Single-ended primary-inductor converter
The single-ended primary-inductor converter is a type of DC/DC converter that allows the electrical potential at its output to be greater than, less than, or equal to that at its input. The output of the SEPIC is controlled by the duty cycle of the control transistor. A SEPIC is a boost converter followed by a buck-boost converter, therefore it is similar to a traditional buck-boost converter, but has advantages of having non-inverted output, using a series capacitor to couple energy from the input to the output, being capable of true shutdown: when the switch is turned off, its output drops to 0 V, following a hefty transient dump of charge. SEPICs are useful in applications in which a battery voltage can be above and below that of the regulator's intended output. For example, a single lithium ion battery discharges from 4.2 volts to 3 volts. The schematic diagram for a basic SEPIC is shown in Figure 1; as with other switched mode power supplies, the SEPIC exchanges energy between the capacitors and inductors in order to convert from one voltage to another.
The amount of energy exchanged is controlled by switch S1, a transistor such as a MOSFET. MOSFETs offer much higher input impedance and lower voltage drop than bipolar junction transistors, do not require biasing resistors as MOSFET switching is controlled by differences in voltage rather than a current, as with BJTs. A SEPIC is said to be in continuous-conduction mode if the current through the inductor L1 never falls to zero. During a SEPIC's steady-state operation, the average voltage across capacitor C1 is equal to the input voltage; because capacitor C1 blocks direct current, the average current through it is zero, making inductor L2 the only source of DC load current. Therefore, the average current through inductor L2 is the same as the average load current and hence independent of the input voltage. Looking at average voltages, the following can be written: V I N = V L 1 + V C 1 + V L 2 Because the average voltage of VC1 is equal to VIN, VL1 = −VL2. For this reason, the two inductors can be wound on the same core.
Since the voltages are the same in magnitude, their effects of the mutual inductance will be zero, assuming the polarity of the windings is correct. Since the voltages are the same in magnitude, the ripple currents from the two inductors will be equal in magnitude; the average currents can be summed as follows: I D 1 = I L 1 − I L 2 When switch S1 is turned on, current IL1 increases and the current IL2 goes more negative. The energy to increase the current IL1 comes from the input source. Since S1 is a short while closed, the instantaneous voltage VL1 is VIN, the voltage VL2 is −VC1. Therefore, the capacitor C1 supplies the energy to increase the magnitude of the current in IL2 and thus increase the energy stored in L2; the easiest way to visualize this is to consider the bias voltages of the circuit in a d.c. state close S1. When switch S1 is turned off, the current IC1 becomes the same as the current IL1, since inductors do not allow instantaneous changes in current; the current IL2 will continue in fact it never reverses direction.
It can be seen from the diagram that a negative IL2 will add to the current IL1 to increase the current delivered to the load. Using Kirchhoff's Current Law, it can be shown that ID1 = IC1 - IL2, it can be concluded, that while S1 is off, power is delivered to the load from both L2 and L1. C1, however is being charged by L1 during this off cycle, will in turn recharge L2 during the on cycle; because the potential across capacitor C1 may reverse direction every cycle, a non-polarized capacitor should be used. However, a polarized tantalum or electrolytic capacitor may be used in some cases, because the potential across capacitor C1 will not change unless the switch is closed long enough for a half cycle of resonance with inductor L2, by this time the current in inductor L1 could be quite large; the capacitor CIN is required to reduce the effects of the parasitic inductance and internal resistance of the power supply. The boost/buck capabilities of the SEPIC are possible because of capacitor C1 and inductor L2.
