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F1206A Datasheet, PDF (10/12 Pages) AVX Corporation – SMD Thin-Film Fuse
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Accu-Guard®
SMD Thin-Film Fuse
DESIGNING FOR CURRENT
PULSE SITUATIONS
1. Sine wave current pulse
The Joule integral for sine wave pulse is
[(Imax.)2 x t]/2,
see Fig. 1a.
l max.
2. Triangular current pulse
The Joule integral for triangular pulse is
[(Imax.)2 x t]/3,
see Fig. 2a.
l max.
t
Fig. 1a. Sine wave pulse parameters for Joule
integral calculation, example #1.
Thus, for the current pulse in Figure 1b, the Joule integral is
[(4.8A)2 x 7.7 x 10-6 sec]/2 = 8.9 x 10-5 A2 sec.
10 μsec/div
t
Fig. 2a. Triangular pulse parameters for Joule
integral calculation, example #2.
Thus, for the current pulse in Figure 2b, the Joule integral is
[(1.5A)2 x 3 x 10-3 sec]/3 = 2.25 x 10-3 A2sec.
2 msec/div
1A/div
0.5A/div
Fig. 1b. Sine wave pulse, example #1.
The pulse duration is 7.7μsec. We must find a fuse that can
absorb at least 8.9 x 10-5 X 2 = 1.8 x 10-4 A2sec Joule inte-
gral within 7.7 μsec without actuation. According to the I2t
graph on page 6, pre-arcing Joule integral is 2.3x10-4 A2sec
for the 0.5A fuse, which is slightly more than needed. The
next lower rating (0.375A), has only 6x10-5 A2sec, which is
not enough. Therefore, 0.5A fuse should be chosen for this
application, see Figure 1c.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
100 PRE-ARCING TIME l2t, A2 sec
10
1
10-1
10-2
0.5A
10-3
10-4
x
10-5
10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 10
PRE-ARCING TIME, sec
Fig. 1c. Choice of 0.5A fuse, example #1.
Pre-arcing I2t
Maximum I2t design rule
X I2t for sample current pulse
32
Fig. 2b. Triangular pulse, example #2.
The pulse duration is 3 msec. In the I2t graph on page 6, pre-
arcing Joule integral for 3 msec pulse is 4 x 10-3A2sec for the
0.5A fuse (not enough) and 2 x 10-2 for the 0.75A fuse (more
than enough). Therefore, 0.75A fuse should be chosen for
this application, see Figure 2c.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
PRE-ARCING TIME l2t, A2 sec
100
10
1
10-1
0.75A
10-2
10-3
x
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. 2c. Choice of 0.75A fuse, example #2.
Pre-arcing I2t
Maximum I2t design rule
X I2t for sample switch-on pulse
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