▁the ▁input ▁current ▁required ▁is ▁always ▁the ▁same ▁as ▁the ▁output ▁current . ▁As ▁the ▁input ▁voltage ▁must ▁always ▁be ▁higher ▁than ▁the ▁output ▁voltage , ▁this ▁means ▁that ▁the ▁total ▁power ▁( vol t age ▁multip lied ▁by ▁current ) ▁going ▁into ▁the ▁ 7 8 xx ▁will ▁be ▁more ▁than ▁the ▁output ▁power ▁provided . ▁The ▁difference ▁is ▁diss ip ated ▁as ▁heat . ▁This ▁means ▁both ▁that ▁for ▁some ▁applications ▁an ▁ade qu ate ▁he ats ink ▁must ▁be ▁provided , ▁and ▁also ▁that ▁a ▁( o ften ▁substantial ) ▁portion ▁of ▁the ▁input ▁power ▁is ▁was ted ▁during ▁the ▁process , ▁rendering ▁them ▁less ▁efficient ▁than ▁some ▁other ▁types ▁of ▁power ▁supplies . ▁When ▁the ▁input ▁voltage ▁is ▁significantly ▁higher ▁than ▁the ▁reg ulated ▁output ▁voltage ▁( for ▁example , ▁power ing ▁a ▁ 7 8 0 5 ▁using ▁a ▁ 2 4   vol t ▁power ▁source ), ▁this ▁in e ffic iency ▁can ▁be ▁a ▁significant ▁issue . ▁Buck ▁conver ters ▁may ▁be ▁preferred ▁over ▁ 7 8 xx ▁regul ators ▁because ▁they ▁are ▁more ▁efficient ▁and ▁do ▁not ▁require ▁heat ▁s inks , ▁though ▁they ▁might ▁be ▁more ▁expensive . ▁ ▁When ▁using ▁them ▁in ▁' LM 3 1 7 ▁mode ', ▁with ▁an ▁R 1 / R 2 ▁voltage ▁div ider , ▁note ▁that ▁the ▁bias / ad just ▁current ▁drawn ▁is ▁several ▁orders ▁of ▁magnitude ▁higher ▁( 5 ▁m A ▁vs ▁ 5 0 ▁ μ A ), ▁so ▁this ▁extra ▁current ▁makes ▁the