The Fundamentals of PWM Switching Power Supplies

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The operation of switching power supplies can be relatively easy to understand. Unlike linear regulators which operate the power transistor in the linear mode, the PWM switching power supply operates the power transistors in both the saturated and cutoff states. In these states, the volt-ampere product across the power transistor is always kept low (saturated, low-V/high-I; and cutoff, Hi-V/No-I). This EI product within the power device is the loss within all the power semiconductors.
This more efficient operation of the PWM switching power supply is done by “chopping” the direct current (dc) input voltage into pulses whose amplitude is the magnitude of the input voltage and whose duty cycle is controlled by a switching regulator controller. Once the input voltage is converted to an ac rectangular waveform, the amplitude can be stepped up or down by a transformer.
Additional output voltages can be derived by adding secondaries to the transformer. Ultimately these ac waveforms are then filtered to provide the dc output voltages. The controller, whose main purpose is to maintain a regulated output voltage, operates very much like a linear style controller. That is, the functional blocks, voltage reference, and error amplifier are arranged identical to the linear regulator’s. The difference is, the output of the error amplifier (the error voltage) is then placed into a voltage-to-pulsewidth converter stage prior to driving the power switches.
There are two major operational types of switching power supplies
: the forward-mode converter and the boost-mode converter. Although their arrangements
of parts are subtly different, their operation is very different and each
has advantages in certain areas of application.
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Basic Test Equipment Needed

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Power supplies, especially switching power supplies, require the designer to viewparameters not commonly encountered in the other fields of electronics. Aside from ac and dc voltage, the designer must also look at ac and dc current measurements and waveforms, and RF spectrum analysis. Although the vision of large capital expenditures flashes through your mind when this is mentioned, the basic equipment can be obtained for under US $3000. The equipment can be classified as necessary and optional, but somewhere along the line, all the equipment will have to be used whether one buys the items or rents them.

Necessary test equipment
1. A 100MHz or higher bandwidth, time-based oscilloscope. The bandwidth is especially needed for switching power supply design. A digital oscilloscope may miss important transients on some of the key waveforms, so evaluate any digital oscilloscope carefully.
2. 10 : 1 voltage probes for the oscilloscope.
3. A dc/ac volt and ampere multimeter. A true RMS reading meter is optional.
4. An ac and/or dc current probe for the oscilloscope. Especially needed for switching power supply design. Some appropriate models are Tektronics P6021 or P6022 and A6302 or A6303, or better.
5. A bench-top power supply that can simulate the input power source. This will be a large dc power supply with voltage and current ratings in excess of what is needed. For off-line power supplies, use a variac with a current rating in excess of what is needed.
Note: Please isolate all test equipment from earth ground when testing.
Optional test equipment
1. Spectrum analyzer. This can be used to view the RFI and EMI performance of the power supply prior to submission to a regulatory agency. It would be too costly to set up a full testing laboratory, so I would recommend using an third-party testing house.
2. A true RMS wattmeter for conveniently measuring efficiency and power factor. This is needed for off-line power supplies.
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A Comment about Power Supply Design Software

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There is an abundance of software-based power supply design tools, particularly for PWM switching power supply designs. Many of these software packages were written by the semiconductor manufacturers for their own highly integrated switching power supply integrated circuits (ICs). Many of these ICs include the power devices as well as the control circuitry. These types of software packages should only be used with the targeted products and not for general power supply designs. The designs presented by these manufacturers are optimized for minimum cost, weight, and design time, and the arrangements of any external components are unique to that IC.

There are several generalized switching power supply design software packages available primarily from circuit simulator companies. Caution should be practiced in reviewing all software-based switching power supply design tools. Designers should compare the results from the software to those obtained manually by executing the appropriate design equations. Such a comparison will enable designers to determine whether the programmer and his or her company really understands the issues surrounding switching power supply design.
Remember, most of the digital world thinks that designing switching power supplies is just a matter of copying schematics. The software packages may also obscure the amount of latitude a designer has during a power supply design. By making the program as broad in its application as possible, the results may be very conservative. To the seasoned designer, this is only a first step. He or she knows how to “push” the result to
enhance the power supply’s performance in a certain area. All generally applied equations and software results should be viewed as calculated estimates. In short, the software may then lead the designer to a result that works but is not optimum for the system.
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Role of the Power Supply within the System and Design Program

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The three major power supply technologies that can be considered within a power supply system are:
1. Linear regulators.
2. Pulsewidth modulated (PWM) switching power supplies.
3. High efficiency resonant technology switching power supplies.
Each of these technologies excels in one or more of the system considerationsmentioned above and must be weighed against the other considerationsto determine the optimum mixture of technologies that meet the needs ofthe final product. The power supply industry has chosen to utilize each of the technologies within certain areas of product applications as detailed in thefollowing.

