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Film Resistors' Construction and Features

Writer:Microhm Page View:Date:2019-05-15

In a film resistor, the resistive material is a very thin coating of carbon ,metal or metal oxide on an insulating substrate, such as ceramic or glass. The value of the resistance is determined by the thickness of the film and the amount of carbon or metal in it. These resistors are available with very accurate and stable values.

Apart from shunt resistor, surface-mount resistors are almost always film resistors. These resistors have no leads at all, so LS is very low. The film is deposited on a ceramic sheet. Because of their extremely small size, surface-mount resistors have very low power ratings — from 1/10 to 1/4 watt.

A drawback of film resistors is that they are unable to handle large amounts of power because the film is so thin. Overloads can also damage the film by creating “hot spots” inside the resistor, changing its value permanently. The value of film resistors is sometimes adjusted before sealing by cutting away some of the film with a laser, a process called trimming.

If the film is deposited on the inside of a tube, the trimming process creates a coil-like current path that raises the LS of the resistor. If your circuit operates at high frequencies, be sure the resistors you select have a low value of LS.

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