Bipolar regulated power supply, 220/5...15 volts 1 amp

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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Often there is a need to power a device with a bipolar stabilized voltage. And a transformer suitable for the manufacture of such a power source has only one secondary winding. How to be? You will find the answer to this question by reading the article published here.

The proposed simple bipolar power supply is based on the integral stabilizer KR142EN5A.

Distinctive features of this device:

• the minimum number of parts;
• no tap is required in the secondary winding of the mains transformer;
• output voltage regulation within %5...15 V at output current up to 1 A.

A schematic diagram of a power supply with a voltage stabilizer is shown in fig. 1. The voltage of 1 ... 13 V removed from the secondary winding of the transformer T15 is supplied to the rectifier with a voltage doubling, assembled on diodes VD1, VD2. Filter capacitors C1-C4 provide smoothing of rectifier ripples.

(click to enlarge)

A bipolar voltage regulator based on a unipolar DA1 microcircuit with a stabilization voltage of 5 V is made according to the scheme of Fig. 12 in [1]. The difference lies in the additional regulated reference voltage source VD3R1R2 [2].

The power transformer T1 must have minimum dimensions and weight and provide the required load current at a voltage of 13 ... 15 V. If a suitable transformer could not be found, you can use the recommendations given in [3] and make it yourself.

Diodes VD1, VD2 - KD202 series with any letter index or other rectifier diodes with an average forward current value of 3 A at a voltage of at least 25 V.

Capacitors C1, C2, C5 - K50-35, K50-16, K50-6 with an operating voltage of 25 V; C3, C4 - tantalum, with a capacity of at least 1 μF, can be replaced by oxide capacitances of more than 25 μF, and if the length of the conductors connecting the voltage stabilizer with the filter capacitors C1, C2 does not exceed 100 mm, they are excluded [1].

Transistor VT1 - KT818 series with any letter index or another series with a permissible collector current of at least 3 A.

Instead of OU K140UD7, K (R) 140UD6A (or B), K153UD6 are suitable (when using the latter, correction of the printed circuit board will be required). Resistors R1, R3, R4 - MLT-0,25; R2 - SP4-1 or similar.

The KR142EN5A chip is interchangeable with K142EN5A, as well as with K (R) 142EN5V.

The design of the power supply, depending on the elements used (transformer, diodes, capacitors, etc.), can be arbitrary. In the author's version, the device is assembled in a case from an industrial unipolar power supply BP-12/10, from which the board, filter capacitor and two rectifier diodes were previously removed.

The main part of the stabilizer elements is placed on a printed circuit board (Fig. 2) made of one-sided foil fiberglass 1,5 mm thick. Capacitors C1, C2 are located separately and are connected by conductors to the rectifier and the main board.

The dimensions of the stabilizer board are chosen so that it is convenient to install it in place of the BP 12/10 board and fix it with screws. A hole with a diameter of 10 mm serves to mount the resistor R2; opposite it, a hole was also drilled in the case for the shaft of a variable resistor.

The transistor VT1, the DA1 chip are fixed through mica gaskets on the heat sink from the BP-12/10, for which two additional holes are drilled in it and an M3 thread is cut.

A power supply made from serviceable parts does not need to be adjusted.

With an appropriate choice of transformer T1, DA1 microcircuit and the resistance of resistors R1-R4, the output voltage of the stabilizer can be increased to 25 V, and by introducing additional elements according to the recommendations given in [1], the load current can be significantly increased.

Zener diode VD3 can be excluded. In this case, the upper (according to the diagram) output of the resistor R1 must be connected to pin 2 of the DA1 microcircuit, and the resistance of the variable resistor R2 should be reduced to 1 kOhm. Capacitor C4 is also optional, but to reduce ripple, it is useful to connect an oxide capacitor with a capacity of at least 8 microfarads for an operating voltage of at least 1 V between pin 47 of the DA10 chip and the common wire.

Literature

1. Shcherbina A., Blagiy S., Ivanov V. Application of microcircuit stabilizers of series 142, K142 and KR142. - Radio, 1991, No. 3, p. 47-51.
2. Savin S. Option to turn on the K142EN5 stabilizer. - Radio, 1989, No. 12, p. 66.
3. Nikolaev Yu. Homemade power supply? There is nothing easier. - Radio, 1992, No. 4, p. 53, 54.

Author: V. Kobrin, village of Sescha, Bryansk region.

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