Reversible voltage converter. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Reversible voltage converter. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Surge Protectors

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The proposed device is intended for emergency power supply of volatile electronic devices with low current consumption from a backup source in case of power failure (for example, a generator and an electronic clock pulse counter installed in a car).

The converter (see Fig. 4.1) contains a backup battery GB1, a master generator on the elements DD1.1 ... DD1.3, a two-digit counter on D-flip-flops DD2.1, DD2.2, a double four-channel multiplexer DD3 and a capacitive storage divider - capacitors C2 ... C5.

(click to enlarge)

If there is voltage in the on-board network, the device operates in the mode of dividing its voltage and recharging the GB1 battery. The buffer mode is provided by a bidirectional multiplexer DD3, which alternately connects the battery in parallel to one of the capacitors C2 ... C5 of the capacitive voltage divider. As a result, the battery is charged to a voltage equal to a quarter of the voltage of the on-board network.

At the moment of power failure in the network, the converter automatically switches to the backup battery voltage multiplication mode. In this mode, capacitors C2 .... C5 are sequentially charged from the GB3 battery through the DD1 multiplexer, and since they are connected in series, a voltage equal to the quadruple battery voltage is created at the output of the device, which feeds not only the serviced electronic device, but also the microcircuits of the converter itself.

The multiplexer control signals come from the outputs of the counter (DD2.1, DD2.2), which is connected through the buffer element DD1.3 to the output of the pulse generator with a repetition rate of about 5 kHz. Since in the voltage multiplication mode the converter nodes are powered by its output voltage, for the initial start-up it is necessary to briefly apply the voltage of the on-board network to the power circuit. After the generator is self-excited, the converter runs on battery GB1. If the device is supposed to be used as a backup power source for an electronic clock, the generator on the elements DD1.1, DD1.2 may not be needed: it can be completely replaced by a master clock generator. This will reduce the current consumed by the converter to the level of 10...20 μA.

As the test showed, when using a GB1 battery from three D-0,25 batteries connected in series, the output voltage of the converter at a load with a resistance of 68 kOhm (load current - 150 μA) is 10,1 V, and in idle mode - 10,8 V. When installing the device in a car for emergency power supply of the clock on K561 series microcircuits, it is allowed to connect it to the on-board network with a voltage of 12 V through a decoupling diode, which prevents overloading of the converter. The converter does not need to be adjusted, however, it must be borne in mind that the voltage of the backup battery should not exceed 4 V. Otherwise, the amplitude of the output (multiplied) voltage will exceed the maximum allowable voltage of input signals for K561 series microcircuits, which will lead to their failure. The absence of decoupling diodes and transistor switches in the converter provides an efficiency of up to 80...90%.

Simplicity, reversibility of functions, the possibility of implementing a buffer mode for a backup source with low EMF allow using the described voltage converter as an emergency power source for various devices with memory. In order to eliminate the possibility of overcharging the GB1 battery, it is advisable to stabilize the supply voltage of the device by choosing it so that the voltage at terminals 3 and 13 of the multiplexer does not exceed the voltage of the GB1 battery.

In the case when the activation of the backup source is a rare and short-term event, to prevent overcharging of the battery, it is enough to connect a current-limiting resistor shunted by a diode in series with it. The resistor is selected from the condition of providing a charging current equal to the self-discharge current. In the voltage multiplication mode, the battery is connected to the multiplexer through an open diode.

Author: Semyan A.P.

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