Abstract: A charger includes a first housing, a second housing connected with the first housing, and a PCB assembled between the first and second housings. The first housing is defined with a plurality of battery chambers. Each battery chamber is assembled with first and second resilient plates for respectively contacting positive and negative poles of a rechargeable battery. Each resilient plate has a contact portion and a soldering portion. A circuit system is defined at the PCB and includes an AC-DC circuit, a charging circuit, and a power output and input circuit. The circuits are connected with each other and connected with the soldering portions of the first and second resilient plates of each battery chamber. A power input socket and a power output socket are formed to connect with the power output and input circuit.

Abstract: A DC-DC converter is used for raising input voltage, and has a substrate forming a plurality of conductive pins, and a circuit system formed on the substrate and appropriately coupled to the conductive pins. The circuit system includes a step-up circuit coupled in series to a MOSFET with threshold voltage of 20V. A Zener diode and a diode are coupled in parallel between two transistors of the step-up circuit and are coupled in series with each other for limiting working voltage of the step-up circuit no more than 20V thereby assuring MOSFET working normally and preventing damage of electronic components in the DC-DC converter.