TPA751

700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER

WITH DIFFERENTIAL INPUTS

SLOS336C – DECEMBER 2000 – REVISED OCTOBER 2002

14

POST OFFICE BOX 655303

APPLICATION INFORMATION

BTL amplifier efficiency (continued)

Although the voltages and currents for SE and BTL are sinusoidal in the load, currents from the supply are very

different between SE and BTL configurations. In an SE application, the current waveform is a half-wave rectified

shape, whereas in BTL it is a full-wave rectified waveform. This means RMS conversion factors are different.

Keep in mind that for most of the waveform both the push and pull transistors are not on at the same time, which

supports the fact that each amplifier in the BTL device only draws current from the supply for half the waveform.

The following equations are the basis for calculating amplifier efficiency.

Efficiency of a BTL amplifier

+

P

L

P

SUP

(3)

where

(4)

P

L +

V

L

R

L

, and V

LRMS +

V

P

2

, therefore, P

L +

V

P

2

2R

L

power supply

and PSUP + VDD IDDavg and IDDavg +

1

p

p

0

V

P

R

L

sin(t) dt

+ 1p

V

P

R

L

p

0 +

2V

P

p R

L

therefore,

P

SUP +

2V

DD

V

P

p R

L

Efficiency of a BTL amplifier

+

V

P

2

2R

L

2V

p R

L

+

p V

P

4V

DD

V

P +

2P

L

R

L

h

p 2P

L

R

L

4V

DD

where

therefore,