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Why Choose Low Inductive Resistors?

Writer:Microhm Page View:Date:2019-06-13
Since resistors are made of conductive materials, they, too, exhibit inductance as an unwanted, parasitic effect. This effect is especially noticeable if the resistor is made out of wire formed into a coil shape. Depending on the application, resistor inductance might be easily disregarded, especially in DC circuits. However, parasitic resistor inductance can be a significant factor in high-frequency AC applications. The reason for this is that the impedance of a resistor rises with the applied voltage frequency due to the increase in its reactance.

Parasitic inductance usually manifests itself either in resistors with inferior properties such as helical wire wound resistors or in other resistors at very high frequencies.
Generally, Inductance for different resistor types vary as below
Wirewound      0.03 – 56 μH
Foil   <0.08 μH
Metal oxide      3 – 200 nH
Film  <2 nH
 To demonstrate the high frequency problem, a typical foil resistor of 220 Ω with an inductance of 0.05 μH has an impedance of approximately 380 Ω at 1GHz, which is a relative change of approximately 70% above the nominal value, which an engineer would expect if parasitic effects were not taken into account. Microwave applications, or RF applications in general are particularly sensitive to parasitic effects. Microhm provides borad range low inductive resistors, including MVR4618.It also has the characteristics of 10W power rating, 4-terminal connection, low TCR to 5ppm and hig precision to 0.05%.

The main difference between ideal resistors and ideal inductors is therefore that resistors dissipate electrical power as heat, while inductors turn electrical power into a magnetic field. Ideal resistors have zero reactance and as a result zero inductance. Unfortunately, electrical devices are not ideal in practice and even the simplest resistors have a slight parasitic inductive reactance.
The B-field of an inductor coil


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