By Corey Boles Of DOW JONES NEWSWIRES WASHINGTON -(Dow Jones)- Senate lawmakers voted by a wide bipartisan majority to extend the Export-Import Bank's authorization after easily defeating a handful of Republiacn amendments aimed at limiting the bank's ability to function. The 78-20 vote came a week after the House approved the bank's extension by an even stronger bipartisan margin and ends a debate that at one point looked like it might threaten the bank's continued existence. The bill will now go to the White House for President Barack Obama's signature, two weeks before the bank's mandate expires on May 31. The legislation extends the bank's mandate through September 2014, increasing its financing cap to $140 billion from the current $100 billion over that period. The Export-Import bank helps U.S. exporters by offering financing assistance to foreign buyers of their products, often at better terms than those commercially available. -By Corey Boles, Dow Jones Newswires; 202-862-6601; corey.boles@dowjones.com