Session 1b: Electronic Principles and Capacitors

Capacitors

Are passive elements designed to store energy (charge) within its electric field

Used extensively in electronics, communications (tuning radio receivers), computers (dynamic memory elements), and power systems

What does Capacitors Consist of ?

•of two conducting plates separated by an insulator or dielectric

oThe two plates may be aluminium foil, while the dielectric may be air, ceramic, paper, or mica

Capacitors: Charge and Capacitance

When a voltage source is connected to the capacitor, the source deposits a positive charge +q on one plate, and a negative charge -q on the second plate

Capacitance

The ratio of charge on one plate of a capacitor to the voltage difference between the two plates

C=Q/V , and V=Q/C

Parallel plate capacitor: C=εA/d

̶C is capacitance measured in Farads (F)

̶A is surface area (m^2)

̶d is distance between the conductors

̶ε is the permittivity constant of the dielectric material

Typical capacitor values are in…

microfarad (μF), and picofarad (pF)

Value should be chosen based on…

on the applications (decoupling, filtering, etc.) and tolerances needed

Capacitors calculated in parallel. What is the Calculation?

C_T=C_1+C_2+C_3+…C_n

Capacitors calculated in series. What is the Calculation?

1/C_T =1/C_1 +1/C_2 +1/C_3 +…1/C_n

OR 

C_Total=1/(1/C1+1/C2+1/C3+…1/Cn)

•First, calculate the capacitance in series

o1/CT=1/(1×10^(-6) )+1/(5×10^(-6) )=1.2×10^6

̶CT_Series=1/(1.2×10^6 )=8.33×10^(-7)

̶CT_Series=0.833×10^(-6)

̶〖CT〗_Series=0.833 μF

•Next, calculate the capacitance in parallel

CT_Parallel=0.833 μF+8 μF

CT_Parallel=8.833 μF