I'm trying to make a circuit that will light the led with progressive intensity one second after the circuit is powered. For that I created an RC net with tau equal to 1 sec. At 1 second I expect the Vb to reach 63% of the dc voltage(1.2v) which is ~0.7v, that will forward bias the transistor and the led will start lighting. The problem I got is that the voltage at the test point gets stuck at 555 mv when I add the transistor. I'd expect it to eventually reach the 1.2v. Moreover, this doesn't happen if I reduce the RC values to, i.e 1K and 1mf, for maintaining the tau constant.
Why the voltage at the base of the transistor doesn't reach the 1.2v?