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power inductors
A coil is a generic name for an electrode in the shape of a spiral. Among the different types of coils, there are coils called “inductors” which are used for electrical applications. Inductors can be further categorized into RF inductors used for signal processing, and power inductors for power supply lines. The power inductors discussed in this section form part of the voltage conversion circuit in a DC-DC converter or other device.
Here we will explain the operation of a power inductor in a DC-DC converter. A power inductor is used in a step-up, step-down, or step-up/step-down circuit to convert a certain voltage to the required voltage. Among those different circuits, it is primarily used in a type of circuit called a “switching regulator.”
Figure 1-1 shows an example of a switching regulator step-down circuit.
It uses an IC, power inductor, and capacitor to convert a DC input voltage to the required output voltage. The power inductor works with the capacitor to play the role of rectifying the rectangular wave output from the IC to a direct current.
If either one of these components is missing, the output cannot be properly rectified.
What is a transformer?
A transformer is a 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.
Where are transformers used?
Transformers are employed for widely varying purposes. For example, a transformer is often used to reduce the voltage of conventional power circuits to operate low-voltage devices and to raise the voltage from electric generators so that electric power can be transmitted over long distances.
Why is the iron core of a transformer laminated?
The iron core of a transformer is laminated to reduce eddy currents. Eddy currents are the small currents that result from the changing magnetic field created by the alternating current in the first coil. They need to be minimized so they won’t disturb the flow of electricity from the primary coil to the secondary coil.
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. Transformers are employed for widely varying purposes; e.g., to reduce the voltage of conventional power circuits to operate low-voltage devices, such as doorbells and toy electric trains, and to raise the voltage from electric generators so that electric power can be transmitted over long distances.
Transformers change voltage through electromagnetic induction; i.e., as the magnetic lines of force (flux lines) build up and collapse with the changes in current passing through the primary coil, current is induced in another coil, called the secondary. The secondary voltage is calculated by multiplying the primary voltage by the ratio of the number of turns in the secondary coil to the number of turns in the primary coil, a quantity called the turns ratio.
Operation
Current transformers are unique because they usually have only one winding. The primary is connected to the line load in series. When the primary has a high current rating, the primary winding may be a straight conductor that runs through the magnetic circuit's center. This straight conductor indicates a one-turn winding.
When the primary has a low current rating, the primary winding may consist of several turns wrapped around the core. This provides the required flux on low-current applications or to compensate for line drop to a power meter.
The secondary consists of many turns of wire wrapped around a core. The number of turns is determined by the desired turns ratio of the current transformer. The primary current of a current transformer is not controlled by the secondary, as it would be in a two-winding potential transformer. The secondary of a current transformer cannot affect the current in the primary, as the load on the feeder determines the primary current.
When the primary circuit is energized, the secondary of a current transformer must never be left open. When the circuit is operational, the load on the secondary maintains low magnetizing currents and thus low turn-to-turn potentials. When the secondary becomes an open circuit, the magnetizing currents rise, and the current transformer acts as a step-up potential transformer. The voltage can rise to a destructive level and cause a short between the turns as the result of the degradation of the insulation. Therefore, a current transformer should always have its secondary shorted when not connected to an external load.
What is a High Voltage Transformer?
A high voltage transformer is a type of transformer that operates at a high voltage level. High voltage transformers are normally used in high voltage labs for testing purposes. These high voltage transformers are subjected to transient voltages and surges during their normal operation when the insulation under test breaks down.
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