Pulsed DC

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Types of electric current
Rectification of a sine wave produces pulsed DC.

Pulsed DC (PDC) or pulsating direct current is a periodic current which changes in value but never changes direction. Some authors use the term pulsed DC to describe a signal consisting of one or more rectangular ("flat-topped"), rather than sinusoidal, pulses.[1]

Pulsed DC is commonly produced from AC (alternating current) by a half-wave rectifier or a full-wave rectifier. Full wave rectified ac is more commonly known as Rectified AC. PDC has some characteristics of both alternating current (AC) and direct current (DC) waveforms. The voltage of a DC wave is roughly constant, whereas the voltage of an AC waveform continually varies between positive and negative values. Like an AC wave, the voltage of a PDC wave continually varies, but like a DC wave, the sign of the voltage is constant.

Pulsating direct current is used on PWM controllers.

Smoothing[edit]

Most modern electronic items function using a DC voltage, so the PDC waveform must usually be smoothed before use. A reservoir capacitor converts the PDC wave into a DC waveform with some superimposed ripple. When the PDC voltage is initially applied, it charges the capacitor, which acts as a short term storage device to keep the output at an acceptable level while the PDC waveform is at a low voltage. Voltage regulation is often also applied using either linear or switching regulation.

Difference from AC[edit]

Pulsating direct current has an average value equal to a constant (DC) along with a time-dependent pulsating component added to it, while the average value of alternating current is zero in steady state (or a constant if it has a DC offset, value of which will then be equal to that offset). Devices and circuits may respond differently to pulsating DC than they would to non-pulsating DC, such as a battery or regulated power supply and should be evaluated.

Uses[edit]

Pulsed DC may also be generated for purposes other than rectification. It is often used to reduce electric arcs when generating thin carbon films,[2] and for increasing yield in semiconductor fabrication by reducing electrostatic build-up.[3] It is also generated by the voltage regulators in some automobiles, e.g., the classic air-cooled Volkswagen Beetle.

References[edit]

  1. ^ Chapter 2 of "Introductory Signals and Circuits" by Jose B. Cruz, Jr. and M. E. Van Valkenburg, Blaisdell Publishing Company, 1967.
  2. ^ http://www.astex.com/eni-rcsi-TN.html
  3. ^ http://www.freepatentsonline.com/5249094.html

Bibliography[edit]