Linear
Linear regulators are used predominantly in ground-based equipments where
the generation of heat and low efficiency are not of major concern and also where
low cost and a short design period are desired. They are very popular as boardlevel
regulators in distributed power systems where the distributed voltage is less
than 40VDC. For off-line (plug into the wall) products, a power supply stage
ahead of the linear regulator must be provided for safety in order to produce
dielectric isolation from the ac power line. Linear regulators can only produce
output voltages lower than their input voltages and each linear regulator can
produce only one output voltage. Each linear regulator has an average efficiency
of between 35 and 50 percent. The losses are dissipated as heat.
PWM switching power supplies 
PWM switching power supplies are much more efficient and flexible in their use than linear regulators. One commonly finds them used within portable products, aircraft and automotive products, small instruments, off-line applications, and generally those applications where high efficiency and multiple output voltages are required. Their weight is much less than that of linear regulators since they require less heatsinking for the same output ratings. They do, however, cost more to produce and require more engineering
development time.
High efficiency resonant technology switching power supplies
This variation on the basic PWM switching power supply finds its place in applications where still lighter weight and smaller size are desired, and most importantly, where a reduced amount of radiated noise (interference) is desired. The common products where these power supplies are utilized are aircraft avionics, spacecraft electronics, and lightweight portable equipment and modules. The drawbacks are that this power supply technology requires the greatest amount of engineering design time and usually costs more than the other two technologies.
The trends within the industry are away from linear regulators (except for board-level regulators) towards PWM switching power supplies. Resonant and quasi-resonant switching power supplies are emerging slowly as the technology matures and their designs are made easier.
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High Power Output Amplifier TDA7294

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The famous SGS-THOMSON ST Microelectronics has introduced a Hi-Fi DMOS high-power amplifier circuit TDA7294, its sound great taste bile, which due to its internal circuit from input to output are field-effect devices, rounded sound Mild, delicate Rounuan. 
 
However, with its assembly amplifier, only TDA7294 single-output power is only 70 W, BTL access law is 100 W from top to bottom, do not feel that power cushion. The author several tests, used to promote TDA7294-level, direct-drive one to four pairs of high-power transistor parallel, the output of strong currents, the power output of 400 W (mono), and the circuit is simple and no need to debug that can reliably work Basically, the IC has maintained a sound and performance. 
Ruzuo The figure below shows, R6 for the feedback resistor, the author of the value in debugging 22 k Ω more appropriate, R6 also decided this circuit gain, the gain value will increase. 
Quiescent current depends on the power of R7, R8, when its value in the following 10 k Ω, the circuit will be in a Group A state of quiescent current adjustable to 100 mA ~ 2A, the author from 30 k Ω, the circuit works in Group B and fairly stable, power of With no radiator, in 2 / 3 the volume, to promote 10-inch speaker and 10 minutes later, the power does not feel that hot, thick sound quite strong. 
The author of the trial of the power of T1, T2, had used A1943/C5200, K1530/J201, A1302/C3281, which K1530/J201 the best sound quality, particularly soft Naiting. A map of the parameters, the output power of 200 W, in Group B work, with a small heat sink (I use 14 cm × 5cm × 3cm) to meet their cooling needs. Commissioning of the circuit without a ring box.
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Toshiba Thrive Tablet Computer

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The Toshiba Thrive computer tablet uses Android 3.1 “Honeycomb” interface, allowing users to enjoy customizable desktops for widgets and shortcuts.  In terms of UI, the device is quite notable not only because it can be customized but also since the icons such as alerts, clocks, and battery level are placed with the convenience of users in mind.

As with most new Android-powered tablets, the Thrive features multi-tasking button on the bottom left of the taskbar, allowing users to easily scroll the list of thumbnails that represent applications.  And to further deliver a better UI, it has two virtual keyboards: the Swype which allows people to type quicker by tracing lines between letters, and the standard Android.

In terms of design, the computer tablet is heavier and thicker than its rivals such as the Apple iPad 2, Samsung Galaxy Tab 10.1, and Asus Eee Pad Transformer with its 10.75 x 6.7 x 0.6 inches and 1.6 pounds chassis.  But despite its cumbersome appearance, it has at least rubberized back plate to allow users to grip it with much ease.

Meanwhile, the tablet only comes in black color, although users can purchase covers which are available in several hues including Blue Moon, Silver Sky, Green Apple, and Raspberry Fusion (about $20 each).
Just like the iPad, the Toshiba Thrive boasts front- and back-facing cameras which have chrome cover that gives them a sleek appearance.
While the 1280 x 800-resolution screen can support sharp images and strong colors, its viewing angles fall short especially in the presence of a bright overhead light.  Another consideration is that fingerprints and dirt can easily taint the display panel, but at least it can support high-definition videos without any problem.
To complement the sharp images, the tablet has built-in speakers that are surprisingly loud.  Meanwhile, other features include full-size USB port, head phone jack, full-size HDMI-out ports, full-size SD card reader, and mini USB.
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Sony Alpha NEX-C3 Camera

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The Sony Alpha NEX-C3 is a 16.2-megapixel digital camera that is smaller and lighter than its predecessor despite having an improved resolution and ability to provide impressive images even in low-light environment; this is possible with the removal flash in addition to technologies almost comparable to a D-SLR.

But just like its predecessors, the digital camera has interchangeable lens (18-55mm zoom lens or 16mm pancake prime lens) and pop-up flash.
The 2.4 x 4.4 x 1.3 inches (HWD) camera weighs 9.8 ounces, lighter than most of its rivals with almost the same size and features.  The standard 18-55mm kit zoom lens is almost the same size and weight of D-SLR’s (7 ounces and 2.4 x 2.5-inch body), while the 16mm pancake prime lens weighs just 2.4 ounces.

