JPH046974B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a power supply control circuit using two transistors and a Zener diode, and particularly to a power supply control circuit using an output signal of a microcomputer system (hereinafter referred to as microcomputer system). This invention relates to a device that controls the power supply of the microcomputer system.

[Prior art]

A conventional device of this type is shown in FIG. In the figure, 1 is a microcomputer system, 2
3 is a power input terminal of the microcomputer system 1, and 4 is a reset input terminal. Also resistance 5,
The capacitor 6 and the diode 7 are a circuit for stably starting the operation of the microcomputer system 1 when the power is turned on. 8 is a switch for turning on or off the power of the microcomputer system 1.

FIG. 2 shows a timing chart of the operation of the device shown in FIG. The vertical axis shows the potential from ground, and the horizontal axis shows time. In the figure, 9 is the voltage waveform of the output of the power switch 8, 10
is the voltage waveform of the power input terminal 3 of the microcomputer system 1, and 11 is the voltage waveform of the reset input terminal 4. As shown in FIG. 3A, the power switch 8 is turned on when the waveform is rising, and the power switch 8 is turned off when the waveform is falling. It is thought that a lot of chattering occurs in the rising and falling portions of this waveform.
The voltage 10 at the power input terminal 3 of the microcomputer system 1 shown in FIG.
It rises more slowly and smoothly than the rise of the voltage waveform 9 of the switch 8. The reset signal input terminal voltage 11 of the microcomputer system 1 shown in FIG. This avoids instability when the power is turned on, and the microcomputer system 1 starts operating after the power becomes stable. Furthermore, when the power is off, that is, when the waveform 9 shown in FIG. It can be stopped.

The power control circuit of the conventional microcomputer system is configured as described above, and the power of the microcomputer system can only be turned off using the manual switch 8.

[Summary of the invention]

The present invention has been made in view of the above points, and includes a first transistor for turning on and off the supply of power to the microcomputer system, and a second transistor for turning off the first transistor. , a microcomputer capable of stopping power supply to the microcomputer system by a signal from the microcomputer system itself by controlling the second transistor and the first transistor by a power-off signal from the microcomputer system; Its purpose is to provide a system power control circuit.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 3, 12 is a power off signal output terminal of the microcomputer system 1, and the power off signal output from the terminal 12 is the power off signal output terminal of the microcomputer system 1.
This is to turn off the power. 13 is a power switch, which can be turned off once the microcomputer system 1 starts operating. 14 is a PNP type first transistor whose emitter is connected to the power supply 2, and serves as a switch that sends current to the power input terminal 3 of the microcomputer system 1 connected to its collector. 16 and 17 are resistors for adjusting the current flowing to the power supply input terminal 3; 15 is an NPN whose collector is connected to the base of the first transistor 14 via the resistor 17 and whose emitter is grounded;
The second transistor of this type serves as a switch that turns on and off the transistor 14 in response to a signal from the power-off terminal 12 connected to its base. That is, the current flowing to the base of the transistor 15 is drawn into the microcomputer system 1 side via the power off terminal 12, thereby turning off the transistor 15, and thereby turning off the transistor 14.
is turned off, and the current supply to the power input terminal 3 is stopped. Further, the resistor 18 is connected to the base of the transistor 15 and adjusts the switching level of the transistor 15.
Further, a resistor 19 and a Zener diode 20 are connected in series between the collector of the transistor 14 and the base of the transistor 15, and are connected to the power input terminal 3.
A part of the current flowing through the transistor 15 is sent to the transistor 15,
It plays the role of always keeping the transistor 15 in the on state. Naturally, if no current flows through the power input terminal 3, the transistor 15 cannot be turned on. The Zener diode 20 and the resistor 21 have the following roles. That is, the transistor 15 is turned off by drawing the current flowing through the resistor 18 into the microcomputer system 1 through the terminal 12, but if the Zener diode 20 and resistor 21 are not present, the current flows in the direction of the transistor 15. The current cannot be completely stopped, transistor 15 cannot be completely turned off, and transistor 14 cannot be completely turned off. This makes it impossible to completely stop the current to the microcomputer system 1. Zener diode 20, resistor 21
This eliminates such a situation and makes it possible to completely stop the current supply to the microcomputer system 1 at the same time as the power off signal is output. Note that the resistor 21 may be omitted if the current flowing through the transistor 14 is small. Note 5, 6
are the same resistors and capacitors as conventional ones.

