JP2723404B2 - Power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device for switching a power supply to a built-in battery when an AC power supply fails, and more particularly to a power supply device capable of compensating for a decrease in battery voltage when the power supply is switched.

[0002]

2. Description of the Related Art FIG. 7 is a circuit diagram partially showing a conventional power supply device in a block diagram. In FIG.
The primary side is connected to an AC power supply, for example, a commercial power supply (not shown). Reference numeral 2 denotes a rectifying / smoothing circuit which is connected to the secondary side of the transformer 1 and which rectifies and smoothes the transformed AC voltage from the transformer 1 to obtain a DC voltage. The reverse current blocking diode 4 whose anode is connected to the output side is another reverse current blocking diode whose cathode is connected to the cathode of this diode 3, and these diodes 3 and 4 constitute a power supply switching circuit. Reference numeral 5 denotes a built-in battery, for example, a lithium battery in which the positive terminal is connected to the anode of another diode 4, the negative terminal of which is grounded. Reference numeral 6 denotes a constant voltage circuit in which the input side is connected to both diodes 3 and 4.

When such a power supply device is used in an electronic watt-hour meter, for example, another transformer and a current transformer (both not shown) are provided in parallel with the A pulse from a circuit (not shown) for converting the amount of electric power obtained from the AC current into a frequency is sent to a microcomputer (not shown), and the processing result is displayed on a display (not shown). At this time, the output voltage of the constant voltage circuit 6 becomes the power supply of the microcomputer.

[0004] In the conventional power supply device configured as described above, an AC voltage input from an ordinary AC power supply is usually converted by the transformer 1.
For example, step down (or step up), rectify and smooth with the rectifying and smoothing circuit 2, and then pass through the diode 3 to the constant voltage circuit 6.
And the microcomputer is driven by the output voltage of the constant voltage circuit 6. When the AC power supply is cut off, the power supply of the computer is switched from the AC power supply to the lithium battery 5 by the diodes 3 and 4, and this time, the lithium battery 5 applies the output voltage e to the constant voltage circuit 6 through the diode 4 and uses the output voltage. I was driving a microcomputer.

[0005]

However, when the AC power supply does not lose power for a long period of time, and thus when the lithium battery does not discharge for a long period of time, a chemical conversion film is formed inside the battery and the internal resistance increases. The output voltage e of the lithium battery is as shown in FIG.
As disclosed in Japanese Patent Publication No. 83, there has been a problem that Δe _{1 is} reduced, the microcomputer stops operating suddenly, and data in a memory in the microcomputer is damaged. In addition, such a voltage drop becomes larger when the temperature is low or when the battery capacity is small. Therefore, there is a problem that an IC having an operation voltage lower than that of a standard IC is required.

Accordingly, the present invention has been made to solve such a problem, and an object of the present invention is to provide a power supply device capable of reducing the voltage drop when switching to a lithium battery that has not been discharged for a long time. I have.

[0007]

A power supply device according to the present invention is connected between at least one of an input side and an output side of a DC conversion circuit for converting a voltage of an AC power supply into DC and a built-in battery, A battery activation circuit for discharging the built-in battery once after stopping and before switching power is provided. Further, the battery activation circuit may include a one-shot multivibrator connected to the input side of the DC conversion circuit, a comparator connected to the output side of the DC conversion circuit, and the one-shot multivibrator and the comparator and the built-in battery. Composed of logic circuits connected between them,
The first and second one-shot multivibrators or a comparator and a one-shot multivibrator connected in series between the input side of the DC conversion circuit and the internal battery.

[0008]

According to the present invention, the internal battery is discharged once after the power failure of the AC power supply and before the power supply is switched, so that the voltage drop of the internal battery when the power supply is switched is reduced. The one-shot multivibrator and the logic circuit, the first and second one-shot multivibrators, the comparator and the one-shot multivibrator discharge the built-in battery. This is performed by a shot multivibrator or a one-shot multivibrator.

