JPH0315410B2 - - 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 devices such as LIS in calculators has been reduced, and calculators with solar batteries that directly drive the calculators are now available. The disadvantages of such equipment are
In particular, if the incident light to the solar cell is cut off during the calculation, the stored information during the 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 is connected in parallel with the solar cell to protect the operation of the LIS, which is an element used, and this capacitor protects against temporary interruption of incident light to the solar cell. (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. In other words, (i) circuit method (see Figure 1) As shown in Figure 1, this method is a circuit method in which the backup capacitor _C1 protects the temporary light incident on the solar cell SB. Backup capacitor when blocking incident light in parallel with battery SB
If C ₁ is connected and more incident light than necessary is applied to the battery SB in parallel with this capacitor C ₁ ,
Constant voltage LEDs (D ₁ , D ₂ ) are connected to prevent excessive voltage from being applied to the LIS. That is, this
D ₁ and D ₂ make the output voltage of battery SB constant. According to this circuit, when the light incident on the battery SB is cut off, the output of the solar battery SB becomes zero volts, so 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 backup capacitor C ₁
The operation of LIS is guaranteed by 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. In other words, if the charge on 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 on backup capacitor _C1 reaches the voltage required to operate the LSI. , it took a considerable amount of time, which caused the inconvenience that the equipment could not be used during this time. The time required to return to 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 incident light to the solar cell.

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

In equation (1) above, to shorten the recovery time T ₁ ,
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. It had the disadvantage of being connected. 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 system (ii) (see Figure 2), this system uses a backup battery to protect against temporary interruption of incident light to the solar cell, and the battery backup system uses a primary battery. There are two types: one that uses a rechargeable 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 so that the primary battery E ₁ is not charged by the electromotive force of the solar cell SB, and if the electromotive force of the solar cell SB decreases, the primary battery E ₁ is charged.
Power is supplied to the LSI. On the other hand, the latter is a secondary battery when the electromotive force of the solar cell SB is large as shown in the figure.
Power is supplied to the LSI while charging E ₂ (for example, 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 capacitor battery has a limited lifespan, regardless of whether a secondary battery (such as a Ni-CD battery) or an ordinary primary battery is used as a backup battery. However, it is necessary to replace the battery, which has the disadvantage that the marketability of semi-permanent semiconductor solar cells is significantly halved.

The present invention has been made in view of the above-mentioned conventional drawbacks, and in particular, it is possible to back up circuit elements (such as LSI) directly driven by solar cells even if the incident light to the solar cells is temporarily interrupted. In addition, the time required until a device equipped with a solar cell can be taken out of the darkness and used can be significantly shortened by minimizing the area of the solar cell.

An embodiment of the present invention will be described in detail below with reference to the drawings. Figure 3 shows an example of a protection circuit according to the present invention. In the figure, D ₁ and D ₂ are LEDs that stabilize the output voltage of the solar cell SB, C ₁ is an LSI backup capacitor, and a is a battery power source. The voltage detection circuit, LSI, is a large-scale integrated circuit that includes various components such as calculation, memory, and clock pulse generation, and DISP is a display unit. The voltage detection circuit a detects a voltage for stopping a clock pulse generator inside the LSI, which will be described later, when the incident light of the solar cell SB is interrupted.
Figure 4 is a detailed block diagram of the LSI system. In the figure, CG is the clock pulse generator,
SW ₁ is a switching element with built-in LSI, for example
Consists of MOS transistors. M is a memory element, Cpu is a central processing unit in charge of calculations, control, etc., V ₁ is an applied voltage of the LSI, and I ₁ is an LSI current.
Here, suppose the normal operating voltage range of the above CPU is
The voltage should be 2.4V to 3.2V. And the above constant voltage LED
The voltage normally supplied to the LSI by D ₁ and D ₂ is defined as A voltage, and this is set to 3.1V.

Also, when the clock pulse generator CG stops
The static state holding voltage range of LSI is 1.5V to 3.2V.

