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What is the mechanism of fuse fusing during over current?

The fusing of fuse mainly depends on its Joule heat generation and dissipation. During short time of over current stressing, the fuse element will be melted and thus open the circuit in case the heat generation is much more than heat diffusion.

What are the types of fuse?

The types of fuse are classified as surface mount device (SMD) fuse, miniature fuse and power fuse according to the dimension and function

What is the difference between fast-acting (F) and time-lag (T) fuse?

● Fast-acting fuse — suitable and available for the electric circuit without or with seldom impact by inrush current,
ex: integrated circuit (IC) or precision instrument.

● Time-lag fuse — suitable and available for the electric circuit with frequent impact by inrush current,
ex: motor or adapter in consumer electronic product.

What is the difference between fuse and fusible resistor?

● Fuse ─ the fusing time is precisely estimated and evaluated including over current and breaking test.
The safety regulation is approved by international safety agency.

● Fusible resistor ─ the fusing time is not evaluated under over current stressing. It is only suitable for inrush protection sometimes. However, its fusing time is not more precise than fuse.

What are the criteria for fuse selection?

1. Operating current
2. Operating voltage (AC or DC)
3. Ambient temperature
4. Pulse power
5. Breaking capacity (or interrupting capacity)
6. Safety certificate
7. Others (dimension, shape, type)

What is the breaking (IR) capacity of fuse?

The breaking capacity is an important index for fuse selection criterion. It tells that the maximum current passing through the fuse and fuse body without any damage under rating voltage application. The breaking capacity correlates to the strength of fuse body to against electric arcing and arcing extinction ability of fuse.

What is the difference and correlation of operating current and fuse rating current approval between UL and IEC?

● For UL approval fuse, the operating current is suggested to less than 75% of fuse rating current.

● For IEC approval fuse, the operating current is suggested to less than 100% of fuse rating current.

How to determine the rating voltage of fuse?

The rating voltage of fuse is at least the same as maximum operating voltage or higher of device to ensure the safety from impact by abnormal pulse current.

What is the effect of ambient temperature on efficiency of fuse?

The electrical characteristic of fuse is designed and approved under 25℃, 1atm environment. The efficiency of fuse is prominently influenced by ambient temperature. With ambient temperature higher than 25℃, the derating behavior occurs to shorten the lifetime of fuse.

How to evaluate the effect of pulse current on life time of fuse?

It is inevitable to generate the transient pulse current on electronic device while turning on/off the power switch. The certificated fuse adopted in the electric circuit is durable and reliable to withstand the impact by pulse current stressing. The ratio of pulse current (Irms) to specific melting current of fuse (It), Irms/It <50%, is the threshold for fuse safety evaluation.