And that is precisely what I wrote:
Power drawn from PSU = power consumption
total power dissipated = 49 W
output power * 2 = 2 * 22.5 W
This equation tells you that some of the energy is lost in the IC as heat and the rest goes to the speakers. Of the 94 W power consumption, 49 W is lost in the IC and the rest (2 * 22.5 W) finds its way into the speakers.
No it isn't. It's right there in the datasheet in the text just below the equation:
Quote from the datasheet:
"The package dissipation is twice the number which results
from Equation 2 since there are two amplifiers in each
LM4780."
The datasheet is fine, your interpretation is the mess.
The equation for PDmax is for one amp and hence needs to be multiplied by two to get the figure for both channels in the IC. It says so in the text I just quoted from the datasheet.
The graph shows total power dissipation vs output power per channel. The word "total" indicates it's the power dissipation of the entire IC and that automatically means both channels (don't be misled by the "Output Power/Channel" on the other axis!).
If the datasheet were wrong, the calculated PDmax (+/- 30 V PSU and 8 ohm load) of 45.6 W would not nearly be so close to the 49 W from the graph.
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If power dissipation were to include the power output, the graphs could never show a dropping TPD curve whith increasing power output. So yes, I'm pretty sure.
no "if"s. Is "total power dissipation" what the IC needs to operate?
which one is it? is TPD the same as power consumption, or not? you've said both.
which one is it? is TPD the same as power consumption, or not? you've said both.
You're misinterpreting me.
Total power dissipation is the total amount of power that is lost (or dissipated) as heat in the IC in order to be able to deliver the power output to the speakers. ALL power will come from the PSU.
So while the amplifier IC is pumping 2 * 22.5 W into the speakers, the IC itself is needing (dissipating) an extra 49 W of power. All of this power must come from somehere, and that is the PSU. So, the PSU is supplying the 2 * 22.5 W for the speakers AND the 49 W for the IC. Together this forms the total power consumption of 94 W. (But it's only the 49 W you need to take into account while calculating the thermal resistance of the heatsink).
TPC = TPD + PO (but you already know this, you wrote it yourself in post #20).
Total power dissipation is the total amount of power that is lost (or dissipated) as heat in the IC in order to be able to deliver the power output to the speakers. ALL power will come from the PSU.
So while the amplifier IC is pumping 2 * 22.5 W into the speakers, the IC itself is needing (dissipating) an extra 49 W of power. All of this power must come from somehere, and that is the PSU. So, the PSU is supplying the 2 * 22.5 W for the speakers AND the 49 W for the IC. Together this forms the total power consumption of 94 W. (But it's only the 49 W you need to take into account while calculating the thermal resistance of the heatsink).
TPC = TPD + PO (but you already know this, you wrote it yourself in post #20).
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i am not misinterpreting you. I read exactly what you wrote. That the "total power dissipation is what the IC needs to operate." No, what the IC needs to operate is the "total power consumption". Quit twisting meanings or claiming i misinterpreted. You wrote a very simple, very concise, sentence. There is no room for misinterpreting. Also, you've described the rest already more than i needed. I'm a physicist with an MSc, i'm familiar with how an IC operates. It's just that the datasheet is sometimes confusing. You agreed that what the datasheet says is not clear enough and that it could have been indicated more clearly: "don't be misled by the "Output Power/Channel" on the other axis!". When writing a datasheet, there should be no "it's implied". Read an RFC for an example of how to write something in order to avoid any misinterpretations.
I disagree. TPC is what the IC needs (TPD) plus what the speakers get (PO).
But I will agree that you will always deal with TPC from a PSU point of view. The separation needed to be made to calculate the heatsink.
For a while I was under the impression that the distinction between TPC, TPD and PO wasn't clear. Partly because of your confusion in post #13.
It may seem that I wrote different things in different posts, but I actually wrote the same thing in different ways.
If both of us have the same concept of TPC and TPD, this would be true.
No, I didn't write that the datasheet is unclear. I did point out the possible source of misinterpretation.
The title of the graph explicitly states that it is total power dissipation vs power output per channel. Maybe what the datasheet seems to imply is the practice of specifying the power output of any amp per channel.
I will let it rest now by answering your last post: yes, 1 degr. C/W should be more than sufficient.
yeah, as i was saying, the pdf is not at all clear. Turns out i'm right.
here is the chitchat with TI itself, regarding the +/- 30 V at 40 W output which is indicated in the pdf:
Doesn't matter who is right or wrong, now. It is proven that the pdf can be interpreted in various ways.
so.... what now?
here is the chitchat with TI itself, regarding the +/- 30 V at 40 W output which is indicated in the pdf:
Doesn't matter who is right or wrong, now. It is proven that the pdf can be interpreted in various ways.
so.... what now?
Actually a class B amplifier will have maximum power dissipation at 50% power output. See table #1.
Amplifier Efficiency
Amplifier Efficiency
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