Sourcing Hotline
To improve the reliability of its line of portable automated external defibrillators (AEDs), a medical device manufacturer required a high-voltage resistor that could withstand harsh environmental conditions while maintaining reliable performance. The firm turned to specialist electronics design company Welwyn Components Ltd. (Bedlington, Northumberland, UK; www.welwyn-tt.co.uk), a subsidiary of TT electronics plc.
The resistor is used in the defibrillator charge control circuit. The stable and repeatable measurement of the charging voltage is a critical function of this circuit, as it determines the amount of electrical energy that is delivered to the patient.
As the AED is a miniaturized version of a hospital-based defibrillator, the manufacturer required a physically smaller resistor for its portable device. Moreover, the component needed to have excellent linearity and long-term stability under voltage stress.
The design team at Welwyn Components developed a new high-voltage planar resistor incorporating thick-film resistor ink based on a ruthenium oxide/glass system encapsulated with a specially formulated high-density epoxy. The encapsulant provides better environmental protection than the traditional porous conformal coating, according to the manufacturer.
