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89-484: Before the development of power semiconductors, one way to convert the voltage of a DC supply to a higher voltage, for low-power applications, was to convert it to AC by using a vibrator , then by a step-up transformer , and finally a rectifier . Where higher power was needed, a motor–generator unit was often used, in which an electric motor drove a generator that produced the desired voltage. (The motor and generator could be separate devices, or they could be combined into

178-485: A BJT. Because the FETs are controlled by gate charge, once the gate is closed or open, there is no additional power draw, as there would be with a bipolar junction transistor or with non-latching relays in some states. This allows extremely low-power switching, which in turn allows greater miniaturization of circuits because heat dissipation needs are reduced compared to other types of switches. A field-effect transistor has

267-417: A DC voltage by an integer value, typically delivering only a small current. In these DC-to-DC converters, energy is periodically stored within and released from a magnetic field in an inductor or a transformer , typically within a frequency range of 300 kHz to 10 MHz. By adjusting the duty cycle of the charging voltage (that is, the ratio of the on/off times), the amount of power transferred to

356-458: A FET is doped to produce either an n-type semiconductor or a p-type semiconductor. The drain and source may be doped of opposite type to the channel, in the case of enhancement mode FETs, or doped of similar type to the channel as in depletion mode FETs. Field-effect transistors are also distinguished by the method of insulation between channel and gate. Types of FETs include: Field-effect transistors have high gate-to-drain current resistance, of

445-454: A buzzer. This same rapidly pulsing contact applies the rising and falling DC voltage to the transformer which can step it up to a higher voltage. The primary use for this type of circuit was to operate vacuum tube radios in vehicles , but it also saw use with other mobile electronic devices with a 6 or 12 V accumulator , especially in places with no mains electricity supply such as farms. These vibrator power supplies became popular in

534-405: A certain amount of audible noise (a constant buzzing sound) while in operation, which could potentially be heard by passengers in the car while the radio was on. To help contain this sound within the vibrator's enclosure, the inside surface of the can was often lined with a thick soundproofing material, such as foam rubber . Since vibrators were typically plugged into sockets mounted directly on

623-428: A few watts. This makes them expensive, and they are subject to energy losses in their windings and due to eddy currents in their cores. DC-to-DC techniques that use transformers or inductors work at much higher frequencies, requiring only much smaller, lighter, and cheaper wound components. Consequently these techniques are used even where a mains transformer could be used; for example, for domestic electronic appliances it

712-416: A high DC voltage, which was required to operate vacuum tube (thermionic valve) equipment. For lower-power requirements at voltages higher than supplied by a vehicle battery, vibrator or "buzzer" power supplies were used. The vibrator oscillated mechanically, with contacts that switched the polarity of the battery many times per second, effectively converting DC to square wave AC, which could then be fed to

801-457: A high quality Si/ SiO 2 stack in 1960. Following this research, Mohamed Atalla and Dawon Kahng proposed a silicon MOS transistor in 1959 and successfully demonstrated a working MOS device with their Bell Labs team in 1960. Their team included E. E. LaBate and E. I. Povilonis who fabricated the device; M. O. Thurston, L. A. D’Asaro, and J. R. Ligenza who developed the diffusion processes, and H. K. Gummel and R. Lindner who characterized

890-437: A layer of silicon dioxide over the silicon wafer, for which they observed surface passivation effects. By 1957 Frosch and Derrick, using masking and predeposition, were able to manufacture silicon dioxide transistors and showed that silicon dioxide insulated, protected silicon wafers and prevented dopants from diffusing into the wafer. J.R. Ligenza and W.G. Spitzer studied the mechanism of thermally grown oxides and fabricated

979-419: A load can be more easily controlled, though this control can also be applied to the input current, the output current, or to maintain constant power. Transformer-based converters may provide isolation between input and output. In general, the term DC-to-DC converter refers to one of these switching converters. These circuits are the heart of a switched-mode power supply . Many topologies exist. This table shows