Figure 4 is a timing chart of Figure 3,
The vertical and horizontal axes are the same as in FIG. 2. 22 indicates the on/off state of the switch 13, and chattering occurs at the rising and falling edges. Further, 23 is a power off signal output from the microcomputer system 1.

Next, the operation will be explained.

Now, if you want to supply power to the microcomputer system 1, turn on the switch 13 and turn on the transistor 15.
All you have to do is short-circuit the collector and emitter of the microcomputer system 1. This turns on the transistor 14 and current begins to flow toward the power input terminal 3 of the microcomputer system 1. However, due to the action of the resistor 5 and capacitor 6, the Potential 10 of power input terminal 3
rises slowly, and after a period of chattering of switch 13, rises completely, while the potential 11 of reset signal input terminal 4 is equal to the voltage 10 of terminal 3.
It will rise at a slightly slower speed. As a result, the microcomputer system 1 is initialized when the power supply voltage reaches a steady state, and starts a series of operations without being affected by the chattering of the power switch 13. When the power supply input terminal voltage 10 becomes stable, even if the switch 13 is turned off, the transistor 15 is
continues to be on, the power input to the microcomputer system 1 is stably on.

Next, when stopping the power supply to the microcomputer system 1, the microcomputer system 1 outputs a power off signal 23, which causes the transistor 1
As a result, the transistor 14 is also turned off, and the power supply voltage 10 and reset input voltage 11 to the microcomputer system 1 fall smoothly and rapidly, and the microcomputer system 1 stably stops operating.

As described above, according to the power supply control circuit of the microcomputer system according to the present embodiment, the operation of the microcomputer system 1 can be started from a state where the power supply is stable, as in the conventional case, and the second transistor 1
5 is turned off, thereby turning off the first transistor 1
4 to turn off the power supply to the microcomputer system 1, the power can be turned off without requiring any external operation, which is very convenient in devices where the system cannot be turned off manually. Also,
Power consumption will also be reduced.

In the above embodiment, the power is turned on using the manual switch 13, but a device which receives an external signal and functions similarly to the switch 13 may be used to turn on the power. Furthermore, when turning off the power of the microcomputer system, a device that outputs a signal similar to the power-off signal output terminal 12 may be provided in place of the resistor 21.

Further, the present invention may be applied to any microcomputer system that can send a power off signal, and the same effects as those of the above embodiments can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the first
A transistor and a second transistor for turning off the first transistor are provided, and the second and first transistors are controlled by the signal from the microcomputer system, so the power to the microcomputer system can be manually turned off. This eliminates the need to turn off the system manually, making it effective for use in systems that cannot be turned off manually or in systems that reduce power consumption.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a power control circuit of a conventional microcomputer system, Fig. 2 is a timing chart showing signals of each part of the conventional circuit, and Fig. 3 is a power control circuit of a microcomputer system according to an embodiment of the present invention. FIG. 4 is a timing chart of the circuit shown in FIG. 1... Microcomputer system, 2...
Power supply, 3... Power input terminal, 12... Power off signal output terminal, 13... Power supply switch, 1
4, 15...first and second transistors, 16,
17, 19...first to third resistor, 20...
Zener diode. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1 A PNP-type first transistor whose emitter is connected to a power supply terminal, whose collector is connected to a power input terminal of a microcomputer system, and whose base is connected to its emitter via a first resistor;
The emitter is grounded, the collector is connected to the base of the first transistor via a second resistor, and the base is provided in the microcomputer system and serves as an output terminal for a power off signal for stopping power supply to the system. a second transistor connected thereto; a power supply switch that shorts the collector-emitter of the second transistor; and a power supply switch connected in series between the collector of the first transistor and the base of the second transistor. A power supply control circuit for a microcomputer system, comprising a third resistor and a Zener diode.