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Old 17th July 2012, 07:01 PM   #31
jitter is offline jitter  Netherlands
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Quote:
Originally Posted by tsiros View Post
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".
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.

Quote:
Quit twisting meanings or claiming i misinterpreted.
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.

Quote:
You wrote a very simple, very concise, sentence. There is no room for misinterpreting.
If both of us have the same concept of TPC and TPD, this would be true.

Quote:
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!".
No, I didn't write that the datasheet is unclear. I did point out the possible source of misinterpretation.

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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.
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.
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Old 23rd July 2012, 01:08 PM   #32
tsiros is offline tsiros  Greece
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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:

Quote:
Dear George Tsiros,

Thank you for contacting Texas Instruments. Your request has been received and Service Request number 1-800854376 has been assigned to your inquiry.

85W is the power consumption per channel so for two channels total power consumption should be around 2*85W=170W

[THREAD ID:1-D8T374]
-----Original Message-----
From: tsiros@upatras.gr Sent: 7/23/2012 11:49:30 AM
To: <asktexas@ti.com>
Subject: RE: George Tsiros, Greece
>> question regarding LM4780

Actually, there is.
40 W power dissipation for 45 W output per channel
So is the power consumption 85 W or 130 W?
Because it says "power output / CHANNEL" under the graph.
Doesn't matter who is right or wrong, now. It is proven that the pdf can be interpreted in various ways.
so.... what now?
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Old 23rd July 2012, 03:52 PM   #33
RJM1 is offline RJM1  United States
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Actually a class B amplifier will have maximum power dissipation at 50% power output. See table #1.
Amplifier Efficiency
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Old 23rd July 2012, 04:18 PM   #34
tsiros is offline tsiros  Greece
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i don't know what class is the LM4780, indeed it has PDmax at 50% output power, but how is this helping? i don't understand
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