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120 votes

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

I think I may have the definite answer to this. This naming comes from a 1963 IEEE standard 255-1963 "Letter Symbols for Semiconductor Devices" (IEEE Std 255-1963). I'm an electronics ...
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  • 7,267
81 votes

What does this symbol mean on my Samsung travel adapter?

That's the Ukrsepro mark. It means the product has passed the certification of UkrSEPRO, the safety certification requirement symbol for trading in the Ukraine region. Scope of products covered by ...
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  • 8,991
73 votes
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Why do CPUs need so much current?

CPUs are not 'simple' by any stretch of the imagination. Because they have a few billion transistors, each one of which will have some small leakage at idle and has to charge and discharge gate and ...
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66 votes
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Why don't we use low voltage Power Sources for high wattage applications?

You are right in that power is the product of voltage and current. This would indicate any voltage x current combination would be fine, as long as it comes out to the desired power. However, back in ...
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58 votes
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Why is root mean square used when calculating average power, and not simply the average of voltage/current?

Take a simple example where the sums are trivial. I have a voltage that is on 50% of the time and off 50% of the time. It is 10V when it is on. The average voltage is thus 5V. If I connect a resistor ...
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51 votes
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Shocked by beginner circuit kit

OK. You say that it was a single jolt, and you pulled your hand away immediately. It was one of two things -- either it was static discharge and a true shock, but exactly what you would have gotten ...
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  • 36.3k
49 votes
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What type of glass fuse is this and what does the spring do?

20 amp glass cartridge type slow blow. It has a thermal mass that generates a delay before the solder melts at the left hand end. The spring pulls the mass away from the wire, making sure the two ...
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  • 1,654
48 votes
Accepted

How does a USB C port provide the power to charge laptops?

USB-C will use the Power Delivery specification, a first connexion is done at 5V, then "negotiate" whether it can use a higher profile to charge. There are 5 profiles available : Profile 1 : 5V@2A ...
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  • 739
47 votes
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Power rating on Zero Ohm resistor

While it may be true that distributors don't want to check every single part individually, in this case it is not down to laziness that the 0Ω resistor has a specified rated power of 125mW. As ...
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47 votes

Could data transmission power consumption be lessened by transmitting more zeroes?

TL;DR: no, there's no such scheme that we wouldn't already be using. There's reasons, below. Information theory tells us that we have to transmit the least bits (using less energy than transmitting ...
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45 votes
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Scam? Does having this capacitor wired as shown provide any surge protection?

All I find is this giant capacitor. Is this literally a capacitor with a switch that turns on a light? Would this capacitor provide any surge protection in either direction? Wondering if it might ...
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  • 7,613
44 votes
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Watts - I think I'm getting free energy from a circuit?

Congratulations for having the wit to know something was wrong! simulate this circuit – Schematic created using CircuitLab Figure 1. Parallel and series arrangements of batteries will have the ...
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  • 160k
44 votes
Accepted

Is there a reason why we don’t supply power to a 2.5 mm or 3.5 mm jack?

It's possible, and I've seen it done (the gear in question being a wideband amplifier for an EMC probe set), but for isolated low voltage only. The main drawback is the possibility of shorting the ...
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  • 40.6k
41 votes

Why does power dip during a lightning storm?

Janka comes close, but there are are several more details. (Note, recalling from EE classes about 45 years ago.) On many high voltage lines there are arc electrodes at various points. When ...
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  • 752
41 votes

Do power plants supply their own electricity?

Nuclear power plants in particular have extremely critical needs for power even when they are not generating, as decay heat requires circulating cooling water through not only the reactor long after ...
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39 votes
Accepted

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

Anixter says: Even though copper has a long history as the material of choice for conducting electricity, aluminum has certain advantages that make it attractive for specific applications. Aluminum ...
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  • 160k
39 votes
Accepted

Short circuit = no power?

You should not be so hard on your professor. Much of the confusion newcomers to EE struggle with is that we talk about theoretical IDEAL circuits as part of the teaching process. In ideal circuits ...
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  • 45.7k
38 votes

Scam? Does having this capacitor wired as shown provide any surge protection?

A pretty thorough debunking of these ‘power saving’ devices can be found here: http://www.nlcpr.com/Deceptions1.php Besides this, the box appears to be shoddily made and has no safety approvals. You ...
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  • 40.6k
37 votes
Accepted

Why is the power consumption of electrical lamps specified in kWh/1000h?

Anyone who has a clue about how physical units works will of course realize that kWh/1000h means "1000 watt-hours per 1000 hours" which can be shortened to just <...
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  • 461
37 votes

How do solar inverter systems easily add AC power sources together?

Because UL 1741 does all the heavy lifting for you. That's what makes it "so easy". UL 1741 is a complicated spec for "grid-tie solar inverters". Aside from doing their usual inverter thing (...
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36 votes

Why can I use P = I²R but not P=V²/R when calculating energy lost in a circuit?

The problem assumes you understand something that is not clearly spelled out: the wires and the (unknown) load are in series. Therefore they share the current, not the voltage of the battery. That's ...
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35 votes
Accepted

How can AC current power anything?

@The Photon's answer is quite extensive, the only thing missing is, how electrical energy is now actually transferred. In a simple case where you just have some kind of ohmic load, it is exactly the ...
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  • 625
35 votes

Why is root mean square used when calculating average power, and not simply the average of voltage/current?

For power to be average i must be average current, so I am surmising that the effective current is the average current. In short, average voltage x average current only equals average power when ...
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  • 385k
34 votes

Why has my tweeter speaker burned up?

Your linked description shows that the tweeter is intended to be used with a woofer for music reproduction. The description doesn't cover use of the tweeter as a specialist ultrasonic transducer on ...
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  • 2,720
33 votes
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Does AC Power have Polarity?

When you're looking at an AC source in isolation such as in your question, indeed there's no polarity and you can connect the wires either way round. When combining two or more AC sources in series ...
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  • 6,057
33 votes
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Why can I use P = I²R but not P=V²/R when calculating energy lost in a circuit?

60A through a 0.01ohm resistance gives a 600mV drop. That is the voltage you need to use in the equation.
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32 votes

Why does power dip during a lightning storm?

Lightning brownout procedure: When lightning hits an overhead power line, there is overvoltage at first, for about 100 milliseconds. This overvoltage creates an arc at a nearby pole. The arc works as ...
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  • 13.1k
32 votes
Accepted

What is the maximum voltage that silicon can handle?

You can get 8 kV rated (at several thousand amps) thyristors for use in HVDC converters. The gate is optically coupled for the obvious reasons and also because, when used in tandem on HVDC links, the ...
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  • 385k
32 votes
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Why do power grids tend to operate at low frequencies like 60 Hz and 50 Hz?

Higher frequencies are much more affected by the inductance of the power lines. 400 Hz is fine on an aircraft, but over long distances the power factor would be extremely poor. 60 Hz was an educated ...
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  • 5,425
31 votes
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How can low voltage, high current (kA) power be dangerous?

The voltage for the Hall–Héroult process is inconveniently low (and the current too high) for efficient parallel operation so they use a whole bunch of cells in series. From this source ("Studies on ...
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