Further, a voltage value of 2.5V, which is slightly larger than the normal operating voltage lower limit of 2.4V for the CPU, is defined as the B voltage. When the incident light to the solar cell is cut off and the LSI applied voltage _V1 drops from voltage A to voltage B as shown in Figure 5, the voltage detection circuit a operates,
When the LSI built-in switching element _SW1 opens,
The supply of charging voltage from the backup capacitor C1 to the clock pulse generator CG is cut off, and the generation of clock pulses by the clock pulse generator CG is stopped. Furthermore, when this generator CG stops,
If the LSI is configured with C-MOS transistors,
The LSI becomes static, and almost no LSI current flows through _I1 (see Section 5b).

For this reason, the backup capacitor shown in Figure 3
In order to back up only the static current of the LSI, _C1 is
Capacitor capacity can be made extremely small. In the static state of the LSI, a voltage of 1.5V or higher, which is the lower limit voltage of the static state holding voltage, is applied to the CPU and memory element M in Fig. 4 by the capacitor _C1 . The internal state of is maintained. Now, the capacitance of capacitor C ₁ is
Assuming that the static current of 10μF and LSi is 0.1μA, the static state holding time △t is calculated as △t=C・△V/i = 10μF×(2.5V-1.5V)/0.1μA = 100sec. Ru.

In other words, the capacitor C ₁ makes it possible to maintain a static state for 100 seo. In this way, when the LSI is in a static state and the sunlight hits the incident light again, and the _V1 voltage reaches the level of point B in Figure 5, _SW1 of the LSI built-in switch closes and the clock pulse generator CG turns on. The LSI starts to move and enters a dynamic state. At this time, the internal state of the LSI is the same as before the clock pulse generator CG of the LSI stopped, so subsequent processing can be continued as is.

As explained above, according to the present invention, even if the incident light to the solar cell that supplies the battery power is temporarily cut off, the charging voltage of the charged backup capacitor can be applied to the arithmetic control unit in the circuit element or the memory. In this case, since the power supply to the clock pulse generator is cut off, sufficient backup is possible even if the amount of the capacitor is sufficiently small.

Therefore, even when the electronic device is taken out of the dark and used, the time required to charge the capacitor is very short, and the time it takes to start using the device can be significantly shortened.

[Brief explanation of the drawing]

Figures 1 and 2 are protection circuit diagrams of a conventional solar battery-powered machine, Figure 3 is a protection circuit diagram of an example of a battery-powered machine according to the present invention, and Figure 4 is a block diagram of the LSI internal system. 5a and 5b respectively represent characteristic curve diagrams of the voltage V ₁ and the current I ₁ as a function of time. In the diagram, C ₁ ... backup capacitor, a
...Voltage detection circuit, CG...Clock pulse generator, CPU...Central processing unit, M...Memory element.

Claims (1)

[Scope of Claims] 1. A central processing unit CPU, a memory element M, which is used in a device driven by a battery power source of a solar cell, and is connected to the battery power source and is supplied with power, and which manages arithmetic control.
and a circuit element including a clock pulse generator CG that controls the operation of the system; and a circuit element that is connected in parallel with the battery power source and supplies a charging voltage to protect the operation of the central processing unit CPU and the memory element M among the circuit elements. a backup capacitor for detecting the voltage of the battery; a battery voltage detection circuit for detecting whether the voltage of the battery power supply is within the operating range of the circuit element; Based on the output of the detection circuit, a battery power supply path is formed to the clock pulse generator CG of the circuit element to make the clock pulse generation state, and when the voltage is outside the operating range, the battery voltage is supplied to the clock pulse generator CG based on the output of the battery voltage detection circuit. switching means for cutting off the supply path of the charging voltage from the backup capacitor, and when the battery voltage drops, the central processing unit CPU and the memory element M among the circuit elements are switched to the charging voltage from the backup capacitor. A protection circuit for a battery-powered electronic device, characterized in that it is maintained in a static state.