Phil Frost
• Member for 8 years, 11 months
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## 706 Answers

4 answers
150 votes
72k views
Accepted answer
247 votes

An LED requires a minimum voltage before it will turn on at all. This voltage varies with the type of LED, but is typically in the neighborhood of 1.5V - 4.4V. Once this voltage is reached, current ...

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4 answers
64 votes
327k views
Accepted answer
80 votes

mAh (or mA&middot;h) is not how many milliamperes a battery can deliver in an hour. That would be mA/h. Current, measured in amperes, is already a rate of stuff. Specially, one ampere is one coulomb ...

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1 answers
46 votes
55k views
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74 votes

Probably you already have it, and just didn't know it. If you are driving a motor with a half-bridge or H-bridge and PWM or similar, you have regenerative braking. Let's consider a half-bridge, since ...

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14 answers
73 votes
30k views
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73 votes

Let's try this Wittgenstein's ladder style. First let's consider this: simulate this circuit &ndash; Schematic created using CircuitLab We can calculate the current through R1 with Ohm's law: $${... View answer 3 answers 65 votes 27k views Accepted answer 72 votes Myth: manufactures conspire to put internal diodes in discrete components so only IC designers can do neat things with 4-terminal MOSFETs. Truth: 4-terminal MOSFETs aren't very useful. Any P-N ... View answer 5 answers 30 votes 35k views Accepted answer 69 votes Capacitors don't store charge. That's such a worthless statement because it's based on this word "charge" that has multiple meanings. Please forget you ever heard it. They also do not smooth energy. ... View answer 6 answers 50 votes 69k views Accepted answer 59 votes Leaving it on would use more energy, absolutely. Sometimes, people try to convince themselves that turning a light on and off uses more energy because there is some high inrush current, or some such ... View answer 4 answers 75 votes 92k views 55 votes Sometimes people get confused just by the many definitions of the word. ground noun the solid surface of the earth; firm or dry land: to fall to the ground Often, grounds. the foundation or basis on ... View answer 2 answers 43 votes 150k views Accepted answer 52 votes The short answer: input impedance is "high" (ideally infinite). Output impedance is "low" (ideally zero). But what does this mean, and why is that useful? Impedance is the relationship between ... View answer 2 answers 38 votes 79k views Accepted answer 43 votes The two are largely the same, fundamentally. However, they differer in intended application. A stepper motor is intended to be operated in, well, steps. A BLDC motor is intended to be operated to ... View answer 5 answers 2 votes 6k views Accepted answer 39 votes You are confused about what the concept of infinity means. Infinity isn't a number that can ever actually measure a quantity of something, like resistance, because it's not a real number. As Wikipedia ... View answer 8 answers 62 votes 35k views 36 votes The alligator clip on the scope probe: (image source) is connected, through the power cord, to Earth. If you clip it to something that isn't at Earth potential, you get a large current, and things ... View answer 3 answers 25 votes 10k views Accepted answer 36 votes A motor driven by an H-bridge is also a boost converter. Here's an H-bridge: Replace the motor with an inductor, resistance, and voltage source (back-EMF): Let's just consider that we are driving ... View answer 5 answers 33 votes 35k views Accepted answer 34 votes Strong means low resistance. Weak means high resistance. Of course low and high are relative terms, and so are strong and weak. The reference for this relationship must be inferred from context. A ... View answer 5 answers 54 votes 44k views 33 votes A transmission line has distributed inductance and capacitance along its entire length. We can think of it as infinitely many little inductors and capacitors along the line: simulate this circuit &... View answer 7 answers 14 votes 3k views Accepted answer 32 votes It's difficult to come up with an analogy because the usual analogies for electrical systems are fluid systems. A great thing about fluid systems is that the working fluid is also good at cooling ... View answer 2 answers 21 votes 10k views Accepted answer 32 votes These bulbs contain a shunt wire which is normally insulated from the bulb but closes when a high voltage is applied. From How Stuff Works: You can also see the wire in your image, below the burned ... View answer 7 answers 37 votes 44k views Accepted answer 31 votes I'm guessing you don't understand how current can flow if there is no complete circuit. Let's take a simple quarter-wave dipole as an example: simulate this circuit &ndash; Schematic created using ... View answer 2 answers 9 votes 39k views Accepted answer 30 votes If by charges you mean electric charges, then no, a capacitor does not store charges. This is a common misconception, maybe due to the multiple meanings of the word charge. When some charge goes in ... View answer 3 answers 8 votes 14k views Accepted answer 29 votes An equivalent circuit for what you describe is: simulate this circuit &ndash; Schematic created using CircuitLab Note that the resistors aren't in parallel, so we can't use the usual parallel ... View answer 1 answers 26 votes 27k views Accepted answer 27 votes One way to do this is to briefly stop driving the motor, long enough to let any residual current from the driving voltage die down, and then simply measure the voltage. The time it takes the current ... View answer 5 answers 9 votes 97k views 27 votes A 9V battery has approximately a stored energy of:$$ \require{cancel} \frac{560\cancel{m}A\cancel{h} \cdot 9V}{1} \frac{3600s}{\cancel{h}} \frac{1}{1000\cancel{m}} \approx 18144VAs \approx 18 kJ  ...

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5 answers
26 votes
32k views
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27 votes

"Can" and "should" are two things. Should you do this? No: this use is outside the specified operating parameters of ordinary electrolytic capacitors. You seem to understand this already. Can you do ...

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3 answers
36 votes
139k views
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27 votes

Ground means whatever is attached to this symbol in the schematic: Everything that touches this symbol in the schematic is actually connected to everything else that touches the symbol. Since so many ...

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6 answers
17 votes
21k views
25 votes

The reasons you would not want to use global variables in an 8-bit system are the same you would not want to use them in any other system: they make reasoning about the program's behavior difficult. ...

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6 answers
39 votes
3k views
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25 votes

How fast does electricity flow? This is a good question, because it seems like a simple enough question, but usually it indicates some underlying misconceptions. The first difficulty in answering the ...

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3 answers
23 votes
14k views
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25 votes

From the driver to the gates, the wires are ~15cm. Does this cause rining? Almost certainly, and it's a fair bet that this is destroying your MOSFETs, by one or more of these mechanisms: exceeding \\$...

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4 answers
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25 votes

Thinking about current in terms of electrons moving around is the start down a path to a poor mental model of how electricity works. Here are just a few things wrong with it: Electrons are but one of ...

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3 answers
21 votes
134k views
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25 votes

The datasheet gives an example. By adjusting the pot we can null any offset error. An offset error is when the inputs are exactly equal but the output isn't exactly zero. This error is also ...

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10 answers
29 votes
14k views
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24 votes

The underlying difficulty seems to be the belief that some current must flow to measure voltage. This is false. Since you are a physics teacher, I'll explain by making analogies to other physical ...

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