Non-standard inclusions of microcircuits in UMZCH. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Non-standard inclusions of microcircuits in UMZCH. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Audio equipment

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The article proposes several options for UMZCH on common microcircuits. The use of amplifiers with feedback on the load current improves the performance of wideband dynamic heads - reducing distortion and expanding the bandwidth of reproducible frequencies.

Radio amateurs are well aware of microcircuits for UMZCH series K174UN14, K174UN15, K174UN19 (analogues TDA2003, TDA2005, TDA2030). These are very reliable microcircuits with good parameters, but in many cases their switching circuit can be simplified without a significant deterioration in the performance of amplifiers.

Moreover, with a modified switching scheme, you will receive new properties that are not in the standard version. For example, the introduction of current feedback compensates for the influence of the frequency dependence of the load resistance on the gain.

As one of the options for possible inclusion, the UMZCH circuit is shown (Fig. 1) with a reduced number of resistors: inside the TDA2003, TDA2005 microcircuits, there is already a 20 kΩ feedback resistor between the output and the inverting input. With this ratio of resistors in the amplifier, the voltage gain Ku is 26 dB. It is easy to change it by appropriate selection of resistor R2.

In the UMZCH circuits with integrated circuits shown in Fig. 2-4 also with less detail, current feedback is implemented, and in the amplifier in fig. 4, the TDA2030 chip is used in an inverting connection, which achieves greater resistance to self-excitation and better transient characteristics.

It should be noted that in the last two circuits (Fig. 3, 4), the midpoint between the capacitors C4 - C7 is not connected to the common wire of the power source, this provides complete 3% voltage feedback. In all UMZCH variants proposed here with current feedback, the UMZCH gain depends on the ratio of the load resistance to the resistance R2 (Fig. 4). R3 (Fig. 6), R4 (Fig. 26); for all these amplifiers it is equal to XNUMX dB.

I often use non-standard inclusions of UMZCH microcircuits when repairing automotive electronics, when it is not possible to find a suitable replacement for one or another microcircuit.

(click to enlarge)

The proposed schemes for switching on UMZCH integrated circuits can be successfully used in the design of multiband UMZCH with the division of the audio range into several bands in a crossover (separation filter in front of the bandpass UMZCH). In addition to increasing the actual total output power, such amplifiers achieve the mode of operation of the loudspeaker head with a current generator that controls its moving coil (see the article by S. Ageev "Should UMZCH have a low output impedance" in "Radio" 1997, No. 4 p. 14) .

Such a direct (without crossover filter) matching of the amplifier with the load can significantly reduce the intermodulation distortion of the head, and the integral design of the UMZCH simplifies the design of an active loudspeaker.

Author: M. Sapozhnikov, Israel, Ganei Aviv

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