Da Vinci Xi Surgical Robot !!!

Intuitive Surgical's da Vinci series of surgical robots have been conducting FDA-approved minimally invasive surgery on humans for well over a decade now, and the company is continuallt trying to make its robots better at performing operations with the absolute minimum of cuttingyouopeness.
Last week, Intuitive released a fancy new version of the da Vinci robot, the Xi, which it says has more capabilities than previous models and is optimized for complex procedures.

A quick reminder if you're not familiar with the da Vinci: It's not an automated surgical system. Rather, it's remote controlled by a human surgeon. The word "remote" might be a bit misleading, though: while the system is capable of being operated from just about anywhere, it's most common to have the surgeon sitting right next to it, in the operating room with the patient. The benefit of the da Vinci system isn't really the potential for remote access; instead, it's that the surgeon can use tiny robotic tools that mean a much smaller incision, along with visual enhancements like infrared imaging that provide valuable information than their eyes might not.

In case you didn't catch all that, here's the rundown on what's new and improved in the Xi:

A new overhead instrument arm architecture designed to facilitate anatomical access from virtually any position.
A new endoscope digital architecture that creates a simpler, more compact design with improved visual definition and clarity.
An ability to attach the endoscope to any arm, providing flexibility for visualizing the surgical site.
Smaller, thinner arms with newly designed joints that offer a greater range of motion than ever before.
Longer instrument shafts designed to give surgeons greater operative reach.

In addition, the da Vinci Xi System is built to be compatible with Intuitive Surgical's Firefly Fluorescence Imaging System. While it is not currently available, we plan to seek regulatory clearance for use of Firefly Imaging with the da Vinci Xi System. This technology is currently available as an option with the da Vinci Si model, and it is used to provide the surgeon with additional visual information in a variety of surgical procedures by enabling real-time visualization and assessment of vessels, bile ducts and tissue perfusion.

That last bit in there is a good example of one of the benefits of using a robot for surgery: you can add a bit of augmented reality into the mix to make the job of the surgeon significantly easier by providing information overlaid on the important bits of the patient directly, instead of having to glance back and forth at images while you try not to poke the wrong squishy thing.
Still, we should point out that the benefits of robotic assisted surgeries are still open to debate: they are minimally invasive, but the systems are expensive, making the surgeries more expensive, and the overall benefit to the patient is not always certain.

However, a UCLA study from February of this year did find that "prostate cancer patients who undergo robotic-assisted prostate surgery have fewer instances of cancer cells at the edge of their surgical specimen and less need for additional cancer treatments like hormone or radiation therapy than patients who have traditional 'open' surgery."
This is the sort of study that we need more of, especially as surgical robots get more advanced: the technology that da Vinci systems represent is very impressive, but it's important to know that it's definitely worth using before our healthcare system invests in it.

For more information check on the below website.
Intuitive Surgical

Wireless Charging For Electric Vehicles

Wireless charging is on the way hitting up on the road for electric vehicles. Vehicles with wireless charging has a revolutionary inductive charging technology. Batteries being charged wirelessly when the bus stops to pick up the passengers. With no need to plug in the charge, its a breakthrough that should speed up the widespread adoption of electric vehicles.

Since charging in a electric vehicle is laborious as owner has to find charging point, connect up their cable and leave the vehicle for hours. This replaced by wireless power transfer technology which was developed decades ago, but its low efficiency restricted to little industrial settings, providing power for robotic vehicles and cranes.

It relies on the principle of electromagnetic induction. A magnetic field generated by an alternating current in a primary coil induces a current in a nearby secondary coil. It allows an energy transfer efficiency of 90%or higher.

John Boyes and Grant Covic at the University of Auckland in New Zealand worked out the optimal design for the shape of the coils to minimize energy losses. They also figured out how power can be transferred when the coils are misaligned so it still functions even if you are terrible at parking. The magnetic field has to be controlled so it stays within a safe limit, otherwise metals carried by passengers, from coins to pacemakers can get heated.

Two firms – IPT Technology of Efringen-Kirchen in Germany and Qualcomm Halo of London – have licensed the Auckland patents and are developing their own variants.On 9 January, the UK city of Milton Keynes launched a full-scale electric bus service, plying a 24-kilometer route with eight buses running from the city center to Bletchley, charged using IPT's pads.

In a test of the technology's potential, Paul Drayson, a British racing driver and entrepreneur, last October set the world land-speed record for a lightweight electric vehicle in a racing car charged by one of Qualcomm Halo's wireless pads. The company's technology will also charge the safety cars in Formula-E – the electric version of Formula 1 which kicks off later this year.

A full Detailed Article by QUALCOMM HALO..
Click Here..

Ultra Capacitors- New Efficiency for Power Train !!!

Electric and hybrid vehicles have been under development for as long as anyone can
remember, but have so far failed to become widely adopted. There have been some
fundamental problems of energy storage and delivery that have yet to be successfully
and cost-effectively overcome. Many of these issues can be traced to the limitations of
batteries – heavy, large in size, with a limited charging rate and potentially high
maintenance.

System designs can take advantage of the power of ultra capacitors to conserve energy
by allowing the engine to stop while the vehicle is not moving and then to be restarted
nearly instantly on tip in of the throttle. The design also allows regenerative braking
energy to be captured thereby significantly increasing efficiency and reducing pollution.
The use of engine start/stop and regenerative braking has been estimated to produce
between 7 and 15% increased fuel efficiency while reducing pollution by an even greater
percentage.

Announced programs for integrating ultra capacitors into vehicle power trains include big
names such as BMW, VW, Honda, Nissan and Toyota, among st many others. These
vehicles run the gamut from concept to production-intent, and include systems for hybrid
trucks, buses, and passenger vehicles are underway.

Problems with hybrid vehicles 

 Batteries have difficulty functioning in cold weather. 

 Batteries require a sophisticated charge equalization management. 

 Batteries have limited cycle life under extreme conditions, which results in high 

cost replacement throughout the life of the vehicle. A new battery has to be 

purchased and installed; the old battery has to be removed and disposed. Battery 

disposal can be problematic unless the manufacturer has a recycling program. 

 Batteries are limited in their ability to capture and provide bursts of high power 

during short duration events such as acceleration and regenerative braking. This 

high power limitation reduces the efficiency of the hybrid electric drive system 

design. 

What is an ultra capacitor? 

Ultra capacitors are based on an electric double layer technology that has been 

understood for over a hundred years, but only available for commercial applications for 

about ten years. 

What are the advantages of ultra capacitors as compared to batteries? 

 They function well in cold weather, down to –40° Celsius, whereas without heating, 

batteries do not operate well below 0° degrees Celsius. 

 They are extremely safe because a pack with equalization is discharged over night. 

 They have a long life cycle, basically built to last the time of the machine into 

which they are incorporated. This means that they are maintenance-free which 

ultimately results in costs-savings. This is particularly important for applications 

where life-cycle cost is of high value, such as embedded power modules, hybrid 

buses and trucks. 

 They are more efficient than batteries; 84-95% as compared to an average of 

below 70% for batteries in this application. 

 They are very environmentally friendly as they are 70% recyclable and do not 

include any heavy metals which are detrimental to the environment. 

 Ultra capacitors offer up to ten times the power of batteries, which plays an 

important role in boosting the acceleration of a vehicle. 

Detailed Case Study of Maxwell Technologies.

Click Here..

Microcontroller Based Dynamic Display using LED..

Here we describe a microcontroller-based dynamic display system using LED strip that can be used for advertising message display. The display works by flashing characters sequentially and then the entire text together. Different lighting effects are possible, like flashing in zig-zag, increasing, decreasing and random patterns.Surface-mount device (SMD) LEDs are becoming popular because of their low power consumption and high brightness. These LEDs are readily available in the market in many colours both as single LEDs and LED strips.

LED strip
An LED strip is made up of a number of SMD LEDs affixed to a PCB surface. LED strips are mainly of two types—flexible and rigid. These come in different lengths and light outputs.

Circuit for microcontroller based dynamic display using LED strip

The type of LED strip can be selected as per the desired application:

Bare strip. This LED strip is ideal for indoor (inside or under cupboards and stairs) and indirect lighting applications.

Silicon-covered strip. This LED strip is suitable for use in humid places like bathrooms and for outdoor use (accent lighting in houses and buildings).

Silicon-sleeved LED strip. This strip is fully encapsulated by a silicon sleeve and is suitable for use in swimming pools, saunas and outdoors where direct contact with rain or water is unavoidable.

The LED strip has in-built series dropper resistors and works off +12V, 400mA DC supply. It can be cut or trimmed to a smaller size of about 5 cm in length, and pasted on any flat surface (LED strips come with a self-sticking gum). In this dynamic display, we have cut the LED strip to form the word ‘EFY’.

Circuit description

Fig. 1 shows the circuit for microcontroller-based dynamic display using LED strip while its power supply is shown in Fig. 2. It comprises microcontroller AT89C51 (IC1), octal peripheral driver array ULN2803 (IC2, IC3, IC4 and IC5), regulator IC 7805 (IC6) and a few discrete components.

Microcontroller AT89C51 is at the heart of the circuit. It is an 8-bit micro-controller with 4 kB of Flash programmable and eras-able read-only memory (PER-OM), 128 bytes of RAM, 32 input/output (I/O) lines, two 16-bit timers/counters, a five-vector two-level interrupt architecture, a full-duplex serial port, on-chip oscillator and clock circuitry.

power supply

Ports 1, 2 and 3 of the microcontroller are 8-bit bidirectional I/O ports with internal pull-ups but port 0 is an 8-bit open-drain bidirectional I/O port. Therefore port 0 is pulled up by resistor network RNW1. Port pins P0.0 through P0.7 of the microcontroller are connected to input pins 1 through 8 of IC2, respectively. Similarly, pins of ports 1, 2 and 3 are connected to input pins of IC3 through IC5, respectively, without pull-up resistors.

ULN2803 is a monolithic, high-voltage and high-current Darlington transistor array. It consists of eight npn Darlington pairs that have high-voltage outputs with common-cathode clamp diode for switching inductive loads. The collector-current rating of a single Darlington pair is 500 mA. ULN2803 has a 2.7-kilo-ohm base resistor for each Darlington pair to connect directly with the transistor-transistor logic (TTL) or complementary metal-oxide semiconductor (CMOS) devices.

LED strips are connected to output pins 11 through 18 of the ULN2803 ICs. The microcontroller drives the LED strips through ULN2803 according to the source program.

Power-on reset for the microcontroller is provided by the combination of resistor R1 and capacitor C1. Switch S1 is used for manual reset. A 12MHz crystal along with two 33pF capacitors connected between pins 18 and 19 provides the basic clock frequency to microcontroller AT89C51.

Fig. 2 shows the circuit for power supply. The 230V AC mains is stepped down by transformer X1 to deliver a secondary output of 12V, 5A. The transformer output is rectified by full-wave bridge rectifier BR1, filtered by capacitor C4 and regulated by IC 7805. Capacitor C5 bypasses the ripples, if any, present in the regulated supply. LED1 acts as the power indicator and R2 limits the current through LED1. Regulated 5V DC supply is used for the microcontroller section. Unregulated supply (12V) is used for the LED strips and ULN2803 ICs.

Software

The source program (strip.c) for microcontroller-based dynamic display using LED strip is written in ‘C’ language. It is compiled using the Keil µVision4 compiler to generate the hex code. The generated hex code is burnt into the microcontroller using a suitable programmer.

The source program allows for lighting effects like flashing in zig-zag, increasing, decreasing and random patterns. Different delay combinations make the lighting effect more attractive. Function rand( ) is used to generate the random lighting effects.

Click for Source Code

Electric Garage adds Tesla High Power Charger for Public Use !!!

A high power wall connnector for Tesla Electric cars have been installed for public use at CMU's Electric garage in Oakland. Thisn is the largest charging infrastyructure of any instittution in Pennsylvania. The tesla charger is also available to public locally and available at no cost for 24 hrs on first come first served basis.

