JPH0161011B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for electronic equipment driven by a battery power source such as a solar battery. Recently, the power consumption of elements such as LSIs used in calculators and the like has been reduced, and calculators with solar cells that directly drive the calculators with solar cells have appeared. A drawback of such equipment is that, especially if the incident light to the solar cells is interrupted during calculation, the stored information during calculation will be destroyed and lost. In order to eliminate this drawback, two protection circuit systems have conventionally been adopted.

That is, (i) LSI which is an element used in parallel with the solar cell
A backup capacitor is connected to protect the operation of the solar cell, and this capacitor protects the solar cell from temporarily blocking light incident on it. (ii) A backup battery is built-in, and even if the incident light to the solar cells is blocked, the backup battery can be used for operation. However, the above conventional methods (i) and (ii) both have the following drawbacks.

That is, in the case of circuit system (i) (see Figure 1), as shown in Figure 1, this system is a circuit system in which the backup capacitor _C1 protects the temporary light incident on the solar cell SB, Backup capacitor C ₁ for blocking incident light in parallel with solar cell SB
is connected, and if more incident light than necessary is applied to the battery SB in parallel with this capacitor _C1 ,
These D ₁ and D ₂ are used to prevent excessive voltage from being applied to the LSI, and make the output voltage of the battery SB constant. According to this circuit, when the incident light to the battery SB is cut off, the output of the solar battery SB becomes zero volts, so the voltage required to operate the electronic device is reduced by the capacitor.
Compensated by C ₁ . Therefore, even if the incident light to the solar cell SB is blocked, the operation of the LSI is protected by the backup capacitor _C1 . Therefore, in order to extend the guaranteed time, it was necessary to increase the capacitance of capacitor _C1 as much as possible. However, a drawback of this circuit system is that, for example, even if a calculator with a solar battery is taken out of the darkness and light is applied to the solar battery, it takes some time for the calculator to reach a usable state. That is, capacitor C ₁
If the charge of the solar cell is taken out from the dark to a place with light when the charge is "0", the output of the solar cell will take a considerable amount of time until the voltage of the backup capacitor _C1 reaches the voltage required to operate the LSI. This resulted in the inconvenience that the equipment could not be used during this time. The time required to reach the usable state (hereinafter referred to as recovery time) T ₁ is approximately expressed by the following equation.

T ₁ = C ₁・V/I・A ……(1) Here, C ₁ ……capacity of backup capacitor.

V: The voltage required to be applied to the LSI elements used in order to operate the device normally.

A: Illuminance of light incident on the solar cell.

I...The output current of the solar cell when an illuminance of A is applied.

In equation (1) above, to shorten the recovery time T ₁ ,
It is necessary to reduce C ₁ and V and increase I and A. In this case, reducing C ₁ will reduce its effectiveness as a backup capacitor, and reducing V will lower the yield of LSI and increase the cost of LSI. It had the disadvantage of being connected. Furthermore, increasing A will narrow the range of illuminance that can be used for equipment equipped with solar cells, and increasing I will require increasing the area of the solar cells, but solar cells are currently used in general batteries. It is relatively expensive, and increasing the area of the solar cell has the disadvantage of increasing the cost of the solar cell.

(ii) In the case of a circuit system (see Figure 2) This system is a circuit system that uses a backup battery to protect against temporary interruption of incident light to the solar cells.The battery backup system uses a primary battery. There are two types: one that uses a secondary battery (see figure a) and one that uses a secondary battery (see figure b). The former is a primary battery as shown in the diagram.
A diode D is inserted to prevent E ₁ from being charged by the electromotive force of the solar cell SB.
When the electromotive force of SB decreases, power is supplied from the primary battery _E1 to the LSI. On the other hand, in the latter case, as shown in the figure, when the electromotive force of the solar cell SB is large, power is supplied to the LSI by charging a secondary current E ₂ (for example, a Ni--Cd battery, etc.) via a charging current limiting resistor R. Otherwise, power is supplied to the LSI from the secondary battery _E2 . However, in this method of incorporating a backup battery, whether a secondary battery (such as a Ni-CD battery) or an ordinary primary battery is used as a backup battery, the battery has a limited lifespan. It is necessary to replace the semi-permanent semiconductor solar cell, which has the disadvantage that the marketability of the semi-permanent semiconductor solar cell is significantly halved.

