Guide to Fuse Selection ppt

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Slide 1:

www.schurterinc.com Fuse Selection Guide 1 Guide to Fuse Selection

Purpose of Fuses :

www.schurterinc.com Fuse Selection Guide 2 Purpose of Fuses Circuit protection is critical, and in many cases required, in electrical and electronic products. Fuses are an inexpensive and effective way to protect your device from damage due to overcurrent conditions. Fuses can prevent safety hazards to the end user such as fire and catastrophic failure of the product. Fuses help design engineers comply with regulatory agencies such as UL and IEC.

Characteristics of Fuses :

www.schurterinc.com Fuse Selection Guide 3 Characteristics of Fuses Schurter offers a wide variety of fuses to meet any application: > Package type (SMD, thru hole, cartridge) > Current and voltage ratings (AC and DC power) > Trip characteristics (quick-acting or time-lag) > Breaking capacity ratings > Approvals (UL, CSA, ENEC, CCC)

Size and Mounting :

www.schurterinc.com Fuse Selection Guide 4 Size and Mounting > Schurter offers 0402, 0603, 1206 SMD fuses > Thru hole microfuses > Cartridge fuses 5x20mm, 6.3x32mm and 10.3x38mm > Cartridge fuses can be mounted in fuseholders , fuseblocks or fuseclips > We also offer pigtails for a low cost thru hole solution

Fuse Current Rating:

www.schurterinc.com Fuse Selection Guide 5 The rated current of the fuse is either designed according to IEC characteristic or UL characteristic . A fuse, which is designed according to a IEC standard, can continuously operate at 100% of rated current of the fuse. A fuse, which is designed according to a UL standard, can continuously operate at 75% of rated current of the fuse. The fuse current rating should be based on the operating current in the application . Fuse Current Rating

Breaking Capacity :

www.schurterinc.com Fuse Selection Guide 6 Breaking capacity is the maximum short circuit current a fuse can safely blow without a catastrophic failure such as a fire, breakage or explosion. Low and high breaking capacity ratings typically range from 35A up to 10kA. The short circuit condition in the final product determines what fuse breaking capacity is needed. Our UMT is a compact SMD fuse with a high breaking capacity of 200A. Breaking Capacity

Trip Characteristic :

www.schurterinc.com Fuse Selection Guide 7 Fuses are either quick-acting or time-lag. Time-lag fuses trip at a slower rate at high currents. Trip Characteristic Quick-acting Time-lag Load type Resistive Capacitive Inrush Current Withstand Low High (10 times rated current) Applications Data/signal lines Electronic components Power supplies Motors Circuits with capacitors Advantage Avoid damage downstream due to inrush Avoid nuisance tripping during inrush

Temperature Derating:

www.schurterinc.com Fuse Selection Guide 8 Temperature Derating Fuse current ratings are measured at 23degC. Fuses are temperature dependant so higher the ambient temperature the quicker the fuse will blow. Ambient temperature of the application must be considered when choosing the current rating of the fuse.

Temperature Derating Example UMT 250 SMD Fuse:

www.schurterinc.com Fuse Selection Guide 9 Temperature Derating Example UMT 250 SMD Fuse Application example: Fuse type: UMT 250 Operating current : 1.0 A @ 60 C Operating voltage: 230 VAC Ambient temperature: < 60  C Calculation of rated current of the fuse with the derating curve: Choice: UMT 250, 1.25 A (1 A @ 60 C) Derating-curve UMT 250 (see data sheet)

Heat Issues:

www.schurterinc.com Fuse Selection Guide 10 Heat Issues Heat dissipated from fuses can affect other components in close proximity and vice versa. Sufficient airflow and ventilation should be considered when designing fuses in the application. Schurter fuseholder and fused module datasheets have power acceptance ratings which show how much heat dissipation it can withstand safely. If a fuse dissipates more heat than the fuseholder can withstand, the fuseholder can degrade such as melt or burn . Fused module Fuse and fuseholder

Power(heat)Dissipation :

www.schurterinc.com Fuse Selection Guide 11 Power(heat)Dissipation > Fuses dissipate heat during normal operation and this can increase as ambient temperature increases. Time-lag fuses generally have lower power dissipation values than quick-acting fuses because they have a thicker fuse wire diameter. Here’s our FST spec sheet where we publish the typical Power Dissipation value. When choosing a fuseholder or fused module, the power acceptance value should exceed the fuse power dissipation value.

