JP3183325B2 - Bus system power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a bus system for transmitting power and communication signals using the same bus,
The present invention relates to a power supply device of a bus system that supplies power to a bus. More specifically, the present invention relates to a power supply device of a bus system which is improved to suppress a voltage change on a bus when a load on the bus fluctuates.

[0002]

2. Description of the Related Art In a bus system for transmitting power and a communication signal using the same bus, the output impedance of a power supply for supplying power to the bus needs to be a predetermined value or more. This is because if the output impedance of the power supply device is low near the frequency of the communication carrier, the amplitude of the communication carrier becomes small, causing attenuation of the communication carrier and making it impossible to increase the communication distance.

[0003] A field bus is connected to the plant control system. The field bus is a bus that connects a control station that controls the plant with sensors, valves, and the like that exist in the plant. Some field buses transmit power and communication signals on the same bus. A device such as a sensor connected to the field bus (hereinafter referred to as a field device) receives a constant DC current from the bus to obtain energy for operating the circuit, and also increases the frequency of the communication carrier on the DC current. The transmission operation is performed by superimposing the changed AC component. The physical layer protocol for fieldbus communication specifies that the impedance in a system including a terminator is approximately 50Ω ± 10Ω within a range of 50 Hz to 39 kHz.

[0004] When the impedance of the terminator is subtracted, the output impedance required for the power supply device is, as shown in FIG.
In the range of 1.6 kHz, it is constant at about 50Ω, and is 1.6
In the range of kHz to 39 kHz, the characteristic increases linearly with frequency. The range of M in FIG. 4 is a range in which the output impedance is defined. In the graph of FIG. 4, the vertical axis indicates the output impedance, and the horizontal axis indicates the frequency of the communication carrier. Both the vertical and horizontal axes are on a logarithmic scale.

Conventionally, a power supply device satisfying such output impedance characteristics has a configuration shown in FIG. This power supply device is used as an example of a test circuit based on the physical layer protocol. In FIG. 5, V _CC is a power supply, R ₁₀ is a resistance of 50Ω, and L ₁ is a 5 mH coil. Coil L ₁
Is connected to the bus 2. Bus 2
Is supplied with power from the power supply device. Power and communication signals are transmitted using the bus 2.

However, the power supply device shown in FIG. 5 has the following problems. A field device is added to or removed from the bus 2 while power is supplied to the bus 2. At this time, the current of the bus 2 changes rapidly. This is because the field devices are connected in parallel between the bus 2 and the ground potential point, and when the number of connected field devices changes, the number of field devices that receive current supply from the bus 2 changes. When the current bus 2 changes rapidly, also fluctuates abruptly current flowing through the coil L _1. Thereby, a large electromotive force at both ends of the coil L ₁ occurs, there is a problem that the voltage on the bus 2 varies greatly.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and a field device is attached to and detached from a bus by adding a circuit in which diodes are connected in parallel with opposite polarities. It is an object of the present invention to realize a power supply device of a bus system in which a voltage change that sometimes occurs on a bus is suppressed.

[0008]