Inductor L1 and switch S1 create a standard boost converter, which generates a voltage, higher than VIN, whose magnitude is determined by the duty cycle of the switch S1. Since the average voltage across C1 is VIN, the output voltage is VS1 - VIN. If VS1 is less than double VIN the output voltage will be less than the input voltage. If VS1 is greater than double VIN the output voltage will be greater than the input voltage; the evolution of switched-power supplies can be seen by coupling the two inductors in a SEPIC converter together, which begins to resemble a Flyback converter, the most basic of the transformer-isolated SMPS topologies. A SEPIC is said to be in discontinuous-conduction mode or discontinuous mode if the current through the inductor L2 is allowed to fall to zero; the voltage drop and switching time of diode D1 is crit
A light-emitting diode is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons; this effect is called electroluminescence. The color of the light is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device. Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared light. Infrared LEDs are used in remote-control circuits, such as those used with a wide variety of consumer electronics; the first visible-light LEDs were of low intensity and limited to red. Modern LEDs are available across the visible and infrared wavelengths, with high light output. Early LEDs were used as indicator lamps, replacing small incandescent bulbs, in seven-segment displays. Recent developments have produced white-light LEDs suitable for room lighting.
LEDs have led to new displays and sensors, while their high switching rates are useful in advanced communications technology. LEDs have many advantages over incandescent light sources, including lower energy consumption, longer lifetime, improved physical robustness, smaller size, faster switching. Light-emitting diodes are used in applications as diverse as aviation lighting, automotive headlamps, general lighting, traffic signals, camera flashes, lighted wallpaper and medical devices. Unlike a laser, the color of light emitted from an LED is neither coherent nor monochromatic, but the spectrum is narrow with respect to human vision, functionally monochromatic. Electroluminescence as a phenomenon was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector. Russian inventor Oleg Losev reported creation of the first LED in 1927, his research was distributed in Soviet and British scientific journals, but no practical use was made of the discovery for several decades.
In 1936, Georges Destriau observed that electroluminescence could be produced when zinc sulphide powder is suspended in an insulator and an alternating electrical field is applied to it. In his publications, Destriau referred to luminescence as Losev-Light. Destriau worked in the laboratories of Madame Marie Curie an early pioneer in the field of luminescence with research on radium. Hungarian Zoltán Bay together with György Szigeti pre-empted led lighting in Hungary in 1939 by patented a lighting device based on SiC, with an option on boron carbide, that emmitted white, yellowish white, or greenish white depending on impurities present. Kurt Lehovec, Carl Accardo, Edward Jamgochian explained these first light-emitting diodes in 1951 using an apparatus employing SiC crystals with a current source of battery or pulse generator and with a comparison to a variant, crystal in 1953. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide and other semiconductor alloys in 1955.
Braunstein observed infrared emission generated by simple diode structures using gallium antimonide, GaAs, indium phosphide, silicon-germanium alloys at room temperature and at 77 kelvins. In 1957, Braunstein further demonstrated that the rudimentary devices could be used for non-radio communication across a short distance; as noted by Kroemer Braunstein "…had set up a simple optical communications link: Music emerging from a record player was used via suitable electronics to modulate the forward current of a GaAs diode. The emitted light was detected by a PbS diode some distance away; this signal was played back by a loudspeaker. Intercepting the beam stopped the music. We had a great deal of fun playing with this setup." This setup presaged the use of LEDs for optical communication applications. In September 1961, while working at Texas Instruments in Dallas, James R. Biard and Gary Pittman discovered near-infrared light emission from a tunnel diode they had constructed on a GaAs substrate. By October 1961, they had demonstrated efficient light emission and signal coupling between a GaAs p-n junction light emitter and an electrically isolated semiconductor photodetector.
On August 8, 1962, Biard and Pittman filed a patent titled "Semiconductor Radiant Diode" based on their findings, which described a zinc-diffused p–n junction LED with a spaced cathode contact to allow for efficient emission of infrared light under forward bias. After establishing the priority of their work based on engineering notebooks predating submissions from G. E. Labs, RCA Research Labs, IBM Research Labs, Bell Labs, Lincoln Lab at MIT, the U. S. patent office issued the two inventors the patent for the GaAs infrared light-emitting diode, the first practical LED. After filing the patent, Texas Instruments began a project to manufacture infrared diodes. In October 1962, TI announced the first commercial LED product, which employed a pure GaAs crystal to emit an 890 nm light output. In October 1963, TI announced the first commercial hemispherical LED, the SNX-110; the first visible-spectrum LED was developed in 1962 by Nick Holonyak, Jr. while working at General Electric. Holonyak first reported his LED in the journal Applied Physics Letters on December 1, 1962.
