How much current can a 0 ohm resistor handle?
How much current can a 0 ohm resistor handle? This question should be checked by every hardware engineer. And related to this is another question, namely, how big is resistance of 0 ohm resistor?
These two questions were originally very simple, and answers should be very clear, but netizens on Internet gave different answers. Some people say that 0 ohm resistance is 50 mΩ, while others say that it is actually only 20 mΩ; some people say it can only carry 1A and some people say it can only carry 1.5A...
So how big is it? Let's take a look at it step by step.
Resistance value 0 Ohm
To solve these two problems, I specifically tested resistance standard. According to standard resistance document EN60115-2, resistance value of 0 ohm resistor is 0 ohm, but deviations are possible. There are three options for maximum 0 ohm resistance deviation: 10 mΩ, 20 mΩ, and 50 mΩ.
In other words, a resistance deviation of 0 ohms can allow for several deviations, which mainly depends on what kind of resistance manufacturers make.
I downloaded some major brands such as ROHM, Yageo and Guangjie and checked general specifications of 0 ohm resistors and found that maximum resistance value of 0 ohm resistors marked on them is 50mΩ.
From this we can conclude that resistance value of conventional 0 Ohm resistors does not exceed 50 mOhm.
0 ohm resistor overload capacity
There is also an opinion on Internet that current of a 0Ω resistor is calculated based on power, and resistance is calculated based on 50mΩ. In this case, 0805's resistance power is typically 1/8W, and calculated rated current should be 1.58A. However, I checked specs and found that Rohm, Yageo, and Guangjie are all 2A, which is somewhat different from calculated ones.
The nominal current of conventional 0 ohm resistors of three main manufacturers Rohm, Yageo and Guangjie is as follows:
As you can see from above figure, current rating of 0 ohm resistors of three major manufacturers is still slightly different. I propose to combine all products and choose at lowest cost, so that no matter what brand, design does not exceed specification.
The table after full rated current looks like this:
We see that current of conventional resistors is small, if you choose minimum value after synthesis, then maximum is only 2A. What if, when designing a circuit, I find out that I want to use a 3A or 4A 0 ohm resistor? It's actually very simple, you can connect two 0 ohm resistors in parallel.
Speaking of which, you might be wondering why some packets got bigger and overcurrent didn't? For example, both 0805 and 1206 are 2 A. It should be so that rated current does not increase, and instantaneous current should be greater. If you open Yageo resistor data sheet, you will find that there are two parameters written there, one is rated current and other is the maximum current. Rated current 2A, but maximum current 5A for 0805 and 10A for 1206.
Note. The jumper is a 0 ohm resistor (this is what is written in standard document, as shown in figure below).
Special 0 ohm high current rating resistor
If it's more current, a resistor is also optional. However, these resistors are not ordinary. For example, this Rohm ultra-low resistance resistor has a maximum resistance of 0.5mΩ, which is 100 times less. a few for pennies.
Using 0 ohm resistors for PCB design
Many newcomers to hardware often get confused when they see 0 ohm resistors used on a PCB. They often ask: since there is nothing in this thing, why use it?
Actually, 0 ohm resistor is very useful. When used correctly, it can greatly facilitate PCB design and debugging. Next, let's briefly talk about role of 0 ohm resistor.
For example, your boss asks you to design a single-sided board for cost reasons, that is, installation and connection of components can only be on one side. Line connection, punch two holes with a jumper? If this method is still possible during R&D, but one day your design becomes a product and requires mass production, it will be more of a hassle for machine to throw in a jumper than to put in a resistor. A 0 ohm resistor can help you a lot! Depending on your space, you can use resistors 0805, 0603 or 0402.
1. Isolation before and after debugging
If you have a new design and are not sure about function of many parts of PCB and performance that can be achieved, you will experience exciting debugging when you receive board back. An important principle of debugging is to limit problem. Therefore, at least isolation between several circuits is very important.
When debugging circuit A, you don't want circuit B to affect debugging, so best way is to break connection between them, and a 0 ohm resistor is best way to isolate!
Welding is not required during debugging. After debugging is completed and circuit is confirmed to be healthy, a 0 Ω resistor can be installed. Of course, it can be completely removed in final product.
2. To test current
If you want to check current of a certain path, one way is to measure voltage across resistor along path with a voltmeter (make sure internal resistance of voltmeter does not affect accuracy of measurement). Ohm's law can be used to calculate current outside circuit.
Another way is to connect ammeter directly to circuit so that a 0 ohm resistor can be placed in circuit. When measuring current, use two ends of an ammeter to replace resistor. After completing measurement, you can install a resistor.
3. The flexibility of self-debugging
All kinds of possibilities can be reserved, and various resistors can be selected according to actual needs. It can replace jumper, avoiding drilling and installing jumper, and taking up relatively much space, and jumper will also cause high-frequency interference.
For example, if PCB has a low-pass filter, if you find that you don't need it at end or you don't have time to debug low-pass filter at beginning of debugging, but you should miss signal, you can replace original design resistor 0 ohm Resistors / inductors without installation of capacitors. When parameters of matching circuit are not clear, replace them with 0 ohm resistors, and then replace them with specific numerical components after determining parameters during actual debugging.
4. Single point analog and digital ground connection for signal integrity
Some people say that a 0 ohm resistor means nothing, why not connect it directly? Imagine if you don't have that 0 ohm resistor on circuit diagram, you can ignore single point connection principle when laying out PCB and CAD software will also connect randomly without achieving your original single connection intent. - point connection.
Of course magnetic beads can be used for a single point connection as well, but my personal point of view is that with right connection location magnetic beads are of no use other than being more expensive than resistors. . In real work, you can use 0 ohm resistors in relatively small packages like 0402 and 0201 and just use a soldering iron to connect two ends together when soldering, so that connection resistor will also be saved.
5. Increase complexity of reverse engineering
If you put multiple 0 ohm resistors in different colors, in different packages, and without resistance labels, it will not affect performance of circuit, but it will instantly drive person who copied your board crazy.
The PCB supports various configurations. In some versions, some schemes may not be installed. You can use it to isolate unidentified parts of a circuit. For example, there is a WiFi version and a WiFi+3G version of iPhone that actually use design.
How about this? This 0 ohm resistor is very useful! In future projects, let's try it out slowly. In many cases, flexible usage will solve a lot of headaches for you.
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