JPH08149085A - Data transmission device - Google Patents

Abstract

PURPOSE: To set the peak current flowing through the light emitting element of the photocoupler and the holding current independent of each other by the use of a simple circuit constitution in a data transmission device which performs data transmission between two equipments by means of the photocoupler. CONSTITUTION: A receiving equipment 4 is provided with a photocoupler 10, and a transmitting equipment 2 connects and disconnects the path for energization of a light emitting diode Df of the photocoupler 10 in response to the transmit data. Thus the data are transmitted. The speed-up capacitors C1 and C2 are connected in parallel to the holding current limit resistors R1 and RB which are provided on the path for energization of the diode Df. So that a sudden rise is secured for the current (i) when the energization is started. Then a resistor RA is connected in series to the capacitor C2. Therefore, it is possible to set the peak current generated at the start of energization of the diode Df independently of the holding current by controlling the resistance value of the register RA.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transmission device for transmitting data using a photocoupler composed of a light emitting element and a photoelectric conversion element.

[0002]

2. Description of the Related Art Conventionally, as a data transmission device for performing data transmission between two devices a and b, for example, FIG.
As shown in FIG. 5, a photocoupler PC including a light emitting diode Df and a phototransistor Trf is provided in the receiving side device b for receiving data, and the light emitting diode of the photocoupler PC is provided between the transmitting side device a and the receiving side device b. By connecting a pair of positive and negative communication lines L1 and L2 for energizing Df, the power supply voltage VCC is applied to the positive side communication line L1 connected to the anode side of the light emitting diode Df in the transmitting device a. By connecting the negative side communication line L2 connected to the cathode side of the light emitting diode Df to the ground line according to the transmission data via the transistor Tr1,
There is known a device configured to control light emission / non-light emission of the light emitting diode Df according to transmission data.

As described above, in the device for transmitting data using the photocoupler PC, the input (light emitting diode Df) and the output (phototransistor Trf) of the photocoupler PC are used.
Since and are electrically insulated, the loop current flowing between the devices a and b can be significantly reduced due to fluctuations in the ground potential of the devices a and b, which reduces the error rate of the transmission data and reduces the loop current. Elimination of deterioration and destruction of circuit elements due to
And so on.

By the way, in this type of device, in order to operate the photocoupler PC without deterioration or destruction, it is necessary to limit the current flowing through the light emitting diode Df to the maximum allowable current (usually several tens mA) or less. . For this reason, conventionally, as shown in FIG. 2, resistors R1, R2, and R3 are provided in the energizing paths of the light emitting diode Df in the transmitting side device a and the receiving side device b, and the light emitting diode Df is turned on when the transistor Tr1 is turned on. The current i flowing in the current is limited to a predetermined current (hereinafter referred to as a hold current) iH shown in FIG.

Further, when the resistors R1 to R3 are provided in the energizing path of the light emitting diode Df and the energizing current i is limited to the hold current iH, the transistor Tr1 is turned on and then the light emitting diode Df is turned on. The current i flowing through the threshold current exceeds the threshold current, and it takes time for the light emitting diode Df to emit light.

That is, the light emitting diode Df does not emit light until the energizing current i thereof reaches the threshold current. Therefore, in order to perform data communication with high accuracy, the current i of the light emitting diode Df is turned on when the transistor Tr1 is turned on. However, when the resistors R1 to R3 are provided in the energizing path of the light emitting diode Df as described above, the time constant determined by the resistance value of the energizing path and the stray capacitance is To increase, turn on transistor Tr1
After that, the response time until the light emitting diode Df emits light becomes long.

Therefore, conventionally, in order to eliminate such a response delay, for example, as shown in FIG.
Of R3, speed-up capacitors C1 and C2 are respectively connected in parallel to resistors R1 and R2 arranged on the anode side of the light emitting diode Df, and resistors R1 and R2 are connected immediately after the transistor Tr1 is turned on. Limited current i
Is bypassed by speed-up capacitors C1 and C2.

[0008]

Thus, the resistor R1
, R2 in parallel with speed-up capacitors C1, C2
In the case of connecting, the current i flowing through the light emitting diode Df rises immediately after the transistor Tr1 is turned on, so that the light emission delay of the light emitting diode Df (in other words, the data transmission delay) can be prevented. But,
At this time, the current i flowing through the light emitting diode Df becomes larger than the hold current iH limited by the resistors R1 to R3, as shown in FIG. 3, so that not only the hold current iH but also the current at that time is obtained. The peak current iP must be limited to the maximum allowable current at which the light emitting diode Df can operate normally.

In this case, if the resistance values of the resistors R1, R2 and R3 are reduced in order to secure the hold current iH, the peak current iP becomes too high and the light emitting diode Df of the photocoupler PC is deteriorated and extended. However, this leads to destruction, and with the increase of the peak current iP, the problem that the radiation noise from the communication device increases, and conversely, in order to suppress the peak current iP, the resistors R1 and R2
, R3 is increased, the hold current iH becomes too low, the light output of the light emitting diode Df in the photocoupler PC becomes insufficient, and the output waveform of the photocoupler PC (that is, the ON / OFF waveform of the phototransistor Trf) changes. It may become shorter than the input waveform, and erroneous data may be output to the receiving device b.

Therefore, when the speed-up capacitors C1 and C2 are connected in parallel with the resistors R1 and R2 for limiting the conduction current of the light emitting diode Df, the hold current iH
Can make the light emitting diode Df emit light normally,
Moreover, the values of the resistors R1 and R2 and the capacitors C1 and C2 must be set within a range in which the peak current iP does not cause deterioration of the light emitting diode Df.
It was difficult to individually set the hold current iH and the hold current iH to the optimum values.

