TDA7294

3

1

4

13

7

815

2

14

6

10

R3 680

C11 22

µF

L3 5

µH

270

R16

13K

C15

22

µF

9

R16

13K

C13 10

µF

R13 20K

C11 330nF

R15 10K

C14

10

µF

R14 30K

D5

1N4148

PLAY

ST-BY

270

L1 1

µH

T1

BDX53A

T3

BC394

D3 1N4148

R4

270

R5

270

T4

BC393

T5

BC393

R6

20K

R7

3.3K

C16

1.8nF

R8

3.3K

C17

1.8nF

Z2 3.9V

Z1 3.9V

L2 1

µH

270

D4 1N4148

D2 BYW98100

R1

2

R2

2

C9

330nF

C10

330nF

T2

BDX54A

T6

BC393

T7

BC394

T8

BC394

R9

270

R10

270

R11

29K

OUT

IN

C7

100nF

C5

1000

µF

C8

100nF

C6

1000

µF

C1

1000

µF

C2

1000

µF

C3

100nF

C4

100nF

+40V

+20V

D1 BYW98100

GND

-20V

-40V

D93AU016

Figure 18: High Efficiency Application Circuit

APPLICATION INFORMATION

HIGH-EFFICIENCY

Constraints of implementing high power solutions

are the power dissipation and the size of the

power supply. These are both due to the low effi-

ciency of conventional AB class amplifier ap-

proaches.

Here below (figure 18) is described a circuit pro-

posal for a high efficiency amplifier which can be

adopted for both HI-FI and CAR-RADIO applica-

tions.

The TDA7294 is a monolithic MOS power ampli-

fier which can be operated at 80V supply voltage

(100V with no signal applied) while delivering out-

put currents up to

±10 A.

This allows the use of this device as a very high

power amplifier (up to 180W as peak power with

T.H.D.=10 % and Rl = 4 Ohm); the only drawback

is the power dissipation, hardly manageable in

the above power range.

Figure 20 shows the power dissipation versus

output power curve for a class AB amplifier, com-

pared with a high efficiency one.

In order to dimension the heatsink (and the power

supply), a generally used average output power

value is one tenth of the maximum output power

at T.H.D.=10 %.

From fig. 20, where the maximum power is

around 200 W, we get an average of 20 W, in this

condition, for a class AB amplifier the average

power dissipation is equal to 65 W.

The typical junction-to-case thermal resistance of

the TDA7294 is 1

avoid that, in worst case conditions, the chip tem-

perature exceedes 150

of the heatsink must be 0.038

bient temperature of 50

As the above value is pratically unreachable; a

high efficiency system is needed in those cases

where the continuous RMS output power is higher

than 50-60 W.

The TDA7294 was designed to work also in

higher efficiency way.

For this reason there are four power supply pins:

two intended for the signal part and two for the

power part.

T1 and T2 are two power transistors that only op-

erate when the output power reaches a certain

threshold (e.g. 20 W). If the output power in-

creases, these transistors are switched on during

the portion of the signal where more output volt-

age swing is needed, thus ”bootstrapping” the

power supply pins (#13 and #15).

The current generators formed by T4, T7, zener

TDA7294

10/16