Datasheet

5
Determine the rated value of the micro fuse, and select the micro fuse for your circuit. If you select the micro fuse , safety of your circuit
can be ensured.
How to determine the rated value of the micro fuse is described below:
■Flow for fuse selection
1. Measurement of circuit values using actual device
Measure the circuit values, such as operating current of the circuit.
2. Calculation from operating current
From the obtained operating current and the category temperature, calculate minimum rated value to determine the applicable fuse.
3. Calculation from overload current
From the obtained overload current, calculate the maximum rated value to determine the applicable fuse.
4. Calculation from inrush current
From the inrush current, calculate the minimum rated value to determine the applicable fuse.
5. Final determination of rated value
From the calculation results of steps 2 through 4, determine the rated value.
6. Operation check using actual device
After selecting the rating, confirm if the device works properly under the pre-determined conditions.
■Fuse selection
1. Measurement of circuit values using actual device
Before determining the rated value of the fuse, preliminarily measure the following condition by using the actual device.
1-1. Operating current
Using an oscilloscope or equivalents, measure operating current of the circuit.
1-2. Overload current
Using an oscilloscope or equivalents, measure the overload current that needs to break the circuit.
1-3. Inrush current
Using an oscilloscope or equivalents, measure the inrush current of circuit at power-on or power-off. In addition, determine
the number of inrush current applied.
1-4．Category temperature
Measure the ambient temperature of the fuse circuit.
<The notes to the design of substrate wiring>
In a 25℃ environment under normal circumstances, please design substrate wiring so that the surface temperature of a fuse does
not exceed 80℃.
EXAMPLE TO SELECT RATINGS OF TYPE JHC
<Fuse selection>
Effective operating current : 30 A
Effective overload current : 140 A
Inrush current waveform : Fig. A
(Pulse width : 2 ms, Wave height : 300 A)
Numbers to withstand inrush current : 100,000 times
Category temperature : 85°C
Operating time：4,000h
2. Calculation from operating current
2–1. Measurement of operating current
Using an oscilloscope or equivalents, measure operating current (effective current) of the actual circuit.
Example : Effective operating current = 30 A
2–2 Derating
①Temperature derating factor
Using Fig. B, find the temperature derating factor correspond to the Temperature.
However, in order to be allowed to check an operating condition in use to the
apparatus used for a long time that the operating time exceeds 4,000 h,
please ask our Sales Department.
②Rated derating factor
Rated derating factor = 0.94 (Constant irrespective of temperature)
Use Formula 1 to calculate the rated current of the fuse to be used for the circuit.
Rated current of fuse ≥ Operating current/(①×②) ... Formula 1
Example : Category temperature = 85°C, Operating current =30 A
①Temperature derating factor = 0.90 (Refer to Fig. B.)
②Rated derating factor = 0.94 (Constant irrespective of temperature)
2ms
300A
Fig. A：Inrush current waveform
0
20
40
60
80
100
120
140
-50 -25 0 25 50 75 100 125
Temperature（℃）
Derating factor (%)
JHC temperature derating
Fig. B