JP2651187B2 - Charge level detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is to detect a charging voltage level of a capacitive element without being affected by a voltage drop due to an impedance of a protection circuit during charging and discharging of the capacitive element. The present invention relates to a charge level detection circuit that enables the following.

[Conventional technology]

The conventional charge level detection circuit has a configuration as shown in FIG.

That is, one resistive element, two capacitive elements, and three first external terminals formed in the semiconductor integrated circuit 10, and a second external terminal
It comprises an external terminal, a first protection circuit of 5, a second protection circuit of 7, an operational amplifier of 8, and a level detection circuit of 9.

Here, the resistance value of the resistance element 1 is R,
Where Vin is the input voltage, C is the capacitance value of the capacitive element 2, Vc is the charging voltage at the second external terminal 4, and Vout is the output voltage of the operational amplifier 8. Vc = −Vin / R C × t (t: calculation time), and the charging voltage Vc has a waveform proportional to the time shown in FIG. The level detection circuit 9 detects the detection voltage Vk.
And perform any operation. At this time, by the charge voltage Vc counts the detection time t _k until reaching the detection voltage Vk, it can be applied to the detection voltage Vk as the A / D converter to be replaced with a digital value.

[Problems to be solved by the invention]

However, in the conventional charge level detection circuit, a potential difference occurs between both ends of the second protection circuit due to the resistance component of the second protection circuit 7. Therefore, the output voltage Vout of the operational amplifier 8 and the charging voltage Vc of the capacitive element 2 are equal to the third voltage.
As shown in the figure, the difference | Vc | <| Vout | occurs.
At this time, the input side of the level detection circuit 9 is connected to the operational amplifier 8
Since the output voltage Vout is detected, the charging voltage Vc becomes the detection voltage at the time when the output voltage Vout reaches the detection voltage Vk.
It is determined that it detects a detection voltage Vk in spite of the not reached the Vk, had gotten a count of the false detection time t _k. In addition, the successful component of the second protection circuit 7 is formed of a semiconductor material, and its resistance value largely changes due to the influence of heat, light, etc., and the difference between the output voltage Vout and the charging voltage Vc is not constant but always constant. There was a problem that it was stable and lacked reliability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a charge level detection circuit which eliminates erroneous detection of a charge voltage and has excellent detection accuracy.

[Means for solving the problem]

In order to achieve the above object, a configuration of the present invention comprises first and second external terminals, an operational amplifier having an input side connected to the first external terminal and an output side connected to a second external terminal, A semiconductor integrated circuit having a level detection circuit having an input connected to a second external terminal; a capacitive element connected between the first and second external terminals; and a capacitor connected to the first external terminal. In a charge level detection circuit constituted by a signal input section comprising a resistance element, a first protection circuit is provided between the first external terminal and the input side of the operational amplifier, and a level detection circuit is provided between the second external terminal and the input terminal. A second protection circuit is connected to the input side of the circuit, and a connection circuit that does not pass through the second protection circuit is formed between the second external terminal and the output side of the operational amplifier.

Further, a third protection circuit is connected to a connection circuit between the second external terminal and the output side of the operational amplifier.

〔Example〕

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

FIG. 1 is a configuration diagram of a charge level detection circuit according to the present invention. In the configuration diagram of FIG. 1, the same parts as those of the configuration diagram of FIG. In FIG. 1, a portion different from FIG. 2 will be described. Reference numeral 6 denotes a third protection circuit, which is formed between the second external terminal 4 and the output side of the operational amplifier 8. Thus, an independent connection path is provided between the output side of the operational amplifier 8 and the input side of the level detection circuit 9 with the second external terminal 4.

Next, the operation of the charge level detection circuit having the above configuration will be described. However, the description of the operation of the common part of the block diagram of FIG. 1 with the block diagram of FIG. 2 is omitted.

The charging voltage Vc of the external terminal 4 and the output voltage Vout of the operational amplifier 8 have the waveforms shown in FIG. 3, which are the same as those in the conventional configuration shown in FIG. However, the input side of the level detection circuit 9 has an independent connection path through which no current flows between the input terminal and the second external terminal 4, so that no potential difference occurs between both ends of the second protection circuit 7. That is, the level detection circuit 9 determines the true value of the charging voltage Vc,
The detection voltage Vk can be detected with high accuracy.

[Configuration of the invention]

As is apparent from the above description, according to the present invention, a voltage drop does not occur in the connection path from the capacitive element to the level detection circuit, thereby preventing erroneous voltage detection and realizing a highly accurate charge level detection circuit. Is possible.

[Brief description of the drawings]

1 is a configuration diagram of a charge level detection circuit according to the present invention, FIG. 2 is a configuration diagram of a charge level detection circuit according to the prior art, and FIG. 3 is a charge voltage Vc at the second external terminal and an output voltage of the operational amplifier 8. FIG. 9 is a characteristic diagram showing a relationship between a charging waveform and an integration time t of Vout. DESCRIPTION OF SYMBOLS 1 ... resistance element, 2 ... capacitive element, 5 ... 1st protection circuit, 6 ... 3rd protection circuit, 7 ... 2nd protection circuit, 8 ... operational amplifier, 9 ... level detection circuit 10 ... Semiconductor integrated circuit.

Claims (1)

(57) [Claims] An operational amplifier having an input side connected to the first external terminal and an output side connected to the second external terminal; and an input side connected to the second external terminal. A semiconductor integrated circuit having a level detection circuit formed by connecting
In the charge level detection circuit including a capacitive element connected between the first and second external terminals and a signal input unit including a resistance element connected to the first external terminal, A protection circuit is provided between an external terminal and the output side of the operational amplifier, and a connection circuit that does not pass through the protection circuit is formed between the second external terminal and the level detection circuit. Charge level detection circuit.