How to make pure DC voltage?

How to make pure DC voltage:

This is a circuit to make ac to dc voltage. we make dc voltage using a diode. and we make pure dc to using a diode and capacitor. we use a transformer according to our needs. we make primary section and secondary section. primary section for Ac 220 or 110 voltage. and we make a secondary section according to our needs. primary and secondary are both Ac voltage. when we need Dc voltage we use a diode. one diode can make dc. but for one diode can’t make a suitable dc voltage. there have less ac. for pure dc voltage we use a capacitor to make pure dc voltage.

We can check the ac and dc voltage using an oscilloscope.  we need a transformer to step down or step up the Ac voltage. and then need a diode. we can use one diode to make dc. but we have to use 4 diodes to make a good dc volt. and after we need a capacitor to store the voltage. here we can see. used 2 capacitors. one capacitor after the diode. after the diode here used one inductor coil. this inductor coil helps to make 100% dc voltage. after this coil here used another capacitor. 

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