JPS62189522A - Power source circuit for microcomputer - Google Patents

Abstract

PURPOSE:To prevent latch-up and malfunction by connecting a transistor, instead of connecting a diode between a supply node to the peripheral circuits of a microcomputer and that to the microcomputer main frame part. CONSTITUTION:In terms of a pnp transistor 16 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. Where load currents flowing in the supply nodes P and Q are the same value IL, the case where the transistor 16 is connected has a smaller drop in a voltage, which arises between the supply nodes P and Q, than the case where the diode is connected, as DELTAv and DELTAV show. Thus the destruction of a CMOS circuit and malfunction never occur.

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, backup voltage is supplied from the battery to the volatile memory in order to preserve data stored in the volatile memory within 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 18 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 bank-up voltage supplied to the memory 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 back amplifier 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 18 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 18 connected between
A load current of about A flows, and here 0.6 solt
A slight voltage drop will occur. 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 by the latch knob.

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 and 14 are regulators, 15 is a diode, 16 is a transistor, and 17 is a switch open/close detection circuit. Furthermore, 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 pnpl-transistor 16 connected therebetween has an emitter connected to a power supply node P, a collector connected to a power supply node Q, and a base grounded via a resistor R.

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 voltage stabilized by this regulator 13 is supplied to the microcomputer 2 via the first power supply node P.
0 peripheral circuits 22 and 23, and is also supplied to the main body portion 21 of the microcomputer via the transistor 16 and the second power supply node Q. When the switch open/close detection circuit detects the closing of the power switch 12, it supplies an activation signal to the main body portion 21 of the microcomputer.

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. When the microcomputer body section 21 receives a notification from the switch open/close detection circuit 17 that detects that the power switch is off, it supplies the bank-up voltage supplied to the power supply terminal Vcc only to the built-in volatile memory.

FIG. 2 is a characteristic diagram illustrating the magnitude of the voltage drop occurring in the transistor 16 connected between the 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 voltage between the supply nodes P and Q, and in the case of the transistor 16, this corresponds to its collector voltage (2), and in the case of a conventional diode, this corresponds to the voltage between its terminals. The vertical axis is the current flowing through the power supply nodes P and Q, that is, the load current during operation that is supplied to the main body part 21 of the microcomputer. Directional current value 1. falls under this category. Collector current of transistor 16■. is displayed as a plurality of solid lines with several base current values I as parameters according to a conventional display method. On the other hand, the forward V-1 characteristic of the diode is indicated by a dotted line.

If the load current flowing through the power supply nodes P and Q is the same value IL in both the case of the transistor 1G 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 Δ■, the transistor 16 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 of about 100 mA (collector current 1c)
V (collector voltage VaE) has a value of about 0.2 volt, which is the value in a typical diode (0.6 volt).
0.4 volts).

Above, the configuration in which the regulators 13 and 14 are arranged between the DC power supply 11 and the power supply nodes I''P and Q, respectively, has been illustrated, but the regulator 14 can be omitted if the backup voltage does not require much stability. Furthermore, when using a DC power supply with high voltage stability, the regulators 13 and 14 can be omitted.Furthermore, when the backup voltage is made the same as the operating voltage, the diode 15 can also be omitted.

In addition, although a configuration in which the power switch 17 starts/stops the operation of the main body part 21 of the microcomputer has been illustrated, in a microcomputer for indoor installation, the power switch and a separate start/stop command input terminal are connected to the microcomputer. It may also be provided in the main body.

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. Because of this, the voltage drop between the power supply nodes is typically reduced to about ⅓ compared to conventional circuits, and the risk of latch-up and malfunction can be effectively prevented.

[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, and FIG. 2 is a block diagram showing the voltage between power supply nodes for explaining the effects of the present invention. -Current characteristic diagram, 3rd
The figure is a block diagram showing the configuration of a conventional power supply circuit together with a microcomputer to which power is supplied. 11...DC power supply, 12...Power switch, 13...Regulator (first voltage stabilization circuit), 14...Regulator (second voltage stabilization circuit), 15...Diode, I6...Transistor, P...first power supply node, Q
...Second power supply node. Figure 1] 0 Figure 2

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 an operating power supply voltage when the microcomputer is in an operable state and a backup power supply voltage for the volatile memory when the operation is stopped to the main body portion of the microcomputer that has a built-in volatile memory. 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 diode in a forward conduction state; 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 resistor.