JP2009100582A - Current limiting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a current limiting device which can also cope with such a case that a rush current is generated. <P>SOLUTION: The current limiting device for preventing overcurrent by limiting the current value of a circuit comprises a current restriction means for restricting the current of a circuit below a fixed value, and a switch for opening/closing a circuit wherein the current restriction means is arranged to start operation upon elapsing a predetermined time after a current above a fixed value flowed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a current limiting device that limits an electric current value of a circuit to prevent an overcurrent.

2. Description of the Related Art As a current limiting device used for a process control related device, there is known a device that prevents an overcurrent by limiting a current that is equal to or higher than a certain current value. The current limiting device incorporates a semiconductor switch that turns on and off the circuit, and protects the external load, the connection circuit, or the semiconductor switch by turning off the semiconductor switch as necessary.
JP 2006- 211737 A

  However, the current limiting device employs an operation that instantaneously turns off the semiconductor switch and shuts off the output when an overcurrent is detected. If there is an inrush current at the start of operation of a device connected as an external load, It is detected as a current and the circuit is interrupted. Therefore, it is impossible to connect a lamp or a capacitive load that generates an inrush current.

  An object of the present invention is to provide a current limiting device that can cope with an inrush current.

The current limiting device of the present invention is a current limiting device that limits the current value of a circuit to prevent overcurrent, current limiting means for limiting the current of the circuit to a certain current value or less, a switch for opening and closing the circuit, The current limiting means starts operation after a lapse of a predetermined time after a current of a constant current value or more flows.
According to this current limiting device, the current limiting means starts operation after a predetermined time has elapsed since a current of a predetermined current value or more flows, so that an inrush current immediately after closing the switch can be allowed.

  The current limiting means may be a constant current circuit.

The current limiting device of the present invention is a current limiting device that limits the current value of a circuit to prevent overcurrent, current limiting means for limiting the current of the circuit to a certain current value or less, a switch for opening and closing the circuit, And control means for determining whether or not the current limiting means can limit the current based on a current value acquired a plurality of times during a transition period after the switch is closed.
According to this current limiting device, whether to limit the current is determined based on the current value acquired a plurality of times during the transition period after the switch is closed, so that the inrush current during the transition period can be allowed. .

  According to the current limiting device of the present invention, the current limiting means starts operation after a predetermined time has elapsed since a current of a certain current value or more flows, so that an inrush current immediately after closing the switch can be allowed.

  According to the current limiting device of the present invention, whether to limit the current is determined based on the current value acquired a plurality of times during the transition period after the switch is closed, so that the inrush current during the transition period is allowed. Can do.

  Hereinafter, an embodiment of a current limiting device according to the present invention will be described with reference to FIGS.

  FIG. 1A is a block diagram showing the configuration of the current limiting device of this embodiment.

  As shown in FIG. 1A, the current limiting device 3 according to the present embodiment includes a P-MOSFET switch 31 provided in a current path between a power supply 1 and an external load 2, and a current inserted in the current path. A resistor 32 for detection, a control unit 33 for controlling the operation of the current limiting device 3, and a switch control circuit 35 for turning on / off the switch 31 via a switch 34 by a P-MOSFET according to a command of the control unit 33, And a current monitoring circuit 36 that monitors current based on the voltage generated in the resistor 32. In addition, the polarity of a current limiting device can be reversed and it can also be set as the circuit which uses N-MOSFET.

  As shown in FIG. 1A, the current limiting device 3 is provided with a constant current circuit as a current limiting means including a reference voltage source 41 and an operational amplifier 42. The operational amplifier 42 obtains constant current characteristics by applying feedback to the gate of the switch 31 so that the voltage generated in the resistor 32 becomes equal to the reference voltage of the reference voltage source 41.

  2A and 2B are diagrams showing an operation mode of the current limiting device 3. FIG. 2A shows a normal mode in which the external load 2 is operated, and FIG. 2B shows an on-pulse diagnosis mode when the external load 2 is not operated. Respectively.

  FIG. 2A shows the power-on time in the normal mode, and corresponds to the case where the operation of the external load 2 in a non-operating state is started.

  FIG. 3 is a diagram illustrating threshold values at which current limiting works.

The current monitoring circuit 36 monitors the current flowing through the resistor 32, and the constant current circuit performs a constant current operation after a predetermined time (t0) has elapsed since a current of a certain current value (threshold value B) or more flows through the resistor 32. Start and current is limited by threshold B. The elapsed time t0 can be adjusted by adding a constant of the phase compensation circuit of the operational amplifier 42 or adding a delay circuit to the inverting input terminal. FIG. 1B shows an example of a delay circuit. In this example, a delay circuit 43 composed of a resistor and a capacitor is added.

  The control unit 33 determines that the current exceeds the threshold value C1 for a predetermined time (t1) after a current of a certain current value (threshold value C) or more flows through the resistor 32, and the switch control circuit 35 The switch 34 is turned on and the switch 31 is turned off to shut off the circuit.

  On the other hand, in the on-pulse diagnosis mode shown in FIG. 2B, a short-time on-pulse is given to the external load 2 that is not operating, thereby diagnosing a conduction state in a range where the external load 2 is not operated. Thereby, it is possible to diagnose the standby external load 2 and the circuit.

  The controller 33 may determine an overcurrent when the threshold value C2 is exceeded. Thus, the detected value of the overcurrent may be distinguished between the threshold value C1 and the threshold value C2 according to the operation mode.