The present invention has been made to eliminate the above-mentioned conventional drawbacks.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In Figure 3, SB is a solar cell, D ₁ , D ₂
is for making the output voltage of the solar cell constant.
LED, C ₁ is a backup capacitor, D ₃ is a diode, and C ₂ is a backup capacitor. This method charges the backup capacitor _C1 because the incident light on the solar cells changes moment by moment depending on the surrounding environment of the solar cells.
This is done only when sufficient incident light hits the SB to drive the LSI, which is the operating element of the device, and the circuit system separates the charging circuit for the backup capacitor from the drive power source for the LSI, which is the operating element. That is, if more incident light than necessary hits, current begins to flow through the constant voltage LEDs, D ₁ and D ₂ , and charges the backup capacitor C ₁ via the transistor Tr ₁ .

On the other hand, when the solar cell SB is taken out of the darkness with the charge on the backup capacitor _C1 being zero, it takes until the solar cell output reaches the voltage required to operate with the element used Lsi. It depends on the charging time of backup capacitor _C2 , but is unrelated to the charging time of backup capacitor _C1 .
The capacity of C ₁ can be increased regardless of the time it takes for Lsi to operate.

Note that the backup capacitor C ₂ is a backup capacitor for blocking the minimum amount of incident light in an environment where there is not enough incident light to the solar cell to charge C ₁ , and it is set as C ₁ ≫ C ₂ . do.

Now, when the backup capacitor _C1 is fully charged and the incident light to the solar cell is cut off, the operation of the element Lsi used is such that the backup capacitor _C1 backs up Lsi via the diode _D3 .

Note that _D3 is a diode provided to supply the charge of the backup capacitor _C1 to Lsi. FIG. 4 shows another embodiment of the present invention, in which the same parts as in FIG. 3 are designated by the same reference numerals. In the figure, P ₁ is a piezoelectric buzzer, and I ₁ is an inverter for driving the piezoelectric buzzer. This method uses a backup capacitor _C1 as a power source for a strong discharge circuit. In the figure, when the command to drive piezoelectric buzzer P ₁ is output from terminal K of Lsi, there is not enough solar cell output to drive piezoelectric buzzer P ₁ because the incident light of the solar cell output is small. Also, the piezoelectric buzzer drive current can be supplemented by the backup capacitor _C1 .

As explained above, according to the present invention, even if the incident light to the solar cell is temporarily interrupted, it is possible to back up elements directly driven by the solar cell. In addition, we can take equipment equipped with solar cells out of the dark and reduce the capacity of backup capacitors to reduce the time until the equipment can be used.Also, we can minimize the area of solar cells without reducing the yield of LSI. It can be shortened.

[Brief explanation of drawings]

1 and 2 are protection circuit diagrams of a conventional battery-powered electronic device, FIG. 3 is a protection circuit diagram of a battery-powered electronic device according to an embodiment of the present invention, and FIG. 4 is a diagram of another protection circuit of the same circuit. FIG. 2 is a circuit diagram showing an example. In the figure, SB: solar cell, C ₁ , C ₂ : backup capacitor, D ₃ : diode, D ₁ , D ₂ :
LED, P ₁ : Piezoelectric buzzer, I ₁ : Inverter.

Claims (1)

[Claims] 1. In a device driven by a battery power source such as a solar battery, the backup capacitor is configured to be charged by a switching element that conducts the electromotive force of the solar battery above the operating range of the battery load. A protection circuit for battery-powered electronic equipment characterized by: