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0 ohm resistor its role
2020-04-22
 
In our impression, the resistance is to hinder the current. But 0 ohm resistance? Why do we want a resistor that cannot block current? In fact, the 0 ohm resistor did not appear at the beginning, and most of the 0 ohm resistors-are chip resistors. This is closely related to its use.

When most of the circuit boards are designed with double-hole vias, there is not much room for 0 ohm resistors. At that time, if a company wanted to save some costs or other reasons and used a single-layer circuit board, it was impossible Where wiring is used, flying leads or vias are used to connect the two parts where the circuit is divided. With the passage of time, more and more SMD components are used in large-scale industrial production, which also causes the same problem when producing SMD single-sided circuit boards. It is difficult for flying leads to be soldered to SMD In the pad, the use of 0 ohm resistors can "leap" past on 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 the jumper and jumper cap to control the 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 0 ohm resistor matching method can play the same role as the jumper, which plays a certain role in production The role of configuration. On the other hand, in the case of a traditional jumper without a jumper cap, when the signal frequency at both ends is high, the interference signal will be radiated, which is not as good as the empty pad.

In fact, in addition to these reasons, the use of 0 ohm resistors has one or more additional effects. For example, it can be used as a lead for grounding point, constructing a current loop, etc. There are other reasons that are difficult to consider, such as removing the measurement for convenience, using an unmarked 0 ohm resistor as a copy-protection board, and so on. These are all developed for additional usage. Usually in the DIY process, we rarely use 0 ohm resistors, but for it on the circuit board, we also need to understand its role.

The following summarizes the multiple uses of 0 ohms:

1. There is no function in the circuit, just on the PCB for debugging convenience or compatible design and other reasons.

2. Can be used as a jumper, if a certain section of the line is not used, just do not paste the resistor directly (it does not affect the appearance)

3. When the matching circuit parameters are uncertain, replace with 0 ohms. When actually debugging, determine the parameters and replace with specific value components.

4. When you want to measure the current consumption of a 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 the cloth can not be passed, you can also add a 0 ohm resistor.

6. Under high frequency signal, act as inductance or capacitance. (Related to external circuit characteristics) Inductance is mainly used to solve EMC problems. Between ground and ground, between power supply and IC Pin.

7. Single-point grounding (refers to protective grounding, working grounding, and DC grounding that are separated from each other on the equipment and each becomes an independent system.)

8. Fuse function

9. Single point grounding of pseudo-ground and digital ground

As long as it is the ground, it will eventually be received together and then into the earth. If it is not connected, it is "floating ground", there is a pressure difference, and it is easy to accumulate charge and cause static electricity. The ground is referenced to the zero potential, and all voltages are derived from the reference ground. The ground standards must be consistent, so the various grounds should be shorted together. It is believed that the earth can absorb all charges and maintain stability at all times, which is the ultimate reference point. 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 and enter the ground. If the analog ground and digital ground are directly connected in a large area, it will cause mutual interference. It is not short-circuited and inappropriate. There are four ways to solve this problem:

(1) Connect with magnetic beads;

(2) Connect with a capacitor;

(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 only has a significant effect on suppressing noise at a certain frequency point. 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, the magnetic beads are not compatible.

Capacitors are connected directly, causing floating ground.

The inductor has a large volume, 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. The resistance has an attenuation effect in all frequency bands (0 ohm resistance also has an impedance), which is stronger than the magnetic beads.

10. Used for current loop when jumper

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 to form a large loop area. The influence of the electric field and the magnetic field becomes stronger, and it is easy to interfere / be disturbed. Connecting a 0 ohm resistor across the split area can provide a shorter return path and reduce interference.

11. Configure the circuit

Generally, the jumper and DIP switch should not appear on the product. Sometimes the user will set up disorderly, which is easy to cause misunderstandings. In order to reduce maintenance costs, 0 ohm resistors should be used instead of jumpers to solder on the board.

The vacant jumper is equivalent to an antenna at high frequencies, and the effect of using chip resistors is good.

12. Other uses

Cross-over when wiring;

For debugging / testing;

Temporarily replace other SMD devices;

As a temperature compensation device;

More often, it is due to the need for EMC countermeasures. In addition, the 0 ohm resistance is smaller than the parasitic inductance of the via, and the via will also affect the ground plane (because the hole needs to be dug).

There are different sizes of 0 ohm resistors that allow different passing currents, generally 0603 1A, 0805 2A, so different currents will use different sizes. When reserved positions for magnetic beads, inductors, etc., according to the magnetic beads, inductors The size is also packaged, so 0603, 0805 and other different sizes are available.
 
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