Questions tagged [current]

Flow of electric charge - typically movement of charge carriers, such as electrons. Measured in amperes (A).

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327 votes
6 answers
420k views

Choosing power supply, how to get the voltage and current ratings?

Power supplies are available in a wide range of voltage and current ratings. If I have a device that has specific voltage and current ratings, how do those relate to the power ratings I need to ...
Olin Lathrop's user avatar
175 votes
12 answers
19k views

How does the current know how much to flow, before having seen the resistor?

With the following circuits as examples : and How will the current I know how much to flow? Would any other wave travel first in the circuit and then come back ...
Prabhanjan Naib's user avatar
157 votes
4 answers
79k views

How can I efficiently drive an LED?

I understand that I can not connect an LED directly to a battery because it will draw too much current. Thus, there must be something else in the circuit to limit the current. What options are there? ...
Phil Frost's user avatar
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111 votes
9 answers
117k views

Why does a resistor need to be on the anode of an LED?

Please be kind, I am an electronics nub. This is in reference to getting an LED to emit photons. From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons ...
Spechal's user avatar
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96 votes
10 answers
181k views

How to get more than 100mA from a USB port

I heard that the current limit for a USB port is 100mA. However, I also heard that some devices can get up to 1.8A from a port. How do you get past the 100mA limit?
200ok404notfound's user avatar
78 votes
10 answers
460k views

How much voltage/current is "dangerous"?

Related: Safe current/voltage limit for human contact? From what I've heard: 110 V (or 220 V; household voltage pretty much) is dangerous (i.e. can kill you) I think there's consensus on this, ...
user541686's user avatar
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55 votes
7 answers
64k views

What is the usage of Zero Ohm & MiliOhm Resistor?

I am new to PCB design and I noticed that some schematics use 0Ω or 100mΩ resistors. What is their purpose and why do we need to use them in our PCB design? Normally if we wish to probe how much ...
Dennis's user avatar
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48 votes
2 answers
8k views

Why don't electrons take the shorter path in coils?

Below is a copper coil, presumably forming an electromagnet. From my understanding the electrons travel around the coil to produce a magnetic field. But why don't the electrons jump the wires and take ...
rrswa's user avatar
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46 votes
6 answers
8k views

Why aren’t the main conductors in this underground power cable made from copper?

I’ve found a piece of electrical cable left by the electricity company that supplies the area. They did a repair recently underground. I’m curious why the three big triangular conductors aren’t made ...
i-CONICA's user avatar
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44 votes
2 answers
17k views

Sharp corners in PCB traces

Why does a typical PCB always has rounded tracks? What harm can a sharp edged PCB track can cause? Please explain!
Vinit Shandilya's user avatar
43 votes
10 answers
16k views

Is current source also a voltage source?

I'm confused between current and voltage sources; I get the text book definition but I am not able to understand real world difference. To me both current and voltage sources seem as the same. I ...
user3551094's user avatar
43 votes
2 answers
26k views

Why do CPUs need so much current?

I know that a simple CPU (like Intel or AMD) can consume 45-140 W and that many CPUs operate at 1.2 V, 1.25 V, etc. So, assuming a CPU operating at 1.25 V and having TDP of 80 W... it uses 64 Amps (a ...
Leonardo Bosquett's user avatar
42 votes
12 answers
166k views

Is it really OK to supply more current than what the component is rated for?

In this heavily upvoted answer the answerer states that it is okay to supply a component with more current than what it's rated for. The analogy is that (paraphrasing here) "If Johnny wants to eat two ...
Zac's user avatar
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40 votes
13 answers
11k views

Why can current only flow in loops? [duplicate]

In the following image: Why can't current flow across the following wire? It's a simple question, but I've kind off always wondered. Thanks!
Physco111's user avatar
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36 votes
7 answers
89k views

When people talk about a device "drawing" current, what do they mean? Why do devices under load "draw" more current?

In my (extremely rudimentary) understanding, the amount of current flowing in a circuit is determined by a) its resistance, and b) the voltage of the power source (voltage from beginning to end), ...
Chris Cooper's user avatar
34 votes
3 answers
11k views

Whats inside a resistor?

How does a resistor "resist" current/potential? I know it's an elementary question, but I'm sure others are wondering too.
Shubham's user avatar
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34 votes
8 answers
3k views

Two black boxes display the same impedance at all frequencies. Which has the single resistor?

Two black boxes display the same impedance at all frequencies. The first contains a single 1 Ohm resistor. Each end is connected to a wire, so that two wires protrude from the box. The second box ...
Paskualino's user avatar
33 votes
8 answers
52k views

Current flow in batteries?

