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| CAP-XX超级电容常见问题解答 | |
| 必威尔科技 | |
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What is a supercapacitor?
Supercapacitors utilize high surface area carbon as the energy storage medium, resulting in an energy density much higher than conventional capacitors, and a power density surpassing all known types of batteries. Supercapacitors have been in production for many years but most products were designed for applications such as memory backup that need very low currents and these products have very high internal resistance, 100 ohms in many cases. CAP-XX’s proprietary technology enables supercapacitors with very low ESR or internal resistance to enable applications requiring high pulse currents. Pulse power is a particular strength of supercapacitors and the consequent markets are very broad, including mobile phones, PDAs, PCMCIA and flash cards, medical devices, PCs, digital cameras, and AMRs.
How do supercapacitors and capacitors differ?
A traditional capacitor has three essential parts: two electrical conductors, which are usually metal plates, separated and insulated by the third part called the "dielectric". The plates are charged with equal amounts of positive and negative electrical charge, respectively. The greater the area for storing charge (plate surface area), and the thinner the dielectric (distance separating the charged plates) the greater the capacitance. This is a "physical" storage of electricity as compared with the "chemical" storage in a battery.
A supercapacitor has a very large storage area because it utilizes highly porous carbon materials which can have greater than 2000 square meters of surface area per gram. The separation distance between the charged areas is also much less due to the use of an electrolyte to conduct the charged ions, which can butt against the porous carbon, and as such the separation distance is measured in angstroms. CAP-XX adds very low ESR through patented technology to enable many new application areas.
What is the difference between power and energy?
Energy is the amount of work that can be done. Power is the amount of work that is done over a specific time period. In other words, power measures how fast energy is transferred. Power is measured in watts (W), energy in Joules (J). A low ESR supercapacitor can deliver much higher power than traditional memory back up product such as Panasonic's Gold Caps.
Are your supercapacitors surface mountable?
CAP-XX supercapacitors are a prismatic surface mountable design. Due to the nature of the materials used special handling is needed for attachment to a PCB. A post wave solder or post IR reflow process is necessary using a soldering iron for attachment. More information on handling can be found in the “CAP-XX Assembly Notes” (PDF, 53KB).
Are CAP-XX supercapacitors environmentally friendly?
Yes, CAP-XX supercapacitors are lead-free and contain no toxic substances, as opposed to most types of batteries, so products containing supercapacitors can be recycled without their removal. Supercapacitors have no heavy metals such as cobalt or cadmium. CAP-XX supercapacitors have received Sony’s Green Partner Certification.
What is the difference between an ultracapacitor, supercapacitor, and an electrochemical double-layer capacitor (EDLC)?
These are all basically the same concept as they use carbon and an electrolyte as their charge storage media and have no dielectric. EDLC is the generic name used for super- and ultra-capacitors. However there are technology and physical differences that affect operating voltage, ESR, etc.
What is operating life of a supercapacitor versus a battery?
The operating life of a supercapacitor is between 10 and 100 times the operational life of conventional secondary batteries.
What is the failure mode of a supercapacitor?
If a supercapacitor is exposed to excessive voltage or temperature for extended periods it gradually degrades to essentially an open circuit. The time taken for this to occur depends on how much over voltage or over temperature is applied. Other than physically puncturing the supercapacitor there are no short circuit failure modes. There are no catastrophic failure modes.
Why do CAP-XX supercapacitors require external balancing resistors?
The balancing requirements for a supercapacitor vary with application and product type so CAP-XX elected not to add internal balancing but to instead work with customers to determine the optimum solution for each system. These solutions range from a simple resistor that is suitable for most systems to an active balance circuit for more demanding applications.
What temperature ranges do you offer?
CAP-XX offers -30°C to +75°C and a -40°C to +85°C series of products. The higher temperature product is derived from our standard GW/GS family on a customer need basis so please contact our sales team for further information.
Can CAP-XX supercapacitors be connected in series to achieve higher voltage?
Yes, the GW2 and GS2 devices are essentially two of the respective devices connected in series to achieve a higher voltage. Please contact our sales team with your requirements.
What is the difference between cylindrical and prismatic supercapacitors?
A prismatic supercapacitor such as CAP-XX produces, consists of a number of layers that are connected in parallel. This results in a flat, very low-ESR device. A cylindrical supercapacitor is “wound” into a roll and while cost effective for larger devices a cylindrical device typically is larger and has higher ESR and inductance.
What is the self discharge or leakage of your supercapacitors?
A fully charged CAP-XX supercapacitor will typically have leakage current of under 1 micro amp. For a multi-cell devices such as the GS2/GW1 series the balance resistors will determine the total leakage rate as the resistors are typically sized such that they have a about 10 times the leakage of the supercapacitor itself. For applications requiring very low leakage CAP-XX’s application team has several active balancing circuits that can cut the total leakage current from the supercapacitor and balance circuit to less than 2 micro amps.
What is the frequency response of your supercapacitors?
Typically supercapacitors are used for low-frequency, less than 100Hz, applications but this is not true of all supercapacitors. CAP-XX supercapacitors can be used in pulsed applications such as GPRS and GSM with pulses
= 500 µS. In fact, our supercapacitors are still very effective at pulse widths down to 100 µS. CAP-XX has found that a term we call effective capacitance or Ceff is a much better indication than a traditional frequency response plot of supercapacitor behavior in pulse power applications. Ceff reflects the percentage of DC capacitance available at a given pulse width and can be thought of the time domain representation of the frequency response curve. For a 1 millisecond pulse a typical CAP-XX supercapacitor will have approximately 50% of the DC capacitance. Ceff varies with device type and temperature so contact CAP-XX for more information.
