TS4985 datasheet(20/29 Pages) STMICROELECTRONICS

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Application Information

TS4985

20/29

4.4

Power dissipation and efficiency

Hypotheses:

●

Voltage and current in the load are sinusoidal (Vout and Iout).

●

Supply voltage is a pure DC source (Vcc).

Regarding the load we have:

and

Therefore, the average current delivered by the supply voltage is:

The power delivered by the supply voltage is:

Then, the power dissipated by each amplifier is:

and the maximum value is obtained when:

and its value is:

Note:

This maximum value is only depending on power supply voltage and load values.

The efficiency,

η, is the ratio between the output power and the power supply:

The maximum theoretical value is reached when

VPEAK = VCC, so that:

out

= V

PEAK

sin

ωt

(V)

out =

out

-------------

(A)

out =

PEA K

-------------------------

(W)

AVG

= 2

PEA K

πR

---------------------

(A)

supply

AV G

⋅

()

diss

supply

out

–

()

diss

22V

π R

-----------------------

out

–

⋅

()

∂P

diss

∂P

out

--------------------- = 0

diss ma x

π2R

--------------

()

η =

out

supply

-------------------- =

πV

PEAK

-------------------------

----- = 78.5%

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