In terms of speed, the NEX-C3 can compete with most D-SLRs with its ability to take initial shot in 1.5 seconds.  And when it is set to focus, the camera averages approximately 0.5 second between pushing the shutter button and taking the shot.
The camera’s image sharpness and noise greatly vary on the lens, aperture setting, and focal length.  But when tested with 18-55mm kit zoom lens with its widest aperture used, the image is still sharp, although reducing the “opening” so there will be less light to pass through can deliver better and sharper photos.
Alternatively, the image quality of 16mm f/2.8 prime lens is relatively soft around the edges particularly when the maximum aperture is used (not surprisingly for a wide-angle design).
While the camera has no eye-level viewfinder, at least it has a 3-inch articulating rear LCD which can display 921,600 dots, resulting to an extremely sharp image.  And because the display panel provides enough brightness, glaring is not a problem when it is used outdoor.
Because of the tilting mechanism of the LCD, it can be displayed upward while holding the camera to waist level.  This results to a steadier shot since the gadget is held closer to the body’s center of gravity.
The NEX-C3, which has a polycarbonate plastic body, boasts easy-to-navigate menu system in addition to some impressive settings and image technologies including Anti-Motion Blur (for low-light environment) and Sweep Panorama which captures a series of photos while a person pans the camera.
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Lavnav helps you aim straight at night

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Do you envy those who are able to sleep through the night without having to worry about getting up halfway in the middle in order to take a leak? Well, I suppose all the shuffling around is all right when you’re single, but some of us who are married might have spouses who are light sleepers and do not take it too kindly whenever you keep on getting up and turning on the lights just to get some relief from all the pressure that’s building up in your bladder.

Well, how about getting the �16.99 Lavnav instead? Yes sir, this unique gizmo will do away with the unpleasant experience of getting yourself half-blind when you turn on the bathroom lights with a 1,000-watt light bulb in place. All you need to do is stick the Lavnav onto the inside of your lavatory and you’re good to go – after all, the motion sensor kicks itself into action the moment it detects anyone within the vicinity. Heck, when the seat is up, it will be red in color, but goes green when the seat is left down.
Powered by a couple of AA batteries, we suspect you won’t be changing these batteries anytime soon for sure.
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Veebeam HD brings Internet to your TV

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 Smart TVs have been around for some years now, but it is safe to say that they haven’t really caught on just yet in the mass market. Well, for those who are sick and tired of watching videos as well as playing catchup on your TV programmes on a much smaller notebook display, here is the Veebeam HD to solve your woes. With this little puppy, you are able to effortlessly stream just about any content from your notebook to your home TV. You name it – live sports, streaming music, movie websites, home videos from your hard drive, the possibilities are more or less endless as long as you can view it on your computer.

Since the Veebeam HD works over the wireless spectrum, you have one less cable to worry about when it comes to keeping your home clutter-free and neat. All you need to do is plug in the USB receiver into the funky-looking �139.99 Veebeam HD unit, hook it up to your TV while plugging the separate USB antenna into your computer or notebook – it doesn’t matter whether it runs on the Mac OS X platform or Windows.
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Smartfish Mouse Pad Travel Pouch

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All mice these days no longer feature a trackball, relying on an optical sensor instead. Unfortunately, the optical sensor’s limitations are there, as it will not work across all surfaces, especially glass. That’s when you need an impromptu mouse pad, which makes the Smartfish Mouse Pad Travel Pouch a real genius as a practical traveling companion.
This mouse pad features a smooth 9� diameter surface work area for you to mouse around with, and once you’re done with your work, you can always slip the mouse inside, zip it up, and it doubles up as a protective pouch instead.
The nclusion of padded neoprene ensures your accessories (and mouse, of course) inside remains safe and sound when tucked away, and you can also opt to hang it from your backpack or suitcase for easy accessibility via the snap handle. At just $14.95 a pop, the Smartfish Mouse Pad Travel Pouch will come in blue and black shades from early next month onwards.
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Portal 2 PotatOS Science Kit

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What are some of the memories that you carry around from playing Portal 2? For some of us, it would be toting the PotatOS around the test facility, where you felt this unnatural bond as though you were kindred spirits, never mind that this is not the case.
Well, for folks who skipped the children’s Science Fair at Aperture Labs, here is something that might just redeem your absence – the $29.99 Portal 2 PotatOS Science Kit. Yes sir, just about everything that is required by you is packed into a handy Portal 2 PotatOS Science Kit, where it even sports a miniature science fair poster complete with brand new content from Valve’s writing team!
The only thing that you will need to come up with would be your very own potato, but that should not be too hard to get, right? If you’re great at following instructions, it will take mere minutes to transform your potato into your very own PotatOS, where it will light up and send verbal repartees your way, just like in the game. Nice to know that the CR2030 batteries required to run this thing is included. Just a note of caution – skip on eating the potato after using it for PotatOS.
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Archos 35 Home Connect.

