JPH0369215B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a power supply circuit that controls power supply to a load circuit by a single momentary switch.

[Technical background of the invention and its problems]

Conventionally, in various electronic devices, a toggle switch or a combination of a momentary switch and a flip-flop for latching has been used as a power switch. Although toggle switches are highly reliable, they are not suitable for small devices such as electronic thermometers due to the space they occupy and the ease of operation, and it is also difficult to make them waterproof.

Therefore, in devices such as waterproof electronic thermometers, it is desirable to use a momentary switch such as a rubber switch as the power switch. When using a momentary switch, separate switches are normally used for powering on and powering off, but in that case, there are naturally two switch knobs, which is also disadvantageous in terms of space. Therefore, it is conceivable to use a single momentary switch and use a logic circuit mainly consisting of a flip-flop to alternately turn the power on and off each time the switch is pressed. However, momentary switches such as rubber switches are generally prone to chattering, and therefore it is difficult to turn the power on and off reliably with a single switch. There is a risk that it may not turn on and may become unstable. The same goes for turning off the power; even if you press the switch to temporarily turn off the power, it may return to the power on state when you release your hand.

[Purpose of the invention]

An object of the present invention is to provide a power supply circuit that can reliably turn on and off the power supply using a single momentary switch without being affected by chattering.

[Summary of the invention]

The present invention is directed to a load circuit that includes an oscillation circuit, that is, a circuit that has a function of outputting an oscillation signal when power is supplied, and a circuit that supplies power to this load circuit when in a set state. 1. In addition to providing a second flip-flop,
By controlling the states of these flip-flops according to the state of the power switch and the state of the oscillation signal output from the load circuit, the third flip-flop absorbs the influence of the chattering of the power switch.

That is, when the power switch is turned on for the first time, the first flip-flop goes into the set state and starts supplying power to the load circuit, and then, after chattering, when the power switch continues to turn off, the third flip-flop goes into the set state. , the second flip-flop is sequentially set. on the other hand,
When the power switch is turned on again to stop the power supply, the first flip-flop and the third flip-flop go into the reset state in sequence, and then, after a period of chattering, when the power switch is turned off continuously, the third flip-flop goes into the reset state. The set state and the second flip-flop enter the reset state, and power supply is stopped.

〔Effect of the invention〕

According to this invention, since the power switch can be a single momentary switch, it is suitable for small devices such as electronic thermometers or pocket calculators, and it also ensures that the power supply is turned on and off without being affected by chattering. It becomes possible to do so.

Since the power supply circuit according to the present invention uses the output of a flip-flop as a power supply output, it cannot obtain a large amount of power, but it can be sufficiently used as a power supply circuit for a CMOS circuit or the like.

[Embodiments of the invention]

In FIG. 1, 1 is a power switch, and a momentary switch, for example a rubber switch as shown in FIG. 2, is used. This has electrodes 31 and 32 that become contacts 1a and 1b formed on a substrate 30, and a rubber knob 33 placed on top of them.When the knob 33 is pressed, a movable electrode 34 formed on the lower surface
short-circuits between the electrodes 31 and 32, resulting in a switch.

One contact 1b of the switch 1 is grounded, and the other contact 1a is connected via a resistor 2 to a power supply +Vc.c. The status signal of switch 1 is sent to inverter 3.
This signal 4 is taken out as output 4 of NAND
It becomes an input to first and second flip-flops 7 and 8 via gates 5 and 6. The first flip-flop 7 is configured by NAND gates 7a and 7b, and the second flip-flop 8 is configured by NAND gates 8a and 7b.
8b, and both are R-S
It is a flip-flop type. The power clear circuit 9 generates an initial power clear signal 10 to reset the first and second flip-flop circuits 7 and 8 when a battery is attached.

Q outputs 11 and 12 of the first and second flip-flops 7 and 8 are combined by a NOR gate 13 to become a power supply output 14 to a load circuit 15. The load circuit 15 is, for example, a body temperature measurement circuit in an electronic thermometer using an oscillation frequency comparison method, and includes an oscillation circuit 16. Note that the output 14 of the NOR gate 13 is passed through the inverter 17 and the LED driver 18,
It is also given to the power display LED 19.

The oscillation signal output 20 of the oscillation circuit 16 is logically processed with the state signal of the power switch 1 appearing at the output 4 of the inverter 3 via an AND gate 21 and an EOR (exclusive OR) gate 22, and is outputted as J-
This serves as a trigger input for the third K-type flip-flop 23. This flip-flop 23 is configured to be reset each time the power switch 1 is turned on by applying a power switch status signal 4 to a reset terminal via an inverter 24. AND gate 25, NAND gate 26, 27
is for controlling the first and second flip-flops 7 and 8 based on the output of the third flip-flop 23.

