JP2006253776A - OVERLOAD AND SHORT-CIRCUIT PROTECTING CIRCUIT OF SLAVE FOR AS-i - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an enhanced overload and short-circuit protecting circuit of a slave for an interface (AS-i) for an input/output apparatus including an actuator, a sensor and a load. <P>SOLUTION: To the overload and short-circuit protecting circuit comprising transistors T1 to T4, resistors R1 to R7, and a capacitor C1 or the like provided to the slave 1 including a slave main circuit 1A and receiving an AS-i power supply, a capacitor C3 is attached to prevent the overload and short-circuit protecting circuit from being operated at an overcurrent whose duration time is a prescribed time or below, and further a resistor R10 (or a series circuit comprising a resistor and a PTC thermister) is provided to supply a current I2 to the overload and short-circuit protecting circuit via the resistor R10 even when the overload and short-circuit protecting circuit is activated so as to prevent a sensor power supply current I from being zero thereby attenuating a rush current at sensor connection and to be capable of normally supplying power to the sensor. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an actuator used as a process input / output device, an actuator that controls an interface with a sensor, a load, and the like, and a slave overload / short circuit protection for a sensor interface circuit (Actuator Sensor interface, hereinafter also abbreviated as AS-i). Regarding the circuit.

AS-i is a network that mainly handles bit-level signals defined by the IEC standard (IEC620262-2) and EN standard (EN50295), and is located in the lowest layer in the field network.
FIG. 7 shows an example of the AS-i network configuration. There is a master 2 at the upper level, and two wires extending from the master 2 are used for both communication and power (AS-i + (positive), AS-i- (negative)). The AS-i + and AS-i- are connected to a DC30V power supply and an AS-i dedicated power supply (AS-i power supply) 3 having a built-in decoupling circuit for preventing a communication signal from being attenuated. 4 is a DC 24V power source. Although four slaves 11 to 14 are shown here, a maximum of 31 slaves are connected (in recent years, up to 62 can be connected).

The slaves 11 to 14 have only an output for controlling a load (slave 11), have an input for taking in a sensor or actuator signal (slave 14), or have both an output and an input. There are types of things (slave 12, 13) and the like. In addition, as described above, the sensor or actuator signal is input to the slave input, but the slave has a built-in sensor power supply so that the sensor power can also be supplied. Reference numerals 51 to 54 denote various input / output devices.
The master 2 is combined with a programmable controller (PLC), and in order to operate the load required for the inputs of the sensor and actuator, a necessary program is assembled in the master 2 to control the operation. .

FIG. 8 shows a conventional example of a slave.
In these circuits, the AS-i + side is connected to a slave main circuit 1A incorporating an AS-i slave IC circuit (ASIC) and a coil L1 through a diode D1 for preventing reverse connection. The AS-i- 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 formed by these coils and the capacitor, and a signal between the capacitors C2 is used as a power source for the sensor so that no signal is transmitted to the subsequent circuits. . The voltage supplied to the sensor is supplied from an AS-i power source connected between AS-i + and AS-i-. Further, the slave main circuit 1A has a terminal portion IN for capturing the input. The slave main circuit 1A determines the input state based on the voltage level applied to the terminal portion or the current level flowing into the terminal portion, and the determined input. A state signal is placed between AS-i + and AS-i-.

  In a normal state, the transistor T3 is turned on because a base current flows through the resistor R2 (T4 is turned off). Therefore, a base current is supplied to T1 by T3, and T1 is normally in an ON state. Thereby, the sensor consumption current I flows between the collector and the emitter of the transistor T1. As the sensor current consumption increases, the voltage across the resistor R1 increases. The resistor R1 determines the current value at which the overload / short-circuit protection circuit operates, and is set to a value of R1 = Vbe2 / Iop, for example. Here, Vbe2 represents the base-emitter voltage of the transistor T2, and Iop represents the operating current of the overload / short-circuit protection circuit.

When a current I that causes the voltage across R1 to be equal to or higher than Vbe2 flows, a base current flows through T2 and T2 is turned on. The capacitor C1 is normally charged to about 30V. However, when an overload or short-circuit current flows and T2 is turned on, the capacitor C1 is instantaneously discharged to about 0V. Therefore, the base current of T4 flows through the resistor R2 and the resistor R6, and T4 is turned on instantaneously. When T4 is turned on, the base potential of T3 rises and T3 is turned off, whereby T1 is turned off.
The capacitor C1 is charged by the current I1 passing through the resistor 7 and the base current I2 of the transistor T4, and the voltage gradually increases. And the voltage Vc between terminals of the capacitor C1 is
Vc≈ [30 × R5 / (R2 + R5)] − Vbe4
T4 is turned off again. Vbe4 represents the base-emitter voltage of the transistor T4.