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Archos intends to further push the envelope when it comes to technological boundaries as well as innovation with the introduction of their latest device, the Archos 35 Home Connect.
This is an Android-powered web radio that was specially designed for the home user. Touted to be the most advanced Android-based web radio in the market (which makes perfect sense after all, since how many web radios that run on the Android OS do you see hanging around store shelves, virtual or otherwise?), the Archos 35 Home Connect is perfectly sized to deliver streaming radio and music anywhere at home, ranging from the bedroom to the kitchen, bathroom or kids room.
Being diminutive in size certainly makes it a whole lot easier to tote around, and the Archos 35 Home Connect will boast Wi-Fi connectivity as well as amazing audio quality, once again lending wisdom to the adage that one ought not to judge a book by its cover – and in this case, the audio quality by its size. Let us take a close look at what the Archos 35 Home Connect is able to deliver after the jump.
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Quad Lock Case announced

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Annex Products has announced the rollout of its Quad Lock Case, which is touted to be the ultimate multipurpose mounting system for your precious iPhone.
Just what is the Quad Lock Case capable of? For starters, this is touted to be a safe and easy mounting solution which is capable of mounting itself to just about any surface, ensuring that your iPhone remains in a convenient position regardless of either it being in a portrait or landscape mode, letting you view your favorite photos, enjoy movies and read news, hands-free.
The Quad Lock Case Mount comes in an ultra slim form factor, where it is made up of tough polycarbonate plastic in order to help protect your iPhone’s back during everyday use. You know what they say – the simpler something is, the more beautiful it becomes, and that is exactly the case (pun not intended) with the Quad Lock Case Mount. Featuring a built-in holder which enables it to snap securely on to any of the Quad Lock Mounts, you need not worry about your iPhone’s safety any more even though it might seem as though it is hanging precariously from some other place.
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Diodes 90W mosfet controller rated to 25V

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Diodes 90W mosfet controller rated to 25V

Diodes is offering a 25V-rated synchronous MOSFET controller for notebook and laptop power supply designs of 90W and above.

Designed to replace Schottky diodes in flyback converters, the ZXGD3104N8 is claimed to increase power supply efficiency by up to 3.5% through a reduction in rectifier losses of up to 70%. As a result, the device helps power supplies more easily attain the 87% Energy Star V2.0 rating.
With its wide operating voltage range of 5V to 25V, this SO8-packaged mosfet controller is able to be directly powered from the adaptor’s 19V supply rail.
The ZXGD3104N8’s proportional gate-drive operation guards against premature mosfet turn-off as the drain current decays, thereby maximising circuit efficiency and ensuring body diode conduction losses are minimized.

This, combined with the short turn-off propagation delay of typically 15ns, helps to maximize power supply circuit efficiency.

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Plastic circuitry breakthrough may revolutionizeelectronics industry

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Researchers from the University of Cambridge's Cavendish Laboratory have a chance to revolutionize the electronics industry if they can develop plastic semiconductors.
The idea is to replace the silicon wafers in standard microchips with layers or circuitry on plastic substrates. While the concept of plastic semiconductors may seem like a pipe dream, Cambridge-based startup Plastic Logic has been talking about commercializing the technology since 2000. The company is putting money where it's mouth is, too, as it has more than $100 million worth of investment funds for a factory that it plans to open in Dresden, Germany.

The technology has "tremendous potential," said Morry Marshall, vice-president for strategic technologies at Phoenix semiconductor research group Semico, adding that it was a "breakthrough that is waiting to happen."
The final product should be a plastic sheet roughly the same size as a piece of A4 sized paper, being produced at a rate of about 2.2 million a year. They will be composed of polyethylene terephthalate -- the same type of plastic used to make soft drink bottles -- and initially supplied to other companies as the basis for pieces of "electronic paper," which can display the pages of thousands of books.
We hope to make it as easy to carry around large amounts of written information using devices based on our technology as it is now to have easy access to large amounts of music using an iPod or MP3 player," said Hermann Hauser, one of Plastic Logic's founders and a Cavendish Laboratory alumnus.
The proposed plastic semiconductors will have one disadvantage compared to traditional silicon-based substrates: There is between 5 and 10 micrometers (1 micrometer is 1 millionth of a meter) between adjacent circuitry lines in the plastic semiconductors, whereas the same space in traditional semiconductors is measured in nanometers (1 nanometer is a billionth of a meter). However, Plastic Logic Chief Executive Officer John Mills said that they are developing plastic circuits with only 60 nanometers between adjacent circuitry lines.
If they could be made smaller, plastic microchips could be used for tasks for which it would not be cost-effective to employ silicon microchips. For example, a toy could have a surface where it could display its own instruction manual.
"Plastic electronics could lead to a fundamental revolution in the way the electronics industry evolves", said Mr Hauser, who also said he would not be surprised if Plastic Logic's chief scientist Henning Sirringhaus was awarded the Nobel Prize for his work in the field.
The Cavendish Laboratory has been lauded for it's discoveries during the past 136 years, including the genetic building blocks known as DNA and the electron.


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First Molybdenite Microchip

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First Molybdenite Microchip

Molybdenite, a new and very promising material, can surpass the physical limits of silicon. EPFL scientists have proven this by making the first molybdenite microchip, with smaller and more energy efficient transistors.After having revealed the electronic advantages of molybdenite, EPFL researchers have now taken the next definitive step. The Laboratory of Nanoscale Electronics and Structures (LANES) has made a chip, or integrated circuit, confirming that molybdenite can surpass the physical limits of silicon in terms of miniaturization, electricity consumption, and mechanical flexibility.

