Fuseology Selection Guide Page 15 Fuseology Selection Guide

www.littelfuse.com Fuseology Selection Guide 1. Define the circuit operating parameters. Normal operating current in amperes: .................................................................................................... Normal operating voltage in volts: .................................................................................................... Maximum interrupt current: .................................................................................................... Ambient temperature: .................................................................................................... Typical overload current: .................................................................................................... Required opening time at specified overload: .................................................................................................... Transient pulses expected: .................................................................................................... Agency approvals: .................................................................................................... Mounting type/form factor: .................................................................................................... Typical resistance (in circuit): .................................................................................................... 2. Select the proper circuit protection component. ( Refer to Table on Page 3 and specifications with Data Sheets ) 3. Determine the opening time at fault. Consult the Time-Current (T-C) Curve of each PTC series to determine if the selected part will operate within the constraints of your application. If the device opens too soon, the application may experience nuisance operation. If the device does not open soon enough, the overcurrent may damage downstream components. To determine the opening time for the chosen device, locate the overload current on the X-axis of the appropriate T-C Curve and follow its line up to its intersection with the curve. At this point read the time tested on the Y-axis. This is the average opening time for that device. If your overload current falls to the right of the curve the device will open. If the overload current is to the left of the curve, the device will not operate. 4. Verify ambient operating parameters. Ensure that the application voltage is less than or equal to the device's rated voltage and that the operating temperature limits are within those specified by the device. 5. Verify the device's dimensions. Compare the maximum dimensions of the device to the space available in the application. The dimension of each product is included within each data sheets on the following pages. 6. Test the selected product in an actual application. PTC Selection Worksheet A robust web-based tool to help circuit designers identify the optimal electronic fuses for their products. Littelfuse iDesign TM Online Fuse Design and Selection Tool 15

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