M. George Craford, a former graduate student of Holonyak, invented the first yellow LED and improved the brightness of red and red-orange LEDs by a factor of ten in 1972. In 1976, T. P. Pearsall created the first high-brightness, high-efficiency LEDs for optical fiber telecommunicat
A television set or television receiver, more called a television, TV, TV set, or telly, is a device that combines a tuner and loudspeakers for the purpose of viewing television. Introduced in the late 1920s in mechanical form, television sets became a popular consumer product after World War II in electronic form, using cathode ray tubes; the addition of color to broadcast television after 1953 further increased the popularity of television sets in the 1960s, an outdoor antenna became a common feature of suburban homes. The ubiquitous television set became the display device for the first recorded media in the 1970s, such as Betamax, VHS and DVD, it was the display device for the first generation of home computers and video game consoles in the 1980s. In the 2010s flat panel television incorporating liquid-crystal displays LED-backlit LCDs replaced cathode ray tubes and other displays. Modern flat panel TVs are capable of high-definition display and can play content from a USB device. Mechanical televisions were commercially sold from 1928 to 1934 in the United Kingdom, United States, Soviet Union.
The earliest commercially made televisions were radios with the addition of a television device consisting of a neon tube behind a mechanically spinning disk with a spiral of apertures that produced a red postage-stamp size image, enlarged to twice that size by a magnifying glass. The Baird "Televisor" is considered the first mass-produced television, selling about a thousand units. In 1926, Kenjiro Takayanagi demonstrated the first TV system that employed a cathode ray tube display, at Hamamatsu Industrial High School in Japan; this was the first working example of a electronic television receiver. His research toward creating a production model was halted by the US after Japan lost World War II; the first commercially made electronic televisions with cathode ray tubes were manufactured by Telefunken in Germany in 1934, followed by other makers in France and America. The cheapest model with a 12-inch screen was $445. An estimated 19,000 electronic televisions were manufactured in Britain, about 1,600 in Germany, before World War II.
About 7,000–8,000 electronic sets were made in the U. S. before the War Production Board halted manufacture in April 1942, production resuming in August 1945. Television usage in the western world skyrocketed after World War II with the lifting of the manufacturing freeze, war-related technological advances, the drop in television prices caused by mass production, increased leisure time, additional disposable income. While only 0.5% of U. S. households had a television in 1946, 55.7% had one in 1954, 90% by 1962. In Britain, there were 15,000 television households in 1947, 1.4 million in 1952, 15.1 million by 1968. By the late 1960s and early 1970s, color television had come into wide use. In Britain, BBC1, BBC2 and ITV were broadcasting in colour by 1969. During the first decade of the 21st century, CRT "picture tube" display technology was entirely supplanted worldwide by flat panel displays. By the early 2010s, LCD TVs, which used LED-backlit LCDs, accounted for the overwhelming majority of television sets being manufactured.
Television sets may employ one of several available display technologies. As of the mid-2010s, LCDs overwhelmingly predominate in new merchandise, but OLED displays are claiming an increasing market share as they become more affordable and DLP technology continues to offer some advantages in projection systems; the production of plasma and CRT displays has been completely discontinued. There are four primary competing TV technologies: CRT LCD OLED Plasma The cathode ray tube is a vacuum tube containing one or more electron guns and a fluorescent screen used to view images, it has a means to deflect the electron beam onto the screen to create the images. The images may represent electrical waveforms, radar targets or others; the CRT uses an evacuated glass envelope, large, deep heavy, fragile. As a matter of safety, both the face and back were made of thick lead glass so as to be block most electron emissions from the electron gun in the back of the tube. By the early 1970s, most color TVs replaced leaded glass in the face panel with vitrified barium glass, which blocked electron gun emissions but allowed better color visibility.
