AN580
Application note
Voltage to current waveform conversion,
example of the 10/700 µs surge
Introduction
CCITT members have generated a great deal of recommendations which have permitted
national administrations to publish local standards. In particular CCITT members have
defined a 10/700 µs surge waveform (see Figure 1) and its associated generator diagram
(see Figure 2).
Figure 1. CCITT 10/700 µs surge definition
V
1
0.9
t1 = 1.67
t'1 = 10 s
t2 = 700 s
0.5
0.3
0
t'1
t1
t
t2
Figure 2. Surge generator diagram
C1
20
F
R2 15
R3 25
R1
C2
50
0.2
F
It is important to note that the given standard waveform is the generator output voltage
without load. For a protection component designer the most important parameter to take into
account is the current waveform flowing through the surge suppressor. The goal of this
paper is to define the current waveform parameters.
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Waveform calculation
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Waveform calculation
1.1
Generator output voltage without load
Figure 3. Voltage rise time
v
(Vp) 1
0.9
t’1 = t(0.9) - t(0.3)
t1 = 1.67 t’1
0.3
t’1
t1
1.1.1
t
02AB0504
Rise time
The equation of this curve is:
Equation 1
v(t) = Vp (1 - exp (- t/T))  t = - T logn (1 - (v(t)/Vp))
In this case the time constant may be estimated as:
T = R2 C2
So t(0.3) and t(0.9) will be calculated respectively with v(t)/Vp = 0.3 and 0.9
t(0.3) = 1 µs
t(0.9) = 6.9 µs
and then
t1 = 1.67 (t(0.9) - t(0.1)) = 9.8 µs ≈ 10 µs
Figure 4. Voltage duration
v
(Vp) 1
0.5
t
t2
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1.1.2
Waveform calculation
Voltage surge duration
The equation of this curve is:
Equation 2
v(t) = Vp exp (- t/T))  t = - logn (v(t)/Vp))
with a time constant due essentially to R1 and C1
T = R1 C1
So t2 may be calculated with v(t)/Vp = 0.5
t2 = 693 µs ≈ 700 µs
1.2
Generator with output in short circuit
The generator output in short circuit (see Figure 5), is generally the case during the surge
suppressor action (for example the Trisil™ technogy devices from STMicroelectronics).
Figure 5. CCITT 10/700 µs generator with output in short circuit
R2
R3
i
C1
R1
C2
04AB0504
TM: Trisil is a trademark of STMicroelectronics
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Waveform calculation
1.2.1
AN580
Rise time
Figure 6. Current rise time
i
(Ip) 1
0.9
t’1 = t(0.9) - t(0.3)
t1 = 1.67 t’1
0.3
t’1
t1
t
05AB0504
Equation 1 remains true, but the time constant must take into account R3 and may be
estimated as:
T = (R2 R3/(R2 + R3)) C2
So t(0.3) = 0.67 µs and t(0.9) = 4.3 µs
Thus
t1 = 1.67 (t(0.9) - t(0.1)) = 6 µs ≈ 5 µs
1.2.2
Current surge duration
Figure 7. Current duration
i
(Ip) 1
0.5
t
t2
06AB0504
Equation 2 remains true but the time constant is now due to the capacitor C1 with the
resistor R1 in parallel with R2 + R3
T = (R1 (R2 + R3)/(R1 + R2 + R3) C1  t2 = 308 µs ≈ 310 µs
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Summary
Summary
The 10/700 µs surge waveform given by the CCITT recommendation is a voltage wave
produced by the generator in open circuit. This curve is very important as a test reference
for telecommunication equipment.
The protection function designers or users have to know the actual current waveform
flowing through the protection device in order to optimize the device.
The 10/700 µs CCITT generator gives a 5/310 µs current wave when its output is in short
circuit. (In the case of a crowbar device, for example Trisil).
For certain cases the resistor R3 is equal to zero and then the duration time becomes
160 µs.
Note that in certain documents one can find a 8/320 µs current wave which represents the
same surge test.
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Revision history
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Revision history
Table 1. Document revision history
6/7
Date
Revision
Changes
March-1993
1
First issue.
01-Jun-2004
2
Stylesheet update. No content change.
29-Jul-2014
3
Updated trademark statements.
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