JPS62189521A - Power source circuit for microcomputer - Google Patents

Abstract

PURPOSE:To evade latch-up and malfunction and to effectively avoid a supply current from leaking to peripheral circuits at the time of the stoppage of an action by connecting a transistor, instead of connecting a diode between a supply node to the peripheral circuit of a microcomputer and that to the microcomputer main frame. CONSTITUTION:In terms of a pnp transistor 18 connected between the supply nodes P and Q instead of a diode in a conventional power source circuit, its emitter and collector are connected to the supply nodes P and Q, respectively, and its base is grounded through a resistance R and an npn transistor 19. The base terminal of the transistor 18 is grounded through the transistor 19 conducting only at a action state where the resistance R and a power source switch 12 are closed, and a current flowing from the collector of the transistor 18 to the base is inhibited by the nonconductive transistor 19. Thus the destruction and malfunction of a CMOS circuit, which is caused by latch-up, can be prevented, and the leakage of a current to the peripheral circuit is eliminated at the time of stopping the action.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply circuit for a microcomputer.

BACKGROUND OF THE INVENTION Microcomputers are used to control the engine and speed change of automobiles.

While the car is running, the voltage stabilization circuit (
The operating voltage is supplied to the microcomputer via the regulator. Furthermore, after the engine is stopped, a backup voltage is supplied from the battery to the volatile memory in order to preserve the data stored in the H-emitting memory in the microcomputer.

Conventionally, a typical microcomputer and its power supply circuit as described above is constructed as shown in FIG.

That is, the DC voltage of the battery 11 is applied to the regulator 1 via the power switch 12, which is closed when the engine is started.
3. The operating voltage stabilized by this regulator 13 is supplied to the peripheral circuits 22 and 23 of the microcomputer 20 via the first power supply node P.
The power is supplied to the main body portion 21 of the microcomputer via the diode 16 and the second power supply node Q. When the switch 12 is opened when the engine is stopped, backup voltage for the volatile memory is supplied from the battery 11 via the regulator 14 and diode 15 to only the microcomputer main body portion 21. The microcomputer main body part 21 detects that the power switch is turned off.
Upon receiving the notification from the closed detection circuit 17, the power supply terminal Vcc
The backup voltage supplied to the device is supplied only to the internal volatile memory.

The power supply voltage during operation supplied from the regulator 13 is
Typically, the value is about 5 volts, and the backup voltage supplied from the regulator 14 when the operation is stopped is:
Typically, the value is about 3 volts, which is somewhat lower than the operating voltage. Therefore, a diode 15 is connected to prevent the output current of the regulator 13 from flowing back to the regulator 14 side during operation of the microcomputer. Further, a diode 16 is connected between power supply nodes P and Q to prevent the backup voltage from the regulator 14 from being supplied to the peripheral circuits 22 and 23 when the microcomputer stops operating.

Problems to be Solved by the Invention In the conventional power supply circuit shown in FIG.
The diode 16 connected between
A load current of about A flows, where Q, 5 vol
A voltage drop of about t occurs. Therefore, a similar difference in power supply voltage occurs between the peripheral circuits and the main body of the microcomputer, and there is a risk that the CMO3 circuit or the like may be destroyed due to latch-up.

Also, if the power supply voltage on the microcomputer main body side is set to the standard value, the power supply voltage on the peripheral circuit side will be higher than this standard value, and conversely, if the peripheral circuit side is set to the standard value, the main body side will be lower than the standard value. Become. For this reason, there is also a problem that the margin width of the guaranteed operation voltage becomes narrow, making malfunctions more likely to occur.

Means for Solving the Constituent Problems of the Invention The power supply circuit of the present invention which solves the problems of the above-mentioned prior art is as follows:
By connecting a transistor instead of connecting a diode between both power supply nodes, the potential difference between these power supply nodes is reduced.

Hereinafter, the operation of the present invention will be explained in detail together with examples.

Embodiment FIG. 1 shows the configuration of a power supply circuit 10 according to an embodiment of the present invention.
It is a block diagram shown together with a microcomputer 20 to which power is supplied.

In the power supply circuit 10, 11 is a battery, 12 is a power switch, 13.14 is a regulator, 17 is a switch open/close detection circuit, and 18.19 is a transistor. Further, in the microcomputer 20, 21 is the main body of the microcomputer, and 22 and 23 are peripheral circuits of the microcomputer.

Power supply nodes P and Q instead of diodes in conventional power supply circuits
The pnp transistor 18 connected between the two has an emitter connected to the power supply node P, a collector connected to the power supply node Q, and a base grounded through the resistor R and the npn transistor 19.

The DC voltage of the battery 11 is supplied to the regulator 13 via a power switch 12 that is closed when the engine is started. The operating power supply voltage stabilized by the regulator 13 is supplied to the peripheral circuits 22 and 23 of the microcomputer 20 via the first power supply node P, and the transistor 18 is turned on as the transistor 19 is turned on. The power is supplied to the main body portion 21 of the microcomputer via the second power supply node Q. When the switch open/close detection circuit 17 detects that the power switch 12 is closed, it supplies an activation signal to the main body portion 21 of the microcomputer.

Thereafter, when the switch 12 is opened as the engine is stopped, the backup power supply voltage for the volatile memory is supplied from the battery 11 via the regulator 14 only to the microcomputer main body portion 21. regulator 14
As shown in the figure, it is composed of a Zener diode ZD and a resistor, and supplies a stabilized backup voltage of about 3 volts to the main body portion 21 of the microcomputer when the operation is stopped. The microcomputer main body part 21 detects that the power switch is turned off.
Upon receiving the notification from the closed detection circuit 17, the power supply terminal Vcc
The backup voltage supplied to the device is supplied only to the internal volatile memory.

