JPS645261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power-off detection circuit for a digital system.

A conventional circuit of this type is shown in FIG. In the figure, 1 and 2 are resistors, 3 is a capacitor, 4 is an inverter, and 4a is its input terminal.
4b is the same output terminal, 4c is the same power input terminal, and 5 is a power supply device.

Next, the operation will be explained. When the power supply voltage rises, the input of the inverter 4 is charged with the time constant of the RC circuit of the resistor 1 and the capacitor 3, as shown by A in FIG. 2, so it rises even later than the rise of the power supply voltage Vcc. The time constants of the resistors 1 and 2 and the capacitor 3 are taken into consideration so that the inverter input voltage reaches the threshold voltage _VTH after Vcc reaches the operation start voltage Vs of the inverter 4. Therefore, the output of the inverter 4 is outputted as an alarm as shown by B in FIG. ₂ from the time when the power supply voltage Vcc reaches Vs until _t2 when the input voltage reaches _VTH .

Since the conventional power failure detection circuit is configured as described above, no alarm is output when the power supply voltage drops. In addition, when the power is cut off for a long time, the capacitor 3 is sufficiently discharged, so a power-on reset pulse can be output. However, when the power is cut off for a long time, the capacitor is not sufficiently discharged, so the input voltage of the inverter 4 becomes the threshold voltage V _TH It was not possible to output a warning because the aircraft did not descend below this level. Therefore, momentary interruption of the AC input voltage of the power supply (0.5 cycles at 100 VAC, 50 Hz)
(several cycles), digital equipment malfunctions and erroneous output occurs. FIG. 3 shows the effect on the power supply voltage when there is a momentary interruption of the AC input voltage. Also power supply voltage
If the Vcc droop characteristic is long, on the order of several milliseconds, various integrated circuits are used in digital equipment, so some integrated circuits may operate while others do not, resulting in malfunctions. .

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional devices, and provides an alarm output for instantaneous power outages.

An embodiment of the present invention shown in FIG. 4 will be described below. In FIG. 4, the same reference numerals as in FIG. 1 indicate the same or equivalent parts, 6 a resistor, 7 a capacitor, 8 a diode, and 9 a comparator. The power supply voltage is divided by resistors 1a and 2a and connected to the positive phase input terminal 9a of the comparator. Reverse phase input terminal 9b
The power supply is divided and connected using resistors 1b and 2b. Again, a capacitor 3 is connected in parallel to the resistor 2b. The output of the comparator 9 is connected to the input terminal 4a of the inverter 4, and the comparator 9 is connected to the power supply 5 via the diode 8. A resistor 6 and a capacitor 7 are connected in parallel to the power input terminal 9c of the comparator 9. has been done.

Next, the operation will be explained based on FIG.

Here, in FIG. 5, Vcc is the power supply voltage waveform, V is the voltage waveform of the power input terminal 9c of the comparator 9, CA (the waveform indicated by a solid line) is the positive phase input waveform of the comparator 9, and CB ( The waveform shown by the broken line) is the comparator 9
C is the input waveform of the inverter 4, and D is the output waveform of the inverter 4. When the power supply voltage Vcc is normal, the positive phase input terminal 9a side of the comparator 9 is set to a higher value than the negative phase input terminal 9b side, and the output of the comparator 9 is logic "H". If the power supply voltage Vcc drops instantaneously, the voltage at the positive phase input terminal 9a will drop in proportion to the power supply voltage Vcc, but the voltage at the negative phase input terminal 9b will fall slowly because it forms an RC circuit. side is lower than the opposite phase input terminal 9b side, and the output of the comparator 9 becomes logic "L". Power to the comparator is supplied through a diode 8, and a resistor 6 and a capacitor 7 are connected in parallel, so that when the power supply voltage Vcc fluctuates, power is supplied from the capacitor 7, and the comparator is not affected much by Vcc fluctuations. In this way, when the positive phase input of the comparator 9 becomes lower due to the negative phase input, an alarm is outputted through the inverter 4.

Power supply voltage Vcc is the guaranteed operation voltage of inverter 4
If the voltage does not drop below Vs, the power supply of the comparator 9 will not fall below the guaranteed operation voltage Vc of the comparator 9, and a normal alarm output will be obtained. On the other hand, for instantaneous power outages such as when the power supply voltage Vcc drops below the guaranteed operating voltage Vc of the inverter 4, the power supply voltage drooping characteristic has a certain slope. An alarm output is obtained from time t ₃ when the positive phase input and negative phase input of 9 are reversed to time t ₄ when Vcc reaches the guaranteed operation voltage Vc. In addition, the comparator 9 generally becomes logic "L" when the voltage drops below the guaranteed operation voltage Vc, so when the power supply voltage Vcc rises, the power supply voltage Vcc becomes the guaranteed operation voltage of the inverter.
An alarm output is obtained from the time when Vs is reached until the operation guaranteed voltage Vc of the comparator 9 is reached. (From t ₅ to t ₆ ) In the above embodiment, the output of the comparator 9 itself is not used as an alarm output, but the output of the comparator 9 may be used as an alarm output and used as an abnormality interrupt input to the computer.

As described above, according to the present invention, it is possible to obtain a warning output in response to a momentary power outage, thereby making it possible to prevent malfunctions of the digital system.

[Brief explanation of drawings]

Figure 1 is a configuration diagram of a conventional power on-clear circuit, and Figure 2 is an explanatory diagram of Figure 1, where Vcc is a power supply voltage waveform diagram, A is an input voltage waveform diagram of the inverter 4, and B is an output voltage waveform diagram. , FIG. 3 is an explanatory diagram for explaining the conventional one, FIG. 4 is a configuration diagram showing an embodiment of the present invention, and FIG. 5 is an explanatory diagram of FIG. 4, where Vcc is a power supply voltage waveform diagram, V is a power supply voltage waveform diagram of the comparator, CA is a positive phase input voltage waveform diagram, CB is a negative phase input voltage waveform diagram, C is an input waveform diagram of the inverter gate, and D is an output waveform diagram. In the figure, 1, 1a, 1b, 2, 2a, 2
b and 6 are resistors, 3 and 7 are capacitors, 8 is a diode, 9 is a comparator, 4 is an inverter, and 5 is a power supply device. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1 Equipped with a comparator, the power supply voltage is divided by a resistor and applied to one of its inputs, and the power supply voltage is divided by a resistor at a ratio different from the above to the other input, and a capacitor is connected in parallel to one of the resistors. A power supply instantaneous power source characterized in that power is supplied through a diode, a resistor and a capacitor are connected to the power supply terminal of the comparator, and when the power supply voltage drops, power is supplied from the capacitor to operate the comparator and output an alarm. disconnection detection circuit.