tisp7072f3 Bourns, Inc., tisp7072f3 Datasheet - Page 12

• Manufacturer Part Number: tisp7072f3
• Description: Low-voltage Triple Element Bidirectional Thyristor Overvoltage Protectors
• Manufacturer: Bourns, Inc.

The output rise time is controlled by the time constant of R 2 and C 2 , which is 15 x 200 = 3000 ns or 3 µs. Virtual voltage rise times are given
by straight line extrapolation through the 30 % and 90 % points of the voltage waveform to zero and 100 %. Mathematically, this is equivalent to
3.24 times the time constant, which gives 3.24 x 3 = 9.73 which is rounded to 10 µs. Thus, the open circuit voltage rises in 10 µs and decays in
700 µs, giving the 10/700 generator its name.
When the overvoltage protector switches, it effectively shorts the generator output via the series 25 Ω resistor. Two short circuit conditions
need to be considered: single output using R 3 only (top circuit of Figure 18) and dual output using R 3 and R 4 (bottom circuit of Figure 18).
For the single test, the series combination of R 2 and R 3 (15 + 25 = 40 Ω) is in shunt with R 1 . This lowers the discharge resistance from 50 Ω to
22.2 Ω, giving a discharge time constant of 444 µs and a 50% current decay time of 309.7 µs, which is rounded to 310 µs.
For the rise time, R 2 and R 3 are in parallel, reducing the effective source resistance from 15 Ω to 9.38 Ω, giving a time constant of 1.88 µs.
Virtual current rise times are given by straight line extrapolation through the 10 % and 90 % points of the current waveform to zero and 100 %.
Mathematically, this is equivalent to 2.75 times the time constant, which gives 2.75 x 1.88 = 5.15, which is rounded to 5 µs. Thus, the short
circuit current rises in 5 µs and decays in 310 µs, giving the 5/ 310 wave shape.
The series resistance from C 1 to the output is 40 Ω giving an output conductance of 25 A/kV. For each 1 kV of capacitor charge voltage, 25 A
of output current will result.
For the dual test, the series combination of R 2 plus R 3 and R 4 in parallel (15 + 12.5 = 27.5 Ω) is in shunt with R 1 . This lowers the discharge
resistance from 50 Ω to 17.7 Ω, giving a discharge time constant of 355 µs and a 50 % current decay time of 247 µs, which is rounded to
250 µs.
For the rise time, R 2 , R 3 and R 4 are in parallel, reducing the effective source resistance from 15 Ω to 6.82 Ω, giving a time constant of 1.36 µs,
which gives a current rise time of 2.75 x 1.36 = 3.75, which is rounded to 4 µs. Thus, the short circuit current rises in 4 µs and decays in 250
µs, giving the 4/250 wave shape.
ITU-T 10/700 Generator (continued)
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
MARCH 1994 - REVISED JANUARY 2007
Lightning Surge (continued)
TISP70xxF3 (LV) Overvoltage Protector Series
20 µF
C
1
2.8 kV
V
C
10/700 GENERATOR - SINGLE TERMINAL PAIR TEST
SW
50 Ω
R
1
20 µF
C
1
5.2 kV
V
C
15 Ω
10/700 GENERATOR - DUAL TERMINAL PAIR TEST
R
2
200 nF
SW
C
2
50 Ω
R
1
APPLICATIONS INFORMATION
15 Ω
R
2
200 nF
C
2
25 Ω
R
Figure 18.
3
5/310
70 A
5/310
70 A
T AND G
T
TEST
25 Ω
25 Ω
R
R
G
3
4
R
190 A
4/250
4/250
95 A
T AND G,
R AND G
T
DUAL
R AND G
TEST
R
4/250
95 A
TEST
G
G
R
T
R AND T
TEST
R
T
G