"We have built an initial prototype, putting from two to six serial transistors in place, and shown that basic binary logic operations were possible, which proves that we can make a larger chip," explains LANES director Andras Kis, who recently published two articles on the subject in the scientific journal ACS Nano.
In early 2011, the lab unveiled the potential of molybdenum disulfide (MoS2), a relatively abundant, naturally occurring mineral. Its structure and semi-conducting properties make it an ideal material for use in transistors. It can thus compete directly with silicon, the most highly used component in electronics, and on several points it also rivals graphene.
Three atoms thick
"The main advantage of MoS2 is that it allows us to reduce the size of transistors, and thus to further miniaturize them," explains Kis. It has not been possible up to this point to make layers of silicon less than two nanometers thick, because of the risk of initiating a chemical reaction that would oxidize the surface and compromise its electronic properties. Molybdenite, on the other hand, can be worked in layers only three atoms thick, making it possible to build chips that are at least three times smaller. At this scale, the material is still very stable and conduction is easy to control.
Not as greedy
MoS2 transistors are also more efficient. "They can be turned on and off much more quickly, and can be put into a more complete standby mode," Kis explains. Molybdenite is on a par with silicon in terms of its ability to amplify electronic signals, with an output signal that is four times stronger than the incoming signal. This proves that there is "considerable potential for creating more complex chips," Kis says. "With graphene, for example, this amplitude is about 1. Below this threshold, the output voltage would not be sufficient to feed a second, similar chip."
Built in flexibility
Molybdenite also has mechanical properties that make it interesting as a possible material for use in flexible electronics, such as eventually in the design of flexible sheets of chips. These could, for example, be used to manufacture computers that could be rolled up or devices that could be affixed to the skin.
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UltraSonic Switch

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UltraSonic Switch
 
Circuit of a new type of remote control switch is described here. This circuit functions with inaudible (ultrasonic) sound. Sound of frequency up to 20 kHz is audible to human beings. The sound of frequency above 20 kHz is called ultrasonic sound. The circuit described generates (transmits) ultrasonic sound of frequency between 40 and 50 kHz. As with any other remote control system this cirucit too comprises a mini transmitter and a receiver circuit. Transmitter generates ultrasonic sound and the receiver senses ultrasonic sound from the transmitter and switches on a relay. The ultrasonic transmitter uses a 555 based astable multivibrator.

It oscillates at a frequency of 40-50 kHz. An ultrasonic transmitter transducer is used here to transmit ultrasonic sound very effectively. The transmitter is powered from a 9-volt PP3 single cell. The ultrasonic receiver circuit uses an ultrasonic receiver transducer to sense ultrasonic signals. It also uses a two-stage amplifier, a rectifier stage, and an operational amplifier in inverting mode. Output of op-amp is connected to a relay through a complimentary relay driver stage. A 9-volt battery eliminator can be used for receiver circuit, if required. When switch S1 of transmitter is pressed, it generates ultrasonic sound. The sound is received by ultrasonic receiver transducer. It converts it to electrical variations of the same frequency. These signals are amplified by transistors T3 and T4. The amplified signals are then rectified and filtered. The filtered DC voltage is given to inverting pin of op-amp IC2. The non- inverting pin of IC2 is connected to a variable DC voltage via preset VR2 which determines the threshold value of ultrasonic signal received by receiver for operation of relay RL1. The inverted output of IC2 is used to bias transistor T5. When transistor T5 conducts, it supplies base bias to transistor T6. When transistor T6 conducts, it actuates the relay. The relay can be used to control any electrical or electronic equipment. Important hints:
1. Frequency of ultrasonic sound generated can be varied from 40 to 50 kHz range by adjusting VR1. Adjust it for maximum performance.
2. Ultrasonic sounds are highly directional. So when you are operating the switch the ultrasonic transmitter transducer of transmitter should be placed towards ultrasonic receiver transducer of receiver circuit for proper functioning.
3. Use a 9-volt PP3 battery for transmitter. The receiver can be powered from a battery eliminator and is always kept in switched on position.
4. For latch facility use a DPDT relay if you want to switch on and switch off the load. A flip-flop can be inserted between IC2 and relay. If you want only an ‘ON-time delay’ use a 555 only at output of IC2. The relay will be energised for the required period determined by the timing components of 555 monostable multivibrator.
5. Ultrasonic waves are emitted by many natural sources. Therefore, sometimes, the circuit might get falsely triggered, espically when a flip-flop is used with the circuit, and there is no remedy for that.
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FANCY CHRISTMAS LIGHT

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FANCY CHRISTMAS LIGHT

This simple and inexpensive circuit built around a popular CMOS hex inverter IC CD4069UB offers four sequential switching outputs that may be used to control 200 LEDs (50 LEDs per channel), driven directly from mains supply. Input supply of 230V AC is rectified by the bridge rectifiers D1 to D4. After fullwave rectification, the average output voltage of about 6 volts is obtained across the filter comprising capacitor C1 and resistor R5. This supply energises IC CD4069UB.


