
The RC time constant, denoted τ (lowercase ), the (in ) of a (RC circuit), is equal to the product of the circuit (in ) and the circuit (in ): It is the required to charge the , through the , from an initial charge voltage of zero to approximately 63.2% of the value of an applied A smaller time constant means the capacitor charges or discharges more quickly, resulting in a faster rate of change. The time constant is also used to determine the frequency response of the circuit. [pdf]
Thus the time constant of the circuit is given as the time taken for the capacitor to discharge down to within 63% of its fully charged value.
Thus every time interval of tau, (τ) the voltage across the capacitor increases by e-1 of its previous value and the smaller the time constant tau, the faster is the rate of change. We can show the variation of the voltage across the capacitor with respect to time graphically as follows:
An RC series circuit has a time constant, tau of 5ms. If the capacitor is fully charged to 100V, calculate: 1) the voltage across the capacitor at time: 2ms, 8ms and 20ms from when discharging started, 2) the elapsed time at which the capacitor voltage decays to 56V, 32V and 10V.
So after 3 seconds, the capacitor is charged to 63% of the 9 volts that the battery is supplying it, which would be approximately 5.67 volts. If R=1KΩ and C=1000µF, the time constant of the circuit is τ=RC= (1KΩ) (1000µF)=1 second. If R=330KΩ and C=0.05µF, the time constant of the circuit is τ=RC= (330KΩ) (0.05µF)=16.5ms.
That is, at 5T the capacitor is “fully charged”. An RC series circuit has resistance of 50Ω and capacitance of 160µF. What is its time constant, tau of the circuit and how long does the capacitor take to become fully charged. 1. Time Constant, τ = RC. Therefore: τ = RC = 50 x 160 x 10-6 = 8 ms 2. Time duration to fully charged:
The result is that unlike the resistor, the capacitor cannot react instantly to quick or step changes in applied voltage so there will always be a short period of time immediately after the voltage is firstly applied for the circuit current and voltage across the capacitor to change state.
We are deeply committed to excellence in all our endeavors.
Since we maintain control over our products, our customers can be assured of nothing but the best quality at all times.