JPH0739063A - Overcurrent protection apparatus - Google Patents

Abstract

PURPOSE:To protect a DC power supply circuit by intercepting a DC power source to be supplied to a load when an overcurrent is generated. CONSTITUTION:A power supply board 1 is connected with a display apparatus 3 provided in an operator's seat through a constant current circuit 2. In this case, the constant current circuit 2 and the display 3 are connected with a harness H. The constant current circuit 2 is also connected with a second transistor TR2 and the constant current circuit 2 intercepts a DC power source from the power supply board l by turning ON the transistor TR2. Moreover, the display apparatus 3 is connected with a control apparatus C for transmitting and receiving various data to and from the display apparatus 3. Moreover, the control apparatus C is connected with the transistor TR2 and when exchange of various data is disabled between the control apparatus C and the display apparatus 3 due to the short circuit, for example, of the harness H, the transistor TR2 is turned ON. In this case, the constant current circuit 2 intercepts the DC power source from the power supply board 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent protection device for protecting a DC power supply circuit or the like from overcurrent.

[0002]

2. Description of the Related Art Conventionally, in a battery-powered forklift or the like, there has been proposed an overcurrent protection device using a three-terminal regulator between a power supply and a display device such as a display provided in the driver's seat of the forklift.

As shown in FIG. 2, a display device 33 is connected to a power supply board 31 as a DC power supply circuit to which a battery B is connected via a three-terminal regulator 32. At this time, capacitors 34 and 3 are provided on the three-terminal regulator 32 side of the power board 31 and the display device 33, respectively.
5 are connected in parallel to smooth the voltage output from the power supply board 31 and the voltage applied to the display device 33.

The three-terminal regulator 32 is a constant voltage circuit, which controls the voltage output from the power supply board 31 and always controls the voltage applied to the display device 33 to a constant voltage.

[0005]

By the way, the display device 3
Since 3 is provided in the driver's seat, it is connected to the three-terminal regulator 32 via the harness H. And
When the harnesses H are short-circuited for some reason, an excessive current flows through the three-terminal regulator 32. At this time,
The three-terminal regulator 32 suppresses a large current on the display device 33 side and protects the power supply board 31. However, although the three-terminal regulator 32 suppresses overcurrent, current continues to flow in the regulator 32.

As a result, in the three-terminal regulator 32, the internal elements and the like are eventually destroyed by the continuous flow of this current. Then, the power supply board 31 may be destroyed due to the destruction of the three-terminal regulator 32.

The present invention has been made to solve the above problems, and its purpose is to protect the DC power supply circuit by shutting off the DC power supply supplied to the load when an overcurrent occurs. The present invention is to provide an overcurrent protection device.

[0008]

In order to solve the above problems, a first aspect of the present invention relates to a direct current power supply circuit which supplies control data to a load which is exchanged with a control circuit and which is drive-controlled. In the overcurrent protection device adapted to supply the driving DC power source through the constant current circuit, the constant current circuit is provided with an interruption circuit for interrupting the DC power source from the DC power source circuit, and the control circuit is connected to the load. The gist of the invention is to provide an abnormality detection unit for operating the cutoff circuit when it becomes impossible to exchange control data between them.

According to a second aspect of the present invention, in the first aspect, the load is a display device, the load is provided at a position separated from the DC power supply circuit, and the load is connected to the constant current circuit through a harness, and the control circuit is provided. Is to perform control data to be displayed on the screen of the display device with the display device.

[0010]

Therefore, according to the first aspect of the present invention, in the overcurrent protection device, the DC power supply for driving from the DC power supply circuit is applied to the load whose control data is transmitted and received to and from the control circuit. Are supplied via a constant current circuit.

At this time, when the control circuit cannot exchange the control data with the load, the abnormality detecting section of the control device operates the shut-off circuit provided in the constant current circuit so that the DC power supply circuit operates. Turn off the DC power supply.

According to the second aspect of the invention, in the overcurrent protection device, control data for display is transmitted to and received from the control circuit and the display device driven and controlled is driven by the DC power supply circuit. DC power for use is supplied through a constant current circuit. This display device is provided at a position separated from the DC power supply circuit, and is connected to the constant current circuit via a harness.

At this time, for example, when the display device becomes inoperable due to a short circuit of the harness for some reason, and the control circuit cannot exchange control data with the display device, the abnormality detection unit of the control device is fixed. The cutoff circuit provided in the current circuit is operated to cut off the DC power supply from the DC power supply circuit.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is embodied in a battery type forklift will be described below with reference to FIG.

As shown in FIG. 1, a battery B is connected to a power supply board 1 as a DC power supply circuit, and a predetermined voltage is output from the power supply board 1. The power supply board 1 is connected via a constant current circuit 2 to a display device 3 as a load provided in the driver's seat.

The constant current circuit 2 is provided with a first transistor TR1. This first transistor T
The collector side of R1 is connected to the power supply board 1, and the first resistor R1 is connected between the collector and base of the first transistor TR1. Also, the first transistor TR
One end side of the second resistor R2 is connected to the emitter side of 1, and the other end side of the second resistor R2 is connected to the display device 3. Further, a variable Zener diode D is connected to a connection point a between the base of the first transistor TR1 and the first resistor R1 and the other end of the second resistor R2. That is, the cathode side of the variable Zener diode D is connected to the connection point a.
And the anode side is connected to the other end of the second resistor R2. The variable Zener diode D is controlled in voltage applied across the variable Zener diode D based on the voltage Vb at the connection point b between the emitter of the first transistor TR1 and the second resistor R2. ing.

