* Retailer says total buyback authorization now $290 mln
* Authorization has no expiration date
SAN FRANCISCO, Aug 20 (Reuters) - RadioShack Corp RSH.N said on Thursday that it has approved the repurchase of an additional $200 million of its common stock under a current share repurchase program.
The gadget retailer said it now has authority to purchase about $290 million of its common stock under its existing share repurchase program.
The buyback authorization does not have an expiration date, RadioShack said.
Its shares closed down 6 cents at $14.61 in New York Stock Exchange trading on Thursday ahead of the announcement. (Reporting by Nicole Maestri; Editing Bernard Orr)