..... Click the link for more information. . The simplest type of transformer consists of two coils of wire, electrically insulated from one another and arranged so that a change in the current in one coil (the primary) will produce a change in voltage in the other (the secondary). In many transformers the coils are wound on a core made of a material with high magnetic permeability; this intensifies the magnetic field induced by the current in the primary, increasing the transformer's efficiency. Neglecting power losses (which are made small by careful design), the ratio of primary voltage to secondary voltage is the same as the ratio of the number of turns in the primary coil to the number of turns in the secondary coil. The primary and secondary currents are in inverse proportion to the number of turns in the coils. The primary and secondary impedances impedance, in electricity, measure in ohms of the degree to which an electric circuit resists the flow of electric current when a voltage is impressed across its terminals.
..... Click the link for more information. are in the same ratio as the squares of the numbers of turns in the primary and secondary coils. For example, if a 10-volt, 2-ampere alternating current were to flow through a 10-turn primary of a transformer, theoretically a 20-turn secondary would exhibit a 20-volt, 1-ampere alternating current, with the output impedance four times as great as the input impedance. Transformers are frequently classified according to their uses; the details of construction depend on the intended application. Power transformers are generally used to transmit power at a constant frequency. Audio transformers are designed to operate over a wide range of frequencies with a nearly flat response, i.e., a nearly constant ratio of input to output voltage. Radio frequency (RF) transformers are designed to operate efficiently within a narrow range of high frequencies.
transformer
Device that transfers electric energy from one alternating-current circuit to one or more other circuits, either increasing (stepping up) or reducing (stepping down) the voltage. Uses for transformers include reducing the line voltage to operate low-voltage devices (doorbells or toy electric trains) and raising the voltage from electric generators so that electric power can be transmitted over long distances. Transformers act through electromagnetic induction; current in the primary coil induces current in the secondary coil. The secondary voltage is calculated by multiplying the primary voltage by the ratio of the number of turns in the secondary coil to that in the primary.
transformer
A device that is mostly used to change the voltage in an alternating current (AC); however, it can also be used to maintain the same voltage but act as an electrical isolator. The most common type is the laminated core transformer, which is found in myriad power supplies. Made of steel laminations wrapped with two coils of wire, the ratio of windings between the "primary" input coil and the "secondary" output coil determines the voltage change. For example, if the primary has 1,000 windings and the secondary 100, an input of 120 volts is changed to 12v.
Via ElectroMagnetic Induction
There are numerous transformer architectures, and they span the size gamut. Small ones are used in the myriad black boxes that plug into the wall and create low DC voltage for every electronic gadget, while transformers weighing tons are used to transmit 50,000 volts of AC over the nation's power grid. However, they all work via electromagnetic induction. The changing current in the primary coil induces a voltage across the secondary coil.
Switching Power Supplies
The greater the current needed to power the device, the thicker the wire in the coils and the larger the transformer. However, if a high frequency is used, the number of windings can be reduced to make the transformer small. To accomplish this, the incoming voltage is converted to DC (rectified), and a high-frequency oscillator pulses a transistor that passes the rectified voltage as square waves into a "pulse transformer." The on/off DC pulses cause the changing current in the primary coil just the same as AC does. This square wave generation turns a power supply into a "switching power supply." See power adapter, power supply and wall wart.
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| The Switching Power Supply |
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| In order to reduce the number of windings in transformer coils, a high frequency pulse transformer is used. This is a hypothetical example; voltages and frequencies vary. For example, the oscillator can generate frequencies from 1 kHz to 200 kHz. Following is a simplified circuit diagram of this power supply. |
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transformer
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