WFF

Fast Fusible Metal Film Resistors WFF Series Welwyn Components • • • Low power fusing Predictable fusing characteristics Flameproof protection Electrical Data WFF1/4 Power rating at 70˚ C Resistance range Limiting element voltage TCR Resistance tolerance Standard values Thermal impedance Ambient temperature range ˚ C/watt ˚C 150 watts ohms volts ppm/˚ C % 0.25 0R1 - 10K 250 WFF1/2 0.5 0R10 - 27K 350 250 5 E24 preferred 120 -55 to 155 100 WFF1 1 0R2 - 1K5 350 Physical Data Dimensions (mm) & Weight (g) Type L max 6.2 9.0 12.5 D max 2.3 2.5 3.4 4.2 f min 21.0 19.6 17.8 d nom 0.6 0.8 0.8 PCB mounting centres 10.2 12.7 18.4 Min. bend radius 0.6 1.2 1.2 Wt. nom 0.3 0.6 0.9 d D WFF1/4 WFF1/2 WFF1 L f Construction 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. Marking 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. Solvent Resistance The body protection and marking are resistant to all normal industrial cleaning solvents suitable for printed circuits. Terminations Material Strength Solder-coated copper wire. The terminations meet the requirements of IEC68.2.21. Flammability The resistors will not burn or emit incandescent particles under any condition of applied temperature or power overload. Solderability The terminations meet the requirements of IEC 115-1 Clause 4.17.3.2. 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. A subsidiary of TT electronics plc Issue E 01.07 Issue D · 03.06 © Welwyn Components Limited · Bedlington, Northumberland NE22 7AA, UK Telephone: +44 (0) 1670 822181 · Facsimile: +44 (0) 1670 829465 · Email: info@welwyn-tt.com · Website: www.welwyn-tt.com 161 Fast Fusible Metal Film Resistors WFF Series Welwyn Components Performance Data Maximum Load: 1000 hrs at 70˚ C Shelf life: 12 months at room temperature Derating from rated power at 70˚ C Temperature rapid change Resistance to solder heat R% R% R% R% 3 2 zero at 155˚ C 0.5 0.5 Pulse Handling Graphs Graph 1 10000 1.2/50μS Pulse Withstand Graph 2 10000 10/700μS Pulse Withstand Test Voltage (V) 1000 Test Voltage (V) 1000 100 WFF 1/4 WFF 1/2 WFF 1 10 100 1000 Value (OHMS) 10000 100000 100 WFF 1/4 WFF 1/2 WFF 1 10 10 10 100 1000 Value (OHMS) 10000 100000 Above tests carried out in accordance with IEC 115.1. Change of value after test ±1% Graph 3 10000 WFF 1/4 Peak Voltage (V) Peak Power (W) WFF 1/2 WFF 1 1000 10 Maximum peak pulse voltage as a function of pulse duration (ti) Graph 4 100 Maximum peak pulse power as a function of pulse duration (ti) WFF 1/4 1 WFF 1/2 WFF 1 100 0.0001 0.0010 0.0100 ti (s) 0.1000 1.0000 0 0.0001 0.0010 0.0100 ti (s) 0.1000 1.0000 Test Method (for graph 3 and 4) 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. tp = Applied Pulse Power Rated Power x ti Figure 1 Voltage (V) ti tp Time (secs) © Welwyn Components Limited Bedlington, Northumberland NE22 7AA, UK Telephone: +44 (0) 1670 822181 · Facsimile: +44 (0) 1670 829465 · Email: info@welwyn-tt.com · Website: www.welwyn-tt.com 162 Issue E 01.07 Issue D · 03.06 Fast Fusible Metal Film Resistors 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. Welwyn Components Figure 2 52 Body Location f 1.4 m Standard Quantities Per Package Type Large ammo pack WFF1/4 5000 WFF1/2 2500 WFF1 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: info@welwyn-tt.com · Website: www.welwyn-tt.com Issue E 03.06 Issue D · 01.07 163