JPH03224024A - Memory card - Google Patents

Abstract

PURPOSE:To prevent the power consumption of a battery that is caused by the deterioration of a capacitor by inserting a fuse in series into the capacitor connected in parallel to the power supply of a storage holding IC memory. CONSTITUTION:A capacitor C1 is connected in parallel to a storage holding battery B, the storage holding IC memories IC1-IC4, a diode D1 which prevents the charging to the battery B, a diode D2 which prevents the reverse current of a current to the device side from the battery B, and the power supply for the memories IC1-IC4 respectively. Then a fuse is put into the capacitor C1. Thus the capacitor C1 is separated from a power circuit by the fusing of the capacitor C1 itself when the performance of the C1 is deteriorated. As a result, the consumption of the battery can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a memory card used in an external storage device such as a personal computer, a handy terminal, or a word processor.

[Conventional technology]

Conventionally, this type of memory card has a memory retention battery (B) such as a lithium battery and a memory retention I as shown in FIG.
C memo! J (ICI to IC4), a diode D1 to prevent charging to the battery, a diode D2 to prevent current from flowing backward from the battery to the device side such as a personal computer, a capacitor C2 for smoothing the power supply, and a capacitor CWt for high frequency absorption. ~C24.

[Problem to be solved by the invention]

In the storage holding circuit of the conventional memory card described above, the capacitor C1 is required to have a large capacitance value of several μF to several tens of μF. Tantalum capacitors, aluminum electrolytic capacitors, etc. are used because of the need for ultra-compact integration such as portable business card-sized memory cards. The high-frequency absorbing capacitors 021 to C24 are usually arranged in the immediate vicinity of the memory holding IC memory, and are ceramic capacitors having a capacitance value of about 0.1 μF.

The large-capacity tantalum capacitors and aluminum electrolytic capacitors mentioned above have poor moisture resistance; for example, if left in a temperature and humidity environment of 85°C and 85% for 1000 hours, the initial value will be 0.1μ.
A leakage current of about A deteriorates from several μA to several tens of μA.

In extreme cases, it may lead to a short circuit. The high frequency absorption capacitors 021 to c24 are ceramic capacitors, and there is almost no deterioration in moisture resistance or deterioration in specific leakage current compared to tantalum or aluminum electrolytic capacitors. Therefore, the leakage current of the large capacity capacitor C1 is supplied from the battery B via the diode D1, resulting in a shortened battery life. As a result, there was a drawback that the contents stored on the memory card were unexpectedly lost.

[Means to solve the problem]

The present invention provides a memory retention battery B and a memory retention IC memory (I Cl to IC4) 1! In the memory card, a capacitor is connected in parallel to a diode D2 for preventing charging to the battery, a diode D2 for preventing current from flowing back from the battery to a device such as a personal computer, and a power supply for the memory holding IC memory. It is characterized by incorporating a fuse or a resistor into the capacitor.

[Example] The memory holding circuit of a memory card is as shown in FIG.
Memory retention battery B and memory retention IC memo! j (I
CI to IC4), a diode D1 for preventing charging to the battery.
Diode D2 and power supply smoothing capacitor C that prevent current from discharging from battery B to the device side such as a personal computer
Consists of I.

C2 and C24 are capacitors for absorbing high frequency noise of the IC memory. Capacitor C! is an IC memo!
j (C21" C24) in parallel.

If the memory card is removed from the device and carried around or stored, and capacitor C3 deteriorates due to moisture resistance, etc., the battery will generate an extra current corresponding to the leakage of the capacitor from battery B via diode D. It will be consumed. Therefore, if the capacitor C1 is a conventional capacitor as shown in FIG. 2, the discharge will continue until the battery B is completely discharged, and the current capacity of the battery will eventually disappear. On the other hand, the above drawback can be eliminated by using a self-fusing type capacitor as the capacitor C1 as shown in FIG.

