JPH02128209A - memory backup device - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a backup device for volatile memory such as RAM.

[Prior Art] Conventionally, in devices using volatile memory such as RAM, batteries or nickel-cadmium (Ni) are used to prevent data stored in the volatile memory from being erased when the power is turned off.
Cd) It is backed up by a rechargeable battery such as a battery.

[Problems to be Solved by the Invention] In a device whose volatile memory is backed up by a battery, data in the memory will be erased if the device is powered off when the battery is replaced. Therefore, to prevent this,
Batteries must be replaced while the device is turned on, but this poses safety problems such as short circuits.

In addition, for devices whose volatile memory is backed up by rechargeable batteries such as NlCd batteries, the rechargeable battery must be fully charged when used for the first time or when the voltage of the rechargeable battery has decreased due to long periods of non-use. In order to do this, the device must be left on for a long time (about 8 hours or more). Therefore, even if you turn off the power with an incomplete charge and then turn on the power, the memory will be lost. In some cases, data may have been deleted. In other words, this limits the use of the rechargeable battery until it is fully charged.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a memory backup device that prevents data from being erased even if the battery is replaced with the power turned off. It's about doing.

Another object of the present invention is to prevent erasure of data in the memory even if the power is turned off while the rechargeable battery is incompletely charged in a configuration in which volatile memory is backed up by a rechargeable battery. The purpose of the present invention is to provide a memory backup device.

[Means for Solving the Problems] In the invention described in item 1, there is provided a volatile memory, a power source that supplies voltage necessary for data retention to the volatile memory, and a A memory backup device comprising a battery that supplies the voltage to the memory is characterized in that an electric double layer capacitor charged by the power source is inserted in parallel with the battery.

The invention described in item 2 is characterized in that the battery in the invention described in item 1 is a rechargeable battery that is charged by the power source.

[Function] In the invention described in item 1, when the power is turned on, the electric double layer capacitor is charged by the power.

Therefore, even if you replace the battery with the power turned off, the electric double layer capacitor backs up the volatile memory, so the data in the memory will not be erased. Safety can be ensured since there is no need to replace the battery at the same time.

In the invention described in item 2, when the power is turned on, charging of the rechargeable battery is performed for a long time, but charging of the electric double layer capacitor is completed in a few seconds. Therefore, even if the power is turned off while the rechargeable battery is incompletely charged, the electric double layer capacitor backs up the volatile memory until the power is turned on again, so the data in the memory will remain intact. It is never erased, so usage is not restricted until the rechargeable battery is fully charged.

[Example] Hereinafter, one embodiment of the present invention will be described based on the drawings.

A first embodiment of the present invention is shown in FIGS. 1 and 2. In FIG. 1, 11 is a volatile memory such as a RAM. A power supply 14 is connected to a power supply line 12 of the volatile memory 11 via a power supply switching circuit 13 . The voltage +5V (more than the data retention voltage of the volatile memory 11) supplied from the power supply 14 is detected by the reference voltage detection circuit 15.

The reference voltage detection circuit 15 monitors the rise or fall of the voltage supplied from the power supply 14, and outputs a control signal to the power supply switching circuit 13 when the voltage of the power supply 14 becomes higher than or lower than the reference voltage.

When it is detected by the control signal C8 from the reference voltage detection circuit 15 that the voltage of the power supply 14 has become equal to or higher than the reference voltage, the power supply switching circuit 13 transfers the voltage from the power supply 14 to the volatile memory 11 through the power supply line 12. supply to

A 4ct battery 17 is connected to the power supply line 12 via a backflow prevention diode 16, and an electric double layer capacitor 18 is connected to the series circuit of the backflow prevention diode 16 and battery 17. inserted in parallel. The electric double layer capacitor 18 completes charging in a few seconds and has discharge characteristics comparable to a battery.For example, if the volatile memory 11 is 65 bytes, it can be backed up for about one week.

Therefore, as shown in FIG.
) or below and the battery 17 needs to be replaced,
Even if the power supply 14 is turned off, the power supply voltage of the volatile memory 11
11 is maintained at a data retention voltage v11- or higher of the volatile memory 11 by the electric charge charged in the electric double layer capacitor 18.

Therefore, even if you use the device after replacing the battery 17,
Data in volatile memory 11 is never erased.

匪λm concave second embodiment is shown in FIGS. 3 and 4.
As shown in FIG. 3, in place of the battery 17 in the first embodiment, Ni
A rechargeable battery 21 such as a CD battery is used, and a charging resistor 22 is inserted in parallel with the backflow prevention diode 16 between the soil scraper of the rechargeable battery 21 and the power supply line 12 of the volatile memory 11. be.

Therefore, as shown in FIG. 4, when the power supply 14 is turned on, the rechargeable battery 21 is charged little by little through the charging resistor 22, while the electric double layer capacitor 18 is completely charged in a few seconds. , the power supply voltage v of the volatile memory 11
11 rises with a slight delay from the power supply voltage "14. After a while, when the power supply 14 is turned off, the voltage V21 of the rechargeable battery 21 reaches the data retention voltage V11- of the volatile memory 11 due to incomplete charging. However, since charging of the electric double layer capacitor 18 is completed, until the power supply 14 is turned on next time, the electric double layer capacitor 18 will
Data in memory 11 is backed up.

[Effect of the invention] As described above, according to the present invention, the following effects are achieved.

In the invention described in item 1, when the power is turned on, the electric double layer capacitor is charged by the power.

Therefore, even if you replace the battery with the power turned off, the electric double layer capacitor backs up the volatile memory, so the data in the memory will not be erased. Safety can be ensured since there is no need to replace the battery.

In the invention described in item 2, when the power is turned on, charging of the rechargeable battery is performed for a long time, but charging of the electric double layer capacitor is completed in a few seconds. Therefore, even if the power is turned off while the rechargeable battery is incompletely charged, the electric double layer capacitor backs up the volatile memory until the power is turned on again, so the data in the memory will remain intact. It is never erased, so usage is not restricted until the rechargeable battery is fully charged.

[Brief explanation of drawings]

1 and 2 show a first embodiment of the present invention, FIG. 1 is a circuit diagram, and FIG. 2 is a diagram showing the power supply voltage of the memory when replacing the battery in the circuit of FIG. 1. . 3 and 4 show a second embodiment of the present invention, FIG. 3 is a circuit diagram, and FIG. 4 is a circuit diagram of the circuit shown in FIG. 3 when the voltage of the rechargeable battery is lower than the data retention voltage. FIG. 7 is a diagram showing the power supply voltage of the memory when the power is turned off. DESCRIPTION OF SYMBOLS 11... Volatile memory, 14... Power source, 17... Battery, 18... Electric double layer capacitor, 21... Rechargeable battery. Figure Figure

Claims (2)

[Claims] (1) A memory backup that includes a volatile memory, a power supply that supplies voltage necessary for data retention to the volatile memory, and a battery that supplies the voltage to the volatile memory when the power is turned off. A memory backup device characterized in that: an electric double layer capacitor charged by the power source is inserted in parallel with the battery. (2) The memory backup device according to claim 1, wherein the battery is a rechargeable battery that is charged by the power source.