Figure 19: P.C.B. and Components Layout of the Circuit of figure 18 (1:1 scale)

diodes Z1,Z2 and resistors R7,R8 define the mini-

mum drop across the power MOS transistors of

the TDA7294. L1, L2, L3 and the snubbers C9,

R1 and C10, R2 stabilize the loops formed by the

"bootstrap" circuits and the output stage of the

TDA7294.

In figures 21,22 the performances of the system

in terms of distortion and output power at various

frequencies (measured on PCB shown in fig. 19)

are displayed.

The output power that the TDA7294 in high-

efficiency application is able to supply at

Vs = +40V/+20V/-20V/-40V; f =1 KHz is:

- Pout = 150 W @ T.H.D.=10 % with Rl= 4 Ohm

- Pout = 120 W @ "

= 1 % "

"

"

- Pout = 100 W @ "

=10 % with Rl= 8 Ohm

- Pout = 80 W @ "

= 1 % "

"

"

Results from efficiency measurements (4 and 8

Ohm loads, Vs =

±40V) are shown by figures 23

and 24. We have 3 curves: total power dissipa-

tion, power dissipation of the

TDA7294 and

power dissipation of the darlingtons.

By considering again a maximum average

output power (music signal) of 20W, in case

of the high efficiency application, the thermal

resistance value needed from the heatsink is

2.2

All components (TDA7294 and power transistors

T1 and T2) can be placed on a 1.5

with the power darlingtons electrically insulated

from the heatsink.

Since the total power dissipation is less than that

of a usual class AB amplifier, additional cost sav-

ings can be obtained while optimizing the power

supply, even with a high headroom.

TDA7294

11/17