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Questions tagged [voltage]

Voltage, otherwise known as electrical potential difference (denoted ∆V and measured in volts) is the difference in electric potential between two points (adapted from Wikipedia). Voltage can be constant (DC) or varying (AC).

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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 ...
64
votes
3answers
83k views

What is ground and what does it do?

I'm a bit confused about the concept of ground, and perhaps voltage as well, particularly when trying to analyze a circuit. When I learned about Ohm's law in grade school, I learned how to apply the ...
62
votes
8answers
348k 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, ...
273
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8answers
250k views

What is the difference between \$V_{CC}\$, \$V_{DD}\$, \$V_{EE}\$, \$V_{SS}\$

I've seen lots of schematics use \$V_{CC}\$ and \$V_{DD}\$ interchangeably. I know \$V_{CC}\$ and \$V_{DD}\$ are for positive voltage, and \$V_{SS}\$ and \$V_{EE}\$ are for ground, but what is the ...
22
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5answers
333k views

how to reduce DC voltage using resistors?

How would one go about using a 12 V DC power source to power something which needs 4.5 V DC using resistors? Is there a way to determine how much adding a resistor would drop the voltage?
69
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9answers
9k views

What exactly is voltage?

Bit of a strange question, but what is it? My physics teacher said it was kind of like a "push" that pushes electrons around the circuit. Can I have a more complex explanation? Any help is much ...
21
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6answers
213k views

Reducing voltage with resistors

I have been looking around for an easy way to convert 12V to 5V. I have seen some people saying that a simple resistor is all that is needed. $$ Volts = Ohms \cdot Amps $$ $$ Amps = \frac{Volts}{...
9
votes
3answers
42k views

Analog voltage level conversion (level shift)

I have a joystick that puts out analog voltage somewhere between 1.5V and 3.5V. I want to transform this range of voltage to control a motor controller that takes analog voltage between 0V and 5V. ...
44
votes
7answers
175k views

230V AC to 5V DC converter, lossless

Is there any IC which converts 230V AC to 5V DC? As lossless as possible. I want to connect my microcontroller to an ordinary electrical socket and I don't have enough space available. Thanks.
12
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4answers
18k views

Thermistor control of peltier voltage with Arduino (for DSLR chill box project)

I am mildly familiar with electronics, mostly from playing around with electronics kits as a kid. That was a long time ago, though, maybe as much as 20 years ago. I am currently working on a cold or "...
36
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3answers
22k views

What does 3V3 or 1V8 mean?

While reading a datasheet for an IC I came across the pin voltages being presented as 3V3 or 1V8. What does this representation stand for?
14
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2answers
7k views

Is it normal for DC wall adapter power supplies to provide voltages above the nominal ones?

When I measure a 9V DC wall adapter power supply with a multimeter it shows 11.8V. When connected to my board this voltage lowers to 10V. Is this normal? Should I be afraid of toasting my 1117CD-5.0 ...
2
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1answer
8k views

Troubleshooting why Powerbank Doesn't Charge Cell Phone [closed]

I have powerbank that provides 5v (presumably regulated) power, as typical of most usb interface powerbanks. I have been trying out my powerbank with different phones. It works on all except one. I ...
27
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12answers
20k views

Is voltage the speed of electrons?

Current is the amount of electrons passing through a wire. Can we say that voltage is the speed of those electrons?
17
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6answers
10k views

What are the highest DC and AC voltages or currents that can be considered as safe?

By safe I mean safe for us when we touch a wire that is not insulated. I have heard that human body resistance is normally 50k Ohm when dry and 20K Ohm when wet. Therefore, these voltages or currents ...
40
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8answers
7k views

Why isn't there a potential difference across a disconnected diode?

