Iron–hydrogen resistor

An iron–hydrogen resistor consists of a

positive temperature coefficient of resistance. This characteristic made it useful for stabilizing circuits against fluctuations in power-supply voltages.^[1] This device is often called a "barretter" because of its similarity to the barretter used for detection of radio signals. The modern successor to the iron–hydrogen resistor is the current source

.

Operation

When the current increases, the temperature will increase. The higher temperature leads to a higher

oxidation

and also enhances the effect, since the solubility of hydrogen in iron increases as temperature increases, resulting in higher resistance.

Uses

Iron–hydrogen resistors were used in the early

NTC-type thermistor made of UO₂ until 1936, known as Urdox resistor and acting as an inrush current limiter for the series heater strings of domestic AC/DC

tube radios.