Why would a circuit have a zero ohm resistor (3 black bands) in it?

In summary, a circuit might have a zero ohm resistor in it because it is a placeholder for a low-value resistor, or because it is used to switch between multiple configurations of the same circuit.
  • #1
EIRE2003
108
0
Why would a circuit have a zero ohm resistor (3 black bands) in it?
 
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  • #2
EIRE2003 said:
Why would a circuit have a zero ohm resistor (3 black bands) in it?

Zero ohn resisitors are used as jumpers.
 
  • #3
faust9 said:
Zero ohn resisitors are used as jumpers.
And often they are placeholders for low value resistors whose value you haven't decided on yet. Also, you use zero Ohm resistors to let you stuff different configuration options.
 
  • #4
berkeman said:
Also, you use zero Ohm resistors to let you stuff different configuration options.

What do you mean there?
 
  • #5
EIRE2003 said:
What do you mean there?
You wouldn't run into this use of zero Ohm jumpers on a production board, probably. But on test and prototype assemblies, especially mixed signal analog + digital emulation boards, you often are not sure what the best configuration will be in an analog area. So if there are two or three likely candidate configurations of the basic topology, you put all the hooks into be able to switch between the configurations by stuffing different combinations of zero Ohm jumpers. Parasitics are often a concern in analog circuits, so you don't want to have to be reworking flying components too much onto an SMT assembly to try different options. I'll use the SMT zero Ohm jumpers to short around a component that I want to remove from the circuit (like a signal transformer) for particular characterization tests, for example. Or maybe I want to try a couple different topologies of an analog filter section, so I'll place zero Ohm jumper positions in places that I can use to change the way the parts are connected in the filter. Make sense?
 
  • #6
Hmmmmm... A zero ohm resistor sounds like a weird item indeed... We know that even "wire" has some resistance per unit length. It would be logical to say that a "zero" ohm resistor then has some finite resistance. Suppose you put an voltmeter across this resistor. Let's say 5Vdc was the potential preceding the zero ohm resistor. How much current would you say is running through the resistor?? I = V/R = 5/small = 5/.0000001 = 250MAmps That would burn up! Even a small potential above such a resistor would measure a large current through it.

So how do you avoid such a high current through a zero ohm resistor?
 
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  • #7
I don't think you would put them across your power supply. If you did, you would either smoke the wire or your supply(if not current protected).
 
  • #8
dlgoff said:
I don't think you would put them across your power supply. If you did, you would either smoke the wire or your supply(if not current protected).
It doesn't have to be directly across the PS to have a voltage on it.
 
  • #9
Ouabache said:
Hmmmmm... A zero ohm resistor sounds like a weird item indeed... We know that even "wire" has some resistance per unit length. It would be logical to say that a "zero" ohm resistor then has some finite resistance. Suppose you put an voltmeter across this resistor. Let's say 5Vdc was the potential preceding the zero ohm resistor. How much current would you say is running through the resistor?? I = V/R = 5/small = 5/.0000001 = 250MAmps That would burn up! Even a small potential above such a resistor would measure a large current through it.

So how do you avoid such a high current through a zero ohm resistor?
LOL. You use them for interconnect, just like wires and traces. Not as a circuit element. Funny guy :rofl:
 
  • #10
berkeman said:
You wouldn't run into this use of zero Ohm jumpers on a production board, probably.
Hey, I just remembered an application for zero Ohm jumpers where they are actually used in high volume production of low-cost assemblies. I'd make it a Quiz Question for y'all, but it's probably too obscure.

Zero Ohm jumpers are used to help a designer use the cheapest PCB possible in low-cost consumer goods like TVs and radios and calculators. Since jumpers are so cheap, adding a few to a single-sided PCB to keep from having to use a 2-sided PCB makes great economic sense. Same thing for a 2-sided PCB over a 4-layer PCB, although jumpers are less commonly used for this purpose on 2-sided PCBs. If you open up just about any low-cost radio and check out the PCB, it will be single sided with a few jumpers to help route the signals.
 
