JPH08172732A - Memory backup circuit - Google Patents

Abstract

PURPOSE: To provide a memory backup circuit which prevents the breakdown due to the charging of a lithium battery used for the backup circuit of a memory such as a RAM or the like. CONSTITUTION: In a memory backup circuit by which a RAM 1 installed at a computer is backed up by a lithium battery 6, a contact (b) 11b for a relay which is operated only when a power supply 2 for a computer body is turned on is interposed and installed in series with a backup power-supply line 7 across the lithium battery 6 and the RAM 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a memory backup circuit for charging protection of a lithium battery which backs up a volatile memory such as a RAM.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing a configuration of a conventional memory backup circuit, for example, a memory backup circuit of a microcomputer (hereinafter referred to as a computer). In the figure, 21 is a RAM as a volatile memory, 22 is a power source for a device such as a computer, and 23.
Is a power supply line for connecting the RAM 21 to the power supply 22 of the device to supply power to the RAM 21, 24 is a power switch of the device, and 25 is a diode.

Reference numeral 26 is a lithium battery for memory backup, and 27 is a backup power source line for the RAM 21, which is used when the power switch 24 of the apparatus is off.
Is to back up. The backup power supply line 27 includes a resistor 28 and a diode 29.
Reference numeral 30 is an electrolytic capacitor connected to the power supply line 27 on the downstream side of the diode 25.

The diode 25 prevents the lithium battery 26 from discharging due to current flowing from the lithium battery 26 to the power source 22 side at the time of backup when the power switch 24 is off. The resistor 28 protects the lithium battery 26 from deterioration due to overcurrent when a short circuit occurs on the RAM 21 side, and the diode 29 serves as the power switch 2.
4 is on, the device power supply 22 to the lithium battery 26
This prevents the charging current from flowing to the lithium battery 26 and prevents the lithium battery 26 from being destroyed.

[0005]

However, in this conventional memory backup circuit, only the diode 29 protects the lithium battery 26 from being charged. Therefore, when the diode 29 is attached reversely when assembling this memory backup circuit, or when the used diode 29 does not operate sufficiently and a reverse current flows, the power switch 24 is turned on. There is a risk of charging current flowing through the battery 26.

[0006] In particular, the lithium battery is very dangerous because it is destroyed when a charging current flows, and there is a risk of explosion or fire in some cases. Therefore, conventionally, the conduction of the diodes 29 constituting the already assembled backup power supply circuit has been checked one by one using a tester or the like to confirm whether or not the charging current flows through the lithium battery 26. Therefore, the workability of assembling the memory backup circuit is poor and has been a major cause of cost increase.

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a memory backup circuit that prevents damage due to charging of a lithium battery used for a backup circuit of a memory such as a RAM. There is.

[0008]

That is, the present invention is a memory backup circuit for backing up a volatile memory provided in an apparatus with a lithium battery, and a relay b that operates only when the apparatus is powered on. It is characterized in that a contact is provided in series with a backup power supply line between a lithium battery and a memory.

[0009]

In the above invention, the power supply of the device is turned off by inserting the b-contact of the relay, which operates when the power of the device is turned on, in series with the backup power supply line between the lithium battery and the memory. B of the relay when
The contacts are closed and the memory can be backed up. On the other hand, when the power supply of the device is turned on, the b contact is opened, and the current does not flow from the power supply of the device to the lithium battery, so that the charging current can effectively be prevented from flowing to the lithium battery. The lithium battery will not be destroyed.

[0010]

1 is a memory backup circuit showing an embodiment of the present invention, for example, a memory backup circuit of a computer (hereinafter referred to as a device).

In the figure, 1 is a RAM which is an example of a volatile memory, 2 is a power source for the device, 3 is a power supply line for supplying power to the RAM 1, 4 is a power switch for the device, and 5 is a diode. That is, the electric power supplied from the power supply 2 of the device passes through the power supply line 3 and is supplied to the R via the power switch 4, the diode 5 and the a-contact 11a of the relay described later.
Supplied to AM1. Further, the diode 5 is for preventing current from flowing back to the power supply 2 side when the power supply switch 4 is turned off.

Reference numeral 6 denotes R when the power switch 4 is off.
As a backup power source for backing up the AM1, a lithium battery is a battery which has a particularly long life and is suitable for keeping a minute current flowing for a long time, and 7 is a backup power source line for the RAM1. This backup power supply line 7 is connected to the downstream side of the a-contact 11a of the power supply line 3. The backup power supply line 7 is provided with a resistor 8, a diode 9 and a relay b contact 11b, which will be described later, so as to supply power to the RAM 1. Reference numeral 10 is an electrolytic capacitor provided on the power supply line 3 in front of the RAM 1.

Reference numeral 11 is a coil of an electromagnetic relay (hereinafter referred to as a relay coil) which is connected to the power supply line 3 and operates when the power switch 4 of the apparatus is turned on. The a contact point 11a and the b contact point 11b are These are an a contact and a b contact that are opened and closed by the operation of the relay coil 11.

