Transforming impluse to DC Current
What you need is a capacitor to store the energy and some kind of regulator to adjust the voltage. Depending on your source a diode on the input to prevent the energy to flow back. 

For the regulator you can choose an linear one, if you want to have it simple and cheap and if you don't mind to loose a big part of the energy provided by the pulse. 
If your circuit should work as long as possible with a single feeding pulse, you may want to choose a DC-DC regulator. They are more complicated to build but will allow you to use the power much better.