The Working Principle of an Inductor
InductanceInductance is a property of a closed circuit. When the current flowing through a closed circuit changes, an electromotive force (EMF) is generated to oppose that change in current. It is essentially a manifestation of the phenomenon known as electromagnetic induction.InductorAn inductor is an electrical component that generates an electromotive force when the current flowing through it changes, thereby opposing the change in current.The term inductor is usually used to describe components whose primary function is based on self-inductance or its effects. Devices that do not primarily rely on self-inductance are generally referred to by other names instead of being called inductors. For example, transformers and the electromagnetic windings inside motors are typically not referred to simply as inductors.Working Principle of an InductorWhen an alternating current (AC) is applied to an inductive coil, the changing current causes a change in the magnetic flux within the coil, which in turn induces an electromotive force. This phenomenon is called self-induction.The direction of the induced current produced by self-induction always opposes the change in the original current that caused it (according to Lenz’s Law).
[*]When the AC current increases, the induced current flows in the opposite direction.
[*]When the AC current decreases, the induced current flows in the same direction as the original current.
As a result, the inductor provides opposition to alternating current.1. Self-InductionWhen current flows through a coil, a magnetic field is generated around it.If the current in the coil changes, the magnetic field surrounding it also changes accordingly. This changing magnetic field induces an electromotive force in the coil itself.
(Electromotive force, or EMF, represents the terminal voltage of an ideal voltage source in active components.)
Working Principle of an InductorWhen an alternating current (AC) is applied to an inductive coil, the current within the coil changes continuously. This change in current causes a change in the magnetic flux linked with the coil, which in turn induces an electromotive force (EMF). This phenomenon is called self-induction.The direction of the induced current generated by self-induction always opposes the change in current that produced it (in accordance with Lenz’s Law).
[*]When the AC current increases, the induced current flows in the opposite direction to the applied current.
[*]When the AC current decreases, the induced current flows in the same direction as the applied current.
Therefore, an inductor provides opposition to alternating current.1. Self-InductionWhen current flows through a coil, a magnetic field is generated around it.When the current in the coil changes, the surrounding magnetic field also changes accordingly. This changing magnetic field induces an electromotive force in the coil itself.
(Electromotive force, or EMF, represents the terminal voltage of an ideal voltage source in active components.)
Inductance CoefficientThe voltage across an inductor is directly proportional to the rate of change of current through it.Relationship Between Voltage and CurrentThe relationship between voltage and current in an inductor is expressed as:v=Ldidtv = L \frac{di}{dt}v=LdtdiWhere:
[*]vvv = voltage across the inductor
[*]LLL = inductance (inductance coefficient), measured in henries (H)
[*]didt\frac{di}{dt}dtdi = rate of change of current with respect to time
This equation shows that the faster the current changes, the greater the induced voltage.In other words, an inductor resists changes in current by generating a voltage proportional to how quickly the current is changing.
The proportional constant L is called the inductance coefficient (inductance). It depends on the physical parameters of the inductor, such as the shape of the coil, the number of turns, and the core structure.The unit of inductance is the henry, abbreviated as H.
An inductance of 1 H means that when the current changes at a rate of 1 ampere per second (1 A/s), an induced voltage of 1 volt (1 V) is generated.
Function of an InductorBlocking AC and Passing DCFor direct current (DC), an inductor behaves like a short circuit.
For alternating current (AC), an inductor provides opposition to the current. The higher the frequency of the AC, the greater the opposition provided by the inductor.
TransformerThe most commonly used application of inductance is the transformer. Figure 1 shows the circuit symbol of a transformer.Assume that the number of turns in the left coil is 100, and the number of turns in the right coil is 50. If 220 V AC is applied to the left side, the induced voltage on the right side will be 110 V.This demonstrates that:Turns ratio = Voltage ratioHowever, the current relationship is the opposite.If 1 A of current flows into the left coil, then 2 A of current will flow out of the right coil. In other words:Turns ratio = Inverse current ratioThis is because a transformer changes voltage and current, but it does not change power (in an ideal case).
If both voltage and current increased proportionally at the same time, it would violate the principle of energy conservation.
RL低通滤波器
RL Low-Pass FilterA low-pass filter is a circuit that allows low-frequency signals to pass while blocking high-frequency signals. The circuit schematic is shown in Figure 2.If the input signal is direct current (DC), the inductor behaves like a piece of wire (a short circuit). In this case, the signal passes through the inductor directly to the output without passing through the resistor.As the frequency of the current is gradually increased, the inductor begins to oppose the alternating current. As a result, the signal passing through the inductor becomes progressively smaller.When the frequency reaches a certain value, signals with frequencies higher than this value can no longer effectively pass through the circuit. At this point, the circuit functions as a low-pass filter.This specific frequency is called the cutoff frequency, and it is given by:f=R2πLf = \frac{R}{2\pi L}f=2πLRWhere:
[*]fff = cutoff frequency (Hz)
[*]RRR = resistance (Ω)
[*]
RL High-Pass FilterThe operating principle of a high-pass filter is similar to that of a low-pass filter, except that the positions of the resistor and the inductor are interchanged, as shown in Figure 3.If the input signal is direct current (DC), the current flows through the inductor and returns to the source.When the frequency is gradually increased, the inductor begins to oppose the alternating current. As the frequency reaches the cutoff frequency, the inductor presents significant opposition to low-frequency components, while the high-frequency signal does not pass through the inductor. Instead, the desired high-frequency signal is taken directly from the output.The cutoff frequency is also calculated as:f=R2πLf = \frac{R}{2\pi L}f=2πLRWhere:
[*]fff = cutoff frequency (Hz)
[*]RRR = resistance (Ω)
[*]LLL = inductance (H)
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