JP2001292568A - Short-circuit detecting circuit in dc converter power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a longer time and complicated procedures are required for finding the cause and a switch contact is fused, when a switch controlling the on/off of load generates vibration, when that an overcurrent protecting circuit of a DC converter power supply operates to disable acquisition of voltage output, thereby a fault of the DC power supply is detected erroneously, resulting in requirement for replacement of parts, if a short-circuit due to wrong wiring is generated at when mounting an underfloor ventilator which is driven with the DC converter power supply. SOLUTION: This short-circuit detecting circuit comprises a switch 5 connected between the DC converter power supply 4 including an overcurrent protecting circuit and a load 2 for switching the load 2, a voltage detecting means 11 for detecting drop in the output voltage, a power failure determining means 12 for determining power failure when voltage drop continues for a prescribed time or longer by turning off the switch 5 for the drop in the output voltage and a display means 16 for displaying generation of short circuiting, when the number of times of power failure reaches the prescribed number of times by counting the number of times of power failure that are repeated, when the switch 5 is turned on again while the voltage is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply device having a built-in low-voltage DC power supply such as an underfloor ventilator and for transmitting DC power for driving to a ventilation fan arranged under the floor, in which a short circuit occurs due to a wiring work mistake or the like. If this is done, it relates to what detects and displays this.

[0002]

2. Description of the Related Art FIG. 6 is a circuit configuration diagram of a conventional underfloor ventilation device that converts a commercial power supply into a low-voltage DC power supply and drives a ventilation fan, and FIG. 7 is a diagram illustrating an internal circuit configuration of the DC conversion power supply. In the figure, 1 is a commercial power supply, 2 is a ventilation fan driven by a low-voltage DC power supply, and 3 is a DC power supply device.
To convert the DC power to drive the ventilation fan 2. The DC power supply 3 includes a DC conversion power supply 4, a switch 5, a clock unit 6, and a clock unit 6. The clock unit 6 includes a power supply circuit 7 that uses a microcomputer to obtain its operating power supply and a power failure compensation battery 8. The switch 5 receives a signal from the clock unit 6 through a transistor 5c and a switch contact 5a by a switch coil 5b.
Is opened and closed to switch the ventilation fan 2 to the set time. The switch contact 5a is normally turned off by the urging force of a spring or the like, but is turned on by energizing the switch coil 5b. The clock section 6 and the switch 5 form a time switch.

In FIG. 7, 41 is a rectifier circuit, 42 is a transformer, 43 is a control IC, and 44 is a switching element. The secondary circuit of the transformer 42 is a circuit that rectifies and smoothes the rectangular wave voltage that has been subjected to switching conversion by the control IC 43 and the switching element 44 and converts it into a DC voltage. 45
Is an overvoltage protection circuit, and when the output voltage exceeds a predetermined voltage, the transistor 46 is turned off to temporarily stop the operation of the DC power supply device. Reference numeral 47 denotes a voltage detection circuit for controlling the output voltage.
By changing the current between the emitters, the switching element 44 is turned on and off through the control IC 43 to control the output voltage to a preset constant voltage. 49 is an overcurrent detection terminal, and 50 is a smoothing circuit inserted on the secondary side of the transformer 42.

[0004] The underfloor ventilation apparatus described above converts the commercial power supply 1 to 12 V DC by the DC conversion power supply 4 and drives the ventilation fan 2. In the daytime, the ventilation fan 2 is actuated to send dry air under the floor to perform ventilation, and the ventilation fan 2 is stopped at night to stop sending air under the floor by the time control preset in the clock unit 6 at night. .

[0005] The conventional underfloor ventilator is constructed as described above. However, if an erroneous connection occurs at the time of mounting and wiring, in particular, some portion of the wiring from the DC output terminal to the ventilation fan 2 is short-circuited. In this case (for example, point A in FIG. 6),
The contact 5a of the switch causes a vibration phenomenon, and finally, light welding is caused, and the contacts are brought into a closed state in which the contacts are stuck together.
The duration of this vibration phenomenon is on the order of several seconds, which is not preferable for the life of the switch. Such a short circuit due to an erroneous connection has been mistakenly regarded as a failure of the DC power supply device 3 because the overcurrent protection function of the DC conversion power supply 4 works and the DC output voltage is reduced so that a voltage output cannot be obtained.

