JP2000354325A - Overload and short-circuit protection circuit of slave unit for interfacing actuator and sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To protect a slave for interfacing input and output devices which include an actuator and a sensor (ASi) for overloading and short-circuiting with a low-cost circuit. SOLUTION: A slave unit 1, that has a slave unit main circuit 1A and is connected to an ASi power supply, is provided with a circuit consisting of resistors R1, 2, 3 to R5, 6, 7, transistors T0 to T4, a capacitor C1, etc. Normally, the transistor 1 is kept in an 'on' state, but momentary 'on' states are repeated for a fixed cycle, if an overcurrent or a short-circuit current is caused to flow. This structure makes an expensive IC circuit that has conventionally been used to be dispensed with.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overload / short-circuit protection circuit for an actuator for controlling an interface with an actuator or a sensor used as a process input / output device and a slave for a sensor interface circuit (hereinafter abbreviated as ASi). About.

[0002]

2. Description of the Related Art ASi is a network that handles bit-level signals defined by the EN standard (EN50295), and is located at the lowest layer in a field network. FIG. 4 shows an example of an ASi network configuration. There is a master 2 at the upper level, and the master 2 uses both communication and power.
The wires extend (ASi +, ASi-). ASi
+ And ASi- have a power supply 4 of 30 V DC and a decoupling circuit for preventing a communication signal from being attenuated.
The dedicated power supply 3 is connected. Although four slaves 11 to 14 are shown here, a maximum of 31 slaves can be connected.

The slaves 11 to 14 have only an output for controlling a load (slave 11), have only an input for receiving a signal of a sensor or an actuator (slave 14), or have an output and an input. There are types such as those having both (slaves 12, 13). For the slave having an output, a DC power supply 4 is connected to operate the load (slaves 11 and 12), and a power supply for operating the load is also taken from the ASi power supply 3. (Slave 13). The master 2 is combined with a programmable controller (PLC), and in order to operate a load required for a sensor and an input, a program necessary for the master 2 is set and the operation is controlled.

FIG. 5 shows a conventional example of a slave. this is,
The power for operating the load is also taken from the ASi power source, and the ASi + side is connected to a slave main circuit 1A including an ASi slave ASIC and a coil L1 through a diode D for preventing reverse connection. Also, A
The Si- side is connected to the slave main circuit 1A and the coil L2. A capacitor C2 is connected between the coils L1 and L2, and a filter is applied by these coils and the capacitor so that no signal is applied to the subsequent circuits. The output signal from slave main circuit 1A is output transistor T
Connected to 0. The load (X) 7 is the output transistor T0
To the ASi + side through coil L1 and the collector of
When the output transistor T0 is turned on by the output signal from the slave main circuit 1A, a voltage is supplied from the ASi power supply to the load (X) 7, and the load (X) 7 is turned on. Also, when the sensor 6 is used as an input, a voltage is supplied from an ASi power supply. Furthermore, overload / short circuit detection circuit 1B
Are provided in the current path portion to detect an overload current or an overcurrent of sensor current consumption or a load short-circuit current. The overload / short circuit detection circuit 1B is usually provided with a dedicated I
C is used.

[0005]

As mentioned above, the load
Although a dedicated IC is used as the short-circuit detecting circuit, there is a problem that the cost is increased because the dedicated IC is generally expensive. Also, since the load and the sensor are supplied with power from the ASi power supply through the coil,
A voltage of about 30 V is applied to the load and the sensor. For this reason, for example, in the case of a sensor or a load having a rated voltage of 24 V ± 10%, there is a problem that the voltage becomes higher than the rated voltage and cannot be used. Therefore, an object of the present invention is to reduce the cost and eliminate the limitation by the rating.

[0006]

In order to solve such a problem, the invention according to claim 1 has a slave main circuit,
An output signal of the slave main circuit is introduced into a base of an output transistor for an actuator which controls an interface with an input / output device including an actuator or a sensor and a power supplied from a sensor interface circuit (ASi). The collector of the first transistor is connected, the emitter of the first transistor is connected to the first resistor and the base of the second transistor, and the base of the first transistor is connected to the junction between the collector of the third transistor and the third resistor. Connected, the emitter of the third transistor is connected to the second resistor, the emitter of the fourth transistor is connected to the emitter of the third transistor, the base is connected to the sixth resistor, and the other end of the sixth resistor is connected to the seventh resistor. First
The other end of the seventh resistor is connected to the side of the second resistor not connected to the transistor, and the other end of the first coil connected to the ASi power supply + side through the diode is connected to the capacitor and the collector of the second transistor. And the other end of the first capacitor to which the sixth resistor is not connected is connected to the first, third and fifth resistors,
It is characterized in that it is connected to the other end of the second coil connected to the ASi power supply side. In the first aspect of the present invention,
A constant voltage circuit can be provided between the first coil and the input / output device (the invention of claim 2).