FIG. 2 is a characteristic diagram illustrating the magnitude of the voltage drop occurring in the transistor 18 connected between power supply nodes P and Q while comparing it with the magnitude of the voltage drop occurring in the diode of a conventional power supply circuit.

The horizontal axis is the supply node P,! = voltage between Q, and in transistor 18, its collector voltage ■. This corresponds to this, and in the case of a conventional diode, the voltage between its terminals corresponds to this. The vertical axis represents the current flowing through the power supply nodes P and Q, that is,
This is the load current supplied to the main body portion 21 of the microcomputer during operation, and in the case of the transistor IB, its collector current c corresponds to this, and in the case of a diode, its forward current value corresponds to this. The collector current I of the transistor 18 is displayed as a plurality of solid lines using several base current values Ill as parameters according to a conventional display method. On the other hand, the forward direction ■−■ characteristics of the diode are indicated by dotted lines.

If the load currents flowing through the power supply nodes P and Q are the same value It in both the case of the transistor 18 and the diode, the voltage drop occurring between the power supply nodes P and Q is ΔV as shown in the figure.
As illustrated by and ΔV, the transistor 18 is smaller. If a transistor with a low saturation voltage such as 2SA 1385 is used, the voltage value Δ between power supply nodes P and Q under a load current (collector current re) of about 100 mA
V (collector voltage Ve is about 0.2 volt, which is about 0.2 volt, which is about 0.6 volt)
The value is about 4 volts smaller than Q, which is about 4 volts.

The reason why the base terminal of the transistor 18 is not directly grounded through the resistor R but through the transistor 19 which is conductive only when the power switch 12 is closed is as follows. That is, even if the base of the transistor 18 is directly grounded through the resistor R, there is no problem in the operating state when the power switch 12 is closed. However, during shutdown when the power switch 12 is open, the transistor 18 connected to the power supply node Q
A current corresponding to the reverse bias current of the collector junction flows from the collector to the grounded base via the resistor,
A part of it passes through the emitter and the power supply node P to the peripheral circuit 22.
And it flows into 23. Although this current value is small,
Depending on the value of the input impedance of the peripheral circuits 22 and 23, the power supply voltage to the peripheral circuits 22 and 23 may rise to the level of their operating voltage, and the peripheral circuits 22 and 23 may start operating.

Therefore, in the power supply circuit of the present invention, the base terminal of the transistor 18 is grounded through the resistor R and the transistor 19, which is conductive only when the power switch 12 is closed, and the collector of the transistor 18 is connected to the ground when the operation is stopped. Transistor 19 in which the current flowing to the base is in a non-conducting state
By preventing this, the above problem is avoided.

Above, the configuration in which the regulators 13 and 14 are arranged between the DC type 'tA11 and the power supply nodes P and Q, respectively, has been illustrated. However, if the backup voltage does not require much stability, the regulator 14 can be replaced with a resistor. A step-down circuit with a voltage converter may also be used. In this case, a diode for preventing reverse current may be connected within this back amplifier system in order to prevent power loss due to reverse current flowing from the power supply node Q to the DC power supply ll side.

Further, when the backup voltage value is made substantially the same as the operating voltage value, the step-down circuit in the backup system can be omitted.

Furthermore, when using a DC power supply with high voltage stability, both regulators 13 and 14 can be omitted.

In addition, although the configuration has been illustrated in which the microcomputer is started and stopped by opening and closing the power switch 12, in a microcomputer installed indoors, it may be configured to start and stop the microcomputer independently of the opening and closing of the power switch 12. good.

Effects of the Invention As explained in detail above, the power supply circuit of the present invention has a configuration in which a transistor is connected instead of a diode between the power supply node to the peripheral circuits of the microcomputer and the power supply node to the main body of the microcomputer. Therefore, the voltage drop between the power supply nodes is typically reduced to about ⅓ compared to the conventional circuit, and the risk of latch-up and malfunction can be effectively prevented.

Furthermore, since the power supply circuit of the present invention has a configuration in which the base of the transistor connected between the power supply nodes is grounded via a transistor that is conductive only during operation, the problem of leakage power supply current to peripheral circuits when the operation is stopped is avoided. Can be effectively avoided.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a power supply circuit of a microcomputer according to an embodiment of the present invention together with a microcomputer to which power is supplied; FIG. 2 is a VI characteristic diagram for explaining the effects of the present invention; 11. DC power supply, 12.
- Power switch, 13... Regulator (first voltage stabilization circuit), 14... Regulator (second voltage stabilization circuit), 18.19... Transistor, P... First power supply node, Q... Second feeding node. Patent applicant: NEC Home Electronics Co., Ltd.

Claims (1)

[Scope of Claims] A DC power supply, a power switch that sets the microcomputer to either an operable state or an inoperable state, and a first power supply node that supplies a power supply voltage in an operable state to peripheral circuits of the microcomputer. and a second power supply node that supplies the main body of the microcomputer with a built-in volatile memory with an operating power supply voltage when it is in an operable state and a backup power supply voltage for the volatile memory when it is in an operation stopped state. In the power supply circuit, a first power supply path that stabilizes the power supply voltage received from the DC power supply via the power switch in the operable state or supplies it to the first power supply node as is; and in the operation stop state. a second power supply path that stabilizes the power supply voltage received from the DC power supply or directly supplies it to the second power supply node via a forward-energized diode or directly; 1. A power supply circuit for a microcomputer, comprising a transistor whose emitter and collector are connected to a power supply node, and whose base is grounded via a transistor that is conductive only in the operable state.