Next, the mechanism by which the switch contact 5a causes a vibration phenomenon will be described with reference to FIG. In FIG. 6, when point A is short-circuited, the secondary side impedance of the transformer 42 becomes close to zero ohm, so that a large current flows to the primary side of the transformer 42 through the switching element 44 and the resistor 50 connected in series to the switching element 44. . The potential of the overcurrent detection terminal 49 rises due to the voltage drop at the resistor 50, and the control IC 4
3 recognizes that an overcurrent has occurred, and switches the switching element 44.
Since the current is suppressed by narrowing the pulse width of the switching waveform, the secondary-side output voltage of the transformer 42 decreases.

The switch coil 5b of the switch 5 turns on the switch contact 5a by the exciting force of the secondary voltage of the transformer 42. However, when the voltage decreases, the exciting force of the switch coil 5b is weakened to reduce the switch contact. Release 5a. Accordingly, the short-circuit state is released, and the secondary-side impedance of the transformer 42 increases, so that the current flowing through the resistor 50 connected in series with the switching element 44 on the primary side of the transformer 42 decreases.

As a result, the potential of the overcurrent detection terminal 49 decreases, and the control IC 43 recognizes that the overcurrent state has been released, restores the normal switching state, and returns to the DC conversion power supply 4.
Is restored. Switch 5 by return of voltage
The switch coil 5b returns to the exciting force and the switch contact 5a
Turn on. Since the short-circuit state at the point A remains unchanged, a short-circuit current flows again, and the output voltage of the DC conversion power supply 4 decreases. By repeating the above operation, the switch contact 5a eventually causes slight welding, so that even if the output voltage of the DC conversion power supply 4 decreases, the switch contact 5a remains attached and does not turn off.

[0009]

A conventional underfloor ventilator driven by a DC conversion power supply is configured as described above.
If a short circuit due to erroneous connection occurs in the load circuit during installation wiring, it is difficult to determine the cause, and the output voltage cannot be obtained because the overcurrent protection circuit of the DC conversion power supply operates. It takes time and effort to replace the product. In addition, there is a problem that the repair result of the short circuit cannot be confirmed. Further, there is another problem that the switch controlling the opening and closing of the load causes a vibration phenomenon in an energized state, and the contact of the switch is welded.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and detects a short-circuit generated in a wiring between a ventilation fan as a load from a DC conversion power supply and displays the detected short-circuit. To inform the user of the problem, thereby facilitating the identification of the cause of the malfunction, preventing the DC power supply from being regarded as a failure, and preventing the switch from vibrating and preventing welding of the switch contacts. The purpose is to

[0011]

Means for Solving the Problems Claim 1 according to the present invention.
The short circuit detection circuit of the DC current conversion power supply has a control means to reduce its own output voltage when overcurrent is detected.When the output voltage is normal from the DC conversion power supply, the connection with the load circuit is turned on and the output voltage is insufficient. A switch to turn off the connection when
Voltage detection means for detecting the output voltage drop, power failure determination means for determining a power failure when the output voltage reduction duration is a predetermined time or more, and counting the number of times the determined power failure is repeated,
Display means for displaying that a short circuit has occurred in the load circuit when the number of power failures reaches a predetermined number.

According to a second aspect of the present invention, there is provided a short-circuit detection circuit for a DC current conversion power supply, which is connected between a DC conversion power supply having control means for reducing its own output voltage and a load when an overcurrent is detected, and turns on the load. A switch to be turned off, voltage detection means for detecting the output voltage of the DC conversion power supply, and a power failure is determined when the output voltage of the DC conversion power supply has been reduced to a predetermined voltage or less for a predetermined time. A power failure determination means, an on / off means for turning off the switch at the time of the power failure determination, turning on the switch after waiting for a certain time, and a frequency counting means for counting repeated power failures due to voltage recovery, and the number of power failures is predetermined. Display means for displaying that a short circuit has occurred in the load circuit when the number of times has been reached.

Further, a voltage holding capacitor is provided between the DC conversion power supply and the switch.

