JPH01152521A - Memory backup power supply circuit for ic card - Google Patents

Abstract

PURPOSE:To attain battery exchange work in a condition which is connected to an external energizer by providing an output selection circuit which supplies the output of a battery to the power source line of a memory storage. CONSTITUTION:An output selection circuit is constituted by diodes D1-D4, and the forward direction lowering voltage of D1-D4 is set to 0.6V. When an IC card is set to a device and a 5V power source is applied to an external energizer line L1, 4.4V is supplied to a power source line L4 of a memory storage 3, and consequently, D2-D4 are cutoff. In a condition in which the external energizer is not supplied to a terminal T1, only the D2 is ON, 2.4V is supplied to the line L4 of the memory storage 3 by the output of a battery 1, and the data of the memory storage 3 are held. When a voltage E2 of the battery 1 is lowered and becomes less than 2.4V, the D2 is OFF, the D3 and D4 are ON, 1.8V is supplied to the line L4 of the memory storage 3 by the output of a battery 2, and the data of the memory storage 3 are held by the output of the battery 2.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an IC card that has at least an IC memory built into a card-like package, and particularly relates to an IC card that has at least an IC memory built into a card-like package. This invention relates to improvements in memory backup power supply circuits.

(Prior Art) A conventional IC card has a built-in high-energy lithium battery as a power source for memory backup. When the IC card is set in the reader/writer, an external power source is applied to the IC card, but in a normal state when the card is removed from the device, the stored information in the memory is retained using the built-in battery as the power source.

(Problem to be solved by the invention) Lithium batteries have a fairly long lifespan, but they cannot be used forever and must be replaced at appropriate times. What is important here is that the memory backup power supply must not be cut off even when replacing the battery. Therefore, in conventional IC cards, batteries must be replaced while applying external power to the card. Therefore, general users cannot easily replace the battery, and are forced to install a battery replacement device and perform the replacement work with a card set in the device.

This is extremely inconvenient in practice.

Furthermore, if you connect the card to an external device that supplies memory backup power and replace the battery while the power is on, you will have to apply force to the card by hand. Otherwise, a connection failure may occur. If such a connection failure occurs, there is a risk that the power supply to the card will be cut off and the data held within the card will be reduced. Therefore, even if you set the card in a battery replacement device and perform the replacement work,
It must be done with great care.

There is also a problem in determining battery life. There is a way to exchange it at a predetermined time limit, but this is very easy to forget. Therefore, there is a way to set up a battery voltage check function and use this to notify when it is time to replace the battery. However, high-performance batteries such as lithium batteries rapidly drop in voltage due to wear and tear, so if a drop in voltage is detected, they must be replaced within a short period of time, but replacement cannot be done as easily as in Moe's case. As a result, a situation is likely to occur where the replacement is not in time.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to be able to easily replace the battery without connecting it to an external power source, and to be able to replace the battery with sufficient time. An object of the present invention is to provide a memory backup power supply circuit for an IC card.

[Structure of the Invention] (Means for Solving the Problems) Therefore, in the present invention, at least two backup batteries are built into the card, and when an external power supply of a specified voltage or higher is not applied, these batteries are activated. Configure one of the outputs to be supplied to the memory power supply line, and
An output selection circuit is provided that supplies the output of a predetermined one battery to the battery line of the memory while the output voltage of that battery is higher than a specified value, and otherwise supplies the output of the other battery to the power supply line of the memory. Established.

(Function) Ueno: When one battery is exhausted and the output voltage drops below the specified value, the memory is backed up by the other battery, which was not used until then. This “other battery”
All you have to do is replace "one battery" during a long period of time until it runs out. Even during this replacement work, there is no need for an external power source because the battery is backed up by the "other battery."

(Embodiment) FIG. 1 shows a schematic configuration of a memory backup power supply circuit according to an embodiment of the present invention. A battery 1 and a battery 2 are built into the card for backing up a memory 3 consisting of a static RAM.

In this example, batteries 1 and 2 are lithium batteries with the same specifications,
Both rated outputs are 3V.

When this IC card is inserted into the reader/writer, terminals T1 to T4 of the card are connected to the connector on the device side, and a specified power of 5V is applied between the power terminal T1 and the ground terminal 2.

The line L1 of the outer power terminal T1 is connected to the ffi & line L4 of the memory 3 via the diode D1, and the output line L2 of the battery 1 is connected to the power line 1 via the diode D2.
-4, and the output line L3 of the battery 2 is connected to the power supply line L4 via series diodes D3 and D4. These diodes D1 to D4 constitute a Moe's output selection circuit. In this example, diode D1
~The forward voltage drop of D4 is set to 0.6V.

When the IC card is set in the device (reader/writer) and 5V power is applied to the external power line L1, 4.4V is supplied to the power line L4 of the memory 3 (in this state, the memory 3 is accessed). ), hence diode D2,
D3 and D4 are cut off. When no external power is supplied to terminal T1, only diode D2 is turned on,
2°4V is supplied to the power line L4 of the memory 3 by the output of the battery 1, and the data in the memory 3 is held.

Due to long-term use, the voltage E2 of battery 1 decreases to 2.4
When the voltage drops below v, the diode D2 turns off and the series diodes D3 and D4 turn on, and the output of the battery 2 supplies 1.8V to the power supply line L4 of the memory 3. 3 data are retained.

Further, in this embodiment, the following battery voltage check circuit is provided.

When the card is inserted into the device and the specified external power is supplied to the line L1, the two comparators 4 and 5 operate, and the reference voltage Vs divided by the resistors R1 and R2 is the reference voltage for both comparators 4 and 5. Applied as input. Then, the voltage E2 of the battery 1 is changed to the reference voltage E by the comparator 4.
The voltage E3 of the battery 2 is compared with the reference voltage VS by the comparator 5. Voltage E2 or E3 is voltage V
When the voltage drops below S, comparator 4 or 5 connects terminal T3.
Alternatively, a voltage drop notification signal is output to T4. The reader/writer side receives this signal and performs a predetermined display. Note that the comparator 4.5 may be provided on the reader/writer side, and the voltages of the batteries 1 and 2 may be simply derived from the card.

[Effects of the Invention] As explained in detail above, in this invention, the two backup batteries built into the card are configured to be sequentially and selectively used (discharged), so that when the first battery is It is only necessary to replace the exhausted battery within a long period of time from when it is exhausted until the next battery is exhausted. Moreover, there is no need to apply external power when replacing the battery, and the card can be replaced by itself. Therefore, there is sufficient time to replace the battery, and even a general user can easily replace the battery, thereby almost eliminating the possibility of accidentally losing data in the memory.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a memory backup power supply circuit according to an embodiment of the present invention. 1.2...Battery 3...Memories D1 to D4...Diode 4 configuring the output selection circuit
．． 5...Comparator

Claims (1)

[Claims] (1) A power supply circuit that constantly supplies power for memory retention to the memory of an IC card, has at least two built-in batteries, and is in a state where an external power supply with a voltage higher than the specified voltage is not applied to the external power supply terminal. , an output selection is made in which the output of a predetermined one battery is supplied to the power supply line of the memory while the output voltage of that battery is equal to or higher than a specified value, and the output of the other battery is supplied to the power supply line of the memory otherwise. A memory backup power supply circuit for an IC card characterized by being provided with a circuit.