  When T4 is turned off, the transistors T3 and T1 are turned on. However, since overcurrent flows, T2 is turned on instantaneously to discharge C1 and turn off T1. A circuit composed of resistors R2, R3, R5 and transistors T3, T4 forms a Schmitt circuit for providing hysteresis on the on level and off level. The transistor T1 is turned on instantaneously at a cycle determined by the Schmitt circuit and the resistors R6, R7 and C1. FIG. 9 shows changes in the waveforms of the voltages Vc and Va. Since T1 is instantaneously on, the current is almost shut down. Thus, the sensor power supply is protected from an overload current or a short-circuit current.

  In the overload / short circuit protection circuit as described above, even if an instantaneous overload current flows, the overload / short circuit protection circuit operates by detecting the current. However, since a normal sensor has a built-in capacitor, an inrush current flows when the power is connected. For this reason, when the sensor's inrush current exceeds the set value even when the sensor is connected, the overload / short-circuit protection circuit will operate, and the sensor may not be supplied with power, limiting the sensors that can be used. Will be.

Therefore, the applicant previously proposed a circuit as shown in FIG.
This is different from that shown in FIG. 8 in that a capacitor C3 is connected to the base of the transistor T4, and a delay time td is provided by this C3 as shown in FIG. As a result, when an overload or short-circuit current flows, T1 repeats the operation of turning off after turning on for a delay time td as shown in FIG. Therefore, in the case of an overload / short circuit state, the current I supplied from the sensor power supply only flows the overload / short circuit current Ip for a minute time td within the period T, thereby protecting the sensor power supply. .

Japanese Unexamined Patent Publication No. 2003-218673 (page 3, FIG. 1-2)

However, some sensors have inrush current that does not fall below the level at which the overload / short-circuit protection circuit operates within the delay time td. For such sensors, the overload / short-circuit protection circuit operates when the sensor is connected. As a result, there arises a problem that power is not supplied to the sensor.
Accordingly, an object of the present invention is to enable power supply to a sensor even when a large inrush current flows for a relatively long time, and to prevent a sensor (type) that can be used from being restricted.

In order to solve such a problem, in the invention of claim 1, a power source is provided from an actuator, sensor interface circuit (AS-i), which has a slave main circuit and manages an interface with an input / output device including an actuator, a sensor and a load. And an AS-i slave having a power supply terminal for sensor connection,
The collector of the first transistor is connected to the power source (−) terminal for sensor connection, the emitter of the first transistor is connected to the base of the first resistor and the second transistor, and the base of the first transistor is connected to the collector of the third transistor. And the third resistor are connected to each other, the emitter of the third transistor is connected to the second resistor, the base is connected to the connection point between the collector of the fourth transistor and the fifth resistor, and the emitter of the fourth transistor is connected. The base of the third transistor 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 second resistor. And the other end of the first coil connected to the AS-i power source (+) terminal through the diode and the sensor. The side of the first capacitor that is not connected to the sixth resistor is connected to the side of the first capacitor that is not connected to the sixth resistor. The first, third, and fifth resistors are connected to the side that is not connected. AS connected to the other end of the second coil connected to the i power source (−) terminal, one end of the second capacitor connected to the base of the fourth transistor, and the other end connected to the connection point of the second and seventh resistors. -I overload / short-circuit protection circuit for slave
An eighth resistor is connected between the collector of the first transistor and the emitter of the second transistor.

In the first aspect of the present invention, a PTC thermistor can be connected in series with the eighth resistor (the second aspect of the present invention).
In other words, even if the overload / short-circuit protection circuit is activated, the inrush current at the time of sensor connection is attenuated by eliminating the time that the sensor power supply current I is completely turned off (zero) and allowing the current I2 to flow through the resistor. Let Even if a sensor whose inrush current value does not fall below the overcurrent operating level within the delay time is connected, if the inrush current decay value falls below the overcurrent operating level, the overload / short circuit protection operation is canceled and the sensor The power can be supplied normally.

