Rectifier diodes are usually used in applications which require high currents such as power supplies, the range in which the diode can handle current will vary from one ampere to hundreds of amperes. Average current-carrying range of this rectifier diode is one ampere and they have a peak inverse voltage between 50 – 1000 volts, larger rectifier diodes can carry current up to 300 amperes. It can be considered as the electrical equivalent to one way valve, it will allow the current to flow in one direction and not in another direction basically it is a semiconductor device. When the diode is conducting it is said to be forward-biased. The diode will offer very little resistance to the current flow under these conditions. When opposing current flow the diode is said to be reverse-biased, under reverse bias condition the diode has a high resistance
What is rectification
Rectifier diodes are designed to convert ac to dc and to do this properly they must have, low resistance to current flow in the forward direction and high resistance to current flow in the reverse direction. Mostly all semiconductor rectifier diodes are silicon junction types. In order to do the rectification high-performance power diodes are used which can operate efficiently throughout a wide temperature range. Two power diodes are connected into each phase, one to the positive side and the other to the negative side, six power diodes are connected to form a full-wave rectification circuit. The positive half-waves pass through the positive side diodes, and the negative half-waves through the negative side diodes. Rectification takes place
What are the types of rectifier diodes
Selenium rectifiers
The aluminum base serves as a surface for the dissipation of the heat. The rectifying junction covers one side of the base apart from a narrow strip at the edges and an area around the fixing hole, which is sprayed with insulating varnish
The counter electrode is a thin layer of low melting point alloy, sprayed over the selenium coating and insulating varnish. The counter electrode is the cathode and the base is an anode. These rectifiers are suitable for high voltages in series or for high current in parallel. The maximum operating temperature of these rectifiers is in the order of 70 degrees.
Silicon rectifier
Silicon rectifiers can be considered as an ordinary rectifier with a control element the current to the control element which is termed the gate determines the anode to cathode voltage at which the device commences to conduct. The gate bias may keep the device off or it may permit conduction to commence at any desired point in the forward half cycle of a sinusoidal input, silicon rectifiers are used as an ac power control device. They are used in a brushless ac generator, the silicon slice is extremely small. On one face it has a fused aluminum alloy contact to which the anode and lead are soldered. The other face is soldered to a base usually copper. This is the cathode and acts as a heat sink.
The aluminum-silicon junction forms the barrier layer these rectifiers operate at a temperature up to 150 degrees. The ability of the SCR to remain on when the triggering current is removed is called as latching. The two major important qualities while selecting a silicon rectifier is the voltage and current for a particular application that the device can survive without breaking down.
