What is an inductance coil?
Common magnetic ring inductance coil, inductance coil is also one of the commonly used components in household appliances, instrumentation and other electronic products, is the use of electromagnetic induction principle to work electronic components. Its electrical characteristics are the opposite of those of capacitors, "low frequencies and high frequencies". High-frequency signals encounter great resistance when passing through the inductance coil, making it difficult to pass;However, the resistance to the passage of the low-frequency signal is relatively small, that is, the low-frequency signal can pass through it more easily. The resistance of the inductor coil to DC is almost zero.
In electronic circuits, inductance coils are mainly used to isolate and filter AC signals or form resonant circuits with capacitors and resistors.
There are many types of inductance coils, and a brief introduction to several common magnetic ring inductance coils:
1. Single-layer coil.
A single-layer coil is made of insulated wires that are wound around a paper tube or bakelite skeleton one by one. Such as transistor radio, medium wave antenna coils.
2. Honeycomb coil.
If the plane of the coil wound is not parallel to the rotating plane, but intersects at a certain angle, this kind of coil is called a honeycomb coil. The number of times the wire bends back and forth after one rotation is often called the number of vertices. The advantages of the honeycomb winding method are small size, small distributed capacitance, and large inductance. The honeycomb coils are wound by the honeycomb winding machine, and the more vertices, the smaller the distributed capacitance.
3. Ferrite core and iron powder core coil.
The amount of inductance of the coil is related to the presence or absence of a magnetic core. Inserting a ferrite core into an air-core coil increases the amount of inductance and improves the quality factor of the coil.
4. Copper core coil.
Copper core coils are used more in the ultra-short wave range, and the position of rotating copper core ** ring is used to change the inductance, which is more convenient and durable.
5. Color-coded inductors.
Color-coded inductors are inductors with a fixed amount of inductance, and the inductance is marked with a color ring in the same way as a resistor.
6. Choke ring (choke).
The coil that restricts the passage of alternating current is called a choke, which is divided into a high-frequency choke and a low-frequency choke.
7. Deflection coil.
The deflection coil is the load of the output stage of the TV scanning circuit, and the deflection coil requirements: high deflection sensitivity, uniform magnetic field, high Q value, and small size.
How to solve the noise of power inductors?
It is sometimes heard when running on laptops, tablets, smartphones, televisions, and in-car electronic devices"Tsk"noise. This phenomenon is called"Howling", which may be caused by passive components such as capacitors and inductors. The principle of acoustic noise generated by capacitors and inductors is different, and the causes of acoustic noise in inductors are various and complex. In this article, we will introduce the causes of noise in power inductors, which are the main components of power supply circuits such as DC-DC converters, and how to counter them.
What is the reason for the noise of power inductors?
The mechanism by which the vibration of the main body of a power inductor and the amplification of noise are amplified.
When an electric current flows through a frequency in the audible range of the human ear, the vibration that occurs in the body of the power inductor causes a whine noise. There are several possible causes of vibration and noise.
What are the causes of vibration in power inductors?
1. Magnetostriction (magnetic strain) effect of magnetic body core.
2. The magnetization of the magnetic body core leads to mutual attraction.
3. Leakage flux causes winding vibration.
Power inductor noise amplification cause:
1. Contact with other components.
2. It is consistent with the overall natural vibration number of the component, including the substrate.
3. The leakage flux leads to an effect on the surrounding magnetic bodies.
Power Inductor Acoustic Cause:
Intermittent operation, variable frequency patterns, load fluctuations, etc., can cause audible frequency vibrations to the human ear.
Sound waves are elastic waves that travel through the air and can be heard by human hearing in the frequency range of about 20 20kHz"Sound"。In the power inductor of a DC-DC converter, the inductor body vibrates when an alternating current flows through a frequency in the audible range of the human ear as well as a pulse wave"Coil noise", which is sometimes heard as a howling phenomenon.
How to effectively improve the noise problem of power inductors?
Therefore, in order to improve this problem, a DC-DC converter that automatically replaces the PWM method with the PFM (Pulse Frequency Modulation) method is used in light load situations. The PFM method is a method that controls the switching frequency at a fixed ON time in order to reduce the load. Since the ON time is constant, the switching frequency decreases gradually by extending the OFF time. Since the switching loss is proportional to the frequency, it is possible to achieve high efficiency at light loads by reducing the frequency. However, the reduced frequency will enter the audible range of about 20 20 kHz, and the power inductor will whistle.
1. Whine caused by load:
Mobile devices such as laptops are equipped with various power-saving technologies to save battery power, which can cause acoustic noise in the inductors. For example, in order to balance power consumption and processing power, laptop CPUs have a pattern that periodically changes the current consumption, and when the cycle is in the audible frequency range, the power inductor may generate acoustic noise due to this effect.
Explanation: The role of a power inductor in a DC-DC converter.
Inductors allow direct current to flow smoothly, and in the case of alternating currents such as alternating currents, they act as resistors by generating an electromotive force in the direction that prevents the change through self-induction. In this case, the inductor converts electrical energy into magnetic energy, accumulates it, and releases it after converting it into electrical energy. The magnitude of this energy is proportional to the inductance value of the inductor.
Power inductors, also known as power coils and power choke coils, are the main components used in switching power supply circuits such as DC-DC converters, and they coordinate with capacitors to smooth out the high-frequency pulses generated by switching devices on off.
Since a large current flows through the power inductor of the power supply circuit, the winding type is the mainstream product. This is because by using a magnetic body with high permeability (ferrite or soft magnetic metal) in the core, it is possible to achieve a high inductance value with a small number of pixels, thereby making the product even smaller. It is the basic circuit of a DC-DC converter (non-isolated type and chopper type) using a power inductor.