Introduction To Capacitance
- 1. Capacitors
- 2. What is a capacitor? Electronic component Two conducting surfaces separated by an insulating material Stores charge Uses Time delays Filters Tuned circuits
- 3. Capacitor construction Two metal plates Separated by insulating material ‘ Sandwich’ construction ‘ Swiss roll’ structure Capacitance set by...
- 4. Defining capacitance ‘ Good’ capacitors store a lot of charge… … when only a small voltage is applied Capacitance is charge stored per volt Capacitance is measured in farads F Big unit so nF, mF and F are used
- 5. Graphical representation Equating to the equation of a straight line Gradient term is the capacitance of the capacitor Charge stored is directly proportional to the applied voltage Q V
- 6. Energy stored by a capacitor By general definition E=QV product of charge and voltage By graphical consideration... Area term is the energy stored in the capacitor Q V
- 7. Other expressions for energy By substitution of Q=CV
- 8. Charging a capacitor Current flow Initially High Finally Zero Exponential model Charging factors Capacitance Resistance I t
- 9. Discharging a capacitor Current flow Initially High Opposite to charging Finally Zero Exponential model Discharging factors Capacitance Resistance I t
- 10. Voltage and charge characteristics Charging Discharging V or Q t V or Q t
- 11. Product of Capacitance of the capacitor being charged Resistance of the charging circuit CR Symbol ‘Tau’ Unit seconds Time constant
- 12. When t equals tau during discharge At t = tau the capacitor has fallen to 37% of its original value. By a similar analysis tau can be considered to be the time taken for the capacitor to reach 63% of full charge.
- 13. Graphical determination of tau V at 37% Q at 37% Compared to initial maximum discharge V or Q t
- 14. Logarithmic discharge analysis Mathematical consideration of discharge Exponential relationship Taking natural logs equates expression to ‘y=mx+c’ Gradient is -1/Tau
- 15. Logarithmic discharge graph Gradient term is the -1/Tau lnV t
Editor's Notes
- #2: Construction and charging and discharging