Further, the short-circuit display is canceled by the short-circuit display cancel command from the operation setting means for inputting the cancel command, and the switch is turned on.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 is a configuration diagram of an underfloor ventilation device that drives a ventilation fan with a DC conversion power supply according to Embodiment 1 of the present invention, and FIG. 2 is a flowchart illustrating the operation of Embodiment 1 of the present invention. In the drawing, reference numerals 1 to 8 are the same as those in the description of the conventional example. Reference numeral 9 denotes a voltage holding capacitor, reference numeral 10 denotes a diode, reference numeral 11 denotes an undervoltage detection unit for detecting a drop in the output voltage of the DC conversion power supply 4, and reference numeral 12 denotes a power failure time measurement unit for measuring a voltage drop duration t in the undervoltage detection unit 11. , 13 is a power failure frequency counting unit that counts the number of power failures within a predetermined time T set by the reset timer 14.
Reference numeral 15 denotes a contact drive control unit, which controls energization of the switch coil 5b of the switch 5 to open and close the switch contact 5a. The contact drive control unit 15 also controls the switch 5 by an on / off signal of the load (the ventilation fan 2) from the clock unit 6. Reference numeral 16 denotes a display unit, which is composed of an LCD element or the like, and displays a time number and a caution / warning character of a clock device. 17
Is a setting operation unit, which includes a setting input key for inputting a current time, a load on / off time setting, and a warning / alarm release operation.

Next, the operation will be described with reference to the flowchart of FIG. First, the number counter n and the delay time counter t are set to zero at the time of the initial processing (n = 0, t = 0). The undervoltage detection unit 11 monitors the output voltage of the DC conversion power supply 4 and restores, for example, a voltage of DC 2.0 V or more, DC2.
When the voltage falls below 0 V, it is determined as a power failure (step 2
1). When it is determined that a power failure has occurred, the power failure duration measuring unit 12 measures whether or not the power failure duration has continued for a predetermined time (for example, 25 ms). If the measurement result is less than 25 ms, it is a noise or a transient short circuit, not a power failure, but is ignored (step 22). If the power failure duration is 25 ms or more, the power failure frequency coefficient unit 13 counts the number of power failures assuming that the power failure has occurred, and integrates the delay time from the beginning of the power failure. (Step 23). If the extension time is equal to or longer than a predetermined time (for example, 10 seconds), the power is turned off or the like, and it is returned to the initial state as not being the vibration phenomenon described in the above-described conventional example (step 24).

If the number counter is less than a predetermined number M (for example, three times), the state returns to the output voltage monitoring state (step
twenty five). At this time, the total number of the counter is stored. If the DC load circuit is still in the short-circuit state, the output voltage is repeatedly reduced and restored by the function of the overcurrent protection circuit built in the DC conversion power supply 4, so that steps 21 to 25 are repeated. Leads to. When the frequency counter becomes equal to or more than a predetermined number M, it is determined that the vibration is caused by the short circuit of the DC load circuit, the excitation of the switch 5 is turned off, the DC load circuit is cut off, and the display unit 16 is short-circuited. Is displayed (steps 25 to 27). Thereby, the user can recognize the short circuit of the DC load circuit and check the wiring.

There is a demand to check or repair the wiring and check whether the short circuit has been eliminated. At this time, a command input for canceling the short-circuit message is input by a key operation or the like from the setting operation unit 17. Once the short-circuit message display is displayed, the display state is maintained as it is, but when the short-circuit message release command input is detected, the short-circuit message display is released and the switch 5 is turned on to supply power to the DC load circuit. Restart (steps 28-30).
Then, each step of the short-circuit detection is restarted.

Therefore, if the short-circuit state has not been eliminated, the same operation as described above is performed, the switch 5 is turned off again, and a short-circuit message is displayed. When there is no display of the short-circuit message, it can be confirmed that the wiring is normal. Further, the switch contact 5a associated with the voltage drop and return
Is limited by counting the number of power failures, so that the welding of the switch contacts 5a can be prevented.

Embodiment 2 FIG. 3 is a configuration diagram of an underfloor ventilator that drives a ventilation fan with a DC conversion power supply according to a second embodiment of the present invention. FIG. 4 is a flowchart illustrating the operation of the second embodiment of the present invention. 6 is a time chart of a switch contact. In the figure, 1 to 17 are the same as those described in the first embodiment. Reference numeral 18 denotes a timer for turning on the switch 5 while keeping the on / off means constant.

