29
Higher Output Current Using
an External Current Buffer:
allowing sensing of the IGBT’s
saturated collector-to-emitter
HCPL-316J
To increase the IGBT gate drive
current, a non-inverting current
buffer (such as the npn/pnp
voltage, V
is “on”) and to block high
voltages (when the IGBT is “off”).
During the short period of time
when the IGBT is switching, there
is commonly a very high dV /dt
voltage ramp rate across the
IGBT’s collector-to-emitter. This
results in I
, (when the IGBT
V
16
15
CESAT
E
V
100 pF
LED2+
DESAT 14
buffer shown in Figure 75) may
be used. Inverting types are not
compatible with the desaturation
fault protection circuitry and
should be avoided. To preserve
the slow IGBT turn-off feature
during a fault condition, a 10 nF
capacitor should be connected
V
13
12
11
10
9
CC2
R
8 Ω
C
CE
V
C
10 Ω
10 nF
V
OUT
(= C
x
CHARGE
D-DESAT
V
V
EE
EE
dV /dt) charging current which
CE
will charge the blanking
capacitor, C
15 V
-5 V
from the buffer input to V and
. In order to
EE
BLANK
a 10 Ω resistor inserted between
the output and the common npn/
pnp base. The MJD44H11 /
MJD45H11 pair is appropriate
for currents up to 8A maximum.
The D44VH10 / D45VH10 pair is
appropriate for currents up to 15
A maximum.
minimize this charging current
and avoid false DESAT triggering,
it is best to use fast response
diodes. Listed in the below table
are fast-recovery diodes that are
suitable for use as a DESAT diode
Figure 74. Use of R to Further Limit
ON,PEAK
C
I
.
(D
). In the recommended
DESAT
application circuit shown in
Figure 62, the voltage on pin 14
DESAT Diode and DESAT
Threshold
(DESAT) is V
= V + V
,
CE
DESAT
F
(where V is the forward ON
F
voltage of D
IGBT collector-to-emitter
voltage). The value of V which
and V is the
DESAT
CE
The DESAT diode’s function is to
conduct forward current,
HCPL-316J
V
16
15
E
CE
100 pF
triggers DESAT to signal a
V
LED2+
FAULT condition, is nominally 7V
DESAT 14
– V . If desired, this DESAT
F
V
13
12
11
10
9
threshold voltage can be
CC2
MJD44H11 or
decreased by using multiple
DESAT diodes in series. If n is
the number of DESAT diodes
then the nominal threshold value
D44VH10
V
C
4.5 Ω
10 Ω
10 nF
V
OUT
2.5 Ω
V
V
EE
EE
MJD45H11 or
D45VH10
becomes V
= 7 V – n
CE,FAULT(TH)
x V . In the case of using two
F
15 V
-5 V
diodes instead of one, diodes with
half of the total required
maximum reverse-voltage rating
may be chosen.
Figure 75. Current Buffer for Increased Drive Current.
Max. Reverse Voltage
Rating, V (Volts)
Part Number
MUR1100E
MURS160T3
UF4007
Manufacturer
Motorola
Motorola
General Semi.
Philips
t
(ns)
75
Package Type
59-04 (axial leaded)
rr
RRM
1000
600
1000
1000
1000
600
75
75
75
75
75
Case 403A (surface mount)
DO-204AL (axial leaded)
SOD64 (axial leaded)
SOD57 (axial leaded)
SOD87 (surface mount)
BYM26E
BYV26E
BYV99
Philips
Philips
Power/Layout
Considerations
Operating Within the
Maximum Allowable Power
Ratings (Adjusting Value of
When choosing the value of R ,
The steps for doing this are:
1. Calculate the minimum desired
G
it is important to confirm that the
power dissipation of the
HCPL-316J is within the
maximum allowable power
rating.
R ;
G
2. Calculate total power
dissipation in the part
referring to Figure 77.
R ):
G
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
