11.1 Function and Types of Power Supplies and Electronic Loads

A regulated power source provides electrical energy which is precisely controlled. The direct-current (dc) source converts electrical energy from the commercial electrical power distribution system from alternating voltage to a tightly controlled source of constant voltage or constant current. The alternating-current (ac) source converts an unregulated source of electrical energy to a regulated source of alternating current. The ac power source usually has the means to vary both the amplitude and frequency of its output. In addition, many ac sources available also can simulate disturbances in the power line waveform and make measurements of line current, power, and power factor.

The electronic load is an instrument capable of absorbing direct current in a controlled fashion. It can function as a variable current sink, variable power resistor, or shunt voltage regulator; i.e., it will maintain a fixed voltage as it absorbs a variable current.

The instruments referred to above and in this chapter all use solid-state semiconductor devices to regulate or control sourcing or absorption of energy. Typically, they are available commercially with power ratings from tens of watts to tens of kilowatts, with maximum voltages from a few volts to tens of kilovolts and with maximum currents from milliamperes to several thousand amperes. These power instruments are more than sources of power. They are instruments that can be used on laboratory benches or automated test systems as sources of precisely controlled power. They...