I know this question sounds silly, as if there was a potential difference a current would be created when the terminals are connected together and this would mean energy has come from somewhere. The ...
34
votes
4answers
7k views

I2C 3.3 to 5.0 V conversion

I'm trying to interface a 3.3V I2C device to a 5V Arduino. I don't have any problem with SCL line. I can use a simple voltage divider but I have an issue with the SDA line as this is bi-directional. ...
12
votes
1answer
4k views

'Voltage Fuse' or better

I have a power supply with multiple outputs (5v, 12, 24v) According to the manufacture (and after testing) there must be a minimum load on the PSU for it to supply the stated voltages. Without a ...
17
votes
7answers
7k 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 ...
9
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6answers
7k views

What is an amp (and other such basic questions) in the simplest possible terms?

I understand that this is a really basic question, but, I've been unable to really understand electrical terminology for some reason. What exactly is an amp? How does it correspond to a watt? And: ...
7
votes
4answers
1k views

Is voltage a delta? Can it always be treated as a potential difference from a reference point?

I've always considered voltage to be absolute, i.e. something that is there or is not there. However, the more I think about it, it seems to be more like a delta. For example, let's say we have a ...
3
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3answers
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Structure of a usb 2.0 connector [duplicate]

What is the role of the outer metal connector? (the one with two square holes) Does it have a potential? Is it insulated from the 4 pins? Are the 4 pins insulated from each other?
2
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3answers
331 views

How to find Voltage based on reference nodes?

I came across this problem and I'm trying to really understand it. VB is the voltage drop across a particular element, it is the change in voltage from node a to node b. Find the value of VB in ...
0
votes
1answer
1k views

Different and opposing voltage sources?

simulate this circuit – Schematic created using CircuitLab The diagram above, the voltage sources are equal and wired parallel, they would increase the current(2x) flow to the load(R), but what ...
92
votes
10answers
213k views

What is negative voltage?

Just a general electronics question: What is negative voltage, like -5 Volt? From my basic knowledge, power is generated by electrons wandering from the minus to the plus side of the power source (...
32
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3answers
126k views

Help me understand the relationship between positive, negative, neutral and ground in AC and DC

This question stems from notations on schematics and seemingly conflicting information I'm seeing. I suspect that I'm seeing different vernacular for the same concepts--but I'm in a place where no one'...
15
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4answers
44k 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 ...
6
votes
3answers
24k views

Adding voltage cutoff to a circuit?

I'm powering a project with a 2-cell 7.4V LiPo battery. What circuit do I add to make the unit stop drawing power when the voltage from the battery drops below 6.4V? The goal is to protect the LiPo ...
0
votes
2answers
11k views

Is 20 watts of electricity dangerous?

I have a few circumstances which invlove someone being shocked with 20 watts of electricity and whether it would be deadly. So here they are: Would 1000 volts at 20 miliamperes of AC (2MHz frequency) ...
21
votes
5answers
25k 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 ...
2
votes
2answers
6k views

How to sense the zero crossing of current?

I am trying to sense the power factor angle using microcontroller. Now the mechanism that I have thought it that Measure the zero crossing of voltage When the voltage zero is sensed, start the ...
11
votes
2answers
3k views

How does the current limiting resistor for an LED affect current and voltage drops?

I'm having a bit of trouble understanding currrent limiting resistors in simple LED circuits. I know that I can determine the optimal resistor like so: \$\displaystyle R=\frac{V_{s}-V_{f}}{I_{f}}\$ ...
12
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5answers
36k views

Can electronics be damaged by undervolting it?

I was wondering if there are some particularly important mechanism by which one can break electronics, when undervolting it. Its pretty obvious that lots of electronics will not work properly if ...
20
votes
3answers
49k views

Is MOSFET gate threshold voltage a limit or minimal “Full-on” switching voltage?

