User manual THOMSON TDA2040

[. . . ] Further the device incorporates a patented short circuit protection system comprising an arrangement for automatically limiting the dissipated power so as to keep the working point of the output transistors within their safe operating area. A thermal shut-down system is also included. [. . . ] Both active and passive filters can be used for crossovers but today active filters cost significantly less than a good passive filter using air-cored inductors and non-electrolyticcapacitors. In addition, active filters do not suffer from the typical defects of passive filters : - power loss - increased impedance seen by the loudspeaker (lower damping) - difficulty of precise design due to variable loudspeaker impedance Obviously, active crossovers can only be used if a power amplifier is provided for each drive unit. This makes it particularly interesting and economically sound to use monolithic power amplifiers. In some applications, complex filters are not really necessary and simple RC low-pass and high-pass networks (6dB/octave) can be recommended. The results obtained are excellent because this is the best type of audio filter and the only one free from phase and transient distortion. The rather poor out of band attenuation of single RC filters means that the loudspeaker must operate linearly well beyond the crossover frequency to avoid distortion. A more effective solution, named "Active Power Filter" by SGS is shown in Figure 20. Figure 20 : Active Power Filter The proposed circuit can realize combined power amplifiers and 12dB/octave or 18dB/octave highpass or low-pass filters. In practice, at the input pins of the amplifier two equal and in-phase voltages are available, as required for the active filter operation. 10/13 TDA2040 The impedance at the pin (-) is of the order of 100, while that of the pin (+) is very high, which is also what was wanted. C1 = C2 = C3 22 nF R1 8. 2 k R2 5. 6 k R3 33 k PRATICAL CONSIDERATION Printed Circuit Board The layout shown in Figure 11 should be adopted by the designers. If different layouts are used, the ground points of input 1 and input 2 must be well decoupled from the gorund return of the output in which a high current flows. [. . . ] Specifications mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. [. . . ]