JPH10201135A - Power-supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a phenomenon in which a high voltage applied from a peripheral circuit latches up a microcomputer in a system in which the microcomputer using a power supply for back up and every power-supply system for the peripheral circuit are made independent. SOLUTION: A main power supply 13 which is operated when a system switch 12 is turned on and which supplies a voltage VM to a microcomputer 15 is installed. A power supply 14, for back up, by which a voltage VB, for backup, lower than the main-power-supply voltage VM is supplied to the microcomputer 15 through a reverse-current preventive diode 15 is installed. A switching circuit 18 which supplies the main-power-supply voltage VM to a peripheral circuit 17 when the system switch 12 is turned on and by which the power-supply terminal of the peripheral circuit 17 is separated from the supply side of the power supply when the system switch 12 is not turned on is installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a power supply circuit of a microcomputer system provided with a backup power supply.

[0002]

2. Description of the Related Art As a power supply method for a microcomputer system having a backup power supply, a power supply is supplied from a main power supply to a microcomputer and peripheral circuits when a main power supply is turned on, and a backup power supply is supplied only to the microcomputer when the main power supply is turned off. Some of them supply more power.

A conventional configuration of this power supply circuit will be described with reference to FIG. In FIG. 2, 1 is a primary power supply, and 2 is a system switch. 3 is a main power supply, 4 is a backup power supply,
Each is composed of a constant voltage circuit such as a switching regulator.

The main power supply 3 operates when the system switch 2 is turned on to supply power. The backup power supply 4 operates regardless of whether the system switch 2 is turned on or not, and generates a lower voltage than the main power supply 3.

[0005] Reference numeral 5 denotes a microcomputer. The output voltage VB of the backup power supply 4 is supplied to the power supply terminal VDD through a backflow prevention diode 6.

Reference numeral 7 denotes a microcomputer peripheral circuit.
The output voltage VM of the main power supply 3 is supplied.

Reference numeral 8 denotes a switch circuit, which is a system switch 2
When the power supply is turned on, the output voltage VM of the main power supply is supplied to the power supply terminal VDD of the microcomputer 5, and the output voltage VB of the backup power supply 4 is not applied to the peripheral circuit 7 when the system switch 2 is not turned on. . When the system switch 2 is turned on, the switch circuit 8 receives the voltage of the primary power supply 1 and conducts.
And a second transistor 10 that conducts by the conduction output of the first transistor 9 and supplies the output voltage VM of the main power supply 3 to the power supply terminal VDD of the microcomputer 5.

In the above configuration, when the system switch 2 is not turned on, the low voltage VB
Is supplied to the microcomputer 5 to maintain the backup state with low power consumption.

When the main power supply is turned on, the voltage VM is supplied from the main power supply 3 to the peripheral circuit 7, and at the same time, the voltage VM is supplied from the main power supply 3 to the microcomputer 5 through the switch circuit 8.
Supply. At this time, the voltage V of the backup power supply 4
Since B is lower than the voltage VM of the main power supply 3, it is cut off by the backflow prevention diode 6.

[0010]

In the above conventional configuration, when the system switch 2 is turned on, the main power supply voltage VM is supplied to the microcomputer 5 after the switch circuit 8 is turned on.

Therefore, when the microcomputer 5 is supplied with the low voltage VB from the backup power supply 4, the microcomputer 5 receives the higher output voltage VM of the main power supply 3 from the peripheral circuit 7 through both connection lines. There is a timing at which a voltage higher than the internal voltage of the computer is applied, whereby the microcomputer 5 may cause a latch-up phenomenon.

It is an object of the present invention to provide a power supply circuit that does not cause latch-up due to a high voltage applied from a peripheral circuit in a microcomputer system using a backup power supply.

[0013]

In order to solve the above-mentioned problems, a power supply with backup provided by the present invention comprises:
A power supply for supplying power to a microcomputer to which a backup voltage VB is supplied when a main power supply is turned off, and to a microcomputer system in which a peripheral circuit having a power supply terminal independent of a power supply terminal of the microcomputer is connected;

A main power supply which operates by turning on a system switch to supply a voltage VM to a power supply terminal of the microcomputer, and a backup voltage VB lower than the output voltage VM of the main power supply are supplied to the power supply terminal of the microcomputer through a backflow prevention diode. And a backup power supply to be supplied to the power supply, and turn on when the system switch is turned on, supply the output voltage VM of the main power supply to the power supply terminal of the peripheral circuit, turn off when the system switch is not turned on, and turn off the power supply terminal of the peripheral circuit. A switch circuit for disconnecting from a power supply side is provided.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1 showing one embodiment of the present invention, reference numeral 11 denotes a primary power supply, and 12 denotes a system switch.