Tesla High Power Charger

This connector is termed as the most intelligent connector making it ideal for long term storage and can be installed by any certified electrician. It has charging rate of 58 miles per hour at Maximum Power. Using the mobile connector it provides a charging rate of 29 miles/hour.

TECHNICAL SPECIFICATION 

Maximum Current- 70A

Voltage- 208-240V, Single phase

Maximum Power- 16.8kW

Cord length- 25 ft

Unit Weight- 47lbs

Intelligent Auto Resettable GFCI Stationary unit

Tesla Model-S charging

It also has a Tesla App that allows you to check the state of charging remotely. Just pull up the apkp to see if you have recovered the range needed to get to your next destination .It can also be used to heat or cool the cabin to your preferred temperature. The Tesla Mobile app is available to download in Apple App Store and the Android App Store.

WATER STRIDERS... New Concept in Microbots...!!!

A microbot have been developed by Chinese researchers that can repeatedly jump over across the surface of water without tanking. They have a porous, highly repellent nickel foam coating so that the strider like bot legs are able to stay afloat with every 14cm leap it makes, despite its high weight of 1100 water striders

bio inspired waterstrider model

bio inspired microstrider

As reported by scientists these tiny robots can walk on water. They could skim across water bodies to monitor water quality or can be used as tiny spies.

But practically, even the most advanced designs can only walk on water. It is difficult to make robot jump because of the downward force needed it to propel it into the air usually pushes the legs through the water surface. To overcome this nickel  foam coating is used to build a true water string robot.

On/Off Control of Fan by Light !!!

Wanna turn On and Off a fan by just directing torchlight or other light using Light Dependent Resistor(LDR).
Check on the circuit below for a 5V power supply.

Preset VR1 and a light-dependent resistor (LDR) work as the potential divider. Normally, the LDR’s resistance is high (20 kilo-ohms) in darkness and low (2 kilo-ohms) in light. This value of high and low resistances varies for other LDRs. Preset VR1 is used for setting the intensity of light, while preset VR2 is used for setting the output time period of IC1. When light falls on the LDR, the monostable (IC1) triggers at pin 2, making its output at pin 3 from low to high. This low-to-high transition forms a clock for D flip-flop. The D flip-flop is operated in toggle mode by connecting its Q output to D point. The flip-flop output goes to an inverter (N1). The inverter output is fed to the relay driver transistor.

When the inverter output is low, diode D1 conducts and the current is diverted into the inverter. Hence the relay does not energise. When the inverter output is high, diode D2 conducts and the current is diverted into transistor T. Hence the relay energises. One terminal of the fan is connected to the normally-open (N/O) contact of the relay, while another terminal is connected to the neutral (N) of mains. The mains live (L) is connected to the pole of the relay. When the relay energises, the fan turns on. Otherwise, the fan remains off.

Switches S1 and S3 are for initial resetting of the monostable (IC1) and D flip-flop (IC2), respectively, and switch S2 is used for setting the D flip-flop. Paste a piece of paper on the face of the LDR so that it doesn’t get activated by ambient light. Use a torch to light the LDR. After initial resetting of the monostable and D flip-flop, the inverter output goes high and the fan turns on via the relay. When light falls on the LDR, the fan goes off. If torchlight is again directed toward the LDR, the fan turns on. The sequence repeats.

Initially if switch S2 is used to set the D flip-flop, the fan is held ‘off’. The relay does not energise as the Q output of D flip-flop goes high to make the inverter output low. Directing the light towards the LDR at this moment turns the fan ‘on.’

Transforming The Smart Grid..!

Represents the future of Electrical Generation and Distribution Infrastructure. Its paradigm for the class of technology being designed to join forces and modernize our entire energy industry.

A smart grid is a modernized electrical grid that uses analog or digital information and communications technology to gather and act on information such as information about the behavior of suppliers and consumers, in an automated fashion to improve the efficiency, reliability, economics, and sustainability of the production and distribution of electricity.

Imagine a country with no lad shedding, power cuts or blackouts. A new era of reliable and efficient electricity supply is what the smart grid concept promises. Integrating modern digital electronics technologies into the electrical power grid enables the utility to detect, monitor and respond digitally to any changes, thus making it a smarter version of the grid and earning it the name.

