# Different time constants for charging and discharging of a circuit with a constant current source and a capacitor

Consider a circuit that only has a constant current source and a capacitor. The voltage across a capacitor is proportional to the integral of the current I, times time. Since the current is constant it may be taken outside the integral. Based on this, the voltage across the capacitor will continue to increase as time goes by. Now let's say I turn the source on for X seconds and then turn it off. Would the time constant for the charging phase, and the time constant for the discharging phase be the same? I'm not sure if the input resistance of the source has any effect on the time constant. Thank you for any advice!

• By "Turn off" do you mean shorting or disconnecting? (zero current or infinite). In either case the time will be infinite (or equal X sec) or zero. There is no meaning of time constant in these circumstances. Jul 13, 2015 at 18:20