JPH0145298B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection circuit for electronic equipment equipped with a solar cell, and an object of the present invention is to protect the operation of a used element (for example, an LSI) when light incident on a solar cell is interrupted.

Recently, the power consumption of the LSI used in electronic desk calculators (hereinafter referred to as calculators) has been reduced, and calculators with solar cells that directly drive the calculators using solar cells have appeared. .

The disadvantage of such equipment is that, especially during calculations,
If the incident light to the solar cell is cut off, the memory contents in the middle of calculation will be destroyed and lost.

In order to eliminate this drawback, two protection circuit systems have conventionally been adopted. That is, (i) A backup capacitor that protects the operation of the LSI used as an element is connected in parallel with the solar cell, and this capacitor protects the solar cell from temporarily blocking incident light.

(ii) A primary or secondary battery for backup is built-in, and even if the incident light to the solar cells is blocked, the battery can be used for operation.

However, both of the conventional methods (i) and (ii) have the following drawbacks. In other words, in the case of the circuit system (i) (see Figure 1), as shown in Figure 1, this system is a circuit system that uses a backup capacitor _C1 to protect the solar cell SB from temporarily blocking light incident on it. , Backup capacitor when blocking incident light in parallel with solar cell SB
C ₁ is connected, and if more incident light than necessary is applied to the solar cell SB in parallel with this capacitor C ₁ , a constant voltage is set to prevent excessive voltage from being applied to the LSI used. Voltage LEDs (D ₁ , D ₂ ) are connected. That is, D ₁ and D ₂ make the output voltage of the solar cell SB constant. According to this circuit, when the incident light to the solar cell SB is blocked, the solar cell SB
Since the output of is zero (“0”) volts, the voltage necessary for the operation of the electronic device is supplemented by the capacitor _C1 . Therefore, even if the incident light to the solar cell SB is blocked, the back-up capacitor _C1
Guarantees LSI operation. 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, 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. In other words, if the charge of capacitor _C1 is 0 and the charge is taken out from darkness to a place where there is light, the solar cell output will continue until the voltage of backup capacitor _C1 reaches the voltage required to operate the LSI. , it will take a considerable amount of time,
This caused the inconvenience of not being able to use the equipment during this time.

The time it takes to reach the above usable state (hereinafter referred to as
This is called recovery time. ) T ₁ is approximately expressed by the following equation.

T ₁ =C ₁・V/I・A…(1) Here, C ₁ …capacity of the backup capacitor V…voltage required to be applied to the LSI used to operate the device normally A ...The output current of the solar cell when the illuminance of the incident light I...A is given to the solar cell In the above formula (1), to shorten the recovery time _T1 ,
It is necessary to make C ₁ and V small and I and A large. In this case, if C ₁ is made small, the effect as a backup capacitor will be reduced, and if V is made small, the yield of LSI will decrease and the cost of LSI will increase. The disadvantage was that it led to Furthermore, increasing A will narrow the range of illuminance that can be used for devices equipped with solar cells, and increasing I will require increasing the area of the solar cells, but solar cells are currently not suitable for 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.

In the case of the circuit method (ii) (see Figure 2), this method uses a backup battery to protect the solar cells from temporarily blocking light incident on them, and a primary battery is used for the battery backup method. There are two types: one that uses a secondary battery (see figure a) and one that uses a secondary battery (see figure b). In the former case, as shown in the figure, a diode D is inserted to prevent the primary battery _E1 from being charged by the electromotive force of the solar battery SB, and a diode D is inserted between the solar battery and the solar battery.
When the electromotive force of SB decreases, LSI power is supplied from the primary battery _E1 . On the other hand, in the latter case, when the electromotive force of the solar cell SB is large as shown in the figure, the secondary battery E ₂ (e.g.
Power is supplied to the LSI while charging a Ni--Cd battery (such as a Ni-Cd battery) via a charging current limiting resistor R. Otherwise, power is supplied to the LSI from the secondary battery _E2 .

However, this method of incorporating a backup battery is a secondary battery (Ni-
Whether using CD batteries, etc.) or ordinary primary batteries, batteries have a limited lifespan and must be replaced, which makes semi-permanent semiconductor solar cells extremely difficult to market. It had the disadvantage of being reduced by half.

The present invention has been made in order to eliminate the various drawbacks of the protection circuits in the conventional electronic devices with solar cells.

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

FIG. 3 shows an example of a protection circuit according to the present invention,
In the figure, D ₁ and D ₂ are LEDs for making the output of the solar cell SB constant voltage, C ₁ and C ₂ are backup capacitors, D ₃ is a diode with a built-in LSI,
SW ₁ and SW ₂ are switching elements composed of, for example, MOS-FETs, and are built into the LSI.