  • #11
One reason zero ohm resistors would be used on production level would be for hardware-programming. The end user cuts various resistors out to 'program' the way the machine is to behave. This can be done with jumper wires too, or even 10 or 100 ohm resistors depending on circuit design. But, wires are not used because it is probably difficult for auto-insert machines to insert them onto a circuit board.
 
  • #12
Well, I get the impression at least a couple of folks, have the idea why the zero ohm resistor doesn't burn up in the circuit, though it would be useful to see some analytical reasoning why that is so.
Quiz time is up, everyone pass in your papers. Come on, please put away your pencils and pass your work in. :biggrin:

The reason the zero ohm resistor does not burn up (fuse open), is because in its application, it would be in series with a large impedance before reaching ground (0Vdc), so the current through it would be very small. (intuitively you may sense that)
However, let's take a closer look. Let's say the zero ohm resistor has 5V (= Vs) applied to it. If a large impedance R2 (e.g. 1Mohm) is in series with it, what would be the voltage drop across the "zero" ohm R1 resistor (real world: R1 = very small resistance = ~.00000001 ohms
We can solve this as a voltage divider. Vs(R1/(R1+R2)) = 5(1M/((1M+0.00000001)) = 5(1M/~1M) = 4.99999999...
So the voltage drop across the zero ohm resistor is 5-4.9999999... = very small voltage and the corresponding current through it, would also be very small (I = V/R = (very small)/small) = very small current.
 
  • #13
Another Question

I have another question on the same topic. Does anybody have any more analog (as opposed to digital -- like a switch -- or mechanical -- like PCB layer avoidance) ideas for the use of 0 ohm resistors? the reason why I ask is because they are sold with very high, very specified ratings (like a surface mount zero ohm resistor from Dale/Vishay might be rated at a maximum current of 4 Amps). Why not make it metal, just like a wire, that might not be rated so high in current? If they have specific deliberate attributes, it seems they might have a component purpose? ... just a question...
MH
 
  • #14
matejhowell said:
I have another question on the same topic. Does anybody have any more analog (as opposed to digital -- like a switch -- or mechanical -- like PCB layer avoidance) ideas for the use of 0 ohm resistors? the reason why I ask is because they are sold with very high, very specified ratings (like a surface mount zero ohm resistor from Dale/Vishay might be rated at a maximum current of 4 Amps). Why not make it metal, just like a wire, that might not be rated so high in current? If they have specific deliberate attributes, it seems they might have a component purpose? ... just a question...
MH
I'm no help on that question, unfortunately, but we will sometimes use a wirewound resistor as an inductor in special situations. Good question, though.
 

1. Why would a circuit have a zero ohm resistor?

A zero ohm resistor, also known as a jumper or shunt, is typically used as a placeholder in a circuit. It allows for easy connection between two points on a printed circuit board (PCB) without having to physically solder components together. It also provides a means to change the electrical path in a circuit without having to remove or replace other components.

2. What do the 3 black bands on a zero ohm resistor represent?

The color bands on a resistor indicate its resistance value according to a color code system. However, a zero ohm resistor has no resistance value, so the 3 black bands are used as a placeholder instead. This is to differentiate it from other resistors that do have a measurable resistance.

3. Can a zero ohm resistor be replaced with a wire?

In most cases, yes, a zero ohm resistor can be replaced with a wire. However, using a zero ohm resistor allows for easier troubleshooting and modifications in a circuit without having to cut and re-solder wires.

4. Are there any drawbacks to using a zero ohm resistor?

The main drawback of using a zero ohm resistor is that it takes up physical space on a PCB. This can be an issue in compact electronic devices where space is limited. Additionally, zero ohm resistors can be more expensive than a simple wire, so cost may be a consideration in large-scale production.

5. Can a zero ohm resistor be used as a regular resistor?

No, a zero ohm resistor cannot be used as a regular resistor. Its purpose is solely for connecting two points in a circuit, and it has no measurable resistance value. If a circuit requires a regular resistor, a zero ohm resistor should not be used as a substitute.

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