Solid-state lighting

Solid-state lighting (SSL) is an innovation in lighting that utilizes light-emitting diodes (LEDs), organic light-emitting diodes (OLED), or polymer light-emitting diodes (PLED) as sources of illumination rather than electrical filaments or gas.

Solid-state lighting has the potential to revolutionize the lighting industry. The most widely used sources of artificial illumination are incandescent and fluorescent lamps, but this is about to change: Solid-state lighting (SSL) devices promise to replace conventional light sources, with impressive economic and environmental savings. By the year 2020, electricity used for lighting may be cut by 50%, sparing the atmosphere 28 million metric tons of carbon emission annually.

Not only will SSL lead to energy and environmental savings, but it will change the way we think about lighting. SSL devices are vibration and shock resistant, and exceptionally long-lived. They will allow for a wide variety of lighting, including artificial lighting similar to natural daylight. Moreover, with appropriate circuitry, the color and intensity of the lighting can be controlled. Because SSL devices can be coupled to light pipes, light may be flexibly and efficiently distributed. SSL devices also offer interesting design possibilities--they can be manufactured as flat packages of any shape that can be placed on floors, walls, ceilings, or even furniture.

SSL devices for white lighting are already being used in certain cost-insensitive jobs. Examples of such uses include illumination for equipment subject to strong accelerations and lighting of objects where space is at a premium, like glove compartments. White LEDs are also used for such special applications as providing nighttime lighting for the text frieze inside the dome of the Jefferson Memorial in Washington, DC.
Illuminated channel letters and light box signs have become the most commonly used type of electrical signs. Channel letters have deep sidewalls with recessed light sources. Box signs utilize a recessed light source to illuminate a translucent front surface made of plastic or glass.

Channel letters and light box signs commonly use Neon, fluorescent or LEDs as their light source. Unlike neon and fluorescent light sources, LEDs are solid state devices that have no filaments and glass parts to break. LED assemblies provide sign companies a versatile ready-to-use light source, reducing sign installation and maintenance cost. LED lit signs provide longer product life and increase efficiency of brightness, minimizing long term maintenance cost.

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RoHS and its Importance

RoHS stands for “restriction of hazardous substance“. The term was coined by European Union (EU) in the year 1998 after it noticed alarmingly large quantities of hazardous waste being dumped into landfill sites. The volumes of these wastes were likely to increase 3-5 times faster than the average municipal waste. This indicated a very fast growing source of environmental contamination. RoHs is often referred to as the “lead-free” legislation, but it restricts the use of the following six substances:

1. Lead (Pb):- LEAD is mostly used and thus requiring the most attention. This is also the case for the entire electronics industry. Any cable sold with the RoHS qualification should be manufactured as such: Lead - Significant use in terminal finish for connectors/components, PWB board finish and solder for
   PWB assembly; use as UV/heat stabilizer in PVC cable jackets.
2. Mercury (Hg):- Not used.
3. Cadmium (Cd):- Very limited use as colorant for plastic materials.
4. Hexavalent Chromium (Cr⁶⁺):- Limited use as corrosion protection for retention hardware (e.g. screws, washers); limited use as conversion coating for metallic housings.
5. Polybrominated biphenyls (PBB):- Very limited use as flame retardant in plastic materials.
6. Polybrominated Diphenyl Ether (PBDE):- Very limited use as flame retardant in plastic materials.

Maximum allowed concentration values are:-

1. Up to 0.1 per cent by weight (1000 PPM) in standardized materials for lead, mercury, hexavalent chromium, PBBs and PBDEs.
2. Up to 0.1 per cent by weight (1000 PPM) in standardized materials for cadmium.

Note that not all electronic equipment fall within the scope of these regulations. For example, batteries are considered to be an ‘old area’ product and not currently covered by the regulations. Similarly, electronic equipment intended to product national security, or with a military purpose, is exempted.

To deal with this problem, the member states of the EU decided to create the waste electrical and electronics equipment (WEEE) directive, whose purpose is to:-

• Improve manufacturers’ designs, to reduce the creation of waste.
• Make manufacturers responsible for certain phases of waste management.
• Create systems to improve treatment, refuse and recycling of WEEE.
• Promote separate collections of electronic waste.

In 1998, a draft proposal called EEE (Environmental of electrical & Electronics Equipment) was also introduced along the same lines. Now, as the implementation of this policy becomes imminent, this policy is generally referred to as the RoHS directive.

As the restricted materials are hazardous to the environment and dangerous in terms of occupational exposure during manufacturing and recycling, the EU countries adhere to the RoHS. All the applicable products in the EU market after July 1, 2006 must be RoHS compliant. Therefore any business that sells applicable electronics products, sub-assemblies or components directly to EU countries, or sells to resellers, distributors or integrators that, in turn, sell products to EU countries, is impacted if it utilizes any of the restricted materials.

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Blu-ray Disc

Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage media format. It is mainly used in high-definition video and data storage. Blu-ray Disc has the same physical dimensions as a standard DVD or CD.

