JPS60254215A - Battery backup circuit - Google Patents

Abstract

PURPOSE:To prevent the battery consumption of a backup circuit for a CMOS memory by actuating a detection circuit only in an application mode of a power supply and storing the information on actuation of the detection circuit to use it as an alarm output. CONSTITUTION:The power is supplied to a CMOS memory 4 from a primary battery 1 via a diode 2. While a comparator 3 delivers an alarm output ALM when the battery voltage is less than a prescribed level. Here a flip-flop FF5 and a lead relay 6 are provided, and a detection circuit part is always cut off by the relay 6 to prevent the supply of a current ID. The detection circuit part works only when RESET is applied after main power supply is applied. The ALM delivered by the comparator 3 after actuation of the detection circuit part is stored to the FF5 and then used for display of alarm. The current ID is also reduced. This can prevent the power consumption of the battery 1.

Description

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

[Technical background of the invention]

CMOS memory battery backup circuit (2) It is necessary to detect the deterioration of the battery and replace it if necessary.

However, conventional circuits consume a large amount of power (approximately 80%) for this detection, which poses the dilemma of shortening battery life.

An example of a conventional circuit is shown and explained in FIG. In the figure, 1
is a primary battery, 2 is a diode, R1, R2゜R3 is a resistor, 3 is a comparator (for example, Intersil 8212
), 4 is a CMOS memory.

Here, if the voltage VB of the secondary battery 1 is 2.5V and the values of the resistors R1 and R2 are 220Ω, the current ID flowing through the resistor R1 is 5.7 μA.

The comparator 3 receives a resistance-divided voltage, and outputs an alarm output ALM if the voltage falls below a predetermined value.

However, in such a conventional example, as described above, current always flows through the resistor R1, which consumes power.
The drawback is that the battery drains quickly.

(3) The present invention has been made to solve the above-mentioned drawbacks, and provides a battery backup circuit that can prevent unnecessary power consumption.

[Summary of the invention]

In order to achieve the above object, the present invention focuses on the fact that no current flows from the battery to the memory when the main unit is powered on, and operates the detection circuit section only when the power is turned on, and stores this information. The device is characterized in that it is stored and used for outputting an alarm, and the detection circuit section is kept off at other times to prevent battery consumption.

[Embodiments of the invention]

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

In the figure, reference numeral 5 indicates a flip-flop, and reference numeral 6 indicates an IJ-reed relay, and the detection circuit section is always cut off by the reed relay 6, so that the current ID does not flow.

The detection circuit operates only when the main power is turned on.
O-254215(2) and only when RESET is applied.

In other words, if +5■ of the main power supply is not turned on, reed relay 6 will remain open and ID = O, so IB-I
It becomes M.

Incidentally, in the conventional example shown in FIG. 2, IB=ID+IM, and a useless current ID flows.

Now, when RESET is applied to the secondary, battery voltage VB<VD
D, IB=ID, and the detection circuit section is activated.

If the comparator 3 issues an alarm ALM at this time, it is stored in the flip-flop 5 and used for alarm display.

Next, if you turn off the reset and go to normal operation, it will become IB-〇.

In other words, in synchronization with the main unit's operation sequence of main power OFF → main power ON, RESET → main power ON, operation,
The current IB flowing out from the battery.

By sorting in the order of IM→ID→0, IB is minimized and unnecessary battery consumption is prevented.

(5) [Effects of the Invention] As described above, according to the present invention, the ID current (5.7 μA) that conventionally always flowed can be eliminated.

In other words, if the time the main power is turned on is 1/2 of the total,
In the conventional example shown in Fig. 2, the average current flowing out from the battery is I = 'I M + I D, so IM = 1.6μ
From A, ID=5.7 μA, I=6.5 μA.

On the other hand, in the present invention, ID=0, so ■=Ding IM
=0.8μA.

Therefore, power consumption can be reduced to about one-eighth of the conventional one.

Of course, as long as the main power is turned on, the current flowing out from the battery will be 0, and no voltage drop will occur.

In this way, the present invention can produce a batch (6) with extremely low power consumption by adding only a few parts to the conventional example. Fig. 1 shows a specific embodiment of the present invention, and Fig. 2 shows a conventional example.

1st primary battery 2: Diode 3: Comparator 4: CMOS memory 5: Flip-flop 6: Reed relay

Claims (1)

[Claims] (1) In a battery backup circuit including a battery voltage drop detection circuit section, the battery voltage drop detection circuit is activated only when an initial reset signal is generated when the main power is turned on, and the detection signal at this time is memorized and the battery backup circuit is A battery backup circuit, characterized in that the signal is used to display an alarm, and the battery voltage drop detection circuit is shut off so as not to operate except when an initial reset signal is generated.