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1068-459: A negative gate-to-source voltage causes a depletion region to expand in width and encroach on the channel from the sides, narrowing the channel. If the active region expands to completely close the channel, the resistance of the channel from source to drain becomes large, and the FET is effectively turned off like a switch (see right figure, when there is very small current). This is called "pinch-off", and

1157-424: A p-channel "enhancement-mode" device, a conductive region does not exist and negative voltage must be used to generate a conduction channel. For either enhancement- or depletion-mode devices, at drain-to-source voltages much less than gate-to-source voltages, changing the gate voltage will alter the channel resistance, and drain current will be proportional to drain voltage (referenced to source voltage). In this mode

1246-489: A patent for FET in which germanium monoxide was used as a gate dielectric, but he didn't pursue the idea. In his other patent filed the same year he described a double gate FET. In March 1957, in his laboratory notebook, Ernesto Labate, a research scientist at Bell Labs , conceived of a device similar to the later proposed MOSFET, although Labate's device didn't explicitly use silicon dioxide as an insulator. In 1955, Carl Frosch and Lincoln Derrick accidentally grew

1335-458: A pre-determined voltage based on the turn ratio of the windings. This current can then be rectified by a thermionic diode , a copper-oxide / selenium rectifier , or by an additional set of mechanical contacts (in which case the vibrator acts as a type of synchronous rectifier ). The rectified output is then filtered, ultimately producing a DC voltage typically much higher than the battery voltage, with some losses dissipated as heat. This arrangement

1424-444: A radio from the typical 6 or 12 volt DC supply available in a car or from a farm lighting battery, it was necessary to convert the steady DC supply to a pulsating DC and use a transformer to increase the voltage. Vibrators often experienced mechanical malfunctions, being constantly in motion, such as the springs losing tension, and the contact points wearing down. As tubes began to be replaced by transistor based electrical systems,

1513-448: A relatively low gain–bandwidth product compared to a bipolar junction transistor. MOSFETs are very susceptible to overload voltages, thus requiring special handling during installation. The fragile insulating layer of the MOSFET between the gate and the channel makes it vulnerable to electrostatic discharge or changes to threshold voltage during handling. This is not usually a problem after

1602-439: A research paper and patented their technique summarizing their work. The technique they developed is known as oxide diffusion masking, which would later be used in the fabrication of MOSFET devices. At Bell Labs, the importance of Frosch's technique was immediately realized. Results of their work circulated around Bell Labs in the form of BTL memos before being published in 1957. At Shockley Semiconductor , Shockley had circulated

1691-457: A single "dynamotor" unit with no external power shaft.) These relatively inefficient and expensive designs were used only when there was no alternative, as to power a car radio (which then used thermionic valves (tubes) that require much higher voltages than available from a 6 or 12 V car battery). The introduction of power semiconductors and integrated circuits made it economically viable by use of techniques described below. For example, first

1780-437: A snubber capacitor with a high voltage rating (C8 in the diagram) is added across the transformer secondary to damp out the unwanted high-voltage "spikes". Since vibrators wore out over time, they were usually encased in a steel or aluminum "tin can" enclosure with a multi-pin plug at the bottom (similar to the contact pins on vacuum tubes), so they could be quickly unplugged and replaced without using tools. Vibrators generate

1869-493: A stable DC independent of input voltage and output load from a higher but less stable input by dissipating excess volt-amperes as heat , could be described literally as DC-to-DC converters, but this is not usual usage. (The same could be said of a simple voltage dropper resistor, whether or not stabilised by a following voltage regulator or Zener diode .) There are also simple capacitive voltage doubler and Dickson multiplier circuits using diodes and capacitors to multiply

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1958-475: A switched-mode converter reduces the heatsinking needed, and increases battery endurance of portable equipment. Efficiency has improved since the late 1980s due to the use of power FETs , which are able to switch more efficiently with lower switching losses  [ de ] at higher frequencies than power bipolar transistors , and use less complex drive circuitry. Another important improvement in DC-DC converters

