JPH1051978A - Power supply backup circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the malfunction and destruction of a memory, by controlling the voltage difference produced between the voltage of a control signal outputted to the memory from a logic circuit and the power supply voltage of the memory, within the tolerance of the input terminal voltage of the memory, by connecting a diode in parallel with a backup means for the memory. SOLUTION: A diode 10 is a reverse-current preventing diode which is connected in parallel with diodes 8 and 9, connects a power source 1 for device to a memory 3, and prevents an electric current from flowing to the power source 1 and a logic circuit 2 with the purpose of preventing the consumption of a large-capacitance capacitor 5 and a primary battery 4. Since the power source 1 is connected to the memory 3 by means of the diode 10 when the power supply is not interrupted, the forward voltage drops by the amount of one diode. Therefore, the voltage difference produced between the voltage of a control signal outputted to the memory 3 from the logic circuit 2 can be controlled within the tolerance of the input terminal voltage of the memory 3, and the malfunction and destruction of the memory 3 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply circuit for backing up a memory, a timer, and the like.

[0002]

2. Description of the Related Art There is a type in which a primary battery such as a lithium battery is incorporated as a power supply for backing up a memory or a timer of a semiconductor, and the above-mentioned primary battery needs to be replaced when the battery runs out. Therefore, there is a power supply circuit in which a large-capacity capacitor is incorporated in a power supply circuit in order to extend the period until the primary battery is replaced or to eliminate the need for replacement.

FIG. 3 is a circuit diagram showing a conventional power supply circuit with a backup function. In FIG. 3, an apparatus power supply 1 is a power supply for supplying power to the logic circuit 2 and the memory 3. The logic circuit 2 is a circuit that does not need a backup when the power is turned off, while the memory 3 is a memory that needs a backup even when the power is turned off.

In order to supply power for backing up the memory 3 when the power is cut off, the primary battery 4 is connected to the memory 3 via a diode 7 to prevent charging of the primary battery.
It is connected to the. In addition, a large-capacity capacitor 5 for delaying power supply to the memory 3 and consumption of the primary battery 4 is connected to the memory 3 via a protection resistor 6 and a diode 9 for preventing the primary battery 4 from being charged. Have been. The diode 8 is a backflow prevention diode for preventing current from flowing to the device power supply 1 and the logic circuit 2 for the purpose of preventing consumption of the large-capacity capacitor 5.

According to the power supply circuit shown in FIG. 3, when the power supply is not cut off, power is directly supplied from the device power supply 1 to the logic circuit 2 and the memory 3 and the large-capacity capacitor 5 is charged via the diode 8 and the resistor 6. . Power failure, power supply O
When the power is cut off by the FF or the like, first, power is supplied from the large-capacity capacitor 5 to the memory 3, and after the voltage of the large-capacity capacitor 5 decreases, power is supplied from the primary battery 4 to retain the contents of the memory 3. ing.

[0006]

In the prior art, as shown in the waveform diagram for explaining the operation of the conventional power supply circuit in FIG. 4, when the power is not cut off, the diode 8 and the diode 9 are stored in the memory 3. , A double voltage drop of Vf occurs when the forward voltage of the diode is Vf.

For example, the output voltage of the device power supply 1 is set to 5.0
Assuming that V and Vf are 0.5 V, the power supply voltage of the memory 3 is 3.
It becomes 0V. On the other hand, the power supply voltage of the logic circuit 2 directly connected to the device power supply 1 is 5 V, and the voltage of the control signal output from the logic circuit 2 to the memory 3 is CMOS.
For output, it is 4.9V. Therefore, assuming that the allowable input terminal voltage of the memory 3 is the power supply voltage + 0.5 V,
Since the input terminal voltage of 4.9 V is applied to the memory 3 having the power supply voltage of 4.0 V, which exceeds the allowable input terminal voltage of 0.4 V, there is a problem that the memory malfunctions and, in some cases, destroys the memory.

The problem to be solved by the present invention is to reduce the voltage difference between the voltage of the control signal output from the logic circuit to the memory and the power supply voltage of the memory to within the allowable value of the input terminal voltage of the memory. It is to solve the problem of malfunction and destruction.

[0009]

SUMMARY OF THE INVENTION The present invention relates to a power supply circuit for backing up a semiconductor memory, a timer, and the like. An element which needs a backup to be supplied with power from a capacitor, a first diode which connects the device power supply and the large capacity capacitor, and which is connected in series with the first diode and which has the large capacity capacitor and the backup required A power supply backup circuit composed of a second diode for connecting a power source of the battery and the element for which the backup is necessary; Connected in parallel with a series connection circuit, the device power supply and the In which a fourth diode that connects.

[0010]

FIG. 1 shows a power supply circuit according to an embodiment of the present invention. The functions of the components denoted by the same reference numerals as those in FIG. . Diode 10 is diode 8 and diode 9
To connect the device power supply 1 and the memory 3 in parallel, and to prevent current from flowing through the device power supply 1 and the logic circuit 2 for the purpose of preventing the consumption of the large-capacity capacitor 5 and the primary battery 4. Is a diode for preventing backflow.

As shown in the waveform diagram for explaining the operation of the power supply circuit of the present invention in FIG. 2, when the power supply is not cut off, the device power supply 1 and the memory 3 are connected by the diode 10, so that one diode is used. A forward voltage Vf for one minute. For example, with the same output voltage value as described in the problem to be solved by the invention, the power supply voltage of the memory 3 is 4.5 V
The input terminal voltage is 4.9 V, which is within the allowable value of the input terminal voltage.

Therefore, the diode 10 is connected in parallel with the diode 8 and the diode 9, and the device power supply 1 and the memory 3 are connected.
, The voltage difference generated between the voltage of the control signal output from the logic circuit 2 to the memory 3 and the power supply voltage of the memory 3 can be set within the allowable value of the input terminal voltage of the memory 3. Malfunction and destruction can be prevented.

[0013]

According to the present invention, by connecting the diode in parallel with the backup means for the memory, the voltage difference generated between the voltage of the control signal output to the memory by the logic circuit and the power supply voltage of the memory is obtained. Can be set within the allowable range of the input terminal voltage of the memory, so that the memory can be stably operated without malfunction or destruction.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply circuit with a backup function according to an embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the operation of the power supply circuit of the present invention.

FIG. 3 is a circuit diagram of a conventional power supply circuit with a backup function.

FIG. 4 is a waveform chart for explaining the operation of a conventional power supply circuit.

[Explanation of symbols]

1 device power supply, 2 logic circuits, 3 memories, 4 primary batteries, 5 large capacity capacitors, 6 resistors, 7-10 diodes.

Claims (1)

[Claims] In a power supply circuit for backing up a semiconductor memory, a timer, or the like, an element that does not need to be supplied with power only from an apparatus power supply, and is supplied with power from an apparatus power supply or a battery or a large-capacity capacitor. An element that needs to be backed up; a first diode that connects the device power supply and the large-capacity capacitor; and a second diode that is connected in series with the first diode and connects the large-capacity capacitor and the element that needs to be backed up. A power supply backup circuit composed of a third diode for connecting a power supply of the battery and the element requiring backup, and a parallel connection with a series connection circuit of the first diode and the second diode And a fourth die for connecting the device power supply and the element requiring backup. Power backup circuit, characterized in that it comprises a chromatography mode.