Question about power transformer terminology?

[mike_mccue]

I have been referring to Hammond's Design Guide for Rectifier Use and I am trying to learn what the terms Peak and Average mean in the context of comparing a transformers secondary vAC with the resulting vDC that is available after rectification to DC.

The Hammond page describes the relationship as:

V (Peak) D.C.= 1.41 X Sec.V A.C.
V (Avg) D.C.= 0.90 X Sec.V A.C.

For half Wave and Bridge rectifiers looking into a capacitor load.

I've been trying to find an explanation of the difference between "Peak" and "Avg" D.C. is in this context and I am not having much luck.

Can some one help explain this?

Thank You.

[soundguruman]

Peak voltage: the amplitude of voltage measured from zero to its highest value (with a scope)
Peak to peak voltage: the amplitude of AC voltage measured from it's positive peak to it's negative peak. (with a scope)
Average voltage: The value of DC voltage when it is rectified from AC voltage. The ratio is dependent on the type of AC waveform that is being rectified.

Delmar's standard textbook of electricity. The best $10 you will ever spend on a textbook. Get one, it has it all in there.

[mike_mccue]

My question is directed at the use of the term "Peak" and the use of the term "Average" when it is contextually applied to direct current as it has been used by Hammond Mfg. in the document I linked to.

I have a general understanding of how to apply the definition of Peak, Peak to Peak, and Root Mean Square to a sinusoidal wave as might be observed in Alternating Current.

My question is asking why Hammond refers to rectified Direct Current after a half wave or bridge recitifier looking into a capacitor load in this manner:

V (Peak) D.C.= 1.41 X Sec.V A.C.
V (Avg) D.C.= 0.90 X Sec.V A.C.

The terms "Peak" or "Average" are causing me confusion in this context especially when I consider that the books I have read explain that I should expect to observe the 1.41x factor (with half wave or bridge rectifiers looking in to a capacitor load) for sound amplification designs.

If all the books describe the use of the 1.41x factor then when does the "Avg" 0.9x factor come in to play?

I am assuming that the type of AC waveform that is being rectified is a 120vAC 60Hz sinusoidal wave from a house outlet running on a Split Phase service.


I asked this question elsewhere and I was, coincidentally, advised to go read a book. To be clear, I've read a few books on the subject including my copy of Merlin Blencowe's (Valvewizard.uk) wonderful book "Designing Power Supplies for Tube Amplifiers" and to put it simply, I can't figure out the answer to the question I am asking.

I'm hoping someone can explain it to me.

As a long shot guess, I thought, perhaps, the 0.9x factor is applicable when the transformer is being used for high current applications... ???

I'll appreciate any help I can get on this subject.

Thank You.

[g1]

Maybe you are thinking of it as filtered DC? Imagine it without a capacitor. The rectified DC is like a sawtooth waveform. The peak is the highest point of the waveform, the average is between the peaks and the troughs.
http://www.aaroncake.net/forum/uploa...ified%20AC.PNG

[mike_mccue]

Thank You!!!

It seems like you figured out exactly what I needed to consider. The illustration you linked to makes it easy to understand. Thank you for helping me with this.

best regards,
mike

[g1]

A bit more on the "why". When you add the capacitor, it will charge up to the full peak value. With no load or a very light load, the supply DC voltage will hold this value.
As you load down the supply more, the voltage will fall. With a heavy load it can drop to the average level. The average level is the real value of the actual energy that exists in the supply.

[mike_mccue]

Thank you for explaining this further.

best regards,
mike