Next, the operation of this embodiment will be explained.

In the initial state, the first and second flip-flops 7 and 8 are reset by the initial power clear signal 10 as described above, their Q outputs 11 and 12 are both "L" (low level), and outputs 28 and 29 are Both are in the "H" (high level) state. When the power switch 1 is pressed in this state, the power switch status signal 4 output from the inverter 3 becomes "H".
However, in reality, due to chattering, the power switch state signal 4 irregularly repeats the "H" and "L" states as shown in period A in FIG. 3A. At this time, at the first rise of period A, the first flip-flop 7 is set via the gate 5, and the Q output 1 is set.
1 becomes "H" and the output becomes "L". On the other hand, the second
The flip-flop 8 maintains its previous state. The Q output (“H”) of the first flip-flop 7 is the power supply output 1 to the load circuit 15 via the gate 13.
It becomes 4. Note that during period A, the reset state is maintained because the power switch operation signal 4 is reset via the inverter 24 at the rising edge shown by the arrow in FIG. 3a.

When the load circuit 15 starts to be supplied with power as shown in FIG. 3b, the oscillation circuit 16 outputs an oscillation signal 2.
0, which is supplied to gates 21 and 22. The output of the gate 22 becomes "H" continuously when the power switch 1 is removed from the power switch 1 and enters the period B shown in FIG.
Since the output (reset signal) of is continuously "L", the third flip-flop 23 is triggered and enters the set state, and its Q output becomes "H". As a result, the output of the gate 25 becomes "H", the output of the gate 26 becomes "L", and the second flip-flop 8 is set. The Q output (“H”) of this second flip-flop 8 is connected to the first flip-flop by the gate 13.
It is combined with the Q output of the flip-flop 7 and becomes the power supply output 14 to the load circuit 15. During this period B, the device including the load circuit 15, such as an electronic thermometer, performs a required operation, such as measuring body temperature.

After the user reads the body temperature measurement result, when the user presses the power switch 1 again, the power switch status signal 4 changes to "H" and "L" due to chattering as in period A, as shown in period C in FIG. 3a. Repeat. In this case, at the first rise of the power switch state signal 4, the first flip-flop 7 is reset via the gate 6, and the third flip-flop 23 is also reset. After period C, that is, when the power switch 1 is released, the third flip-flop 23 is turned on again via the gates 21 and 22.
is set, and the second flip-flop 8 is also reset via the gate 27 by the Q output (“H”) of the flip-flop 23 at this time. As a result, the output of the gate 13 becomes "L", and the power supply to the load circuit 15 is cut off.

In this way, even if there is chattering in the power switch 1, each time the power switch 1 is pressed and then released, the power is alternately supplied and turned off correctly.

It should be noted that the present invention is not limited to the above-mentioned embodiments; for example, a means for resetting the first and second flip-flops after a certain period of time using a timer or the like may be added. Further, the application of the power supply circuit according to the present invention is not particularly limited to electronic clinical thermometers, and may be any device that includes a circuit that starts oscillation when supplied with power. Furthermore, if the power switch is a momentary type, it is also effective to use a power switch other than a rubber switch.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a power supply circuit according to an embodiment of the present invention, FIG. 2 is a sectional view of a rubber switch used as a power switch, and FIG. 3 is an explanatory diagram of the operation of the same embodiment. 1... Power switch, 7... First flip-flop, 8... Second flip-flop, 15...
...Load circuit, 16...Oscillation circuit, 23...Third flip-flop.

Claims (1)

[Claims] 1. A circuit that uses a single momentary switch as a power switch and supplies power to a load circuit including an oscillation circuit, which includes first and second flip-flops that supply power to the load circuit when in a set state; a third flip-flop that controls the states of the first and second flip-flops according to the state of the power switch and the oscillation signal output state of the load circuit; The second flip-flop is arranged to be in the set state and the reset state depending on whether the second flip-flop is in the reset state or the set state, respectively, and the second flip-flop is in the first state when the third flip-flop is in the set state. The third flip-flop is provided to be in a set state and a reset state depending on whether the flip-flop is in a set state or a reset state, respectively, and the third flip-flop is in a state in which the load circuit is receiving power supply and outputting an oscillation signal. What is claimed is: 1. A power supply circuit characterized in that it is in a set state when a power switch is turned off, and is reset each time the power switch is turned on.