Rectification

Rectification, process of converting an alternating electric current (AC), which flows back and forth in a circuit, to direct current (DC), which flows only in one direction. A device known as a rectifier, which permits current to pass in only one direction, effectively blocking its flow in the other direction, is inserted into the circuit for the purpose.

Rectification is carried out at all levels of electrical power, from a thousandth of a watt in the detection of an AM radio signal to thousands of kilowatts in the operation of heavy electrical machinery. The first commercial rectifiers were used in the conversion of alternating to direct current in the operation of electric motors; these early rectifiers were called mechanical commutators. Today, most rectification is carried out by electronic devices, such as combinations of vacuum-tube diodes, and mercury-arc rectifiers. (See Diode; See Vacuum tube.)

Most mechanical rectifiers consist of a rotary switch that is synchronized with the current; the switch is arranged to conduct the current in one direction only. Mechanical rectifiers can be designed and constructed to handle heavy currents (up to thousands of amperes) at levels of several thousand volts, and they are still used in heavy electrical machinery.

Electronic rectifiers conduct current in one direction only by the movement of electrical charges inside the device; they can carry currents as high as 500 amperes and withstand up to 1,000 volts without damage. These rectifiers, therefore, can compete with mechanical rectifiers in many power applications. In low-voltage applications, as in electronic equipment, vacuum-tube or semiconductor rectifiers are used almost exclusively.