JP3175569B2 - Bus system power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply for a bus system used in a bus system for transmitting power and communication signals using the same bus.

[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. Devices such as sensors connected to the fieldbus receive constant DC current from the bus to obtain energy for circuit operation, and superimpose AC components at the frequency of the communication carrier on DC current. Performs the transmission operation. According to the physical layer protocol of the fieldbus communication, the impedance in the system including the terminator is 50 Hz to 39 k.
It is defined to be approximately 50Ω ± 10Ω in the range of Hz.

[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. 15 is a range in which the output impedance is defined. In the graph of FIG. 15, 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. Hereinafter, the same coordinate axis is used for the graph indicating the output impedance.

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. 16, V _CC is a power supply,
₁ 50Ω resistor, L ₁ is a coil 5 mH. One end (−side terminal) of the coil L ₁ is connected to the bus 2. The power of the power supply device is supplied to the bus 2. Power and communication signals are transmitted using the bus 2.

[0006]

However, the power supply device shown in FIG. 16 has the following problems. When a DC current flows through the 50 Ω resistor R ₁ in the power supply, power loss occurs, and the output voltage of the power supply decreases by (DC current value) × 50 Ω. The core of the coil is liable to saturation by the DC current flows through the coil L _1. Thus, the coil L ₁ is required having a large cross-sectional area of the magnetic path, the circuit becomes large.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and realizes the characteristics of a resistor and a coil in a circuit using a transistor and an operational amplifier to thereby reduce the output voltage. It is an object of the present invention to realize a power supply device of a bus system which satisfies the physical layer protocol of fieldbus communication, which suppresses the decrease and prevents the circuit from being enlarged.

[0009]

SUMMARY OF THE INVENTION The present invention is a power supply device for a bus system having the following configuration. (1) In 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, and a plurality of impedance elements The impedance element includes an element whose impedance value changes according to frequency, one end is connected to a reference voltage source, the other end is connected to an output end of a power supply device, A voltage dividing circuit for extracting a voltage obtained by internally dividing the output voltage of the power supply device with the reference voltage, an operational amplifier to which a voltage extracted by the voltage dividing circuit is applied to a positive input terminal, and one end connected to a voltage source; The other end is connected to the negative input terminal of the operational amplifier, the control terminal is connected to the output terminal of the operational amplifier, and a drive transistor driven by the output of the operational amplifier is provided. A current detection resistor that is connected to the other end of the drive transistor, the other end is connected to the output terminal of the power supply device, and generates a voltage corresponding to the current flowing through the drive transistor. A bus for feeding back the voltage to the negative input terminal of the operational amplifier, wherein the operational amplifier controls the drive of the drive transistor so that the voltage applied to the other end of the drive transistor becomes equal to the voltage extracted by the voltage dividing circuit; System power supply. (2) A positive input terminal is connected to the reference voltage source, a negative input terminal is connected to an output terminal of the power supply device, and an output terminal is connected to one end of the voltage divider circuit. The bus system according to (1), further comprising a voltage control operational amplifier that compares the actual output voltage of the power supply device and controls a reference voltage applied to one end of the voltage dividing circuit according to the comparison result. Power supply. (3) A capacitor inserted in a path for feeding back the voltage of the other end of the drive transistor to the negative input terminal of the operational amplifier, and a capacitor inserted in a path for feeding back the voltage of the output terminal of the power supply device to the negative input terminal of the operational amplifier. A DC component of the output voltage of the power supply device is fed back to the operational amplifier via the resistor circuit, and an AC component is fed back to the operational amplifier via the capacitor. (1) The power supply of the bus system according to (1). (4) The voltage dividing circuit includes a parallel circuit formed by connecting a series-connected resistor and a capacitor in parallel, a resistor connected in series to the parallel circuit, and a switch connected in parallel to the resistor in the parallel circuit. And a circuit equivalent to a circuit in which a terminator is connected in parallel to the power supply device when the switch is turned off (1).
(2) The power supply of the bus system according to (3). (5) A control transistor is provided instead of the operational amplifier. The control transistor has a control terminal to which a voltage extracted by the voltage dividing circuit is applied, one end connected to the voltage source, and the other end connected to the drive. (1) or (2), which is connected to a control terminal of a transistor.
A power supply for the bus system as described.

