TPA032D02

10W STEREO CLASSD AUDIO POWER AMPLIFIER

SLOS243B − DECEMBER 1999 − REVISED JUNE 2000

15

POST OFFICE BOX 655303

APPLICATION INFORMATION

the ideal class-D amplifier (continued)

Given these plots, the efficiency of the class-D device can be calculated and compared to an ideal linear

and linear amplifier and the efficiency is calculated.

V

V

P

2

CLASS-D

LINEAR

V

V

P

2

P

I

L

Average I

I

L(rms)

V

L(rms)

V

DD

P

V

L(rms)

2

R

L

+

V

P

2

2R

L

Average I

2

p

V

P

R

L

P

V

DD

Average I

DD

P

V

DD

Average I

V

R

L

2

p

P

V

DD

I

L(rms)

V

L(rms)

V

DD

Efficiency

+ h +

P

L

P

SUP

Efficiency

+ h +

P

L

P

SUP

Efficiency

+ h + V

DD

V

P

2

2R

L

2

p

V

P

R

L

Efficiency

+ h + 1

Efficiency

+ h + p

4

V

P

V

DD

clipping. Then, the highest efficiency that a linear amplifier can have without clipping is 78.5%. A class-D

amplifier, however, can ideally have an efficiency of 100% at all power levels.

The derivation above applies to an H-bridge as well as a half-bridge. An H-bridge requires approximately twice

the supply current but only requires half the supply voltage to achieve the same output power—factors that

cancel in the efficiency calculation. The H-bridge circuit is shown in Figure 7.

VDD

VOUT

L

CL

RL

IL

IOUT

+

−

VA

M2

M1

VDD

L

CL

M4

M3

Figure 7. H-Bridge Class-D Output Stage