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> CRF Nowadays, the safety requirements in electronic circuits are becoming increasingly important. For VITROHM it is a primary issue for years. Typical fusible wirewound resistors are used when it’s required to pass some type of short transient event without failing. The CRF series are designed to be used as a precision safety resistor. This series are used where the electronic circuit need a more robust resistor, a resistor that can withstand high power, either high short-term pulse, where the standard fusible resistor fail. APPLICATION NOTE Precision Fusible Safety Wirewound Resistor > Fusing Performance The CRF uses specially selected resistive winding wire, wounded on a ceramic rod and welded onto a metal caps, with special non-flammable varnish, to absorb the metal-vapour when the resistor wire fuses, to avoid arcing or short-circuit, on the top silicon cement coating material to ensure safe, without flames or explosion, and silent fusing operation when the main voltage is applied. This resistor could also work as a fusing resistor, in case of overload. But unlike fuses, the fusing characteristic is given in power instead of current. The CRF was specially designed to act as a fuse when the main voltage (230[V]RMS or 120[V]RMS) is applied, to prevent the destruction or failing in the electric circuit. This series also acts as a fusible resistor, limiting the inrush current to prevent overload to the circuit. The CRF – 8 series is UL approved, for USA and Canada, with UL file E330640. The maximum power vs time could be found in the graph shown beside. The current for a certain ohmic value could be calculated by I = PR 257-8 254-8 256-8 10 253-8 251-8 1 40 50 60 70 80 90 100 110 120 Power [W] UL - Voltage Approved 230[V] Resistance Range The features for these series are as follows: CRF allows designers to •Immediate interruption easily meet the requirements at main voltage 230[V], of safety approval, while without flame or explosion; eliminating the need to put •Regular manufacturing additional fuses in series with inspections by UL the input resistor, using just one inspector; resistor. This will be typically •Regular tests monitored by less expensive. UL laboratory. 252-8 100 > UL1412 Approval In the table shown beside, you can find the ohmic values according to each main voltage for each series. Fusing Time vs Power 1000 www.vitrohm.com 375[V] 120[V] 170[V] CRF251-8 1R... 100R 1R... 100R CRF252-8 1R... 240R 1R... 240R CRF253-8 10R... 330R 10R... 90R CRF254-8 10R... 330R 10R... 90R CRF256-8 10R... 330R CRF257-8 10R... 90R 1R... 330R 1R... 330R Release: OCT2014 > Features Fusing Time [s] CRF APPLICATION NOTE > Pulse Performance Peak Voltage Limit 7 6,5 6 5,5 Peak Voltage [Kv] The voltage shown in the “Peak Voltage Limit” graph is the net voltage across the resistor. The generator open voltage will be higher due to the generator’s internal impedance 12[Ω]. The pulse shape is according to IEC61000-4-5, 1,2/50[μs], described in the graph. The pulse shape is 10 pulses with a cool down period between 10 to 20[s]. 257-8 5 4,5 253-8 4 3,5 254-8 256-8 252-8 3 2,5 251-8 2 1R0 2R0 10R 20R 47R 100R 180R 220R 240R 330R R-Value [Ω] The maximum energy is given by the following graph: Energy [W/S] The CRF series is designed exclusively for safety fusing applications. It is known that an excellent safety fusing performance is somehow opposite with inrush-current performance. Nevertheless, they also could withstand a certain energy that results from the inrush current, working also as an energy absorber. 18 17 16 15 14 13 12 11 10 9 8 254-8 7 6 5 252-8 4 3 2 251-8 1 0 1R0 Energy Capability Graph 257-8 256-8 253-8 2R0 10R 20R 47R 100R 180R 220R 240R 330R R-Value [Ω] > Lead Configurations > Applications The CRF is also available in a different pre-forming, as shown below. Other configurations are available upon request. The most common applications for CRF are: Electronic energy meter Z-Form Radial Axial Radial Kink Axial Kink Power supplies For these applications the resistor can be used in the power supply that supplies the current to the control circuit, working as a safety fusible resistor. www.vitrohm.com This not only saves the electronic circuit when the main voltage (230 or 120[V]) is applied to the resistor, but also as an inrush limiter to the circuit. •Battery chargers •Fans •Energy saving lamps •Presence detectors •Dimmer switches •Surge protection Date of release: November 2014 The energy described on the graph above is related with the resistor construction.