[0007]

FIG. 1 is a block diagram showing a first embodiment of the present invention, which is characterized in that an overload / short-circuit protection circuit is constituted only by resistors, capacitors and transistors. In a normal state, the base current of the transistor T3 flows through the resistor R2, and the transistor T3 is on (T4 is off). As a result, the base current is supplied to the transistor T1, which is also in the ON state. As a result, a current I, which is the sum of the load current and the current consumption of the sensor, flows between the collector and the emitter of the transistor T1. When the load current or the current consumption of the sensor increases, the resistance R1
The voltage Va between them increases. The resistance R1
The current value at which the short-circuit protection circuit operates is determined. For example, R1 = Vbe2 / Iop. Here, Vbe2 is the transistor T
2, a base-emitter voltage Iop is an overload / short circuit protection circuit operating current.

When the current I at which the voltage Va across the resistor R1 becomes equal to or higher than Vbe2 flows, the base current of T2 flows and T2
Turns on. C1 is normally charged to about 30V, but is discharged instantaneously to about 0V when T2 is turned on due to an overload or short circuit current. Therefore, T4
Flows through the resistors R2 and R6, turning on T4. When T4 turns on, the base potential of T3 rises and T3 turns off, thereby turning off T1.

Thereafter, the capacitor C1 is charged by the current I1 passing through the resistor R7 and the base current I2 of the transistor T4, and the voltage gradually increases. Then, when the voltage Vc across the capacitor C1 becomes Vc３０ [30 × R5 / (R2 + R5)] − Vbe4, T4 is turned off again. In addition, Vbe4
Indicates a base-emitter voltage of the transistor T4.

When T4 is turned off, T3 and T1 are turned on. However, when an overload or short-circuit current flows, T3 is instantaneously turned on.
2 is turned on, the electric charge of C1 is discharged, and T1 is turned off. That is, T1 is repeatedly turned on instantaneously in a cycle determined by the resistors R2, R6, R7 and the capacitor C1. FIG. 2 shows a voltage change example of Vc and Va. FIG. 3A shows Vc, and FIG. 3B shows Va. As is clear from FIG. 3B, since T1 is instantaneously turned on, the load current and the like are almost shut down (blocked) and are protected from an overload or short circuit state.

FIG. 3 is a block diagram showing a second embodiment of the present invention. The difference from FIG. 1 resides in that a constant voltage circuit 1C is inserted before connecting input / output devices such as sensors, and the other configurations are the same. This is because a voltage of 24 V DC is a common voltage in Japan, and the voltage is controlled by the constant voltage circuit 1C.

[0012]

According to the present invention, the overload / short circuit protection circuit can be formed only by inexpensive resistors, capacitors and transistors, so that the cost can be reduced. Further, by inserting a constant voltage circuit between the input section and the output section of the overload / short-circuit protection circuit, the voltage applied to the load, the sensor, and the like can be set to a voltage meeting Japanese specifications.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an operation schematic diagram of FIG. 1;

FIG. 3 is a configuration diagram showing a second embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating an example of an ASi network configuration.

FIG. 5 is a configuration diagram showing a conventional example of a slave.

[Explanation of symbols]

1, 11, 12, 13, 14: slave, 1A: slave main circuit, 1B: overload / short circuit detection circuit (dedicated IC),
1C: constant voltage circuit, 2: master, 3: ASi power supply, 4 ...
DC power supplies, 51, 52, 53, 54 ... input / output devices, 6 ...
Sensor, 7: load (X), L1, L2: coil, C1,
C2: condenser, R1, R2, R3 to R5, R6, R
7: resistor, T0, T1, T2, T3, T4: transistor, D: diode.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) EY12 EY17 EZ14 EZ40 EZ51 EZ66 FX04 FX08 FX13 FX19 FX28 FX32 GX01 GX02 GX05 GX06

Claims (2)

[Claims] An actuator / sensor interface circuit (AS) having a slave main circuit and controlling an interface with an input / output device including an actuator or a sensor.
i) For a slave supplied with power from i), an output signal of the slave main circuit is introduced into a base of an output transistor, and an emitter thereof is connected to a collector of a first transistor.
A resistor and a base of the second transistor; a base of the first transistor connected to a connection between the collector of the third transistor and the third resistor; an emitter of the third transistor connected to the second resistor; The emitter of the transistor is connected to the emitter of the third transistor, its base is connected to the sixth resistor, the other end of the sixth resistor is connected to the seventh resistor, the first capacitor and the collector of the second transistor, and the other end of the seventh resistor is connected to the other end. The end is connected to the side of the second resistor that is not connected to the transistor, and A is connected through a diode.
Connected to the other end of the first coil connected to the Si power supply + side,
A side of the first capacitor, to which the sixth resistor is not connected, is connected to the first, third, and fifth resistors.
An overload and short circuit protection circuit for an actuator and a sensor interface slave connected to the other end of a second coil connected to a power supply side. 2. The overload and short circuit protection circuit of an actuator and a sensor interface slave according to claim 1, wherein a constant voltage circuit is provided between the first coil and the input / output device.