Active speaker with combined power supply. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Speakers

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Due to the small size of portable digital devices (such as tablet computers, laptops, portable LCD TVs, navigators, etc.), the sound quality of their built-in acoustics leaves much to be desired. For loud and good enough sound in stationary conditions, they are usually connected to external power amplifiers AF (UMZCH) with acoustic systems (AS), active speakers (with built-in UMZCH). The latter can often be powered only from a 230 V network. In order to not be satisfied with the sound of the “tweeters” built into multimedia devices in the event of a power outage or lack of power, you can use the active two-way speaker system described below with combined power supply.

The scheme of the proposed AS is shown in fig. 1. Compared to designs [1, 2], it is more functional, it can operate both from the mains power supply in it and from the built-in G1 lithium battery. Its recharging occurs automatically when the device is connected to the network. In addition, the speaker is equipped with an XS2 USB socket, to which you can connect various “pocket” multimedia sound reproducing devices for powering and recharging batteries, while, unlike [1], powering external devices and operating the UMZCH built into the speaker are possible simultaneously.

Rice. 1. AC diagram (click to enlarge)

The input signal enters the XP1 plug, passes through the R2R3 adder, L1C11R14 RLC filter, C14 isolation capacitor and then to the input of the TDA7052A (DA3) microcircuit, which is a AF bridge power amplifier with unipolar power supply and electronic volume control. The microcircuit can operate at a supply voltage of 4,5 ... 18 V, its maximum output power is 1,1 W, the maximum power dissipation is 1,25 W. The volume is controlled by a variable resistor R16. Damping circuits R23C25, R25C26 and resistor R26 prevent possible self-excitation of the microcircuit at ultrasonic frequencies. A BA1 dynamic head and a BA2 piezoceramic horn sounder, designed to reproduce high sound frequencies, are connected to the amplifier output. With a supply voltage of 6,3 V, the maximum signal amplitude at the BA1 head is about 6,5 V.

It is powered by UMZCH with a voltage of 5,3 or 6,3 V through an LC filter L4C23C20. The C2R7R10 circuit included in the UMZCH common wire break prevents damage to the device to which the amplifier input is connected if it is powered from the XS2 socket and its negative power wire is not the common wire of the headphone jack or external UMZCH. You can connect stereo headphones or another UMZCH to the XS1 jack.

The device uses a standard lithium-ion battery with a capacity of 2700 mAh from a mobile phone. Since the nominal voltage of such batteries is usually only 3,7 V, in order to get a large output power, the UMZCH is connected to the battery through a boost converter assembled on the MC34063AP1 (DA1) chip. The voltage of the battery G1 is supplied to its input through the closed contacts of the switch SA1 and the contacts K1.1 of the relay K1. The output voltage of the converter - about 6,3 V - is set by resistors R18, R13. On the transistor VT2, which has a small saturation voltage, an external electronic key is assembled. The maximum load current connected to the output of the voltage converter can reach 0,5 A with a voltage at the DA1 input of at least 3,3 V. The blue LED HL2 glows on the power supply of the UMZCH from the built-in battery.

At a battery voltage of 3,3 V (almost empty battery), the efficiency of the converter is 63%, and at 4,2 V (fully charged battery) it is about 74%. The time of continuous operation of the speaker from the battery at medium volume (output power is about 0,2 W) is approximately 15 hours.

The mains voltage of 230 V is supplied to the primary winding of the step-down transformer T1 through the protective resistor R1. From the secondary winding, an alternating voltage of about 10 V is supplied through a polymer self-healing fuse FU1 to the rectifier bridge VD3. Capacitor C10 smooths out the ripple of the rectified voltage.

A linear voltage regulator is assembled on the KIA78R05PI (DA2) integrated circuit. A distinctive feature of the KIA78RxxPI series microcircuits is their operability at a voltage between the input and output of only 0,5 V at a load current of 1 A (conventional stabilizers, for example, the 7805 series, KR142EN5, require that the input voltage be 2 ... 3 V more, than output). Schottky diode VD5 increases the output voltage of the stabilizer by about 0,3 V.

When the device is connected to the network, the green LED HL3 starts to shine, relay K1 is activated, and its contacts K1.1 disconnect the battery G1 from the voltage converter, and K1.2 switch the UMZCH power circuit from the output of the converter to the output of the linear stabilizer on the DA2 chip. Since the output voltage of the latter is 1 V less than the switching boost converter, the loudspeaker sound volume is automatically reduced when switching to mains power. This is done because the operation of this speaker from the network is not its main function - if there is a network, it is usually possible to connect sound-reproducing devices to stationary UMZCH.

Battery G1 is charged from a linear stabilizer through a current-limiting resistor R4 and diode VD1. When the battery terminals reach a voltage of about 4,25 V, the built-in controller disconnects it from the charging circuit, the germanium transistor VT1 closes, the red LED HL1 goes out.

Most parts of the speakers are mounted on three mounting plates made of fiberglass, mounting - double-sided hinged. The dimensions of the UMZCH board (Fig. 2) are 60x55, the step-up voltage converter (Fig. 3) is 70x68, and the linear power supply (Fig. 4) is 80x55 mm. The modular design of the device nodes greatly facilitates the assembly, layout and subsequent upgrade of the speakers.

