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It suddenly dawned on me that a 0 ohm resistor can still be used like this


It suddenly dawned on me that a 0 ohm resistor can still be used like this

In our opinion, resistance should impede flow. What about a 0 ohm resistor? What kind of resistor do we need that can't stop current?

Actually, 0 ohm resistors didn't show up at the beginning, and most 0 ohm resistors are ICs. This is closely related to its use.

When most PCBs were designed with double-sided through-hole boards, there wasn't much room for 0 ohm resistors. At that time, if a company wanted to cut costs or for other reasons and used single layered PCBs, flying wires or vias are used to connect two parts of a circuit where wiring is not possible.

It suddenly dawned on me that a 0 ohm resistor can still be used like this

As time goes on, more and more SMD components are used in large-scale industrial production, which also leads to same problem that occurs in production of single-sided SMD PCBs, and it will be difficult to solder loose leads. patch pad, a 0 ohm resistor can be used at this time to "jump" over thinner line, reducing design complexity.

For same reason, if you want to customize circuit board in past, you can use jumpers and jumper caps to control turn-on and turn-off hardware.

For SMD circuit boards, it is difficult to use a machine to set jumpers evenly, and using blank pads and 0 ohm resistors can play same role as jumpers that can be used during production. role in configuration.

On other hand, if a traditional jumper is not connected to jumper cap, interference signal will be emitted when signal frequency at both ends is high, which is not as good as when area is empty.

In fact, in addition to these reasons, there are additional effects of using 0 ohm resistors. For example, it can act as a lead wire for an earth point, build a current loop, etc.

There are other reasons that are difficult to consider, such as ease of removal for measurement, use of an unmarked 0 ohm resistor as a copy protection board, etc. . All this is an additional development of use.

We usually rarely use 0 ohm resistors in assembly process, but for this on PCB, we also need to understand its function.

The following are various uses for 0 ohm resistance:

1. There is no function in schematic, but only on PCB for ease of debugging or compatible design and other reasons.

2. Can be used as a jumper. If some line is not used, just do not insert a resistor (does not affect appearance).

3. If parameters of matching circuit are not clear, change them to 0 ohms. During actual debugging, define parameters and replace them with components with specific values.

4. If you want to measure current draw of a certain part of circuit, you can remove 0 ohm resistor and connect an ammeter, which is handy for measuring current draw.

5. When wiring, if wiring really doesn't go through, you can also add a 0 ohm resistor.

6. With high frequency signals, it acts like an inductor or capacitor. (Related to external circuit characteristics) Inductance is mainly used to solve EMC problems. For example, ground and ground, between power supply and IC pin.

7.Single-point grounding (meaning that safety ground, working ground, andThe DC voltages are separated from each other on equipment, and each of them becomes an independent system).

8. Merging effect.

9. Single-point grounding of quasi-ground and digital ground:

As long as it's ground, it must be connected together at end, and then enter ground. If they are not connected together, they will "float" and a voltage difference will occur that easily builds up charges and causes static electricity. Ground is referenced to 0 potential and all voltages are obtained with respect to ground. Grounding standards must be consistent, so various grounds must be shorted together.

Earth is considered final point of reference because it absorbs all charges and always remains stable. While some boards are not connected to ground, power plant is connected to ground and power on board will eventually return to power plant and be grounded.

If analog ground and digital ground are directly connected over a large area, it will cause mutual interference. Short circuit is unacceptable, reason is above, there are four ways to solve this problem.

  • Connect with magnetic beads;

  • Connect to capacitor;

  • Connect to inductor;

  • Connect with a 0 ohm resistor.

  • The magnetic bead equivalent circuit is equivalent to a bandstop wave limiter, which can only significantly suppress noise at a certain frequency point, when using it, it is necessary to estimate frequency of noise point in advance to select appropriate model. In situations where frequency is uncertain or unpredictable, magnetic beads are not suitable.

    The capacitor blocks traffic, causing a floating ground.

    The inductor is large, has many parasitic parameters, and is unstable.

    0Ω resistance is equivalent to a very narrow current path, which can effectively limit loop current and suppress noise. Resistors have a damping effect across all frequency ranges (0 ohm resistors also have an impedance) that is stronger than magnetic beads.

    10, Used for current loop when crossing:

    When electrical ground plane is separated, shortest signal return path is interrupted. At this time, signal loop must be bypassed, forming a large area of ​​the loop, and influence of electric field and magnetic field becomes stronger, and it is easy to interfere/tamper.

    Connecting a 0 ohm resistor across separation area can provide a shorter return path and reduce noise.

    11, Configuration schema:

    In general, there should be no jumpers or DIP switches on product. Sometimes users will fiddle with settings, which can easily cause misunderstandings. To reduce maintenance costs, 0 ohm resistors are used instead of jumpers, which are soldered to theboard.

    A free jumper is equivalent to an antenna at high frequency, and effect of using chip resistors is better.

    12Other targets:

  • Crossover during posting;

  • For debugging/testing;

  • Temporary replacement of other patch devices;

  • As a temperature compensation device

  • This is most often due to need to counter electromagnetic compatibility.

  • Also, 0 ohm resistance is less than parasitic inductance of via, and via will also affect ground layer (due to need for digging holes).

    Also, different sizes of 0 ohm resistors allow different currents, typically 1A for 0603 and 2A for 0805, so different sizes will be used for different currents. other sizes are available.

    It suddenly dawned on me that a 0 ohm resistor can still be used like this

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