Implementing the smart grid concept, will arm the grid with a plethora of sensors, controllers, communication equipment and new technology that enables the grid to be fully automated-enabling it to promptly respond to any incidents in the grid.

How Smart Grid Responds To an Outrage ?

When a disturbance in the grid is initiated, the sensing and monitoring mechanism of the grid detects the cause of the outrage and enables the grid to take measures to quarantine it so it does not affect the rest of the grid. In the quarantined grid, the technology begins working on recovering electricity distribution to the critical services first—providing power to hospitals, police institutions, communications, etc. It will also loop in consumer-controlled power-generation sources when the utility is unable to provide enough power, thus fostering energy trade within the community as well.

Even smarter meters. 

Smart meters are not only limited to measurement, but also play an integral part in deriving the quality of power. “An energy audit meter not only measures the power on a relative parameter, but also measures its quality,” explains A.V. Srinivasan, area manager—south, M.B. Control and Systems Pvt Ltd. He further explains that smart audit meters analyse the power by decoding parameters such as harmonics, power factor and so on.The newer meters not only monitor and provide data to services connected to it but also provide control over the network to designated control centers. With these meters, actions such as overshooting your maximum demand (MD) control or introducing harmonics into the grid will trigger a response from the control center directly to your meter (which is now more of a controller). In smart meter chips, metro-logy is an analogue function where we accurately detect energy across a wide current range. “Integrating multiple analogue functions into one chip is a tremendously difficult task because it involves merging functions that were originally optimised in different process geometries. Ultimately, the biggest challenge is in making the performance of analogue functions similar or better,” says David Andeen, segment manager—smart grid, Maxim Integrated. 

One indigenous example of this technology is in the MREV e2o electric vehicle manufactured by Mahindra Reva Electric Vehicles Pvt Ltd. Stated as Car2Home technology, it allows to power your home by using a car’s power during times of need. An on-board computer smartly regulates the power supplied to your home, and a full battery can ensure that the house is powered up for several hours depending on the load. This technology is complemented by the Sun2Car technology, in which a 10 sq m solar panel is set up to provide sufficient energy to power your car.

Evolving communication standards. 

One of the challenges in this area is the lack of a standard protocol for communication. “Various state utilities are experimenting in a different manner, for instance Maharashtra has looked at Zigbee for AMR-related data collection,” explains Thakurdesai. “The current focus is on powerline communication (PLC), where we have defined G3 and we are also implementing additional solutions. We have also partnered with RadioPulse for ZigBee solutions.,” adds Andeen. Syam Madanapalli, CEO and co-founder, iRam Technologies, explains why a smart grid network is best based on IPv6 (the successor to IPv4; the next generation protocols for the Internet) and IEEE 802.15.4 (the wireless standard from IEEE for the Wireless Personal Area Networks (WPANs)). According to him, “Various devices at a given location in the proposed architecture form a mesh using IPv6 and IEEE 802.15.4 and communicate to rest of the smart grid using a border router. These meshes would be replicated throughout the electrical grid and finally connected to utility using appropriate wide area network (WAN) technologies that are commercially available from the telecom operators or ISPs.”

Advanced metering infrastructure (AMI) and distribution automation. 

AMI is being more deeply integrated into the grid, and its projects are increasingly implemented by utilities, particularly for use in distribution automation (DA) applications. AMI networks require robust communications between individual meters and data concentrators. They use either RF mesh or RF star topology, or implement PLC. For example, to implement AMI, an IPv6-based wireless communication module is attached/integrated into the home energy meter. Few hundreds of homes in a given locality can form a mesh and connect to the utility using one-gateway routers. An additional border router can be provided for load balancing and redundancy purpose.

Automated test equipment. 

The current slew of smart-grid test equipment is automated systems that can test all kinds of relays from manufacturers including ABB and Siemens, as well as different kinds of protection such as overcurrent, distance, differential and generator protection. When enquired about an instrument named smart Megger relay tester (SMRT), a senior engineer explained that conventional test equipment was fully manual and, as with any manual labour, there is a certain amount of human error that is introduced. Modern automated equipment takes away human error and also reduces the amount of work that he/she has to put in.

