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POWER SUPPLY Supercapacitor with ultra-low leakage current to combine with lithium batteries

Editor: Johanna Erbacher

Supercapacitors may be combined with batteries to add the advantages of high capacity and low internal resistance. Low leakage currents will extend battery life in this application. HY-LINE Power Components now offers a new model optimized specifically for this use case.

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PHVL supercapacitor.
PHVL supercapacitor.
(Source: HY-LINE Power Components)

Whether for real-time clocks, memory retention or small buffer solutions: Supercapacitors have been an interesting alternative to batteries and accumulators for decades. They are also increasingly replacing button cell batteries in measuring devices, controls, water and electricity counters and smart meters in general, as well as on embedded boards, in the Internet of Things, telematics and e-call applications.

Supercapacitors have a long life of at least 10 years and may be transported by air and road without restriction. Neither storage, charging cycles in the six-digit range, deep discharge nor low temperatures can harm their performance. They may therefore actually be firmly soldered to an assembly, which rules out failures due to bad contacts.

However, the capacity of a supercapacitor is usually not delivering energy for 10 years, but only for a few weeks without recharging. Lithium batteries, on the other hand, manage 10 years, but without a buffer capacitor they have problems with pulse loads, like in smoke detectors and sensors networked via radio technology. An elegant solution is to connect the supercapacitor and battery in parallel - for example as a hybrid supercapacitor that internally combines the technologies of supercapacitor and rechargeable lithium-ion battery.

A popular alternative is to install two separate components: A high-capacity, non-rechargeable lithium battery and a supercapacitor. Since the maximum voltage of supercapacitors is 2.5 to 3.0 V per cell and lithium batteries deliver 3.6 V per cell, a series connection of supercapacitors is required. Their balancing network and supercapacitor self-discharge can reduce lithium battery life.

In the new PHVL supercapacitor, the lower operating voltage and good selection of supercapacitors for minimum leakage currents and identical capacitances made it possible to dispense with a balancing network. It offers an operating voltage of 3.9 V (peak voltage 5.0 V) and capacitances of 0.47 to 5.0 F at an operating temperature range of -40 to +65°C (-40 to +85°C with restrictions). At the same time, it shows only 10 to 20% of the leakage current of comparable models with up to 5.5 V working voltage; for a 5 F model, this is only 5 µA. This is the most uncompromising combination of the particularly long operating life of the lithium battery with the low internal resistance of the supercapacitor.

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