JPH04217823A - Battery power supply - Google Patents

Abstract

PURPOSE:To prevent erroneous lighting of a battery overdischarge alarm lamp due to power turn OFF operation in a power supply circuit for feeding a voltage from a backup battery through a DC-DC converter to a load. CONSTITUTION:The invention takes advantage of a fact that the variation rate of battery output voltage is remarkably higher at the time of turn OFF of power than at the time of overdischarge. In other words, output voltage drop of a battery 2 is grasped in three stages by means of comparators 9, 15 and the timing of passing through each stage is detected by means of an AND gate 16 producing logical product of the outputs from the comparators 9, 15 and a delay circuit 17. The detection results are employed in ON control of an alarm lamp 12.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery power supply circuit, and more particularly to a battery power supply circuit using a rechargeable battery as a device power supply.

0002

2. Description of the Related Art FIG. 2 is a circuit diagram showing the configuration of a conventional battery power supply circuit. A rechargeable battery 2 can be freely charged by an AC-DC converter 1, and the battery output is connected to a DC-DC converter 4 via a power switch 3.
is being input to. The output DC voltage of this converter 4 becomes the operating power supply voltage of a load (not shown).

In order to compare the input and output voltages of the DC-DC converter 4, a voltage dividing circuit consisting of resistors 5 and 6 is provided on the input side of the converter 4, and a voltage dividing circuit consisting of resistors 7 and 8 is provided on the output side of the converter 4. A comparator 9 is provided to compare the two equal divided voltages.

A transistor 10 is provided which is turned on by this comparison output, and this transistor 10 drives a coil of a latching relay 11. Make contact 1 of this latching relay 11
3 turns on, the alarm display LED 12
This is a configuration in which lighting is controlled.

In such a configuration, when the battery 2 becomes over-discharged and the input voltage of the DC-DC converter 4 decreases, the comparator 9 detects this and the transistor 1
Turn on 0. This drives the coil of the latching relay 11, and the ON operation of the make contact 13 causes the LE
D12 lights up and an alarm is displayed.

[0006] The reason why a latching relay is used is that even if battery 2 becomes completely over-discharged during battery backup and the DC-DC converter stops, it will maintain the abnormal state and then turn on the AC input. This is to notify that the power supply has stopped when the DC-DC converter 4 is operated while charging the battery 2 from the AC-DC converter 1. For example, when the load is a memory or the like, a latching relay is used to maintain an alarm display immediately before the power is turned off in order to indicate the possibility of memory data loss or to facilitate investigation of the cause.

[0007] In such a power supply circuit, the function is simply to detect an undervoltage of the battery and maintain the previous state using a latching relay. Therefore, when the power switch 3 is turned off and the battery 2 is disconnected, has the following problems:

That is, even when the battery is disconnected,
Since the comparator 9 detects the battery undervoltage condition, the alarm display is maintained and the latching relay 11 needs to be reset when the system is started up, and such a condition is not intended to indicate battery over-discharge. It will defeat the purpose.

[0009]

[Object of the Invention] Therefore, the present invention was made to solve the drawbacks of the conventional ones, and its purpose is to make it possible to determine whether the battery is naturally discharging or the power is cut off. Another object of the present invention is to provide a battery power supply circuit that prevents malfunction of a battery over-discharge alarm.

0010

[Structure of the Invention] A power supply circuit according to the present invention includes a battery,
An AC-DC converter that charges this battery,
a power switch that turns on and off the output of the battery; a DC-DC converter to which the output of the battery is supplied via the saw switch and supplies a DC voltage to a load; and a DC-DC converter that divides the DC voltage to generate two different reference voltages. first and second voltage dividing means for comparing the divided voltage of the input voltage of the DC-DC converter and the two reference voltages, respectively;
a comparison means, an AND means for outputting the logical product of both comparison results, a delay means for delaying the output of the logical product, and a latching relay controlled to be turned on by the delayed output;
It is characterized by including a display means whose lighting is controlled in response to the ON operation of the latching relay.

[0011]

Embodiments Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of the present invention, and parts equivalent to those in FIG. 2 are designated by the same reference numerals. Regarding the differences from the conventional example shown in FIG. 2, a second comparator 15 is provided in addition to the comparator 9. The reference voltage of these two comparators is 2, which is obtained by converting the output voltage of the DC-DC converter 4 through a series voltage dividing circuit of resistors 7, 8, and 14.
There are two divided voltages.

A divided voltage obtained by dividing the input voltage of the converter 4 by resistors 5 and 6 is applied to the negative phase input of the comparator 9, and a reference voltage (the higher reference voltage) is applied to the positive phase input. be done. Furthermore, a divided voltage obtained by dividing the input voltage of the converter 4 by resistors 5 and 6 is applied to the positive phase input of the comparator 15, and a lower reference voltage is applied to the negative phase input thereof.

The outputs of both comparators are input to an AND gate 16, subjected to an AND operation, and then introduced to a delay circuit 17. This delayed output turns on the transistor 10, and the other configurations are the same as the conventional example shown in FIG.

In this configuration, if the voltage of the battery 2 is normal during battery backup when the switch 3 is on, the output of the comparator 9 is at a low level, and the output of the comparator 15 is at a high level. It is assumed that each resistance value of the pressure circuit is set.

In this case, since the output of AND gate 16 is at a low level, transistor 10 is off, and therefore LED 12 does not light up.

[0017] When the battery voltage decreases due to overdischarge,
First, the output of comparator 9 is inverted and becomes high level,
Therefore, the output of the AND gate 16 is inverted to a high level and remains in that state thereafter. Therefore, the transistor 10 is turned on, the latching relay 11 remains on, and the LED 12 is turned on to display an alarm.

When the battery voltage further decreases, the output of the comparator 15 first inverts to a low level, but the alarm display continues due to the action of the latching relay 11. Next, turn off the power switch 3 and turn off the battery 2.
If , the outputs of the comparators 9 and 15 are continuously inverted. At this time, there is some time until the output of the comparator 9 is inverted and the output of the comparator 15 is inverted, but if the delay time of the delay circuit 17 is set so that the transistor 10 does not turn on during this time, an alarm can be generated. 12 will not turn on by mistake.

[0019]

[Effects of the Invention] As described above, according to the present invention, the rate of change in the output voltage of the battery is detected using two comparators and a delay circuit, and it is possible to determine whether the battery is naturally discharged or the power is turned off. Therefore, it is possible to prevent malfunction of the battery over-discharge alarm when the power is turned off.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional battery power supply circuit.

[Explanation of symbols]

1 AC-DC converter 2 Battery 3 Power switch 4 DC-DC converter 5~8,14 Voltage division resistor 9,15 Comparator 10 Transistor 11 Latching relay coil 12 LED 16 And Gate 17 Delay circuit

Claims (1)

[Claims] 1. A battery, an AC-DC converter that charges the battery, a power switch that turns on and off the output of the battery, and a saw switch to which the output of the battery is supplied and a DC voltage is applied to a load. supply D
a C-DC converter, voltage dividing means for dividing the DC voltage to generate two different reference voltages, and the DC-DC converter;
first and second comparison means for respectively comparing the divided voltage of the input voltage of the converter and the two reference voltages, and an AND means for outputting an AND of both comparison results, and an AND output of the AND. 1. A battery power supply circuit comprising: a delay means that delays; a latching relay that is turned on by the delayed output; and a display means that is controlled to light up in response to the turned-on operation of the latching relay.