Difference between DC value and average value of current.

1. Difference between DC value and average value of current.

Hi everyone,

In a buck converter, for example 100 V DC has to be decreased to 50 V DC. But here, after design of buck converter we will see average value of output at output side. But we will not see average value of input at input side. That means, the 100V DC has to be reduced to 50V DC but not the average value of 100V DC. Assume 50% duty cycle.

More clearly (in buck converter), DC means we have the value at any time (we will see this type of waveform at input side of buck converter). Average means, we may not have the value at any time (we will see this type of waveform at output side of buck converter ). Are Average and DC same?

Please clarify me if I have mistake anything.

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2. Re: Difference between DC value and average value of current.

the 100V DC has to be reduced to 50V DC but not the average value of 100V DC
Average value of 100 V DC = 100 V

Are Average and DC same?
Average value of a DC quantity is that DC quantity. We usually call DC value to the average of a waveform.

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3. Re: Difference between DC value and average value of current.

The output of a buck chopper is not pure DC. The input of Buck chopper can be pure DC or may contain harmonics depending on the type of supply used, but generally it should be free from ripple and noise. The output of Buck Chopper will contain ripple and this will be there due to switching. So the output of a Buck at steady state has DC and a small amount of ripple. The average value of a pure DC quantity with no harmonics is the value of the DC itself. So no, I don't think the average value and DC are exactly the same even if the terms are used like that. Supposing there is a ripple and it is pure Sinusoidal and it superimposed on a DC which makes up the output voltage then the average value of this output will be the value of DC itself, because the average value of a Sinusoidal signal over a full cycle is zero.

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4. Re: Difference between DC value and average value of current.

Hi,

"DC" and "average" are different things.
* "DC" is a signal waveform. A straight line without ripple and without noise.
* "Average" is a measurement method. It is the "mean" value over a dedicated period of time. The "average value of a DC" is equal to the "DC value".

"Average" may be approximated with a low pass filter. The idea is to attenuate all "AC" components of a signal. The cutoff frequency should be way below the lowest signal frequency component in the signal.
The average of a properly low pass filtered periodic signal should be a DC value without noticable fluctuations.

As said above: the average value of a sine superimposed to a DC will be the DC only.
With "RMS" measurement method this is different, here the sine amplitude will influence the RMS value.

Klaus

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