Rice. 2. UMZCH board

Rice. 3. Boost Converter Board

Rice. 4. Linear power supply

Any small-sized fixed resistors are applicable in the device, with the exception of the resistor R1, it is desirable that it be non-flammable or discontinuous. Variable resistor R16 - SP3-4, SP3-33-32. To prevent damage to the DA3 chip by electrostatic electricity, the metal shield and the bead of this resistor must be connected to a common wire. Capacitor C2 - non-polar oxide or ceramic, C14, C25, C26 - small-sized film. The remaining non-polar capacitors are ceramic K10-17, K10-50 or analogues, including those intended for surface mounting. Capacitors C8 and C20 must be soldered as close as possible to the pins of the respective microcircuits, and C27 - directly to the contacts of the XS2 USB socket. The remaining capacitors are oxide K50-68, K53-19 or analogues.

We can replace the 1N4933GP (VD2) diode with any silicon one with a forward current of at least the working relay K1 and a reverse voltage of at least 30 V, the GBL06 (VD3) diode bridge - with any other of D2SB, RC201 -RC207, RS201 - RS207, BR305-BR310. Instead of a Schottky diode SS12, for example, SS14, 1N5817, 1 N5818, SB120, SB130 are suitable, instead of SR360 (VD4) - SR504-SR506, SR306, SR360, 1N5822. LEDs - any general purpose continuous glow without built-in resistors. Possible replacement of the imported germanium transistor GT2 307 (VT1) - domestic from the series MP25, MP26, MP39-MP42, transistor FZT851 (VT2) - KZT851. Transistor VT2 is installed on a heat sink with a cooling surface area of ​​​​4 cm². It is attached to the heat sink by first lowering the flange with tweezers into the molten solder. In the absence of such transistors, 2SC3746-2SC3748 can be used.

The MC34063AP1 (DA1) chip is interchangeable with MC34063AP, MC33063AP1, KA34063A IP33063N, etc., however, for ease of installation, it is desirable to use a chip in a DIP-8 package. Instead of the KIAT8R05PI (DA2) chip, any of the 78R05 series in a four-pin TO-220 package, such as KA78R05, will do. It is mounted on a duralumin heat sink with a cooling surface area (one side) of 60 cm². A duralumin U-shaped heat sink with a cooling surface area of ​​​​7052 cm is glued to the TDA3A (DA2,5) chip case². A possible replacement for the microcircuit is TDA7052B, other microcircuits of this series are not suitable.

Each of the chokes L1, L5 is several turns of a stranded mounting wire folded in half, wound on a ring magnetic circuit with a diameter of 7 ... 20 mm made of permalloy or low-frequency ferrite (magnetic circuits from electronic ballast transformers of compact fluorescent lamps are also suitable). Inductors L2-L4 - industrial production with H-shaped ferrite magnetic cores (the lower the resistance of their windings, the better). The inductance of the first of them is 100 ... 400 μH, the others - the more the better.

Step-down transformer T1 - modified TS-10-3M1 (75 turns are unwound from its secondary winding) or TP-114-2. For a home-made transformer, a W-shaped magnetic circuit with a central core area of ​​​​4,3 ... 4,5 cm is suitable². The primary winding should contain 2670 turns of winding wire with a diameter of 0,13 ... 0,15 mm, the secondary - 105 turns of wire with a diameter of 0,62 mm. The plates of the magnetic circuit are assembled in an overlap.

Relay K1 - DS2Y-S-DC5V (Matsushita) with two groups of switching contacts (maximum switching power - 60 W). The resistance of the relay winding is about 150 Ohm, the nominal voltage and current are 5 V and 40 mA, respectively. Power switch SA1 - KCD1-101 or KCD-2011, MRC-101-6A. Dynamic head BA1 - E1-77-030 from an old kinescope TV, any suitable broadband power from 0,5 W with a voice coil of 8 ohms will do. Piezoceramic head - unknown model, also from a kinescope TV. Replace the MF-S150 polymer self-resetting fuse with MF-R160, LP30-160. Lithium-ion battery with built-in controller - from a mobile phone (the larger its capacity, the better). Parallel connection of several batteries is allowed. Do not connect such batteries in series.

The body of the device with dimensions of 103x98x125 mm is glued from polystyrene. The front wall at the installation site of the BA1 head is perforated with holes with a diameter of 1 mm, 225 ventilation holes with a diameter of 3 mm are drilled in the rear wall. The BA2 head is mounted on the outside of the housing. A view of the layout of nodes is shown in fig. 5, the appearance of the speakers - in fig. 6.

Rice. 5. View of the layout of nodes 

Rice. 6. Speaker appearance

The quenching resistor R8 in the winding circuit of the relay K1 is selected in such a way that its contacts switch reliably when the device is connected to the network. By selecting resistors R15, R17, the desired interval of volume levels is set, regulated by a variable resistor R16 when the structure is powered from the mains. If the BA1 head is not capable of reproducing higher audio frequencies, the BA2 head connection can be in any phasing.

Literature

1. Butov A. Small active speakers - USB charger. - Radio, 2014, No. 6, p. 14, 15.
2. Butov A. Completion of the computer speaker system SP-P110. - Radio, 2015, No. 8, p. 48, 49.

Author: A. Butov

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