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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Active speaker with a bridge UMZCH on a TDA7266L chip. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Speakers Inexpensive Chinese hand-held lanterns powered by lead-acid batteries are now widely available. The service life of these current sources is short, and since the cost of a battery or galvanic cells for replacement may be more than the cost of the same new lamp, repairing a failed one may not be practical, it is more practical to buy a new one. And what to do with a faulty flashlight? It’s a pity to throw it away, but there’s just no place to store it on a shelf in the pantry. The answer is simple: the body of such a flashlight can become a constructive basis for assembling another useful device. In the presence of the author turned out to be a flashlight "Era" in a plastic case with a diameter (at the location of the reflector) of about 110 and a length of 200 mm. Lantern - with an incandescent lamp, stylized as LED. Since it was easy to install a relatively powerful broadband dynamic head with a diffuser holder with a diameter of about 100 mm in place of the reflector, it was decided to use a case to assemble a compact active speaker in it. The UMZCH scheme is shown in fig. 1. It is assembled on an integrated circuit TDA7266L, which is a single-channel bridge AF power amplifier with unipolar power supply. The microcircuit provides an output power of up to 7 watts into an 8 ohm load. The typical value of the harmonic coefficient at a frequency of 1 kHz with a supply voltage of 11 V and an output power of 1 W is 0,05%, the maximum is 0,2%. The supply voltage of the microcircuit is from 3,5 to 18 V, the maximum power dissipation is 10 W.
Chips of this type were usually used in kinescope TVs, but judging by the ads, they can still be purchased inexpensively in online stores today. Voltage 34 applied to the XP1 input plug goes to the volume control - variable resistor R4 - through resistors R3, R5, and from its engine - to the base of the transistor VT1, connected according to the common emitter circuit. An additional amplifying stage was used for the reason that the amplification of the TDA7266L chip was not enough when the device was connected to mobile multimedia devices. Resistors R10, R7 create a negative OS that reduces the distortion of the audio signal introduced by the transistor VT1. Capacitor C3 prevents RF signals from entering the amplifier stage. The supply voltage of the cascade is supplied through the R11C5 RC filter. The C1R1R6 circuit is designed to eliminate the flow of direct current through the braid of the signal wire if the device will be powered by the same device to which this wire is connected. From the collector of the transistor VT1, the amplified signal is fed through the decoupling capacitor C8 to the input (pin 7) of the DA1 microcircuit. To its output (pins 9, 10) is connected dynamic head BA1. At a supply voltage of 9 V, the amplitude (peak-to-peak) of the AF voltage on the head is about 16 V, and at 5 V - about 8 V. Resistors R13, R14 are selected so that the microcircuit turns off when the supply voltage at pin 8 is less than 4 V. Capacitor C11 delays turning on the microcircuit for 1 ... 2 s after turning on the power. Damping circuits R16C14 and R17d5 prevent self-excitation of the DA1 chip. The device is powered by a network unit consisting of a step-down transformer T1 and a rectifier on diodes VD1-VD4. The alternating mains voltage of 230 V is supplied to the primary winding of the transformer through the current-limiting resistor R2, the thermal fuse FU2 and the closed contacts of the switch SA1. From the secondary winding, an alternating voltage of about 9 V is supplied to the bridge rectifier through a polymer self-resetting fuse FU3. Schottky diodes are used in the rectifier to reduce voltage and power losses. Capacitors C6, C7, C9, C10 shunting them prevent the so-called multiplicative background. The ripple of the rectified voltage is smoothed out by the capacitor C12. The device is not powered by a built-in chemical energy source, but there is an XS1 socket that can be connected to an external power source, such as a solar panel, a laptop USB port, or a rechargeable power source (for example, described by the author in the article "Portable battery power source" in "Radio", 2015, No. 10, pp. 36-38). With a supply voltage of 9 V, the device consumes a current of about 40 mA from such a source. The Schottky diode VD5 prevents damage to the DA1 chip if the polarity of the external power supply is reversed, the capacitor C2 protects this diode from damage by static electricity. Resettable fuse FU1 trips in case of overload. Most parts of the device are mounted on a fiberglass board with dimensions of 90x60 mm (Fig. 2). Installation - unilateral hinged. To prevent self-excitation of the DA1 microcircuit and the growth of the distortions it introduces, as well as the appearance of a background with a frequency of 100 Hz, the power and signal circuits of the device must be correctly routed (in particular, the electrical communication lines shown thickened in the diagram must be made by separate wires). The TDA7266L chip is installed on a ribbed duralumin heat sink with a cooling surface area (one side) of 48 cm2.
Variable resistor R4 - any type with a metal case, for example, SP3-4, SP3-9, SPO-1 with a resistance of 4,7 ... 22 kOhm (the less, the better). Resistor R2 - domestic R1-7-2 or imported non-flammable or discontinuous, the rest - small-sized any type of general use, for example, C1-14, MLT, RPM. Capacitor C1 - oxide imported non-polar, C5 and C12 - oxide polar, the first - with a capacity of 1000 ... 2200 microfarads, the second - 4700 ... 10000 microfarads. Capacitors C4, C8, C13-C15 - film, other non-polar capacitors - ceramic, for example, K10-17, K10-50, KM-5. Capacitor C13 is mounted as close as possible to pins 5 and 8 of the DA1 chip. Schottky diodes 1 N5819 (VD1-VD4) are replaceable by any of the series SR104, SB140, SB150, MBRS140T3, MBR150, and SHK65-45 - by any of the series 1N5822, SR306, SR360, SR504, MBRD350, SK24, SK35, MBRS 360T3, MBR350, MBR360 . The green LED RL30N-YG414S can be replaced with any general purpose LED, for example, from the KIPD66, L-63 series. Instead of the 2SC945 transistor, any low-power npn structure, for example, the KT3102 series, is suitable. In the design, a microcircuit can only work with the index "L". Resettable polymer fuses (FU1 and FU3) MF-R110, LP30-110, MF-S120 can be used. Thermal fuse FU2 - built into the step-down transformer. A step-down transformer is used ready-made (shielded with an overall power of 8 W from a portable Panasonic radio). Instead, you can use the unified TP-1202 or TP-114-6. For a homemade transformer, a W-shaped magnetic circuit with a central core area of \u5,2b\uXNUMXbXNUMX cm is suitable2. The primary winding (2250 turns) is wound with a wire with a diameter of 0,15 mm, the secondary (100 turns) with a diameter of 0,68 mm. Interwinding insulation - several layers of lavsan or fluoroplastic film. In the absence of a thermal fuse, a fusible link for a current of 0,25 A is included in the primary winding circuit. The transformer is installed in the rear part of the lantern housing, ventilation holes with a diameter of 3,5 mm are drilled in the side and rear walls opposite it. Mains power switch - available in the flashlight, fit HT-002A, OR-L, KCD-2011, MRC-101-6A, KCD1-101. The dynamic driver is an imported 5W broadband driver with an 8 ohm voice coil. The head diffuser is protected by a decorative metal grill used to protect computer fans with a diameter of 120 mm (Fig. 3). Assembly weight - 850 g.
Accurately made from serviceable parts, the device starts working immediately and does not require adjustment. Author: A. Butov
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