Electrical & Electronic Components

What is a capacitor

• A passive component designed for storing electric energy (charge)

• Increases efficiency of a circuit system

• Does not dissipate heat but stores energy

• Energy stored can be retrieved at a later time

• Blocks DC and permits AC to pass

Capacitors – electrical components

LSU 08/11/2004 Electronics 2 4

Capacitor types

Ceramic disk Monolithic ceramic

Dipped siver-mica

Mylar Mylar

Solid tantalum, polarized

Radial aluminum electrolytic

Axial aluminum electrolytic

Construction

• Consists of two conducting plates separated by an insulating layer called a dielectric.

• Differs in size, arrangements of plates and dielectric material

Application

• Communications• Instrumentations• Life support equipment• Computers• Power supply systems

Capacitance

• The measure of a capacitor in its ability to store electric charge

• Expressed in Farads (F)

• Electric charge stored is proportional to voltage supplied from Power Supply:

Q = CEQ = Charge stored

C = Capacitance

E = Voltage applied to capacitor

Charging a capacitor

Capacitor not charged yet :

• Capacitor not connected to power source (battery)

• No potential difference between plates

• Therefore no charges stored in capacitor

Charging…cont’d

Battery connected across capacitor:• Electrons flow to and from plates• Electrons cannot flow through

because of dielectric material• Counter emf (reactance) induced

on plates • Electrostatic field induced

between plates• Reactance level = Power Supply

no further flow of current

Charging…cont’d

Power Supply disconnected:• Capacitor retains charges

because of electrostatic force existing between plates

• Unequal charges on both negative & positive plates

• Capacitor is now a source of potential energy

Discharging a capacitor

Capacitor connected to other circuit:

• Electrons flow through from negative plated to positive plate

• Capacitor is discharging

Discharging…cont’d

Current will stop flowing when charges of both positive and negative plates are equal

Capacitor is fully discharged when there’s no more energy left

Capacitors in parallel circuits

• Able to store more charges

C = C1+C2+C3…

Capacitors in series circuits

• Able to store less charges

C = (C1xC2) / (C1+C2)