Chapter | 2 Electronic Concepts: More Interesting Than You Think 33 Power Supplies Electronic circuits require a source of DC for proper operation. A great many electronic products are still powered by batteries because they are small and portable, such as cell phones, iPods, and the like. Other electronic equip- ment is designed to operate from the AC power line. Such equipment contains an electronic power supply that converts AC into the required DC voltages. Computers, TV sets, and other nonportable electronic equipment have an AC power supply. AC Voltage Sources Generators The AC that appears at the outlets of our homes and offices is produced by huge electromechanical generators owned and operated by an electrical util- ity company. A source of mechanical power--such as water, or a steam tur- bine powered by oil, coal, or nuclear fuel--operates the generator. The turbine converts steam into mechanical energy to turn the generator. The genera- tor rotates coils in a strong magnetic field to produce a voltage. The speed of rotation of the coils determines the frequency. That voltage is a 60-Hz sine wave.