A battery charging and/or DC power supply circuitry employs a control circuit through an SCR drive circuit and an MOS drive circuit to control when to turn on/off a semiconductor switch unit and to turn on the semiconductor switch unit while an initial section of each positive half wave of an AC power source and an terminating section of the same are located below a predetermined level for intercepting partial power for charging. While charging a battery, the circuitry is lightweight, small-sized, and to enhance the life of the battery. While being a DC power supply, the circuitry is small-sized, high-efficiency, and low-cost.