Next, the operation will be described with reference to the flowchart of FIG.
This will be described with reference to the time chart of FIG. First, the number counter n and the time counter t are set to zero at the time of initial processing (n = 0, t = 0). By monitoring the output voltage of the DC conversion power supply 4, for example, when the voltage is restored to DC 2.0 V or more,
When the voltage falls below C2.0 V, it is determined that a power failure has occurred (step 21). If it is determined that a power failure has occurred, it is measured whether or not the duration of the power failure has continued for a predetermined time (for example, 25 ms). If the voltage recovery is less than 25 ms, it is a noise or an instantaneous power failure and is ignored (step 22). If the power failure continuation time is 25 ms or more, it is regarded as a power failure. However, when a short circuit occurs between the DC conversion power supply 4 and the wiring between the ventilation fan 2, the voltage of the DC conversion power supply 4 returns as described above. This voltage recovery also returns in a substantially constant time depending on the structure of the DC conversion power supply 4. Here, the case of returning in less than 50 ms will be described as an example. If the power outage duration is 50 ms or more, it is determined that the commercial power supply 1 is a continuous power outage, and a power outage measure is performed (step 31,
34). If the voltage is restored within less than 50 ms, the excitation of the switch coil 5b is turned off, the number of power failures is counted up (n = n + 1), and the process waits for a fixed time (T) set in the timer 18 (steps 31 to 31). 33). The total number of the counter is stored.

If the power failure frequency counter is less than a predetermined number M (for example, three times), the excitation of the switch coil 5b is turned on to return to the output voltage monitoring state (steps 25 and 35).
At this time, if the DC load circuit is still in the short-circuit state, the output voltage drops again due to the operation of the overcurrent protection circuit built in the DC conversion power supply 4 as shown in the time chart of FIG. Step 25 is repeated, and the total number of counters reaches a predetermined number M. When the frequency counter becomes equal to or more than the predetermined number M, it is determined that the DC load circuit is short-circuited, the excitation of the switch 5 is turned off, and the DC load circuit is shut off. A message indicating that there is is displayed (steps 25 to 27). Thereby, the user can recognize the short circuit of the DC load circuit and check the wiring. Hereinafter, steps 28 to
Reference numeral 30 is the same as in the first embodiment, and a description thereof will be omitted.

The configuration of the second embodiment is such that the contact 5a of the switch 5 is opened and closed by the on / off means comprising the timer 18 without depending on the presence or absence of the voltage for the excitation of the switch 5 at the time of power failure detection and voltage return. As a result, contact vibration is eliminated and contact welding can be prevented.

The undervoltage detection unit 11, the power failure time measurement unit 12, the power failure frequency counting unit 13, the reset timer 14, the timer 18 and the like for executing the above processing flow may be individually constituted by circuits such as electronic components. Alternatively, it may be realized by software processing using a microcomputer of the clock unit 6.

Here, the operation of the voltage holding capacitor 9 will be described. When the output voltage of the DC conversion power supply 4 decreases due to the occurrence of a short circuit in the DC load circuit, the excitation of the switch coil 5b is released, the switch contact 5a is turned off, and the DC load circuit is cut off. The period of the voltage recovery of the output voltage becomes shorter. If the duration of the voltage drop is measured by the power failure time measurement unit 12 and the voltage recovers within the time t for determining the power failure, the occurrence of the short circuit cannot be detected. On the other hand, by providing the voltage holding capacitor 9, even if the output voltage of the DC conversion power supply 4 decreases, the voltage holding capacitor 9
By holding the excitation of the switch coil 5b with the accumulated charge for more than the power failure determination time, the occurrence of a short circuit can be reliably detected. The diode 10 prevents the charge stored in the voltage holding capacitor 9 from flowing out of the switch coil 5b.

The release of the short-circuit display is performed by a key operation or the like from the setting operation unit 17. When the current time reaches the on time or the off time of the time switch function, a release command input is generated. It is also possible to do so. The switch 5 has the same effect even when a semiconductor device such as a photo-mos switch is used.

