The use of the K548UN1 chip. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The use of the K548UN1 chip. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Preamplifiers

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The integrated dual preamplifier K548UN1 is, as you know, a multi-purpose microcircuit. Compared to general-purpose operational amplifiers, the K548UN1 amplifier has a significantly lower noise level, internal correction that ensures stable operation of devices based on it at deep environmental feedback, is not critical to instability and ripple of the supply voltage, which, by the way, can be in the range from 9 to 30 C. The identity of the parameters of completely independent channels of the microcircuit allows it to be used in high-quality stereo paths. Below are examples of building some common devices based on this chip.

Non-inverting linear amplifier obtained when the microcircuit is turned on, as shown in Fig. 1 (numbers of outputs of the second channel similar in purpose are indicated in brackets). The maximum input voltage of the device is approximately 0,3V. The DC current gain is K=1+R3/R1.

The use of the K548UN1 chip
Fig. 1

The maximum resistance of the resistor R1 is determined with such an inclusion by the base current I_б transistor V2 (0,5 μA) of the differential stage of the microcircuit: the current flowing through the resistor must be at least. 10 times the base current. Considering that the voltage on the basis of the transistor V2 should be the same as on the basis of the transistor V4 of this stage (and there it is 1.3 V), the maximum resistance of the resistor R1 is calculated by the formula R1 = 1,3 / 10I_б, from which it follows that it should be no more than 260 kOhm.

The resistance of the resistor R3, depending on the supply voltage, is determined from the relation R3=(U_Pete/2,6-1)R1. Since the smallest IC supply voltage is 9V, the minimum DC gain is approximately 3,5. Its maximum value (at a supply voltage of 30 V) is about 12.

Gain of a non-inverting AC amplifier K_u=1+R3/R2. With a supply voltage of 25 V, in the frequency range of 20 ... 20 Hz, it can be made any within 000 ... 10.

The capacitance of capacitor C4 (it is connected in parallel to the correction capacitor of the microcircuit) depends on the required gain and operating frequency band and for the unity gain mode is 39 ... 47 pF. Capacitor C1, which decouples the microcircuit from previous DC circuits, can have a capacitance of 0,2 μF or more, capacitor C2, which eliminates parasitic coupling in the power circuit, can be 0,1 ... 0,2 μF.

Noise if needed of the non-inverting amplifying stage can be reduced (by about 1,4 times) using not both, but only one of the transistors of the differential stage. In this case, pin 2(13) of the microcircuit is connected to a common wire, and the RIC3R2R3 divider is connected to pin 3(12). The maximum resistance of resistor R1 is determined from the condition that the current flowing through it is at least 5 times higher than the emitter current I_э transistor V4 (100 µA): R1=0,65/5I_э (0,65 - voltage - in volts - at the emitters of transistors V2, V4). With the specified ratio of currents, the resistance of this resistor should be no more than 1,3 kOhm. As for the resistor R3, its resistance when using one transistor at the input is calculated by the formula
R3=(U_Pete/1,3-1)R1.

Inverting linear amplifier (Fig. 2) avoids clipping of the input signal and is stable without additional correction if the DC gain is equal to or greater than 10. The slew rate of the output signal of the amplifier in this connection is at least 4V/µs (in the absence of an external correction capacitor). The DC gain is determined by the ratio of the resistances of the resistors of the OOS circuit R3 and R2 (K = R3 / R2), for the variable - resistors R3 and RI (K_u=R3/R1).

The use of the K548UN1 chip
Fig. 2

What has been said above regarding the choice of the resistance of the resistors R1 - R3, the capacitance of the capacitor C4, as well as the capacitors at the input of the amplifier (C1) and in the power circuit C2, fully applies to the case of using the microcircuit as an inverting amplifier.

It should be noted that with this inclusion, the microcircuits are used for. noise reduction with only one transistor of the differential stage is impossible.

Reel-to-Reel Recorder Playback Amplifier can be assembled according to the scheme shown in Fig. 3. When using a universal magnetic head 6D24N.1.U (from Mayak-203) and a tape speed of 19,05 cm / s, the amplifier has the following technical characteristics:

Operating frequency range, Hz. . . . . . . . 40...18000

Rated voltage, mV, at a frequency of 1 kHz;

input . . . . . . . . . . . . . . . . . . one

holiday . . . . . . . . . . . . . . . . 250

Harmonic distortion coefficient at a frequency of 1 kHz, %, no more than . . . . . 0,2

Relative noise level in the playback channel, dB, not more than . . . -53

The use of the K548UN1 chip
Fig. 3

As can be seen from fig. 3, the K548UN1 chip is connected in this case according to the non-inverting amplifier circuit using both transistors of the differential stage. The required frequency response correction is provided by the frequency-dependent R4R5C5 circuit. The correction time constant - 75 µs - is set by the parameters of the resistor R4 and capacitor C5. To correct the frequency response in the higher frequencies of the operating frequency range, capacitor C1 is used, which, together with the inductance of the magnetic head, forms an oscillatory circuit tuned to a frequency of 18 ... 20 kHz.

microphone amplifier - another area of application of the microcircuit, where a low level of intrinsic noise is important. Such an amplifier should, as a rule, have a linear frequency response in the nominal frequency range and have a sufficiently high overload capacity.

The device, assembled according to the scheme in Fig. 4, has the following specifications:

Nominal frequency range, Hz, with frequency response unevenness not more than 1 dB. . . . . . 20...20000

Rated voltage, mV:

input . . . . . . . . . . . . . . . . . . . . . one

holiday . . . . . . . . . . . . . . . . . . . .250

Maximum input voltage, mV. . . . . . . thirty

Input resistance, kOhm. . . . . . . . . . . 4,7

Signal-to-noise ratio in the nominal frequency range, dB, not less. . . . . . . . . . 60

Harmonic coefficient, %, at output voltage 5 V . . . . . . . . . . . . . .0.2

The use of the K548UN1 chip
Fig. 4

The microcircuit in this case is connected according to the non-inverting amplifier circuit using one differential stage transistor, which reduces the noise level.

Tone blocks high-quality stereo bass amplifiers can be made but the circuits shown in fig. 5 and 6. In the first of them (Fig. 5), a passive bridge regulator is used to change the frequency response. and the microcircuit serves to compensate for the losses introduced by it at medium frequencies, in the second (Fig. 6) the bridge regulator is included in the OOS circuit that surrounds the microcircuit (active regulator).

The use of the K548UN1 chip
Fig. 5

The use of the K548UN1 chip
Fig. 6

The range of tone control at frequencies of 40 and 16 Hz of the first device is +/-000 dB, the second is at least +/- 15 dB. The transfer coefficient of both devices when the resistor sliders are set to the middle position is 12, the frequency response unevenness in this position of the sliders depends on the deviation of the parameters of the elements from those indicated in the diagram and, if this deviation does not exceed +/-1%, is approximately +/-5 dB V frequency range 1...20 20 Hz. The advantage of an active tone control is the possibility of using variable resistors of group A (in the regulator according to the diagram in Fig. 000, they should be of group B). For normal operation of both devices, the output impedance of the previous stage must be small (no more than 5 kOhm).

The examples considered, of course, do not exhaust the possibilities of using the K548UN1 chip in sound recording and playback equipment. With no less success, it can be used in mixing consoles, active filters, multi-band tone controls, etc.

Authors: Yu. Burmistrov, A. Shatrov; Publication: cxem.net

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