2047-423: A transformer of the required output voltage(s). It made a characteristic buzzing noise. A further means of DC to DC conversion in the kilowatts to megawatts range is presented by using redox flow batteries such as the vanadium redox battery . DC-to-DC converters are subject to different types of chaotic dynamics such as bifurcation , crisis , and intermittency . Vibrator (electronic) A vibrator

2136-449: A vehicle's battery . A vibrator was used to provide pulsating DC which could be converted to a higher voltage with a transformer, rectified , and filtered to create higher-voltage DC. It is essentially a relay using normally closed contacts to supply power to the relay coil, thus immediately breaking the connection, only to be reconnected very quickly through the normally closed contacts. It happens so rapidly it vibrates, and sounds like

2225-403: A voltage amplifier. In this case, the gate-to-source voltage determines the level of constant current through the channel. FETs can be constructed from various semiconductors, out of which silicon is by far the most common. Most FETs are made by using conventional bulk semiconductor processing techniques , using a single crystal semiconductor wafer as the active region, or channel. Among

2314-449: Is an electromechanical device that takes a DC electrical supply and converts it into pulses that can be fed into a transformer . It is similar in purpose (although greatly different in operation) to the solid-state power inverter . Before the development of switch-mode power supplies and the introduction of semiconductor devices operating off low voltage, there was a requirement to generate voltages of about 50 to 250 V DC from

2403-411: Is connected to the highest or lowest voltage within the circuit, depending on the type of the FET. The body terminal and the source terminal are sometimes connected together since the source is often connected to the highest or lowest voltage within the circuit, although there are several uses of FETs which do not have such a configuration, such as transmission gates and cascode circuits. Unlike BJTs,

2492-522: Is converting the DC power supply to high-frequency AC as an input of a transformer - it is small, light, and cheap due to the high frequency — that changes the voltage which gets rectified back to DC. Although by 1976 transistor car radio receivers did not require high voltages, some amateur radio operators continued to use vibrator supplies and dynamotors for mobile transceivers requiring high voltages although transistorized power supplies were available. While it

2581-422: Is essentially an electromechanical inverter circuit. The vibrator's primary contacts alternately make and break current supply to the transformer primary. As it is impossible for the vibrator's contacts to change over instantaneously, the collapsing magnetic field in the core will induce a high voltage in the windings, and will cause sparking at the vibrator's contacts. This would erode the contacts very quickly, so

2670-399: Is increased further, the pinch-off point of the channel begins to move away from the drain towards the source. The FET is said to be in saturation mode ; although some authors refer to it as active mode , for a better analogy with bipolar transistor operating regions. The saturation mode, or the region between ohmic and saturation, is used when amplification is needed. The in-between region

2759-417: Is necessary to create one. The positive voltage attracts free-floating electrons within the body towards the gate, forming a conductive channel. But first, enough electrons must be attracted near the gate to counter the dopant ions added to the body of the FET; this forms a region with no mobile carriers called a depletion region , and the voltage at which this occurs is referred to as the threshold voltage of

DC-to-DC converter - Misplaced Pages Continue

2848-457: Is preferable to rectify mains voltage to DC, use switch-mode techniques to convert it to high-frequency AC at the desired voltage, then, usually, rectify to DC. The entire complex circuit is cheaper and more efficient than a simple mains transformer circuit of the same output. DC-to-DC converters are widely used for DC microgrid applications, in the context of different voltage levels. Switching converters or switched-mode DC-to-DC converters store

2937-417: Is replacing the flyback diode with synchronous rectification using a power FET, whose "on resistance" is much lower, reducing switching losses. Before the wide availability of power semiconductors, low-power DC-to-DC synchronous converters consisted of an electro-mechanical vibrator followed by a voltage step-up transformer feeding a vacuum tube or semiconductor rectifier, or synchronous rectifier contacts on

3026-424: Is sometimes considered to be part of the ohmic or linear region, even where drain current is not approximately linear with drain voltage. Even though the conductive channel formed by gate-to-source voltage no longer connects source to drain during saturation mode, carriers are not blocked from flowing. Considering again an n-channel enhancement-mode device, a depletion region exists in the p-type body, surrounding

3115-776: Is supplied to the wheels while driving, but supplied by the wheels when braking. Although they require few components, switching converters are electronically complex. Like all high-frequency circuits, their components must be carefully specified and physically arranged to achieve stable operation and to keep switching noise ( EMI / RFI ) at acceptable levels. Their cost is higher than linear regulators in voltage-dropping applications, but their cost has been decreasing with advances in chip design. DC-to-DC converters are available as integrated circuits (ICs) requiring few additional components. Converters are also available as complete hybrid circuit modules, ready for use within an electronic assembly. Linear regulators which are used to output

3204-433: Is that the energy flows in both directions of the converter. These converters are commonly used in various applications and they are connected between two levels of DC voltage, where energy is transferred from one level to another. Multiple isolated bidirectional DC-to-DC converters are also commonly used in cases where galvanic isolation is needed. Switched capacitor converters rely on alternately connecting capacitors to

3293-623: Is the MOSFET (metal–oxide–semiconductor field-effect transistor). The concept of a field-effect transistor (FET) was first patented by the Austro-Hungarian born physicist Julius Edgar Lilienfeld in 1925 and by Oskar Heil in 1934, but they were unable to build a working practical semiconducting device based on the concept. The transistor effect was later observed and explained by John Bardeen and Walter Houser Brattain while working under William Shockley at Bell Labs in 1947, shortly after

3382-423: Is the MOSFET . The CMOS (complementary metal oxide semiconductor) process technology is the basis for modern digital integrated circuits . This process technology uses an arrangement where the (usually "enhancement-mode") p-channel MOSFET and n-channel MOSFET are connected in series such that when one is on, the other is off. In FETs, electrons can flow in either direction through the channel when operated in

3471-480: The MTBF ), bipolar switches generally can't so require the use of a snubber (or two). High-current systems often use multiphase converters, also called interleaved converters. Multiphase regulators can have better ripple and better response times than single-phase regulators. Many laptop and desktop motherboards include interleaved buck regulators, sometimes as a voltage regulator module . Specific to these converters

3560-413: The emitter , collector , and base of BJTs . Most FETs have a fourth terminal called the body , base , bulk , or substrate . This fourth terminal serves to bias the transistor into operation; it is rare to make non-trivial use of the body terminal in circuit designs, but its presence is important when setting up the physical layout of an integrated circuit . The size of the gate, length L in

3649-475: The point-contact transistor in 1947, which was followed by Shockley's bipolar junction transistor in 1948. The first FET device to be successfully built was the junction field-effect transistor (JFET). A JFET was first patented by Heinrich Welker in 1945. The static induction transistor (SIT), a type of JFET with a short channel, was invented by Japanese engineers Jun-ichi Nishizawa and Y. Watanabe in 1950. Following Shockley's theoretical treatment on

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3738-472: The point-contact transistor . Lillian Hoddeson argues that "had Brattain and Bardeen been working with silicon instead of germanium they would have stumbled across a successful field effect transistor". By the end of the first half of the 1950s, following theoretical and experimental work of Bardeen, Brattain, Kingston, Morrison and others, it became more clear that there were two types of surface states. Fast surface states were found to be associated with

3827-441: The 17-year patent expired. Shockley initially attempted to build a working FET by trying to modulate the conductivity of a semiconductor , but was unsuccessful, mainly due to problems with the surface states , the dangling bond , and the germanium and copper compound materials. In the course of trying to understand the mysterious reasons behind their failure to build a working FET, it led to Bardeen and Brattain instead inventing

3916-402: The 1940s, replacing more bulky motor-generator systems for the generation of AC voltages for such applications. Vacuum tubes require plate voltages ranging from about 45 volts to 250 volts in electronic devices such as radios. For portable radios, hearing aids and similar equipment, B batteries were manufactured with various voltage ratings. In order to provide the necessary voltage for

4005-408: The FET operates like a variable resistor and the FET is said to be operating in a linear mode or ohmic mode. If drain-to-source voltage is increased, this creates a significant asymmetrical change in the shape of the channel due to a gradient of voltage potential from source to drain. The shape of the inversion region becomes "pinched-off" near the drain end of the channel. If drain-to-source voltage

