CAPACITOR CHARGING DISCHARGING

                                    CAPACITORS                        

Capacitor , one of the passive device commonly known is used in variety of applications. Almost in every electrical and electronic circuit, capacitors are used. There are various types of capacitors in the market with different electrical properties and materials. In this tutorial I am going to talk about basic electrolytic capacitor and making clear simple charging and discharging concepts. To understand this topic read my previous pages about LED and capacitors basic although this project is very easy and can be easily grasped but knowledge about basics which can help everyone ,specially those who want to design complex circuits. 

CHARGING OF CAPACITOR

The voltage across battery is given by 

                                                   V(capacitor) = V(battery){1 - e^( t / RC )

        where R is the resistance between battery and capacitor 

        and C is the capacitance of the capacitor

     The product of RC is  known  as Time Constant. It is the time taken by the capacitor to charge fully. when electrolytic capacitor  is charged fully, it does not allow any current to pass through . In other words charged electrolytic capacitor acts as an open circuit. The charging rate of the capacitor is given by the above equation. when the capacitor is fully charged ( which occurs after infinite duration theoretically but practically occurs after 5 TIME constant) the voltage across capacitor is the maximum voltage that it can achieve at any time without changing the circuit. This state of capacitor is called as steady state.

• The capacitor will charge only when the input voltage is greater than the capacitor voltage.
• The voltage written on the capacitor is the maximum voltage that it can withstand without getting damaged.

                                              CAPACITOR CHARGING

DISCHARGING OF CAPACITOR

When the capacitor is fully charged, then fundamentally it has voltage across it and can give current to the device connected to it for short duration provided that the voltage across the capacitor is more than the load as shown in the below circuit representation. Now the rate at which capacitor discharges or provides current to the load depends upon the resistance of the load. let us assume that the voltage across the capacitor when it is fully charged is Vo , then the voltage across the capacitor at any time is given by 

  

                                                      V = Vo x e^(-t/R1C)

where x denotes the multiplication and R1C is the time constant. 

CAPACITOR DISCHARGING

• The voltage across the capacitors falls exponentially
• Smaller the time constant, steeper would be the voltage graph.

components required

1. SPST switch
2. 1000 uf 25V electrolytic capacitor
3. LED
4. 1k 1/4 W resistor
5. battery

WORKING OF THE CIRCUIT

whenever SPST is  pressed, the capacitor starts to charge and since there is no resistance in the path between  a battery and a 1000 uf capacitor, capacitor will charge instantaneously. When the switch is pressed, the current divides into two paths, one part is used to charge the capacitor and other part is used to glow the LED. Whenever switch is released, the capacitor starts to discharge through the resistance path , the LED would glow only for R1C seconds.