Resistor helps save cardiac patients

Welwyn's new resistor is a core component in automated external defibrillators.

TT electronics Welwyn Components has released a high-voltage resistor for use in life-saving technology for cardiac arrest patients.

The resistor is a core component in automated external defibrillators (AEDs) - portable systems which give patients immediate access to essential treatment.

Previously, patients who suffered cardiac arrests had to wait until they had been transported to hospital before they could receive defibrillation treatment.

But in an attempt to reduce the delay in receiving this treatment and thus improve cardiac arrest survival, many healthcare providers are now using the portable AEDs.

The challenge was to adapt hospital-based defibrillation equipment by miniaturising the defibrillator to a small portable device whilst ensuring it could withstand harsher temperatures and humidity environments without compromising reliability.

Welwyn was asked to develop a high-voltage resistor which could be 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 delivered to the patient.

In addition to the requirement for a physically smaller component with better environmental performance, the high-voltage resistor needed to have excellent linearity - expressed by voltage coefficient (VCR) and temperature coefficient (TCR) - and long-term stability under voltage stress.

Welwyn's design team developed a high-voltage planar resistor incorporating a thick-film resistor ink based on a ruthenium oxide/glass system which is subsequently encapsulated with a specially formulated high-density epoxy protection to give improved environmental performance over the traditional porous conformal coat protection.

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