Brief capacitor discharge RC time constant circuit

Discharging a capacitor through a resistor provides a voltage curve that drops extremely fast at first and then changes very slowly towards the end of the discharge.

Simple discharging capacitor RC time constant circuit schematic diagram by electronzap electronzapdotcom
Simple discharging capacitor RC time constant circuit schematic diagram by electronzap electronzapdotcom

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Video below shows how I build this circuit on a breadboard.

  • Time constant is usually indicated by it’s initials (TC) or the greek letter tau ( τ ).
  • RC time constant is determined by the capacitance of the capacitor in farads times the resistance in ohms. τ = RC
  • First time constant changes from the starting voltage to about 63% of the final voltage. Each time constant after that changes about 63% of the remaining voltage. After 5 time constants, the voltage is practically completely changed, and therefore the capacitor is usually declared as being fully charged or discharged after 5 time constants.

Video

Quick discharging capacitor RC time constant circuit schematic to breadboard build and oscilloscope

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Updated video and diagram:

Capacitor RC time constant curve schematic diagram by electronzap
Capacitor RC time constant curve schematic diagram by electronzap

A 1,000µF (same as 0.001F) capacitor with a 1,000Ω resistor has a time constant of 1 second. Therefore it will take about 5 seconds to go from 5 volts to 0V.

Discharging capacitor component RC time constant curve oscilloscope measured

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