The display section 16 also serves as the time display of the clock section 6 and normally displays the current time and the on / off time. However, when a short circuit occurs, a message indicating that a short circuit has occurred is displayed. A blinking display may be used, or a lamp such as an LED for short-circuit display may be used.

Although the present invention has been described with respect to the DC conversion power supply of the underfloor ventilator, it is apparent that the present invention is not limited to the underfloor ventilator and can be used for a DC converter for converting commercial power into DC and supplying power. is there.

[0029]

As described above, according to the present invention, when the wiring between the DC conversion power supply and the load (ventilation fan 2) is short-circuited, the output voltage drops due to the operation of the overcurrent protection function of the DC conversion power supply 4 and the switch thereby. 5 is detected by the under-voltage detecting unit 12, the power failure time measuring unit 12, the power failure frequency counting unit 13, and the like.
To inform the installation worker that a short circuit has occurred. Then, when the display release command is input from the setting operation unit 17 or the like, the switch 5 is turned on and the short-circuit detection is restarted, so that the result of the short-circuit repair can be confirmed.

Further, since the number of times the switch contact 5a is opened and closed when the load is short-circuited is limited, it is possible to prevent the switch contact 5a from being damaged by welding or the like.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an underfloor ventilation device that drives a ventilation fan with a DC conversion power supply according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating the operation of the first embodiment of the present invention.

FIG. 3 is a configuration diagram of an underfloor ventilation device that drives a ventilation fan with a DC conversion power supply according to Embodiment 2 of the present invention.

FIG. 4 is a flowchart illustrating an operation according to the second embodiment of the present invention.

FIG. 5 is a time chart of a DC conversion power supply voltage and a switch contact according to the second embodiment.

FIG. 6 is a circuit configuration diagram of a conventional underfloor ventilation device driven by a DC conversion power supply.

FIG. 7 is a diagram showing an internal circuit configuration of a DC conversion power supply.

FIG. 8 is a diagram for explaining a mechanism in which a switch contact causes a vibration phenomenon.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Commercial power supply, 2 Ventilation fan, 3 DC power supply DC conversion power supply, 5 Switch, 5a Switch contact 5b Switch coil, 6 Clock part, 9 Voltage holding capacitor Under voltage detection part, 12 Power failure time measurement part, 13
Power failure frequency counting section 16 display section, 18 timer, 41 rectifier circuit transformer, 43 control IC, 44 switching element 45 overvoltage protection circuit, 46, 48 transistor,
47 Voltage detection circuit

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Claims (4)

[Claims] 1. A DC conversion power supply having a control means for reducing its own output voltage when an overcurrent is detected, and a connection between a DC conversion power supply which is energized by a normal output voltage of the DC conversion power supply and a load circuit is turned on and the output voltage becomes insufficient. A switch that is sometimes turned off, voltage detection means for detecting a drop in the output voltage of the DC conversion power supply, power failure determination means for determining a power failure when the voltage reduction time is longer than a predetermined time, It is provided with a number counting means for counting the number of repetitions of the power failure due to the ON of the switch, and a display means for displaying that a short circuit has occurred in the load circuit when the number of power failures reaches a predetermined number. Characteristic short circuit detection circuit of DC conversion power supply. 2. A DC conversion power supply having control means for reducing its own output voltage when an overcurrent is detected, a switch connected between the DC conversion power supply and a load for turning on and off the load, Voltage detection means for detecting the output voltage of the conversion power supply, and power failure determination means for determining a power failure when the duration of the output voltage of the DC conversion power supply falls below a predetermined voltage is within a predetermined time, On / off means for turning off the switch at the time of the power failure determination and waiting for a certain time and then turning on the switch again, a number counting means for counting the number of repeated power failures in the power failure determination means, A short-circuit detection circuit for a DC conversion power supply, comprising: a display means for displaying the occurrence of a short-circuit in the load circuit when a predetermined number of times has been reached. 3. The short-circuit detection circuit for a DC conversion power supply according to claim 1, wherein a voltage holding capacitor is provided between the DC conversion power supply and the switch. 4. An operation setting means for inputting a release command, wherein the short-circuit display is released in response to the short-circuit display release command, and the switch is turned on. 3. The short-circuit detection circuit for a DC conversion power supply according to 1.