12v DC from USB port

Using this circuit we can convert 5V DC from the computer USB port to 12V DC and a circuit like this will find a lot of application in USB powered systems. The heart of this circuit is IC LT1618 which is a constant current, constant voltage boost converter. The IC has a wide input voltage range of 1.8 to 18V DC and output voltage can be up to 35V DC.

In the circuit resistors R1, R2 sets the output voltage. Pin number 9 is the shutdown pin, less than 0.3V to this pin will shut down the IC. Pin number four is the current sense adjust pin. The current sense voltage can be reduced by applying a DC voltage to this pin. If this adjustment is not needed connect this pin to ground and you can omit components R3, R5 and Q1.

Notes :

• C2 and C3 must be rated at least 15V.
• Less than 0.3V at the shutdown pin will shutdown the IC.
• Output voltage is governed by the following equation R1 = R2 (  (Vout /1.263V) -1).
• This circuit can be used to convert 5v to 12v