[0010]

According to the first aspect, the voltage applied to the other end of the drive transistor is fed back to the negative input terminal of the operational amplifier. The operational amplifier controls the driving of the drive transistor so that the voltage applied to the other end of the drive transistor becomes equal to the voltage extracted by the voltage dividing circuit. In the state of (voltage applied to the other end of the drive transistor) = (voltage extracted by the voltage dividing circuit), the output impedance of the power supply device is (resistance value of current detecting resistor) / (internal dividing ratio of voltage dividing circuit). . In the second invention, the voltage control operational amplifier controls the reference voltage so that the average value of the AC output voltage is equal to the DC output voltage. In the third invention, the DC component of the output voltage of the power supply device is fed back to the operational amplifier via the resistor circuit, and the AC component is fed back to the operational amplifier via the capacitor, so that the operational amplifier has a voltage control operational amplifier. It also works. In the fourth invention, the voltage dividing circuit is configured by a circuit including a resistor, a capacitor, and a switch, and when the switch is turned off, a circuit equivalent to a circuit in which a terminator is connected in parallel to the power supply device is configured. In the fifth invention, a control transistor is provided in place of the operational amplifier, the drive transistor is controlled by the control transistor, and the present invention corresponds to a case where communication is performed using a high-frequency carrier that cannot operate the operational amplifier.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating the principle of the present invention. In FIG. 1, _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 connected in series, and has one end connected to the reference voltage source _Vr and the other end connected to the output terminal B of the power supply device. The voltage dividing circuit 1 extracts a voltage obtained by internally dividing the reference voltage and the output voltage of the power supply device.
In the circuit of FIG. 1, the voltage dividing circuit 1 is composed of only a resistor. However, in the embodiment of the present invention, a frequency dependent impedance element such as a capacitor is used, and the voltage dividing characteristic has a frequency dependence. A ₁ is an operational amplifier, the voltage taken out by 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 voltage source V _1, and the other end is connected to the negative side input terminal of the operational amplifier A _1, the control terminal is connected to the output terminal of the operational amplifier A _1. The drive transistor Tr1 is driven by the output of the operational amplifier A _1. Rs is a current detection resistor. One end is connected to the other end of the drive transistor Tr1, and the other end is connected to the output end B of the power supply device. The current detection resistor Rs is connected to the drive transistor Tr1
Generates a voltage corresponding to the current flowing through

[0012] 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 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 voltage V _p extracted in the voltage divider circuit 1 is given by the following equation. V _p = V _o · (1−K) + V _r · K where K: internal division ratio of voltage divider circuit 1, V _r : reference voltage source V _r
Of the reference voltage V _o: output voltage of the power supply _{device, R 1 = R · K,} R 2 = R (1
-K) R _1, R _2: the resistance value of the resistor _{R 1, R 2, R =} R 1 + R 2 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.

FIG. 2 is a block diagram showing an embodiment of the present invention. In the circuit of FIG. 2, a capacitor is provided in the voltage dividing circuit 1,
The internal division ratio has frequency dependency. In FIG.
C ₁ and C ₂ are capacitors provided in the voltage dividing circuit 1.
The capacitor C ₁ is connected in series with the resistors R ₁ and R ₂ . Capacitor C ₂ are connected in parallel to the series connection portion of the resistor R ₁ and capacitor C _1. Reference numeral 3 denotes an additional circuit for simulation 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.

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.

FIG. 3 is a diagram showing voltage waveforms at various parts when an AC voltage simulating a carrier is applied to the output terminal of the power supply device of FIG. AC voltage V applied from the additional circuit 3 for simulation
_SOURCE is a sine wave voltage having an amplitude of 1 V and a frequency of 100 Hz. Amplitude of the AC voltage V of the output voltage V _o of the power supply unit
Since that is a half of the amplitude of the _SOURCE, the output impedance of the power supply is equal to the source impedance RL of the signal source S _1.

FIG. 4 is a diagram showing output impedance characteristics of the power supply device of FIG. As shown in FIG. 4, in the output impedance of the power supply device, in a band of 50 Hz or less, the resistance value of the current detection resistor Rs (5Ω in the example of FIG. 2) is the output impedance as it is. Moreover, 50 Hz-1.
At 6 kHz, it increases in proportion to the frequency in a band of about 50Ω and 1.6 kHz or more. Such frequency characteristics satisfy the required characteristics in the fieldbus physical layer.

FIG. 5 is a block diagram showing another embodiment of the present invention. In Figure 5, A ₂ is a voltage controlled operational amplifier, C ₄ a capacitor, R ₃ to R ₅ is a resistor. These circuits, voltage controlled operational amplifier A ₂ has positive input terminal connected to a reference voltage source Vr, the output end of the power supply through a resistor circuit negative input terminal of a resistor R ₃ to R ₅ Connected to
The output terminal is connected to one end of the voltage divider 1. Voltage controlled operational amplifier A ₂ compares the actual output voltage V _o of the target output voltage and the power supply of the power supply, and controls the reference voltage applied to the minute one end of the pressure circuit 1 according to the comparison result. In the circuit of FIG. 5, the reference voltage of 2.5 V is amplified eight times,
The output voltage is 0V. In the example shown in FIG. 5, a resistor circuit is provided to amplify the reference voltage. However, when it is not necessary to amplify the reference voltage, the resistor circuit may not be provided.

