Application
Supercapacitors for IoT and Wireless Devices
Pulse buffering for LoRa, NB-IoT, LTE-M and BLE transmissions.
Power requirements
Wireless sensor nodes spend most of their time asleep, then draw short bursts — typically tens to hundreds of milliamps for milliseconds to seconds during transmission.
Why supercapacitors fit
A supercapacitor in parallel with a coin cell or harvester can supply the pulse, preventing battery voltage collapse and extending usable battery capacity.
Selection factors
- Pulse current × ESR must keep voltage above the radio brown-out level.
- Capacitance sized for the pulse charge: C ≥ I·t / ΔV.
- Leakage current relative to sleep current.
- Size and profile constraints.
Limitations
- Leakage may exceed sleep current in ultra-low-power designs
Worked example: NB-IoT burst
250 mA for 1.5 s with an allowed 0.6 V droop: C ≥ 0.25 × 1.5 / 0.6 ≈ 0.63 F. ESR drop at 250 mA with a 0.2 Ω part is 0.05 V. With tolerance and aging margin, a ~1 F part would be a starting point for evaluation.
Supercapacitor types
Coin-Cell Supercapacitors
Low-profile button cells for RTC and memory hold-up where current is in the microamp range.
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Radial-Lead Supercapacitors
Through-hole cylindrical cells for PCB mounting, typically from about 0.5 F to around 100 F.
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Lithium-Ion Capacitors
Hybrid devices combining an EDLC-type cathode with a pre-lithiated anode for higher energy density.
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