Possibilities of automotive ULF on the TDA2030 chip. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Automotive power amplifiers

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The TDA2030A low-frequency amplifier chip from ST Microelectronics enjoys well-deserved popularity among radio amateurs. It has high electrical characteristics and low cost, which makes it possible to assemble high-quality ULF with a power of up to 18 W at minimal cost. However, not everyone knows about its "hidden advantages": it turns out that a number of other useful devices can be assembled on this IC.

The TDA2030A chip is an 18W Hi-Fi Class AB power amplifier or VLF driver up to 35W (with powerful external transistors). It provides a large output current, low harmonic and intermodulation distortion, a wide bandwidth of the amplified signal, a very low level of intrinsic noise, built-in output short-circuit protection, an automatic power dissipation limiting system that keeps the operating point of the IC output transistors in a safe area. The built-in thermal protection ensures that the IC is turned off when the crystal is heated above 145°C. The microcircuit is made in a Pentawatt package and has 5 pins. First, let's briefly consider several schemes for the standard use of ICs - low-frequency amplifiers. A typical TDA2030A switching circuit is shown in fig. one.

The microcircuit is connected according to the scheme of a non-inverting amplifier. The gain is determined by the ratio of the resistances of the resistors R2 and R3 that form the OOS circuit. It is calculated by the formula Gv=1+R3/R2 and can be easily changed by selecting the resistance of one of the resistors. This is usually done with a resistor R2. As can be seen from the formula, a decrease in the resistance of this resistor will cause an increase in the gain (sensitivity) of the ULF. The capacitance of the capacitor C2 is chosen based on the fact that its capacitance Xc=1/2?fC at the lowest operating frequency is at least 2 times less than R5. In this case, at a frequency of 40 Hz Xs₂=1/6,28*40*47*10^-6=85 Ohm. The input resistance is determined by the resistor R1. As VD1, VD2, you can use any silicon diodes with current I_ETC0,5 ... 1 A and U_OBR more than 100 V, for example KD209, KD226, 1N4007. The circuit for switching on the IC in the case of using a unipolar power supply is shown in fig. 2.

Divider R1R2 and resistor R3 form a bias circuit to obtain at the output of the IC (pin 4) a voltage equal to half the supply voltage. This is necessary for symmetrical amplification of both half-waves of the input signal. The parameters of this circuit at Vs=+36 V correspond to the parameters of the circuit shown in fig. 1, when powered from a source of ±18 V. An example of using a microcircuit as a driver for ULF with powerful external transistors is shown in fig. 3.

At Vs = ±18 V at a load of 4 ohms, the amplifier develops a power of 35 watts. Resistors R3 and R4 are included in the IC power circuit, the voltage drop across which is opening for transistors VT1 and VT2, respectively. With a low output power (input voltage), the current consumed by the IC is small, and the voltage drop across resistors R3 and R4 is not enough to open transistors VT1 and VT2. The internal transistors of the microcircuit work. As the input voltage increases, the output power and the current consumed by the IC increase. When it reaches a value of 0,3 ... 0,4 A, the voltage drop across resistors R3 and R4 will be 0,45 ... 0,6 V. Transistors VT1 and VT2 will start to open, while they will be connected in parallel to the internal transistors of the IC. The current supplied to the load will increase, and the output power will increase accordingly. As VT1 and VT2, you can use any pair of complementary transistors of the appropriate power, for example, KT818, KT819. The bridge circuit for switching on the IC is shown in fig. four.

The signal from the output of the IC DA1 is fed through the divider R6R8 to the inverting input DA2, which ensures the operation of the microcircuits in antiphase. In this case, the voltage on the load increases, and, as a result, the output power increases. At Vs=±16 V at a load of 4 ohms, the output power reaches 32 watts. For fans of two-, three-band ULF, this IC is an ideal option, because it is possible to assemble active low-pass and high-pass filters directly on it. The scheme of a three-band ULF is shown in fig. 5.

The low-frequency channel (LF) is made according to the scheme with powerful output transistors. At the input of IC DA1, a low-pass filter R3C4, R4C5 is included, and the first link of the low-pass filter R3C4 is included in the amplifier circuit. Such a circuit design allows simple means (without increasing the number of links) to obtain a sufficiently high slope of the filter frequency response. The mid-frequency (MF) and high-frequency (HF) channels of the amplifier are assembled according to a typical circuit on ICs DA2 and DA3, respectively. At the input of the midrange channel, high-pass filter C12R13, C13R14 and low-pass filter R11C14, R12C15 are included, which together provide a bandwidth of 300 ... 5000 Hz. The RF channel filter is assembled on the elements C20R19, C21R20. The cutoff frequency of each link of the low-pass filter or high-pass filter can be calculated by the formula fCP \u160d 2030 / RC, where the frequency f is expressed in hertz, R - in kiloohms, C - in microfarads. The examples given do not exhaust the possibilities of using the IMC TDA3,4A as bass amplifiers. So, for example, instead of a bipolar power supply for a microcircuit (Fig. 1), you can use a unipolar power supply. To do this, the minus of the power supply should be grounded, and a bias should be applied to the non-inverting (pin 2) input, as shown in Fig. 1 (elements R3-R2 and C4). Finally, at the output of the IC between pin XNUMX and the load, it is necessary to turn on the electrolytic capacitor, and exclude blocking capacitors along the -Vs circuit from the circuit.

