TISP61089A
DUAL FORWARD-CONDUCTING P-GATE THYRISTORS
PROGRAMMABLE OVERVOLTAGE PROTECTORS
JUNE 1999
In Figure 6, the positive gate charge (Q
GS
) is about 0.1 µC which, with the 0.1 µF gate decoupling capacitor
used, increased the gate supply by about 1 V (= Q
GS
/C1). This change is just visible on the -72 V gate
voltage, V
BAT
. This increase does not directly add to the protection voltage as the supply voltage change
reaches a maximum at 0.4 µs when the gate current reverses polarity; whereas the protection voltage peaks
at 0.3 µs. In Figure 6, the peak clamping voltage (V
(BO)
) is -77.5 V, an increase of 5.5 V on the nominal gate
supply voltage. This 5.5 V increase is the sum of the supply rail increase at that time, (0.5 V), and the
protection circuits cathode diode to supply rail breakover voltage (5 V). In practice, use of the recommended
220 nF gate decoupling capacitor would give a supply rail increase of 0.25 V and a V
(BO)
value of about
-77.25 V.
0
-20
Voltage - V
VK
VBAT
-40
-60
-80
0.0
0.5
Time - µs
1
0
Current - A
-1
-2
-3
-4
-5
0.0
0.5
Time - µs
1.0
1.5
IK
QGS
1.0
1.5
IG
Figure 6. PROTECTOR FAST IMPULSE CLAMPING AND SWITCHING WAVEFORMS
application circuit
and Tip (T), connect to the relay matrix via the series overcurrent protection. Fusible resistors, fuses and
positive temperature coefficient (PTC) resistors can be used for overcurrent protection. Resistors will reduce
the prospective current from the surge generator for both the TISP61089A and the ring/test protector. The
TISP7xxxF3 protector has the same protection voltage for any terminal pair. This protector is used when the
ring generator configuration may be ground or battery-backed. For dedicated ground-backed ringing
generators, the TISP3xxxF3 gives better protection as its inter-conductor protection voltage is twice the
conductor to ground value.
PRODUCT
INFORMATION
7
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