Rectifier Types Comparison Tutorial

Rectifiers Introduction:

The converter circuit which converts AC into DC is called as rectifiers.

Remember that rectifiers and converters are swapped in most of time in the power electronics text books. Generally the term converter indicates rectifier. In this post we will discuss about various types of recitifier circuits.

  • The rectifier circuits using only diodes is known as uncontrolled rectifier circuit.
  • When SCRs are used to convert AC into DC they have control on the output voltage so it is known as controlled rectifier circuit.
  • Unlike diode, an SCR does not become conducting immediately after its voltage has become positive.
  • It requires triggering by means of pulse at the gate.
  • So it is possible to make the thyristor conduct at any point on the half wave which applies positive voltage to its anode. Thus the output voltage is controlled.

Classification of Rectifier circuits:

(a) Depends upon the control characteristics of the various circuits the Rectifiers are classified as

(i) Uncontrolled Rectifiers
(ii) Half controlled Rectifiers

(iii) Fully controlled Rectifiers

(i) Uncontrolled Rectifiers

  • These circuits contain only diodes and give DC load voltage fixed in magnitude relative to AC supply voltage magnitude.
  • They are further classified as half wave, full wave( transformer center tapped) and bridge type rectifiers.

Half Wave Rectifier:

  • The half wave rectifier circuit consists of one semiconductor diode and load resistance.
  • In half wave rectification, the circuit conducts current only during the positive half-cycles of input AC supply.
  • The negative half cycles are suppressed. ie, Current will flow during positive half cycles and no current will be conducted during negative half cycles.
  • Therefore current always flows in only one direction through the load.

Full Wave Rectifier:

In full wave rectification, current flows through the load in the same direction for both half cycles of the input supply. It can be achieved with two diodes working alternatively.

There are two types circuit configuration used for full wave rectification.
(a) Center tap Full wave Rectifier.
(b) Bridge type Rectifier.

Center tap Full wave Rectifier:

  • This circuit consists of two diodes.
  • A centre tapped secondary winding is used to conned two diodes [A centre tapped secondary winding has three terminals, namely 1,2 and 3.
  • The centre point is the neutral point.
  • The total secondary voltage is divided into two parts.
  • The total secondary voltage is divided into two equal parts.
  • They are available across the terminals 1&2 and 3&2 so that each diode uses one half cycle of input ac voltage.

Full wave Bridge Rectifier:
The centre tapped transformer is not needed in the bridge rectifier. It contains four diodes D1, D2, D3 and D4 connected to form a bridge.
Uncontrolled Diode Bridge rectifierThe waveforms of the full wave rectifier is shown below.
Full wave Diode Bridge Rectifer waveforms
The advantages and disadvantages of various configuration is shown in the below table.

Parameters Half-wave    Centre tapped
No of Diodes 1 2 4
Max. Efficiency 40.6% 81.2% 81.2%
Peak Inverse Voltage VM 2VM VM
Average Current/Diode Idc Idc/2 Idc/2
Vdc (no load) Vm/π 2Vm/π 2Vm/π
Output Frequency f 2f 2f
Transformer Utilisation
0.287 0.693 0.812
Ripple Factor 1.21 0.48 0.48
Form Factor 1.57 1.11 1.11
Peak Factor 2 √2 √2

 (ii) Half controlled Rectifiers
These circuits contain a mixture of SCRs and diodes which prevent a reversal of load voltage. But these converters allow control of average value of the dc load voltage

(iii) Fully controlled Rectifiers

  • Here, all the rectifying elements are SCRs.
  • In this circuits, by suitable control of the phase angle at which the SCR are turned ON, it is possible to control the average value of dc voltage and also to reverse the polarity of the dc load voltage.
  • Thus this converter circuit is bidirectional one and it permits the power flow in either direction between supply and dc load.

(B) Depends upon the period of conduction during each cycle of ac input voltage, they are classified into two groups namely 

(i) Half wave Rectifiers
(ii) Full wave Rectifiers
There are two types of full wave Rectifiers namely
Full wave Rectifier using centre tapped transformer
Full wave Rectifier using bridge configuration

(C) Depending upon the number of phase in the supply network, converters are classified as
(i) Single phase Rectifiers
(ii) Three phase Rectifiers

(D) Depending upon the number of pulse on the dc side in one period of the input ac voltage, Rectifiers are classified as
(i) Single pulse Rectifiers
(ii) Two pulse Rectifiers
(iii) Three pulse Rectifiers
(iv) Six pulse Rectifiers etc.

Thanks for reading about rectifier types....

Read More:
How does the Diode Bridge Rectifier Ciruit works?

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