1- What happens when we have a constant (DC) voltage as input for RC circuit ?

Question

2- If there is only a peak in the voltage (without any
reputation in time) , is it possible to filter it by
one RC circuit ? if yes how ? how could we define the
frequency in this case ?

Answer 1

All potential drops on capacitor and current through circuit without load is 0.
There is no frequency but there is charachteristic time (period) during which voltage drop on resistor reduces e = 2.78 times.

Answer 2

You will have to regulate the input voltage to some specific level and then choose one of the fixed voltage DC to DC step up converter circuits from that voltage. Two fairly simple circuits to track down.

Answer 3

1. @ t=0, the voltage drop across the resistor is V, the drop across the capacitor is 0. As t-->infinity, the voltage drop across the capacitor goes to V, the voltage across the resistor goes to 0 (current stops flowing as the capacitor charges). For times < RC, the voltage of the capacitor goes as Vc = V(1 - e^(t/RC)), the voltage across the resistor is what is left, or, Vr = V - Vc. The frequency of a DC signal is 0.

Answer 4

In DC the condenser acts as an open circuit, that is, as if one of the two connections to the DC source is broken, So the conclusion is..? You think now! :-)