JPH0311414A - Detection circuit for voltage drop of backup battery - Google Patents

Abstract

PURPOSE:To realize correct detection in a memory backup state by flowing a current from a backup battery during a short time only when the voltage drop of the backup battery is detected. CONSTITUTION:When a switch 2 is closed, the switch 3 is connected to terminal 3a, and a main power source 1 is connected to a backup RAM 4, and the current does not flow out of the backup battery 5. When the switch 7 is closed under this state, the current flows out of the battery 5 through a resistor 6. At that time, the voltage drop of the battery is detected by a comparator 9. The value of the resistor 6 is set equal to the input resistance of the RAM 4 in the backup state. Thus, the correct detection in the memory backup state can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a battery voltage drop detection circuit for backup memory.

[Conventional technology]

In conventional technology, in order to reduce fluctuations in battery voltage due to detection circuit connection, the input stage of the detection circuit has a high input resistance such as the gate input of an FET, and almost no current flows out from the backup battery. The circuit was designed to detect a voltage drop in the backup battery.

In addition, related devices of this type include
-23491 etc.

[Problem to be solved by the invention]

The above conventional technology uses backup memory batteries (hereinafter referred to as
No consideration was given to the voltage drop caused by the internal resistance of the battery (assumed to be a battery), and there was a problem in that a difference occurred between the voltage value detected by the battery voltage detection circuit and the battery voltage in the memory backup state.

The purpose of the present invention is to detect the voltage value of a battery as described above.
It is an object of the present invention to provide a backup battery voltage drop detection circuit that eliminates the difference between the battery voltage value in a memory backup state and further reduces the consumption of one battery power by the battery voltage drop detection circuit.

[Means to solve the problem]

In order to achieve the above object, current is caused to flow from the battery for a short time only when detecting a voltage drop in the backup battery.

Further, the current value flowing out from the 1X battery is equal to the current value flowing out from the battery when actually backing up the memory.

[Effect]

The output terminal of the backup battery is left open except when a drop in backup battery voltage is detected, and when backing up the memory, when a drop in backup battery voltage is detected.
It operates so that a current equal to the current flowing out from the battery is caused to flow out from the battery only while the output terminal voltage value of the battery becomes stable and hair spinning is determined. This eliminates wasteful consumption of one power of the backup battery, and makes it possible to detect a drop in battery voltage at a voltage value equal to the battery voltage value when backing up the memory.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG.

First, when switch 2 is open, switch 3 is connected to terminal 3b.
The backup RAM 4 is in a backup state. At this time, it is assumed that the switch 7 is in an open state, the input resistance of the comparator 9 is infinite, and all the current from the backup battery 5 flows to the backup RAM 4.

Next, when switch 2 closes, switch 3 closes terminal 3a.
, the outflow of current from the backup battery 5 is stopped, and the battery enters a waiting state for detecting a voltage drop.

Next, the switch 7 is closed, current flows out from the backup battery 5 through the resistor 6, and the output of the comparator 9 at that time is taken as the detection result.

The value of the resistor 6 at this time is set equal to the input resistance when the backup RAM 4 is in the backup state.

Next, the switch 7 is opened to end the detection of the backup battery voltage drop.

〔Effect of the invention〕

According to the present invention, the power consumption of the backup battery in the backup battery voltage drop detection circuit can be minimized, so that the life of the backup battery is hardly affected.

Furthermore, since a current equal to the current flowing out from the battery when the memory is being backed up is caused to flow out from the battery when the battery voltage is detected, it can be compared and detected as the battery voltage when the memory is actually being backed up.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention. 1... Main power supply, 2... Switch, 3... Switch, 3a... Terminal, 3b... Terminal, 4... Backup RAM. 5...Backup battery, 5a...Internal resistance, 6.
...Resistor, 7...Switch, 8...Reference voltage source, 9
...Comparator. Figure 1... Backup RAf/'I ・ Backup @ Death... Internal 4-work;

Claims (1)

[Claims] A memory for storing necessary data when the main power is cut off, a battery for backup power for the memory, a switching circuit for switching the power for the memory between the main power and the backup battery, and a voltage control circuit for the backup battery. A backup battery voltage drop detection circuit comprising a comparator and a circuit for detecting a voltage drop below a reference voltage.