[0009]

[Embodiment 1] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram partially showing a block diagram of a first embodiment of a power supply device according to the present invention.
6 are exactly the same as those shown in FIG. Reference numeral 10 denotes a battery activation circuit connected between the input and output sides of the rectifying / smoothing circuit 4 and the lithium battery 5, especially the positive terminal thereof, and is a one-shot in which the input side is connected to the secondary side of the transformer 1. A multivibrator 11, a comparator 12 having an input connected to the output side of the rectifying and smoothing circuit 2, and an input terminal connected to the output side of the one-shot multivibrator 11 and the comparator 12 and a positive terminal of the lithium battery 5; The output terminal is constituted by a connected logic circuit, for example, a negative logic AND circuit 13.

FIG. 2 is a waveform diagram showing the voltage, output, etc. of each part of the first embodiment. The operation of the first embodiment will be described with reference to this waveform diagram. During energization of the AC power supply before the time point t1, the transformer 1 generates a voltage similar to that shown in FIG. 2A, and the rectifying / smoothing circuit 2 outputs a DC voltage shown in FIG. The one-shot multivibrator 11 in the battery activation circuit 10 generates a high-level output shown in FIG. At this time, since the output voltage of the rectifying and smoothing circuit 2 is not lower than the reference voltage of the comparator 12 which will be described later,
The comparator 12 generates a low level output as shown at D in FIG. Since the high-level output and the low-level output are applied to the two input terminals, the negative logic AND circuit 13
A high level output is generated at its output terminal. Since the output terminal of the negative logic AND circuit 13 is in the high level state, the lithium battery 5 generates the output voltage shown in FIG. 2E, but a current flows from the lithium battery 5 to the negative logic AND circuit 13. Absent. Finally, the constant voltage circuit 6 supplies a constant output voltage shown in FIG.

However, if the AC power supply that has not been powered down for a long time has a power failure at time t1, the AC power supply voltage becomes A in FIG.
As shown in FIG. 2, the rectifying and smoothing circuit 2 keeps the previous state for a while, as shown in FIG. However, the one-shot multivibrator 11 changes its state to a low level at a time point t2 after a predetermined time after the AC power supply becomes zero voltage, and the negative logic AND circuit 13 receiving this changes the state of its output terminal to a low level. As a result, the discharge current i flows from the lithium battery 5 to the negative logic AND circuit 13, and the output voltage of the lithium battery 5 instantaneously drops considerably as shown in FIG. Trying to recover towards.

When the output voltage of the rectifying / smoothing circuit, which has been gradually reduced from the time point t2, becomes lower than the reference voltage REF of the comparator 12 at the time point t3 as shown in FIG. 2B, the comparator 12 becomes as shown in FIG. The state of the output terminal of the negative logic AND circuit 13 also changes to a high level, so that the discharge current from the lithium battery 5 no longer flows to the negative logic AND circuit 13,
When the output voltage of the rectifying / smoothing circuit 4 becomes lower than the output voltage of the lithium battery 5, the current flows through the diode 4 to the constant voltage circuit 6. At this time, the output voltage of the lithium battery 5 slightly decreases as shown in FIG. 2E, but is smaller than the voltage decrease at the time point t2. Therefore, the output voltage of the constant voltage circuit 6 also becomes as shown in FIG. But only a little. Therefore, such a small voltage drop does not prevent the microcomputer from operating or the data in the internal memory from being damaged.

Embodiment 2 FIG. FIG. 3 is a circuit diagram partially showing the second embodiment in a block diagram, and is different from the first embodiment in FIG. 1 in the configuration of the battery activation circuit. That is, in the second embodiment, the battery activation circuit 10A includes the first one-shot multivibrator 14 and the second one-shot multivibrator connected in series between the input side of the rectifying and smoothing circuit 2 and the lithium battery 5. 15.

The operation of the second embodiment will be described with reference to FIG. 4 showing the voltage, output, etc. of each part of the second embodiment. When the AC power is supplied before time t1, the transformer 1 is shown in FIG. The rectifying / smoothing circuit 2 outputs a DC voltage shown in FIG.
First one-shot multivibrator 14 during 0A
Produces a low level output as shown in FIG. The second one-shot multivibrator 15 receiving this low-level output generates a high-level output shown in FIG.
Thus, the second one-shot multivibrator 1
5 is in the high level state, the lithium battery 5 generates the output voltage shown in FIG. 4E, but the second one-shot multivibrator 15
No current flows to Finally, the constant voltage circuit 6 supplies a constant output voltage shown in FIG. 4F based on the output voltage of the rectifying and smoothing circuit 2.

However, if the AC power supply that has not been powered down for a long time has a power failure at time t1, the AC power supply voltage becomes A in FIG.
As shown in FIG. 4, the voltage immediately becomes zero, but the rectifying / smoothing circuit 2 keeps the previous state for a while as shown in FIG. However, the first one-shot multivibrator 14 operates at time t2 after a predetermined time after the AC power supply has become zero voltage.
, The state of the output terminal of the second one-shot multivibrator 15 also changes to a low level, so that the discharge from the lithium battery 5 to the second one-shot multivibrator 15 is performed. The current i flows, and the output voltage of the lithium battery 5 instantaneously drops considerably as shown in FIG. 4E, and then gradually recovers toward the original output voltage value. However, since the second one-shot multivibrator 15 returns to the high level at a time point t3 after a predetermined time after the time point t2, the output voltage of the lithium battery 5 quickly recovers to the original output voltage value and the lithium battery 5 No longer flows to the second one-shot multivibrator 15.

When the output voltage of the rectifying and smoothing circuit, which has been gradually reduced from the time t2, becomes lower than the output voltage of the lithium battery 5 at the time t4 as shown in FIG.
Flows through the diode 4 to the constant voltage circuit 6. At this time, the output voltage of the lithium battery 5 becomes E in FIG.
As shown in FIG. 2, the output voltage of the constant voltage circuit 6 is smaller than the voltage drop at the time point t2.
As shown in F of FIG.

Embodiment 3 FIG. FIG. 5 is a circuit diagram partially showing the third embodiment in a block diagram, and differs from the first embodiment in FIG. 1 in the configuration of the battery activation circuit. That is, in the third embodiment, the battery activation circuit 10B includes the above-described comparator 12 and one-shot multivibrator 16 connected in series between the output side of the rectifying and smoothing circuit 2 and the lithium battery 5.

The operation of the third embodiment will be described with reference to FIG. 6 showing the voltage, output, etc. of each part of the third embodiment.
The rectifying / smoothing circuit 2 having received the DC voltage shown in FIG. At this time, the comparator 12 in the battery activation circuit 10B determines that the output voltage of the rectifying / smoothing circuit 2 is not lower than the reference voltage of the comparator 12, which will be described later.
The low level output shown in FIG. 6B is generated. The one-shot multivibrator 16 generates a high-level output at its output terminal since a low-level output is applied to its input terminal. Since the output terminal of the one-shot multivibrator 16 is in the high level state, the lithium battery 5 generates the output voltage shown in FIG.
No current flows from the lithium battery 5 to the one-shot multivibrator 16. Finally, based on the output voltage of the rectifying and smoothing circuit 2, the constant voltage circuit 6 supplies a constant output voltage shown in FIG.

However, when the AC power supply that has not been powered down for a long time is powered down at time t1, the AC power supply voltage immediately becomes zero voltage, but the rectifying / smoothing circuit 2 has a short period of time as shown in FIG. After maintaining the state, the voltage becomes lower than the reference voltage REF of the comparator 12 at time t2. Therefore, the state of the comparator 12 changes to a high level as shown in FIG. 6B, and the one-shot multivibrator 16 receiving this also changes the state of its output terminal to a low level as shown in FIG. 6C. The discharge current i flows from the lithium battery to the one-shot multivibrator 16, and the output voltage of the lithium battery 5 instantaneously drops considerably as shown in FIG. 6D, and then gradually recovers toward the original output voltage value. try to. However, since the one-shot multivibrator 16 returns to the high level at a time point t3 after a predetermined time after the time point t2, the lithium battery 5
Quickly recovers to the original output voltage value and the discharge current from the lithium battery 5 no longer flows to the one-shot multivibrator 16.

