How Dc current flows from capacitor at startup

[nikhilele]

I know Dc current does not flow from capacitor.
But when it is just power on Dc current flows through it.
now when there is not electrical connection between capacitor plates how current can flow.
I remeber my class lecutures which say that there is displacement current rather then the current due to electrons. Displacement current is due to Electric fields between plates.

But I am not able to physicall visualize the situation here. can anyone here can explain this physically or mathematically.

 

[Miguel Gaspar]

Hey, you are wrong DC current flows in a capacitor

c= q/V basic equation

q=cV integrating

dq/dt = d(cV)/dt

i = c dV/dt

dV = 1/c i dt

∫dV = 1/c ∫idt if i= constant (DC)

∫dV = i/c ∫dt and it means tha DC current flows trrough a capacitor and it charges



At start, when you turn on you power supply, the capacitor experiment a voltage step and a high frequency so Xc = 1/( f c ) is very low. If the internal resistance is very low capacitor suffers damage.

 

[vicky]

HI DEAR I HAVE JUST POSTED AN ARTICLE HAVING NAME DIFFERRENT TYPES OF CAPACITORS IN THAT I HAVE GIVEN A COMPLETE DETAIL

 

[claudiocamera]

Hey, you are wrong DC current flows in a capacitor

.

There is a matter of neurolinguistic here, particulary I think we should be carefull when pointing someone and say " you are wrong" .

The equations presented shown that if dv/dt is constant then the current is constant, it is mathematically correct, whereas in the sense presented should be followed by a practical approach.

Imagine a practical situation: A constant current source feeding a circuit with a capacitor and a resistor in serie. So what happens ? The capacitor keeps with a constant current throught its terminal indefinitely or it gets charget after a while and opens the circuit?

Imagine a situation with a capacitor with a constant corrent throught its terminals. For how long this condition remains ? Is there any practical circuit where it happens ?

So lets try to figure out what the first question mean: When a circuit is powered on DC current flow thought the capacitor, It is really DC current or the circuit is feed for a DC voltage and a decreased exponencial current flow throught it untill it get charged ? Is that the situation raised here ? If so , the current is not DC.

 

[mohammad mokhtar]

Hi
When you have dc voltage connected to a condenser the condenser starts to charge , this lead to a current it has an average value ( dc component ) .you may be confused about dc current in a condenser it is only 0 in the case of steady state only but not in transient state and this is the case you have ( you have transient and not steady state).
Regards

 

[Naveed Alam]

when charge starts developing on plates, we see that there is charge flow..charge flow means current flow...i think this is enough to visualize it..


Regards

 

[safwatonline]

i think u may look on it as if at the instant of switching power ON the DC doesnt reach its DC value instantaneously but follow some transient behaviour hence it is considered AC.