Benefit Vs Cost Control Scheme Of PCB Fuse Resistor Technology
Benefit vs cost control scheme of PCB fuse resistor technology
Selecting resistors for practical applications
Because of the dual role of both fuse and resistors, fuse to become the preferred passive component design engineer. With a component instead of two can save cost, but also can save the space of the PCB. In the application of low power level, film type fuse resistor is ideal for this type of application requirements for overload control and the anti surge capacity is not too strict. The power supply and control circuit generally used in power tools, electric meter, communication equipment, kitchen appliances and smoke detectors, and this kind of device usually requires more robust to withstand the resistor, higher power, higher short-term surge and higher temperatures. These applications need to have a variety of resistors anti surge force, and achieve conflict free or incidental damage to fuse fault requirements, Wirewound resistors can meet these requirements.
Film type fuse resistor
Film fusing resistor technology generally uses standard resistor film alloys and materials as the base for fusing parts. In order to ensure reliable and repeatable melting characteristics, the thickness and composition of sprayed films must be monitored more closely. To ensure uniformity in batch manufacturing. This step is crucial when the coating process is completed and calibrated. The fuse action of the part is controlled by this process, and an accurate resistance value can be indicated. The more calibration adjustments, the shorter the melting time, The lower the power required to fuse a given size and resistance value.
However, when the calibration adjustment is used to control the melting time, the resistance value of a particular manufacturing lot will fluctuate greatly. The fluctuation of the resistance value will lead to the instability of the melting performance, because the high resistance value accelerates the melting speed, so, Many fuse-off resistors provide only 5% or higher absolute resistance tolerances. Standard melting-off characteristics specify the melting time (usually less than 30 seconds, 15 seconds, 5 seconds, etc.) at a specified amplification rate (e.g. 10 or 25 times). The fuse resistor is suitable for many low power and low surge applications, Examples include low-level fire safety monitoring and management, high-end audio / video systems, environmental management controls and systems, and laser printers.
Wire wound fuse resistor
Standard wire-wound fuse applications require a fuse resistor to transmit some type of short transient event without causing malfunction. Electrical and white appliances industry, power tools, ammeter, communication equipment, Fire safety equipment and HVAC systems both require this type of resistor. For example, it can transmit hundreds of 6000Vt 20 μ s pulses. But the fusible wire wound resistor, which can break fast and do not catch fire at 120V short circuit overload, is this kind of resistor. It is relatively easy to make a wire-wound resistor that can withstand a 6kV surge, but to maintain this performance, At the same time, it is much more difficult to open the fuse characteristics without fire or overheating.
Some manufacturers simply by weakening the two element and the end cap of the solder joint in one of them, creating a fuse action wirewound resistors. It is realized the fault safety features, but the repeatability of design this fuse is far lower than expected. In some cases, this part will be in normal under the condition of the fuse circuit, and in some cases, only PCB burn or cause a fire, this part will fuse wire fuse. And advanced technology makes use of the material properties of the alloy resistance wire, wire core size and shape, and thermal management.
Another factor that affects the performance of wire-wound fuse resistors is the adjustment process. Any adjustment will reduce the effective carrier current of the cable element. In some cases, The traverse cross section can be reduced by as much as 40%. This adjustment process usually does not significantly reduce the steady-state power capacity of the wire-wound resistor, but has a serious impact on the equipment's surge resistance.
Many power design engineers use a single fault-safe wire-wound resistor instead of a wire-wound resistor and an independent fuse. But in order to achieve the goal of using only a single device, UL has recently focused on motor control and protection applications. Resistors and fuses. Compared with two separate parts, Individual parts are more reliable, reproducible, and generally cheaper. While the use of hot fuses reduces the effective power capacity of a resistor, it does provide a distinctive fuse action. And can guarantee to provide protection for the circuit above a certain temperature level.
The greatest advantage of a wire-wound resistor is also its greatest disadvantage in some applications: it is a very powerful resistor technology. The wire-wound resistor will continue to heat up and eventually self-destruct or damage all adjacent components. Create a reliable one without significantly reducing the steady-state power capacity. Repeatable fuse characteristics that can be used in many applications where standard wire-wound resistors cannot be safely used. We use careful scrutiny of materials and strict control of manufacturing processes. Under the condition of not raising the cost substantially, the resistance device which can safely fuse and withstand 6 kV or higher short surges is produced.
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