JPH04163652A - Backup circuit - Google Patents

Abstract

PURPOSE:To execute backup operation for which a battery need not be renewed by charging a secondary battery or a super-capacitor, etc., connected to a second potential supply terminal during a period that external power supply is supplied to a first potential supply terminal. CONSTITUTION:The supply voltage of 5V normally is impressed to the first potential supply terminal 1, and the power supply 3 like a lithium cell or the supercapacitor, etc., for memory backup is connected to the second potential supply terminal 2. Here, the secondary battery or the supercapacitor, etc., connected to the second potential supply terminal 2 is charged while the external power supply is supplied to the first potential supply terminal 1. Thus, it becomes possible to execute the memory backup operation for which no battery need be renewed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an operation control circuit for memory backup using a backup secondary battery, supercapacitor, or the like.

[Prior Art] The conventional memory backup circuit configuration uses a lithium battery and uses a diode to connect the first
The circuit configuration was such that the higher voltage among the voltages applied to the potential supply terminal 1 and the second potential supply terminal 2 of the second potential supply terminal 2 was supplied to the backup memory.

[Problem to be solved by the invention] However, in the conventional circuit configuration, the backup lithium battery has only a charging path using reverse leakage current of the diode, and if current is continuously supplied from the lithium battery to the backup memory for a long time, The problem was that the circuit configuration was such that memory backup could not be performed unless the voltage dropped and the battery was replaced. However, recent ICs
One of the essential conditions for the widespread use of cards is that the cards can be used semi-permanently, and the need to replace batteries for memory backup has become one of the factors that hinder the convenience of cards. Further, while conventional lithium batteries are primary batteries that cannot be recharged, lithium batteries that can be used as rechargeable secondary batteries have recently been developed.

The present invention is intended to solve these problems, and its purpose is to perform memory backup operation that does not require battery replacement by controlling charging using a secondary battery such as a lithium battery or a supercapacitor. The goal is to provide a backup circuit that can be implemented.

[Means for Solving the Problems] The backup circuit of the present invention includes a first potential supply terminal having a source electrode and a drain electrode connected between a first potential supply terminal and a second potential supply terminal, with at least a common potential as a reference. 1 transistor, a voltage comparator having the first potential supply terminal and the second potential supply terminal as inputs, a normal output and an inversion output of the voltage comparator having gate electrode inputs, and a source electrode. a second transistor pair whose respective drain electrodes are connected to a first potential supply end and a second potential supply end with the voltage in common; and the voltage comparator using the potential of the source electrode of the second transistor pair as a power source. and a charging control circuit that controls the gate electrode of the first transistor based on the output of the first transistor.

[Function] According to the above configuration of the present invention, during the period when the power supply voltage of 5V is applied to the first potential supply end from the outside, the voltage between the first potential supply end and the second potential supply end is Since the circuit configuration is such that the current flowing through the first transistor whose source electrode and drain electrode are connected is operated at a constant current to charge the backup power supply, it is possible to realize a memory backup operation that does not require battery replacement.

[Examples] Hereinafter, the present invention will be described in detail based on Examples. FIG. 1 is a circuit diagram showing one embodiment of a backup circuit of the present invention. Reference numeral 1 denotes a first potential supply end, to which a power supply voltage of 5μ is normally applied from the outside. 2 is a second potential supply end to which a power source such as a lithium battery for memory backup or a supercapacitor is connected. 3 is a memory backup power source such as a lithium battery or a super capacitor. 4 is a first transistor whose source electrode and drain electrode are connected between the first potential supply end 1 and the second potential supply end 2; and a backup power supply connected to the second potential supply end. to charge. 5 is a voltage comparator in which the first potential supply end 1 and the second potential supply end 2 are manually operated. 6
is an inverter for inverting the output of the voltage comparator. 7.8 uses the normal output of the voltage comparator 5 and the inverted output of the inverter 6 as inputs to the gate electrodes, and uses the source electrode in common to supply the first potential! The potential of the source electrode of the second pair of transistors whose respective drain electrodes are connected to the terminal 1 and the second potential supply terminal 2 is supplied to the backup memory. Reference numeral 9 denotes a charging control circuit which controls the gate electrode of the first transistor 4 using the potential of the source electrodes of the second transistor pair 7 and 8 as a power source and the output signal of the voltage comparator 5; It controls the gate electrode of No. 4 to charge the backup power supply with a constant current, and also has a function to prevent overcharging. FIG. 2 shows an example of a specific circuit diagram.

10 is a backup memory.

Next, the operation in the embodiment shown in FIG. 1 will be explained.

When a power supply voltage of 5V is applied to the first potential supply terminal 1,
In the voltage comparator 5, the power supply voltage 5 is applied to the first potential supply terminal 1 and the backup battery voltage (3 in the case of a lithium battery) is connected to the second potential supply terminal 2.
■ Compare the degree).

The output signal and the inverted output signal of the voltage comparator 5 make the transistor 7 conductive and the transistor 8 non-conductive. A voltage of (2) is applied. The charging control circuit 9 detects that 5V is applied from the outside using the output signal of the voltage comparator 5 or the inverted a-power signal, and applies a voltage to the first transistor 4 such that the first transistor 4 operates at a constant current. It monitors the backup power supply voltage and operates a timer to control the charging operation to prevent overcharging. When a power supply voltage of 5■ is not applied to the first potential supply terminal 1, the output signal and the inverted output signal of the voltage comparator 5 cause the transistor 8 to be in a conductive state and the transistor 7 to be in a non-conductive state to cause the backup memory 10 to be in a non-conductive state. A backup battery voltage connected to the second potential supply terminal 2 is applied to the charging control circuit 9 . The charging control circuit 9 uses the output signal or the inverted output signal of the voltage comparator 5 to
When it is detected that (2) is not applied, the operation is controlled so that the first transistor 4 is rendered non-conductive. Therefore,
Connect a rechargeable secondary battery or super capacitor, etc.
A secondary battery or a supercapacitor that is connected to the potential supply terminal 2 of By charging the battery, etc., it is possible to realize a memory backup operation that does not require battery replacement.

[Effects of the Invention] As described above, according to the present invention, a rechargeable secondary battery, a supercapacitor, or the like is connected to the second potential supply terminal 2, and an external power supply ( Usually 5V)
By charging the secondary battery or supercapacitor connected to the second potential supply terminal 2 during the period when the voltage is being supplied, it is possible to realize a memory backup operation that does not require battery replacement. It is effective.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a backup circuit of the present invention. FIG. 2 is a circuit diagram showing one embodiment of a charging control circuit. FIG. 3 is a circuit diagram showing a conventional memory backup circuit. 1 First potential supply terminal 2 Second potential supply terminal 3 Memory backup power supply 4 Charging transistor 5 Voltage comparator 6 Inverter 7 N source switching transistor 8 Power supply switching transistor 9 Charging control circuit 10 Backup memory or more People Seiko Epson Corporation

Claims (1)

[Claims] a first transistor having a source electrode and a drain electrode connected between a first potential supply end and a second potential supply end with reference to at least a common potential; a voltage comparator whose input is the potential supply end of the voltage comparator; a normal output and an inversion output of the voltage comparator are respectively input to gate electrodes; a second pair of transistors each having a drain electrode connected to the second transistor pair; and charging control for controlling the gate electrode of the first transistor by the output of the voltage comparator using the potential of the source electrode of the second transistor pair as a power source. A backup circuit characterized by comprising a circuit.