Can't find solution of Ramp function
Separate the variables and integrate:
$$ α = \frac{V}{RC} + \frac{dV}{dt}$$
$$ \frac{dV}{dt} = α - \frac{V}{RC}  $$
$$ (\frac{1}{α-\frac{V}{RC}})dV = dt $$ 
$$ RC\int \frac{dV}{αRC - V} = \int dt $$
$$ RC\ln(αRC - V).(-1) = t + C_1 $$ 
$$ \ln(αRC - V) = \frac{-t}{RC} + C_2 $$ 
$$ e^{-t/RC + C_2} = αRC - V  $$ 
$$ e^{-t/RC}.C_3 = αRC - V  $$ 
$$ V = αRC - e^{-t/RC}.C_3 $$ 
Assuming initial conditions to be V = 0 at t = 0,
$$ C_3 = αRC $$ 
$$ V = αRC - e^{-t/RC}.αRC $$ 
$$ V = αRC(1 - e^{-t/RC}) $$