Are you clear about the inductance in analog circuit?

The current on the inductor cannot change abruptly.(when the voltage at both ends of the inductor is withdrawn, the current does not immediately disappear, thus creating a reverse electromotive force.)

Inductance is a kind of energy storage element, used in LC oscillation circuit, low and medium frequency filter circuit, dc-dc energy conversion, etc., its application frequency range rarely exceeds 50MHz

The main parameters

(1) inductance value range: 1-470uh

(2) dc resistance: there are a variety of dc resistance to choose, the greater the value of inductance, the corresponding dc resistance is greater.General signal with inductance, its dc resistance than high frequency signal with inductance and power supply with inductance is some larger, the smallest dc resistance is generally a few milliohms, large several ohms

(3) since the resonant frequency: dozens of MHZ to hundreds of MHZ.The higher the value of inductance, the smaller the corresponding self-resonance frequency.

(4) rated current: a few milliamperes to tens of milliamperes.The higher the inductance value, the smaller the corresponding rated current.

When the working frequency is lower than the resonant frequency, the inductance value basically remains stable: but when the working frequency exceeds the resonant frequency, the inductance value will first increase, and then rapidly decrease after reaching a certain frequency.

When the working frequency is lower than the resonant frequency, the inductor device shows the sensibility, and the impedance increases with the increase of frequency: when the working frequency is higher than the resonant frequency, the inductor device shows the capacitance, and the impedance decreases with the increase of frequency.

Therefore, in the application, should choose the resonant frequency point higher than the operating frequency of the inductance as the power filter to choose the inductance, need to pay attention to the following points.

(1) inductance and capacitance composed of low-pass filter, inductance value is a very key parameter.The nominal inductance value of the inductance device data is the value whose working frequency is lower than the resonant frequency point. If the working frequency is higher than the resonant frequency, the inductance value will decrease sharply with the increase of working frequency and gradually show capacitance.

(2) when the inductor is used for power filtering, the voltage drop caused by its dc resistance needs to be considered.

(3) for power filter, the inductance of the operating current must be less than the rated current.If the operating current is greater than the rated current, the inductance may not be damaged, but the inductance value may be lower than the nominal value.

Cause of inductance screaming

If the ear can hear a squeak, it is certain that there is a switching current of around 20HZ-20KHZ at both ends of the inductor.

For example, the inductive howling of a dc-dc circuit due to excessive load current

There is a current limiting protection circuit inside the DC. When the load exceeds the switch (MOS) current inside the IC, the current limiting detection circuit judges that the load current is too large. It will immediately adjust the duty ratio of the switch inside the DAC, or stop the switch work immediately.

The time period from the stop switch to the restart switch is exactly a few KHZ frequency, and it is because of the switching frequency of this period that the whistle is generated

Improvement measures: reduce the load current or replace the dc-dc with slightly larger power, change the output capacitance and other methods

Excessive load current or voltage

Noise problems caused by inductance:

Inductance - induced voltage due to current changes causes transmission line effects, mutations, crosstalk, switching noise, track collapse, ground bombs, and most electromagnetic interference sources (EMI)

Such as:

Digital circuits are noisy. Saturated logic briefly draws large current from the source during the switching process, which causes large noise on the digital ground. However, due to the noise immunity of logic level, it can reach over hundreds of millivolts.

Inductors are added to the core for the purpose of increasing the inductance (or mutual inductance) of the inductor coil.

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Post time: Aug-31-2019
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