Background The niche that supercapacitors (also known as ultra-capacitors or supercaps) have served in the market space between conventional capacitors and batteries continues to grow as more new applications are found. Supercaps are replacing batteries in data storage applications, requiring medium-to-high current/short duration backup power and battery backup due to sudden disconnect. Specific applications include 3.3V memory backup solid state drives (SSDs), battery-powered industrial and medical portable equipment, industrial alarms and smart power meters.
Compared to batteries, supercaps provide better power density with higher peak power delivery capability, smaller form factors, higher charge cycle life over a wider operating temperature range, and lower ESR. Compared to standard ceramic, tantalum or electrolytic capacitors, supercaps offer higher energy density in a similar form factor and weight. A supercap’s lifetime is maximized by reducing the capacitor’s top-off voltage and avoiding high temperatures (>50°C). See the Table 1 below for a comparison of key features.
Table 1: Supercapacitors vs. capacitors vs. batteries
Summary- Supercaps vs. batteries: Batteries: • Good energy density • Moderate power density • High equivalent series resistance (ESR) at cold temperatures
Supercaps: • Moderate energy density • Good power density • Low ESR – even at cold temperatures ( ~2x increase at -20°C vs. 25°C)
Supercap limitations: • Limited to 2.5V or 2.75V maximum per cell • Must compensate for leakage differences in stacked applications • Lifetime degrades quicker at high charge voltages and high temperatures
Early generation 2-cell supercap chargers were designed for low current charging from 3.3V, 3xAA, or a Li-Ion/Polymer battery. However, supercap technology improvements have expanded the market, resulting in a slew of medium to higher current opportunities not necessarily confined to the consumer product space. Primary applications include solid state disk drives and mass storage backup systems, high current portable electronic devices such as industrial PDAs and handy terminals, data loggers, instruments, medical equipment, and miscellaneous “dying gasp” industrial applications such as security devices and alarm systems. Other consumer applications include those with high power bursts including LED flash in cameras, PCMCIA card and GPRS/GSM transceivers, and Hard Disk Drives (HDDs) in portable devices.