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PederBass 7th October 2004 07:16 PM

opamp buffers power output q
Just want to get some input in a question I been thinking about...

What is the relationship between a opamp-buffer's output current vs supply current when looking at it's power dissipation?

Tryin to make my q clearer...If a buffer's data say's :
output current 100 mA
supply current 10 mA
And...PD 1W

Does this means that, with 30v ps, u can take out:

(1W/30v = 33.3 mA
and supply current 10 mA = 33.3 - 10 )= 23.3 mA?
That is u cant take out MORE than 23.3 mA?

Or is there another relationship since one data is DC mA and the other AC mA?

Greatly appreciate any answer...



PMA 7th October 2004 07:28 PM

Supply current of 10 mA is with no load.
Output current (up to 100mA) is added to supply current in appropriate supply lead (+V or -V).
Pd will depend not only on load current, but supply voltage and output voltage as well. Power dissipation also depends on output stage class of operation, we can assume class B/AB.

PMA 7th October 2004 08:00 PM

Please also have a look at maximum power dissipation vs. temperature and package type.

For BUF634 in TO-220, max. allowed power dissipation is 2W without heatsink (free air). With infinite heatsink, maximum allowed power dissipation increases to 9W ! This says that reasonable heatsink may increase Pd considerably.

PederBass 8th October 2004 09:32 PM

Thanx PMA!
Guess that confirmed what I was into..I think..:)

anyway thnx..


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