0R resistors, beads and inductors

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0R resistors, beads and inductors [Copy link]

01

0 ohm resistor

0 ohm resistors are often seen in circuit design, and people are often confused: since it is a 0 ohm resistor, it is a wire, why do we need to install it? Are there any such resistors on the market? In fact, 0 ohm resistors are quite useful. There are probably the following functions, and the most important and frequently used functions are:

Key introduction: Single-point grounding of analog ground and digital ground

As long as it is a ground, it must be connected together and then enter the earth. If it is not connected together, it is a "floating ground", there is a voltage difference, it is easy to accumulate charge and cause static electricity. The ground is the reference 0 potential, and all voltages are obtained by reference to the ground. The ground standard must be consistent, so various grounds should be short-circuited together. People believe that the earth can absorb all charges and always maintain stability, and is the final ground reference point. Although some boards are not connected to the earth, the power plant is connected to the earth, and the power on the board will eventually return to the power plant and enter the ground. If the analog ground and digital ground are directly connected over a large area, it will cause mutual interference. It is not appropriate not to short-circuit, and the reasons are as follows. There are four ways to solve this problem:

①, connect with magnetic beads;　

②, connect with capacitors;

③, connect with inductors;

④, connect with 0 ohm resistors.　

Differences:

①, the equivalent circuit of magnetic beads is equivalent to a band-stop limiter, which only has a significant suppression effect on the noise of a certain frequency point. When using it, it is necessary to estimate the noise frequency in advance in order to select the appropriate model. For situations where the frequency is uncertain or unpredictable, magnetic beads are not suitable;

②, capacitors block direct current and pass alternating current, resulting in floating ground;

③, inductors are large in size, have many stray parameters, and are unstable;

④, 0 ohm resistors are equivalent to very narrow current paths, which can effectively limit loop currents and suppress noise. Resistors have attenuation effects in all frequency bands (0 ohm resistors also have impedance), which is stronger than magnetic beads.

Other functions of 0 ohm resistor:

①. It has no function in the circuit, but is only used on the PCB for debugging convenience or compatible design;

②. It can be used as a jumper. If a certain section of the line is not used, just do not paste the resistor (it does not affect the appearance);

③. When the matching circuit parameters are uncertain, use 0 ohm instead. When actually debugging, determine the parameters and then replace them with components with specific values;

④. When measuring the current consumption of a certain part of the circuit, you can remove the 0ohm resistor and connect the ammeter, which is convenient for measuring the current consumption;

⑤. When wiring, if it is really impossible to lay it, you can also add a 0 ohm resistor;　

⑥. Under high-frequency signals, it acts as an inductor or capacitor. (Related to the characteristics of the external circuit) The inductor is mainly used to solve EMC problems. Such as ground and ground, power supply and IC, pin;

⑦, single point grounding (referring to the protection grounding, working grounding, and DC grounding being separated from each other on the equipment, each becoming an independent system);　　

⑧, fuse function;

⑨, used for current loop when jumper;

when the electric ground plane is divided, the shortest return path of the signal is broken. At this time, the signal loop has to take a detour, forming a large loop area, and the influence of the electric field and magnetic field becomes stronger, which is easy to interfere/be interfered. Jumpering a 0 ohm resistor on the split area can provide a shorter return path and reduce interference.

⑩, configure the circuit;

generally, jumpers and dip switches should not appear on the product. Sometimes users will mess with the settings, which may cause misunderstandings. In order to reduce maintenance costs, 0 ohm resistors should be used instead of jumpers and soldered on the board. The vacant jumper is equivalent to an antenna at high frequencies, and the effect is good with chip resistors.

, other uses;　

cross-line during wiring, debugging/testing, temporary replacement of other chip devices, as a temperature compensation device, more often due to the need for EMC countermeasures. In addition, the parasitic inductance of a 0 ohm resistor is smaller than that of a via, and vias will also affect the ground plane (because holes need to be dug). In addition, different sizes of 0 ohm resistors allow different currents to pass through, generally 1A for 0603 and 2A for 0805, so different sizes will be used for different currents. In addition, when reserving space for magnetic beads, inductors, etc., they must be packaged according to their sizes, so different sizes such as 0603 and 0805 are available.

Appendix: The role of 1 ohm resistor

1 ohm resistor is often used for testing in circuits. For example, when we need to measure the current in a circuit, we can connect a 1 ohm resistor in series in the circuit. The voltage measured across the resistor is the current in the circuit (I=U/R, because R=1, the measured voltage value is the current value).

02

Magnetic beads

Magnetic beads are specially used to suppress high-frequency noise and spike interference on signal lines and power lines, and also have the ability to absorb electrostatic pulses. Magnetic beads are used to absorb ultra-high frequency signals. Some RF circuits, PLLs, oscillation circuits, and ultra-high frequency memory circuits (DDR, SDRAM, RAMBUS, etc.) all require magnetic beads to be added to the power input part. Inductors are energy storage components used in LC oscillation circuits, medium and low frequency filter circuits, etc., and their application frequency range rarely exceeds 50MHZ. Magnetic beads have high resistivity and permeability, which is equivalent to resistors and inductors in series, but the resistance and inductance values vary with frequency.

The function of magnetic beads: mainly to eliminate RF noise existing in the transmission line structure (circuit). RF energy is an AC sine wave component superimposed on the DC transmission level. The DC component is a useful signal that is needed, while the RF energy is useless electromagnetic interference transmitted and radiated along the line (EMI). To eliminate these unwanted signal energies, chip magnetic beads are used to play the role of high-frequency resistors (attenuators). The device allows DC signals to pass through and filters out AC signals. Usually the high frequency signal is above 30MHz, however, the low frequency signal will also be affected by the chip ferrite beads.

Magnetic beads have high resistivity and permeability, which is equivalent to a resistor and an inductor in series, but the resistance and inductance values vary with the frequency. It has better high frequency filtering characteristics than ordinary inductors, and is resistive at high frequencies, so it can maintain a high impedance within a fairly wide frequency range, thereby improving the FM filtering effect.

As a power supply filter, an inductor can be used. The circuit symbol of the ferrite bead is an inductor, but the model shows that a ferrite bead is used. In terms of circuit function, the principle of the ferrite bead and the inductor is the same, but the frequency characteristics are different.

Note: The unit of the ferrite bead is ohm, not Henry, so pay special attention to this.

03

inductance

Inductance is a property of a closed loop. When current passes through a coil, a magnetic field is formed in the coil, and the induced magnetic field generates an induced current to resist the current passing through the coil. This interaction between the current and the coil is called electrical reactance, or inductance, and its unit is Henry (H).

Note: Inductance is only briefly introduced here, and this content will be reflected in the following text.

The difference between magnetic beads and inductors:

Inductors are energy storage components, while magnetic beads are energy conversion (consumption) devices. Inductors are mostly used in power supply filter circuits, focusing on suppressing conducted interference; magnetic beads are mostly used in signal circuits, mainly for EMI. Magnetic beads are used to absorb ultra-high frequency signals. Some RF circuits, PLLs, oscillation circuits, and ultra-high frequency memory circuits (DDR, SDRAM, RAMBUS, etc.) all require magnetic beads to be added to the power input part, while inductors are an energy storage component used in LC oscillation circuits, medium and low frequency filter circuits, etc., and their application frequency range rarely exceeds 50MHz. In terms of circuit function, magnetic beads and inductors have the same principle, but different frequency characteristics.

This post is from the Motor Control forum