Electrical engineering

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It would be helpful if you listed some more details because picking the appropriate components depends on the level of power you need.

Basically, however, the usual configuration takes voltage from the positive terminal and it goes through a diode to prevent backwards flow of power during the low level of the pulse. Then this feed through the diode is accumulated in a capacitor that charges up to the peak voltage. As current is drawn from the capacitor, the voltage decreases gradually until the incoming peak voltage (minus a 0.6 volt drop across the forward biased diode) is greater than the charge on the capacitor. During the time that the input voltage is higher than the charge on the capacitor, current will flow from the source into the capacitor, in what tends to be a 3rd harmonic of the fundamental pulse frequency. This may or may not be an issue depending on what else is connected.

In order to prevent early failure of the diode and capacitor, you must select carefully and possibly employ some current limiting devices such as a resistor or possibly a current source transistor circuit. There may also be other filters that need to be added depending on how steady you need your dc voltage to be.

There are several possible solutions depending on exactly what you are trying to accomplish. More information will always produce a better answer.

Maybe it is just me, but pulsating DC sounds like an AC voltage. Maybe there is something I don't understand. AC does not have to be sinusoidal. It can be pulsed or square wave or anything along those lines. DC would indicate that it is steady state voltage for a given long term period of time.

I would suggest looking at a rectifier. If you have no swings below the zero mark, then a half wave rectifier is all you need. If you have swings below the zero mark, then you need a full wave rectifier.

A general question gets a general answer.

You can use the diode and capacitor mentioned previosly if the voltage is one polarity or as the next message atated you will need full wave recifier if the voltage swings both sides of zero.

You can smooth it out much more if you add filtering. LC filters do a very good job but take a little design effort to ensure no ringing. You may have to consider loop stability if this is a closed loop system.

A good answer requires more info...

What is supplying the waveform, what are the characteristics of the waveform, what are you powering with the filtered DC, How much current will you draw, what are the tolerances of the final output?