Reed relays in the defibrillator high-voltage path
Automatic External Defibrillators (AEDs) are portable medical devices that diagnose specific cardiac arrhythmias and deliver a controlled electric shock to restore the heart’s normal rhythm. They are built for use by non-specialists during cardiac arrest and are deployed wherever people gather — airports, stations, office buildings and homes. Because an AED runs from its own battery, every part of its charge and delivery path has to combine low power draw with dependable high-voltage operation. SHR AUTOSENSOR high-voltage reed relays are used directly in the AED high-voltage charging path, where they offer low coil power together with high-voltage isolation and stable, repeatable switching.
What the switching path asks of the relay
- High-voltage charge and transfer switching: the relay switches the kilovolt-class capacitor charge and delivery path, so contact-to-coil dielectric strength and breakdown margin have to be designed in rather than assumed.
- Low coil power on a battery supply: the device may stand ready for long periods, so coil hold power must stay at milliwatt level without sacrificing pull-in margin over temperature and battery voltage.
- Low leakage and high isolation: minimal leakage across the open contact and between contact and coil protects the measurement and safety chain that sits next to the patient.
- Reliability after long idle time: an AED may sit unused for months, then have to work on the first cycle. Sealed contacts that do not oxidize in storage are well suited to this duty.
- Fast, bounce-controlled closure: a clean, fast make supports predictable capacitor charging without the arcing and wear seen on unprotected open contacts.
Why a hermetic reed contact fits
The reed contact is sealed inside a glass capsule with an inert fill, so it is unaffected by humidity, dust or oxidation over long standby periods. Contact resistance is low and stable, coil power is small, and the contact-to-coil construction can be specified for high dielectric withstand. These characteristics match a battery-fed medical device that must hold its charge path ready, switch a high-voltage capacitor reliably on demand, and keep the patient-side circuitry isolated. Exact breakdown, coil and lifetime figures are part-number specific and should be confirmed against the datasheet for the chosen SHR high-voltage series.
Related reading: the 10 kV-class HVR series overview, and the application note reed relays in cardiac defibrillators. Send your target voltage, capacitor size, coil supply and isolation requirement through engineering RFQ for a part-level recommendation.
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