For the transformer and inductors, we always test Q value. While, what's Q value?What factors are it related to?

Q value, as know as  quality factor, its basic meaning refers to the ratio of inductance to loss pressented by a transformer (inductor) when operating at a certain frequency of AC voltage, it is an important parameter for measuring the transformers and inductors. The higher Q value is, the smaller the loss, and the higher efficiency of the transformer(inductors).

Formula Q=XL/R=2πfL/R (XL is inductance, R is loss, and f is operating frequency)

The Q value is related to the operating frequency, and the higher the frequency, the higher the Q value.When testing, pay attention to the frequency. There is a significant difference in Q values between 1KHz and 100KHz.

The Q value is related to the loss. By increasing the wire diameter and using multi strand wire winding, the number of turns of the winding can be reduced to a certain extent, which can reduce the resistance of the wire and improve the Q value. In addition, selecting high-quality magnetic materials and using shielded magnetic materials can reduce magnetic core losses and increase Q values.

The Q value is also related to susceptibility. The larger the Q value, the greater the inductance, and the smaller the corresponding distributed capacitance (capacitance corresponds to capacitance, which often has a trade-off with inductance). here, let’s talk about distributed capacitance.

Distributed capacitance is a widely existing distributed parameter, and as long as there is a voltage difference between two insulating conductors, distributed capacitance will be generated. This principle can be analogized to the conditions for the generation of capacitance: when a voltage is applied between two electrodes with a certain distance, capacitance will be generated.

Distributed capacitance has little effect at low frequencies, but has a significant impact on the circuit at high frequencies. At present, the distributed capacitance of transformers mainly includes inter turn distributed capacitance, inter layer distributed capacitance, winding distributed capacitance, and stray distributed capacitance. The existence of distributed capacitors not only reduces the Q value of transformers, but may also cause problems such as transformer heating and EMI, so it is necessary to minimize them as much as possible.

C=ε S/4 π kd

Capacitance is inversely proportional to distance.

In transformers, the distributed capacitance of transformers is often reduced by increasing the distance between windings, using triple insulated wires, increasing insulation thickness, and improving winding methods.

Usually, the larger the Q value, the better, but in some application conditions, it is also necessary to limit the Q value, which depends on the actual usage scenario.

Q value is also commonly used for failure analysis for daily application. If there are cracks inside the magnetic core and there is no difference in sensing, it can be determined by the Q value. In addition, when there is a short circuit or open circuit between multiple wires, the Q value often decreases, which can be used as a basis for judging transformer abnormalities.