What are the functions of the resistors and capacitors on both sides of the crystal oscillator?

　　What are the functions of the resistors and capacitors on both sides of the crystal oscillator?

　　Scanner power adapter background knowledge

　　The crystal oscillator refers to a slice (referred to as a wafer) cut from a piece of quartz crystal at a certain azimuth angle. The quartz crystal resonator is referred to as quartz crystal or crystal or crystal oscillator; and the crystal element that adds IC inside the package to form an oscillator circuit is called Crystal oscillator. The charger is generally packaged in a metal shell, but also in a glass shell, ceramic or plastic package.

　　The general applications of crystal oscillators are:

　　1. A general-purpose crystal oscillator, used in various circuits to generate oscillation frequency.

　　2. Quartz crystal resonators for clock pulses are used in conjunction with other components to generate standard pulse signals, which are widely used in digital circuits.

　　3. Quartz crystal resonators for microprocessors.

　　4. CTVVTR uses quartz crystal resonator.

　　5. Quartz crystal oscillators for watches.

　　Today's problem

　　In the daily charger circuit design, we often use crystal oscillators, and we often see capacitors and resistors at both ends of the crystal oscillator, such as the two pictures below. So what are the functions of such capacitors and resistors? How are their values selected? You can combine theory and practical projects to give your own views.

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　　Inductance and chokes in chargers

　　The charger manufacturer introduced the following winding components (inductance and holding ring)

　　1. Simple inductance (no DC current through)

　　2. Common-mode line filter inductance (especially dual-winding inductance with large symmetrical power frequency current)

　　3. Series line filter inductor (inductance carrying large and asymmetric power frequency current)

　　4. Flow coil (inductance wrapped around a ferrite core with an air gap and carrying a large DC bias current)

　　5. Rod-shaped flow ring (a flow-throwing ring wound on a ferrite core or a rod-shaped iron powder core)

　　In order to facilitate the discussion, the "inductance" we are talking about here refers to the winding components without DC current, and the "choke coil" refers to the winding components with large bias current and relatively small AC ripple.

　　The design and material selection of winding components must fully consider the place of application. In addition, the design must be repeated many times, and the relationship between some interconnected but opposite variables must be coordinated.

　　If the engineer can fully understand and grasp the theoretical and actual specifications required for the optimal design of various winding components in the charger, then the design skills he possesses will be precious and unique.

　　The design method used here is mainly based on its scope of application, focusing on the three aspects of cost, size and loss. The final design can only be a compromise solution. Since these three main aspects are contradictory, it can only be used. A compromise solution. The task of the designer is to obtain the best compromise.

　　In charger applications, inductors without DC bias are generally limited to low-pass filters used in the charger circuit. Here, their main function is to prevent high noise from being transmitted back to the charger circuit. For this type of application, we should choose a core material with a high conductivity.

　　Chokes (inductors carrying large bias DC currents) are used in high-frequency power output filters and continuous buck-boost converter "transformers". In these applications, low permeability and high frequency should be preferred Magnetic core material with low magnetic loss.

　　In order to reduce the number of turns and reduce the copper loss, the most ideal core material should have high permeability and small magnetic loss. Unfortunately, in the design of the current-carrying circle, the existence of large DC components and the actual use The limited saturation magnetic flux density of magnetic materials makes us have to choose low-conductivity materials or introduce air into the core. However, due to the too low effective permeability, more windings are required to achieve the required inductance. value. Therefore, in the choke coil design, in order to pass a larger DC current, both low copper loss and high efficiency must be taken into account.

　　Simple inductor

　　In the application field of charger, pure inductance (cannot carry DC current component or forced AC high current component) is rare. Unlike the common-mode filter inductors that will be introduced below, since no air gap is required, the value of this inductance can be obtained directly from the given core inductance A value, so the design is relatively simple, and this will not be described. But it must be remembered that the size of this type of inductance is proportional to the square of the number of turns. Therefore, A1 must be given for 1 turn (as shown in the following formula), or A1 for multiple turns must be given. At this time, the value of A should be reduced to the value of 1 turn by dividing by the square of the number of turns.

　　L=N2AL

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