Notebook PCs are great but stray too far from a source of power and it’s not long before low-battery warnings start to appear. Mains adapters come as standard but car adapters are expensive accessories. Good enough reason to get the soldering iron out!Designs for switchmode power supplies or inverters always pose a problem for home constructors because they usually include inductive elements, transformers, chokes or ferrite cores that are difficult to procure. This dc-to-dc converter design uses just one standard inductor. In the prototype this inductor was part of the notebook’s existing supply lead, here it is built onto the PCB.This adapter design is suitable for notebooks requiring a dc input voltage in the range of 14 V to 19 V. It can provide a continuous current of 2 A with short duration peaks of around 2.5 A. The efficiency of the design is in the order of 60 to 80 % depending on the output voltage and current. A big advantage of this design is its low quiescent current of only 75 mA (more on this later).