In the case of the sawtooth in Figure 25 the mean

level was increased by the TIM distortion, for a

sawtooth in the other direction the opposite is true.

The result is an AC signal at the output whole

peak-to-peak value is the TIM voltage, which can

be measured easily with an oscilloscope. If the

peak-to-peak value of the signal and the peak-to-

peak of the inverting sawtooth are measured, the

TIM can be found very simply from:

TIM

=

⋅ 100

In Figure 25 the experimental results are shown for

the 30W amplifier using the TDA2030A as a driver

and a low-cost complementary pair. A simple RC

filter on the input of the amplifier to limit the maxi-

mum signal slope (SS) is an effective way to reduce

TIM.

Figure 25 : TIM Distortion versus Output Power

The diagram of Figure 26 originated by SGS-

THOMSON can be used to find the Slew-Rate (SR)

required for a given output power or voltage and a

TIM design target.

For example if an anti-TIM filter with a cutoff at

30kHz is used and the max. peak-to-peak output

voltage is 20V then, referring to the diagram, a

Slew-Rate of 6V/

µs is necessary for 0.1% TIM.

As shown Slew-Rates of above 10V/

µs do not

contribute to a further reduction in TIM.

Slew-Rates of 100/

µs are not only useless but also

a disadvantage in Hi-Fi audio amplifiers because

they tend to turn the amplifier into a radio receiver.

POWER SUPPLY

Using monolithic audio amplifier with non-regulated

supply voltage it is important to design the power

supply correctly. In any working case it must pro-

vide a supply voltage less than the maximum value

fixed by the IC break-down voltage.

It is essential to take into account all the working

conditions,in particular mains fluctuationsand sup-

ply voltage variations with and without load. The

substitution of the standard IC power amplifiers

An example, using a simple full-wave rectifier fol-

lowed by a capacitor filter, is shown in the table 1

and in the diagram of Figure 27.

Figure 27 : DC Characteristics of

50W Non-regulated Supply

TDA2030A

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