Understand the Q and D values ​​of SMD capacitor

When doing radio frequency, pay special attention to their Q value when selecting inductors and capacitors. So what is the Q value? What does Q-value mean and why is it important?Today qihe smd machine smt pick and place machine sharing the knowledge of the Q and D values of SMD capacitor.

Quality factor Q: A quality index that represents the ratio of the energy stored in an energy storage device (such as inductor, capacitor, etc.) and resonant circuit to the energy lost per week. The larger the Q value of the component, the better the selectivity of the circuit or network composed of the component.

Quality factor Q

Or Q=reactive power/active power, or the ratio of characteristic impedance to loop resistance.

The higher the Q value, the smaller the loss and the higher the efficiency;

The higher the Q value, the more frequency stable the resonator is and, therefore, can be more accurate. Factor Q is an important parameter indicating the quality of the coil. The size of the Q value indicates the size of the loss of the inductor coil. The larger the Q value, the smaller the loss of the coil; conversely, the greater the loss.smd machine

The definition of quality factor Q is: when the coil operates under an AC voltage of a certain frequency, the ratio of the inductive reactance presented by the coil to the DC resistance of the coil. It can be expressed as follows:

In the formula: W——working angular frequency L——coil inductance R——total loss resistance of the coil

Depending on the use occasion, the requirements for the quality factor Q are also different. For the inductor coil in the tuning loop, the Q value is required to be higher, because the higher the Q value, the smaller the loop loss and the higher the loop efficiency; for the goose coil, the Q value can be lower; and for low frequency Or high-frequency choke, there is no requirement.

In fact, the improvement of Q value is often limited by some factors, such as the DC resistance of the wire, the dielectric loss of the coil bobbin, the loss caused by the core and shielding, and the skin effect during high-frequency operation. Therefore, the Q value of the coil cannot be made very high. Usually the Q value is tens to one hundred, and the highest is only four or five hundred.

The Q value is equivalent to the reciprocal of the D value. The loss angle is the D value: Generally, electrolytic capacitors have a high D value because of their large internal resistance. Their specifications are determined by the capacitance value, which is below 0.1-0.24. Plastic film capacitors have a lower D value, which is 0.001-0.001 depending on their material. Below 0.01. The ceramic capacitor depends on its material. Hi-K type and S/C type are below 0.025. The specifications of T/C type, expressed in Q value, need to be higher than 400-1000.smd machine

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