Consider other possible uses for this chip. The TDA2030A IC is nothing more than an operational amplifier with a powerful output stage and very good performance. Based on this, several schemes for its non-standard inclusion were designed and tested. Some of the circuits were tested "live", on a breadboard, some were simulated in the Electronic Workbench program.

Powerful signal repeater

The signal at the output of the device fig. 6 repeats the shape and amplitude of the input, but has more power, i.e. the circuit can operate on a low-resistance load. The repeater can be used, for example, to amplify power supplies, increase the output power of low-frequency generators (so that loudspeaker heads or acoustic systems can be directly tested). The operating frequency band of the repeater is linear from DC to 0,5 ... 1 MHz, which is more than enough for a low-frequency generator.

Boosting power supplies

The microcircuit is included as a signal repeater, the output voltage (pin 4) is equal to the input (pin 1), and the output current can reach 3,5 A. Thanks to the built-in protection, the circuit is not afraid of short circuits in the load. The stability of the output voltage is determined by the stability of the reference, i.e. zener diode VD1 fig. 7 and integral stabilizer DA1 fig. 8. Naturally, according to the diagrams shown in fig. 7 and fig. 8, you can assemble stabilizers for a different voltage, you just need to take into account that the total (total) power dissipated by the microcircuit should not exceed 20 watts. For example, you need to build a stabilizer for 12 V and a current of 3 A. There is a ready-made power source (transformer, rectifier and filter capacitor) that produces U_FE= 22 V at the required load current. Then a voltage drop occurs on the microcircuit U_IC= U_FE - OR_EXIT = 22 V -12 V = 10V, and at a load current of 3 A, the dissipated power will reach the value P_RAS= U_IC*I_Н \u10d 3V * 30A \u2030d XNUMX W, which exceeds the maximum allowable value for TDAXNUMXA.

The maximum allowable voltage drop on the IC can be calculated using the formula:

U_IC= P_RAS.MAX / I_Н

In our example U_IC\u20d 3 W / 6,6 A \uXNUMXd XNUMX V, therefore the maximum voltage of the rectifier should be U_FE = U_EXIT+U_IC \u12d 6,6V + 18,6 V \uXNUMXd XNUMX V. In the transformer, the number of turns of the secondary winding will have to be reduced.

Ballast resistor resistance R1 in the circuit shown in fig. 7 can be calculated using the formula:

R1 = (U_FE - OR_ST) / I_ST,

where U_ST и I_ST - respectively, the voltage and current of stabilization of the zener diode.

The stabilization current limits can be found in the reference book; in practice, for low-power zener diodes, it is chosen within 7 ... 15 mA (usually 10 mA). If the current in the above formula is expressed in milliamps, then the resistance value will be obtained in kiloohms.

Simple laboratory power supply

The electrical circuit of the power supply is shown in fig. 9. By changing the voltage at the input of the IC using the potentiometer R1, a continuously adjustable output voltage is obtained.

The maximum current given by the microcircuit, depends on the output voltage and is limited by the same maximum power dissipation on the IC.

It can be calculated using the formula:

I_MAX = P_RAS.MAX /U_IC

For example, if the output voltage is U_EXIT \u6d XNUMX V, a voltage drop occurs on the microcircuit U_IC = U_FE - OR_EXIT \u36d 6 V - 30 V \uXNUMXd XNUMX V, therefore, the maximum current will be I_MAX = 20 W / 30 V = 0,66 A. At U_EXIT = 30 V, the maximum current can reach a maximum of 3,5 A, since the voltage drop across the IC is negligible (6 V).

Stabilized laboratory power supply

The electrical circuit of the power supply is shown in fig. 10. The source of a stabilized reference voltage - the DA1 chip - is powered by a 15 V parametric stabilizer assembled on a VD1 zener diode and a resistor R1. If the IC DA1 is powered directly from a +36 V source, it may fail (the maximum input voltage for the IC 7805 is 35 V). The DA2 IC is connected according to the non-inverting amplifier circuit, the gain of which is defined as 1 + R4 / R2 and equal to 6. Therefore, the output voltage when adjusted with the R3 potentiometer can take on a value from almost zero to 5 V * 6 = 30 V. As for the maximum output current , for this circuit, all of the above is true for a simple laboratory power supply (Fig. 9). If a lower regulated output voltage is expected (e.g. 0 to 20 V at U_FE = 24 V), elements VD1, C1 can be excluded from the circuit, and a jumper can be installed instead of R1. If necessary, the maximum output voltage can be changed by selecting the resistance of the resistor R2 or R4.