SUMMARY OF THE INVENTION The present invention is a power supply device for a bus system having the following configuration. (1) A power supply device of a bus system connected to a bus system for transmitting power and a communication signal using the same bus and supplying power to the bus, comprising: a reference voltage source for applying a reference voltage to the bus; A resistor and a coil connected in series and a diode are connected in parallel with opposite polarities, and when a voltage higher than the voltage of the communication signal is applied between the terminals of the parallel connection, one side of the parallel connection is connected. A power supply device for a bus system, comprising: a parallel diode circuit connected in parallel to the coil between terminals connected in parallel, with forward bias current flowing through the diode. (2) A power supply device of a bus system connected to a bus system for transmitting power and a communication signal using the same bus and supplying power to the bus, a reference voltage source for generating a reference voltage, a resistor, and An impedance circuit including an impedance element whose impedance value changes according to frequency is connected in series, the resistor is connected to the reference voltage source, the impedance circuit is connected to an output terminal of a power supply device, the reference voltage and A voltage dividing circuit for extracting a divided voltage obtained by internally dividing the output voltage of the power supply device, and a diode are connected in parallel with opposite polarities, and a voltage higher than the voltage of the communication signal is applied between the terminals of the parallel connection. And a forward bias current flows to the diode on one side of the parallel connection, and a parallel diode circuit connected in parallel with the resistor between the terminals of the parallel connection. A drive voltage source for generating a drive voltage for the element, an operational amplifier for applying the divided voltage to a positive input terminal, one end connected to the drive voltage source, and the other end connected to a negative input terminal of the operational amplifier. Connected, the control terminal is a drive transistor connected to the output terminal of the operational amplifier,
One end is connected to the other end of the drive transistor, the other end is provided with a current detection resistor connected to the output end of the power supply device, and the voltage applied to the other end of the drive transistor is connected to the negative input terminal of the operational amplifier. A power supply apparatus for a bus system, wherein the operational amplifier controls the driving of the drive transistor so that a voltage applied to the other end of the drive transistor is equal to the divided voltage. (3) A control transistor is provided instead of the operational amplifier. The control transistor has the control terminal to which the divided voltage is applied, one end connected to the drive voltage source, and the other end connected to a control terminal of the drive transistor. (2) The power supply device for a bus system according to (2), wherein

[0009]

According to the first aspect of the invention, when a voltage higher than the voltage of the communication signal is applied to both ends of the coil, a forward bias current flows to the diode on one side of the parallel diode circuit. As a result, the voltage across the coil is suppressed to the forward voltage of the diode. In the second invention, when a voltage higher than the voltage of the communication signal is applied to both ends of the resistor in the voltage dividing circuit, a forward bias current flows to the diode on one side of the parallel diode circuit. As a result, the voltage across the resistor is suppressed to the forward voltage of the diode, and the voltage on the bus is also suppressed to a certain range. In the third aspect, the control transistor operates in a manner similar to that of the operational amplifier.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of the present invention.
1 that are the same as those in FIG. 5 are given the same reference numerals. In FIG. 1, reference numeral 10 denotes a parallel diode circuit in which diodes D ₁ and D ₂ are connected in parallel with opposite polarities. When a voltage higher than the voltage of the communication signal is applied between the terminals of the parallel diode circuit 10, a forward bias current flows to _{one of} the diodes D ₁ and D ₂ . The diodes D ₁ and D ₂ have such characteristics. The parallel diode circuit 10 has a coil L ₁
Are connected in parallel. Note that one or more diodes D ₁ and D ₂ may be provided.

The operation of the apparatus shown in FIG. 1 will be described. The field devices voltage across the coil L ₁ increases by the detachable bus 2, the voltage across the diode D _1, D ₂ exceeds the forward voltage, the diode D _1, D ₂ is a forward bias current Flow out. Thus, the voltage across the coil L ₁ becomes the forward voltage of the diode, the coil L ₁
Is suppressed, and a decrease in the potential on the bus 2 is also suppressed. A current flows through _{one of} the diodes D ₁ and D ₂ depending on which side of the coil L ₁ has a higher voltage.

FIG. 2 is a block diagram of another embodiment of the present invention. In FIG. 2, _Vr is a reference voltage source for generating a reference voltage. Reference numeral 1 denotes a voltage dividing circuit, which includes resistors R ₁ and R ₂ , capacitors C ₁ and C _2, and a parallel diode circuit 10. Resistors R ₁ and R ₂ are connected in series. One end of the resistor R ₁ is connected to a reference voltage source V _r. The capacitor C ₁ is connected in series with the resistors R ₁ and R ₂ . Capacitor C ₂ is
They are connected in parallel to the series connection portion of the resistor R ₁ and capacitor C _1. One end of the capacitor C ₁ is connected to the output terminal B of the power supply. The parallel diode circuit 10 includes a resistor R ₂
And are connected in parallel. The voltage dividing circuit 1 has a reference voltage V _r
(Reference voltage the reference voltage source V _r outputs also represented by V _r) and takes out the partial pressure V _P obtained by internally dividing the output voltage V ₀ which power supply. Since a capacitor is provided in the voltage dividing circuit 1, the internal division ratio changes according to the frequency of the communication carrier.

