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Accu-Guard ?
SMD Thin-Film Fuse
DESIGNING FOR CURRENT PULSE SITUATIONS (CONT.)
3. Trapezoidal current pulse
The Joule integral for a trapezoidal pulse is
[ (I min. ) 2 + I min. x (I max. - I min. ) + ( I max - I min ) 2 ] x t,
3
4. Lightning strike
A lightning strike pulse is shown in Figure 4a. After an initial
linear rise, the current declines exponentially.
see Fig. 3a.
l max.
[ ]
l max.
l min.
t
Fig. 3a. Trapezoidal pulse parameters for Joule
integral calculation, example #3.
Thus, for current pulse in Figure 3b, the Joule integral is:
{(0.56A) 2 +0.56A x (1A-0.56A)+ (1A-0.56A) 2 } x 3 x 10 -3 s = 1.9 x 10 -3 A2sec.
3
0.5 msec/div
0.51 max.
t 0.5
Fig. 4a. Lightning pulse parameters for Joule
integral calculation, example #4.
Joule integral for the linear current rise is calculated as for a
triangular pulse, see example #2.
The Joule integral for the exponential decline is
I max. 2 x t 0.5 x (-1/2In 0.5) = 0.72I max. 2 x t 0.5
Thus, for the sample lightning strike pulse in Figure 4b, the
total Joule integral is:
(25A) 2 x 2 x 10 -6 sec/3+0.72 x (25A) 2 x 10 x 10 -6 sec = 4.92 x 10 -3 A 2 sec.
10 μ sec/div
0.5A/div
5A/div
Fig. 3b. Trapezoidal pulse, example #3.
According to the I 2 t graph on page 6, the 0.5A fuse should
be chosen for this application, see Figure 3c.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
PRE-ARCING TIME l 2 t, A 2 sec
100
10
1
10 -1
Fig. 4b. Lightning strike pulse, example #4.
For practical calculations, the duration of exponential decline
may be assumed to be 3t 0.5 , because within this time 98.5%
of the pulse energy is released. Thus, the total pulse duration
in this example is 30 μsec, and the 1.25A fuse should be
chosen for this application, see Figure 4c.
FUSE PRE-ARCING JOULE INTEGRALS
vs. PRE-ARCING TIME
10 -2
10 -3
0.50A
x
100
PRE-ARCING TIME l 2 t, A 2 sec
10 -4
10
10 -5
10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1
1
10
1
10 -1
1.25A
PRE-ARCING TIME, sec
Fig. 3c. Choice of 0.5A fuse, example #3.
Pre-arcing I 2 t
10 -2
10 -3
10 -4
x
Maximum I 2 t design rule
10 -5
10 -7 10 -6 10 -5 10 -4 10 -3 10 -2 10 -1
1
10
X
I 2 t for sample switch-on pulse
PRE-ARCING TIME, sec
Fig. 4c. Choice of 0.5A fuse, example #4.
Pre-arcing I 2 t
Maximum I 2 t design rule
X
I 2 t for sample switch-on pulse
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相关代理商/技术参数
F1206A2R00FWTR3 制造商:AVX Corporation 功能描述:
F1206B0R20FSTR 功能描述:保险丝 1206 0.2AMPS SMD RoHS:否 制造商:Littelfuse 产品:Surface Mount Fuses 电流额定值:0.5 A 电压额定值:600 V 保险丝类型:Fast Acting 保险丝大小/组:Nano 尺寸:12.1 mm L x 4.5 mm W 安装风格: 端接类型:SMD/SMT 系列:485
F1206B0R20FWTR 制造商:AVX 制造商全称:AVX Corporation 功能描述:Accu-Guard, SMD Thin-Film Fuse
F1206B0R25FSTR 功能描述:保险丝 0.25A SMD RoHS:否 制造商:Littelfuse 产品:Surface Mount Fuses 电流额定值:0.5 A 电压额定值:600 V 保险丝类型:Fast Acting 保险丝大小/组:Nano 尺寸:12.1 mm L x 4.5 mm W 安装风格: 端接类型:SMD/SMT 系列:485
F1206B0R25FWTR 功能描述:保险丝 1206 2.5amp 0.06ohm SMD RoHS:否 制造商:Littelfuse 产品:Surface Mount Fuses 电流额定值:0.5 A 电压额定值:600 V 保险丝类型:Fast Acting 保险丝大小/组:Nano 尺寸:12.1 mm L x 4.5 mm W 安装风格: 端接类型:SMD/SMT 系列:485
F1206B0R37FSTR 功能描述:保险丝 1206 0.37AMPS SMD RoHS:否 制造商:Littelfuse 产品:Surface Mount Fuses 电流额定值:0.5 A 电压额定值:600 V 保险丝类型:Fast Acting 保险丝大小/组:Nano 尺寸:12.1 mm L x 4.5 mm W 安装风格: 端接类型:SMD/SMT 系列:485
F1206B0R37FWTR 功能描述:保险丝 1206 0.37AMPS SMD RoHS:否 制造商:Littelfuse 产品:Surface Mount Fuses 电流额定值:0.5 A 电压额定值:600 V 保险丝类型:Fast Acting 保险丝大小/组:Nano 尺寸:12.1 mm L x 4.5 mm W 安装风格: 端接类型:SMD/SMT 系列:485
F1206B0R50FSTR 功能描述:保险丝 1206 0.5AMPS SMD RoHS:否 制造商:Littelfuse 产品:Surface Mount Fuses 电流额定值:0.5 A 电压额定值:600 V 保险丝类型:Fast Acting 保险丝大小/组:Nano 尺寸:12.1 mm L x 4.5 mm W 安装风格: 端接类型:SMD/SMT 系列:485