8051 microcontrollers

The distinction between AC and DC motors has become blurred as controllers for DC motors make increasing use of pulse-width modulation , which can be viewed as a form of alternating current. All motors that consume DC power are referenced in the DC mo­tor section of this encyclopedia, regardless of whether they modulate the power inter­nally. Stepper motors and servo motors are considered as special cases, each with its own entry. AC motors, described here, are those that consume alternating current, usu­ ally in the form of a sine wave with a fixed frequency. What It Does An AC motor uses a power supply of alternating current to generate a fluctuating magnetic field that turns a shaft. How It Works The motor consists primarily of two parts: the stator , which remains stationary, and the r otor , which rotates inside the stator. Alternating cur­ rent energizes one or more coils in the stator, creating fluctuating magnetic fields that interact with the rotor. A simplified repr...

In this section, the term “traditional DC motor” is used to describe the oldest and simplest design, which consists of two brushes delivering power via a rotating, sectioned com ­mutate to two or more electromagnetic coils mounted on the motor shaft. Brushless DC motors (in which DC is actually converted to a pulse train) are also described here because “brushless DC” has become a commonly used phrase, and the motor is powered by direct current, even though this is modified internally via pulse-width modulation . What It Does A traditional DC motor uses direct current to cre­ ate magnetic force, which turns an output shaft. When the polarity of the DC voltage is reversed, the motor reverses its direction of rotation. Usu­ ally, the force created by the motor is equal in either direction. How It Works Current passes through two or more coils that are mounted on the motor shaft and rotate with it. This assembly is referred to as the r otor . The mag­ netic force produced by the...

  The term diode almost always means a semiconductor device, properly known as a PN junction diode , although the full term is not often used. It was formerly known as a crystal diode . Before that, diode usually meant a type of v acuum tube , which is now rarely used outside of high-wattage RF transmitters and some high-end audio equipment. What It Does A diode is a two-terminal device that allows cur­ rent to flow in one direction, known as the for­ ward direction, when the anode of the diode has a higher positive potential than the c athode . In this state, the diode is said to be forward biased . If the polarity of the voltage is reversed, the diode is now r everse biased , and it will attempt to block current flow, within its rated limits. Diodes are often used as r ectifiers to convert al­ternating current into direct current. They may also be used to suppress voltage spikes or pro­tect components that would be vulnerable to re­ versed voltage, and they have specializ...