The voltage levels faced whilst testing circuit breakers are very dangerous. “Modern equipment allows you to do dual-ground testing, which enhances safety levels considerably. Conventionally, with both sides grounded, you are unable to even make a measurement, but our new solution is so unique in that this can be carried out,” explains Ajay Goyal, managing director, Megger (India).

A switchgear will have electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. V. Narayanan, senior application engineer, Megger (India), says, “To check one switchgear, they needed the help of two to three people in order to test it properly. A new tool targeting this problem is the protection condition analyser. This tool allows to test simultaneously all of the key elements of substation protection systems—including protection relay, circuit breaker, DC system and protection circuitry—even whilst the system is on-load. Once the test is completed, it outputs the results on the display.

Multiphysics simulation. 

The huge engineering project of migrating the electrical grid to a smart grid involves modernising several electrical components. For engineers at ABB Corporate Research Power Technologies in Sweden, multiphysics tools have proved an invaluable tool for modelling the coupled electromagnetic, thermal and fluid phenomena that take place within these systems.

Data modelling and forecasting

This is where all the data gathered by the sensors, smart meters and other equipment are put into use.

Avoid gold plating the electrical grid. 

Unlike how it sounds, ‘gold plating’ is where everything is over-designed to be safe, by going overboard with thresholds and limitations. Without smart technology to optimise the operation of the power network, gold-plating has been a common approach to ensure that the network is not going to melt during abnormal events.

One of the approaches to overcome gold-plating is the dynamic rating of equipment. This can be applied to overhead lines, underground cables, transformers, etc.

“A recently developed, groundbreaking technology is a 3D model of the electricity network which provides numerous applications including modelling and forecasting applications. An aeroplane loaded with sensors is flown over the network, where it gathers Lidar data point and other relevant data—such as temperature, wind speed, electromagnetic field, heatmaps, etc. An algorithm is run over the Lidar data to automatically extract the utility’s assets, resulting into a 3D model and exact position of the utility’s assets and nearby environment such as trees,” explains Diethelm.

Is an automated power grid secure?

In addition to terrorist activities, natural disasters and ageing equipment can also bring down the electrical grid. Cumulative smart-grid cyber security investment from 2011 to 2018 will total $14 billion, forecasts Pike Research.

“This requires a better emergency management system with appropriate electronic access control and video surveillance to mitigate problems. The system should also be able to isolate problems and restore electrical services as quickly as possible when disaster happens,” says Madanapalli. The existing SCADA systems are more prone to cyber attacks as the utilities start using more and more computer-based applications without an end-to-end design for the smart grid implementation.

SUPERCAPS Lightening the Load in LED flash Applications !!!

The use of supercaps in combination with an application specific driver IC alleviates stress on the battery in powering an LED flash bulb in cell phone cameras.

Cell Phones are Becoming the ultimate consumer all-in-one portable appliance, producing digital-still camera-quality pictures, supplying WiFi/Web access and delivering high-quality audio. As customers demand a wider array of new features, however, designers are struggling to ensure the phone battery provides enough peak power to drive these increasingly complex mobile applications.

Of all functions in today's high-performance phones, the camera flash consumes the highest peak current. As a result, demand is building for circuits that can store high currents for short periods without overloading the battery to provide the power required for high-performance operation.

As designers have increased the resolution of camera phones to 3 megapixels and beyond, they also have increased the amount of light required to achieve a high-quality image. To match the photo quality of digital-still cameras, today's cell phones must either drive flash LEDs at currents as high as 2 A or xenon flash tubes charged to more than 330 V. Other applications in the phone such as the RF power amplifier, GPS mapping, Internet access, music and video — can exceed source current availability as well.

When flash LEDs are the chosen light source, a compact power design can be created by combining a flash LED controller (a stepup converter IC) with a supercapacitor, which supplies high levels of current for short durations. This approach allows the use of smaller, lighter and less-expensive power sources while extending battery life. The advantages of this approach are illustrated by a reference design in which two flash LEDs are driven at 1 A each, delivering more light than a K800i xenon strobe. At less than 2 mm, the supercapacitor is thin enough to meet the rigorous footprint requirements of the cell-phone market; it can be used to enhance other features in the phone such as longer talk time and better audio.

