JP3248286B2 - Data transmission equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current type wired data transmission apparatus.

[0002]

2. Description of the Related Art In principle, as shown in FIG. 4, when a transistor 1 is turned on and off on a transmission side, a current flows through a photocoupler 2 on a reception side, and a transmission signal is transmitted to a reception side. . In this case, assuming that the current is 20 mA, for example, if Vcc = 24 V, the resistance value of the resistor 3 connected in series to the photocoupler may be 1.2 kΩ. This configuration is sufficient when a capacitive component having a high capacitance is not loaded on the transmission line. In addition, 4 and 5 are resistors.

[0003]

However, if the transmission line is installed in a place where the noise environment is poor, it becomes necessary to employ a noise filter to remove the noise.
In the case of noise having a low frequency component, the noise removing component tends to be large. In order to prevent the rise characteristic of the current waveform from deteriorating, it is advantageous to reduce the capacitance of the capacitor as a component of the noise filter and increase the inductance of the coil as the other component. However, a filter having a coil having a large inductance generally becomes large and expensive.

[0004]

SUMMARY OF THE INVENTION In order to solve this problem, the present invention provides a noise removing filter having a large capacitance provided at a transmitting / receiving end, and a PNP provided at a transmitting side.
Current supply circuit comprising two transistors forming a pair of a PNP type and an NPN type;
A resistor for detecting as a voltage drop between the emitter of the type transistor and the power supply, another PNP type transistor, and controlling the two transistors so that the current value of this circuit does not exceed a certain value; A base of the PNP transistor for supplying a large current instantaneously so that a data waveform becomes a correct rectangular wave, and for detecting a current;
And a capacitor connected between the emitters.

[0005]

According to the present invention, a small-sized and low-cost capacitive filter (a noise removing filter in which the same performance is ensured by suppressing the inductance of a coil constituting a filter and increasing the capacitance of the capacitor). Hiring,
Waveform distortion due to a capacitor in this filter is prevented to prevent the influence of noise.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) FIG. 1 shows a data transmission apparatus according to an embodiment of the present invention. In FIG. 1, reference numerals 6 and 7 denote a capacitive element for noise removal having a large capacitance provided at a transmitting / receiving end. The filters 8 and 9 are provided on the transmission side, and constitute a current supply circuit with two transistors that form a pair of a PNP type and an NPN type. Reference numeral 10 denotes a resistor for detecting the current value of the current supply circuit as a voltage drop between the emitter of the PNP transistor 8 and a power supply. Reference numeral 11 denotes a PNP transistor having a base connected to the resistor 10. Also,
12 and 13 are NPN transistors, 14 is a capacitor, 15 is a photocoupler, and 16 to 23 are resistors.

In this figure, the rising characteristics of the signal are to be improved by charging the capacitors in the capacitive filters 6 and 7 by the PNP transistor 8 on the transmission side. Since the charge of the capacitor is instantaneously discharged by the NPN transistor 9 at the time of the fall, the waveform distortion does not occur.
The operation is the same as that of the PN transistor. Further, since the PNP-type and NPN-type transistors 8 and 9 are used in series on the transmission side circuit, a current limiting circuit constituted by the transistor 8 is provided so that an excessive load is not applied to the transistors 8 and 9. It also serves to protect the transistor 8 from damage even in the event of a line ground fault. That is, the operating principle is that the resistance 16 is 20 to 100 m.
When the current of A flows, the transistor 11 is turned ON by the voltage drop at the resistance end, and functions to reduce the current value of the transistor 8. However, a capacitor 14 is connected between the emitter and the base of the transistor 11 so that the rising waveform of the signal waveform does not deteriorate due to the current limitation.
And a resistor 10 is inserted between the base of the transistor 11 and the emitter of the transistor 8 so that the current is not limited for a time determined by these time constants, thereby improving the signal waveform.

Here, the capacitance of the capacitors in the capacitive filters 6 and 7 usually requires at least about 1 μF. The sum of the input side and the output side is about 2 μF. When the Vcc power supply voltage is 24 V, if the resistance value of the current limiting resistor 23 on the receiving side is Vcc = 24 V and I = 20 mA, 24 V / 20
mA = 1.2 kΩ. In this case, the time constant T1 of the rising waveform is T1 = 1.2 kΩ × 2 μF = 2.4 mse
c. Even when the communication baud rate is 1200 bps, the pulse width of one pulse is 0.833 msec, and the waveform is greatly distorted (see FIGS. 2A and 2B).

