JPS603725A - Voltage limiting circuit - Google Patents

Abstract

PURPOSE:To obtain a voltage limiting circuit which is operated stably with a low power consumption, by transmitting an output voltage from a comparator when the non-inverted input voltage of the comparator is higher than a prescribed value and controlling a power source voltage through a switching element in this case. CONSTITUTION:A proportional potential obtained by resistance division of resistances R1 and R2 is inputted to the plus input of a comparator 6, and a potential VPN corresponding to one stage of PN junction due to a diode D1 is inputted as a reference potential to the minus input. Since the potential in the plus input is given by V1-VDDR2/(R1+R2), the output is ''1'' in case of (the second term) >=VPN and the output is ''0'' otherwise with respect to the operation of the comparator. If the output of this comparator is ''1'', a switching element 7 consisting of an N-channel transistor is made conductive to reduce a power source voltage VDD. Thus, a power source voltage VDD0 supplied to the voltage limiting circuit is limited.

Description

[Detailed Description of the Invention] <Industry - Second Field of Application> The present invention is suitable for use in small electronic devices that use solar cells as a driving source, and can be incorporated into semiconductor integrated circuits (hereinafter referred to as LSi). This relates to voltage control circuits.

<Prior art and its problems> In recent years, the spread of electronic desks (hereinafter referred to as "dentocho") has been remarkable, but on the other hand, as a way to save energy and resources, solar cells have been used as a power source. A so-called solar cell calculator has already been developed and is being supplied to the market. That is, as shown in FIG. 1, in the conventional solar cell calculator, the output of the LSil, which performs calculations based on input signals, is displayed on an output means such as a liquid crystal display device 2, and the calculation results and notes 1.
v contents etc. are output. (The LSi+ and the liquid crystal display j'j2 execute predetermined calculations and display operations using the electromotive force output from the solar cell 3 as a power source. When using the output of the solar cell as a power source, a general battery is used as a power source. Unlike devices with high illuminance, the voltage generated depends on the illuminance of light under usage condition F, and under high illuminance conditions, standard usage 1 is not possible.
The output voltage is considerably higher than that at 141 degrees below.

When such a high voltage is applied, even the non-lit segments of the liquid crystal display become partially lit, making it difficult to see the displayed content.
i also has the disadvantage that it imposes a heavy burden and requires a wide operating tolerance range.

In order to deal with this problem, solar cell calculators currently in practical use connect a resistor, LED, etc. between the solar cell 3 and LSil, as shown by the broken line in Figure 1. In this case, a voltage control circuit 4 configured by I-
In addition to the display drive circuit and the display drive circuit, there are resistors and L
It is necessary to provide a voltage regulating circuit 4 using an ED, and it is not suitable for small electronic devices with a reduced number of parts, such as quartets and electronic game machines, and is not suitable for meeting the demand for lower prices. However, it also requires a large amount of space for mounting, which is insufficient for small devices.

<Purpose> The present invention was made in order to eliminate the various drawbacks of the conventional voltage control circuit mentioned in 2. and LSi(
It is an object of the present invention to provide an inexpensive voltage control circuit that can be manufactured integrally within a C-MOS LSi (for example, a C-MOS LSi) and operates with low power consumption.

<Example> Fig. 2 shows a power absorption control circuit for, for example, a telephone, which uses a solar battery as a driving source.
2 is the sun? A circuit that generates a potential proportional to the power supply voltage of the reservoir (hereinafter referred to as -1 proportional potential) is constructed, and a diode l
) J and resistor R3 constitute a circuit that generates a reference potential.

6 is a comparator for comparing the proportional potential and the reference potential; 9 is a D-type flip-flop; 7 is a switching element, for example, an N-channel transistor connected in parallel to the solar cell 5; This is a transistor controlled by a clock pulse φ to cause the operation to occur.

Next, to explain the operation, Konnoshi Ichiyo 6) Brass (
→The proportional potential obtained by the resistance division of resistors R1 and R2 is input to the input, and the negative (-) input is connected to the PN junction 1 by diode DJ as a reference potential.
The potential VI'N for each stage is input.

Since it is given by , the action of the excreta is a force.
Outputs 0゛. When the comparator output is "1", the switching element 7 made of an N-channel transistor becomes conductive and lowers the power supply voltage (old)0.

The N-channel transistor 7 is turned on or off, thereby limiting the power supply voltage VDDO supplied to the voltage control circuit. Figure 3 shows power 11: control circuit 0)
Vl) D-I Qe property-, m 4 Fig. VIH)-VD
I) Shows 0 characteristics. Further, the transistor 8 is a switching knob for performing these operations intermittently, and is effective for saving power consumption at low voltage. The reference potential provided by the diode D1 is stable, and the detected voltage is accurate because the PN junction voltage is used as the reference voltage.
Furthermore, the detection voltage can be set arbitrarily by the resistance ratio of R1r and R2, and the device operates stably with low power consumption. Moreover, C-MOS
It can be manufactured integrally within an LSi, and is suitable for use in small electronic devices powered by solar cells, and can reduce costs.

<effect>,.

As described above, the voltage control circuit of the present invention is suitable for use in small electronic devices powered by solar cells, and can be integrated into LSi such as CMO5-LSi. This has two effects: it is possible to obtain an inexpensive voltage control circuit that can be manufactured and operates stably with low power consumption.

[Brief explanation of the drawing]

Figure 1 is a diagram of a conventional solar cell (117); It is a characteristic curve diagram.

Claims (1)

[Scope of Claims] l A solar battery power source, a first potential generating means for generating a reference potential, a second potential generating means for generating a potential proportional to the solar battery power source, and the first potential generating means for generating a potential proportional to the solar battery power source. It is characterized by comprising a comparator that compares the potential and the second potential, and a switching element that performs a switching control operation based on the output signal of the comparator, and that the switching element is connected in parallel to the +)iJ solar battery power source. voltage limiting circuit. 2. Claim v11, wherein the first and second potential generating means and the comparator are operated intermittently.
The voltage control circuit described in HH.