Simple model of Fuse(LTspice)

FuseSimplified SPICE Behavioral Model

All Rights Reserved Copyright (C) Bee Technologies Corporation 2011 1

Contents

1.Benefit of the Model

2.Model Feature

3.Parameter Settings

4.Fuse Specification (Example)

5.Fusing Time vs. DC Current

6.Fusing Time vs. Current Pattern

7.Specific Fuse Model

Library Files and Symbol Files Location

Simulation Index


1. Benefit of the Model

• Easily create your own fuse models by setting a few parameters, that’s usually provided by the manufacturer’s datasheet.

• Enables circuit designer to safely test and optimize their circuit protection design, and to predict component and circuit stress under extreme conditions (e.g. at the fuse blow).

• The model is optimized to reduce the convergence error.


2. Model Feature

The model accounts for:

• Current Rating

• Fuse Factor

• Internal Resistance

• Normal Melting I2t

Enable the model to simulate fusing time (blow time) as a function of I2t.

The model can be used for testing the blow time for the different current pattern.

A one-shot switch, once fuse is opened it cannot be closed.


Fig.1 Fusing Time vs. Fusing Current Characteristic

0.001

0.01

0.1

1

10

0.1 1 10 100

Fu

sin

g T

ime

(S

ec

.)Fusing Current (A)

3. Parameter Settings

Irate = the current rating of fuse [A]

FF = Fusing Factor, the ratio of the minimum fusing current (the current that fuse start to heat up) to Irate.

(e.g. Irate =400mA and the minimum fusing current is 620mA then FF = 620m/400m = 1.55)

Rint = internal resistance of fuse

I2t = Normal Melting value [A2, seconds]

• From the fuse specification, the model is characterized by setting parameters Irate, FF, Rint and I2t.


Model Parameters:

Fig.2 Fuse model with default parameters

IRATE = 400mFF = 1.55RINT = 650mI2T = 0.024

0.001

0.01

0.1

1

10

0.1 1 10 100

Fu

sin

g T

ime

(S

ec

.)

Fusing Current (A)

4. Fuse Specification (Example)

Fig.3 Shows the complete setting of fuse model parameters by using data from the datasheet of CCF1N0.4 provided by KOA Speer Electronics, Inc.


Part No.Current Rating (mA)

Internal R. max.

(m)

I2t (A2, seconds

)

CCF1N0.4 400 650 0.024

the minimum fusing current is 620mA, FF = 20m/400m = 1.55

IRATE = 400mFF = 1.55RINT = 650mI2T = 0.024

5. Fusing Time vs. DC Current

• The simulation result shows the fusing times, tF, (the time that fuse blows) at the different fuse currents, IF .


tF = 956.677usec. at IF = 5A

tF = 5.9221msec. at IF = 2A

tF = 23.7861msec. at IF = 1A

Simulation Circuit

*Analysis directives: .TRAN 0 1s 0 100u.STEP PARAM dc_current LIST 1, 2, 5 *Integration Method: trapezoidal

Simulation Result

0.001

0.01

0.1

1

10

0.1 1 10 100

Fu

sin

g T

ime

(Se

c.)

Fusing Current

Measurement

Simulation

5. Fusing Time vs. DC Current

Graph shows the comparison result between the simulation result vs. the measurement data. The fusing current error (average from 0.001-10 sec.) = 4.9%


Comparison Graph

6 Fusing Time vs. Current Pattern

• The simulation result shows the fusing times, tF, (the time that fuse blows) for the same peak current but different in current patterns(waveforms).


tF = 59.984msec. for sine wave

tF = 150.041msec. for triangle wave

Simulation CircuitSimulation Result

.TRAN 0 0.2s 0 100u*Integration Method: trapezoidal

0.001

0.01

0.1

1

10

0.1 1 10 100F

us

ing

Tim

e (S

ec

.)Fusing Current

Measurement

Simulation

7. Specific Fuse Model

If the most accurate result is required, we could provide the specific model that optimized for each part number of fuse. The fusing current error (average from 0.001-10 sec.) will reduce from 4.9% (simplified model) to 0.4% (specific fuse model)


Model of fuse part number CCF10.4, all parameters

and function are already set

Model of fuse part number CCF10.4, all parameters

and function are already set

Error reduce to 0.4%

Error reduce to 0.4%

Comparison Graph

Library Files and Symbol Files Location


…\Fuse_smpl

C:\Program Files\LTC\LTspiceIV\lib\sub

C:\Program Files\LTC\LTspiceIV\lib\sym

Copy/Paste into

Copy/Paste into

Copy/Paste into

Copy/Paste into

1. Copy the library files (.lib) from the folder …\Fuse_smpl\.sub\, then paste into the folder C:\Program

Files\LTC\LTspiceIV\lib\sub

2. Copy the symbol files(.asy) from the folder …\Fuse_smpl\.asy\, then paste into the folder C:\

Program Files\LTC\LTspiceIV\lib\sym

Simulation Index


Simulations Folder name

1. Fusing Time vs. DC Current..................................

2. Fusing Time vs. Current Pattern............................

DC

Pattern

Simple model of Fuse(LTspice)

Technology

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