Two Diode Full Wave Rectifier Circuit

- notes and details about the two diode format for a full wave rectifier circuit, detailing its circuit, circuit details, advantages and disadvantages.

The two diode format for a full wave rectifier circuit is one of the simplest forms of full wave rectifier circuit in terms of the actual component count.

The two diode full wave rectifier circuit was widely used in the days of thermionic valves or vacuum tubes because it only required the use of two diodes - these could be encapsulated in one device, thereby reducing cost and size.

Two diode full wave rectifier circuit

The basic full wave rectifier circuit using two diodes and a centre tapped transformer is shown below.

Full wave bridge rectifier using two diodes
and centre tapped transformer

This circuit is very easy to implement, although it does need a centre tapped transformer.

The current flow within the circuit can be seen from the diagram below. This is useful in seeing how the circuit operates and how it is not as efficient in terms of usage of the transformer as circuits such as the bridge full wave rectifier.

Current flow within the two diode full wave rectifier circuit

Looking at the current flow diagram, it can be seen that current each half of the secondary winding is only used of half the cycle. This makes for very inefficient use of the transformer in terms of cost and resources.

• Transformer output voltage half what it could be:   Utilising a centre tap in the transformer means that only half the full voltage across the two halves of the wind together can be utilised.
• Increased heating losses:   As a result of the way in which the two diode full wave rectifier circuit operates, each half of the transformer is used for half of the time. This means that the current through each winding is twice what it would be if a true half wave rectifier such as a bridge rectifier were used. As heating losses are equal to the square of the current times the resistance, this means that there is four times the heat dissipated for half the time. Over the complete cycle this means that there is twice the heating loss of an equivalent full wave bridge rectifier circuit..

As a result of the points noted above, to create a full wave bridge rectifier using the two diode full wave rectifier system would require a transformer √2 times the size of the one needed for the bridge rectifier. This would cost more as well as being heavier and more bulky. With bridge rectifiers now costing very little, this is the preferred option for most applications.

By Ian Poole

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