V ₁ is a drive voltage source for generating a drive voltage for the device. A ₁ is an operational amplifier, the partial pressure of the voltage divider circuit 1 is applied to the positive input terminal. Tr1 is a drive transistor, one end of which is connected to a drive voltage source V _1,
The other end is connected to the negative input terminal of the operational amplifier A _1, the control terminal is connected to the output terminal of the operational amplifier A _1. R
s is a current detection resistor, one end of which is connected to the other end of the drive transistor Tr1, and the other end of which is connected to the output end B of the power supply device. The current detection resistor Rs generates a voltage according to the current flowing through the drive transistor Tr1.

Reference numeral 3 denotes a simulation additional circuit for generating a signal simulating a communication carrier. In the example of FIG. 2, the additional circuit for simulation 3 is provided to measure the output impedance of the power supply device, and this circuit is not provided in actual communication. In the simulation for adding circuit 3, S ₁ is a signal source for generating an AC voltage of a sine wave, C ₃ are capacitors, RL is the resistance that is the source impedance, I ₁ is a current source which simulates the load current. Generation signal of the signal source S ₁ is a signal simulating a communications carrier.

[0015] In such a circuit, the drive transistor Tr1 is driven by the output of the operational amplifier A _1,
Controlling the current flowing based on the voltage of the drive voltage source V _1. Voltage V _m in accordance with the other end of the drive transistor Tr1 (D point) varies by a voltage flowing to the drive transistor Tr1. The voltage V _m is fed back to the negative input terminal of the operational amplifier A _1. The operational amplifier A ₁ controls the current flowing through the drive transistor Tr1 so as to be equal to the voltage V _p the voltage V _m fetched in the voltage divider circuit 1.

Here, the output impedance of the power supply device is as follows. Voltage divider circuit 1, since the internally dividing output voltage of the reference voltage and the power supply of the reference voltage source V _r, the partial pressure V _p of the voltage divider circuit 1 is given by the following equation. V _p = V _o · (1−K) + V _r · K where K is the internal division ratio of the voltage dividing circuit 1 K = (combined resistance value of the circuit portion composed of R ₁ , C ₁ and C ₂ )
/ R R: dividing circuit 1 overall combined resistance value, R _1: the resistance value of the resistor R ₁ V _r: reference voltage of the reference voltage source V _r, V _o: output voltage of the power supply, also the output voltage V _o Is given by the following equation. V _o = V _m −Rs · I where I: current flowing through the current detection resistor Rs, Rs: resistance value of the current detection resistor Rs In the formula, R >> Rs, and the current flowing through the voltage dividing circuit 1 is current detection. It is omitted because it is sufficiently smaller than the current flowing through the resistor Rs. The following equation from the imaginary short of the operational amplifier A ₁ is satisfied. V _p = V _m ~ V _p from the equation, clearing the V _m becomes as follows. Output impedance Z of _{V o = V o · (1} -K) + V r · K-Rs · I V o · K = V r · K-Rs · I power supply is given by the following equation. Z = −ΔV _o / ΔI = Rs / K As shown in the equation, the output impedance Z is determined only by the ratio between the resistance value Rs of the current detection resistor and the voltage division ratio K. In the circuit of FIG. 2, since a capacitor is provided in the voltage dividing circuit 1, the internal division ratio changes according to the frequency of the communication carrier. Therefore, the output impedance Z given by the equation also changes according to the frequency of the communication carrier.

In the circuit shown in FIG.
So that if connected in parallel with the resistor R _2, the voltage across the resistor R ₂ increases, the voltage across the diode D _1, D ₂ exceeds the forward voltage, current flows through the diode D _1, D ₂ , reduce the partial pressure V _p in the range of V _r ± (forward voltage of the diode D _1, D _2). Therefore, the voltage V _o on bus 2, (forward voltage of the diode _{D 1, D 2) V r} ± - is suppressed to the range of (voltage drop across the current detection resistor Rs). Thus, a voltage change occurring on the bus 2 when a field device is attached to or detached from the bus 2 can be suppressed.

In the circuit of FIG. 2, since the characteristics of the resistor and the coil of the circuit of FIG. 1 are realized by a circuit using transistors, the circuit can be downsized.

