JPS60123892A - Display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control circuit for a display device that uses a solar cell or a dry battery as a power source and forms a power supply voltage for a display circuit using a booster circuit.

When light hits a solar cell, the original energy is converted into electrical energy, which can power digital devices. However, if the digital device is left in a dark place and is not charged by the solar cell, the power supply voltage of the digital device will drop and eventually it will malfunction. If the operator notices the other name of the digital device.

By shining light on the solar cell, it can be charged and the digital device can be operated normally again.

Conventionally, a method for notifying an operator that the power supply voltage is one generation below has been to detect malfunction of a digital device due to a drop in the power supply voltage, and to generate an auto-clear command from a control circuit. That is, the auto-clear operation caused the display circuit to go into a non-lit state and the 1 display to disappear, allowing the operator to know that the power supply voltage had dropped. However, this control circuit actually malfunctions before charging the solar cells.

It had the disadvantage that it could not be used in digital devices that required clock functions or nonvolatile memory functions.

An object of the invention is to obtain a display device including a power supply control circuit that can detect a drop in power supply voltage before the circuit malfunctions.

The non-invention is that in digital devices powered by solar cells or dry batteries, a booster circuit is required as a power source for the display circuit, and the voltage consumed by the booster circuit and the display circuit is greater than that of the remaining parts of the digital device. Considering that the power consumption is large compared to the power consumed by the digital device, we installed a transistor with a threshold voltage that can detect a drop in the power supply voltage while the digital device is operating normally. By stopping the power supply, the display circuit is turned off and the operator is notified of the drop in power supply voltage.

Hereinafter, the present invention will be specifically explained using examples.

FIG. 1 is a circuit diagram showing one embodiment of the invention. 1
is a solar cell, 2 is an LSIC large-scale circuit), one pole of solar cell 1 is connected to the ground terminal of LSI 2,
The other pole is connected to the power supply terminal. Further, 3 is a display device. 4 is a clock generator in the LSIZ, 5 is an arithmetic circuit, 6 is a booster circuit, and 7 is a display circuit, all of which are powered by one pole of the solar cell 1. Trl is a transistor that has a higher threshold than other transistors.

Normally, the output of the clock generator 4 is sent to the booster circuit 6, and when the power supply voltage drops, other transistors are turned on earlier than other transistors, and the output of the clock generator 4 is sent to the booster circuit 6. Note that the transistor +1+ rl with a high threshold value is doped with reverse conduction type ion gold channel doping to the substrate.
It can be constructed from the amount of threshold voltage variation depending on the amount of implanted charge. 8 and 9 are inverters of the booster circuit 61FJ! ;1.10.11 is a transistor, 12.1
3 is a capacitor.

Here, the circuit operation will be explained. FIG. 2 is a graph of the operation f near r, "j when the conventional circuit is used.

There is no charge from the solar battery, and time 1. Malfunctions can be prevented if the operator shines light on the solar cell before the power supply voltage begins to drop at time t1, at which point the power supply voltage drops to the voltage at which the digital device malfunctions. However, as mentioned above, in the conventional circuit, the 1 display is turned off and the operator is notified only after the malfunction is detected (after time t1), so after charging, the data before time 11 must be used as is to continue calculation. I can't. FIG. 3 is a graph showing the operation when using the inventive circuit. From time to to 12, the transistor Tr of the circuit in FIG.
l is on. Therefore, the output of the clock generator 4 is sent to the inverter 8 of the booster circuit 6. When the output of the inverter 8 is at a high level, the transistor 10 is turned on to charge the capacitor 12 with the power supply voltage,
When the output of inverter 8 is at level 9, transistor l
With O off and 11' on, the voltage at the other end of the capacitor (twice the supply voltage) causes capacitor 1
3. Charge the battery. That is, since the display circuit 7 is driven with a voltage twice the power supply voltage, the display device 3 displays normally.

Next, after time t2, the transistor Tr1, which has a higher threshold than the other transistors, is turned off, so the booster circuit 6 stops operating and the display on the display device 3 disappears. Note that at this point, all transistors except transistor 1 are operating normally, so the clock generator 4.
'The arithmetic circuit 5 is operating normally. Moreover, the power consumption at this point decreases because the booster circuit 6 and the display circuit 7 do not operate, and as shown in Fig. 3, the power supply voltage decreases gradually.The display disappears after time t2. Therefore, before the arithmetic circuit 5 starts malfunctioning at time t3, if the operator applies a photovoltaic power to the solar cell, the transistor Tr1 will be turned on again, and the arithmetic circuit 5, which displays normally, will not malfunction during this time. Therefore, calculations can be continued using the data before the voltage drop.

As described above, the present invention can be widely used in digital devices such as electronic watches having a booster circuit. Moreover, since the element added due to the invention is, in principle, only one transistor with a high threshold value, the increase in cost can be negligible.

In addition, the invention can be applied not only to power sources using solar cells, but also to detect voltage drops in dry cell batteries before the circuit malfunctions.

[Brief explanation of the drawing]

Figure m1 is a circuit block diagram showing one embodiment of the present invention, Figure 2 is a graph showing the operation when using a conventional circuit,
FIG. 3 is a graph showing (1) operation when using the circuit according to the invention. 1...Solar cell, 2...LSI, 3...
... Display device, 4 ... Clock generation section, 5
... Arithmetic circuit, 6... Boost circuit, 7.
... Display circuit, 8, 9 ... Inverter, 1
0.11...transistor, 12.13...
...Capacitor, Ver...Operating voltage k VT
R...Threshold value of transistor Trl. Horse! flash

Claims (1)

[Claims] In a display device in which a power supply voltage is boosted using a booster circuit to drive a display circuit, the sources and drains of transistors having a high threshold are connected to the clock generation circuit output of the booster circuit and the input of the booster circuit. A display device characterized in that the power source voltage is applied to a gate electrode.