USB ports available in computer, laptop provides 5V DC supply through VCC and GND pin. If we need more than 5V from the USB port, we can use this circuit to get high voltage as up to 35V. This circuit constructed with step up DC/DC converter IC LT1618.
This integrated circuit has many features they are wide VIN range that is 1.6V to 18V and 1.4MHZ switching frequency.
Circuit construction & working
Heart of this circuit is IC LT1618 and other components are biasing elements. Here the VIN 5 volt taken from the USB port (Red wire +5V and Black wire GND), choose the resistor R5 and R6 depends on you output voltage requirements.
Here pin number 4 is the current adjust pin, this current sense voltage can be varied by applying DC voltage. If this adjustment is not needed connect the pin 4 to ground and remove Q1, R2 and R3. Pin 9 is shutdown pin, less than 0.3V to this pin will shutdown the IC.