In the design, as long as the inductor is used, the parameter of the inductance Q value cannot be avoided. But often many people don't understand, what is the inductance Q value? What is the effect of the inductor Q on the inductor and the circuit? So let's talk about the meaning of the Q value of the inductor and the problems that should be paid attention to during the application process.
Q value: Also called the quality factor of the inductor, it is the main parameter to measure the inductance device. Refers to the ratio of the inductive reactance exhibited by the inductor to its equivalent loss resistance when operating at an AC voltage of a certain frequency. The higher the Q value of the inductor, the smaller the loss and the higher the efficiency. The quality factor of the inductor and the DC resistance of the coil wire, the dielectric loss of the bobbin and the core. The requirements for the quality factor Q vary depending on the application. For the inductive coil in the tuning loop, the Q value is higher, because the higher the Q value, the smaller the loss of the loop, the higher the efficiency of the loop; for the coupled coil, the Q value can be lower; and for the low frequency or High frequency chokes can be left unrequested.
The increase in Q value is often limited by factors such as the DC resistance of the wire, the dielectric loss of the bobbin, the loss caused by the core and the shield, and the skin effect at high frequencies. Therefore, the Q value of the coil cannot be made very high, usually the Q value is tens to 100, and the highest is only four or five hundred.
What is the function of the inductance Q value?
The Q value is too large, causing the inductor to burn out, the capacitor breakdown, and the circuit to oscillate. When Q is large, there will be a phenomenon of VL=VC》V. This phenomenon in power systems often leads to insulation of the inductor and breakdown of the dielectric in the capacitor, causing losses. Therefore, resonance should be avoided in the power system. In some radios, the characteristics of the resonance are often used to increase the amplitude of the weak signal.
How to convert the Q value of the inductor?
The factor can be written as Q=2pi* energy stored in the circuit/energy consumed in one cycle of the circuit. The relationship between the passband BW and the resonant frequency w0 and the quality factor Q is: BW=wo/Q, which indicates that the Q is large, the passband is narrow, and the Q is small, the passband bandwidth.
The calculation formula of Q value: Q=wL/R=1/wRC
Q is the quality factor
w is the power supply frequency when the circuit is resonant
L is the inductance
R is the resistance of the string
C is the capacitance
Q value is the quality factor, it is useful work The ratio of total work.
Factors Affecting the Q Value of the
Inductor The quality factor of the inductor is related to the DC resistance of the coil wire, the dielectric loss of the bobbin, and the loss caused by the core and the shield.
Some people have deliberately reduced the Q value of the inductor in order to avoid excessive frequency resonance/gain. The way to lower the Q value can be to increase the resistance of the winding or to use a magnetic core with a relatively large power consumption.
The Q value is generally referred to as the quality factor, which is a dimensionless unit that measures the performance of a component or resonant tank. Simply put, it is the ratio of the ideal component to the loss present in the component. This component can be an inductor, a capacitor, a dielectric resonator, a surface acoustic wave resonator, a crystal resonator or an LC resonator. The size of the Q value depends on the actual application, not the bigger the better. For example, if you design a wideband filter, an excessively high Q value will degrade the in-band flatness if no other measures are taken. In the case of LC decoupling applications, the high-Q inductors and capacitors are prone to self-resonant state, which is not conducive to eliminating interference noise in the power supply. Conversely, we expect a higher Q value for the oscillator, and the higher the Q value, the better the frequency stability and phase noise of the oscillator. There are different requirements for Q values for different applications.
The quality factor of the component, that is, the Q value depends on the manufacturing process, manufacturing materials, and application environment of the component. For example, for the same inductor, if the other parameters are unchanged and only the thickness of the wound inductor wire is changed, the inductance Q of the wire is higher than the Q of the wire. If silver is plated on the wire, the inductance of the silver-plated wire is higher than the inductance of the non-silvered wire. As for the dielectric resonator, the Q value is more dependent on the dielectric resonator material and fabrication process.
The size of the Q value is also related to the operating frequency. The general inductance will increase as the frequency increases. But it has a limit. When the limit frequency is exceeded, the Q of the inductor drops sharply, and the inductor loses its inductance. At this point, the dielectric resonator, the surface acoustic wave resonator, and the crystal resonator are more conspicuous. When the operating frequency deviates from their resonant frequency, their Q values will drop sharply and they will not work.
The quality factor describes the ratio of the energy stored in the loop to its energy consumption per week.
Because the product of the same frequency band and the quality factor is the resonant frequency of the loop. Therefore, in the case of ensuring the resonance point, the quality factor and the width of the pass band are contradictory. Therefore, it cannot be said that the higher the quality factor, the better, and the larger the Q value required for the frequency band, the narrower the passband of the resonance, that is, the narrower frequency range included. If a wider passband is required, the Q value is required. The smaller the better.
In the frequency selection circuit (selecting a certain frequency), the wave blocking circuit (blocking a certain frequency), the absorbing circuit (attenuating a certain frequency), and the trap circuit (removing a certain frequency), a certain frequency f is utilized or removed. At this time, the larger the Q value, the better. This is the frequency f at the resonance of the resonant circuit. When the LC parallel resonant circuit resonates, the circuit impedance is the largest, which is equivalent to an open circuit, so that the frequency signal with the frequency f cannot pass, and this is prevented. The purpose of the signal. When the LC series resonant circuit resonates, the impedance is minimal, and is relatively short-circuited. At this time, the frequency of f is easy to pass, and other signal frequencies are blocked, so that the frequency selection can be achieved.
Regarding the relationship between magnetic loss and the influence of Q-value of magnetic loop inductance, the design requirements of power supply are becoming more and more strict. This requires us to carefully analyze and calculate each problem. The calculation of magnetic loss is generally based on the volume and correlation of the core. The loss curve is simply calculated but appears in the actual work. The winding method of the same core is different, and the same winding method of the same core has different degrees of tightness, but brings different temperature rise differences.
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