# Single-phase rectifier circuits

The rectifying systems can be divided into:

• single-phase
• multi-phase

depending on the structure and number of phases of supplying alternating voltage.

If the voltage is rectified during one half-period of each phase, then such a rectifier is called half-wave or unidirectional rectifier. If the voltage is rectified during both half-periods, then such a rectifier is called full-wave, bidirectional or bridge rectifier. Additionally the rectifying system can be divided due to the elements of which the system is made:

• non-controlled rectifiers (diode)
• controlled rectifiers (thyristor or transistor)
• heterogeneous rectifiers (containing both diodes and thyristors or transistors)

The most important rectifier parameters are as follows:

• supply voltage (U2)
• components of output voltage (Uos) and output current (Ios)
• efficient value of output voltage (Uo)
• allowed output current (Ios max)
• watt-hour efficiency (ηp) calculated as the relation of the direct current power at the output to the apparent power of alternating current at rectifier input

• pulsation coefficient (kt), defined as the relation of amplitude of pulsation basic component of at the output (Uo1m) to the constant component (Uos

• maximal value of reverse voltage (URm) which occurs on the rectifying element

The values which characterize the rectifiers can be easily presented by means of diagram and runs of voltage and current for single-phase semi-wave rectifier with resistance load:

 a) b) Single-phase rectifier with resistance load: a) diagram; b) voltage and current runs in the system  Description: Odbiornik - Receiver

Half-wave rectifier with resistance load is characterized by a very low efficiency (below 29%) and a great pulsation. It means that 71% of energy absorbed from the source is lost. In such a case a network transformer, through which the current constant component (Ios) also flows (causing the magnetization of transformer core), is used in a small degree. It causes the necessity to use a transformer with dimensions greater than it results from power generated in the load. In practice the half-wave system is used rarely, usually at low power.
Full-wave rectifying system, which have better properties, are applied more often. General principle of full-wave rectifier operation is shown on the diagram below:

 a) b) Diagram of full-wave rectifier with resistance load and runs of voltage and current: a) with directed centre of transformer secondary winding; b) in Graetz bridge system

In both systems the current flows through the load in one direction and has a pulsating character. The most of parameters are the identical for both systems. However in the bridge system the reverse voltage is twice lower on each diode, which allows to apply the diodes with lower allowed reverse voltage. The bridge ensures also better using of transformer power. The disadvantage of this solution is the necessity to use for diodes.
The basic parameters of single-phase rectifying system with resistance load are presented in the table below:

 SYSTEM HALF-WAVE FULL-WAVE WITH DIRECTED CENTER FULL-WAVE BRIDGE Voltage constant component Uos Effective voltage value on load Uo Watt-hour efficiency ηp Pulsation coefficient kt Maximal voltage value on diode  URm

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