JPS61206018A - Power source circuit - Google Patents

Abstract

PURPOSE:To obtain an electric power source in which the number of parts is small and the circuit is made simple by turning on and off the electric power source with one push-switch, executing the constant voltage interruption to a CPU without a constant voltage circuit an building in the automatic power off function. CONSTITUTION:When a push switch PS of a push switch circuit 3 is pushed, a transistor Tr2 is turned on, through a constant voltage circuit 4, a constant voltage VD is supplied, a CPU 5 is operated and an output voltage VP1 is VD. The voltage VP1 is compared with a reference voltage at a voltage dropping detecting circuit 7, and when the voltage is lower than the reference voltage, a base electric current holding circuit 6 is turned on, and the base electric current of Tr2 is made to flow. At the circuit 3, an output voltage VPS is the input voltage of an interruption input terminal INT of the CPU 5, the first interruption input is neglected, the switch PS is separated and the circuit 6 is on. Next, when the switch PS is pushed, the CPU 5 stops the action, the circuit 6 is turned off, Tr2 is also turned off and the voltage VD is dropped. Since the reference voltage is set to V3 or above at the circuit 7 in the excessive condition of the dropping, an output voltage Vb is zero, and the circuit 6 is not turned on.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply circuit for products such as blood pressure monitors and thermometers which are powered by batteries and further employ microcomputers.

BACKGROUND OF THE INVENTION Batteries are often used as power sources for blood pressure monitors and thermometers, which consume less power, and microcomputers (hereinafter referred to as CPUs) are used as signal processing means. The power supply circuits used in these devices may not be used for a long time after the power is turned on, or
It has a built-in auto power second circuit that automatically turns off the power after a certain period of time to prevent shortening of battery life due to forgetting to turn off the power.

Problems that the invention aims to solve: Therefore, it is necessary to turn on the power with a push switch, etc., supply power with a self-holding circuit, and configure the power supply circuit to facilitate automatic power-off and power-off control. .

Furthermore, since the switching circuit is connected between the power supply and the constant voltage circuit, in order to configure the circuit with a small number of components, it is necessary to use a power supply voltage whose output voltage decreases as the capacity decreases. At this time, the output voltage of the push switch circuit is CP
As an input signal for U, in order to turn off the power, it is necessary to output a constant voltage output signal to a constant voltage driven CPU.

Also, to release the self-holding circuit using the CPU output signal,
If the output voltage of the constant voltage circuit that powers the CPU drops to zero instantaneously or gradually decreases, a circuit that does not turn on the self-holding circuit at voltages that are beyond the CPU's control is required, making the circuit configuration complicated. It had become.

The present invention provides a blood pressure monitor and a thermometer that use a battery as a power source.
The purpose is to provide a power supply circuit with a simple circuit configuration and a small number of parts.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides a power supply circuit that uses a battery or the like as a power source whose output voltage decreases as the capacity decreases, and that drives a CPU at a constant voltage, by using a transistor for switching the power source. , a push switch circuit that switches the base current of the transistor, a constant voltage circuit that converts the output voltage of the transistor into a constant voltage, an output of the constant voltage circuit as a power source, and an output voltage of the push switch circuit as an input. a voltage drop detection circuit that detects that the output voltage of the CPU is equal to or higher than a predetermined value, a base current holding circuit of the transistor that receives the output of the voltage drop detection circuit as an input, and a push switch circuit. In order to keep the output voltage constant, a power supply circuit is configured with a diode connecting the output terminal of the CPU and the input terminal of the push switch circuit.

Function The present invention has a power on/off function and an auto power off function with a simple circuit configuration due to the above-described configuration.
This prevents malfunctions due to transient phenomena when the power supply voltage is turned off.

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to FIGS. 1 and 2. In Figure 1, 1 is a power source such as a battery, 2
is a transistor that switches the power supply 1, 3 is a push switch circuit in which a resistor R1, a push switch PS, and a resistor ~ are connected in series between the base of the transistor 20 and ground, 4 is a constant voltage circuit, 5 is a CPU, and 6 is a transistor 2
7 is a voltage drop detection circuit, and D is a diode. FIG. 2 shows a specific example of the voltage drop detection circuit.