This eliminated the need for cadmium phosphors in earlier color televisions. Leaded glass, less expensive, continued to be used in the funnel glass, not visible to the consumer. In television sets and computer monitors, the entire front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster. An image is produced by controlling the intensity of each of the three electron beams, one for each additive primary color with a video signal as a reference. In all modern CRT monitors and televisions, the beams are bent by magnetic deflection, a varying magnetic field generated by coils and driven by electronic circuits around the neck of the tube, although electrostatic deflection is used in oscilloscopes, a type of diagnostic instrument. Digital Light Processing is a type of projector technology; some DLPs have a TV tuner, which makes them a type
A low-dropout or LDO regulator is a DC linear voltage regulator that can regulate the output voltage when the supply voltage is close to the output voltage. The advantages of a low dropout voltage regulator over other DC to DC regulators include the absence of switching noise, smaller device size, greater design simplicity; the disadvantage is that, unlike switching regulators, linear DC regulators must dissipate power, thus heat, across the regulation device in order to regulate the output voltage. The adjustable low-dropout regulator debuted on April 12, 1977 in an Electronic Design article entitled "Break Loose from Fixed IC Regulators"; the article was written by Robert Dobkin, an IC designer working for National Semiconductor. Because of this, National Semiconductor claims the title of "LDO inventor". Dobkin left National Semiconductor in 1981 and founded Linear Technology where he was the chief technology officer; the main components are a differential amplifier. One input of the differential amplifier monitors the fraction of the output determined by the resistor ratio of R1 and R2.
The second input to the differential amplifier is from a stable voltage reference. If the output voltage rises too high relative to the reference voltage, the drive to the power FET changes to maintain a constant output voltage. Low-dropout regulators work in the same way as all linear voltage regulators; the main difference between LDO and non-LDO regulators is their schematic topology. Instead of an emitter follower topology, low-dropout regulators use open collector or open drain topology. In this topology, the transistor may be driven into saturation with the voltages available to the regulator; this allows the voltage drop from the unregulated voltage to the regulated voltage to be as low as the saturation voltage across the transistor. For the circuit given in the figure to the right, the output voltage is given as: V OUT = V REF If a bipolar transistor is used, as opposed to a field-effect transistor or JFET, significant additional power may be lost to control it, whereas non-LDO regulators take that power from voltage drop itself.
For high voltages under low In-Out difference there will be significant power loss in the control circuit. Because the power control element functions as an inverter, another inverting amplifier is required to control it, which increases schematic complexity compared to simple linear regulator. Power FETs may be preferable to reduce power consumption, but this poses problems when the regulator is used for low input voltage, as FETs require 5 to 10 V to close completely. Power FETs may increase the cost; the power dissipated in the pass element and internal circuitry of a typical LDO is calculated as follows: P LOSS = I OUT + V IN I Q where I Q is the quiescent current required by the LDO for its internal circuitry. Therefore, one can calculate the efficiency as follows: η = P IN − P LOSS P IN where P IN = V IN I OUT However, when the LDO is in full operation generally: I OUT ≫ I Q; this allows us to reduce P LOSS to the following: P LOSS = I OUT which further reduces the efficiency equation to: η = V OUT V IN It is important to keep thermal considerations in mind when using a low drop-out linear regulator.
Having high current and/or a wide differential between input and output voltage could lead to large power dissipation. Additionally, efficiency will suffer. Depending on the package, excessive power dissipation could damage the LDO or cause it to go into thermal shutdown. Among other important characteristics of a linear regulator is the quiescent current known as ground current or supply current, which accounts for the difference, although small, between the input and output currents of the LDO, that is: I Q = I IN − I OUT Quiescent current is current drawn by the LDO
Solid-state electronics means semiconductor electronics. The term is used for devices in which semiconductor electronics which have no moving parts replace devices with moving parts, such as the solid-state relay in which transistor switches are used in place of a moving-arm electromechanical relay, or the solid-state drive a type of semiconductor memory used in computers to replace hard disk drives, which store data on a rotating disk; the term "solid state" became popular in the beginning of the semiconductor era in the 1960s to distinguish this new technology based on the transistor, in which the electronic action of devices occurred in a solid state, from previous electronic equipment that used vacuum tubes, in which the electronic action occurred in a gaseous state. A semiconductor device works by controlling an electric current consisting of electrons or holes moving within a solid crystalline piece of semiconducting material such as silicon, while the thermionic vacuum tubes it replaced worked by controlling current conducted by a gas of particles, electrons or ions, moving in a vacuum within a sealed tube.