  According to the present invention, even when a large inrush current is relatively long when the sensor is connected, the power (current) can be normally supplied to the sensor, so that there is no limitation on the sensors that can be connected (used). The advantage is that the degree of freedom is increased.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
As is apparent from FIG. 1, this circuit is different from that shown in FIG. 10 in that a resistor R10 is connected between the collector of the transistor T1 and the emitter of T2. As a result, the current I supplied from the sensor power supply in a normal state (when the overload / short-circuit protection circuit is not operating) includes the current I1 flowing through the overcurrent detection resistor R1 and the current I2 flowing through the resistor R10. To be diverted to

Increasing the current I increases the current I1,
I1 * R1≈I * R1 * R10 / (R1 + R10) = Vbe2
(Vbe2: Base-emitter voltage of the transistor T2), the transistor T2 is turned on, and the transistor T1 is turned off after the delay time td. When the transistor T1 is off, the current I is only the current I2 flowing through the resistor R10, and the current value is a value limited by the resistor R10.

  A waveform of the current I when an overload or short-circuit current flows is shown in FIG. The difference from the waveform of the conventional circuit shown in FIG. 11 is that the current I does not become 0 and the current I2 flows even when the transistor T1 is off. That is, even if the overload / short-circuit protection circuit is activated by the inrush current when the sensor is connected, the charging current of I2 flows through the sensor. Therefore, when overload / short circuit detection is performed after the period T, the inrush current is attenuated by the amount that the sensor is charged with I2. The inrush current of the sensor is attenuated by the charging current of I2, and when it becomes below the detection level, the overload / short-circuit protection operation is canceled, and power (current) is normally supplied to the sensor.

If the value of the current I2 is as large as possible (R10 is as small as possible), the sensor can be charged more quickly, the sensor inrush current can be rapidly attenuated, and the sensor inrush current allowable value can be increased. When I2 is increased, the watt loss at R10 increases, so the value of R10 is determined in consideration of this watt loss. Wattorosu W _R in R10 when a dead short (time between terminals 1 and 3 short) is a W _R ≒ Vs ² / R10 (delay time td is sufficiently small time to the period T.).

FIG. 2 shows a second embodiment of the present invention.
The difference from FIG. 1 is that a PTC thermistor (Positive temperature Coefficient Thermistor) Rp is connected in series with R10. The PTC thermistor is a thermistor having a positive characteristic in which the resistance value increases as the temperature rises. When an excessive current flows, the PTC thermistor generates heat and suddenly increases its resistance value, thereby limiting the current flowing through the circuit. In addition, there is a self-recovery function that returns to the original low resistance value when the cause of overcurrent is removed and heat generation is stopped.

  Such thermistors are sold by various manufacturers, and various thermistors are available. For current detection, the resistance value is usually a small value of 1Ω or less to several tens of Ω as described above. However, when an overcurrent flows, the resistance value rapidly increases to limit the current. Such a PTC thermistor is called a posistor (R), a positive (R), a polyswitch (R) or the like in a unique name of each manufacturer.

In FIG. 2, such a series circuit of the PTC thermistor Rp and the resistor R10 is connected between the collector of the transistor T1 and the emitter of T2. As described above, since the resistance value of the PTC thermistor Rp suddenly increases and current is limited when an excessive current flows, the value of the series resistance R10 can be reduced. If the current value at which the resistance suddenly increases with the PTC thermistor is I _2T , the maximum power loss at the resistor R10 can be suppressed to R10 × (I _2T ) ² . I _2T is called the operating current or trip current of the PTC thermistor.

  Since only the resistor R10 is shown in FIG. 1, considering the watt loss at the resistor R10, the value could not be made very small. However, in the example of FIG. A large current I2 can flow immediately after T1 is turned off. As a result, the sensor is quickly charged and the sensor inrush current is rapidly attenuated. By doing this, even when a large inrush current that occurs for a relatively long time occurs when the sensor is connected, the overload / short-circuit protection circuit does not continue to operate, so the current is normally supplied to the sensor. .

Here, the operation of FIG. 2 will be described.
The current I supplied from the sensor power supply in a normal state (when the overload / short circuit protection circuit is not operating) is a series circuit of a current I1 flowing through the overcurrent detection resistor R1, a PTC thermistor Rp, and a resistor R10. Is shunted to a current I2 flowing through At this time, I2 is I2≈I × R1 / (R1 + Rp + R10), but R10 and the PTC thermistor Rp are selected and I2 is determined so that the PTC thermistor does not operate until an overcurrent is detected.