A single-Layer Blu-ray has storage capacity of 25GB, while a dual-layer BD can store up to 50GB of data. As the name suggests, a blue-violet laser is used to write data on a Blu-ray disk, unlike the traditional method wherein red laser employed to store data on DVDs.

A Blu-ray disk can hold 9-hour high definition video and standard-definition (SD) video that can run 23 hours, on a 50GB disk. The BD-ROM movies will require a rate of MBPS for data transfer, so the expected speed is 2x (72 Mbps). There is also a scope for having much higher speed because of the larger numerical aperture (NA) adopted by the BD. It implies that a Blu-ray disk will need less recording power and lower disk rotation speed vis-à-vis conventional DVDs and HD DVDs. The sole limiting factor for blu-ray is the capacity of the hardware.

The storage capacity of Blu-ray disk (BDs) is five times that of conventional DVDs. BDs supports NPEG-2, MPEG-4 AVC and SMPTE VC-1 formats (codecs).

Blu-ray Disc uses a "blue" (technically violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and near infrared lasers at 650 nm and 780 nm respectively.

The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85 and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. For Blu-ray Disc, the spot size is 580 nm In addition to the optical improvements; Blu-ray Discs feature improvements in data encoding that further increase the capacity.

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Signal Processing Process

• Signal processing is the analysis, interpretation, and manipulation of signals. Signals of interest include sound, images, and biological signals such as ECG, radar signals, and many others. Processing of such signals includes filtering, storage and reconstruction, separation of information from noise (for example, aircraft identification by radar), compression (for example, image compression), and feature extraction (for example, speech-to-text conversion).
  In communication systems, signal processing only occurs at OSI layer 1, the physical layer (modulation, equalization, multiplexing, radio transmission, etc) in the seven layer OSI model, as well as at OSI layer 6, the presentation layer (source coding, including analog-to-digital conversion and data compression).
  
  
  Signals are electrical representations of time-varying or spatial-varying physical quantities, either analog or digital, and may come from various sources. In the context of signal processing, arbitrary binary data streams are not considered as signals, but only digital signals that are representations of analog physical quantities.
  
  For analog signals, signal processing may involve the amplification and filtering of audio signals for audio equipment or the modulation and demodulation of signals for telecommunications. For digital signals, signal processing may involve digital filtering and compression of digital signals.
  
  Analog signal processing — for signals that have not been digitized, as in classical radio, telephone, radar, and television systems
  Discrete-time signal processing – for signals that are defined only at discrete points in time, and as such are quantized in time, but not magnitude. This theoretical discipline establishes the mathematical basis for digital signal processing, the technology of processing signals that are quantized in time and magnitude.
  
  Digital signal processing — for signals that have been digitized. Processing is done by general-purpose computers or by digital circuits such as ASICs, FPGAs, or specialized digital signal processors (DSP chips).
  
  Statistical signal processing — analyzing and extracting information from signals based on their statistical properties
  
  Audio signal processing — for electrical signals representing sound, such as speech or music
  
  Speech signal processing — for processing and interpreting spoken words
  
  Image processing — in digital cameras, computers, and various imaging systems
  
  Video processing — for interpreting moving pictures
  
  Array processing — for processing signals from arrays of sensors

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Battery Charging Technology

For rechargeable batteries, great care is required in the design of charging circuits and especially the Fast charging circuits. These circuits are dependent on the battery chemistry. On the other hand slow charging circuits – charging time more than 12 hours – are simpler than fast charging circuits.

Fast charging circuits have in-built means to terminate the charge because, overcharging the batteries may cause reduced battery life and sometimes even destroy the battery. Overcharging the battery may also lead to over-heating and emission of dangerous corrosive gases.

Below is a figure which shows the specifications of various types Rechargeable batteries:
Li-ion batteries are better than NiCd and NiMH in regard of self discharge.
The discharge rate is defined as the Max. allowable load or discharge current and is expressed in units of C-Rate.
The no. of charge and discharge cycles is the avg. no. of times a battery can be discharged and then re-charged and is measure of battery’s service life.
Memory in case of NiCd batteries usually disappears if the cell is almost fully discharged before recharging. However it is very rare that NiCd battery are discharged to that level before re-charging.

Below is the Battery Charging generalized circuit:
The battery is charged to full with a constant current supply. Voltage across the current sense resistor is used to maintain constant current supply. Control circuits and microprocessor is used to monitor voltage. Temperature sensors are used to monitor battery temperature and ambient temperature.

The above type of circuit is used for Fast charging applications.

Most difficult thing is to determine correctly that when to terminate the charging, since overcharging can damage the battery.

The charge may be terminated by monitoring battery voltage, voltage change vs. time, temperature change, temperature change vs. time, min. current at full voltage, charge time and various combinations of these depending upon the battery type.

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Advantage of Next Generation IGBTs

IGBTs –Insulated Gate Bipolar Transistor. IGBTs have always been known for high efficiency and fast switching semiconductor devices which transfers the electrical power to various appliances such as refrigerators, air conditioners etc. The article will throw light on the advantage of next generation IGBT (IGBT4) that is “Saving of Energy” and this is done by the characteristics and operational behavior of these new generation IGBTs.

