Encyclopedia of radio electronics and electrical engineering / radio reception

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The operation of radio-electronic equipment with autonomous power sources in stationary conditions, from the point of view of efficiency and safety of battery life, is more expedient from an alternating current network. And this is not difficult to implement if you make the simple power supply proposed in this article.

In recent years, portable, small-sized, battery-powered broadcast receivers have become more and more widespread. Often such receivers work for 6...8 hours a day, which quickly exhausts the battery life. However, the cost of elements of type 316 (European type AA), for which most modern small-sized radio receivers are designed, is quite high. At the same time, in some cases, radios operate in conditions where there is a 220 V electrical network (dacha, industrial premises, office, etc.). Therefore, when operating the receiver for more than two hours a day, it is more expedient to power it from a stabilized mains small-sized power supply.

Schematics of such devices have already been published in amateur radio literature, including the Radio magazine. The most suitable for these purposes, according to the author, is O. Sidorovich's stabilized power supply [1], if the values ​​of the output voltages are corrected taking into account the radio receivers actually used. So, for example, the author has not seen industrial small-sized radio receivers with supply voltages of 7,5 and 12 V. When repeating this design of the power supply for radio amateurs, especially beginners, certain difficulties arise in the independent manufacture of a network transformer with numerous taps of the secondary winding.

The author offers his own version of the design for small-sized radio receivers, the repetition of which saves the radio amateur from the laborious manufacture of a step-down transformer. The power supply has the following characteristics: output stabilized voltage - 3; 4,5; 6; 9 V; load current at an output voltage of 9 V - 200 mA.

The power supply has been working for the author for more than a year with daily use on average 4 ... 5 hours a day and has proven itself from the best side.

When feeding radio receivers from this unit, there was no unpleasant, low-frequency background in dynamic heads, which, unfortunately, happens when using some industrial power supplies.

The scheme of the proposed power supply is shown in fig. one.

Capacitors C1 and C2 in the secondary winding of the transformer T1 are designed to reduce the multiplicative interference that occurs when switching rectifier diodes [2]. Diodes VD1 - VD4 form a bridge rectifier, capacitor C3 - filtering. Resistor R1 and zener diode VD5 - a parametric stabilizer for creating a constant voltage of about 10 V across resistors R3 - R7. They determine the voltage based on the control transistor VT2, which, in turn, controls the control transistor VT1. Capacitor C4 provides additional filtering of the output voltage.

Any ready-made transformer is used, suitable in size with a W-shaped or tape magnetic circuit, for example, TP-122-7, TP-122-17 [3]. The voltage on the secondary winding should be 12 ... 14 V at a current of 0,35 ... 0,45 A.

If there are transformers of other ratings with primary windings rated for 220 V, the no-load current is not more than 30 mA (the measurement procedure is given in [4]) and meets the requirements for acoustic noise and dimensions, then it is enough to rewind the secondary winding to the required voltage value .

Before installation, it is advisable to dip the transformer (both factory-made and self-modified) on a thread into molten paraffin or stearin to reduce the noise it emits during operation. Fusible insert FU1 of any type for a current of 150 mA, bridge diodes VD1 - VD4 are silicon, designed for a direct average current in the range of 0,5 ... 0,7 A. Capacitors C1 and C2 are ceramic, C3 and C4 are K50-35. All resistors are of the MLT, VS or similar type with the dissipation power indicated on the diagram. We will replace the VD5 zener diode with D814V, KS210B. Transistors VT1, VT2 can be used with any letter index. Switch SA1 - with a linear movement of the engine in four positions (the choice in stores is quite rich).

Setting up the power supply is reduced to setting the values ​​​​of the output voltages of the unit close to the nominal ones. This is done by selecting resistors R3 - R7. The peculiarity lies in the fact that changing the value of one of these resistors, selected for a certain voltage, leads to some change in the values ​​of other voltages. In practice, this manipulation is done as follows: take five resistors of each desired value (510 Ohm. 3, 1,5 kOhm, etc.), which will always have a small spread relative to the selected value. Alternately soldering them into the device, the output voltages are set close to the required ones. If the resistors R4 - R6 are installed with a tolerance of 5%, it will be enough to select only R3 and R7.

The block parts are mounted on a printed circuit board, the drawing of conductors and the arrangement of elements on the board are shown in fig. 2.

The control transistor VT1 should be installed on a finned heat sink with a dissipation area of ​​the order of 15 ... 20 cm2, the place of thermal contact should be lubricated with a thin layer of heat-conducting paste of the KPT-8 type.

It is necessary to ensure proper cooling of the heat sink of the regulating transistor and transformer, for this, holes are made in the appropriate places of the case (in the author's version, the holes are made in the printed circuit board along the perimeter of the projection of the power transformer and under the heat sink of the regulating transistor VT1).

Switch SA1 is installed outside the board and connected to the contact pads with mounting conductors.

Capacitors C3 and C4 should be placed on the board from the side of the tracks, soldering the leads to the contact pads.

Literature

1. Sidorovich O. Stabilized for six output voltage values. - Radio, 1997, No. 7, p. 43, 44.
2. Avdonin D., Grechikhin A. Multiplicative interference from secondary power sources. - Radio, 2002, No. 3, p. 64.
3. Koltsov I. Low-power network transformers of the TP series of increased electrical safety. - Radio, 2001, No. 7, p. 47, 48.
4. Polyakov V. Using a transformer from the TV. - Radio, 1999, No. 4, p. 38, 39.

Author: D. Borodin, settlement of Moscow, Tyumen region.

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