The relationship between the backup capacitors C ₁ and C ₂ above is set as C ₁ ≫ C ₂ , and when the device with solar battery SB is taken out of the darkness, it is the element used in the initial state.
Switching element SW ₁ built into the LSI closes, SW ₂ opens, and capacitor C ₂ is charged by the output of solar cell SB. In this case, the capacity value of C ₂ is set so that it can be charged in a short time using the solar cell output. Afterwards, when C ₂ has finished charging and the voltage has exceeded the voltage required for the LSI to operate normally,
Switching elements SW ₁ and SW ₂ built into the LSI are opened and closed. When SW ₁ is open, SW ₂ is closed, and when SW 1 is closed, SW ₂ is closed _.
It is controlled based on the CPU inside the LSI so that the time when SW ₁ is open and the time when SW ₂ is closed is approximately 9:1. In other words, charging of the capacitor _C1 is started from the moment when the voltage applied to the LSI used is a voltage higher than the voltage required for the LSI to operate normally. Therefore, capacitor C ₁ takes 10 times longer to charge than the conventional method shown in FIG. However, when _C1 is being charged, the operation of the LSI is maintained by the backup capacitor _C2 , so when you take out the solar cell from the darkness, you can start the operation of the equipment without waiting for the backup capacitor _C1 to complete charging. The capacitance of the capacitor _C1 can be increased regardless of the time during which the LSI can operate. After charging of the backup capacitor _C1 is completed in this way, when the incident light to the solar cell SB is cut off, the operation of the LSI, which is the element used, is controlled by the capacitor _C1 via the diode _D3 . It backs up and protects the operation of the LSI used.

In this way, the circuit system that charges the backup capacitor after the LSI, which is the element that uses it, starts normal operation, uses a backup capacitor without using a battery, so there is no need to replace the battery. This can also be achieved by reducing the capacity of the backup capacitor, which takes the time it takes to take out the solar cell from the dark and use a device such as a calculator. Also LSI
The solar cell area can be reduced to the necessary minimum without reducing the yield.

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, I ₁ is an inverter for driving the piezoelectric buzzer P ₁ , and a signal Ka instructing to drive the piezoelectric buzzer P ₁ is applied to the inverter I ₁ from the CPU. It is also configured to supplement the driving current of the piezoelectric buzzer _P1 from the backup capacitor _C1 via the inverter _I1 . That is, this circuit is an example in which the backup capacitor IC ₁ is used as a power source for a strong discharge circuit. In the figure, when the command Ka to drive the piezoelectric buzzer P ₁ is output from the CPU, the incident light from the solar cell SB output is small and even if there is not enough solar cell output to drive the piezoelectric buzzer P ₁ . The drive current for the buzzer _P1 can be supplemented by the backup capacitor _C1 .

The switching element shown in FIGS. 3 and 4 above
SW ₁ and SW ₂ are built into the LSI and can be built in, and are always turned ON/OFF with a duty ratio of 9:1, for example.
These switching elements are controlled by the fifth switching element.
As shown in the figure, it can be configured with a transfer gate made of a MOS transistor. TM indicates a timing signal generation circuit.

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 an element directly driven by the solar cell.

In addition, the time required to take a device equipped with a solar battery out of the darkness and use the device can be realized by using a backup capacitor with a small capacity. Furthermore, when an LSI is used as an element, there are advantages such as the ability to significantly shorten the solar cell area by reducing it to the necessary minimum without reducing the yield of the LSI.

[Brief explanation of drawings]

1 and 2 are protection circuit diagrams of conventional solar cell-equipped electronic equipment, FIG. 3 is a circuit diagram of one embodiment of the protection circuit according to the present invention, and FIG. 4 is a circuit diagram of another embodiment. Figure 5 is a transfer gate circuit diagram consisting of switching elements built into an LSI used in the above circuit. In the figure, SB...Solar cell, _D1 , _D2 ...LED,
SW ₁ , SW ₂ ... switching element, LSI ... large-scale integrated circuit, CPU ... central processing unit, C ₁ , C ₂ ...
...backup capacitor, DISP...display unit, _D3 ...diode.

Claims (1)

[Scope of Claims] 1. A first charging circuit used in a device using a solar cell as a power source, and connecting a first capacitor _C2 in parallel with the solar cell via a first switching transistor; a second charging circuit that connects a second capacitor C ₁ in parallel with the solar cell via a second switching transistor; a capacitance C ₂ of the first capacitor C ₂ and a capacitance of the second capacitor C ₁ ; _C1 has _the relationship _C1≫C2 , and the time constant of the first charging circuit is smaller than the time constant of the second charging circuit, while the first and second switching transistors are The first and second capacitors _C2 are provided with means for intermittently opening and closing at different duties so that the closing time of the first switching transistor is longer than the closing time of the second switching transistor; , C ₁ are used as backup capacitors for the LSi. During charging, the first capacitor C ₂ is used to back up the LSi during charging due to rapid charging in the first charging circuit. This is a protection circuit for electronic equipment equipped with a solar battery, in which LSi backup is performed using capacitor _C1 of 2.