If you are asking from where you can obtain a d.c. supply without using a rectifier supplied from an a.c. source, then the answer is that d.c. supplies are directly available from batteries or from d.c. generators.
The type of power supply being used (AC or DC) should match the power requirements of the device it will be supplying power to.
to convert AC into DC voltage without fluctuation
AC voltage is more sufficient than DC voltage. Moreover, an AC transformer can be developed but DC voltage will make it harder. Without a transformer, we cannot turn the high and low voltaged into each-other.
A DC to DC converter is basically a type of switching power supply. The switcher converts the input DC to AC. A transformer is used to convert the AC to the desired voltage. A rectifier, filter, and optional regulator is used to convert the AC back to DC.
we can convert a dc supply to an ac supply using inverters. Its a common operation which we observe in our daily lives dc can be converted to Ac using an undulator.
the universel motor can runs at both ac and dc supply.
Radios use DC power supplies to operate. If a radio is powered from a mains AC supply, a power supply circuit will convert the AC supply to DC. Therefore, a radio may have both a DC and an AC power input but ultimately, the internal circuitry will always use DC.
"Voltage peak" is generally used to denote the maximum(amplitude) of AC voltage supply. It can not be approximated as dc value. The closest approximation one can make for dc value of a ac supply is the RMS(root mean square) value of the voltage. So that the ohmic loss caused by the given AC voltage supply is equivalent to that caused by a dc supply having value equal to the RMS of this AC supply (for given impedance & time).
ac supply converted with dc supply
ac supply converted with dc supply
dc power supply
when the dc supply given, dc load line lies in the Ic and Vcc. when the AC supply given, AC load line lies in the Ic and Vcc.