There is this voltage source that generates different types, it is not a sine wave properly(A), then passing it to a full bridge rectifier, the outcome is like B, then you use a smoothing capacitor and the outcome is like C, what do you use to generate a steady voltage? I tried with a 5v voltage regulator, but it is not working, and the inputs are usually higher than 5v. It is to charge a battery (3.7 v), do you strictly require constant dc ?

 

What kind of voltage source makes that wave? Why not use a clean source? Like a household outlet???

 

I tried with a 5v voltage regulator, but it is not working...

You did something wrong, and we can't guess what that might have been without a schematic or photo, or something.

A voltage regulator such as 7805 is the general answer to your question about how to smooth a rough DC input into a steady DC output.

A DC-DC converter is another option, and is popular because a) it can be more efficient, and b) you can get buck-boost converters that can accept a wide ranging input yet still produce a steady output.

 

If the trough of the voltage across the 7805's regulator gets too low the regulator will come out of regulation.

On the power supply side, two ideas come to mind. The first one is to put a very large choke in series with the bridge output -the minimum inductance would depend on the load current, but it would probably need to be at least hundreds of millihenries (I am assuming 50Hz or 60Hz power). The choke could provide current to fill in the valleys when the lower amplitude peaks occur.

The other solution, much easier, is to just get a much larger capacitor. (I hope your capacitor goes from the bridge output to ground)

Please tell us the frequencies and voltages involved and the load current when you post the schematic.