Radio uninterruptible power supply. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Radio uninterruptible power supply. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur

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In some regions of our country, power outages, both for technical and economic reasons, have become, unfortunately, not uncommon. Moreover, such shutdowns are often systematic, which deprives people of useful and necessary information and distracts them from the life of the country, because even listening to the radio becomes problematic. Galvanic batteries do not last long, but they are not so cheap, and constantly charging batteries with a special charger is too troublesome.

Under these conditions, the task of ensuring uninterrupted power supply becomes important, which can be solved with the help of a special power supply. It necessarily includes a battery that serves to power the receiver in the absence of mains voltage and is automatically charged when it is. Blocks similar in principle of operation are used in computer technology, where they ensure the operability or preservation of information during power outages. With regard to the radio receiver, such a block makes it possible to obtain information.

A diagram of a simple block designed to power small-sized radio receivers with a voltage of 9 V is shown in fig. 1.

Radio uninterruptible power supply

It contains a rectifier assembled on a step-down transformer T1, a diode bridge VD1 and a capacitor C1. A voltage stabilizer is made on the DA1 chip, and a current limiter is used on the VT1 transistor to charge the GB1 battery. The device works as follows. In the presence of mains voltage, the supply voltage through the diode VD3 will go to the output of the unit. At the same time, the battery will be charged through the transistor VT1. The LED indicates that the radio is powered from the mains.

The elements of the circuit are selected so that it can use a battery of seven nickel-cadmium batteries with a capacity of 0,1 to 0,25 Ah (7D-0,125, "Nika" and similar imported ones). Switch SA1 disconnects the device from the mains and at the same time the battery from the device.

In order to ensure the most complete charge of the battery, the supply voltage must be at least 1,35x7 = 9,45 V. To do this, the voltage stabilized by the DA1 microcircuit is increased by 0,7 V by including the common output of the VD2 diode in the circuit. It should be noted that the battery is charged not with a stable current, but with a current whose value changes during the charging process. At the very beginning, this current exceeds the recommended one by 1,5 ... 2 times, and then, as the battery voltage increases, the current decreases and at the end becomes close to the self-discharge current.

In the absence of voltage in the network, the output of the unit will receive voltage from the battery through the diode VD4 and the channel of the transistor VT1, and the diode VD3 eliminates the discharge of the battery through the microcircuit. Thus, switching from mains to autonomous power occurs automatically. To use the unit for radio receivers with a lower supply voltage, it is necessary to reduce the stabilization voltage accordingly by using a microcircuit stabilizer with a lower stabilized voltage.

A sketch of the printed circuit board of the block is shown in fig. 2. Holes in the board are not drilled - the leads of the parts are superimposed on the pads and soldered to them.

Radio uninterruptible power supply

Due to the simplicity of the circuit, in the variant of the block described above, there are no indicators of charge or battery status, as well as its protection against excessive discharge. Such indicators and protection can be introduced at the expense of some complication of the scheme.

If during the operation of the device an alternating current background is noticeable, it can be weakened by shunting each diode of the rectifier VD1 with a capacitor with a capacity of about 0,01 uF.

Author: I.Aleksandrov, Kursk

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