5V to 12V DC DC Step-Up Converter
by LT1073-12

In order to step up the voltage output from four rechargeable AA batteries from around 5 Volts to the required 12 Volts the following circuit is used.

The key component is the LT1073-12 DC/DC Converter Chip from Linear Technology. Click here for the comprehensive LT1073 Specification Sheet which includes many example circuits using this chip.
This £2 device (the 5V output version LT1073-5 is pictured above) requires just a few off-the-shelf components and operates with supply voltages from 1V to 30V.

The only additional components required to use an LT1073-12 as a 5V-12V DC/DC converter are a 150uH inductor, two 100uF capacitors,and a 50 Ohm Resistor. Total cost of these components is around £1.

Read More Source:
http://www.reuk.co.uk/Power-12V-LED-Spotlight-with-4-AA-Batteries.htm
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