Alternating current

• An alternating current (a.c) is defined as:

  A current which periodically varies from positive to negative and changes its magnitude continuously with time

  • This means the direction of an alternating current varies every half cycle
• he relationship between time period T and frequency  f of an alternating current is given by: T=1/f
• A Transformer is a device used to raise or lower the voltage in an ac circuit. It consists of a primary and a secondary coil wound on the same iron

  core. An alternating current in one coil creates a continuously changing magnetic flux through the core. This change of flux induces an alternating emf in the other coil.
• A rectifier is an electronic device that converts an alternating current into a direct current by using one or more P-N junction diodes. A diode behaves as a one-way valve that allows current to flow in a single direction. This process is known as rectification.
• Uncontrolled Rectifiers

  The type of rectifier whose voltage cannot be controlled is known as an uncontrolled rectifier. Uncontrolled rectifiers are further divided as follows:

  • Half Wave Rectifier
  • Full Wave Rectifier

  The type of rectifier that converts only the half cycle of the alternating current into the direct current is known as a half-wave rectifier. Likewise, a full-wave rectifier converts both positive and negative half cycles of the AC. An example of this is a bridge rectifier. A bridge rectifier uses 4 diodes that are connected in the form of a Wheatstone bridge.
• The power of alternating current is proportional to the square of the voltage: P=VI=V×V/R=V^2/R.
• Transformer equation: Vp/Vs=np/ns where Vp is the potential difference across the primary coil in volts and Vs is the potential difference across the secondary coil in volts. np is the number of turns in the primary coil and ns is the number of turns in the secondary coil.
• For step up transformers Vs>Vp
• For step down transformers Vs<Vp