You should try with BUCK-BOOST DC/DC converter. There are avalivble with efficiency above 90% Check out TI.com and linear.com there are "calculators" that would help you http://www.ti.com/lsds/ti/analog/powermanagement/power_portal.page

You should try with BUCK-BOOST DC/DC converter. There are available with efficiency above 90% Check out TI and Linear websites; there are "calculators" that would help you:

• http://www.ti.com/lsds/ti/analog/powermanagement/power_portal.page
• http://parametric.linear.com/buck-boost_regulator

Options:

• TPS63031
• TPS63001