Tapped Resistor

There are three resistor types: Fixed, variable and tapped.

A fixed resistor is a two-terminal device whose resistance value cannot be changed. Variable resistors divide into rheostats and potentiometers. Rheostats usually have two connections – one fixed and one moveable – while a potentiometer has two fixed and one movable connection. Typically, rheostats are used in high-current applications such as lighting control, while potentiometers are used as voltage dividers in electronic circuits, for example as audio amplifier volume controls.

A tapped resistor has a contact at either end of its resistance path, and one or more taps at intervals along the path. These are set to pick up resistance and therefore voltage values as required. Sometimes the taps can be adjustable to pick up any resistance value (within the limits of the resistor’s range) as required.

Originally, tapped resistors were available as discrete components, and could be physically large, wire-wound devices. Today, however, they are also available as PCB-mounting devices such as Vishay’s CTR series. These are thin film, centre-tapped resistor divider networks that can handle power levels to 250 mW. They can be used either as single resistors, or as two resistors with a centre tap.

Applications are mainly in amplifier feedback circuits where ratio matching, high power and tracking between two resistors is critical. Resistance ranges are from 10 Ω to 1 MΩ.