When the output voltage of the rectifying and smoothing circuit, which has been gradually reduced, becomes lower than the output voltage of the lithium battery 5 at time t4 as shown in FIG. 6A, the discharge current from the lithium battery 5 passes through the diode 4. It flows to the constant voltage circuit 6. At this time, the output voltage of the lithium battery 5 slightly decreases as shown in FIG. 6D, but is smaller than the voltage decrease at the time point t2. Therefore, the output voltage of the constant voltage circuit 6 also becomes as shown in FIG. But only a little.

[0021]

As described above in detail, the present invention is connected between at least one of the input side and the output side of the DC conversion circuit for converting the voltage of the AC power supply into DC and the internal battery, and After a power failure and before switching power, a battery activation circuit for once discharging the internal battery is provided, and this battery activation circuit is a one-shot multivibrator connected to the input side of the DC conversion circuit, A comparator connected to the output side, and a logic circuit connected between the one-shot multivibrator and the comparator and the built-in battery, or connected in series between the input side of the DC conversion circuit and the built-in battery Or the first and second one-shot multivibrators, or the comparator and the one-shot multivibrator. When the AC power supply that has not been interrupted for a long time stops and the power supply is switched to the built-in battery, the voltage drop of the built-in battery can be reduced, and a lithium battery with a small capacity can be used. A standard IC can be used without using a low voltage IC,
This has the effect of reducing the cost and improving the reliability of the device at the time of power supply switching.

[Brief description of the drawings]

FIG. 1 is a circuit diagram partially showing a first embodiment of the present invention in a block diagram.

FIG. 2 is a waveform diagram for explaining the operation of the first embodiment.

FIG. 3 is a circuit diagram partially showing a second embodiment in a block diagram;

FIG. 4 is a waveform diagram for explaining the operation of the second embodiment.

FIG. 5 is a circuit diagram partially showing a block diagram of a third embodiment;

FIG. 6 is a waveform diagram for explaining the operation of the third embodiment.

FIG. 7 is a circuit diagram partially showing a block diagram of a conventional power supply device.

FIG. 8 is a waveform diagram for explaining the operation of the conventional power supply device.

[Explanation of symbols]

 2 Rectifier smoothing circuit 3, 4 Diode 5 Lithium battery 10, 10A, 10B, battery activation circuit 11, 16 One-shot multivibrator 12 Comparator 13 Negative logic AND circuit 14 First one-shot multivibrator 15 Second one Shot multivibrator REF Reference voltage

Claims (4)

(57) [Claims] 1. A power supply device for switching a power supply to a built-in battery at the time of a power failure of an AC power supply. A battery activation circuit that once discharges the internal battery after the AC power supply fails and before the power supply is switched, and is connected between the DC conversion circuit and the internal battery, and the output voltage of the DC conversion circuit is A power supply switching circuit for switching power from the AC power supply to the internal battery when the output voltage of the internal battery becomes lower than the output voltage of the internal battery. 2. A battery activation circuit comprising: a one-shot multivibrator connected to an input side of a DC conversion circuit; a comparator connected to an output side of the DC conversion circuit; and a one-shot multivibrator and a comparator. A logic circuit connected between the built-in batteries, wherein the one-shot multivibrator and the logic circuit discharge the built-in battery in response to the stop of the AC power supply, and output voltage of the DC conversion circuit The power supply device according to claim 1, wherein the comparator and the logic circuit stop discharging the built-in battery when the voltage of the internal battery becomes lower than the reference voltage. 3. The battery activation circuit has first and second one-shot multivibrators connected in series between an input side of a DC conversion circuit and a built-in battery. 2. The power supply according to claim 1, wherein the first and second one-shot multivibrators discharge the built-in battery in response to the control signal, and after a predetermined time, the second one-shot multivibrator stops discharging the built-in battery. apparatus. 4. A battery activation circuit having a comparator and a one-shot multivibrator connected in series between an output side of a DC conversion circuit and a built-in battery, and the DC conversion circuit after a power failure of the AC power supply. When the output voltage of the comparator becomes lower than the reference voltage of the comparator, the comparator and the one-shot multivibrator discharge the internal battery, and after a predetermined time, the one-shot multivibrator stops discharging the internal battery. The power supply device according to claim 1, wherein