What is a wirewound resistor?

Wirewound resistors are constructed with a resistance wire wound around an insulating skeleton. The wire is generally made of alloys such as nickel-chromium and manganese-copper, which have a certain resistivity. The insulating bobbins are made of ceramics, plastics, metal coated with an insulating layer, and other materials in various shapes such as tubular, flat, etc. The wire is wound on the bobbins as required. Resistor wire in the skeleton according to the need to wind a layer, can also be wound multi-layer, or non-inductive winding method, etc.. This kind of resistance is divided into two kinds: fixed and variable. It is characterized by stable operation, good heat resistance, small error range, resistance value can be accurate to 0.001 ohm, more expensive, mostly used in medical equipment, rated power is generally more than 1 watt. Wirewound resistor value is accurate, theoretically speaking, unless it is to do charger output voltage reference, the general charger are not used wirewound resistor. Charger circuit for SMPS switching power supply circuit, the high voltage end of the signal generating circuit is very demanding, it is not possible to use wirewound resistors, otherwise it will lead to self-excitation, which affects the oscillation frequency, thus making the output fluctuation is large, only the low-voltage end of the sampling reference circuit may use wirewound resistors. Wear and tear will cause the local wire diameter to become thinner, and in the case of long-term use of energized, the long-term role of the current makes the intrinsic composition of the wire changes, thus making the resistance value smaller.