All gates (N1-N6) of the inverter have been utilised here. Gates N1 to N4 have been used to control four high voltage transistors T1 to T4 (2N3440 or 2N3439) which in turn drive four channels of 50 LEDs each through current limiting resistors of 10-kilo-o Base drive of transistors can be adjusted with the help of 10-kilo-ohm pots provided in their paths. Remaining two gates (N5 and N6) form a low frequency oscillator. The frequency of this oscillator can be changed through pot VR1. When pot VR1 is adjusted To get the best results, a low leakage, good quality capacitor must be used for the timing capacitor C2.
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A LOW DISTORTION AUDIO PREAMPLIFIER

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In an audio amplifier the quality of sound depends upon a number of factors, e.g. quality of active and passive components, circuit configuration, and layout. To an extent, the selection of components depends on the constructor’s budget. The discrete active components like transistors have been increasingly replaced by linear ICs, making the task of designer easier. With the passage of time, the general-purpose op-amps like LM741, which were being used in audio/hi-fi circuits, have become The preamplifier circuit presented here is based on a dual precision op-amp for the construction of a low distortion, high quality audio preamplifier.


A dual op-amp OPA2604 from Burr-Brown is used for all the stages. The FET input stage op-amp was chosen in this context it is worthwile to mention another popular bi-polar architecture op-amp, the NE5534A. It has, no doubt, an exceptionally low noise figure of 4nV/ÖHz but rest of the specifications compared to OPA2604 are virtually absent in this IC. Also This IC is also capable of operating at higher voltage rails of ± 24V (max.). Also its input bias current (100 pA) is many orders lower than its bipolar counterpart’s. This ensures a multifold reduction in noise.

A channel seperation of 142 dB exists between In the circuit, buffer is essential for the proper working of the subsequent blocks. A nominal input impedance of 47k is offered by this stage which prevents overloading of the preamplifier. The tone control is a baxandall type filter circuit.The bandwidth limiter is basically a low-pass filter with an upper cut-off ceiling at the end of the useful audio spectrum. The gain at 10 kHz is approximately 17 dB. The design is essentially 3-pole type and the upper frequency is set at 25 kHz. This lSetting the unit is fairly simple. Check the power leads feeding the IC for symmetrical voltages. High quality audio output from the line output socket is to be fed as the input signal to this preamplifier. Output of the preamplifier is fed to the power a The whole circuit consumes about 10 mA when the above-mentioned ICs are used. Power supply requirements are not critical as the circuit works on 7.5V to 15V DC..
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VHF AUDIO VIDEO TRANSMITTER

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The circuit presented here is a simple audio/video transmitter with a range of 3 to 5 metres. The A/V signal source for the circuit may be a VCR, a satellite receiver or a video game etc. The circuit uses inexpensive components which are easily available in the market.A block diagram showing the principle of its operation and complete circuit diagram are shown in the figure. A mixer which also operates as an oscillator at VHF (H) channel 5 TV frequency is amplitude modulated by video signal and mixed with frequency mo enna, contains video carrier frequency of 175.25 Mhz and audio carrier frequency of 180.75 Mhz.

The circuit consists of transistor T1 with its resonant tuned tank circuit formed by inductor L1 and trimmer capacitor VC1, oscillating at VHF (H) channel 5 frequency. Transistor T2 with its tuned circuit formed using SIF coil and inbuilt capacitor forms oscillator. The audio signal applied at the input to T2 results into frequency modulation of 5.5 Mhz oscillator signal. The output of 5.5 Mhz FM stage is coupled to the mixer stage through capacitor C8 while the video signal is coupled to the emitter of T1 via capacitor C4 and variable resistor Inductor L1 can be wound on a 3mm core using 24SWG enamelled wire by just giving 4 turns. Calibration/adjustment of the circuit is also not very difficult. After providing 12V DC power supply to the circuit and tuning your TV set for VHF (H) channel 5 reception, tune trimmer VC1.
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INFRARED TOY CAR MOTOR CONTROLLER

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INFRARED TOY CAR MOTOR CONTROLLER
This add-on circuit enables remote switching on/off of battery-operated toy cars with the help of a TV/ video remote control handset operating at 30–40 kHz.. 
When the circuit is energised from a 6V battery, the decade counter CD4017 (IC2), which is configured as a toggle flip-flop, is immediately reset by the power-onreset combination of capacitor C3 and resistor R6.
LED1 connected to pin 3 (Q0) of IC2 via resistor R5 glows to indicate the standby condition. In standby condition, data output pin of the integrated infrared receiver/demodulator (SFH505A or TSOP1738) is at a high level (about 5 volts) and transistor T1 is ‘off’ (reverse biased). The monostable wired around IC1 is inactive in this condition.

When any key on the remote control handset is depressed, the output of the IR receiver momentarily transits through low state and transistor T1 conducts. As a result, the monostable is triggered and a short pulse is applied to the clock input (pin 14) of IC2, which takes Q1 output (pin 2) of IC2 high to switch on motor driver transistor T2 via base bias resistor R7 and the motor starts rotating continously (car starts running). ResistorR8 limits the starting current.

When any key on the handset is depressed again, depressed again, the monostable is retriggered to reset decade counter IC2 and the motor is switched off. Standby LED1 glows again.

