QTC Technology

Pressure sensitive control and electrical switching

Pressure-sensing and Switching

The potential for the QTC material to transition from an insulator to a conductor (i.e. change its electrical property) is influenced by how much deformation the material is experiencing as a result of the applied mechanical pressure.

QTC can be used to produce low profile, low cost, pressure activated switches or sensors that display variable resistance with applied force and return to a quiescent state when the force is removed. The difference between a QTC switch and a QTC sensor is arguably only the speed and amount of physical input required to achieve the required switching point or resistance range.

QTC insulating

▲ Open circuit: Rest state > QTC insulating
    In unstressed state, QTC behaves as an insulator (R>1012 Ω) .

QTC conducting

▲ Closed circuit: Compressed state > QTC conducting
    Under compression, tension or torsion the resistance drops gradually and
    controllably. QTC can be capable of passing high currents.


Switching Performance

Force (N) and Resistance (Ω) QTC Switching Performance Force Resistance curve
The transition from insulator to conductor follows a smooth and repeatable curve, with the resistance dropping exponentially.

In theory, the resistance of QTC decreases exponentially with compression – subsequently, allowing increasing current flow through the material. In practice uniform compression is rarely achieved and therefore the resistance change with compression will deviate from a true exponential.

► The graph shows the effect of varying the current at constant voltage.

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