Product Top » Precautions for use » Fuses
Fuses
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Precautions for Use of Fuses | |||||||||||||||||||||||||||||||||||||||||||||
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Safety Standards |
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KOA's fuse components comply with the following safety standards: |
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Rated Current |
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Current specified by us to be suitable for safety standards of fusing time, not the current stationary applicable. Stationary current of a current of a circuit can be calculated with the following equation:
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| Deratings for Ambient Temperatures The following Deratings for Ambient Temperatures are required: |
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Regard the peak current as stationary current when current waveform is repeated pulse or AC waveform. Do not use the effective value of the current waveform. |
Rated Current Value |
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Rated Voltage |
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A rated voltage indicates the voltage that does not run through electrodes after the fuse blows. In case of exceeding the rated voltage, the circuit voltage should be applied at voltage not higher than the rated voltage because the current may run again or may break the elements. |
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Interrupting Capacity |
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An interrupted capacity indicates current and voltage that can be interrupted when an abnormal situation arises. Make sure beforehand that voltage and current at the time of abnormality occurring in the circuit are within the interrupting capacity. |
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Fusing Current |
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It indicates a current that interrupts a circuit. Refer to the following list to quickly interrupt an abnormal current occurred in the circuit: | |||||||||||||||||||||||||||
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If its fusing time is within 1 second, the variance in the fusing time affected by the surroundings (temperature, mounting pad dimensions, substrate material, etc.) will be negligible. But if it is not less than 1 second, it will be largely affected by them, so its verification should be made with an actual circuit. |
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Anti-Surge Characteristics | |
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| There are limits to applications of transient overcurrents (inrush current, reversible current at motor-lock, etc.) that occur in circuits. It is necessary to select proper products that withstand such overcurrents without fusing. Select proper fusing components considering the following conditions: |
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The transient phenomenon varies with the ambient temperature, charging/discharging conditions of capacitors, etc. Check the wave form of current under such conditions that the current becomes the maximum. Also check it beforehand under such conditions that the current becomes the maximum if parts highly dependent on temperatures such as thermisters, etc. are used in the circuit. | |
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For a peak current observation, shorten the sampling time of an oscilloscope to verify the maximum value of the wave-form of the surge current. | |
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We recommend the current measurement using current probe. If a current measuring is performed by measuring voltages of shunt resistors, etc., use the lowest possible resistances of them to the impedance in the circuit. |
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Operation Check |
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Before you decide which fuse product you use, please mount the selected fuse on actual device and confirm that rush current and surge current have enough margin and that the product has performance that enables to interrupt the abnormal current quickly. |
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Soldering |
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This product is suitable both for reflow-soldering and for flow-soldering, but an excessive heat may cause an open and change its characteristics. | |
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The part shall be soldered at the maximum temperature of 260 or less. |
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If a soldering iron is used, it shall be at 350 or less and stress shall be not applied to the electrodes at a short time. Further, pay attention that the products are not touched directly by the top of the iron. It may cause disconnection or characteristic change. |
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Placement |
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Please confirm sufficiently the evaluation of reliability and use those that have small contractile stress at a resin stiffening time. By contractile stress at the resin stiffening time, fuses might be broken, resistance value may be changed and disconnection might occur in case of resin coating/potting or molded sealing. Further, be sure to consider the dispersion of constant of other components in the actual circuit. There is a possibility that heat may fill the surrounding of the fuses by shielding and may cause the fusing characteristics to change. | |
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The fusing characteristics may change when there are components that generate heat very much around the fuses. Keep fuses away from those parts. |
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Storage |
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Avoid storing components under the condition of high temperature/high humidity (40/70%RH or more) which may deteriorate solderability. |
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Also avoid direct sun light which may deteriorate solderability and induce changes in taping strength. |
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Parts selection |
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If you have any questions about the way of selecting fuses, please do not hesitate to ask us with the information on rated voltage, operating temperature, wave-forms of steady-state current and rush current, and fusing current. |
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Reference |
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For basic precautions, refer to EIAJ technical report RCR-4800 "Safety application guide on fuse for use in electronic and electrical equipment". You can visit below URL for free view. http://www.jseita.or.jp/cgi-bin/standard/search.cgi |
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