That is, in the constant current circuit 2, for example, the first
When the current flowing from the emitter of the transistor TR1 changes from a predetermined value, the value of the current i flowing through the connection point b changes, and the voltage Vb at the connection point b changes. At this time,
The variable Zener diode D adjusts the voltage applied to the base of the first transistor TR1 based on the voltage Vb,
The current flowing from the emitter is held at the predetermined value. Therefore, the current flowing from the constant current circuit 2 to the display device 3 is always controlled to a constant value.

Further, capacitors 4 and 5 are connected in parallel on the constant current circuit 2 side of the power supply board 1 and the display device 3, respectively, and the voltage output from the power supply board 1 and the voltage applied to the display device 3 are connected to each other. It is designed to be smoothed. At this time, since the display device 3 is provided in the driver's seat of the forklift, it is connected to the constant current circuit 2 and the like via the harness H.

Furthermore, the collector side of the second transistor TR2 as a cutoff circuit is connected to the connection point a. The control circuit C is connected to the base side of the second transistor TR2, and the power supply board 1 is connected to the emitter side of the second transistor TR2.
Is connected to the negative terminal of. That is, the second transistor TR2 is connected in parallel to the DC power supply of the power supply board 1.

The control circuit C is connected to the display device 3. That is, the control circuit C exchanges various control data such as display data with the display device 3 when the display device 3 is operating normally. At this time, the control circuit C holds the second transistor TR2 in the off state. or,
The control circuit C has an abnormality detection unit Ca, and when the abnormality detection unit Ca cannot exchange various data with the display device 3, it is determined that an abnormality such as a short circuit has occurred in the display device 3. The second transistor TR2 is turned on.

Next, the operation and effect of the circuit configured as described above will be described. When current is supplied from the power supply board 1 to the constant current circuit 2, the constant current circuit 2 causes the display device 3 to operate.
The current flowing through is always controlled to be a constant value. Therefore, a current having a constant value always flows through the display device 3, and the display device 3 operates normally. At this time, the control circuit C exchanges various data for display with the display device 3 because the display device 3 is operating normally. Therefore, the control circuit C holds the second transistor TR2 in the off state.

When the harness H or the like is short-circuited from this state for some reason and it becomes impossible to send and receive various data between the display device 3 and the control circuit 8, the abnormality detecting section Ca of the control circuit C causes the display device 3 to operate. The second transistor TR2 is turned on because an abnormality has occurred.

Then, the second transistor TR2 has the first
To turn off the transistor TR1 of
No current flows from R1. That is, the transistor TR
Since no current flows through the transistor 1, the same transistor TR1
The constant current circuit 2 is protected since the above is not damaged.

Therefore, when the harness H is short-circuited, the constant current circuit 2 is protected, which in turn protects the power supply board 1. That is, the control circuit C
Stops the supply of the current flowing through the constant current circuit 2 when the harness H is short-circuited and it becomes impossible to exchange various data with the display device 3. Therefore, the constant current circuit 2 can be protected.

The present invention is not limited to the above-mentioned embodiments, but may be implemented as follows with a part of the structure appropriately modified without departing from the spirit of the invention. (1) In the above embodiment, various switches such as a contactor may be used as the cutoff circuit instead of the transistor.

(2) In the above embodiment, a power supply board for converting an AC power supply into a DC power supply may be used as the DC power supply circuit. (3) In the above embodiment, the case where the harness H is short-circuited has been described, but it is also possible that an abnormality such as a short circuit occurs in the display device 3. At this time, for example, the display device 3
A current amount detection sensor may be provided inside, and the control circuit C may determine an abnormality such as a short circuit in the display device 3 based on the current amount detected by the current amount detection sensor.

(4) In the above embodiment, the display device 3 is used as a load. However, the present invention is not limited to the display device 3 and may be applied to a DC drive motor for traveling as a load. Good. At this time, for example, when the exchange of various control data between the control circuit and the DC drive motor becomes impossible, the DC drive motor is stopped.

(5) In the above embodiment, the second transistor TR2 is provided between the power supply board 1 and the constant current circuit 2.
Alternatively, it may be connected between the constant current circuit 2 and the display device 3.

[0029]

As described in detail above, according to the present invention, when an overcurrent is generated, the DC power supply circuit can be protected by cutting off the DC power supply supplied to the load. There is.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment embodying the present invention.

FIG. 2 is a circuit diagram of a conventional example.

[Explanation of symbols]

1 ... Power supply board as DC power supply circuit, 3 ... Display device as load, TR2 ... Second transistor as cutoff circuit, C ... Control circuit, H ... Harness.

Claims (2)

[Claims] 1. A DC power supply for driving from a DC power supply circuit, which supplies power to a load to be drive-controlled by exchanging control data with a control circuit, is supplied through a constant current circuit. In the current protection device, the constant current circuit is provided with a cutoff circuit that cuts off DC power from a DC power supply circuit, and the control circuit is configured to cut off the cutoff circuit when control data cannot be exchanged with a load. An overcurrent protection device provided with an abnormality detection unit for operating the. 2. The overcurrent protection device according to claim 1, wherein the load is a display device, the load is provided at a position separated from the DC power supply circuit, and the load is connected to the constant current circuit through a harness. Is an overcurrent protection device for performing control data for displaying on the screen of the display device with the display device.