I've been shopping for some mosfet transistors, for a starter kit, and noticed listings that state a mosfet is suitable for 5v logic, but the data sheets says Gate Threshold is 1-2v. 4v gated mosfets,...
8
votes
10answers
4k views

12V input on microcontroller pin

I'm trying to count pulses/sec. on a microcontroller pin in the ~5 to 100Hz range. The µC can operate at 5V input, so I have to get the voltage level down safely. A simple resistor comes to mind, yet ...
4
votes
3answers
7k views

Convert from a specifc range to another one

Can anyone explain how one would convert one voltage range to another? I'm going to need to convert a range of -10 to +10 volts into a range of 0 to +5 volts. How would this be accomplished? Thanks! ...
9
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4answers
3k views

Bi-Directional Step up and Step down (3.3v <-> 5, etc)

So I've been reading a few threads here and on other forums. I understand there are various solutions for stepping down or up a voltage. What I have found are the LVC series shift regs that give a ...
4
votes
3answers
401 views

Source-free, under-damped, parallel RLC with 2 intial conditions

I think I'm suffering from brain-drain. I'm trying to solve a 2nd order differential equation for the natural response of an under-damped parallel RLC circuit with initial conditions of \$I_L\$ and \$...
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vote
1answer
210 views

Full Bridge VSI problem

The above problem was asked in GATE(Graduate Aptitude Test in Engg) 2015 in India. I have no idea where to start so I can't show my attempt. But through google, I got solution by 2 different coaching ...
71
votes
8answers
12k views

Can a bird, previously at earth potential, get electrocuted by landing on a powerline at high-enough voltage due to the initial “equalization charge”?

At the voltage levels of typical overhead transmission lines in the US, a bird can land on one and be just fine (as long as it doesn't do something like spread its wings and touch a tree or something ...
20
votes
7answers
11k views

Why is the diode forward voltage constant?

When you have a diode with a certain barrier voltage (e.g., 0.7 V for Si) and you apply a voltage higher than this barrier potential, why does the voltage across the diode remain at 0.7V? I ...
10
votes
5answers
9k views

Single terminal of voltage source attached to earth ground

This is a conceptual question I continue to struggle with as I have started studying electronics. Say we have a battery, and one of its terminals is connected directly to a nice patch of highly ...
6
votes
5answers
116k views

Three phase power supply - what is line to line voltage

Well this seems like a basic principle, yet I can't seem to get it. (We're expect to "know" this already). In a three phase situation I'm given a source voltage of 230V. - So the waveform of each of ...
8
votes
1answer
154k views

How to calculate voltage drop over and power loss in wires

How do I calculate the voltage drop over wires given a supply voltage and a current? How do I anticipate on voltage drop so that the final load has the correct supply voltage? What will be the power ...
3
votes
3answers
28k views

How do i find nichrome temperature

I have 2 meters, 32wg, 19 ohm per meter. NIchrome wire I want to calulate what amps and volts i need so 2 meters of nichrome heats to 35 celsius. How can i calulate this and what formula do i need ...
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8answers
90k views

High Voltage Capacitor, in a low voltage system?

Quick question, is using a Capacitor rated for High Voltage (lets say 35v) in a System that lets say supplies 5v (like for LEDS.....or what have you) Dangerous? Since it can store UP to 35v, will it ...
12
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4answers
52k views

if a standard three-phase 400V AC connection is rectified what DC voltage comes out of it?

If a standard (in Europe and a large part of the world except North America and Japan) three-phase 400V AC (three lines having 230V RMS voltage if measured to neutral each) mains supply is rectified ...
12
votes
3answers
18k views

I2C: 3.3V and 5V devices without level-shifting on 3.3V-bus?

do I really need a level-shifter if I use 5V-powered devices on an I2C-bus that has pull-ups to 3.3V? In my understanding the devices will only pull the lines (SDA, SCL) low (to ground) and never ...
8
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2answers
30k views

Switching 9V using a NPN transistor and an Arduino

First of all, I'd like to say I'm not an Electrical engineer so please bear with me. I haven't got a sketch for what I'm trying to achieve but hopefully I can explain it ok. I have an NPN transistor (...
7
votes
1answer
6k views

Connecting multiple grounds

As I'm relatively new to the electronics world, I was wondering if you can connect multiple ground terminals (corresponding to several different voltage outputs) to the same ground. Or do they each ...