efficiency of half wave and full wave rectifiers

why the efficiency of FWR is double that of HWR.

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Thread Starter

ashuprasad1990

Joined Sep 25, 2009
3
as we know that the efficiency of a half wave rectifier ~=40.6% and that of a full wave rectifier is 81.2%,nearly double that of the HWR...so why this is so...the reason i know is that in HWR only one diode is used and due to rev.biasing it does not conduct so it looses the negative part and in FWR there are 2 diodes(center tapped and also bridge 2 diodes conduct at a time) so its efficiency also doubles....but my professor isn't satisfied with this he wants to know something else.........help needed
 

t_n_k

Joined Mar 6, 2009
5,455
as we know that the efficiency of a half wave rectifier ~=40.6% and that of a full wave rectifier is 81.2%
Where did you get these values and for what circuit conditions do they apply? Are you considering the rectifier in isolation from all other circuit components such as isolation transformers?
 

beenthere

Joined Apr 20, 2004
15,819
Just as a thought problem - imagine a capacitor with a constant load drawing current. What difference might be between full wave and half wave charging off a transformer?
 

Skeebopstop

Joined Jan 9, 2009
358
The transformer efficiency depends on the output power and should be read from the transformer spec.

The rectifier efficiency can be easily calculated from the datasheet and input voltage.

For example, lets say Vf (forward voltage) of the diodes is 1V @ 4A RMS. If we consider an RMS in voltage of 100V, the efficiency becomes.

((100V*4A - 1V*4A) / 100V*4A)*100 => 99%.

Now consider a similar scenario, 4A RMS @ 10V RMS in.

((10V*4A - 1V*4A) / 10V*4A)*100 => 90%.

As you can see, the efficiency of a rectifier varies with loading. The same principle applies to Transformers but frequency must also be considered (easier to find a curve in the spec sheet).
 

Skeebopstop

Joined Jan 9, 2009
358
With relevance to my previous post, you must define what you mean by efficiency. Efficiency is typically a term applied to power and not to 'rectification purity'.

The power efficiency between full wave/half wave won't be inherently obvious, however the 'ripple voltage' on the output side will be drastically different.

This question can become quite tricky unless you very accurately define it.
 
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