Wire-wound resistors are formed by winding resistance wires around an insulating skeleton. The resistance wire is generally made of nickel-chromium, manganese-copper and other alloys with a certain resistivity. The insulating skeleton is made of ceramic, plastic, metal coated with an insulating layer and other materials into various shapes such as a tube shape and a flat shape. The resistance wire can be wound on the skeleton according to the need for one layer, multiple layers, or non-inductive winding method.
This resistance is divided into two types: fixed and variable. Its characteristics are stable operation, good heat resistance, small error range, resistance value can be accurate to 0.001 ohms, the price is more expensive, and it is mostly used for medical equipment. The rated power is generally above 1 watt.
The value of wire-wound resistor is accurate. In theory, unless it is used as a reference for the charger output voltage, the general charger does not use wire-wound resistor. The charger circuit is a SMPS switching power supply circuit. The high-voltage-side signal generating circuit has high requirements. It is impossible to use wire-wound resistors, otherwise it will cause self-excitation and affect the oscillation frequency, which will cause large output fluctuations. The reference circuit may use wire-wound resistors.
The abrasion will cause the local wire diameter to become thinner. In the case of long-term use of electricity, the long-term action of the current changes the internal composition of the wire, thereby reducing the resistance value.
