# efficiency of half wave and full wave rectifiers

Discussion in 'Homework Help' started by ashuprasad1990, Sep 27, 2009.

## why the efficiency of FWR is double that of HWR.

Poll closed Oct 7, 2009.

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1. ### ashuprasad1990 Thread Starter New Member

Sep 25, 2009
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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

2. ### t_n_k AAC Fanatic!

Mar 6, 2009
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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?

3. ### beenthere Retired Moderator

Apr 20, 2004
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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?

4. ### ashuprasad1990 Thread Starter New Member

Sep 25, 2009
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yes sir,in this case we are only concerned with their efficiency's in case of transformers

5. ### ashuprasad1990 Thread Starter New Member

Sep 25, 2009
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yes sir u r right,i want to know teh reasons for the case of transformers

6. ### Skeebopstop Active Member

Jan 9, 2009
358
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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).

7. ### Skeebopstop Active Member

Jan 9, 2009
358
9
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.