Inrush Current:

www.schurterinc.com Fuse Selection Guide 12 Inrush Current Many applications will have inrush or peak currents at start-up and sometimes during normal operation. The inrush current in the application should be measured and used to calculate the proper fuse I 2 t value. I 2 t is the amount of heat energy, in terms of current and time, required to melt the fuse link

Waveforms Inrush Current Peak:

www.schurterinc.com Fuse Selection Guide 13 Waveforms Inrush Current Peak Procedure Step 1: Selection of the appropriate waveform of the inrush current . Most used curve Wave shapes Formulas Wave shapes Formulas

I2t Calculation Inrush Current Peak:

www.schurterinc.com Fuse Selection Guide 14 I 2 t Calculation Inrush Current Peak Step 2: Calculation of the I 2 t-value of the application Application example: Inrush current peak: I p = 13 A,  = 0.006 s Type of waveform: Typical discharge curve Calculation of the I 2 t-value After 5, the inrush current has reached operating current.

Pulse Factor Derating Inrush Current Peak :

www.schurterinc.com Fuse Selection Guide 15 Pulse Factor Derating Inrush Current Peak Continuous exposure to pulses of high current could prematurely age the fuse. The number of pulses the fuse would be exposed to in the application should also be considered when choosing a fuse. Tin plating of new fuse wire Tin plating of aged fuse wire Wire Tin plating

Pulse Factor Derating Inrush Current Peak:

www.schurterinc.com Fuse Selection Guide 16 Pulse Factor Derating Inrush Current Peak Step 3: Determine the minimum value of the I 2 t-value of the fuse. Application example: Total number of pulses in life cycle: 10,000 UMT 250 = time-lag fuses Calculation of time-lag T fuses (Calculation of quick-acting F fuses) Pulse-Derating curve

Selecting a Fuse Part Number :

www.schurterinc.com Fuse Selection Guide 17 Selecting a Fuse Part Number Step 4: Selection of the correct fuse rating and part number from Schurter’s product line. Typical I 2 t-values at 10*I n for Schurter 1 A time-lag T fuses MST 250 (12 A 2 s), UMT 250 (2.8 A 2 s), FST 5x20 (3.3 A 2 s), SPT 5x20 (1.1 A 2 s) (Typical I 2 t-values at 10*I n for Schurter 1 A quick-acting F fuses) OMF 250 (0.23 A 2 s), MSF 250 (0.33 A 2 s), FSF 5x20 (1.13 A 2 s), SP 5x20 (0.75 A 2 s) Choice: UMT 250, 1 A (2.8 A 2 s > 1.748 A 2 s)

Fuse Selection :

www.schurterinc.com Fuse Selection Guide 18 Fuse Selection Normal Operating Mode Inrush Current Peak Choice: UMT 250, 1.25 A (1 A @ 60 C) > The higher value determines the selection of the rated current of the fuse. > The normal operating mode current exceeds that of the inrush current peak. Therefore, the 1.25 A fuse is the recommended fuse rating. Choice: UMT 250, 1 A (2.8 A 2 s > 1.748 A 2 s)

Website Selection, Datasheets, Approval Documents, CAD Drawings :

www.schurterinc.com Fuse Selection Guide 19 Website Selection, Datasheets, Approval Documents, CAD Drawings Website: www.schurterinc.com

Slide 20:

www.schurterinc.com Fuse Selection Guide 20 Thank you Guide to Fuse Selection