I am reading a basic electronics book: "There are no Electrons: Electronics for Earthlings" and I came across a clever passage about the fact that you need a closed circuit in order for current to ...
user avatar
33 votes
7 answers
36k views

How do I calculate the power rating for zero-ohm resistors?

Based on my earlier question, since there supposed to be zero voltage (V=IR) drop across a 0 Ω resistor, how do we select the power rating of such a component? For example, let's say I were to ...
Dennis's user avatar
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32 votes
6 answers
126k views

"Ground" vs. "Earth" vs. common vs. negative terminal

This may just be me not having a degree in electrical engineering or electronics, but the whole notion of "ground" and "earth", when used in electrical circuit diagrams (especially integrated circuits)...
jrista's user avatar
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31 votes
2 answers
43k views

Does MOSFET let current flow through source to drain as it allows it from drain to source?

Does a MOSFET allow current flow in reverse direction (i.e.; from source to drain)? I made a Google search, but couldn't find a clear statement about this matter. I have found this similar question, ...
hkBattousai's user avatar
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30 votes
6 answers
50k views

Parallel MOSFETs

When I went to school we had some basic circuit design and stuff like that. I learned that this was a bad idea: simulate this circuit – Schematic created using CircuitLab Since the current ...
BufferOverflow's user avatar
30 votes
6 answers
18k views

High PCB copper thickness: What are the pitfalls?

We need to carry high currents on a PCB (~30Amps sustained), so we are likely to order our PCBs with high copper thickness. So far we've only used 35 microns (1 oz) in our designs, so 'high thickness' ...
SomethingBetter's user avatar
29 votes
7 answers
47k views

How to carry high current on PCB

I need to pass high current on some part of my circuit. I used an online PCB track width calculator to see that required track width is about 5mm and minimum clearance is 1mm, which makes it about 7mm ...
hkBattousai's user avatar
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29 votes
4 answers
70k views

Why is it bad to mix new and old batteries?

I've seen warnings that it's bad to mix new and old batteries -- why? Is it a matter of a battery's age or a battery's voltage/current (remaining)?
Coldblackice's user avatar
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28 votes
7 answers
10k views

Why are integrated circuits powered by low voltage and high current?

I've heard that a typical graphics card uses around 100 A of current and only 1 V of voltage. Is there a specific reason why not to use the other way around, so high voltage and low amp? Usually high ...
Maxim's user avatar
  • 475
27 votes
4 answers
76k views

Do electrons actually flow when a voltage is applied?

It's said in books that a circuit is a closed path and thus that electrons come back to the source. If that's the case, what would happen when there were an earth fault in a circuit? How would the ...
Ranjit's user avatar
  • 271
27 votes
3 answers
31k views

Why is earth used for ground? Literally earth?

I never considered earth to be particularly conductive. It's just dirt, after all. However, I've seen "earth ground" conductive stakes driven into the ground in order for electricity to be grounded, ...
user3916009's user avatar
26 votes
5 answers
54k views

How much current can Solderless Breadboards handle?

I'm working on a project with a few stepper motors. I want to breadboard them so I know the circuit works well before creating a physical PCB. Each of the three motors is rated 2A, but I'll be ...
Anonymous Penguin's user avatar
25 votes
4 answers
43k views

Sizing a trace on a PCB to carry 2.5 amps

I need a trace on my PCB to carry up to 2.5 amps (average) current, with 5-6 amp spikes (it's going to a switch mode power supply.) How wide should the traces be? I've got a trade off between ...
Thomas O's user avatar
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22 votes
14 answers
7k views

Finding a faulty chip that draws too much current

Note that this is a theoretical question - there is no schematic I can show. I will show some schematic, but it will be a very simplified version of an actual circuit, only for illustration purposes. ...
nettek's user avatar
  • 1,035
22 votes
5 answers
44k views

Whats does "hr" mean among "V" and "Ah" in batteries?

I have a battery which indicates 12V25Ah/10hr. What does 10hr mean here? I guess "hr" stands for "hour". But 25Ah already means if battery is fully charged and if I load 12V 25A (=300W) to it, it ...
Farrukh's user avatar
  • 231
22 votes
2 answers
803 views

Which way does electricity power a circuit?

Working with some circuits this summer, I ran into what everyone eventually does: Current flows from + to - despite the electrons flowing (well, bumping into eachother) from - to +. I understand the ...
Tom's user avatar
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21 votes
9 answers
17k views

How can AC current power anything?