Therefore, by the action of the relay coil 11, either the power supply 2 of the apparatus or the lithium battery 6 is connected to the RAM 1 and the contents of the RAM 1 are held.

The diode 9 is provided with the a contact 11a.
The lithium battery 6 is provided so that the charging current does not flow even if both the and b contacts 11b are closed. The resistor 8 is a resistor that protects the lithium battery 6 from deterioration due to overcurrent even if a short circuit occurs on the RAM 1 side.

Next, the operation of the memory backup circuit of the above embodiment will be described. First, when the power switch 4 is turned on, the relay coil 11 operates and the a contact 11a of the relay closes and the b contact 11b opens. To be done.
Therefore, the power from the power supply 2 of the device is supplied to the RAM 1 through the diode 5 and the a-contact 11a,
The data of 1 is retained.

At this time, since the b contact 11b of the relay is open, the power source 2 of the apparatus is connected to the lithium battery 6
No current flows through Therefore, a charging current does not flow in the lithium battery 6, and an accident such as destruction, explosion, or fire due to the charging of the lithium battery 6 does not occur.

Next, when the power switch 4 is turned off,
The relay coil 11 does not operate and its a contact 1
At the same time as 1a opens, the b contact 11b closes. The electrolytic capacitor 10 backs up the RAM 1 for a short time after the switching.

When the power switch 4 is off, the electric power from the lithium battery 6 is applied to the resistor 8, the diode 9 and the relay b contact 11 on the backup power line 7.
The data of RAM1 is supplied to RAM1 via b and is backed up even after the power switch 4 of the apparatus is turned off. Further, at this time, since the a-contact 11a of the relay is open, no current flows from the lithium battery 6 to the power source 2 side.

That is, since the b contact 11b of the relay is provided in series with the backup power source line 3 as described above, the power source 2 of the device should be completely disconnected from the lithium battery 6 in a circuit manner when the power source switch 4 is on. Therefore, the charging current does not flow from the power supply 2 of the device to the lithium battery 6. Therefore, the destruction of the lithium battery 8 can be effectively prevented.

Since the b contact 11b of the relay is opened only when the power switch 4 is on, the b contact 11b is closed when the power switch 4 is off.
When the lithium battery 6 and the RAM 1 are connected, the lithium battery 6
RAM1 can be backed up by.

Further, as in the above embodiment, by installing the a-contact 11a of the relay in series to the power supply line 3, the a-contact 11a and the b-contact 11b of the relay are connected regardless of the state of the power switch 4. Since either one of them is opened, the power supply 2 of the device and the lithium battery 6 are not connected, and the lithium battery 6 can be reliably prevented from being charged.

In the embodiment described above, by providing the diode 9, even if the a-contact 11a and the b-contact 11b may be closed at the same time, the charging current will flow to the lithium battery 6 side. Although it is configured so as not to be damaged, a general relay such as an electromagnetic relay often has a structure in which its a contact and b contact cannot be closed at the same time. Therefore, the diode 9 can be omitted. By doing so, the structure of the memory backup circuit can be further simplified, the manufacturing labor can be saved, and the manufacturing cost can be reduced.

As described in detail above, the safety is higher if the a-contact 11a of the relay is provided in the power supply line 3, but the a-contact 11a of the relay is not necessarily provided in the power supply line 3. , A-contact 11a of the power line 3
May be omitted and the diode 5 may be directly connected to the RAM 1.

In the above-mentioned embodiment, an example in which an electromagnetic relay is used is shown, but this relay may be any one as long as it has ab contact which is opened only when the power switch 4 of the apparatus is on, and a transistor is used. A non-contact relay using a semiconductor element such as or a reed relay interlocking with the power switch 4 may be used.

Further, the present invention is not limited to the backup circuit of the RAM 1, but may be used for backing up a circuit (such as a clock) including a status signal such as a flip-flop or a memory switch as another memory. It goes without saying that you can do it.

[0027]

As described above, since the b contact of the relay, which operates only when the power of the device is turned on, is interposed in series in the backup power supply line between the lithium battery and the memory, Even if the diode for preventing the charging of the lithium battery is mistakenly attached, or even if the diode does not operate correctly, it is possible to effectively prevent the charging current from flowing to the lithium battery, and to prevent the charging of the lithium battery due to charging. There is no need to worry about destruction, explosion, or fire.

Therefore, it is not necessary to confirm the operation of the diode, and the safety of the memory backup circuit can be improved and the manufacturing cost can be reduced at the same time. Further, the diode for preventing the charging of the lithium battery can be omitted, and in this case, the manufacturing cost can be further reduced.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an example of a memory backup circuit of the present invention.

FIG. 2 is a circuit diagram showing a conventional memory backup circuit.

[Explanation of symbols]

1 ... Memory, 2 ... Device power supply, 6 ... Lithium battery, 9 ...
Backup power supply line, 11b ... b contact.

Claims (1)

[Claims] 1. In a memory backup circuit for backing up a volatile memory provided in an apparatus with a lithium battery, a contact b of a relay, which operates only when the apparatus is powered on, is provided between the lithium battery and the memory. A memory backup circuit characterized by being inserted in series with the backup power supply line.