JPH02306171A - Circuit for detecting voltage drop of power supply - Google Patents

Abstract

PURPOSE:To secure the time necessary for write protecting process against the sudden voltage drop of a power supply by dropping, rectifying three-phase AC power supply voltage and comparing the same with reference voltage. CONSTITUTION:U-, V- and W-phase are rectified by a three-phase rectifier SB1 and rectified voltage ES1 of two phases U, W among the phases U, V, W is inputted to a control DC power supply PS. This power supply PS has a microprocessor MPU and a memory MEM 1 built therein and becomes the power supply for operating a control circuit CPU 1 controlling an external input/output apparatus. In a voltage drop detecting circuit CP1, the voltage ES1 is ripple filtered by a capacitor C1 and divided by registors R1, R2 to obtain comparing voltage EC1 which is, in turn, set to one input voltage of a comparing circuit CMP to be compared with the other reference voltage E1 of said circuit CMP. By this method, since a change of three-phase power supply voltage is detected by a ripple filter circuit with a small time constant, the abnormality thereof is detected at an early stage and light protecting processing can be performed a surplus time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power supply voltage drop detection circuit, and particularly to a power supply voltage drop detection circuit for a numerical control device using three-phase alternating current.

[Conventional technology]

Conventional power supply voltage drop detection circuits use any two phases of three-phase AC, use it as single-phase AC, rectify it and convert it to DC, and detect the three-phase AC power supply by the state in which this DC voltage drops. was measuring the voltage drop.

A conventional power supply voltage drop detection circuit will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing an example of a conventional power supply voltage drop detection circuit.

The power supply voltage drop detection circuit shown in FIG.
, V phase are rectified by a single-phase rectifier SB2, and a rectified voltage ES2 is supplied to a voltage drop detection circuit CP2. In the voltage drop detection circuit CP2, the rectified voltage ES2 is smoothed by a capacitor C2 and divided by a resistor R1°R2 to obtain a comparison voltage EC2, which is used as one input voltage of the comparison circuit CMP and compared with the other reference voltage E1.

When the comparison voltage EC2 falls below the reference voltage E1,
An abnormality signal PF is output from the comparison circuit CMP, and is output to the motor drive circuit DV via the control circuit CPtJ1, and the state of the motor M1 is stored in the memory MEM1.

The microprocessor MPUI performs write protection processing on the memory MEM1.

3(a) and 3(b) are time charts for explaining the operation of the power supply voltage drop detection circuit shown in FIG. 2. FIG.

Assuming that there is an abnormality in the three-phase power supply voltage at time T1, the rectified voltage EC2 begins to decrease, reaches the reference voltage E1 at time T2, and an abnormality signal PF is output.

At time T3, the output voltage Vps of the control DC power supply PS decreases to the minimum guaranteed voltage (■) of the semiconductor.

Therefore, write protection processing must be performed during the period from time T2 to time T3.

[Problem to be solved by the invention]

The above-described conventional power supply voltage drop detection circuit has a drawback that if the power supply voltage drops rapidly, there is a risk that the necessary time may not be secured for write protection processing.

[Means to solve the problem]

The power supply voltage drop detection circuit of the present invention includes a DC power supply for a control circuit which inputs two phases in a three-phase AC power supply, a microprocessor, and a memory, and serves as a DC power supply for operating the microprocessor and the memory. a control circuit that controls an external input/output device using a circuit DC power supply;
Before the output voltage of the control circuit DC power source drops below the minimum operating voltage of the microprocessor and the memory when the three-phase AC power source is cut off, the external input signal is connected to the control circuit until the phenomenon occurs. In a power supply voltage drop detection circuit including a storage circuit that stores the state of an output device in the memory and a protection processing circuit that performs write protection processing on the memory, (A) step down the three-phase AC power supply voltage; Step-down means for outputting a phase step-down voltage; (B) Rectification means for rectifying the three-phase step-down voltage and outputting a rectified voltage; (C) Comparing the rectified voltage with a preset reference voltage and generating a comparison signal. Comparing means for supplying the control circuit to the control circuit.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

The power supply voltage drop detection circuit shown in FIG.

The V and W phases are rectified by a three-phase rectifier S81, and the rectified voltage ESI
is supplied to the voltage drop detection circuit CPI.

In the voltage drop detection circuit CP1, the rectified voltage ES1 is smoothed by a capacitor C1 and divided by registers R1 and R2 to obtain a comparison voltage ECI, which is used as one input voltage of the comparison circuit CMP and compared with the other reference voltage E1.

Although the capacitor C1 can be made smaller than the capacitor C2 at the same ripple voltage, the time T shown in FIG.
Since the period from 1 to time T2 can be shortened, time T2
The period from time T3 to time T3 can be increased.

That is, since changes in the three-phase power supply voltage are detected using a smoothing circuit with a small time constant, abnormalities can be detected early and write protection processing can be performed with sufficient time.

〔Effect of the invention〕

Since the power supply voltage drop detection circuit of the present invention can extend the time available for write protection processing, it has the effect of reducing the probability of failures such as damage to memory contents.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing an example of a conventional power supply voltage drop detection circuit,
3(a) and 3(b) are time charts for explaining the operation of the power supply voltage drop detection circuit shown in FIG. 2. FIG.

SBI... Three-phase rectifier, CPI... Voltage drop detection circuit, CPUI... Control circuit, PS
・・・・・・DC power supply for control.

Agent Patent Attorney Oto Uchihara 〕　〉　≧ Mi　　〉　　(

Claims (1)

[Scope of Claims] A DC power supply for a control circuit that receives two phases of a three-phase AC power supply as input, and a DC power supply for the control circuit that has a built-in microprocessor and memory and serves as a DC power supply for operating the microprocessor and the memory. a control circuit that controls an external input/output device using a control circuit; and a control circuit that controls an external input/output device using a control circuit; A power supply voltage drop detection circuit including a storage circuit that causes the control circuit to store in the memory the state of the external input/output device up to the time when the phenomenon occurs, and a protection processing circuit that causes the memory to perform write protection processing, (A) step-down means for stepping down the three-phase AC power supply voltage and outputting a three-phase step-down voltage; (B) rectifying means for rectifying the three-phase step-down voltage and outputting a rectified voltage; (C) the rectified voltage; A power supply voltage drop detection circuit comprising: comparing means for comparing the voltage with a preset reference voltage and supplying a comparison signal to the control circuit.