Increasing the current I increases the current I1,
I1 × R1≈I × R1 × (Rp + R10) / (R1 + Rp + R10) = Vbe2
(Vbe2: Base-emitter voltage of the transistor T2), the transistor T2 is turned on, and the transistor T1 is turned off after the delay time td. When the transistor T1 is off, the current I is only the current I2 flowing through the PTC thermistor Rp and the resistor R10, and the current value is a value limited by the series circuit of the PTC thermistor Rp and the resistor R10. Since Rp and R10 are relatively small values, the initial stage I2 when the transistor T1 is off can be set to a relatively large current value.

The inrush current when the sensor is connected is rapidly attenuated because the sensor is charged with this I2, and as a result, the overload / short-circuit protection operation is immediately released and the sensor is normally supplied with power. If the overload / short-circuit current continues to flow, the resistance value Rp increases according to the characteristics of the PTC thermistor to limit the current I2, so that the current I becomes small and the overload / short-circuit protection operation starts.
FIG. 5 shows a current waveform during the overload / short-circuit protection operation in FIG. The initial I2 is a relatively large value, but the resistance value Rp increases and I2 decreases according to the characteristics of the PTC thermistor, resulting in a limited current.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.
This is a circuit in which a constant voltage circuit 1B is added immediately after the slave main circuit 1A in FIG. 2 and 24 V is supplied to the sensor. This is basically the same as FIG.
Although an overload / short-circuit protection circuit can be formed by using only the PTC thermistor Rp as shown in FIG. 6, the PTC thermistor generally has a large variation in operating current and fluctuates even at the ambient temperature. Therefore, it is not suitable for overload / short-circuit protection with high accuracy.

  On the other hand, in the case of the circuits of FIGS. 2 and 3, the current I2 flowing through the PTC thermistor is set to a sufficiently small value with respect to I1 in a normal state (when the overload / short circuit protection circuit is not operating). If the resistance value Rp of the PTC thermistor varies and the variation I2 varies, the influence on I1 can be reduced. Therefore, the variation of the overcurrent detection voltage I1 × R1 can be reduced, and the accuracy is not lowered. In addition, the current I2 in the normal state (the state where the overload / short-circuit protection operation is not performed) is set to a value sufficiently smaller than the operating current of the PTC thermistor. I don't get it.

1 is a circuit diagram showing a first embodiment of the present invention. Circuit diagram showing a second embodiment of the present invention Circuit diagram showing a third embodiment of the present invention FIG. 1 is an explanatory diagram of the operation. Operation explanatory diagram of FIG. 2 and FIG. Circuit diagram that can be assumed from FIG. 2 or FIG. Configuration diagram showing a typical AS-i network configuration example Circuit diagram showing conventional example of AS-i slave overload / short-circuit protection circuit Operation explanatory diagram of FIG. Circuit diagram disclosed in Patent Document 1 Explanation of operation in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... AS-i slave, 1A ... Slave main circuit, 1B ... Constant voltage circuit, L1, L2 ... Coil, C1-C3 ... Capacitor, R1-R7, R10 ... Resistance, Rp ... PTC thermistor, T1-T4 ... Transistor, D1 is a diode.

Claims (2)

AS-i which has a slave main circuit, is supplied with power from an actuator and sensor interface circuit (AS-i) that controls an interface with an input / output device including an actuator, a sensor and a load, and has a power terminal for sensor connection For slave for
The collector of the first transistor is connected to the power source (−) terminal for sensor connection, the emitter of the first transistor is connected to the base of the first resistor and the second transistor, and the base of the first transistor is connected to the collector of the third transistor. And the third resistor are connected to each other, the emitter of the third transistor is connected to the second resistor, the base is connected to the connection point between the collector of the fourth transistor and the fifth resistor, and the emitter of the fourth transistor is connected. The base of the third transistor 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 second resistor. And the other end of the first coil connected to the AS-i power source (+) terminal through the diode and the sensor. The side of the first capacitor that is not connected to the sixth resistor is connected to the side of the first capacitor that is not connected to the sixth resistor. The first, third, and fifth resistors are connected to the side that is not connected. AS connected to the other end of the second coil connected to the i power source (−) terminal, one end of the second capacitor connected to the base of the fourth transistor, and the other end connected to the connection point of the second and seventh resistors. -I overload / short-circuit protection circuit for slave
8. An AS-i slave overload / short-circuit protection circuit, wherein an eighth resistor is connected between the collector of the first transistor and the emitter of the second transistor. 2. The AS-i slave overload / short-circuit protection circuit according to claim 1, wherein a PTC thermistor is connected in series with the eighth resistor.

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