GUJARAT TECHNOLOGICAL UNIVERSITYBIRLA VISHVAKARMAMAHAVIDYALAYA

(ENGINEERING COLLEGE)VALLABH VIDYANAGAR

SUBJECT: ELEMENTS OF ELECTRICAL ENGINEERING (CODE-2110005)

BE First Level Second Semester (Self Finance)

Topic : Charging and discharging of capacitors

Capacitors

• A capacitor is a device for storing electric charge.

• It can be any device which can store charges. • Basically, capacitors consists of two metal

plates separated by an insulator. The insulator is called dielectric. (e.g. polystyrene, oil or air)

• Circuit symbol:+

_

Dielectric

Circuit of process charging and discharging

Charging of capacitors

• When a capacitor is connected across a battery, electrons flow from the negative terminal of the battery to a plate of the capacitor connected to it. At the same rate, electrons flow from the other plate of the capacitor to the positive terminal of the battery. This gives a flow of current as the capacitor is being charged.

• As charges accumulate on the plates of the capacitor, electric potential built across the plates. This hinders further accumulation of charges and makes the charge up current decreasing. When the potential difference across the plates equals that of the battery, the current becomes zero.

Charging a Capacitor• Voltage-charge

characteristics• Current flow

I

t

Vc or Q

t

)1(0RCt

C eVV

RCt

oeII

Vc ∝ Q

FORMULA FOR CHARGING PROCESS

a. Time constant , ג = CRb. Initial Charging current I max = V/Rc. Charging voltage of capacitor, Vc = Vmax (1 – e -t/ג )d. Charging current i = Imax (e -t/ג )

e. Initial rate of change potential difference dVc = V / CR dtf. Time when capacitor fully charge t = 5גg. Energy stored, E = ½ CVmax2

Discharging a Capacitor

• Voltage-charge characteristics

• Current flow

VC or Q

t

I

t

RCt

eQQ

0

RCt

oeII

Formula for discharging process

a. Time constant , ג = CRb. Initial disharging current I max = V/Rc. Disharging voltage of capacitor,Vc = Vmax

( e -t/ג )d. Discharging current i = - Imax (e -t/ג )

e. Initial rate of change potential difference dVc = V / CR dtf. Time when capacitor decrease charge t = 5ג

Prepared by :

Kakadiya Krushal (Production) – 130080125006Mehul Ghodasara (Mechanical) – 130080119008

Milind Bhoya (Mechanical) – 130080119004

Thank you