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A capacitor that has much greater energy density and power per pound than electrostatic and electrolytic capacitors. Used in myriad electronic circuits as well as hybrid and electric cars, ultracapacitors are also called "supercapacitors."

With a life cycle of more than a million charges, ultracapacitors are ideal for applications that require frequent, fast charges and discharges, such as hybrid vehicles that are constantly braking and accelerating. However, since they have much less energy density than storage batteries, they do not serve as a long-term energy source.

Ultra Thin Separation Layer
The separation area between the positive and negative electrodes was reduced from millimeters in electrostatic capacitors to microns in electrolytic capacitors to nanometers in ultracapacitors. Thus, the ratio of surface area to separation layer in ultracapacitors is orders of magnitude greater than its predecessors. See capacitor.

A Hybrid Vehicle Application
Maxwell's BOOSTCAP (top image) is a soda can-sized ultracapacitor used in multiples. The size of a coffee table, the 390 volt hybrid bus module (bottom image) holds 144 BOOSTCAP ultracaps that are charged when the bus is braked and discharged when it accelerates. (Image courtesy of Maxwell Technologies,

D-Cell Sized Ultracaps
This Maxwell BOOSTCAP is the size of a flashlight D-Cell. With pins for circuit board attachment, they are used in multiples for numerous applications such as smoothing out incoming power to telecom equipment and turning a windmill into the wind. Smaller BOOSTCAPs are used to power wireless readings from utility meters. (Image courtesy of Maxwell Technologies,


An electronic component that stores an electric charge and releases it when required. It comes in a huge variety of sizes and types for use in regulating power as well as for conditioning, smoothing and isolating signals. Capacitors are made from many different materials, and virtually every electrical and electronic system uses them.

Somewhat Like a Battery
Capacitors act like tiny storage batteries that charge and discharge rapidly. Made of two plates separated by a thin insulator or sometimes air, when one plate is charged negative and the other positive, a charge builds up and remains after the current is removed. When power is required, the circuit is switched to conduct current between the plates, and the charge is released. See ultracapacitor.

Many Applications
Big capacitors are used in computer power supplies. Tiny discrete ceramic and tantalum capacitors are built on the outside of the chip package or surround the chip on the motherboard. In signal processing, a capacitor and resistor smooth the spikes and sharp edges from a signal. In DRAM chips, capacitors are microscopic cells that hold the 0s and 1s (bits). Logic circuits, which are mostly transistors and resistors, may also contain capacitors. See tantalum capacitor and ferroelectric capacitor.


Silver Batteries
Looking like "silver cans," and acting like miniature storage batteries, capacitors are found on countless circuit boards such as this high-end display adapter. Wired between the power and ground planes, they quickly charge up when the computer is turned on. When more transistors switch simultaneously because the application demands extra processing, they are made to release their charge. (Image courtesy of NVIDIA Corporation.)

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