JP2003189467A - Protective circuit for i/o apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it unnecessary to replace a protective device (fuse) every time when an erroneous wiring 6 is produced. <P>SOLUTION: This I/O circuit has a transistor, a drive circuit generating the base signal of the transistor, and a protective device protecting the transistor. Further, the emitter of the transistor is connected to the ground via an external load and the collector of the transistor is connected to an external power supply via the protective device. In this I/O circuit, there are provided an overcurrent detecting circuit, which detects the terminal voltage of the protective device and, if the detected voltage exceeds a prescribed voltage, outputs a signal, and an alarm holding circuit which, if it receives a signal from the overcurrent detecting circuit which shows that the detected current is an overcurrent, discontinues the function of a drive circuit and turns off the transistor and, when the reset signal is received, restores the function of the drive circuit. Further, a polyswitch is employed as the protective device. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive element which is short-circuited due to overcurrent when a load or the like is erroneously wired to an input / output device having a digital input / output circuit. The present invention relates to a protection circuit for an input / output circuit that can prevent the device from being damaged. 2. Description of the Related Art An input / output device having a conventional digital input / output circuit will be described with reference to FIG. In the figure, a drive element drive circuit 5, a drive element 2, and a protection element 8 using a fuse are connected on the input / output device side as shown. Outside the input / output device, an input / output power supply 1, a resistor 3, and a lamp 4 are connected as shown in the figure. In this state, if the driving element 2 is in the ON state by the output ON / OFF control signal 14, the path from the input / output power supply 1 to the ground via the protection element 8, the driving element 2, the resistor 3, and the lamp 4 Electric current flows. At this time, if the connection from the driving element 2 to the ground is erroneously wired, a large current flows through the erroneous wiring 6 and the driving element 2 is broken. To prevent this,
A protection element (fuse) 8 is inserted at the power supply entrance of the driving element 2, and the protection element (fuse) 8 is provided when an overcurrent occurs.
Is blown to protect the driving element 2. However, in the prior art, it is necessary to replace the protection element (fuse) 8 every time an erroneous wiring 6 occurs, and there is a problem that maintenance is poor. Therefore, an object of the present invention is to eliminate the need to replace a fuse as a protection element every time an erroneous wiring occurs. [0004] In order to solve the above problems, the present invention comprises a transistor, a drive circuit for generating a base signal thereof, and a protection element for protecting the transistor. In an input / output circuit whose emitter is connected to ground via an external load and whose collector is connected to an external power supply via the protection element, a predetermined voltage is detected by detecting a terminal voltage of the protection element. When the overcurrent detection circuit outputs a signal indicating that an overcurrent is detected from the overcurrent detection circuit, the function of the drive circuit is stopped, the transistor is turned off, and a reset signal is received. And an alarm holding circuit for restoring the function of the drive circuit when the protection circuit is activated. It is characterized by having done. By doing so, it is possible to protect the drive element from overcurrent and to enable recovery without replacing the protection element after removing the cause of the erroneous wiring. [0005] The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a protection circuit for an input / output device according to the present invention. 2 is different from FIG. 2 in that a protection element 7 using a polyswitch between the driving element 2 and the input / output power supply 1 is detected. 11 in that an overcurrent detection circuit 9 that outputs the signal 11 and an alarm holding circuit that receives the alarm signal 11 and controls the operation of the drive element drive circuit 5 are provided. When the input / output circuit operates under such a configuration, the operation is as follows. Output ON / OFF control signal 1
If the external input / output unit wiring is incorrectly wired 6 when the drive element 2 is in the ON state by 4, an overcurrent flows into the protection element (poly switch) 7 and cuts off the current when the value exceeds a predetermined value. The overcurrent detection circuit 9 outputs an alarm signal 11 when detecting that the current has been cut off. The alarm holding circuit 10 receives and holds the signal 11, outputs the drive element drive circuit control signal 12 to the drive element drive circuit 5, turns off the gate signal of the drive element 2, and turns off the drive element 2.
FF. The protection element (poly switch) 7 cuts off the current due to heat generation at the time of overcurrent, but then returns to a connected state again when the temperature drops to a predetermined temperature. At this time, since the driving element 2 is turned off by the driving element cutoff circuit 15 including the alarm holding circuit 10 and the driving element driving circuit 5, no overcurrent is generated in the driving element 2 again. Thereafter, if the cause of the erroneous wiring 6 is removed and the RESET * signal 13 is input to the alarm holding circuit 10, the interrupted circuit is restored to the original state. As described above, according to the present invention, it is possible to protect a drive element from an overcurrent caused by erroneous wiring of an external input / output unit wiring, and to protect a drive element after removing a cause of erroneous wiring. Since it is possible to return without replacing the element, there is an effect that the maintainability can be greatly improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a protection circuit of an input / output device of the present invention. FIG. 2 is a block diagram showing a configuration of a protection circuit of a conventional input / output device. . 1. Input / output power supply Drive element3. Load resistance4. Lamp5. Drive element drive circuit 6. Incorrect wiring7. 7. Protection element (poly switch) 8. Protection element (fuse) 10. Overcurrent detection circuit Alarm holding circuit 11. Alarm signal12. 12. Drive element drive circuit control signal RESET * signal Output ON / OFF control signal 15. Drive element cutoff circuit

Claims (1)

Claims: 1. A transistor comprising: a transistor; a drive circuit for generating a base signal thereof; and a protection element for protecting the transistor. An emitter of the transistor is connected to ground via an external load. An input / output circuit in which a collector of the transistor is connected to an external power supply through the protection element; an overcurrent detection circuit that detects a terminal voltage of the protection element and outputs a signal if the voltage exceeds a predetermined voltage; When an overcurrent detection signal is received from the overcurrent detection circuit, the function of the drive circuit is stopped, the transistor is turned off, and the function of the drive circuit is restored when a reset signal is received. And a protection circuit, wherein the protection element is a polyswitch.