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A fundamental electronic component that stores energy in an electric field, commonly used in filtering applications.

17 votes

Why is a capacitor considered a short circuit at start up?

So, whenever you excite a discharged capacitor with a signal that "starts up", i.e. is zero before a given instant of time, the capacitor is subjected to a transient response that dies off after some time … EDIT BTW, to answer explicitly the title question, the basic relationship describing a capacitor is this: $$ q(t) = C \cdot v(t) $$ where \$q\$ is the charge "stored" in the capacitor, \$C\$ is the capacitance …
LorenzoDonati4Ukraine-OnStrike's user avatar
17 votes

Why do motor drives have multiple bus capacitors of small value capacitance instead of a sin...

If you have just one big capacitor, once it fails, you are left with a nonworking system. Moreover, a bigger cap can do more damage to nearby components if it fails spectacularly. … A single, big capacitor can be stressed mechanically more heavily when subjected to vibrations. …
LorenzoDonati4Ukraine-OnStrike's user avatar
1 vote

Why doesn’t voltage drop to 0 when a capacitor becomes fully charged?

The plates of the capacitor are metallic, hence most of the electrons of the outer shells of the atoms are in conduction band, not in the valence band. … Actually after 3-5 time constants you may consider the capacitor charged. …
LorenzoDonati4Ukraine-OnStrike's user avatar
2 votes

What capacitors are proper to use for input of AC DC converter?

Note the symbols on that schematic: both Cin1 and Cin2 are electrolytic caps. So, even for high voltage ones, you can get them at reasonable price (10uF-100uF, 400V electrolytic caps are fairly common …
LorenzoDonati4Ukraine-OnStrike's user avatar
2 votes
Accepted

Capacitor Reactance/Impedance Confusion

The "trick" is to remember that if you define reactances as: \[ X_L = \omega L \qquad X_C = \frac{1}{\omega C} \] then the impedance for an inductor and a capacitor are: \[ Z_L = j X_L = j \omega L …
LorenzoDonati4Ukraine-OnStrike's user avatar
1 vote

Can I provide a constant charge to a battery?

If by "trickle charge" you mean "leaving the cell connected to a charge that in a form of another provides the cell with some power (e.g. a small constant current)" the answer is: ABSOLUTELY NOT! You …
LorenzoDonati4Ukraine-OnStrike's user avatar
2 votes

Improving battery life: BLE device with a 100uF capacitor

During high current periods the capacitor will act as the primary power source, while during low current periods the battery will be the primary power source and recharge the capacitor. … When dimensioning the capacitor it is important to know the battery’s internal resistance and the load profile. With this information it’s quite simple to dimension a suitable capacitor. …
Community's user avatar
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0 votes

How do i analyze the following waveform to find out the voltage at t=6us?

Just the outline of the solution: By KCL the currents of the two current sources add up at the upper node and go into the capacitor. … This will give you \$v_c(6\mu s)\$, assuming the capacitor is discharged at \$t=0\$ (i.e., assuming \$v_c(0)=0\$), otherwise the problem is not well specified. …
LorenzoDonati4Ukraine-OnStrike's user avatar
2 votes

Can i use 47uf instead of 10uf in LM317 Adjustable voltage regulated circuit?

You can double-check the design of that power supply using the information in the Texas Instruments LM317 datasheet. At page 10 you find this: which is followed by a detailed design procedure. Th …
LorenzoDonati4Ukraine-OnStrike's user avatar
21 votes
Accepted

Why is a capacitor used to protect CMOS chips?

That's not a protection device, if you intend "protection" as something that prevents the chip to die, but it serves as a so-called bypass capacitor. … The bypass capacitor reduces this risk in a way similar a filter capacitor after a bridge rectifier reduces the ripple of a rectified voltage. …
LorenzoDonati4Ukraine-OnStrike's user avatar
7 votes
Accepted

why are capacitors often not labeled using engineering notation ? (1-999)

It is a matter of history, sadly. Capacitors where built well before the International System of measurement (SI) was established and some prefixes weren't used so much (e.g. nano). For example, usua …
LorenzoDonati4Ukraine-OnStrike's user avatar
4 votes
Accepted

Can a single, large multilayer ceramic capacitor replace the classic electrolytic + ceramic ...

To give further insight: think of a single capacitor as a tank circuit, where the capacitor may resonate with its parasitic inductance. … Assuming a simple model where a capacitor has a single resonant frequency, paralleling different caps, with different resonant frequencies, allows us to "combine" the different frequencies responses so …
LorenzoDonati4Ukraine-OnStrike's user avatar
0 votes

Impedence of 90° out of phase Capacitor and Inductor in parallel

That situation assumes an ideal capacitor and an ideal inductor, which are only mathematical abstractions. Any real component suffers from some parasitic effect that will alter its ideal behavior. … As a first level approximation consider this: a real capacitor has some leakage current, which can be modeled by a resistor in parallel to the ideal capacitor, whereas an inductor has some wire resistance …
LorenzoDonati4Ukraine-OnStrike's user avatar
1 vote
Accepted

Circuit similar to current divider

You don't tell us explicitly, but is seems that is some kind of homework or some textbook explanation. I guess that \$I\$ and \$I_L\$ are not the total currents in those branches, but only the transie …
LorenzoDonati4Ukraine-OnStrike's user avatar
5 votes
Accepted

Calculating the discharge of Ultra Capacitors

If we model the setup with a capacitor in parallel with the load, and let \$i\$ be the current into the load and \$v\$ the voltage across the two, the circuit equations are: $$ \left\{ \begin{aligned} …
LorenzoDonati4Ukraine-OnStrike's user avatar

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