JPH06105482A - Auxiliary power source switching circuit - Google Patents

Abstract

PURPOSE:To prolong the life of a battery by preventing a voltage variation at the time of switching to an auxiliary power source and preventing the leakage of a current at the time of power interruption of a commercial power source. CONSTITUTION:The auxiliary power source switching circuit comprises a DC power source 2 for supplying a DC voltage from a commercial power source, a voltage supply unit 8 for supplying a voltage to circuits, a comparison voltage unit 3 for supplying a divided voltage from a midpoint between the output of the power source 2 and the ground, a reference voltage unit 6, an auxiliary power source 10 having a battery, and an auxiliary power source switch 9. The voltage of the unit 3 is compared with that of the unit 6, when the voltage is large, the switch 9 is not conducted, while when the voltage is small, it is conducted to supply the voltage to the unit 8. A reverse current blocking circuit 4 is provided in the power source 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for switching to an auxiliary power source when a commercial power source fails. The present invention relates to an auxiliary power supply switching circuit capable of preventing current leakage from an auxiliary power supply and keeping a voltage constant.

[0002]

2. Description of the Related Art Conventionally, as shown in FIG. 2, an auxiliary power supply switching circuit of this type has a common anode for diodes constituting a backflow prevention circuit section 4, and supplies a voltage to each circuit from the common anode. A voltage supply unit 8 is provided, and a DC power supply unit 2 for obtaining a DC voltage from the AC 100V from the commercial power supply connection unit 1 and an auxiliary power supply unit 10 composed of a battery are connected to each cathode so that the voltage of the DC power supply unit 2 is A circuit that is switched when the voltage drops and becomes equal to or lower than the voltage of the auxiliary power supply unit 10 has been used.

[0003]

In such a conventional switching circuit, when the voltage of the auxiliary power supply unit is higher than the voltage of the DC power supply unit, the current of the auxiliary power supply unit leaks to the circuit and is connected to the auxiliary power supply unit. Also, there is a problem that the life of the battery is shortened, and the voltage at the time of switching the power supply is not constant due to the voltage at the auxiliary power supply end or the forward voltage of the diode.

The present invention solves such a problem, and provides a circuit capable of preventing the leakage of current from the auxiliary power source section, extending the life of the battery, and keeping the voltage constant during switching. With the goal.

[0005]

According to the present invention, there is provided a voltage supply section for supplying a DC voltage, a DC power supply section for converting an AC voltage from a commercial power supply connection section into a DC voltage and supplying the DC voltage to the voltage supply section. Auxiliary power supply switching circuit including an auxiliary power supply unit that supplies a DC voltage to the voltage supply unit when power supply from the DC power supply unit is stopped, and a backflow prevention circuit unit that prevents a backflow from the voltage supply unit. In, a comparison voltage unit that supplies a voltage divided from a midpoint between the DC power supply unit and the ground, a reference voltage unit that generates a reference voltage, the comparison voltage unit and the reference voltage unit as inputs The voltages are compared, and when the voltage of the comparison voltage unit is higher than the voltage of the reference voltage unit, the impedance is set to high impedance, and when the voltage is low, the comparator grounded and the comparison voltage unit reduces the voltage of the DC power supply unit. When issued, characterized in that an auxiliary power supply switch unit for connecting the auxiliary power unit to the voltage supply unit by the output of the comparator.

The auxiliary power switch unit includes a PNP transistor, the base of which is connected to the output of the comparator through a resistor, the emitter of which is connected to the output of the auxiliary power unit, and the collector of which is connected to the voltage supply unit. It is desirable to be connected to.

[0007]

[Operation] When the comparison voltage section detects the voltage of the DC power supply section by the voltage divided from the midpoint of the potential between the output of the DC power supply section and the ground, the comparator inputs the detection output and the reference voltage for comparison. When the voltage of the comparison voltage section is higher than the reference voltage, its output is set to high impedance to open the auxiliary power switch to prevent the voltage from flowing from the auxiliary power section to the voltage supply section. On the contrary, when the voltage is lower than the reference voltage, that is, when the commercial power supply fails, the auxiliary power switch is grounded to bring the auxiliary power switch into the conductive state, and the voltage is supplied from the auxiliary power supply unit to the voltage supply unit.

As described above, since the threshold value of the switching voltage of the power source does not depend on the voltage of the auxiliary power source section, it can be arbitrarily set by the voltage division ratio of the comparison voltage between the DC power source section and the reference voltage section. The voltage fluctuation from the auxiliary power supply unit at the time of switching can be eliminated, current leakage can be prevented, and the battery life can be extended.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the embodiment of the present invention.

In the embodiment of the present invention, a voltage supply unit 8 for supplying a DC voltage, a DC power supply unit 2 for converting the AC voltage from the commercial power supply connection unit 1 into a DC voltage and supplying it to the voltage supply unit 8,
A backflow prevention circuit unit 4 including an auxiliary power supply unit 10 that supplies a DC voltage to the voltage supply unit 8 when the power supply from the DC power supply unit 2 is stopped, and a diode that prevents a backflow from the voltage supply unit 8. Further, as a feature of the present invention, a comparison voltage unit 3 that supplies a voltage divided from a midpoint between the DC power supply unit 2 and the ground, a reference voltage unit 6 that generates a reference voltage, The comparison voltage unit 3 and the reference voltage unit 6 are input, and the voltages are compared. When the voltage of the comparison voltage unit 3 is higher than the voltage of the reference voltage unit 6, the impedance is set to high impedance; When the unit 3 detects the voltage drop of the DC power supply unit 2, the output of the comparator 7 causes the auxiliary power supply unit 10 to switch to the voltage supply unit 8.
And an auxiliary power switch unit 9 connected to the.