4094-477: The FET. Further gate-to-source voltage increase will attract even more electrons towards the gate which are able to create an active channel from source to drain; this process is called inversion . In a p-channel "depletion-mode" device, a positive voltage from gate to body widens the depletion layer by forcing electrons to the gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile, positively charged acceptor ions. Conversely, in

4183-456: The JFET in 1952, a working practical JFET was built by George C. Dacey and Ian M. Ross in 1953. However, the JFET still had issues affecting junction transistors in general. Junction transistors were relatively bulky devices that were difficult to manufacture on a mass-production basis, which limited them to a number of specialised applications. The insulated-gate field-effect transistor (IGFET)

4272-473: The basis of CMOS technology today. CMOS (complementary MOS), a semiconductor device fabrication process for MOSFETs, was developed by Chih-Tang Sah and Frank Wanlass at Fairchild Semiconductor in 1963. The first report of a floating-gate MOSFET was made by Dawon Kahng and Simon Sze in 1967. The concept of a double-gate thin-film transistor (TFT) was proposed by H. R. Farrah ( Bendix Corporation ) and R. F. Steinberg in 1967. A double-gate MOSFET

4361-405: The battery or an external supply (sometimes higher or lower than the supply voltage). Additionally, the battery voltage declines as its stored energy is drained. Switched DC to DC converters offer a method to increase voltage from a partially lowered battery voltage thereby saving space instead of using multiple batteries to accomplish the same thing. Most DC-to-DC converter circuits also regulate

4450-480: The bulk and a semiconductor/oxide interface. Slow surface states were found to be associated with the oxide layer because of adsorption of atoms, molecules and ions by the oxide from the ambient. The latter were found to be much more numerous and to have much longer relaxation times . At the time Philo Farnsworth and others came up with various methods of producing atomically clean semiconductor surfaces. In 1955, Carl Frosch and Lincoln Derrick accidentally covered

4539-413: The conductive channel and drain and source regions. The electrons which comprise the channel are free to move out of the channel through the depletion region if attracted to the drain by drain-to-source voltage. The depletion region is free of carriers and has a resistance similar to silicon . Any increase of the drain-to-source voltage will increase the distance from drain to the pinch-off point, increasing

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4628-416: The conductivity of the inversion layer. Further experiments led them to replace electrolyte with a solid oxide layer in the hope of getting better results. Their goal was to penetrate the oxide layer and get to the inversion layer. However, Bardeen suggested they switch from silicon to germanium and in the process their oxide got inadvertently washed off. They stumbled upon a completely different transistor,

4717-421: The contacts to open and close rapidly. The contacts interrupt the 6 or 12V direct current from the battery to form a stream of pulses which change back and forth from 0 volts to the battery voltage, effectively generating a square wave . Unlike a steady direct current, when such a pulsating current is applied to the primary winding of a transformer it will induce an alternating current in the secondary winding, at

4806-511: The current is mainly due to a flow of minority carriers. The device consists of an active channel through which charge carriers, electrons or holes , flow from the source to the drain. Source and drain terminal conductors are connected to the semiconductor through ohmic contacts . The conductivity of the channel is a function of the potential applied across the gate and source terminals. The FET's three terminals are: All FETs have source , drain , and gate terminals that correspond roughly to

4895-435: The device has been installed in a properly designed circuit. FETs often have a very low "on" resistance and have a high "off" resistance. However, the intermediate resistances are significant, and so FETs can dissipate large amounts of power while switching. Thus, efficiency can put a premium on switching quickly, but this can cause transients that can excite stray inductances and generate significant voltages that can couple to

4984-420: The device. With its high scalability , and much lower power consumption and higher density than bipolar junction transistors, the MOSFET made it possible to build high-density integrated circuits. The MOSFET is also capable of handling higher power than the JFET. The MOSFET was the first truly compact transistor that could be miniaturised and mass-produced for a wide range of uses. The MOSFET thus became

