OPAMP Power dissipation - It's possible?

[berni80]

Hi,

I would need some help in a power dissipation issue.
I have a power OPAMP that works in a non-inverting topology.

Here some data:

- Single Supply = 12V
- Output voltage = 6+3*sin(wt) V
- Output current = 100*sin(wt + alfa) mA

where:

w = angular frequency
t = time
alfa = angle between current and voltage

Is it possible to estimate what is the power dissipated in the opamp?
I do not know alfa.

Thanks!

 

[FvM]

The voltage/current spec suggests the load's neutral connected to mid supply or connected through a DC blocking capacitor. So the problem is identical to a bipolar +/- 6V supply configuration.

If you are motivated, you can calculate the exact power disspation by integral calculus. If I understand right, alfa = 90° (reactive load) is worst case. I guess, it's sufficient to use a simplified upper bound, I suggest 6V * mean(|iout|), or about 0.38 W. OP bias current adds some losses, of course.

For an amp with real load, there's a simple upper bound with a rectangular output waveform of +/- 3V. You get 3V * 100 mA = 0.3 W maximum power disspitation, for the load and the amplifier as well. When increasing the output voltage, the amplifier dissipation decreases below this value. But the behaviour is different with a reactive or complex load.