Nowadays, energy saving is the prime objective of every country. Demand for the energy is increasing and moreover, factors like rising energy costs, lack of availability of fossil fuels and to reduce the emission of CO2 justify the reason fro energy saving.

Energy can be saved by using efficient machines like inverters which further require optimized power semiconductor components and devices and IGBTs have become one of the significant components to achieve the goal. The next generation IGBT is available in three chip versions which are low, medium and high power IGBT modules.

Low version is IGBT4 – T-4 which gives nominal current from 10 to 300 A with fast switching behavior.

Medium version power module is IGBT4 – E-4 having good on-state and switching characteristics and gives current in the range of 150 to 1000 A.

The other one is IGBT4 – P-4 for high power modules with current greater than 900 A having soft switching characteristics.

The new IGBT4 generation is better than previous IGBT3 in terms of electrical performance. The former is a 1200V optimized chip operates at 1500C as compare to the latter one which is a 600V optimized chip operating at 1250C. Among these two IGBTs, the one which is operating at higher temperature leads to high output power.

Switching characteristics in the IGBT behavior is of real concern. The E-versions of the IGBTs are softer as compare to T-versions i.e. they have a soft switching characteristic. This type of characteristics is compared at nominal current as a function of DC link voltage. Another factor which is significant in the success of new generation IGBTs chips is the low static and dynamic losses with higher output. In addition to this, in the insulated gate transistors the induction of stray inductance with respect to the gate resistance with turn-on and off losses has a greater influence on the voltage characteristics.

The above described behavior of IGBTs plays a major role in achieving the optimization potential for all the IGBT modules because as the stray inductance increases it is necessary to reduce the switching speed which is further obtained by increasing the external gate resistance. The increased gate resistance leads to higher turn-on losses. Therefore higher stray inductance reduces the softness of IGBTs & diodes that results into the desired potential or output power. Hence the operational behavior of the new generation IGBTs due to all these characteristic results in the efficient method of saving energy.

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Advancement in Temperature Sensors

The devices which have dense circuits dissipate lot of power. These devices need Temperature sensor to control battery charging and to prevent damage to microprocessor and other expensive components.

Such devices generally use a Fan to control the temperature. In order to increase the battery life Fan is operated only when it is necessary. Temperature sensors are needed here to know the critical temperatures and control the Fan operation.

Temperature sensors are used in monitoring of Portable equipments temperature, CPU temperature, Battery temperature and ambient temperature. They are also used in process control and instrumentation applications.

Since in most cases the output of temperature sensors are non linear, they are first conditioned and amplified before they are processed.

In past, complex circuits were needed to correct non linearity of temperature sensors. Over this, these circuits needed manual calibrations and precision resistors were required to achieve the desired accuracy. Now days, high resolution ADCs are used to digitize the sensor outputs directly.

There are several types of Temperature sensors available. Resistance Temperature Devices (RTD) is accurate and fairly linear. They have range of -200 Deg C to +850 Deg C. Thermistors have highest sensitivity but are most non linear. They work in the range of 0 to 100 Deg C. Semiconductor temperature sensors are most advanced. They are highly accurate and linear. They work in the range of -55 to 150 Deg C. Internal amplifiers can scale the output to convenient values, such as 10mV/°C.

The bandgap temperature sensors are used as the basis for variety of IC temperature sensors to generate either current or voltage outputs.

In some cases where the temperature sensor output is required to be ratio metric with its supply voltage the Ratio metric voltage output sensors are used.

Digital output temperature sensors are used especially in remote applications. Output of sensor is digitized by a sigma-delta modulator. The output of modulator is encoded in a serial digital output signal with a mark-space ratio format that is decoded by microprocessor into either degrees centigrade or degrees Fahrenheit. As this modulation technique is clock independent, it avoids error sources common to other modulation techniques.

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Nano technology in electronics.

Category: (Integrating techniques)

Whenever we think about Nano technology the first thing comes into the mind is some thing extremely small. Particles in size range 10-9m are known as nano particles or sub-micron Particles. They are also known as quantum dots due to quantum property possessed by them.

In terms of electronics, it makes electronics quicker, cost effective and smaller. Nano technology is the answer to how we can boost the capabilities of electronic devices with keeping their weight and power consumption down. Researchers believe that Nano-devices may help the electronic circuits keep shrinking towards the atomic scale. The semi conducting properties of carbon nano tubes make them a promising alternative to silicon and nano tubes have already been used to fabricate a variety of electronic components, including diodes and FETs. Nano technology is being used in every field of electronics like:

• Displays
• High density data storage
• Non-volatile RAM
• Interconnects
• EMI Shielding
• Small multilayer Capacitors
• Optoelectronics Devices
• Optical Fiber Joining/Coating

Nano electronics promises to enhance the power of computer processors more than with conventional semiconductor fabrication techniques. A number of approaches are currently being researched, including new forms of nano lithography, as well as the use of nano materials such as nano wires or small molecules in place of traditional CMOS components.