What are the key applications for CAP-XX supercapacitors?
Applications which have periodic or occasional pulsed loads which draw greater power than the voltage source (battery or voltage rail such as PCMCIA/CF/USB) can comfortably deliver:
GSM/GPRS from PCMCIA/CF/USB — refer to Application Briefs AB1009 (PDF, 139KB) , AB1010 (PDF, 141KB), AB1011 (PDF, 138KB)
GSM/GPRS for battery operated devices such as mobile phones or PDAs, refer Application Brief AB1004 (PDF, 161KB)
Pulsed loads such as GSM/GPRS for mini PCI cards, refer Application Brief AB1014 (PDF, 141KB)
Pulsed loads at low temperatures where batteries have difficulty delivering the required current, refer Application Brief AB1004 (PDF, 161KB)
Pulsed loads using long life batteries such as Lithium Thionyl Chloride that can only deliver low currents. Examples include Automatic Meter Reading, Toll Tags, Location Tracking Devices
Digital Still Cameras, refer Application Brief AB1012 (PDF, 117KB)
Pulse power for white LEDs such as a camera flash
Pulse power for displays, such as screen refresh of an Organic Electroluminescent Display (OELD)
Battery life extension for pulsed loads with alkaline batteries
What are the key parameters for measuring supercapacitors?
DC Capacitance
Effective capacitance for a given pulse width
ESR (Equivalent Series Resistance)
Leakage current
Do I need to de-rate a supercapacitor?
No. Supercapacitors are inherently safe. A minor over-voltage event that lasts a few milliseconds will not affect the supercapacitor performance. For example, if a CAP-XX supercapacitor rated at 4.5V was subjected to 5V for a few seconds, there would be no effect on the supercapacitor. You can operate a supercapacitor continuously at its rated voltage.
Do your supercapacitors change size when they are charged or discharged?
No, unlike a battery there are no chemical reactions that can cause our part to change size.
What happens if I reverse bias a supercapacitor?
Even though CAP-XX marks a polarity on our supercapacitors they are inherently a non-polarized device. However, once they have been charged the ions in the electrolyte migrate to the positive and negative electrodes. Reversing polarity causes these ions to migrate across the device and will result in an increase in ESR. There are no safety issues if a supercapacitor is reverse biased, there will be no explosion, fire, smoke, or swelling. All of our supercapacitors go though extensive testing and burn-in at voltage and as part of this process they are polarized in the manner indicated on the part.
What happens if I apply excessive voltage to a supercapacitor?
Supercapacitors are inherently safe. They do not contain any chemicals (such as Li) that may explode. If excessive voltage is applied to a supercapacitor all that will happen is the ESR will increase and the device may swell as a result of the electrolyte breaking down and forming gasses. There will be no explosion, fire or smoke.
Are your parts shipped uncharged?
Yes, the parts are discharged prior to shipment.
Will static electricity damage CAP-XX supercapacitors?
No. The reason for this is that even though static electricity discharges are at thousands of volts there is very little current and thus the effective energy in Joules is very low and will not damage the device. CAP-XX does ship our supercapacitors in anti-static packaging. However, this is not to protect our parts but to eliminate the possibility of our packaging materials generating static electricity when handled at the customer.
How are your parts shipped to customers?
CAP-XX supercapacitors are shipped in stackable anti-static trays, each tray holding 10 devices nested within cavities molded in the tray. These trays are designed so that the devices can be removed from the tray by hand or by vacuum pens.
What should I consider when using a supercapacitor in a circuit?
The main issue when using a supercapacitor is inrush current when charging a discharged supercapacitor Assume you are using a CAP-XX GW201 supercapacitor (typical ESR = 80mΩ, typical C = 0.3F), and a battery pack at 3.8V with an output impedance = 150m W (typical for a Lithium-ion battery pack with protection circuit). At the instant you connect the supercapacitor across the battery pack the inrush current = 3.8V/(150mΩ + 80mΩ) = 16.5A! The battery protection circuit will shut the battery pack down. After 100msecs the current would have decayed to 3.9A. CAP-XX Application Note 1002 (PDF, 312KB) has some current limiting solutions.
Can CAP-XX supercapacitors be damaged by charging too fast?
No. We rate out parts at 30 amps of pulse current so they can be charged at that rate. We do have charge current limit circuits available, but those are to protect the system or battery from excessive current in charging a supercapacitor. For more information, please refer to the previous question (using a supercapacitor in a circuit).
How long does it take to charge a supercapacitor? Are they too big to charge between load pulses?
Supercapacitors average the load as seen by the source, and average the source voltage as seen by the load. The bigger the supercapacitor, the better the averaging. It is a misconception that a supercapacitor is “too big” to charge between pulses. The bigger the supercapacitor, the less it is discharged during the pulse and the less it needs to be charged between pulses. In this case, the supercapacitor acts as a low pass filter. In the case of a pulse train with an ideal supercapacitor with infinite capacitance and zero mΩ ESR, the source will see a DC current = average load current, and the Load will see a DC voltage = Source voltage at no load – source impedance x average load current.
Can CAP-XX supercapacitors be bent or compressed?
The supercapacitor device is hermetically sealed and bending or applying too much pressure on the device may damage the seals leading to device failure. CAP-XX supercapacitors should not be exposed to 400kPa pressure across flat surface of device (10 kg or 22lb max). CAP-XX has worked with customers developing “wearable” devices where some flexing of the device was needed. If you have such a requirement, please contact us.
Does CAP-XX offer engineering services?
Yes, CAP-XX has a seasoned applications team that can assist customers in selection and application of our supercapacitors. There are also many application notes in the resources section of this Web site. Contact us about our engineering services.
2/26/2007 | |
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