JPS6027009A - Electronic device - Google Patents

Abstract

PURPOSE:To avoid the consumption of a battery owing to an unnecessary leakage current produced at the time of normal application by providing a means which detects the voltage drop of the battery and a control circuit which executes the discharge to a capacitor in response to the signal given from said detecting means. CONSTITUTION:A display showing a voltage drop is given to a display means IND with the signal of a circuit S which detects the voltage drop of a battery B. At the same time, a swtiching transistor T is controlled. The electric charge stored in a capacitor C is supplied to a memory M through a diode D which functions to discharge the electric charge of the capcitor C. While the charge from the battery B to the capacitor C is prevented by the reverse characteristics of the diode D. Therefore the charge is carried out to the capacitor C only when the transistor T is turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field) The present invention relates to electronic equipment equipped with a backup capacitor for volatile memory, and more particularly to charging control of a single capacitor.

(Sub) 1Mo) In the conventional system of this kind, as shown in Figure 1, the power source is 11,'
ii Volatile memo IJ-, MVC battery B is connected, and a backup capacitor C is connected in parallel to battery B. 9. Replace battery B. When battery B is removed due to
The electric charge stored in the capacitor C supplies power to the memory M and prevents the data in the memory M from disappearing.

In this conventional system, the capacitor C is always connected to the battery B, and the leakage current Ic of the capacitor C is constantly flowing, which accelerates the consumption of the battery B.

(Purpose) The present invention has been developed in view of this point, and is designed to charge a backup capacitor only when the power supply voltage drops due to normal use in electronic equipment using volatile memory and it is time to replace the power supply. The purpose of this is to prevent battery consumption due to unnecessary leakage current during normal use.

(Example) An example of the present invention will be described below with reference to FIG. S is a circuit for detecting the voltage drop of the battery B, and the signal of this S causes the display means INDK to display a voltage drop indicating the voltage drop and also controls one switching transistor T.

D is a diode for discharging the charge of the capacitor C, and supplies the charge stored in the capacitor C to the memory M through this diode D. Furthermore, the reverse characteristic of the third diode prevents charging of the capacitor C from the battery B. Therefore, the capacitor C is charged only when the switching transistor T is turned on.

Next, the operation of this block diagram will be explained. During normal use, the voltage of the battery B is sufficient to operate the memo +7-M, the voltage drop detection means S turns off the switching transistor T, and the display means IND does not display a voltage drop. Not performed. Further, at this time, the capacitor C is not charged by the diode D and no leakage current flows, thereby preventing unnecessary consumption of the battery. When the voltage of battery B drops due to use of the device, the voltage drop is detected by the voltage drop detection means SK and the switching transistor T is turned on.
from battery B to capacitor C via transistor T.
Charging is started, and a display indicating a voltage drop is displayed on the display means IND to inform the user of the device that it is time to replace battery B. At this point, the user of the device removes the battery 1.3 for replacement, but the charge stored in the capacitor C is supplied to the memory M through the diode D, so the data stored in the memory M will not be erased. Next, new battery B
is replaced, and when the voltage increases, the voltage drop detection means 8 [switching transistor T is turned OFF and the display means IND
Since the voltage drop display also disappears, capacitor C will not be charged and battery B will not be consumed by leakage current until the power supply voltage drops next time.

(Effects) As explained above, according to the present invention, the backup capacitor is charged only when the power supply voltage drops, and there is no leakage current from the backup capacitor during normal equipment use, so there is no wasted battery power. It is possible to prevent battery consumption, and there is no problem with the function of the backup capacitor when replacing the battery, and no special operations are required from the device user. This is extremely preferable since it reduces the number of times and reduces running costs. Note that the display means IND can also be used as a sound generating means such as a buzzer.
Alternatively, diode D may be used as a light emitting diode and also serve as a warning.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional system, and FIG. 2 is a block diagram showing an embodiment of the present invention. M +111.0 Memo IJ-C...--Capacitor D
...Fist...Diode TO...Transistor S...
...Voltage detection circuit B...Battery applicant Canon Co., Ltd., ゛・;;

Claims (1)

[Claims] In an electronic device having a volatile memory whose stored data disappears when the power is cut off, and a battery and a capacitor for retaining data in the memory, means for detecting a voltage drop of the battery, and the detecting means 7. An electronic device comprising: a control circuit for charging the capacitor in response to a signal from the electronic device.