Network power supply for car radios. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Network power supply for car radios. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Network power supplies designed to power car radios must be designed and manufactured taking into account the features of this equipment, otherwise they may not be suitable for powering some types of radios, for example, due to RF interference when the power amplifier mismatches with the antenna. As experience shows, it is desirable that the power supply contains the minimum possible number of elements, which increases its reliability.

Power supplies built according to complex circuits with various electronic protections are unsuitable for powering radio stations, as described in more detail in the literature [1]. In this regard, of interest are the practical designs of simple power supplies, which have proven themselves when working with radio stations of various types.

Often, radio amateurs have at their disposal failed and decommissioned network power supplies for GRANIT-M, LEN radio stations, etc. Sometimes a failed unit is difficult to repair. Most often this happens after an accident in the power grid and a violation of the rules of operation, i.e. installation of non-standard fuses in it. In such power supplies, not only the power transformer fails, but also, as a rule, elements of the rectifier and voltage stabilizer.

In the normal external condition of the block housing, the parts inside it and the board can be severely damaged by combustion products. In this case, it is necessary to remove not only faulty parts, but also partially damaged parts, especially those directly connected to the power grid, i.e. switches, fuse holders, mains filter capacitors, etc. After that, clean and rinse the housing with a solvent.

To restore a badly damaged mains power supply or independently assemble it to power a car radio station in stationary conditions, you can use the circuit (see figure), which has proven itself well in practice when working with radio stations up to 15 W.

(click to enlarge)

The circuit uses a standard transformer TN46, since more powerful transformers of the TN type are less common and expensive. Since the alternating voltage supplied to the rectifier diodes from the windings of the transformer T1 is 12,6 V at full load, for normal operation of the voltage regulator, i.e. to ensure the necessary voltage at the input of the stabilizer, it is desirable to use diodes of the D305 type and a filter capacitor C1 with a capacity of at least 10000 microfarads.

The stabilizer is made on a KR142EN5A microcircuit with an additional parametric stabilizer-filter VD3, R1, C6, C7 and an emitter follower on a VT1 transistor. With a load current of more than 3 A in the emitter follower, it is better to use two KT819AM (BM) transistors with separate resistors R2.1 and R2.2. The resistor values should be the same in the range from 0,1 to 0,2 ohms, which helps to equalize the currents flowing through the transistors connected in parallel at points a, b and c.

Various variants of stabilizers on KR142EN5A, which are given in the literature [2,3, 4], were tested. The selected variant turned out to be less sensitive to RF interference and had good repeatability without preliminary selection of any details. An important condition for the stable operation of the stabilizer is the correct installation and selection of grounding points. More details about this are described in the literature [XNUMX].

Capacitors C2, C3, C5, C6 and C10 should be ceramic, preferably of the KM type, and have as short leads as possible. I do not recommend using KLS type capacitors because of their low reliability. These capacitors serve to reduce RF interference, interference and multiplicative background.

If unstable operation of the stabilizer is noted during the operation of the radio station for transmission, additional elements should be installed: capacitor C9 and resistor R3, the values \u1b\u3bof which are selected during setup. In addition, it is possible to select the resistance of the resistor R12 and the zener diode VD4 with a stabilization voltage, in which the output voltage at the rated load will be at least 5 V. The positive aspects of the proposed network power supply are relative simplicity and low material costs with good repeatability, and the disadvantages some deterioration in the operation of the stabilizer at a rated load, which should not exceed XNUMX A, should be attributed to a voltage in the mains below the rated voltage by more than XNUMX%.

References:

Feofilaktov N. Stabilizer for powering an automobile CB radio station // Radio.1997 .- No. 7.- P.67-69.
Gvozditsky G. High power power supply // Radio.1992.- No. 4.- P.43-44.
Shcherbina A., Blagiy S., Ivanov V. Application of microcircuit stabilizers of series 142, K142 and KR142 // Radio.- 1991. No. 3.- P. 47-51.
Barnes J. Electronic design: Methods of dealing with interference.- M.: Mir.- 1990.

Author: V.V. Efremov

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