In this type of circuit configuration, if the line is grounded, there is a danger that a large current will flow.
The current is detected by the mold transistor 11 so that a current of a certain value or more does not flow. Assuming that the resistance value is 10Ω, a limit is applied at about 70 mA. Therefore, as described above, such a current limitation becomes a resistive load and deteriorates the rising waveform similarly to the reception-side resistor 23. Therefore, the capacitor 14 is inserted between the emitter and the base of the transistor 11, and the base of the transistor 11 and the transistor By inserting a resistor 10 between the emitters of
It is intended to improve the rising characteristics of the signal waveform by preventing the current from being limited only at the moment of rising. After a certain time (ms) even if the transmission line is grounded
In the case of (ec order), it is possible to prevent a risk that the current is limited and the transistor 8 is destroyed.

(Embodiment 2) FIG. 3 shows another embodiment of the present invention.

In the first embodiment, the current flowing through the photocoupler 15 on the receiving side is the NPN transistor 9 on the transmitting side,
The NP-type transistor 8 charges the capacitor in the noise filter. In the second embodiment, as shown in FIG. 3, the roles of these transistors are reversed. In other words, although waveform distortion does not occur during charging, the waveform is prevented from being distorted by the resistor 24 during discharging.
The discharge is performed by the NPN transistor 9.
Further, current detection is performed by the resistor 17 and the NPN transistor 25, and instantaneous current limit release is performed by the resistor 26 and the capacitor 27. In the first embodiment, the power supply (Vcc) and GND of the transmission unit and the reception unit need to be shared,
The second embodiment has an advantage that it is sufficient to make the GND common. In FIG. 3, 28 and 29 are NP
N-type transistors, 30 to 35 are resistors.

[0013]

As described above, according to the present invention, it is possible to employ a capacitive noise filter by devising a transmission circuit, thereby providing a small-sized, low-cost, safe and reliable current loop type data transmission apparatus. Is what you can do.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a data transmission device according to an embodiment of the present invention.

FIGS. 2 (a) and 2 (b) are waveform diagrams showing a normal waveform of the apparatus and a waveform having deteriorated waveform.

FIG. 3 is a circuit diagram showing a data transmission device according to another embodiment of the present invention.

FIG. 4 is a circuit diagram showing a conventional data transmission device.

[Explanation of symbols]

6,7 Capacitive filter 8,11 PNP transistor 9,12,13,25,28,29 NPN transistor 10 Resistance 14,27 Capacitor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-206220 (JP, A) JP-A-63-78615 (JP, A) JP-A-53-121405 (JP, A) 44748 (JP, U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04L 25/02 H04L 25/03

Claims (2)

(57) [Claims] (1) When one is ON, the other is OFF.
PNP transistor (8) and NPN transistor
Sending a signal by turning on and off the transistor (9)
And the photocoupler (15) that receives this signal by wire
And the receiver comprises a large-capacity controller.
Capacitive filter for noise removal with a capacitor (6)
Through the receiver, the receiver has a large capacitor capacity
Received through a noise removing capacitive filter (7) having
A data transmission device for communicating with said PNP-type transistor.
Current detection resistor connected between the power supply (8) and the power supply
(16) A series connection of a resistor (10) and a capacitor (14)
And the both ends of this capacitor (14) are PN
Connected between emitter and base of P-type transistor (11)
And the collector of the PNP transistor (11)
A data transmission device connected to the base of the PNP transistor (8) . 2. When one is ON, the other is OFF.
PNP transistor (8) and NPN transistor
Sending a signal by turning on and off the transistor (9)
And the photocoupler (15) that receives this signal by wire
And the receiver comprises a large-capacity controller.
Capacitive filter for noise removal with a capacitor (6)
Through the receiver, the receiver has a large capacitor capacity
Received through a noise removing capacitive filter (7) having
A data transmission device for communicating with said NPN-type transistor.
Resistor for current detection connected between the star (9) and GND
(17) A series connection of a resistor (26) and a capacitor (27)
Connected in parallel with each other, and NP is placed at both ends of this capacitor (27).
Connect between emitter and base of N-type transistor (25)
And the collector of this NPN transistor (25) is
A data transmission device connected to the base of the NPN transistor (9) .