5073-480: The diagram, is the distance between source and drain. The width is the extension of the transistor, in the direction perpendicular to the cross section in the diagram (i.e., into/out of the screen). Typically the width is much larger than the length of the gate. A gate length of 1 μm limits the upper frequency to about 5 GHz, 0.2 μm to about 30 GHz. The names of the terminals refer to their functions. The gate terminal may be thought of as controlling

5162-457: The external field was blocked at the surface because of extra electrons which are drawn to the semiconductor surface. Electrons become trapped in those localized states forming an inversion layer. Bardeen's hypothesis marked the birth of surface physics . Bardeen then decided to make use of an inversion layer instead of the very thin layer of semiconductor which Shockley had envisioned in his FET designs. Based on his theory, in 1948 Bardeen patented

5251-447: The flow of electrons (or electron holes ) from the source to drain by affecting the size and shape of a "conductive channel" created and influenced by voltage (or lack of voltage) applied across the gate and source terminals. (For simplicity, this discussion assumes that the body and source are connected.) This conductive channel is the "stream" through which electrons flow from source to drain. In an n-channel "depletion-mode" device,

5340-410: The gate and cause unintentional switching. FET circuits can therefore require very careful layout and can involve trades between switching speed and power dissipation. There is also a trade-off between voltage rating and "on" resistance, so high-voltage FETs have a relatively high "on" resistance and hence conduction losses. Field-effect transistors are relatively robust, especially when operated within

5429-496: The gate, which in turn alters the conductivity between the drain and source. FETs are also known as unipolar transistors since they involve single-carrier-type operation. That is, FETs use either electrons (n-channel) or holes (p-channel) as charge carriers in their operation, but not both. Many different types of field effect transistors exist. Field effect transistors generally display very high input impedance at low frequencies. The most widely used field-effect transistor

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5518-655: The generator functions wound around a single rotor; both coils share the same outer field coils or magnets. Typically the motor coils are driven from a commutator on one end of the shaft, when the generator coils output to another commutator on the other end of the shaft. The entire rotor and shaft assembly is smaller in size than a pair of machines, and may not have any exposed drive shafts. Motor–generators can convert between any combination of DC and AC voltage and phase standards. Large motor–generator sets were widely used to convert industrial amounts of power while smaller units were used to convert battery power (6, 12 or 24 V DC) to

5607-403: The increased efficiency and smaller size of switch-mode converters makes them a better choice. They are also used at extremely high voltages, as magnetics would break down at such voltages. A motor–generator set, mainly of historical interest, consists of an electric motor and generator coupled together. A dynamotor combines both functions into a single unit with coils for both the motor and

5696-539: The input and output in differing topologies. For example, a switched-capacitor reducing converter might charge two capacitors in series and then discharge them in parallel. This would produce the same output power (less that lost to efficiency of under 100%) at, ideally, half the input voltage and twice the current. Because they operate on discrete quantities of charge, these are also sometimes referred to as charge pump converters. They are typically used in applications requiring relatively small currents, as at higher currents

5785-687: The input energy temporarily and then release that energy to the output at a different voltage, which may be higher or lower. The storage may be in either magnetic field storage components (inductors, transformers) or electric field storage components (capacitors). This conversion method can increase or decrease voltage. Switching conversion is often more power-efficient (typical efficiency is 75% to 98%) than linear voltage regulation, which dissipates unwanted power as heat. Fast semiconductor device rise and fall times are required for efficiency; however, these fast transitions combine with layout parasitic effects to make circuit design challenging. The higher efficiency of

5874-466: The linear mode. The naming convention of drain terminal and source terminal is somewhat arbitrary, as the devices are typically (but not always) built symmetrical from source to drain. This makes FETs suitable for switching analog signals between paths ( multiplexing ). With this concept, one can construct a solid-state mixing board , for example. FET is commonly used as an amplifier. For example, due to its large input resistance and low output resistance, it

5963-456: The magnetic core needs to be dissipated so that the core does not saturate. Power transmission in a flyback circuit is limited by the amount of energy that can be stored in the core, while forward circuits are usually limited by the I/V characteristics of the switches. Although MOSFET switches can tolerate simultaneous full current and voltage (although thermal stress and electromigration can shorten

6052-730: The more unusual body materials are amorphous silicon , polycrystalline silicon or other amorphous semiconductors in thin-film transistors or organic field-effect transistors (OFETs) that are based on organic semiconductors ; often, OFET gate insulators and electrodes are made of organic materials, as well. Such FETs are manufactured using a variety of materials such as silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), and indium gallium arsenide (InGaAs). In June 2011, IBM announced that it had successfully used graphene -based FETs in an integrated circuit . These transistors are capable of about 2.23 GHz cutoff frequency, much higher than standard silicon FETs. The channel of

6141-399: The most common ones. In addition, each topology may be: Magnetic DC-to-DC converters may be operated in two modes, according to the current in its main magnetic component (inductor or transformer): A converter may be designed to operate in continuous mode at high power, and in discontinuous mode at low power. The half bridge and flyback topologies are similar in that energy stored in

6230-428: The most common type of transistor in computers, electronics, and communications technology (such as smartphones ). The US Patent and Trademark Office calls it a "groundbreaking invention that transformed life and culture around the world". In 1948, Bardeen and Brattain patented the progenitor of MOSFET, an insulated-gate FET (IGFET) with an inversion layer. Their patent and the concept of an inversion layer, forms

6319-426: The most significant research ideas in the semiconductor program". After Bardeen's surface state theory the trio tried to overcome the effect of surface states. In late 1947, Robert Gibney and Brattain suggested the use of electrolyte placed between metal and semiconductor to overcome the effects of surface states. Their FET device worked, but amplification was poor. Bardeen went further and suggested to rather focus on

6408-412: The need to generate such high voltages began to diminish. Mechanical vibrators fell out of production near the end of the 20th century, but solid-state electronic vibrators are still manufactured to be backwards compatible with older units. The vibrator was a device with switch contacts mounted at the ends of flexible metal strips. In operation, these strips are vibrated by an electromagnet , causing

6497-404: The opening and closing of a physical gate. This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain. Electron-flow from the source terminal towards the drain terminal is influenced by an applied voltage. The body simply refers to the bulk of the semiconductor in which the gate, source and drain lie. Usually the body terminal

6586-492: The order of 100 MΩ or more, providing a high degree of isolation between control and flow. Because base current noise will increase with shaping time , a FET typically produces less noise than a bipolar junction transistor (BJT), and is found in noise-sensitive electronics such as tuners and low-noise amplifiers for VHF and satellite receivers. It exhibits no offset voltage at zero drain current and makes an excellent signal chopper. It typically has better thermal stability than

6675-560: The output voltage. Some exceptions include high-efficiency LED power sources , which are a kind of DC to DC converter that regulates the current through the LEDs, and simple charge pumps which double or triple the output voltage. DC-to-DC converters which are designed to maximize the energy harvest for photovoltaic systems and for wind turbines are called power optimizers . Transformers used for voltage conversion at mains frequencies of 50–60 Hz must be large and heavy for powers exceeding

6764-403: The plug. Field-effect transistor The field-effect transistor ( FET ) is a type of transistor that uses an electric field to control the current through a semiconductor . It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET (MOSFET). FETs have three terminals: source , gate , and drain . FETs control the current by the application of a voltage to

6853-483: The preprint of their article in December 1956 to all his senior staff, including Jean Hoerni . In 1955, Ian Munro Ross filed a patent for a FeFET or MFSFET. Its structure was like that of a modern inversion channel MOSFET, but ferroelectric material was used as a dielectric/insulator instead of oxide. He envisioned it as a form of memory, years before the floating gate MOSFET . In February 1957, John Wallmark filed

6942-503: The progenitor of MOSFET, an insulated-gate FET (IGFET) with an inversion layer. The inversion layer confines the flow of minority carriers, increasing modulation and conductivity, although its electron transport depends on the gate's insulator or quality of oxide if used as an insulator, deposited above the inversion layer. Bardeen's patent as well as the concept of an inversion layer forms the basis of CMOS technology today. In 1976 Shockley described Bardeen's surface state hypothesis "as one of