I understand the difference between AC and DC. What I don't understand is how does AC power anything when it's reusing the same electrons over and over as they are moving back and forth? A visual ...
Luke's user avatar
  • 505
21 votes
6 answers
55k views

MOSFET: When can we not assume that the gate current is 0?

A common rule of thumb you hear when learning Electrical Engineering is that the gate current of a MOSFET is always approximately 0. When is it not safe to assume that it is 0?
Andres Riofrio's user avatar
21 votes
5 answers
60k views

Is it OK to put LEDs in parallel? [duplicate]

I wonder if it's a good idea to put LEDs in parallel, as below: I've heard that it might not be because the voltage threshold won't be exactly the same for each LED, so they'll shine all with very ...
Kar's user avatar
  • 1,557
21 votes
6 answers
13k views

current sourcing, current sinking

I'm a student studying electronics and I'm having trouble understanding the concept behind current sourcing and current sinking. We've covered it in a lab using a 7404 and an LED and all that. Just ...
user217's user avatar
  • 211
21 votes
2 answers
6k views

Why so many pins for the MOSFET's drain?

The FDC855N comes in a 6-pin package, 4 of which are connected to the drain, and only 1 to the source. Why this difference? The source sees the same current as the drain, doesn't it?
Federico Russo's user avatar
20 votes
9 answers
32k views

How is the internet able to transmit data so fast?

I'm not sure if I'm in the right place or not, but I figured someone here could maybe provide a good answer. I want to know how electricity is able to flow so fast. For example videos games nowadays, ...
Cam Jones's user avatar
  • 341
20 votes
3 answers
107k views

What is CV & CC in power supplies?

In many power supplies, there's CV & CC indicators. What does they mean?
yuvi's user avatar
  • 457
20 votes
4 answers
10k views

Why is home voltage value higher during the night?

I have been monitoring the voltage in my own home (Mexico 120V 60Hz). I have been graphing the values every minute and I'm starting to notice that during the morning voltage gets up to 127, and during ...
GoatZero's user avatar
  • 1,547
19 votes
3 answers
35k views

Lithium Coin Cell CR2032 battery specifications

I am using a CR2032 battery module to operate a BLE 4.1 module. The BLE radio for communication takes around 3.5ma to 5ma of current. But when I look at the datasheet of the battery (https://cdn-shop....
Viral Embedded's user avatar
19 votes
5 answers
9k views

Does a capacitor connected directly to a battery consume any energy?

In this example simulate this circuit – Schematic created using CircuitLab After the initial charging of the cap to 3V, current gets blocked, but over time does it consume any energy from the ...
pmiguelpinto90's user avatar
19 votes
4 answers
11k views

Why don't AC transformers burn up

I'm marginally familiar with the way that an AC transformer works. After viewing this question: Why don't all motors burn up instantly? It got me thinking about the same thing with AC ...
Matt Ruwe's user avatar
  • 1,987
19 votes
2 answers
2k views

What is the dual of a diode?

A diode has an exponential I-V curve. To a first approximation, it will pass whatever amount of current is required to keep the voltage across it constant. Is there a passive component that will (...
user253751's user avatar
  • 12.5k
19 votes
2 answers
46k views

Input impedance of Arduino Uno analog pins?

I'm using the ACS712 hall-effect based current sensing chip on some small robotic arm motors, and reading in the analog voltage with an Arduino Uno. I've had reasonably good results, but only after ...
user avatar
19 votes
4 answers
41k views

What are Guard Rings?

I have heard about Guard Rings many times, and I know they are supposed to avoid currents in places where there shouldn't be no currents, but I never found a good ...
mFeinstein's user avatar
  • 4,333
19 votes
4 answers
11k views

Pulse-powering heavy loads with a coin cell

Lithium coin cells are rated for fairly low standard current draws, on the order of 1 to 5 mA. Also, while they allow greater pulsed current draws (i.e., periodic bursts), this appears to be ...
boardbite's user avatar
  • 4,922
19 votes
9 answers
156k views

How do I calculate the temperature rise in a copper conductor?

If I pass a current through a copper conductor, how can I calculate how hot the conductor will get? For example, if I have a 7.2kW load powered by 240VAC, the current will be 30A. If I transmit this ...
BG100's user avatar
  • 5,818
18 votes
7 answers
9k views

Why can sticking fingers in an electric outlet kill you?

I just wanted to learn some differences between volts, amps, ohms and so forth and came up with this question. If your skin has 100k ohms resistance and the outlet is 220v wouldn't the current flowing ...
Giancarlo's user avatar
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