JPS60138474A - Detecting circuit for abnormality of power supply voltage - Google Patents

Abstract

PURPOSE:To detect exactly low voltage abnormality of a power supply voltage, too, by converting the output of a comparator for detecting the highest detecting voltage or above and the lowest detecting voltage or below, to a logical value signal of normality and abnormality by using a photocoupler. CONSTITUTION:In case a power source to be measured which is applied to two signal lines if ''0''V or abnormally low, a current flowing through a diode in a photocoupler 16 is ''0'' or about ''0''. When a power supply voltage is the lowest detecting voltage or below, an output of a comparator 15 becomes on, and in the same way, a photodiode current is ''0''. Also, when said voltage is the lowest detecting voltage or above, and the highest detecting voltage or below, an output of a comparator 13 becomes on, and both outputs of comparators 14, 15 become off, therefore, the photodiode current flows. When said voltage is the highest detecting voltage or above, the output of the comparator 14 becomes on, the photodiode current does not flow, and normality/abnormality of the power supply voltage can be known by a logical value of ''1'' and ''0''.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a power supply voltage abnormality detection circuit in an electronic circuit.

(Prior art) Conventionally, a display device 1 indicating that the power supply voltage is turned on
(See Figure 1), and whether the power supply voltage is normal or abnormal is determined by whether the light is on or off.

However, in such a circuit, even if it is determined that the power supply voltage is being supplied, it is not possible to determine whether the power supply voltage is within a specified value.

(Objective) The present invention has been made in view of the drawbacks of the conventional example, and it is an object of the present invention to provide a circuit that can accurately detect abnormalities in power supply voltage, especially low voltage abnormalities.

(Structure) The structure of the present invention will be described below based on an embodiment shown in FIG.

In the figure, 2 to 11 are resistors (5 and 8 are variable resistors), 12
is a Zener diode, 13 to 15 are comparators, 1
6 is a photocoupler.

The two signal lines include the e side of the power supply under test and the e side (hereinafter vB).
B+, VBB-) are connected.

The variable resistor 5 is set so that the comparator 13 turns off when (vBB+-VBB-) is below the maximum detection voltage (VTH+) and turns on when it is above. Further, the comparator 14 inverts the on/off state of the signal of the comparator 13. Furthermore, comparator 15 C (VB,,' -■BB)
The variable resistor 8 is set so that it is turned off when the voltage is below the minimum detection voltage (vTi) and turned on when it is above the minimum detection voltage (vTi).

＋ Next, to explain its operation, first (■BB −■BB−
) is OV or abnormally low, the current flowing through the diode in the first coupler 16 is zero or almost zero. When (V''--V-) is less than VTπ, the output of the BE BE comparator 15 is on, and the photodiode current is O as described above. Also, when (vBB+-V-) is more than ■TH, V When the voltage is below -, the outputs of comparators 14 and 15 are both off, and the photodiode current flows.Furthermore, C■B:■BB-) is
When the voltage is equal to or higher than TH, the output of the comparator 14 is on, and no photodiode current flows.

FIG. 3 is a characteristic diagram showing the above operation. In the abnormal high voltage region α of 711 or more, the photodiode current is 0, and in the normal voltage region of vTH("Ti, the photodiode current flows, and furthermore, vTl( Low voltage abnormality area C below
Then the photodiode current becomes 0.

Figure 4 is a timing chart of each comparator output when the horizontal axis is the power supply voltage (■BB'-Vnyi).
The output of is on, i.e. the photodiode output is 0, vT
Between H+ and vTH-, the outputs of comparators 14 and 15 are off, ie, photodiode current flows.

If the output signal extracted in this way is connected to a display device such as an LED, it will become a power supply error display device, and if this signal is used as a status signal for a microcomputer, it can also be used as a check signal for self-diagnosis, etc. Available.

(Effects) The present invention is as described above.According to the present invention, since the normality/abnormality of the power supply voltage can be known from the logical values of 1 and 0, the reliability of electronic circuits can be improved. \Become.

[Brief explanation of the drawing]

Fig. 1 shows a power supply voltage abnormality detection circuit according to a conventional example, Fig. 2 shows a power supply voltage abnormality detection circuit according to an embodiment of the present invention, Fig. 6 shows a voltage waveform characteristic diagram in this circuit, and Fig. 4 shows a power supply voltage abnormality detection circuit. 3 is a timing chart of comparator output with respect to changes in the value of . 16...first comparator, 14...second comparator, 15...sixth comparator, 16...photocoupler. Figure 1 Figure 3 V Figure 4 ve +'8B-

Claims (1)

[Claims] A first comparator is set to turn off when the voltage is below the maximum detection voltage and turn on when the voltage is above the maximum detection voltage, a second comparator that inverts the output of the first comparator, and a second comparator is set to turn off when the voltage is below the minimum detection voltage and turn on when the voltage is above the minimum detection voltage. A power supply voltage abnormality characterized in that the outputs of the second and third comparators are exchanged with logical value signals of normal and abnormal using a photocoupler and taken out as a power supply voltage abnormality detection signal. Detection circuit.