The auxiliary power switch section 9 includes a PNP transistor, the base of which is connected through a resistor to the comparator 7.
Is connected to the output of the auxiliary power supply unit 10, its collector is connected to the voltage supply unit 8, and the comparison voltage unit 3 has two fixed resistors in series between the DC power supply unit 2 and the ground. The output from the midpoint is connected to the non-inverting input terminal 5 of the comparator 7.

Next, the operation of the embodiment of the present invention thus constructed will be described.

AC from the commercial power supply connection section 1 to the DC power supply section 2
When 100V is input, the DC power supply unit 2 will
0V is converted into a DC voltage supplied to the circuit, and the converted DC voltage is separated into a positive polarity output terminal 11 and a negative polarity output terminal 12. The positive polarity output terminal 11 is connected to the comparison voltage unit 3 configured by two resistors and dividing the voltage and the cathode of the backflow prevention circuit unit 4 configured by a diode,
A voltage is supplied from the anode to each circuit via the voltage supply unit 8. At this time, the voltage divided by the comparison voltage unit 3 is connected to the non-inverting input terminal 5 of the comparator 7 and compared with the voltage of the reference voltage unit 6 connected to the inverting input terminal 13.

By setting the voltage of the comparison voltage section 3 to be higher than the voltage of the reference voltage section 6 when the commercial power supply connection section 1 is not in a power failure state, the output from the output terminal 14 of the comparator 7 becomes high. Becomes impedance, PN
Auxiliary power switch unit 9 composed of P transistor
There is no conduction between the collector and the emitter, and no voltage flows from the auxiliary power supply unit 10 to the voltage supply unit 8.

When the commercial power supply connection section 1 fails, the voltage divided by the comparison voltage section 3 is connected to the non-inverting input terminal 5 of the comparator 7 and the voltage of the reference voltage section 6 connected to the inverting input terminal 13. Compare with. At this time, since the commercial power supply connection unit 1 is in a power failure state, the comparator 7 is activated when the voltage of the comparison voltage unit 3 becomes lower than the voltage of the reference voltage unit 6.
Since the output from the output terminal 14 of the above is conducted to the negative output terminal 12, the collector and the emitter of the auxiliary power source switch unit 9 constituted by the PNP transistor are conducted to supply the voltage from the auxiliary power source unit 10 to the voltage supply unit 8. Is done. At this time, the backflow prevention circuit unit 4 prevents the voltage from flowing back to the DC power supply unit 2.

As described above, the threshold value of the switching voltage of the power supply can be arbitrarily set by the voltage dividing ratio of the comparison voltage section 3 without depending on the voltage of the auxiliary power supply section 10.

[0017]

As described above, according to the present invention, the threshold value of the switching voltage of the power supply is arbitrarily set by the voltage division ratio of the comparison voltage without depending on the voltage of the auxiliary power supply, and the switching to the auxiliary power supply is performed. The voltage at the time can be made constant, and further, there is an effect that the leakage of current from the auxiliary power supply unit can be prevented and the life of the battery can be extended.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a conventional example.

[Explanation of symbols]

 1 Commercial power supply connection part 2 DC power supply part 3 Comparison voltage part 4 Backflow prevention circuit part 5 Non-inverting input terminal 6 Reference voltage part 7 Comparator 8 Voltage supply part 9 Auxiliary power switch part 10 Auxiliary power supply part 11 Positive output terminal 12 Negative polarity Output terminal 13 Inverted input terminal 14 Output terminal

Claims (2)

[Claims] 1. A voltage supply unit for supplying a DC voltage, a DC power supply unit for converting an AC voltage from a commercial power supply connection unit into a DC voltage and supplying it to the voltage supply unit, and a power supply from this DC power supply unit. In the auxiliary power supply switching circuit including an auxiliary power supply unit that supplies a DC voltage to the voltage supply unit when the power supply stops, and a backflow prevention circuit unit that prevents a backflow from the voltage supply unit, the DC power supply unit and the ground. A comparison voltage unit that supplies a voltage divided from a midpoint between the reference voltage unit and a reference voltage unit that generates a reference voltage, the comparison voltage unit and the reference voltage unit as inputs, and compare the voltages, When the voltage of the voltage section is higher than the voltage of the reference voltage section, it is set to high impedance, and when it is small, it is grounded, and when the comparison voltage section detects a voltage drop of the DC power supply section, Auxiliary power supply switching circuit is characterized in that an auxiliary power supply switch unit for connecting the auxiliary power unit to the voltage supply unit by the output of the comparator. 2. The auxiliary power switch section includes a PNP transistor, the base of which is connected to the output of the comparator through a resistor, the emitter of which is connected to the output of the auxiliary power supply section, and the collector of which is the voltage. The auxiliary power supply switching circuit according to claim 1, which is connected to the supply unit.