Unusual application of the KR142EN19A chip

Encyclopedia of radio electronics and electrical engineering / Application of microcircuits

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As you know, the KR142EN19A microcircuit is a precision analogue of a zener diode with adjustable stabilization voltage, therefore it is usually used in various power supplies. However, it is also capable of working in other amateur radio designs, which are described in the article.

The possibilities of using this microcircuit in slightly different modes, compared with the main purpose, are due to the fact that it includes such components as a reference voltage source and an operational amplifier with an output stage on a transistor. Its functional diagram is shown in fig. 1 [1], and the symbol and pinout of the conclusions - respectively in fig. 2a and 2b [2].

Fig.1. Functional diagram KR142EN19A

Fig.2. KR142EN19A: a) Symbol, b) Pinout

A diagram of the simplest amplifying stage that can be performed on the indicated microcircuit is shown in Fig. 3, and its transfer characteristic - in Fig. 4. If the load resistor R2 is selected with a relatively large resistance (a few kiloohms), the characteristic turns out to be flat due to the fact that the microcircuit nodes consume a current of about 1 mA. In the case of using a resistor with a resistance of less than a kiloohm, the characteristic will become steep and more linear.

Fig.3. Amplifying stage

Fig.4. Transfer characteristic of the amplifying stage

When the microcircuit operates in a linear mode, it can be used in a voltage stabilizer (its main purpose), a current stabilizer, various generators and amplifiers. In the non-linear mode, it performs the function of a comparator with a response voltage of about 2,5 V. Moreover, such a comparator has a stable response voltage determined by the reference voltage source.

A few words about the microcircuit itself. Unfortunately, one of its shortcomings, which limits the scope of application, is the small allowable dissipation power. So, with a stabilization voltage of 20 V, the maximum current should not exceed 20 mA. It is not difficult to eliminate this shortcoming by "powering" the microcircuit with the help of a transistor (Fig. 5). The main characteristics will be determined by the microcircuit, and the maximum current and power by the transistor. For the one indicated in the diagram, they are 4 A and 8 W, respectively. If there is a negative voltage on the body of the structure, it is permissible to mount the transistor directly on it.

Fig.5. Empowering the microcircuit with a transistor (VT1)

On fig. 6a shows a diagram of a low-power current stabilizer. It works like this. The load current flows through resistor R1. As soon as the voltage across the resistor exceeds 2,5 V, the current through the chip and resistor R3 will increase. The voltage at the load will decrease to a value at which the voltage at the control input of the microcircuit will be set to 2,5V.

Fig.6. a) Low-power current stabilizer, b) Stabilizer with a transistor current "amplifier"

The stabilized current is set by the resistor R1, the resistance of which is determined by the formula
R1 \u2,5d XNUMX / In,
where 2,5 is the voltage drop across the resistor, V; In - current through the load, A, which should not exceed 0,1 A. Knowing the supply voltage Upit and the specified maximum load current, calculate the resistance of the resistor R3:
R3 \u2,5d (Upit - XNUMX) / In.

Moreover, the supply voltage should be chosen so that the required voltage is provided at the load, therefore, such a device is recommended to be used, for example, for charging batteries with a capacity of up to 0,75 Ah.

This formula is needed to determine the minimum resistance of the resistor R3 for the case when Rн = 0 (for example, short circuit). Then stabilization will be, but it is not needed.

Another stabilizer (Fig. 6, b) with a transistor current "amplifier" has much greater opportunities. Here, the resistance of the resistor R1 is determined according to the above formula, and its power is based on the flowing maximum load current, which can reach 4 A with the transistor indicated in the diagram.

The high steepness and satisfactory linearity of the transfer characteristic of the microcircuit makes it possible to make an AF amplifier on its basis, the load of which can be a dynamic head with a resistance of at least 50 ohms (Fig. 7, a). Although it is not very economical, it is very easy to manufacture and provides an output power of up to 150 mW, sufficient for scoring a small room.

Fig.7. a) AF amplifier, b) Preamplifier

In another amplifier (Fig. 7b), which has a gain of about 100 times (40 dB) and can become a preliminary one, resistor R4 is used as a load. The gain here is regulated by a tuned resistor R1, and by selecting the resistor R3 in both amplifiers, the optimal operating point is set, which provides the maximum undistorted output voltage.

The high gain of the KR142EN19A chip allows you to assemble various generators on it. As an example, Fig. 8a shows a circuit of an RC oscillator whose output signal frequency is close to 1000 Hz - it is set by the phase-shifting chain C1R3C2R4C4. The R1R2C3R5 feedback circuit provides automatic setting of the DC mode.

On fig. 8b shows a diagram of another AF generator and at the same time an acoustic signaling device. The frequency-setting element in it is a piezoelectric BQ1 type ZP-1 (another similar one is suitable). Negative voltage feedback through resistor R1 provides DC mode. Generation occurs at the resonant frequency of the piezoelectric emitter.

Fig.8. a) RC generator, b) AF generator and at the same time an acoustic signaling device

It is permissible to perform a sinusoidal-to-rectangular signal converter according to the circuit shown in fig. 9, a. Its sensitivity is set by a tuning resistor R1 from a few millivolts to 2,5 V. The converter is fed with a voltage of 4 ... 30 V, while the amplitude of the output signal can be obtained from 1 V to almost half the supply voltage, and a signal with a frequency of up to 50 kHz can be applied to the input .

Fig.9. a) A sinusoidal-to-rectangular signal converter, b) A multivibrator on two microcircuits

On two microcircuits, it will be possible to build a multivibrator (Fig. 9, b), at the output of which a rectangular signal is formed. The oscillation frequency is determined by the capacitance of the capacitor C1, the values ​​​​of the resistors R3, R4 and can lie in a wide range - from fractions of a hertz to tens of kilohertz.

Of course, the possibilities of "non-standard" use of the KR142EN19A chip are not limited to the examples given.

Literature

1. Yanushenko E. Chip KR142EN19.- Radio, 1994, No. 4, p. 45, 46.
2. Nechaev I. Voltage stabilizers with a KR142EN19A microcircuit. - Radio, 2000, No. 6, p. 57, 58.

Author: I. Nechaev, Kursk; Publication: radioradar.net

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