Although the first solid state electronic device was the cat's whisker detector, a crude semiconductor diode invented around 1904, solid state electronics started with the invention of the transistor in 1947. Before that, all electronic equipment used vacuum tubes, because vacuum tubes were the only electronic components that could amplify, an essential capability in all electronics; the replacement of bulky, energy-wasting vacuum tubes by transistors in the 1960s and 1970s created a revolution not just in technology but in people's habits, making possible the first portable consumer electronics such as the transistor radio, cassette tape player, walkie-talkie and quartz watch, as well as the first practical computers and mobile phones. Today all electronics are solid-state except in some applications such as radio transmitters, in which vacuum tubes are still used, some power industrial control circuits which use electromechanical devices such as relays. Additional examples of solid state electronic devices are the microprocessor chip, LED lamp, solar cell, charge coupled device image sensor used in cameras, semiconductor laser.
Condensed matter physics Laser diode Materials science Semiconductor device Solar cell Solid-state physics
The point-contact transistor was the first type of transistor to be demonstrated. It was developed by research scientists John Bardeen and Walter Brattain at Bell Laboratories in December 1947, they worked in a group led by physicist William Shockley. The group had been working together on experiments and theories of electric field effects in solid state materials, with the aim of replacing vacuum tubes with a smaller device that consumed less power; the critical experiment, carried out on December 16, 1947, consisted of a block of germanium, a semiconductor, with two closely spaced gold contacts held against it by a spring. Brattain attached a small strip of gold foil over the point of a plastic triangle — a configuration, a point-contact diode, he carefully sliced through the gold at the tip of the triangle. This produced two electrically isolated gold contacts close to each other; the piece of germanium used had a surface layer with an excess of electrons. When an electric signal traveled in through the gold foil, it injected holes.
This created a thin layer. A small positive current applied to one of the two contacts had an influence on the current which flowed between the other contact and the base upon which the block of germanium was mounted. In fact, a small change in the first contact current caused a greater change in the second contact current, thus it was an amplifier; the first contact is the "emitter" and the second contact is the "collector". The low-current input terminal into the point-contact transistor is the emitter, while the output high current terminals are the base and collector; this differs from the type of bipolar junction transistor invented in 1951 that operates as transistors still do, with the low current input terminal as the base and the two high current output terminals are the emitter and collector. The point-contact transistor was commercialized and sold by Western Electric and others but was soon superseded by the bipolar junction transistor, easier to manufacture and more rugged. While point-contact transistors worked fine when the metal contacts were placed close together on the germanium base crystal, it was desirable to obtain as high an α current gain as possible.
To obtain a higher α current gain in a point-contact transistor, a brief high-current pulse was used to modify the properties of the collector point of contact, a technique called'electrical forming'. This was done by charging a capacitor of a specified value to a specified voltage discharging it between the collector and the base electrodes. Forming had a significant failure rate, so many commercial encapsulated transistors had to be discarded. While the effects of forming were understood empirically, the exact physics of the process could never be adequately studied and thus no clear theory was developed to explain it or provide guidance on improving it. Unlike semiconductor devices, it was possible for an amateur to make a point-contact transistor, starting with a germanium point-contact diode as a source of material; some characteristics of point-contact transistors differ from the junction transistor: The common base current gain of a point-contact transistor is around 2 to 3, whereas α of bipolar junction transistor cannot exceed 1 and the common emitter current gain of a point-contact transistor cannot exceed 1, whereas β of a BJT is between 20 and 200.
