Hollow coil

Hollow coil:

 

The hollow coil has a simple structure, easy design, and large load current, and can be used at high frequencies.

Hollow coils are widely used in mobile phones, VCOs, TCXO circuits and RF transceiver modules, GPS, wireless networks, Bluetooth modules, communication equipment, LCD TVs, cameras, notebook computers, inkjet printers, Photocopiers, display monitors, game consoles, color TVs, video recorders, optical disc players, video cameras, digital cameras, automotive electronics, common mode filters, multi-frequency transformers, impedance transformers, balanced and unbalanced conversion transformers, suppression electronics Equipment EMI noise, USB lines of personal computers and peripherals, LCD panels, low-voltage differential signals, car remote control keys, etc.

Hollow coil structure
The hollow coil is wound in a round shape by a sheathed insulated wire in a clockwise and counterclockwise direction, and is demoulded after winding. The direction of the magnetic field generated by clockwise and counterclockwise winding is exactly the opposite.
The magnetic field direction of the hollow coil is also determined by the right-handed spiral rule. The specific method is: hold the solenoid with your right hand and let four fingers point in the direction of the current flowing in the coil. The direction of the thumb is the magnetic field direction, as shown in the figure below. The way of the two leads of the hollow coil can be diversified. The legs can be bent according to the mechanical requirements of the product. The surface of the two leads of the hollow coil can be peeled and tinned.

Hollow coil calculation
There are various formulas for the calculation of the inductance of the air-core coil. When we calculate the inductance of the air-core inductor, we must choose the calculation formula of the air-core coil inductance reasonably according to the actual situation, and perform reasonable and accurate calculations to ensure the accuracy of the air-core coil inductance calculation. Here are some formulas and methods for calculating the inductance of air-core coils:

1. Coil inductance calculation formula for hollow coil inductance: l = (0.01 * D * N * N) / (L / D + 0.44)

D ------ coil diameter

N ------ Number of coil turns

D ---- Wire diameter

H ---- coil height

W ---- coil width

The units are millimeters and mH.

  In practical applications, many times, in order to save time and ensure the accuracy of the data, the calculation of the air-core coil inductance is calculated by software. The calculation method is as follows:

 An empirical calculation formula for the calculation software of air-core coil inductance: L = (k * μ0 * μs * N2 * S) / l

Μ0 is the vacuum permeability = 4π * 10 (-7). (Negative power of 10)

Μs is the relative permeability of the magnetic core inside the coil, μs = 1 for hollow coils

N2 is the square of the number of coil turns

S cross-sectional area of the coil in square meters

L the length of the coil in meters

The k factor depends on the ratio of the radius (R) to the length (l) of the coil.

单位 The unit of the calculated inductance is Henry.

K value table:

2R / l k

0.1 0.96

0.2 0.92

0.3 0.88

0.4 0.85

0.6 0.79

0.8 0.74

1.0 0.69

1.5 0.6

2.0 0.52

3.0 0.43

4.0 0.37

5.0 0.32

10 0.2

20 0.12

Applicable for hollow coil

Hollow coils are widely used in microwave technology, power supply filtering, communication transmission, reception, audio-visual technology, television technology, radio wave reception vibration, notch.

What is the role of the hollow coil:

1. Hollow coil current blocking effect
The self-inductive electromotive force in a hollow coil coil is always resistant to changes in the current in the coil. The hollow coil has a blocking effect on the AC current. The size of the blocking effect is called the inductive reactance xl, and the unit is ohm. Its relationship with the inductance l and the alternating current frequency f is xl = 2πfl.
2.Tuning and frequency selection
The hollow coil and the capacitor are connected in parallel to form an lc tuning circuit. That is, the natural oscillation frequency f0 of the circuit is equal to the frequency f of the non-AC signal, the inductive reactance and capacitive reactance of the loop are also equal, so the electromagnetic energy oscillates back and forth in the inductance and capacitance, which is the resonance phenomenon of the lc loop. During resonance, the inductance and capacitance of the circuit are reversed. The inductance of the total loop current is the smallest and the current is the largest (refer to the AC signal of f = "f0"). The lc resonance circuit has the function of selecting the frequency and can An AC signal of a frequency f is selected.
Installation and use of air coils
The electronic component mounting board in any electronic equipment is carefully designed, comprehensively arranged and reasonably designed by engineering and technical personnel according to the performance characteristics of various components used. As the installer of the air-core coil, pay attention to the following issues.

Hollow coil number representation

(1). Wire Gauge:, Wire Gauge: 0.5mm (Wire Gauge: 0.5mm) (0.5)
(2). Coil inner diameter 4.5mm (Internal Diameter): (4.5)
(3). Number of turns: 11.5T (11.5T)
(4). Foot length 6.0mm (Lead length: 6.0mm ref): (6)
(5). Winding direction, R means forward winding, L means reverse winding (Winding direction: R is Clockwise, L is Count