# Understand inductors and their applications

Inductance, also known as inductance coil, is an electromagnetic induction element wound by insulated wire (such as enameled wire, gauze wire, etc.), which is one of the components commonly used in electronic circuits. Inductor is a series of coaxial line turns made of enamel wire, gauze wire or plastic leather wire wound on the insulating skeleton or core, core, represented by the letter "L", the main role is to isolate the AC signal, filter or with capacitors, resistors and other components of resonance circuit.
Inductance is expressed in Henley, and the unit is H. 1H=1000mH=1000000uH.
Inductor packaging types are various, the current inductor packaging can be generally divided into wire-wound common mode inductor, patch inductor, integrated inductor, I-inductor, their roles.
For the common mode inductor, its main function is to filter the common mode signal, prevent the common mode interference, often seen in the power circuit, its purpose is to be able to pass the EMC. The wound inductor, integrated inductor and patch inductor are widely used in DC TO DC circuit. Their function is TO store energy, and at the same time, they have a great influence on the output voltage ripple of the power supply. Therefore, the selection of inductor in DC TO DC circuit is very important.
In the power supply circuit, the selection of inductance includes inductance quantity, saturation current and packaging, which should be selected according to the ripple, current and operating frequency of the circuit. Generally, the inductance quantity can be determined by L=Vout *[(1-D)/I* R * F], where: Vout is the output voltage, D is the duty cycle, I is the output current, R is the ripple rate and F is the operating frequency. Ripple rate is generally 0.3, duty cycle D=Vout/Vin; From this the inductance can be calculated.
For the choice of the inductive current, the stress drop is required, which is the rated power calculation, usually inductance current 1.2 * I choice, the reason for this is the peak of the inductor current waveform is about 20% higher than average numerical, inductor current at the same time to choose a larger inductance is not easy to enter the saturated state (after entering saturation state, inductance wire short circuit). In addition, the inductor current selection is too small in the process of work will be issued "howling" sound, which is caused by the abnormal operation of the inductor, so according to experience, the inductor current selection of 1.2 times ~2 times can, so the inductor heat will not be too large, not easy to fail.
When the inductor and its current selection is completed, basically the inductor package can be determined, the rest is only from the price, height limit to choose the right package.
In addition, the inductance of the power circuit can also be obtained from the data book of the power chip. In practical application, it is necessary to calculate the appropriate inductance parameters according to the specific power chip.