This circuit can be easily fabricated on a general-purpose printed board. After construction, enclose it inside the toy car and connect the supply wires to the battery of the toy car with right polarity. Rewire the DC motor connections and fix the IR receiver module in a suitable location, for example, behind the front glass, and connect its wires to the circuit board using a short 3-core ribbon cable/shielded wire.Since the circuit uses modulated modulated infrared beam for control function,  ambient light reflections will not affect the circuit operation. However, fluorescent tubelights with electronic ballasts and CFL lamps may cause malfunctioning of the circuit
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Audio Amplifier

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Audio Amplifier
The principal component of the amplifier kit is the LM 386 IC. This IC is specifically designed as a low wattage amplifier for small scale projects. The signal enters through R1, the 10Kohm potentiometer. This also serves as a volume control for the circuit. The signal is introduced to pin 3 of the IC.
The amplifier output is passed directly to speaker through C2. The capacitor is used to isolate the speaker from the dc power that drives the amplifier.

The circuit composed of R2, the 1K ohm resistor, and C1 the 10uF capacitor, establishes the gain of the amplifier. For this circuit, the gain is set at 50.To increase the gain you can either increase the value of the capacitor or decrease the value of the resistor.

The 0.uF capacitor placed across the power source is used to eliminate noise that can be generated by power source.

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Semiconductors

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  •  Conductivity in between those of metals and insulators.
  • Conductivity can be varied over orders of magnitude by changes in temperature, optical excitation, and impurity content (doping).
  • Generally found in column IV and neighboring columns of the periodic table.
  • Elemental semiconductors: Si, Ge.
  • Compound semiconductors:

    Binary :

GaAs, AlAs, GaP, etc. (III-V).

ZnS, ZnTe, CdSe (II-VI).

SiC, SiGe (IV compounds).

  • Ternary : GaAsP.
    Quaternary : InGaAsP.
  • Si widely used for rectifiers, transistors, and ICs.
  • III-V compounds widely used in optoelectronic and high-speed applications.
Applications
  • Integrated circuits (ICs) SSI, MSI, LSI, and VLSI.
  • Fluorescent materials used in TV screens II-VI (ZnS).
  • Light detectors InSb, CdSe, PbTe, HgCdTe.
  • Infrared and nuclear radiation detectors Si and Ge.
  • Gunn diode (microwave device) GaAs, InP.
  • Semiconductor LEDs GaAs, GaP.
  • Semiconductor LASERs GaAs, AlGaAs.
Energy Gap
  • Distinguishing feature among metals, insulators, and semiconductors.
  • Determines the absorption/emission spectra, the leakage current, and the intrinsic conductivity.
  • Unique value for each semiconductor (e.g. 1.12 eV for Si, 1.42 eV for GaAs) function of temperature.
Impurities
  • Can be added in precisely controlled amounts.
  • Can change the electronic and optical properties.
  • Used to vary conductivity over wide ranges.
  • Can even change conduction process from conduction by negative charge carriers to positive charge carriers and vice versa.
  • Controlled addition of impurities doping.
Crystal Lattices
  • Semiconductor properties can be strongly affected by crystal structure.
Types of Solids
  • Basically, there are three types of solids: crystalline, amorphous, and polycrystalline.
Crystalline Solids
  • Atoms making up the solid arranged in a periodic fashion, repeated throughout.
  • Have long-range order.
  • Used for IC fabrication.
Amorphous Solids
  • Have no periodic structure at all.
  • Interatomic distance and bond angles are almost the same as in the crystalline material of the same substance, however, a long-range order is missing.
  • Said to have short-range order.
  • a-Si (alloy of amorphous Si with and other similar amorphous alloys) has found important applications in photovoltaic technology and in large-area ICs used in flat displays, printers, copiers, scanners, and imagers.
Polycrystalline Solids
  • Composed of many small regions of single-crystal material of irregular size, separated by grain boundaries.
Lattice
  • 3-D periodic arrangement of atoms in a crystal.
  • Defined by primitive basis vectors a,b,c , which are three independent shortest vectors connecting lattice sites.
  • The coordinates of all points belonging to the crystal lattice are given by vectors , R=ka+lb+mc where k, l, and m are integers.
  • Properties of the periodic crystal determine the allowed energies of electrons that participate in the conduction process. Thus, the lattice not only determines the mechanical properties of the crystal, but also its electrical properties.
Unit Cell
  • Representative of the entire crystal and regularly repeated throughout the crystal.
  • The crystal can be analyzed as a whole by investigating a representative volume.
  • Can find:
    i) the distances between nearest atoms and next nearest atoms,
    ii) the fraction of the unit cell volume filled by atoms, and
    iii) the density of the solid (related to the atomic arrangement).
Primitive Cell
  • Smallest unit cell that can be repeated to form the lattice.
Cubic Lattices
  • Simplest 3-D lattice, where the unit cell is a cube.
  • Three types:
    i) simple cubic (sc) (e.g., Ga),
    ii) body-centered cubic (bcc) (e.g., Na, W), and
    iii) face-centered cubic (fcc) (e.g., Al, Au).
  • Lattice constant: the length of each side of the cube.
The Diamond Lattice
  • Two interpenetrating fcc sublattices spaced 1/4th along the body diagonal.
  • When the constituent atoms of the two sublattices are different, then the structure is Zincblende (e.g. GaAs).