7031-403: The radio chassis, the vibration could potentially be mechanically coupled to the chassis, causing it to act as a sounding-board for the noise. To prevent this, the sound-deadening lining inside the can was sometimes made thick enough to support the vibrator's components by friction alone. The components were then connected to the plug pins by flexible wires, to further isolate the vibration from

7120-431: The resistance of the depletion region in proportion to the drain-to-source voltage applied. This proportional change causes the drain-to-source current to remain relatively fixed, independent of changes to the drain-to-source voltage, quite unlike its ohmic behavior in the linear mode of operation. Thus, in saturation mode, the FET behaves as a constant-current source rather than as a resistor, and can effectively be used as

7209-422: The surface of silicon wafer with a layer of silicon dioxide . They showed that oxide layer prevented certain dopants into the silicon wafer, while allowing for others, thus discovering the passivating effect of oxidation on the semiconductor surface. Their further work demonstrated how to etch small openings in the oxide layer to diffuse dopants into selected areas of the silicon wafer. In 1957, they published

7298-430: The temperature and electrical limitations defined by the manufacturer (proper derating ). However, modern FET devices can often incorporate a body diode . If the characteristics of the body diode are not taken into consideration, the FET can experience slow body diode behavior, where a parasitic transistor will turn on and allow high current to be drawn from drain to source when the FET is off. The most commonly used FET

7387-435: The vast majority of FETs are electrically symmetrical. The source and drain terminals can thus be interchanged in practical circuits with no change in operating characteristics or function. This can be confusing when FET's appear to be connected "backwards" in schematic diagrams and circuits because the physical orientation of the FET was decided for other reasons, such as printed circuit layout considerations. The FET controls

7476-437: The vibrator. Most DC-to-DC converters are designed to move power in only one direction, from dedicated input to output. However, all switching regulator topologies can be made bidirectional and able to move power in either direction by replacing all diodes with independently controlled active rectification . A bidirectional converter is useful, for example, in applications requiring regenerative braking of vehicles, where power

7565-403: The voltage at which it occurs is called the "pinch-off voltage". Conversely, a positive gate-to-source voltage increases the channel size and allows electrons to flow easily (see right figure, when there is a conduction channel and current is large). In an n-channel "enhancement-mode" device, a conductive channel does not exist naturally within the transistor, and a positive gate-to-source voltage

7654-415: The work of William Shockley , John Bardeen and Walter Brattain . Shockley independently envisioned the FET concept in 1945, but he was unable to build a working device. The next year Bardeen explained his failure in terms of surface states . Bardeen applied the theory of surface states on semiconductors (previous work on surface states was done by Shockley in 1939 and Igor Tamm in 1932) and realized that

7743-472: Was first demonstrated in 1984 by Electrotechnical Laboratory researchers Toshihiro Sekigawa and Yutaka Hayashi. FinFET (fin field-effect transistor), a type of 3D non-planar multi-gate MOSFET, originated from the research of Digh Hisamoto and his team at Hitachi Central Research Laboratory in 1989. FETs can be majority-charge-carrier devices, in which the current is carried predominantly by majority carriers, or minority-charge-carrier devices, in which

7832-541: Was possible to derive a lower voltage from a higher with a linear regulator or even a resistor, these methods dissipated the excess as heat; energy-efficient conversion became possible only with solid-state switch-mode circuits. DC-to-DC converters are used in portable electronic devices such as cellular phones and laptop computers , which are supplied with power from batteries primarily. Such electronic devices often contain several sub- circuits , each with its own voltage level requirement different from that supplied by

7921-453: Was theorized as a potential alternative to junction transistors, but researchers were unable to build working IGFETs, largely due to the troublesome surface state barrier that prevented the external electric field from penetrating into the material. By the mid-1950s, researchers had largely given up on the FET concept, and instead focused on bipolar junction transistor (BJT) technology. The foundations of MOSFET technology were laid down by

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