It could be a battery source; however, in most case, the input is a diode rectified ac line voltage with a large filter capacitance, to provide a low internal impedance and low-ripple dc voltage source.

• 该直流电压源可能是一个电池，然而在大多数的情形是一个经二极管整流的交流电压再加上一个大的滤波电容，用以提供一个低内阻、低脉动的直流电压。