  In the current detection device 3 of the present embodiment, when an overcurrent is detected in the normal mode, whether the output can be recovered by turning off the output once to stop the operation of the external load 2 and shifting to the on-pulse diagnosis mode. Can be diagnosed. The current limiting device 3 can execute off-pulse diagnosis even when the external load 2 is operating, but the description thereof is omitted.

When an overcurrent event such as a short circuit occurs on the external load 2 side, the following operation is performed.
(1) When a current that generates a voltage that cuts off the switch 31 flows through the resistor 32, the current is limited by the value (threshold A).
(2) When the above constant current circuit functions, the current is limited to a constant value (threshold value B).
(3) When an overcurrent is detected by the current monitoring circuit 36, the control unit 33 turns off the switch 31 via the switch control circuit 35 and cuts off the current (threshold value C1 or threshold value C2).

  As shown by the thick line in FIG. 3, the current limiting region can be set so as not to flow a current exceeding the element limit curve of the switch 31 by the current limitation in the above three steps. FIG. 3 shows a current limiting region when the detected value of overcurrent detection is the threshold value C1.

  As described above, the current limiting device 3 of the present embodiment does not limit the current at the threshold B until the constant current circuit functions. For this reason, as shown in FIG. 3, the inrush current is allowed without suppressing the peak of the inrush current, the current value quickly shifts to the steady state, and the current value quickly converges toward the normal value. Thereby, the external load 2 can be promptly shifted to the operating state. In addition, by allowing inrush current that could not be handled until now, it is possible to connect lamps or capacitive loads that could not be connected in the past. In addition, since the current value converges to the normal range at an early stage, diagnosis in a short time can be executed while preventing erroneous detection of overcurrent.

  Conventionally, in the on-pulse diagnosis, a current value at a specific timing is acquired for one pulse, and an overcurrent is detected based on the current value. On the other hand, the current value may be acquired and the current waveform may be recognized a plurality of times in one pulse in the on-pulse diagnosis.

  FIG. 4A shows an example in which current values are sampled at high speed for various current waveforms. In this example, the control unit 33 serving as a current limiting unit and a control unit acquires a current value a plurality of times through the current monitoring circuit 36 within a transient period (within one pulse period) immediately after the switch 31 is turned on. . Further, the control unit 33 identifies an inrush current based on the acquired current value. If it is recognized as an inrush current, it is not determined that the overcurrent is abnormal.

  Thus, since the current waveform can be recognized by processing the result of the high-speed sampling in the control unit 33, it is possible to distinguish the overcurrent and the inrush current. In the example of FIG. 4A, it is possible to recognize the inrush current as normal without lowering the overcurrent detection threshold by providing the inrush allowable region.

  FIG. 4B shows an example in which a conventional diagnosis result in which the current value is detected once just before the fall of the pulse is compared with the high-speed sampling diagnosis result in FIG. In this example, it is not possible to detect the overcurrent P shown in FIG. 4A under the condition that the inrush current is determined to be normal in the conventional diagnosis. On the other hand, according to the high speed sampling, the inrush current and the overcurrent P are accurately determined. Can be distinguished.

  As described above, according to the current limiting device of the present invention, the current limiting means starts operation after a predetermined time has elapsed since the switch was closed, and therefore can accept an inrush current immediately after the switch is closed. In addition, according to the current limiting device of the present invention, whether to limit the current is determined based on the current value acquired a plurality of times during the transition period after the switch is closed. can do.

  The scope of application of the present invention is not limited to the above embodiment. The present invention can be widely applied to a current limiting device that limits the current value of a circuit to prevent an overcurrent.

It is a figure which shows the structure of the current limiting device of one Embodiment, (a) is a block diagram which shows the structure of the current limiting device of one Embodiment, (b) is an example of a delay circuit in FIG.1 (b). FIG. It is a figure which shows the operation mode of a current limiting device, (a) shows the normal mode which operates an external load, (b) shows the on-pulse diagnostic mode when not operating an external load, respectively. The figure which shows the threshold value which an electric current limitation works. It is a figure which shows the example which samples a current value at high speed, (a) is a figure which shows the example which samples a current value at high speed about various current waveforms, (b) is a current value only once just before the fall of a pulse. The figure which shows the example which compared the conventional diagnostic result which detects, and the diagnostic result of high-speed sampling.

Explanation of symbols

3 Current Limiting Device 31 Switch 42 Operational Amplifier (Current Limiting Means, Constant Current Circuit)
41 Reference voltage source (current limiting means, constant current circuit)
33 Control section (current limiting means, control means)

Claims (3)

In the current limiting device that limits the current value of the circuit to prevent overcurrent,
Current limiting means for limiting the circuit current to a certain current value or less;
A switch for opening and closing the circuit;
With
The current limiting device is characterized in that the current limiting device starts an operation after a predetermined time has elapsed since a current of a predetermined current value or more flows. The current limiting device according to claim 1, wherein the current limiting means is a constant current circuit. In the current limiting device that limits the current value of the circuit to prevent overcurrent,
Current limiting means for limiting the circuit current to a certain current value or less;
A switch for opening and closing the circuit;
Control means for determining whether or not the current limiting means can limit current based on a current value acquired a plurality of times during a transition period after the switch is closed;
A current limiting device comprising:

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