Voltage stabilizer on KR1158ENx microcircuits. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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The traditional composition of homemade amateur radio power supplies is a step-down transformer, a rectifier and a voltage regulator, made, in most cases, on an integrated circuit. In the manufacture of such blocks, a situation sometimes arises when the output voltage is unstable and there are significant ripples in it. The reason for such phenomena may be insufficient voltage on the secondary winding of the transformer. There are two ways out of this situation: to increase the output voltage of the secondary winding of the transformer, which is not always convenient or possible, or to use elements that require less voltage for their normal operation. The article considers the second option.

The diagram of a part of the power supply (without a network transformer) is shown in fig. 1. The unit includes a rectifier diode bridge VD1-VD4, a smoothing filter capacitor C1, an output capacitor C2 and a voltage regulator made on the DA1 chip. The alternating voltage Uin ~ to the diode bridge comes from the secondary winding of the transformer, is rectified by it and fed to the stabilizer. The parameters of these elements - the diode bridge and the stabilizer - determine the minimum value of the input voltage that must be applied to the diode bridge so that the voltage at the output of the stabilizer is normal.

On fig. Figure 2 shows the experimentally measured dependences of the output voltage of the stabilizer on the value of the input AC voltage at a load current of 150 mA. Curve 1 was recorded when a KR142EN5A microcircuit and RL201 silicon rectifier diodes were installed in the power supply unit. For these elements, the minimum input voltage was about 6,9 V. If Schottky diodes (1 N5819) were used as rectifier diodes, then the minimum input voltage decreased to about 5,7 V (curve 2).

A further decrease in the input voltage is possible if an integrated stabilizer on the KR1158EN5A chip is used. Its distinguishing feature is a low voltage drop: 0,3...0,4 V at a load current of up to 150 mA. In addition, the microcircuit has reverse polarity protection, allows an increase in input voltage up to 37 V, and can be installed by soldering on a board or heat sink, which allows increasing its power dissipation. When using this microcircuit and silicon diodes, the minimum input voltage was about 5,25 V (curve 3), and for Schottky diodes it turned out to be already about 4,7 V (curve 4). The difference between the minimum voltage for a power supply unit assembled on a KR1158EN5A chip with Schottky diodes and a unit on a KR142EN5A chip with silicon diodes was about 2,2 V, which is equal to 30 ... 40% of the input voltage.

As another example, in Fig. 2 (curve 5) shows the dependence of the output voltage for a three-volt power supply with a Schottky diode rectifier and a KR1158ENZA microcircuit as a stabilizer. In this case, the minimum input AC voltage is about 3,5 V

Thus, using the above elements or their analogues, it is possible to significantly improve the parameters of the power supply if the step-down transformer operates "at the limit", or significantly reduce the voltage on the secondary winding of the transformer, reduce its dimensions, power dissipation and facilitate the thermal regime of the entire power supply.

Author: I.Aleksandrov, Kursk

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