JPH02136024A - Service interruption detection circuit - Google Patents

Abstract

PURPOSE:To detect the occurrence of service interruption in an early stage from the time when the interruption occurred by providing a voltage drop section actuated by load current. CONSTITUTION:Between the ground side of a constant voltage power source 14 and a load 7 a voltage drop section 15 composed of a parallel circuit of R4, a resistor 16, and C2, a comparator 17, is connected. When load current IL increases, the input voltage is reduced and the reference voltage is also reduced by the voltage portion across terminals of the voltage drop section 15 which will be generated along with the increases of the load current IL. On the account, if the reference voltage is set to the high value close to the input voltage, the input voltage never gets to the reference voltage by the load fluctuation and is not misidentified as service interruption. When the interruption occurs, no voltage drop section 15 will act, no change will be caused to the reference voltage and an interruption detection signal will be generated inn a short time from the occurrence of interruption, so that a long troubleshooting time T can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a power failure detection circuit used in microcomputer systems and the like.

Conventional technology Generally, in microcomputer systems, etc.
At the time of a power outage, the period from when the power outage state is detected until the logic voltage reaches a certain value is defined as the power outage processing time, and processing such as data protection is performed.

An example thereof will be explained based on FIGS. 3 and 4.

First, an AC commercial power source 1 is connected to a transformer 2, and a rectifier circuit 5 including a full-wave rectifier circuit 3 and a smoothing capacitor 4 is connected to the transformer 2.

For example, a logic power supply 6 whose output voltage is set to +5■ is connected to the rectifier circuit 5, and a load 7 is connected to the rectifier circuit 5.
is connected.

On the other hand, a power failure detection section 8 is connected to the rectification circuit 5 . This power outage detection section 8 consists of a comparator 9, and on the input side of this comparator 9, an input is obtained by dividing the secondary voltage of the rectifier circuit 5 by voltage dividing resistors 10 and 11 of R, R, voltage, resistor 12 labeled R3 and Dz
A constant voltage circuit 14 including a Zener diode 13 indicated as is connected.

In such a configuration, the value of the load current IL varies depending on the state of the load 7. For example, as shown in FIG. 4, there are parts where the load current IL suddenly increases depending on the state of the load 7. At this time, although it depends on the capacity of the rectifier circuit 5, since the secondary voltage of the rectifier circuit 5 usually decreases, the input voltage of the comparator 9 also decreases as the load current IL increases.

On the other hand, when there is a power outage, regardless of the fluctuation of load 7,
The secondary voltage of the rectifier circuit 5 decreases, and the input voltage of the comparator 9 also decreases accordingly. When the input voltage of the comparator 9 reaches the reference voltage, a power failure detection signal (an L level signal in FIG. 4) is generated from the comparator 9.

Then, the voltage of the rectifier circuit 5 gradually decreases, and the output voltage of the logic power supply 6 is no longer maintained after point A in FIG. 4. Therefore, the time T from when the power failure detection signal is output until reaching point A becomes the power failure processing time for processing such as data storage.

Problems to be Solved by the Invention In order to reliably perform processing such as data storage during a power outage, it is necessary that the power outage processing time T be as long as possible. To this end, the power outage processing time T can be lengthened by setting the reference voltage to a high value so that the power outage state can be detected as quickly as possible at the time of power outage.

However, the input voltage to the comparator 9 also fluctuates due to load fluctuations. Therefore, if there is a condition in which the input voltage decreases during load fluctuations and the constant voltage also decreases, the power outage may be mistakenly recognized as a power outage, even though it is not a power outage but a simple load fluctuation. This creates the problem of over processing.

Therefore, the value of the reference voltage must be set to a sufficiently low value that the input terminal will not reach it even if there is a large load fluctuation.

For these reasons, in conventional circuits, the timing from when a power outage occurs until the power outage detection signal is output is delayed, and since the logic voltage of the logic power supply 6 that compensates for the operation is constant, the power outage processing time is delayed. There is a problem that T is short 1.

Means for Solving the Problem A power outage detection circuit equipped with a power outage detection section that generates a power outage detection signal by comparing the input voltage based on fluctuations in the secondary voltage of the rectifier circuit with a reference voltage set in a constant voltage circuit. In this case, a voltage drop section that lowers the reference voltage as the value of the load current increases is connected to the constant voltage circuit that generates the reference voltage.

Since there is a voltage drop section that operates based on the applied load current, the reference voltage also decreases as the input voltage decreases due to load fluctuations, making it possible to set the reference voltage to a high value. However, when the input voltage changes due to load fluctuations, the input voltage does not reach the reference voltage, and in the event of a power outage, the load current does not increase, so the reference voltage is maintained at a constant value. This makes it possible to detect power outages early after they occur.
This allows for a long power outage processing time.

Embodiment An embodiment of the present invention will be explained based on FIGS. 1 and 2. Components that are the same as those described based on FIGS. 3 and 4 are designated by the same reference numerals, and description thereof will be omitted.

In this embodiment, a voltage drop section 15 is connected between the ground side of the constant voltage power supply 14 and the load 7. This voltage drop section 15 includes a resistor 16 called R4 and a capacitor 1 called C2.
It consists of a parallel circuit with 7.

In such a configuration, when the load current IL increases, the input voltage of the comparator 9 also decreases, but the base #! The voltage decreases by the voltage between the terminals of the voltage drop section 15 that occurs as the constant voltage load current IL increases. Therefore, even if you set the reference voltage to a high value close to the input voltage,
Depending on load fluctuations, the input voltage does not reach the reference voltage, and there is no chance of it being mistaken for a power outage.

In addition, when a power outage occurs, the voltage drop section 15 does not act, so there is no change in the reference voltage. Therefore, a power outage detection signal is generated in a short time after a power outage occurs, and as a result,
A long power outage processing time T can be obtained.

Effects of the Invention As described above, the present invention includes a power failure detection unit that generates a power failure detection signal by comparing the input voltage based on fluctuations in the secondary voltage of the rectifier circuit with the base 1g voltage set in the constant voltage circuit. In the provided power failure detection circuit, a voltage drop section that lowers the reference voltage as the value of the load current increases is connected to the constant voltage circuit that generates the base voltage. Therefore, as the input voltage decreases due to load fluctuations, the reference voltage also decreases.
As a result, even if the reference voltage is set to a high value, the input voltage will not reach the reference voltage when the input voltage changes due to load fluctuations, and the load current will increase in the event of a power outage. Therefore, the reference voltage is maintained at a constant value, and this has the effect that the occurrence of a power outage can be detected early after the power outage occurs, and a long power outage processing time can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram showing waveforms of each part, Fig. 3 is a circuit diagram showing a conventional example, and Fig. 4 is a waveform diagram showing waveforms of each part. It is. 5... Rectifier circuit, 8... Power failure detection section, 14... Constant voltage circuit, 15... Voltage drop section

Claims (1)

[Claims] A power outage detection circuit is provided with a power outage detection unit that generates a power outage detection signal by comparing an input voltage based on fluctuations in the secondary voltage of the rectifier circuit with a reference voltage set in a constant voltage circuit, and generates the reference voltage. 1. A power outage detection circuit characterized in that a voltage drop section is connected to a constant voltage circuit that lowers the reference voltage as the value of the load current increases.