Fast Fusible Metal Film Resistors Welwyn Components WFF Series • • • Low power fusing Predictable fusing characteristics Flameproof protection Electrical Data WFF1/4 WFF1/2 WFF1 Power rating at 70˚ C watts 0.25 0.5 1 Resistance range ohms 0R1 - 10K 0R10 - 27K 0R2 - 1K5 volts 250 350 350 Limiting element voltage TCR ppm/˚ C Resistance tolerance 250 % 5 Standard values E24 preferred Thermal impedance ˚ C/watt Ambient temperature range 150 120 ˚C 100 -55 to 155 Physical Data Dimensions (mm) & Weight (g) Type L max D max f min d nom PCB mounting centres Min. bend radius Wt. nom WFF1/4 6.2 2.3 2.5 21.0 0.6 10.2 0.6 0.3 WFF1/2 9.0 3.4 19.6 0.8 12.7 1.2 0.6 WFF1 12.5 4.2 17.8 0.8 18.4 1.2 0.9 d D L f Construction Marking The metal film is deposited on a high purity ceramic rod. End caps are force fitted and termination wires welded to the caps. The resistive film is adjusted to the required value by a special helical cut. A fuse aid coating is then applied. Finally a cement protection is applied to the resistor body prior to marking with indelible ink. Resistors are colour coded with 5 bands. Four of the bands are used to indicate values and tolerance, with IEC 62 colours being used. A fifth yellow band denotes constant voltage fusibility. Terminations Material Solder-coated copper wire. Strength The terminations meet the requirements of IEC68.2.21. Solderability The terminations meet the requirements of IEC 115-1 Clause 4.17.3.2. Solvent Resistance The body protection and marking are resistant to all normal industrial cleaning solvents suitable for printed circuits. Flammability The resistors will not burn or emit incandescent particles under any condition of applied temperature or power overload. General Note Welwyn Components reserves the right to make changes in product specification without notice or liability. All information is subject to Welwyn’s own data and is considered accurate at time of going to print. © Welwyn Components Limited · Bedlington, Northumberland NE22 7AA, UK Telephone: +44 (0) 1670 822181 · Facsimile: +44 (0) 1670 829465 · Email: [email protected] · Website: www.welwyn-tt.com A subsidiary of TT electronics plc Issue D Issue E · 03.06 01.07 161 Fast Fusible Metal Film Resistors Welwyn Components WFF Series Performance Data Maximum Load: 1000 hrs at 70˚ C R% 3 Shelf life: 12 months at room temperature R% 2 Derating from rated power at 70˚ C zero at 155˚ C Temperature rapid change R% 0.5 Resistance to solder heat R% 0.5 Pulse Handling Graphs Test Voltage (V) Test Voltage (V) Graph 2 10000 1.2/50μS Pulse Withstand Graph 1 10000 1000 WFF 1/4 100 WFF 1/2 WFF 1 10/700μS Pulse Withstand 1000 10 WFF 1/4 100 WFF 1/2 WFF 1 10 10 10000 1000 100 100000 10 100 Value (OHMS) 1000 10000 100000 Value (OHMS) Above tests carried out in accordance with IEC 115.1. Change of value after test ±1% Maximum peak pulse voltage as a function of pulse duration (ti) Graph 3 Maximum peak pulse power as a function of pulse duration (ti) Graph 4 10000 100 WFF 1/2 WFF 1 Peak Power (W) Peak Voltage (V) WFF 1/4 1000 100 0.0001 0.0010 0.0100 0.1000 10 WFF 1/4 1 WFF 1/2 WFF 1 0 0.0001 1.0000 0.0010 ti (s) The resistor is subject to 10,000 pulses as shown in figure (1). Maximum resistance change due to test will not exceed 1%. Maximum pulse voltages are detailed in graph 3 above. For any combination of power and pulse length (ti). tp is determined by the need to ensure that the average power does not exceed the rated power. Applied Pulse Power x ti 1.0000 Figure 1 ti tp = 0.1000 ti (s) Voltage (V) Test Method (for graph 3 and 4) 0.0100 Time (secs) tp Rated Power © Welwyn Components Limited Bedlington, Northumberland NE22 7AA, UK Telephone: +44 (0) 1670 822181 · Facsimile: +44 (0) 1670 829465 · Email: [email protected] · Website: www.welwyn-tt.com 162 Issue D Issue E · 03.06 01.07 Fast Fusible Metal Film Resistors Welwyn Components WFF Series Packaging All resistors are supplied tape packed ready for loading onto automatic sequencing and insertion machines. The standard taping method and critical dimensions are shown in figure 2. Lead Formed resistors can also be supplied. Standard options of Lancet, Radial and Goalpost forming are shown in Lead Form Information section. Figure 2 52 Body Location f 1.4 m Standard Quantities Per Package Type Large ammo pack WFF1/4 WFF1/2 WFF1 5000 2500 1500 *Contact Welwyn for R10 - 1R0 fusing data Fusing (Constant voltage) After fusing the final resistance value will be initial value. 50 times the © Welwyn Components Limited Bedlington, Northumberland NE22 7AA, UK Telephone: +44 (0) 1670 822181 · Facsimile: +44 (0) 1670 829465 · Email: [email protected] · Website: www.welwyn-tt.com Issue D 03.06 Issue E · 01.07 163