements are small Equation (1) approximates the total
energy transferred to the diode. It can be seen from this
equation that if the VDD voltage is low compared to the
breakdown voltage of the device, the amount of energy
contributed by the supply during breakdown is small and the
total energy can be assumed to be nearly equal to the energy
stored in the coil during the time when S1 was closed,
Equation (2).
The oscilloscope picture in Figure 8, shows the
MUR8100E in this test circuit conducting a peak current of
one ampere at a breakdown voltage of 1300 V, and using
Equation (2) the energy absorbed by the MUR8100E is
approximately 20 mjoules.
Although it is not recommended to design for this
condition, the new “E’’ series provides added protection
against those unforeseen transient viruses that can produce
unexplained random failures in unfriendly environments.
EQUATION (1):
ǒ Ǔ WAVAL
[
1
2
LI
2
LPK
BVDUT
BVDUT–VDD
CH1 500V
CH2 50mV
A 20ms 953 V VERT
CHANNEL 2:
IL
0.5 AMPS/DIV.
EQUATION (2):
WAVAL
[
1
2
LI
2
LPK
CHANNEL 1:
VDUT
500 VOLTS/DIV.
CH1
1 ACQUISITIONS
SAVEREF SOURCE
217:33 HRS
STACK
CH2
REF
REF
TIME BASE:
20 ms/DIV.
Figure 8. Current−Voltage Waveforms
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