Inductors, Capacitors and Power Supplies

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Inductors, Capacitors and Power Supplies [Copy link]

This is a set of illustrated articles compiled by TDK. I think it is especially suitable for friends who are learning electronic design skills, so I would like to share it here

From the electromagnetic field theory - the "changing" electric field generates a magnetic field, and the changing magnetic field generates an electric field. Therefore, when an alternating current passes through the inductor formed by the coil, the mutual conversion between electromagnetics makes the inductor an important energy storage element, and it processes signal changes by reacting to current changes - the apparent role is to suppress AC signals and pass DC signals directly. To understand the function of the inductor and its various parameters, we need to analyze it from the perspective of electromagnetic theory.

Once we understand its working principle, we can understand the main role of the inductor. Suppress the unwanted changing interference signals and achieve the function of stabilizing the voltage through the mutual conversion of electromagnetic energy (the so-called energy storage).

Don't underestimate the small inductor. In fact, there are many categories. Different application fields have different requirements for their parameters, different materials are required, and their packaging is naturally different.

The largest number of products on the market are basically consumer products, especially mobile phones. Therefore, the application of inductors in mobile phones determines the different functions of mobile phones and drives the continuous progress of inductors.

This picture shows the production and processing process of inductors. It's quite complicated, right? I remember that in order to make a 5V to 400V DC-DC converter, I personally wound a high-frequency transformer with enameled wire. Today, when integrated circuits are highly integrated and developing at the speed of Moore's Law, high-tech technicians around the world are helpless with inductors. They cannot be integrated into the device with other devices. In the power supply circuit, they have to increase the switching frequency so that the inductor can be made smaller. Or try to avoid using large inductors in other ways.

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Capacitors and inductors are like twin brothers. They appear in pairs in many situations. Therefore, when we talk about inductors, we must also talk about capacitors.

For AC signals, inductors are obstacles, but capacitors try to bridge them. Blocking DC and passing AC are the characteristics of capacitors. Just like a flood control dam, capacitors isolate the surging charges on both sides. The positive and negative charges on both sides accumulate continuously and form strong energy. Therefore, capacitors also have the function of energy storage and can even replace batteries.

From this picture, we can see that the functions of capacitors are all around blocking DC and passing AC, including energy storage and filtering. . . . Can you see that they are different from inductors but have the same fate? In mathematics, the two are enemies who are born and killed.

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Just like inductors, different application scenarios of capacitors have different requirements for capacitor parameters and materials, and there are also various packages. On the PCB board, there may be no other devices, but there must be capacitors. As long as there is electricity, there will generally be capacitors. The most common capacitor is probably the 0.1uF chip ceramic capacitor, which is packaged in 0805 and 0603. It is estimated that every engineer has a large number of them on his workbench. They can be safely placed on the pins of each group of power supply voltages on the circuit diagram.

There are several big companies in the world that make passive devices (that is, resistors, capacitors, and inductors). TDK is one of them. This illustrated article is about TDK. This picture shows TDK's technology, process and continuous exploration efforts in capacitors.

After briefly analyzing the principles, applications, and materials of inductors and capacitors, we will now look at how these devices are used. Let's first look at the digital TV equipment that every household has. The biggest application of inductors and capacitors is in power conversion, whether it is directly converting from AC to DC, or obtaining DC through low-voltage DC. Of course, the combination of inductors and capacitors is also an essential component of bandwidth processing in analog signal conditioning. Different compositions of inductors and capacitors can produce different frequency processing effects on the input waveform.

Automotive electronics is a hot spot in the development of the electronics industry today. Its biggest feature is reliability. Therefore, the reliability requirements for various components are also extremely high - high temperature resistance, severe cold resistance, vibration resistance, etc. After all, cars are not household appliances in a greenhouse and the safety requirements during movement are not generally harsh.

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The power supply is the "stomach" of all electrical appliances, providing energy to every part. Good nutrition will also affect the health of the electronic product body. Let's take a look at the basic theory and composition of the power supply. Speaking of power supply, we must first understand the difference between AC and DC and the applicable scenarios of the two. Since alternating current (AC) has the highest efficiency, the electricity on the socket at home is basically AC, but to supply the integrated circuits on the circuit board, DC of various voltages is required. Therefore, it is necessary to convert AC into DC, or convert DC of a certain voltage into DC of other voltages. This is the role of power conversion.

Since everything in the world is not ideal and there are various variables, how to ensure stable supply under various possible changes, that is, how to maintain stable voltage output and provide sufficient current when the input voltage changes and the output load changes, this requires a voltage stabilization circuit to achieve. According to the working state of the key device of regulation - the triode: linear, switch, the voltage stabilization circuit can be divided into linear voltage stabilization and switching voltage stabilization, each of which has its own advantages and disadvantages. The specific application scenario should use an appropriate conversion method, or an organic combination of the two.

To convert the energy carried by the AC power supply into the energy carried by the DC voltage, it is necessary to first transform the power running back and forth into a torrent running in one direction. This process is called "rectification". Then, by smoothing the fluctuations in one direction, you can get a DC that moves in a consistent and stable manner. In this process, the diode with unidirectional conductivity plays the role of sorting out the flow direction, which is indispensable in rectification. To smooth the fluctuations of voltage, inductors and capacitors with energy storage functions are used. The three passive components of inductors, capacitors and resistors are like the three major arms, each performing their own duties and cooperating with each other to play the role of guidance and stability.

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As mentioned earlier, the two voltage stabilization methods have their own advantages and disadvantages. Because of their different structures and different working states of transistors, they are inseparable from the role played by inductors and capacitors as energy storage components.

There are many ways to convert from one DC voltage to another DC voltage. Depending on the values of the two voltages and the current size (that is, the power size) and stability required by the input and output, different conversion topologies and components need to be selected.

Any conversion will have certain losses. In power conversion, what is converted is essentially energy. Therefore, the efficiency requirement for the conversion is as high as possible, that is, the smaller the loss, the better. To improve conversion efficiency, in addition to reducing device losses, you can also avoid unnecessary waste through certain controls. This figure lists several methods that can improve power conversion efficiency and the requirements for various components.