Voltage detection device and insulation detecting apparatus for non-grounded power supply including the voltage detection device

Abstract

A voltage detection device includes a processor that has a first input port, and a second input port grounded at a first ground potential part, a first Schottky barrier diode that has a cathode connected to a junction of an electric wire between the first input port and a voltage detection object part, and an anode grounded at a second ground potential part, and a second Schottky barrier diode that has an anode connected to a junction of an electric wire between the second input port and a third ground potential part, and a cathode connected to a positive terminal of a power supply. When the processor detects a voltage at the voltage detection object part, the processor detects a value obtained by adding a voltage applied to the second input port to a voltage applied to the first input port as the voltage.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to a voltage detection device and an insulation detecting apparatus for a non-grounded power supply includiing the voltage detection device and, more particularly, to a voltage detection device for detecting a voltage using a microcomputer and an insulation detecting apparatus for a non-grounded power supply including the voltage detection device. [0002] A voltage detection circuit for detecting a voltage using a microcomputer is equipped with a clamping diode for preventing the application of an excessive positive or negative voltage which can damage the microcomputer to an input port of the microcomputer to which a part subjected to voltage detection is connected. A rectifier diode may be used as the clamping diode to prevent the application of an excessive positive or negative voltage to the input port of the microcomputer for a relatively short time. However, in order to prevent the application of an excessive posi...

AI Technical Summary

Benefits of technology

[0009] It is a first object of the invention to improve the accuracy of a detection voltage.

[0010] It is a second object of the invention to improve the accuracy of a voltage detected by a voltage detection circuit to achieve a further improvement in the detecting accuracy of the state of insulation.

[0016] In such a configuration, the first Schottky barrier diode used for clamping and the second Schottky barrier diode used for correction are Schottky barrier diodes according to the same leakage current standard. Thus, a voltage substantially equal to a voltage loss attributable to a leakage current at the first Schottky barrier diode for clamping is applied to the second input port of the microcomputer to which the second Schottky barrier diode for correction is connected. It is therefore possible to obtain a detection voltage which has been corrected for any voltage loss attributable to the first Schottky barrier diode for clamping by adding the voltage applied to the second input port of the microcomputer to the voltage applied to the first input port. Since the correction of a detection voltage does not involve any calculation and conversion that can introduce an error as thus described, the accuracy of a detection voltage can be improved.

[0020] Such a configuration makes it possible to improve the accuracy of a detection voltage even when there is provided a resistor which is connected to the first input port of the microcomputer at one terminal thereof and connected to the part under voltage detection at another terminal thereof.

[0033] In such a configuration, since the correction of a detection voltage does not involve any calculation and conversion that can introduce an error as thus described, the accuracy of a detection voltage can be improved. It is therefore possible to improve the accuracy of a voltage detected by the voltage detection device and to thereby further improve the accuracy in detecting the state of insulation.

Problems solved by technology

However, since a Schottky barrier diode has a character that a leakage current at the same becomes greater as the ambient temperature increases, a voltage drop or voltage loss through the Schottky barrier diode increases with the ambient temperature.

For this reason, a voltage detection circuit having a Schottky barrier diode has a problem in the accuracy of a detection voltage detected at an input port of a microcomputer.

However, the characteristics of a Schottky barrier diode do not necessarily agree with specifications shown on the data book and may include variations.

Therefore, the calculation and conversion are repeated with a possibility of an error, and an error between a calculated value of a voltage loss and the actual value of the voltage loss can increase each time a calculation or conversion is repeated.

For this reason, in such a voltage detection circuit using a thermistor, it is difficult to improve the accuracy of a detection voltage detected at the input terminal of the microcomputer.

However, since a voltage detected by the voltage detection circuit is used for the calculation of an insulation resistance in such an insulation detector, when the accuracy of the voltage detected by the voltage detection circuit is questionable, a problem arises in that accuracy cannot be improved in detecting the state of insulation.

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