COMPARING LIGHT SOURCES

Cell phones with cameras greater than 3-megapixel resolution require a high-intensity flash in medium-light to low-light conditions to produce quality pictures. Although designers can use either LED or xenon flash units, each design strategy offers challenges:

High-current flash LEDs need up to 400% more power than a battery can provide to achieve the light intensity needed for high-resolution images. To overcome this power limitation, some camera phones have used longer flash-exposure times to compensate for the lack of light. However, that strategy often results in blurry photos.

Xenon flash tubes deliver excellent light power. Nevertheless, their short flash exposure cannot be used for a video-capture or movie-mode function. They also require electrolytic storage capacitors that are bulky, operate at high voltages, take a long time to recharge between flashes and cannot be used for other peak-power needs in the phone.

Designers can solve this problem with flash LEDs driven at 1 A to 2 A by using a capacitor to store the current and deliver it quickly without draining the main battery. However, conventional capacitor capability would require either a very large case size or multiple devices connected in parallel. A more practical solution for space-constrained portable systems is to use very high-value supercapacitors. These devices offer high levels of capacitance in a relatively small, flat case size.

By using a supercapacitor, designers can deliver the high-current levels needed for these short-duration events, and then recharge from the battery between events. To support the battery, designers can add a thin supercapacitor to handle the phone's peak-power needs — flash photos, audio and video, wireless transmissions and GPS readings — without compromising a slim-handset design.

This approach also allows designers to reduce the system footprint by optimally sizing the battery and power circuitry to cover just the average power consumption instead of peak levels.

DEFINING A SUPERCAPACITOR

What is a supercapacitor? Like any capacitor, a supercapacitor is basically two parallel conducting plates separated by an insulating material known as a dielectric. The value of the capacitor is directly proportional to the area of the plates and inversely proportional to the thickness of the dielectric. Supercapacitors store energy in an electrostatic field rather than in a chemical state like a battery.

Manufacturers building supercapacitors achieve higher levels of capacitance, while minimizing size using a porous carbon material for the plates to maximize the surface area and a molecularly thin electrolyte as the dielectric to minimize the distance between the plates. Using this approach, they can manufacture capacitors with values from 16 mF up to 2.3 F.

The construction of these devices results in a very low internal resistance or equivalent series resistance (ESR), allowing them to deliver high peak-current pulses with minimal drop in the output voltage. These supercapacitors reduce system footprint requirements by delivering a very high capacitance in a relatively small case size. They can be manufactured in any size and shape, and recharged in seconds.

By averaging out high power demands, supercapacitors extend battery life by up to a factor of five and allow designers to specify much smaller, lighter and less-expensive batteries. Supercapacitors also offer an operating life as long as 10 to 12 years with >500,000 cycles. Their failure mode is an open circuit (high ESR) rather than a battery's destructive event. Similarly, if overvoltage is applied to the device, the only consequence will be a slight swelling and a rise in ESR, eventually progressing to an open circuit.

POWER CHALLENGES

Low ESR presents designers with an inherent problem during the charge cycle. In any system, the capacitor is initially discharged. When the supply voltage is then applied, the supercapacitor resembles a low-value resistor. This can result in a huge inrush current if the current is not controlled or limited. Therefore, designers must implement some sort of inrush current limit to ensure the battery does not shut down. Typically, any circuit of this type also requires short-circuit, overvoltage and current-flow protection.

The challenge for designers is how to efficiently interconnect the battery, dc-dc converter and supercapacitor in a way that will limit the supercapacitor inrush charge current and continually recharge the cap between load events. Flash LEDs for digital-still cameras require 1 A to 2 A for up to 300 ms. A supercapacitor can be used to store the required current and deliver it quickly without draining the main battery. Working together with the battery, the supercapacitor discharges its power during peak loads and recharges between peaks, providing the power needed to operate systems from battery-operated hosts up to 200% longer while extending the life of the battery.