Differential negative resistance. When used in the saturated mode in digital logic, in some circuit designs they latched in the on-state, making it necessary to remove power for a short time in each machine cycle to return them to the off-state. Crystal radio Bardeen, J.. H.. "The Transistor, A Semiconductor Triode". Physical Review. American Physical Society. 74: 230–231. The Point-contact Transistor Picture of the first transistor assembled PBS article
A tetrode is a vacuum tube having four active electrodes. The four electrodes in order from the centre are: a thermionic cathode and second grids and a plate. There are several varieties of tetrodes, the most common being the screen-grid tube and the beam tetrode. In screen-grid tubes and beam tetrodes, the first grid is the control grid and the second grid is the screen grid. In other tetrodes one of the grids is a control grid, while the other may have a variety of functions; the tetrode was developed in the 1920s by adding an additional grid to the first amplifying vacuum tube, the triode, to correct limitations of the triode. During the period 1913 to 1927, three distinct types of tetrode valves appeared. All had a normal control grid whose function was to act as a primary control for current passing through the tube, but they differed according to the intended function of the other grid. In order of historical appearance these are: the space-charge grid tube, the bi-grid valve, the screen-grid tube.
The last of these appeared in two distinct variants with different areas of application: the screen-grid valve proper, used for medium-frequency, small signal amplification, the beam tetrode which appeared and was used for audio or radio-frequency power amplification. The former was superseded by the rf pentode, while the latter was developed as an alternative to the pentode as an audio power amplifying device; the beam tetrode was developed as a high power radio transmitting tube. Tetrodes were used in many consumer electronic devices such as radios and audio systems until transistors replaced valves in the 1960s and 70s. Beam tetrodes have remained in use until quite in power applications such as audio amplifiers and radio transmitters; the tetrode functions in a similar way to the triode, from which it was developed. A current through the heater or filament heats the cathode, which causes it to emit electrons by thermionic emission. A positive voltage is applied between the plate and cathode, causing a flow of electrons from the cathode to plate through the two grids.
A varying voltage applied to the control grid can control this current, causing variations in the plate current. With a resistive or other load in the plate circuit, the varying current will result in a varying voltage at the plate. With proper biasing, this voltage will be an amplified version of the AC voltage applied to the control grid, thus the tetrode can provide voltage gain. In the tetrode, the function of the other grid varies according to the type of tetrode; the space charge grid tube was the first type of tetrode to appear. In the course of his research into the action of the "audion" triode tube of Lee de Forest, Irving Langmuir found that the action of the heated thermionic cathode was to create a space charge, or cloud of electrons, around the cathode; this cloud acted as a virtual cathode. With low applied anode voltage, many of the electrons in the space charge returned to the cathode, did not contribute to the anode current. However, if a grid bearing a low positive applied potential were inserted between the cathode and the control grid, the space charge could be made to extend further away from the cathode.
This had two advantageous effects, both related to the influence of the electric fields of the other electrodes on the electrons of the space charge. Firstly, a significant increase in anode current could be achieved with low anode voltage. Secondly the transconductance of the tube was increased; the latter effect was important since it increased the voltage gain available from the valve. Space-charge valves remained useful devices throughout the valve era, were used in applications such as car radios operating directly from a 12V supply, where only a low anode voltage was available; the same principle was applied to other types of multi-grid tubes such as pentodes. As an example, the Sylvania 12K5 is described as "a tetrode designed for space-charge operation, it is intended for service as a power amplifier driver where the potentials are obtained directly from a 12V automobile battery." The space-charge grid was operated at the same as the anode supply voltage. Another important application of the space-charge tetrode was as an electrometer tube for detecting and measuring small currents.
For example, the General Electric FP54 was described as a "space-charge grid tube... designed to have a high input impedance and a low grid current. It is designed for amplification of direct currents smaller than about 10−9 amperes, has been found capable of measuring currents as small as 5 x 10−18 amperes, it has a current amplification factor of 250,000, operates with an anode voltage of 12v, space-charge grid voltage of +4V." The mechanism by which the space-charge grid lowers control-grid current in an electrometer tetrode is that it prevents positive ions originating in the cathode from reaching the control grid. Note that when a space-charge grid is added to a triode, the first grid in the resulting tetrode is the space-charge grid, the second grid is the control grid. In the bi-grid type of tetrode, both grids are intended to carry electrical signals, so both are control grids; the first example to appear in Britain was the Marconi-Osram FE1, designed by H. J. Round, became available in 1920.