Reference numeral 13 denotes a main power supply, and 14 denotes a backup power supply, each of which comprises a constant voltage circuit such as a switching regulator.

The main power supply 13 is connected to the system switch 12.
It operates when power is supplied to supply power. The backup power supply 14 operates regardless of whether the system switch is turned on or off, and generates a voltage lower than that of the main power supply 3.
These output voltages are, for example, the main power supply 13 is 5V,
The power supply 14 for backup is 4.5V.

Reference numeral 15 denotes a microcomputer. The power supply terminal VDD is supplied with the output VM of the main power supply 13 and the output voltage VB of the backup power supply 14 through the backflow prevention diode 16.

Reference numeral 17 denotes a peripheral circuit of the microcomputer, which is connected to the microcomputer 17 by a signal line or the like. The power supply to the peripheral circuit 17 is performed independently of the microcomputer 15, and the power supply terminal V
Have DD.

Reference numeral 18 denotes a switch circuit which supplies the output voltage VM of the main power supply to the peripheral circuit 17 when the system switch 12 is turned on, and outputs the output voltage VB of the backup power supply 14 to the power supply of the peripheral circuit 17 when the system switch 12 is not turned on. It is provided so as not to be applied to the terminal VDD. When the system switch 12 is turned on, the switch circuit 18 receives a voltage of the primary power supply 11 and conducts.
And a second transistor 20 that conducts by the conduction output of the first transistor 19 and supplies the output voltage VM of the main power supply 3 to the power supply terminal VDD of the peripheral circuit 17.

In the above configuration, the system switch 12
Is not turned on, the main power supply 13 does not operate, the backup power supply 14 operates, and the output voltage VB of the backup power supply 14 is supplied to the power supply terminal VDD of the microcomputer 15. At this time, power is not supplied to the peripheral circuit 17 because the switch circuit 18 is off.

Next, when the system switch 12 is turned on, the main power supply 13 starts operating, and supplies the voltage VM to the microcomputer 15. Since the output voltage VB of the backup power supply 14 is lower than the output voltage VM of the main power supply 13, the output voltage VB is blocked by the backflow prevention diode 16 and no voltage is supplied.

When the system switch 12 is turned on, the switch circuit 18 is turned on, so that the output voltage VM of the main power supply 13 is also supplied to the power supply terminal VDD of the peripheral circuit 17.

In the above configuration, when a voltage is supplied from the main power supply 13 to the peripheral circuit 17, the power is always supplied from the main power supply 13 to the microcomputer 15. In the state where the voltage VB is supplied, a situation in which a higher voltage is supplied from the peripheral circuit 17 does not occur, and the latch-up phenomenon can be prevented.

[0025]

As described above, according to the present invention,
In a system in which a microcomputer using a backup power supply and each power supply system of its peripheral circuit are independent, a high voltage is applied to the microcomputer from the peripheral circuit and latch-up of the microcomputer only by changing the circuit design without adding parts The phenomenon which causes it to disappear can be eliminated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a state in which a backup power supply of the present invention is connected between a primary power supply, a microcomputer, and peripheral circuits thereof.

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Primary power supply 12 System switch 13 Main power supply 14 Backup power supply 15 Microcomputer 16 Backflow prevention diode 17 Peripheral circuit of microcomputer 18 Switch circuit 19 First transistor 20 Second transistor B Power supply circuit

Claims (1)

[Claims] 1. A microcomputer system in which a peripheral circuit having a power supply terminal independent of a power supply terminal of the microcomputer is connected to a microcomputer to which a backup voltage is supplied when a main power supply is turned off, A main power supply that operates by turning on the system switch to supply a voltage to the power supply terminal of the microcomputer; and a backup power supply that supplies a backup voltage lower than the output voltage of the main power supply to the power supply terminal of the microcomputer through a backflow prevention diode. A switch circuit that turns on when the system switch is turned on, supplies the output voltage of the main power supply to the power supply terminal of the peripheral circuit, turns off when the system switch is not turned on, and disconnects the power supply terminal of the peripheral circuit from the power supply side. A power supply circuit comprising: