32

Fig. 2c. Choice of 0.75A fuse, example #2.

SMD Thin-Film Fuse

t

l max.

Fig. 1a. Sine wave pulse parameters for Joule

integral calculation, example #1.

Thus, for the current pulse in Figure 1b, the Joule integral is

The pulse duration is 7.7μsec. We must find a fuse that can

for the 0.5A fuse, which is slightly more than needed. The

not enough. Therefore, 0.5A fuse should be chosen for this

application, see Figure 1c.

FUSE PRE-ARCING JOULE INTEGRALS

vs. PRE-ARCING TIME

2. Triangular current pulse

The Joule integral for triangular pulse is

see Fig. 2a.

Fig. 2a. Triangular pulse parameters for Joule

integral calculation, example #2.

t

l max.

Thus, for the current pulse in Figure 2b, the Joule integral is

Fig. 1b. Sine wave pulse, example #1.

Fig. 2b. Triangular pulse, example #2.

than enough). Therefore, 0.75A fuse should be chosen for

this application, see Figure 2c.

FUSE PRE-ARCING JOULE INTEGRALS

vs. PRE-ARCING TIME

0.75A

PRE-ARCING TIME, sec

100

10

1

110

x

X

10 μsec/div

1A/div

2 msec/div

0.5A/div

0.5A

PRE-ARCING TIME, sec

100

10

1

110

x

X

Fig. 1c. Choice of 0.5A fuse, example #1.

DESIGNING FOR CURRENT

PULSE SITUATIONS

1. Sine wave current pulse

The Joule integral for sine wave pulse is

[(I

see Fig. 1a.