First, when push switch PS of push switch circuit 3 is pressed, transistor 2 is turned on, constant voltage VD is supplied between terminals vDD and vss of CPU 5 through constant voltage circuit 4, CPU 5 is activated, and output P1 is Output voltage vP
Let 1 be VD. Next, the output voltage vP is compared with the reference voltage fEVR,f by the voltage drop detection circuit 7, and vPl>vR,
In the case of f, the base current holding circuit 6 is turned on to allow the base current of the transistor 2 to flow. In addition, in the push switch circuit 3, the output voltage vPs is used as the input voltage of the interrupt input terminal INT of the CPU 6. When the push switch ps is pressed for the first time, is applied, and after the CPU 5 is turned on, the output voltage of the CPU 5 is vP1 is connected to push switch circuit 3 via diode D.
and vP8=VD-0,6(v) is applied. However, the CPU 5 is configured to ignore the first interrupt input to the input terminal INT after power is turned on, and the base current holding circuit 3 remains on even if the push switch Ps is released.

Next, when the push switch is pressed, Vp8=VD-Qs(v) is applied to the input terminal INT of the CPU5, the operation of the CPU6 is stopped, and the output vP of the CPU5 is. (2), the base current holding circuit 6 is turned off, the transistor 2 is also turned off, and the voltage VD of the constant voltage circuit 4 is reduced. Voltage VD
In a transient state in which the voltage VD decreases to Ov, when the voltage VD becomes smaller than the minimum operating voltage Va guaranteed by the CPU 5, the output voltage vP1 of the CPU 5 becomes unstable. At this time,
Even if the output voltage vP1 changes from oV to VD, the voltage drop detection circuit 7 maintains the reference voltage Va. Since f is set above Va, the output voltage vb remains oV and the base current holding circuit 6 is not turned on.

Further, in the CPU 5, an auto power-off function for turning off the power after a certain period of time can be easily configured by controlling the output P1.

Next, a specific example of the voltage drop detection circuit 7 will be explained with reference to FIG. In Figure 2 0, there is a resistor R3 between input terminal a and ground C.
and R4 are connected in series, and the connection point of R3 and R4 is connected to the output terminal. R3 and R4 are set to satisfy.

In FIG. 2(b), a Zener diode ZD and a resistor R6 are connected in series between the input terminal d and the output terminal, and a resistor .about. is connected between the output terminal and the ground C. The voltage across the Zener diode ZD is vRef, and R5 (R6).

In Fig. 3(C), the input terminal a is connected to the non-inverting input terminal of the operational amplifier OP, and the reference voltage vrof is connected to the operational amplifier ○P.
The output terminal of the operational amplifier oP is connected to the output terminal via a resistor R7.

In the above three circuits, vPl is Va. When it becomes less than f, the output voltage vb of the voltage drop detection circuit 7 decreases, and the base current holding circuit 6 does not turn on.

Effects of the Invention As described above, according to the present invention, it is possible to turn on and off the power supply with a single push switch, and there is no need to configure a constant voltage circuit (it is possible to output a constant voltage interrupt to the CPU, and it is possible to turn off the power automatically). It is possible to provide a low-cost power supply circuit whose functions can also be installed internally.

[Brief explanation of drawings]

FIG. 1 is a power supply circuit diagram in one embodiment of the present invention, and FIG. 2 is a circuit diagram showing a specific circuit configuration of a voltage drop detection circuit of the power supply circuit. 1...Power supply, 2...Transistor, 3
...Push switch circuit, 4 ... Constant voltage circuit, 6 ... CPU, 6 ... Base current holding circuit, 7 ... Voltage Drop detection circuit. Name of agent: Patent attorney Toshio Nakao, 1st person, 2nd person
Figure a, l (+) (2)

Claims (1)

[Claims] A power supply circuit that uses a battery or the like whose output voltage decreases as the capacity decreases as a power source and drives a microcomputer at a constant voltage includes a transistor that switches the power source, a push switch circuit that switches the base current of the transistor, and an output of the transistor. a constant voltage circuit that converts a voltage into a constant voltage; a microcomputer that uses the output of the constant voltage circuit as a power source and the output voltage of the push switch circuit as an input; and an output voltage of the microcomputer that is equal to or higher than a predetermined value. a voltage drop detection circuit for detecting the voltage drop detection circuit; a base current holding circuit for the transistor that receives the output of the voltage drop detection circuit as an input; and a base current holding circuit for the transistor that receives the output of the voltage drop detection circuit; A power supply circuit equipped with a diode that connects the input terminal of the switch circuit.