I want to discharge a capacitor (0.47μF) through a led (red led: 2V, 15mA) but I want the discharge remains for a while e.g. 60s or 30s. I charged the capacitor with 10V then I calculated the resistance's value (533Ωhm) to have 15mA current but the discharge was very quick.The led lighed up for just a moment. I know that if I put a bigger capacitor the discharge will remain for a longer time. But, I want the specific capacitor to use with 0.47μF capacitance and if it is possible to change the resistance.
So I try to use the function V(t)=Vo*e^(-t/RC) to calculate the RC.
The values for the function are: t=60s Vo=10V and V(t)=2V as a result RC=186,45s
So, if I put in the function C=0.47μF, the value of the R is calculated 79MΩhm but I can't succeed 15mA current with this resistance.
As a result the led never light up! Could you recommend a way to have the above capacitor but with a little bit longer discharge?