Clearly, any time designers use a supercapacitor, they must limit inrush current. In addition, the supercapacitor must be recharged when the voltage drops below the operational limit of the LEDs. Then, when the supercapacitor is fully charged, it has to be disconnected from the source. These flash-lighting systems also require short-circuit, source-overvoltage and current-flow protection.

DESIGN EXAMPLE

LED flash drivers are now available that can manage supercapacitor charging requirements and make the designer's job easier, integrating the circuitry to save space, cost and time to market. One example is AnalogicTech's AAT1282, a 2-A flash-driver IC, which contains a stepup converter used to boost the 3.2-V to 4.2-V battery input voltage up to a regulated 5.5 V. The AAT1282 also offers flash-management capabilities such as movie-mode and supercapacitor charging capabilities.

If the battery voltage is 3.5 V and the boost converter is 90% efficient, then the battery would need to supply more than 3 A for the duration of a 2-A flash pulse. This would either cause the battery-protection circuit to shut the battery down or cause a low-voltage shutdown with plenty of energy still remaining in the battery.

However, the stepup converter includes built-in circuitry that prevents excessive inrush current during startup, as well as a fixed-input current limiter of 800 mA and true-load disconnect after the supercapacitor is charged. The AAT1282's output voltage is limited by internal overvoltage protection circuitry, which prevents damage to the AAT1282 and supercapacitor from open LED (open-circuit conditions).

During an open circuit, the output voltage rises and reaches 5.5 V (typical), and the overvoltage-protection circuit disables the switching, preventing the output voltage from rising higher. Once the open-circuit condition is removed, switching resumes. At this point, the controller will return to normal operation and maintain an average output voltage. An industry-standard I2C serial digital input is used to enable and disable LEDs, and set the movie-mode current with up to 16 movie-mode settings for lower light output.

The schematic in Fig. 1 depicts the components needed to implement this flash-lighting subsystem, with some of the key components identified in the table. A 0.55-F 85-mΩ supercapacitor delivers 9-W LED power bursts using the flash LED driver IC. To achieve high light levels, the flash LEDs are driven at currents between 1 A and 2 A. The forward voltage (VF) across the LED at these high currents can range up to 4.8 V. If the 200 mV of overhead for the current-control circuitry is included, it is easy to see how the total load voltage during a flash event can range up to 5 V and require a 5.5-V stepup voltage.

Fig. 2 shows test results using two LEDs flashing at 1 A each and one LED flashing at 2 A. As the test results indicate, the supercapacitor can easily supply the necessary current for 500 ms while holding the supply voltage sufficiently above the VF of the LEDs. Between flash events, the supercapacitor is recharged at a steady rate to prepare for the next photo.

A current limit is set by the factory at 800 mA. The time to pre-charge an empty supercapacitor is about 5 seconds. The time needed to recharge the supercapacitor between two flashes is very minimal. It depends on the length of each flash. Fig. 3 shows the digital control of the flash function and movie-mode option.

The size of the supercapacitor was determined by the battery voltage, LED flash current, LED forward voltage, the efficiency of the AAT1282 and flash-pulse duration. For a 300-ms of 2-A flash, a 550 mF at 5.5-V type supercapacitor is suitable for most the application. AAT1282 has a built-in circuitry to prevent excessive inrush current to 800 mA during startup while charging the supercapacitor near ground potential. If the inrush current needs further reduction due to the size of the battery, the limit can be decreased. It also can be increased if desired.

The AAT1282 contains a thermal-management system to protect the device in the event of an output short-circuit condition. Thermal protection disables the AAT1282 when internal power dissipation becomes excessive, as it disables both MOSFETs. The junction over-temperature threshold is 140°C with 15°C of temperature hysteresis. The output voltage automatically recovers when the over-temperature fault condition is removed.

A NEW HOME IN PORTABLES

Until recently, supercapacitors have rarely been used in portable systems. Typically, they have been limited to backup or standby functions in fixed applications that use relatively low currents and offer fairly long charge times. But by combining new stepup converters with supercapacitors, designers can now create compact power designs that extend battery life. With a profile of less than 2 mm, the supercapacitor is thin enough to meet even the rigorous footprint requirements of the cell-phone market.