  • Diamond and Zincblende are the two most common crystal structures for cubic semiconductors.
  • Each atom in diamond and zincblende lattice is surrounded by four nearest neighbors.
  • Tetrahedral configuration.
  • By varying the atomic compositions of these two sublattices, one can grow ternary  and quaternary compounds.

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Filter Characteristics

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If an ideal low-pass filter existed, it would completely eliminate signals above the cutoff
frequency, and perfectly pass signals below the cutoff frequency. In real filters, various trade-offs
are made to get optimum performance for a given application.
Butterworth filters are termed maximally-flat-magnitude-response filters, optimized for gain
flatness in the pass-band. the attenuation is –3 dB at the cutoff frequency. Above the cutoff
frequency the attenuation is –20 dB/decade/order. The transient response of a Butterworth filter
to a pulse input shows moderate overshoot and ringing.
Bessel filters are optimized for maximally-flat time delay (or constant-group delay). This means
that they have linear phase response and excellent transient response to a pulse input. This
comes at the expense of flatness in the pass-band and rate of rolloff. The cutoff frequency is
defined as the –3-dB point.
Chebyshev filters are designed to have ripple in the pass-band, but steeper rolloff after the
cutoff frequency. Cutoff frequency is defined as the frequency at which the response falls below
the ripple band. For a given filter order, a steeper cutoff can be achieved by allowing more
pass-band ripple. The transient response of a Chebyshev filter to a pulse input shows more
overshoot and ringing than a Butterworth filter
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To study DC potentiometer.

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Aim:- To study DC potentiometer.
Apparatus:- Power supply,(0-50v)
Battery,(0-30V)
Resister-100W
Circuit Diagram :-
Theory:-
The potentiometer although not consider a bridge has circuit that using a simple
circuit thermo becomes identical to the whetstone bridge. The potentiometer is a device
for measuring the voltage while presenting a very high impedance to the voltage source
under the Test.
The variable resister R1 is the precision device that can be set to an accurate value.
the resister is adjusted so that no current is flow through the galvanometer. which is the
similar to balancing the bridge.
At this point the zero current flow several important characteristics of the
potentiometer cab be determine.
Result:- To study the working of the DC potentiometer.
Viva questions:-
1) What is the importance of std.cell of the Dc potentiometer?
2) How the Unknown emf is calculated by the Dc Potentiometer
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Measurement of the unknown capacitance schering bridge method.

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Aim:- Measurement of the unknown capacitance schering bridge method.
Apparatus:- Sharing bridge kit
digital multimeter,
patch cords,
Circuit Diagram:-
Theory:-
The schering bridge one of the most important ac bridge is used the extensively for the
measurement of capacitors.
In the schering bridge the arm 1 now contains a parallel combination of the
resistor and the capacitor and standard arm contain only one capacitor. The standard
capacitor is usually a standard high quality mica capacitor.
in the balance condition of the bridge the sum of the phase angles of the arms 1
and 4 is equal the sum of the phase angle of arms 2 and 3.at the balance in condition there
is no current flow in the galvanometer.
The balance equation is derived in the usual manner, and by substituting the
corresponding impendence and the admittance the value of the unknown capacitor and
the resister is find as given below.
Cx=C3(R1/R2).
Rx=R2(C1/C2)
Procedure: -
1) Study the circuit provided on the front panel on the kit.
2) Connect the unknown capacitance of the position given.
3) Set the null point of galvanometer by adjusting the variable
4) Calculate the value of unknown capacitance by formula given
Result: -The values of unknown capacitance is measured by shearing bridge
Viva Questions-
1)What is the Q factor of the coil?
2) Which bridges are used for measurement of inductance
3) What is the range of Q?
Experiment no-8
Aim-. Measurement of the 3phase power by the one watt meter method.
Apparatus:-
Three phase variable load.
Wattmeter (0-5A)-, 300v-1no
Ammeter (0-10A)-1no
Voltmeter (0-600v) , (0-300v)-1no
Three phase variance.
Circuit Diagram:-
Theory:-
In this method the total power is consumed is calculated by using the one wattmeter .
This method is used only if the load is balanced The ammeter is connected in between the
coil to the same size and line. The other terminal is connected by the two lines. In this
method the wattmeter is first connected with the R phase and then the B phase The rating
of these two conditions are summed by the total power consumed
Here-V1=V2=V3=V
& I1=I2=I3=Iline
&V13-V12=V23=Ö3V
Reading of wattmeter when connected to phase R
P1=V12*Il*(30-A)
P1=VIÖ3cos(30-A)
Reading of wattmeter when connected to phase B
P2=V12IL(30+A)
P2=Ö3Vicos(30+A)
Sum of two conditions
P=P1+P2
P=Ö3Vi{cos(30-A+cos(30+A)}
P=3VicosA
This equation gives total power consumed by load.
Observation Table:-
Sr no Voltage Current Power 3 phase watt
Procedure:-
1) Make the arrangement as per the circuit diagram.
2) Increase the dimmerstat reading
3) Note the corresponding values of voltmeter ,ammeter and wattmeter.
4) Take consequent 3 readings.
Result:- Hence in that way calculated the 3phase Power by one watt meter method.
Viva Questions:-
1) Explain the short how the wattmeter is connected in the circuit to .
Measure the power delivered to the Load and the Line.
2) Explain How the Resistive Power is measured by the Wattmeter
Method
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