FIG. 6 is a diagram showing voltage waveforms at various parts when an AC voltage simulating a carrier is applied to the output terminal of the power supply device of FIG. 5 by the additional circuit 3 for simulation. AC voltage V applied from the additional circuit 3 for simulation
_SOURCE is a sine wave voltage having an amplitude of 1 V and a frequency of 100 Hz. From the graph of FIG. 6, the circuit of Figure 5 as compared to the circuit of Figure 2, that the average value of the output voltage V _o of the power supply device is maintained more accurately 20V is improved. In the circuit of FIG. 2, the resistance value of the current detection resistor Rs (5 in the example of FIG. 2).
Ω) and the load current I ₁ (20 mA in the example of FIG. 2), the average value of the output voltage V _o has decreased, but the circuit of FIG. 5 solves this.

FIG. 7 is a diagram showing output impedance characteristics of the power supply device of FIG. In FIG. 7, the output impedance in the low frequency range below 50 Hz is lower than that in the graph of FIG.

FIG. 8 is a block diagram showing another embodiment of the present invention. In FIG. 8, C ₅ drive transistor T
The voltage of r1 other end of the (D point) is a capacitor which is inserted in a path for feeding back to the negative side input terminal of the operational amplifier A _1. In the circuit of Figure 8, feedback to the AC component of the capacitor C ₅ is the output voltage to the operational amplifier A _1, resistor R ₃
Resistor circuit consisting to R ₅ is fed back to the DC component of the output voltage to the operational amplifier A _1. The operational amplifier A ₁ is the feedback acts as an amplifier with a gain of 8 times for the DC component, acting as a buffer with a gain of 1 times with respect to the AC component.

FIG. 9 is a diagram showing voltage waveforms at various parts when an AC voltage simulating a carrier is applied to the output terminal of the power supply device of FIG. 8 by the additional circuit 3 for simulation. As shown in the waveform of FIG. 9, in the circuit of FIG. 8, the same operation as that of the circuit of FIG. 5 is realized by _one operational amplifier A1.

FIG. 10 is a diagram showing output impedance characteristics of the power supply device of FIG. The graph of FIG. 10 has a slight difference in the output impedance in the low frequency range of 50 Hz or less as compared with the graph of FIG. 7, but is considered to be equivalent to the characteristics of the graph of FIG. be able to. In the circuit of FIG. 8, the same characteristics as those of the circuit of FIG. 5 can be realized by _one operational amplifier A1.

FIG. 11 is a block diagram showing another embodiment of the present invention. The difference between the circuit of FIG. 11 and the circuit of FIG. 8 is that the resistor R ₆ is connected in series with the capacitor C ₂ and that the setting switch SW is connected in parallel with the resistor R ₆ .

The circuit of FIG. 11 has the same characteristics as the circuit of FIG. 8 when the setting switch SW is closed. When the setting switch SW is open, the output impedance characteristics shown in FIG. 1.6 kHz as shown in FIG.
In the above-mentioned band, the output impedance is maintained at 100Ω, and the same characteristics as when one terminator is connected in parallel to the power supply device of FIG. 8 can be obtained without adding circuit components. The terminator is, for example, 100
This is a circuit in which an Ω resistor and a 1 μF capacitor are connected in series.

FIG. 13 is a block diagram showing another embodiment of the present invention. The circuit of FIG. 13 is the operational amplifier A ₁ of the circuit of FIG.
Instead of using the output transistor Tr2. The output transistor Tr2, the voltage taken out by the voltage divider circuit 1 is applied to the control terminal, one end of which is connected to a 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.

FIG. 14 is a block diagram showing another embodiment of the present invention. The circuit of FIG. 14 is also the operational amplifier A ₁ of the circuit of FIG.
Instead of using the output transistor Tr2. The connection of the output transistor Tr2 is similar to the circuit of FIG. The circuit of FIG. 14 can also cope with a case where communication is performed using a high-frequency carrier that cannot operate the operational amplifier.

