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 PederBass 7th October 2004 07:16 PM

opamp buffers power output q

Hi!
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?

Thanks

/Peder

 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..

/Peder

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