power at input to power opamp, split supply

[Electron_Orbit]

If I know the currents flowing from +Vs and -Vs to the opamp, call them +Is and -Is, is it correct that

Input power = (+Is - -Is) times Vs

This of course assumes that the absolute values of +Vs and -Vs are the same.

For example, if I use a power opamp such as TDA2050 to control a DC motor, I want to measure total power or power to the opamp and motor together and compare that to power that the motor is receiving. In other words I want to calculate how efficient the opamp is in transferring power to the motor.

Hope that this is clear. If not, let me know. Any confirmation or disagreement is appreciated.

Also I was wondering if efficiency would improve with increasing power drawn by the motor.

Regards,
Pete

[ag]

Hi Pete,

Referring to the TDA2050 datasheet, I would say that efficiency improves significantly with increasing power drawn by the motor while moving from 0 Watt to ca. 12 Watt, and above ca. 12 Watt the efficiency degrades slowly with increasing power drawn by the motor. Other opamps will tend to have other efficiency curves and their datasheets must be consulted accordingly.

Regards,