Adjustable current source

The electrical circuit of the stabilizer is shown in fig. 11. At the inverting input of the IC DA2 (pin 2), due to the presence of the OOS through the load resistance, the voltage U is maintained_BX. Under the influence of this voltage, a current I flows through the load_Н = U_BX /R4. As can be seen from the formula, the load current does not depend on the load resistance (of course, up to certain limits, due to the final supply voltage of the IC). Therefore, changing U_BX from zero to 5 V using the potentiometer R1, with a fixed value of resistance R4=10 Ohm, you can adjust the current through the load within 0...0,5 A. This device can be used to charge batteries and galvanic cells. The charging current is stable throughout the entire charging cycle and does not depend on the degree of discharge of the battery or on the instability of the mains.

The maximum charging current, set using the potentiometer R1, can be changed by increasing or decreasing the resistance of the resistor R4. For example, at R4=20 Ohm it has a value of 250 mA, and at R4=2 Ohm it reaches 2,5 A (see formula above). For this circuit, restrictions on the maximum output current are valid, as for voltage stabilizer circuits. Another application of a powerful current stabilizer is the measurement of low resistances with a voltmeter on a linear scale. Indeed, if you set the current value, for example, 1 A, then by connecting a resistor with a resistance of 3 ohms to the circuit, according to Ohm's law, we get the voltage drop across it U = l * R = l A * 3 ohms = 3 V, and by connecting, say, resistor with a resistance of 7,5 ohms, we get a voltage drop of 7,5 V. Of course, only powerful low-resistance resistors can be measured at this current (3 V per 1 A is 3 W, 7,5 V * 1 A \u7,5d XNUMX W) , however, you can reduce the measured current and use a voltmeter with a lower measurement limit.

Powerful square wave generator

Schemes of a powerful generator of rectangular pulses are shown in fig. 12 (with bipolar supply) and fig. 13 (with single supply). The circuits can be used, for example, in burglar alarm devices. The microcircuit is included as a Schmitt trigger, and the whole circuit is a classic relaxation RC oscillator. Consider the operation of the circuit shown in Fig. 12. Suppose, at the moment of power-up, the output signal of the IC goes to the level of positive saturation (U_EXIT = +U_FE). Capacitor C1 starts charging through resistor R3 with time constant Cl R3. When the voltage on C1 reaches half the voltage of the positive power supply (+U_FE/ 2), IC DA1 switches to a state of negative saturation (U_EXIT =-U_FE). Capacitor C1 will start to discharge through resistor R3 with the same time constant Cl R3 to voltage (-U_FE / 2) when the IC switches back to positive saturation. The cycle will be repeated with a period of 2,2C1R3, regardless of the voltage of the power supply.

Pulse repetition rate can be calculated using the formula:

f=l/2,2*R3Cl.

If the resistance is expressed in kiloohms, and the capacitance in microfarads, then we get the frequency in kilohertz.

Powerful low frequency sine wave generator

The electrical circuit of a powerful low-frequency generator of sinusoidal oscillations is shown in fig. 14. The generator is assembled according to the Wien bridge scheme, formed by elements DA1 and C1, R2, C2, R4, providing the necessary phase shift in the POS circuit. The voltage gain of the IC at the same values ​​of Cl, C2 and R2, R4 must be exactly equal to 3. At a lower value of Ku, the oscillations are damped, at a higher value, the distortion of the output signal increases sharply. The voltage gain is determined by the resistance of the filaments of lamps ELI, EL2 and resistors Rl, R3 and is equal to Ky = R3 / Rl + R_EL1,2. Lamps ELI, EL2 work as elements with variable resistance in the OOS circuit. With an increase in the output voltage, the resistance of the filaments of the lamps increases due to heating, which causes a decrease in the gain DA1. Thus, the amplitude of the output signal of the generator is stabilized, and the distortion of the sinusoidal waveform is minimized. A minimum of distortion at the maximum possible amplitude of the output signal is achieved using a tuning resistor R1. To eliminate the influence of the load on the frequency and amplitude of the output signal, the R5C3 circuit is included at the generator output.

Frequency of generated oscillations can be determined by the formula:

f=1/2piRC. The generator can be used, for example, when repairing and testing loudspeaker heads or acoustic systems.

In conclusion, it should be noted that the microcircuit must be installed on a radiator with a cooled surface area of ​​at least 200 cm². When wiring the printed circuit board for low-frequency amplifiers, it is necessary to ensure that the "ground" buses for the input signal, as well as the power supply and the output signal, are connected from different sides (the conductors to these terminals should not be a continuation of each other, but connected together in the form of a "star") "). This is necessary to minimize AC hum and eliminate possible self-excitation of the amplifier at output power close to maximum.

According to the materials of the magazine "Radioamator"

Publication: cxem.net

See other articles Section Automotive power amplifiers.

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