Circuit resonance and choke reactance of SMT inductors

      The role of patch inductor is choke filter and filter high frequency clutter, energy storage, used in power filter circuit, focus on the suppression of conductive interference.Inductive element and EMI filter element are widely used in PCB circuit of electronic equipment.

　　For example, the advantages of SMT are small package size and can meet the requirements of real space.In addition to differences in impedance, current carrying capacity, and other similar physical characteristics, the other performance characteristics of the through-hole connector and the surface mount are basically the same.

　　The chip inductors are required to realize two basic functions: circuit resonance and reactance.

　　Resonance circuit includes resonance generation circuit, oscillation circuit, clock circuit, pulse circuit, waveform generation circuit and so on.The resonant circuit also includes a high Q bandpass filter circuit.To make the circuit resonant, the SMD capacitance and SMD inductance must exist in the circuit simultaneously.

　　There are parasitic capacitors at both ends of the patch inductance, which is caused by the ferrite body between the two electrodes of the device being equivalent to the capacitive medium.In the resonant circuit, the inductor must have high Q, small tolerance and stable temperature coefficient, so as to meet the requirements of narrow band and low frequency temperature drift of the resonant circuit.High Q circuits have sharp resonance peaks.

　　Inductance bias with small tolerance ensures minimum resonance frequency deviation.The stable temperature coefficient guarantees the stable temperature variation characteristic of the resonant frequency.The difference between the standard radial inductance and axial inductance and the SMT inductance is only in the package.

　　The inductance structure of the patch includes coil wound on dielectric material (usually alumina ceramic material), or hollow coil and coil wound on ferromagnetic material.

　　In power inductor applications, when used as a choke coil, the main inductor parameters are dc resistance (DCR), rated current, and low Q value.When used as a filter, it is necessary to look at the broadband characteristics, so the high Q characteristics of the inductor are not required.A low DCR, defined as the dc resistance of a component in the absence of an ac signal, ensures a minimum voltage drop.