Microcircuit voltage stabilizers of wide application. Reference data

Encyclopedia of radio electronics and electrical engineering / Reference materials

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One of the important components of electronic equipment is the voltage regulator in the power supply. More recently, such nodes were built on zener diodes and transistors. The total number of stabilizer elements was quite significant, especially if it required the functions of regulating the output voltage, protecting against overload and output short circuit, limiting the output current at a given level.

With the advent of specialized microcircuits, the situation has changed. The manufactured microcircuit voltage stabilizers are capable of operating within a wide range of output voltage and current, often have a built-in protection system against overcurrent and overheating - as soon as the temperature of the microcircuit crystal exceeds the permissible value, the output current is limited.

At present, the range of domestic and foreign voltage stabilizer microcircuits is so wide that it has become quite difficult to navigate it. The tables below are intended to facilitate the preliminary selection of a microcircuit stabilizer for a particular electronic device.

In table. 1 presents a list of the most common three-pin microcircuits of linear voltage stabilizers on the domestic market for a fixed output voltage and their main parameters; in fig. 1 shows a simplified view of the devices, as well as their pinout. The table includes only stabilizers with an output voltage in the range of 5 ... 27 V - the vast majority of cases of amateur radio practice fit into this interval. The design of foreign devices may differ from that shown in Fig. 1.

It should be borne in mind that information about the power dissipated during the operation of a microcircuit with a heat sink is usually not indicated in the instrument passports, therefore, in Table. 1 and 2 give some of its average values ​​obtained from the graphs available in the documentation. We also note that microcircuits of the same series, but for different voltage values, may differ in power dissipation.

A number of microchips manufactured in near and far abroad have markings that do not correspond to the Russian standardized system. So, before the designation of the stabilizers of groups 78, 79, 78L, 79L, 78M, 79M, listed in the table, in fact, there may be one or two letters encoding, as a rule, the manufacturer. Behind the designations indicated in the table, there may also be letters and numbers indicating certain design or operational features of the microcircuit.

More detailed information about some series of domestic microcircuit stabilizers is placed in [1-5], and on foreign ones - in [6,7].

Some types of domestic stabilizers have an original, well-established digital pin numbering (it is shown in brackets in Fig. 1). This happened because initially the microcircuits of these series were produced in "chip" packages with a standardized pin numbering. After the production was established in "transistor" cases, the pin numbering was preserved.

note 1: An experimental batch was produced with a pinout corresponding to fig. 1a.
note 2: They also produce varieties for load current up to 1 A.

A typical circuit for switching on microcircuit stabilizers for a fixed output voltage is shown in fig. 2, a and b. For all microcircuits, the capacitance of the input capacitor C1 must be at least 2,2 μF for ceramic or tantalum oxide capacitors and at least 10 μF for aluminum oxide capacitors, and the output capacitor C2 must be at least 1 and 10 μF, respectively. Some microcircuits allow smaller capacitance, but the indicated values ​​\u70b\u6bguarantee stable operation of any stabilizers. The role of the input can be played by a smoothing filter capacitor if it is located no further than XNUMX mm from the microcircuit case. In [XNUMX], many schemes have been published for various options for switching on microcircuit stabilizers to provide a larger output current, change the output voltage, implement other protection options, and use a voltage stabilizer as a current generator.

If a non-standard value of a stabilized output voltage or its smooth regulation is required, it is convenient to use specialized adjustable microcircuit stabilizers that maintain a voltage of 1,25 V between the output and the control pin. Their list is presented in Table. 2, and a typical switching circuit for stabilizers with a regulating element in the positive wire is shown in fig. 3. Resistors R1 and R2 form an external adjustable voltage divider, which is included in the circuit for setting the output voltage level Uout, equal to Uout = 1,25 (1 + R2 / R1) + Ipot.R2, where Ipot = 50 ... 100 μA - own current consumption of the microcircuit. The number 1,25 in this formula is the voltage between the output and the control pin mentioned above, which keeps the regulator in operation.

Let's pay attention to the fact that, unlike stabilizers for a fixed output voltage, adjustable ones do not work without load. The minimum value of the output current of low-power adjustable stabilizers is 2,5 ... 5 mA and 5 ... 10 mA - powerful. In most applications, the load is the resistive voltage divider R1R2 in fig. 3.

According to this scheme, stabilizers with a fixed output voltage can also be turned on. However, firstly, the current they consume is much larger (2...4 mA) and, secondly, it is less stable when the output current and input voltage change. For these reasons, the maximum possible stabilization factor of the device cannot be achieved.

To reduce the level of output ripple, especially at higher output voltage, it is recommended to include a smoothing capacitor C3 with a capacity of 10 uF or more. The requirements for capacitors C1 and C2 are the same as for the corresponding fixed stabilizer capacitors.

If the stabilizer operates at the maximum output voltage, then if the input circuit is accidentally closed or the power supply is turned off, the microcircuit is under a large reverse voltage from the load side and can be disabled. To protect the output microcircuit in such situations, a protective diode VD1 is connected in parallel with it.

Another protective diode - VD2 - protects the microcircuit from the charged capacitor C3. The diode quickly discharges this capacitor in the event of an emergency circuit of the output or input circuit of the stabilizer.

All of the above is only for the preliminary selection of the stabilizer, before designing the power supply, you should familiarize yourself with the full reference characteristics, at least in order to know exactly what the maximum allowable input voltage is, whether the output voltage stability is sufficient when the input voltage, load current or temperature changes. We can express confidence that the microcircuits listed in the article are at a technical level sufficient to solve the overwhelming number of problems in amateur radio practice.

The described stabilizers have one noticeable drawback - a rather large minimum required voltage between input and output - 2 ... 3 V, however, it more than pays off with ease of use and low price of microcircuits.

Literature

1. Shcherbina A., Blagiy S. Chip stabilizers series 142, K142, KR142. - Radio, 1990, No. 8, p. 89, 90; No. 9, p. 73,74.
2. Nefedov A., Golovina V. Chips KR142EN12. - Radio, 1993, No. 8, p. 41,42.
3. Nefedov A., Golovina V. Microcircuits KR142EN18A, KR142EN18B. - Radio, 1994, No. 3, p. 41, 42.
4. Nefedov A. Microcircuit stabilizers of the KR1157 series. - Radio, 1995, No. 3, p. 59, 60.
5. Nefedov A., Valyavsky A. Microcircuit stabilizers of the KR1162 series. - Radio, 1995, No. 4, p. 59, 60.
6. Integrated circuits. Microcircuits for linear power supplies and their application. - DODEKA (first ed.), 1996, 288 p.; 1998 (second ed.), 1998, 400 p.
7. Nefedov A. V., Savchenko A. M., Feoktistov Yu. F. Foreign integrated circuits for industrial electronic equipment. Directory. - M.: Energoatomizdat, 1989.

Author: S. Biryukov, Moscow

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