In FIG. 3, the capacitor C1 in FIG. 1 is connected in parallel with a plurality of capacitors having a fuse function. Therefore, even if one or two of these fuses blow out and the capacitor no longer functions as a capacitor, there is an advantage that the remaining capacitor can function as a memory card.

FIG. 4 is a memory holding circuit of a memory card showing another example of the present invention. Diode D1. A Schottky barrier diode with a small forward voltage is normally used for D2. The large capacity capacitor C1 has a value of 1 to 10 μF, and a tantalum capacitor or an aluminum electrolytic capacitor is used as a capacitor having a small external size and a large capacitance value.

As the small capacitance capacitors C21 to C24, ceramic capacitors of about 0.1 μF are selected for high frequency absorption. Here, it is assumed that a memory card is designed using a BR2325 battery with a current capacity of 165 mAH and four 256 Kbit SRAMs. In this case, S at room temperature 25℃
The leakage current in the memory retention state of the RAM is about 1 μ8 or less. Therefore, it is about 4 μA for 4 pieces. Therefore, if this battery handles this amount of current, it can maintain memory for 4.7 years. Here, the high frequency absorption capacitor is a capacitor mainly made of ceramic, and its leakage current does not deteriorate much compared to tantalum capacitors and aluminum electrolytic capacitors. However, if the smoothing large-capacity capacitor C1 deteriorates, tens of microamperes may flow. Here, if the current is 20 μA and the current for memory retention to the memory is 4 μA, the memory retention time will be about 0.8 years. Therefore, in order to guarantee a memory retention time of at least two years at room temperature, it is necessary to suppress the current to 9.4 μA or less. Therefore, the series resistance is 3V/(9,4-4)μ
When A=550 and Ω, even if the large capacitance capacitor C1 is short-circuited in the worst case, a life of two years can be guaranteed at room temperature.

5 and 6 show modifications of R1 and C shown in FIG. 4. That is, when the capacitance value of the large-capacity capacitor C1 does not reach a desired value due to limitations such as the external size of the memory card, a plurality of capacitors can be used. In the case of Fig. 5, if even one of C1l to CI3 is shorted, it will not function as a capacitor, but in the case of Fig. 6, even if one or two are shorted, at least one other one will function as a capacitor. This makes it a highly reliable card.

〔Effect of the invention〕

According to the present invention, in the case of FIG. 1, when capacitor C0 deteriorates, the fuse of the capacitor itself is blown, causing capacitor C
1 is disconnected from the power supply circuit, thereby preventing battery consumption.

In the case of FIG. 3, even if only one of the capacitors CI1 to CI3 deteriorates, only one capacitor is disconnected from the power supply circuit and the other two remain in operation, resulting in the effect that a reliable memory card can be provided.

In addition, even if the power supply smoothing capacitor c1 deteriorates due to the series resistor R1 shown in Fig. 5, and in the worst case is short-circuited, the battery consumption can be limited by the series resistor R1, so that the memory of the memory card can be maintained. This makes it possible to guarantee the service life time, which has the effect of providing a reliable memory card.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a memory holding circuit of a memory card according to the present invention, and FIG. 2 is a diagram showing a memory card according to the prior art.
FIG. 3 is a diagram showing an example in which the capacitor C1 in FIG. 1 is implemented by a plurality of capacitors CIl to CH, and FIGS. 4 to 6 are diagrams showing other embodiments of the present invention. B... Memory retention battery, D... Diode to prevent battery charging, D2... Diode to prevent backflow, IC, ~IC4... Memory IC
, C2, ~C24... High frequency absorption diode, CI, C1l~CI3... Power supply smoothing capacitor.

Claims (1)

[Claims] It has a memory retention battery, a memory retention IC memory, a diode to prevent charging of the battery, a diode to prevent current from flowing backwards from the battery to the device side, and a capacitor connected in parallel to the power supply of the memory retention IC memory. 1. A memory card in which a fuse or a resistor is inserted in series with the capacitor.