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F1206A Datasheet, PDF (12/12 Pages) AVX Corporation – SMD Thin-Film Fuse
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Accu-Guard®
SMD Thin-Film Fuse
DESIGNING FOR CURRENT PULSE SITUATIONS (CONT.)
5. Complex current pulse
If the pulse consists of several waveforms, all of them should
be evaluated separately, and then the total Joule integral
should be calculated as well.
6. Switch-on pulse and steady-state current
In Figure 6a, the switch-on pulse is a triangle pulse with a
5.1 x 10-3 A2sec Joule integral of 5 msec duration; the 0.75A
fuse will meet this requirement, see Figure 6b.
200 μsec/div
2 msec/div
2A/div
0.5A/div
Fig. 5a. Complex pulse, example #5.
In Figure 5a, the Joule integral for the first triangle is
[(4.67A)2 x 294 x 10-6sec]/3=2.14 x 10-3 A2sec
and 0.75A fuse should meet this condition, see Figure 5b.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
100 PRE-ARCING TIME l2t, A2 sec
10
1
10-1
0.75A
10-2
10-3
xx
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10
PRE-ARCING TIME, sec
Fig. 5b. Choice of fuse, example #5.
Pre-arcing I2t
Maximum I2t design rule
X I2t for sample switch-on pulse
The Joule integral for the second triangle is
[(5.33A)2 x 269 x 10-6sec]/3 = 2.55 x 10-3 A2sec, and
0.75A fuse is suitable for this case also, see Figure 5b.
However, for the whole pulse, the Joule integral is
4.7 x 10-3 A2sec, and the total duration is 563 μsec. For the
0.75A fuse, the Joule integral is only 8.6 x 10-3 A2sec for this
pulse duration, so the 1A fuse should be chosen for this
application, see Figure 5b.
Fig. 6a. Switch-on pulse and steady-state current,
example #6.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
100 PRE-ARCING TIME l2t, A2 sec
10
1
10-1
0.75A
10-2
x
10-3
10-4
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10
PRE-ARCING TIME, sec
Fig. 6b. Choice of 0.75A fuse, example #6.
Pre-arcing I2t
Maximum I2t design rule
X I2t for sample switch-on pulse
The steady-state current is 0.5A, and 1A fuse is typically rec-
ommended to meet the steady-state condition. Based on
steady-state current, the 1A fuse should be chosen for this
application.
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