Capacitor RC time constant

Using a steady voltage to charge a capacitor through a resistance, and also discharging a capacitor through a resistance, creates what is called the RC time constant.

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Diagram:



Nice looking larger value capacitor kit.

Electronics RC time constant curve diagram by Electronzap Electronzapdotcom
Electronics RC time constant curve diagram by Electronzap Electronzapdotcom
  • Fully discharge capacitors that start charging through a resistor will initially have a massive voltage change (almost 2/3) of the final voltage at the start of charging (one time constant). After that the voltage rapidly slows down how fast it rises, and it takes about 4 times as long to get to the final voltage as it took to get to that initial approx. 2/3 voltage change. Covered in more detail below.
  • Same basic rules apply to a fully charged capacitor that is discharging through a resistor, but the voltage is dropping instead of rising.

Following links have a short video that cover the schematics above:

Basic RC time constant properties

  • One time constant ( τ / Greek letter tau) is the capacitance of the capacitor in Farads, times the resistance in ohms.  τ = RC
  • It takes 5 time constants to go from fully discharged to fully charged (about 99.99%) through a resistor. Also takes 5 time constants to go from fully charged to fully discharged through  resistor.
  • Voltage changes very rapidly during the first time constant almost 2/3 or 66% of the voltage change. and each following time constant has a much lower voltage change then the previous one. Each time constant changes almost 2/3 or 66% of the remaining voltage.

RC time constant curve diagram

Capacitor RC time constant and constant current curve diagrams by Electronzap Electronzapdotcom
Capacitor RC time constant and constant current curve diagrams by Electronzap Electronzapdotcom
Schematic diagrams used in video
Basic electronics circuit fragments and simple circuits 4 capacitors changing voltage based on capacitance and current diagram by electronzap electronzapdotcom
Basic electronics circuit fragments and simple circuits 4 capacitors changing voltage based on capacitance and current diagram by electronzap electronzapdotcom
Video

Electronics course 5 capacitor component RC time constant circuit fragment tutorial



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