FIG. 3 is a block diagram showing another embodiment of the present invention. Circuit of Figure 3 is in the configuration using the output transistor Tr2 in place of the operational amplifier A ₁ in the circuit of Figure 2. The output transistor Tr2 has a voltage dividing circuit 1
Is applied, and one end is connected to the drive voltage source V ₁ ,
The other end is connected to the control terminal of the drive transistor Tr1. By using a transistor instead of the operational amplifier, it is possible to cope with a case where communication is performed using a high-frequency carrier that cannot operate the operational amplifier.

[0020]

According to the present invention, the following effects can be obtained. According to the embodiment of FIG. 1, a parallel diode circuit is connected in parallel to a coil provided in a power supply device. Therefore, when the field device is attached to or detached from the bus, the coil L ₁
When a large electromotive force is generated at both ends of the diode, a forward bias current starts flowing through the diode of the parallel diode circuit. Thereby, a voltage change occurring on the bus when the field device is attached to or detached from the bus can be suppressed. In addition, the suppression of the voltage change occurring on the bus can be realized by the power supply device that satisfies the physical layer protocol of the fieldbus communication. According to the embodiment of FIGS. 2 and 3, in addition to the effects obtained in the embodiment of FIG.
Since the characteristics of the resistor and the coil of the circuit are realized by a circuit using an operational amplifier and a transistor, the circuit can be downsized.

[Brief description of the drawings]

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

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

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

FIG. 4 is a diagram showing output impedance characteristics required for a power supply device.

FIG. 5 is a diagram illustrating a configuration example of a power supply device of a conventional bus system.

[Explanation of symbols]

1 voltage divider 2 bus R _1, R _2, R ₁₀ resistor Rs current detection resistor C _1, C ₂ capacitors Tr1 drive transistor Tr2 control transistor A ₁ operational amplifier Vr reference voltage source V ₁ driving voltage source 10 parallel diode circuit D ₁ , D ₂ diode

Claims (3)

(57) [Claims] 1. A power supply device for a bus system connected to a bus system for transmitting power and a communication signal using the same bus and supplying power to the bus, comprising: a reference voltage source for applying a reference voltage to the bus; A resistor and a coil connected in series to the bus and a diode are connected in parallel with opposite polarities, and when a voltage higher than the communication signal voltage is applied between the terminals of the parallel connection, one of the parallel connection A forward bias current flows through the diode on the side, and a parallel diode circuit connected in parallel with the coil is provided between the terminals of the parallel connection. 2. A power supply device of a bus system connected to a bus system for transmitting power and a communication signal using the same bus and supplying power to the bus, comprising: a reference voltage source for generating a reference voltage; And an impedance circuit including an impedance element whose impedance value changes according to frequency is connected in series, the resistor is connected to the reference voltage source, the impedance circuit is connected to an output terminal of a power supply device, A voltage dividing circuit for extracting a voltage obtained by internally dividing a voltage and an output voltage of the power supply device; and a diode connected in parallel with opposite polarities, and a voltage higher than the voltage of the communication signal is applied between the terminals of the parallel connection. Then, a forward bias current flows into the diode on one side of the parallel connection, and a parallel diode connected in parallel to the resistor is connected between the terminals of the parallel connection. A drive voltage source for generating a drive voltage for the element; an operational amplifier for applying the divided voltage to a positive input terminal; one end connected to the drive voltage source; A drive transistor connected to the output terminal of the operational amplifier; a current detection resistor connected to one end of the drive transistor at one end and connected to the output end of the power supply device at the other end. And feeding back the voltage applied to the other end of the drive transistor to the negative input terminal of the operational amplifier. The operational amplifier drives the drive transistor so that the voltage applied to the other end of the drive transistor becomes equal to the divided voltage. A power supply device for a bus system, comprising: 3. A control transistor is provided instead of the operational amplifier. The control transistor has the control terminal to which the divided voltage is applied, one end connected to the drive voltage source, and the other end connected to the drive transistor. 3. The power supply for a bus system according to claim 2, wherein the power supply is connected to a control terminal.