[0028]

According to the present invention, since the characteristics of the resistor and the coil are realized by the circuit using the transistor and the operational amplifier, the problem of the power supply device which satisfies the conventional physical layer protocol of the field bus communication is solved. it can. That is, in the conventional power supply device, when a DC current flows through a resistor connected in series to the power supply, the output voltage of the power supply device decreases by (DC current value) × (resistance value). And a circuit using an operational amplifier can suppress the reduction of the output voltage. Further, in the conventional power supply device, since a core of the coil tends to be saturated when a DC current flows through the coil, a coil having a large cross-sectional area of a magnetic path is required, and the circuit becomes large. Since there is no coil in the present invention, it is possible to prevent the circuit from becoming large. As described above, according to the present invention, it is possible to realize a power supply device for a bus system in which a decrease in output voltage is suppressed and a circuit size is prevented from increasing.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present invention.

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

FIG. 3 is a diagram illustrating voltage waveforms at various parts of the power supply device of FIG. 2;

FIG. 4 is a diagram illustrating output impedance characteristics of the power supply device of FIG. 2;

FIG. 5 is a configuration diagram showing another embodiment of the present invention.

6 is a diagram showing voltage waveforms at various parts of the power supply device of FIG.

FIG. 7 is a diagram illustrating output impedance characteristics of the power supply device of FIG. 5;

FIG. 8 is a configuration diagram showing another embodiment of the present invention.

9 is a diagram illustrating voltage waveforms at various parts of the power supply device of FIG.

FIG. 10 is a diagram illustrating output impedance characteristics of the power supply device of FIG. 8;

FIG. 11 is a configuration diagram showing another embodiment of the present invention.

12 is a diagram showing output impedance characteristics of the power supply device of FIG.

FIG. 13 is a configuration diagram showing another embodiment of the present invention.

FIG. 14 is a configuration diagram showing another embodiment of the present invention.

FIG. 15 is a diagram showing output impedance characteristics required for a power supply device.

FIG. 16 is a diagram showing a configuration example of a power supply device of a conventional bus system.

[Explanation of symbols]

1 voltage divider 2 bus R ₁ to R ₆ resistor Rs current detection resistor C ₁ -C ₆ capacitor Tr1 drive transistor Tr2 control transistor A ₁ operational amplifier A ₂ voltage controlled operational amplifier Vr reference voltage source V ₁ voltage source SW switch

Claims (5)

(57) [Claims] 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 generating a reference voltage; An impedance element is connected, and the impedance element includes an element whose impedance value changes according to a frequency. One end is connected to a reference voltage source, and the other end is connected to an output end of a power supply device. A voltage divider circuit for extracting a voltage obtained by internally dividing the reference voltage and the output voltage of the power supply device; an operational amplifier for applying the voltage extracted by the voltage divider circuit to a positive input terminal; one end connected to a voltage source The other end is connected to the negative input terminal of the operational amplifier, the control terminal is connected to the output terminal of the operational amplifier, and the drive transistor is driven by the output of the operational amplifier. One end is connected to the other end of the drive transistor, the other end is connected to the output end of the power supply device, and a current detection resistor that generates a voltage corresponding to the current flowing through the drive transistor. The voltage applied to the terminal is fed back to the negative input terminal of the operational amplifier, and the operational amplifier controls the drive of the drive transistor so that the voltage applied to the other end of the drive transistor becomes equal to the voltage extracted by the voltage dividing circuit. And power supply for the bus system. 2. A power supply device comprising: a positive input terminal connected to the reference voltage source; a negative input terminal connected to an output terminal of the power supply; and an output terminal connected to one end of the voltage divider circuit. 2. A voltage control operational amplifier for comparing a voltage with an actual output voltage of a power supply device and controlling a reference voltage applied to one end of a voltage dividing circuit according to a result of the comparison. Power supply for bus system. 3. A capacitor inserted in a path for feeding back the voltage at the other end of the drive transistor to the negative input terminal of the operational amplifier, and a voltage at the output terminal of the power supply device is fed back to the negative input terminal of the operational amplifier. And a resistor circuit inserted in the path, wherein a DC component of the output voltage of the power supply device is fed back to the operational amplifier via the resistor circuit, and an AC component is fed back to the operational amplifier via the capacitor. The power supply device for a bus system according to claim 1, wherein 4. The voltage dividing circuit is a parallel circuit in which a resistor and a capacitor connected in series are connected in parallel, a resistor connected in series to the parallel circuit, and a resistor connected in parallel to the resistor in the parallel circuit. 4. The bus system according to claim 1, wherein the bus system comprises a switch, and when the switch is turned off, forms a circuit equivalent to a circuit in which a terminator is connected in parallel to a power supply device. Power supply. 5. A control transistor is provided in place of the operational amplifier. The control transistor has a control terminal to which a voltage extracted by the voltage dividing circuit is applied, one end connected to the voltage source, and the other end connected to the voltage source. The power supply device for a bus system according to claim 1, wherein the power supply device is connected to a control terminal of the drive transistor.