In our impression, the resistance is to hinder the current flow. But 0 ohm resistors? What do we want a resistor that can't block current? In fact, 0 ohm resistors did not appear in the first place, and most 0 ohm resistors - are chip resistors. This is closely related to its purpose. When most of the circuit boards were designed with through-hole double-sided boards, there was not much room for 0-ohm resistors. At that time, if a company wanted to save some costs or use a single-layer circuit board for other reasons, it would Where the wiring is made, flying leads or vias are used to connect the two parts of the circuit that are separated. With the passage of time, more and more SMD components are used in large-scale industrial production, which also makes the same problem encountered when producing SMD single-sided circuit boards. It is difficult to solder the flying leads to the SMD. In the pad, at this time, the use of 0 ohm resistors can "leap" over thinner lines, reducing the difficulty of design.
For the same reason, if you want to configure the circuit board in the past, you can use jumpers and jumper caps to control the on-off in hardware. For the SMD circuit board, the jumper method is difficult to use the machine to install uniformly, and the use of the empty pad and the 0 ohm resistor can play the same role as the jumper, and it will play a certain role in production. configuration function. On the other hand, when the traditional jumper is not connected with the jumper cap, the interference signal will be radiated when the signal frequency at both ends is high, which is not as good as the empty pad.
In fact, in addition to these reasons, the use of 0 ohm resistors has some additional effects. For example, leads that can act as ground points, build current loops, etc. There are also some reasons that are difficult to consider, such as the use of unmarked 0 ohm resistors to play the role of anti-copying boards in order to facilitate the removal and measurement, and so on. These are all additional usage development. Usually we rarely use 0 ohm resistors in the process of DIY, but for it on the circuit board, we also need to understand its function.
Here is a summary of the many uses of 0 ohms:
1. There is no function in the circuit, but it is only on the PCB for debugging convenience or compatible design.
2. It can be used as a jumper. If a certain line is not used, just do not paste the resistor directly (without affecting the appearance).
3. When the parameters of the matching circuit are uncertain, use 0 ohms instead. During actual debugging, determine the parameters and replace them with components with specific values.
4. When you want to measure the current consumption of a certain part of the circuit, you can remove the 0ohm resistor and connect an ammeter, which is convenient for measuring the current consumption.
5. When wiring, if it can't be routed, you can also add a 0 ohm resistor.
6. Act as an inductor or capacitor under high frequency signals. (Related to external circuit characteristics) Inductors are mainly used to solve EMC problems. Such as ground and ground, between power supply and IC Pin.
7. Single-point grounding (meaning that the protective grounding, working grounding, and DC grounding are separated from each other on the equipment, and each becomes an independent system.)
8. Fuse function
9. Single-point grounding of analog ground and digital ground
As long as it is the ground, it will eventually be received together, and then enter the earth. If they are not connected together, they are "floating ground", there is a voltage difference, and it is easy to accumulate charges and cause static electricity. The ground is referenced to 0 potential, and all voltages are derived from the reference ground. The standard of the ground should be the same, so the various grounds should be shorted together. The earth is believed to be the ultimate ground reference point, capable of absorbing all electrical charges, remaining stable at all times. Although some boards are not connected to the ground, the power plant is connected to the ground, and the power on the board will eventually return to the power plant into the ground. If the analog ground and the digital ground are directly connected in a large area, it will cause mutual interference. There are four ways to solve this problem:
(1) Connect with magnetic beads;
(2) Connect with capacitors;
(3) Connect with inductance;
(4) Connect with 0 ohm resistor.
The equivalent circuit of the magnetic bead is equivalent to a band-stop wave limiter, which can only significantly suppress the noise at a certain frequency. The frequency of the noise needs to be estimated in advance in order to select the appropriate model. Magnetic beads are not suitable for situations where the frequency is uncertain or unpredictable.
The capacitor blocks the direct traffic, causing floating.
The inductor is large in size, has many stray parameters, and is unstable.
The 0 ohm resistor is equivalent to a very narrow current path, which can effectively limit the loop current and suppress the noise. Resistors have attenuation in all frequency bands (0 ohm resistors also have impedance), which is stronger than magnetic beads.
10. Used for current loop when connected across
When the electrical ground plane is divided, the shortest return path of the signal is broken. At this time, the signal loop has to be detoured, forming a large loop area, and the influence of the electric field and the magnetic field becomes stronger, and it is easy to be disturbed/disturbed. Connecting a 0 ohm resistor across the partition can provide a short return path and reduce interference.
11. Configuration circuit
Generally, jumpers and DIP switches should not appear on the product. Sometimes users will tamper with the settings, which is easy to cause misunderstandings. In order to reduce maintenance costs, 0 ohm resistors are used instead of jumpers to be welded on the board.
The vacant jumper is equivalent to the antenna at high frequency, and the chip resistor is effective.
12. Other uses
Cross the line when wiring;
Temporarily replace other SMD devices;
as a temperature compensation device;
More often it is due to the need for EMC countermeasures. Also, 0 ohm resistors have less parasitic inductance than vias, and vias also affect the ground plane (due to digging).
In addition, different sizes of 0 ohm resistors allow different currents, generally 1A for 0603 and 2A for 0805, so different currents will use different sizes, and when reserving places for magnetic beads, inductors, etc., it must be based on the magnetic beads, inductors, etc. The size is also packaged, so 0603, 0805 and other different sizes are available.