That is, the peak current iP and the hold current iH are not determined only by the resistors R1 and R2 and the capacitors C1 and C2, but the power supply voltage VCC and the light emitting diode Df including the communication lines L1 and L2 are energized. Since it is determined by the characteristics of the entire path, it is necessary to review the entire transmission equipment in order to set these peak current iP and hold current iH individually. Even if set to, the power supply voltage Vcc and the communication lines L1 and L2 between the devices a and b
Since the characteristics change when the length of the peak current is changed, it is practically difficult to individually set the peak current iP and the hold current iH in the conventional device.

In FIG. 2, the receiving device b is
In the series circuit consisting of the resistor R2 for limiting the energizing current and the light emitting diode Df, the resistor R bypassing this circuit is used.
4 is provided, this resistor R4 shunts the current flowing in the light emitting diode Df, and the optical output of the light emitting diode Df increases the currents in the communication lines L1 and L2 required to drive the phototransistor Trf. It can be set to improve the noise resistance of the photocoupler PC. In the data transmission device provided with such a resistor R4, in order to individually set the peak current iP and the hold current iH as described above, the current value shunted to the resistor R4 is also taken into consideration. Since it is necessary, it becomes more difficult to set each of these current values.

The present invention has been made in view of these problems, and in a data transmission device for performing data transmission using a photocoupler, it is possible to individually set the peak current and the hold current with a simple circuit configuration. The purpose is to do.

[0014]

In order to achieve the above object, the invention according to claim 1 is a light emitting element, and a photoelectric conversion element for receiving light from the light emitting element and converting the light into an electric signal. A transmission device transmits transmission data from the transmission side device to the reception side device by providing a photo coupler consisting of, on the reception side device, and the transmission side device connecting / disconnecting the conduction path of the light emitting element according to the transmission data. A data transmission device that comprises one or a plurality of energization current limiting resistors that are connected in series to an energization path of the light emitting element and that limit a current when the light emitting element is energized to a predetermined operating current, Connected in parallel to at least one of the current limiting resistors,
The light emitting element is provided with a speed-up capacitor that sharply rises the energization current at the start of energization, and further, at least one of the speed-up capacitors is connected in series, and the peak current immediately after the start of energization of the light-emitting element becomes a predetermined current. It is characterized by including a peak current limiting resistor for limiting.

The invention described in claim 2 is the same as claim 1
In the data transmission device according to, the current control circuit formed by connecting the series circuit of the speed-up capacitor and the peak current limiting resistor in parallel with the energization current limiting resistor in the receiving side device. Is provided in the energization path of the light emitting element.

The invention described in claim 3 is the same as that of claim 2
In the data transmission device described in the above item 1, a threshold setting resistor is connected in parallel to a series circuit including the current control circuit and the light emitting element.

[0017]

In the data transmission device according to claim 1 configured as described above, one or a plurality of energization current limiting resistors are connected in series to the energization path of the light emitting element. Therefore, when the light emitting element is energized (at steady state),
The energizing current (hold current) is limited by the energizing current limiting resistor.

Further, since a speed-up capacitor is connected in parallel to at least one of the energizing current limiting resistors, the speed-up capacitor is connected to the energizing current limiting resistor immediately after the light emitting element is energized. A current path that bypasses the container. Therefore, immediately after the start of energization of the light emitting element, the energizing current is quickly raised by the speed-up capacitor.

On the other hand, the energization current of the light emitting element immediately after the start of energization is larger than the hold current because it is bypassed to the speed-up capacitor, but at least one of the speed-up capacitors is connected in series with a peak current limiting resistor. Therefore, the energizing current at this time is limited by the peak current limiting resistor.

Therefore, according to the data transmission device of the present invention, the peak current generated when the energization of the light emitting element is started in order to cause the light emitting element to emit light, and the hold current thereafter, the peak current limiting resistor and the peak current limiting resistor are provided. It can be set individually by the resistance value of the energization current limiting resistor, and the adjustment work to set the hold current to the optimum value is extremely easy while suppressing the peak current within the normal operating range of the light emitting element. It will be possible.

Further, when the power supply voltage or the path length of the light-emitting element energization path (in other words, the transmission path) is changed, the rising characteristics of the current immediately after the light-emission element starts energization, or the like, or the photocoupler to be used. Even if the current characteristics of the LEDs are different, if the resistance value of each resistor is adjusted according to the characteristics, the peak current and the hold current can be set individually to optimize the rising characteristics of the conduction current of the light emitting element. Can be set to. Therefore, according to the present invention, even a system in which the data transmission path or the photocoupler itself is different can be easily diverted.

Next, in the data transmission device according to the second aspect of the present invention, it is formed by connecting the series circuit of the speed-up capacitor and the peak current limiting resistor and the energization current limiting resistor in parallel. A current control circuit is provided in the receiving device. Therefore, the peak current and the hold current can be adjusted only by the receiving side device provided with the photocoupler, and the adjustment work becomes easier.

That is, when a plurality of energizing current limiting resistors and peak current limiting resistors are provided in the energizing path of the light emitting element, the hold current and the peak current are the resistance values of any one of these resistors. Can be adjusted by changing. However, if a current control circuit consisting of a current-carrying current limiting resistor, a speed-up capacitor, and a peak current limiting resistor is provided in the transmitting device and not in the receiving device, hold In order to adjust the current and peak current, it is necessary to adjust the resistance value of each resistor in the transmitter device while checking the hold current and peak current in the receiver device, which makes the adjustment work complicated. Become. On the other hand, in the present invention, the receiving side device is provided with the current control circuit. Therefore, when adjusting the hold current and the peak current, the receiving side device has a resistor for controlling the conduction current in the current control circuit and It is only necessary to adjust the resistance value of the peak current limiting resistor, and this adjustment work can be performed easily.

In the data transmission device according to the third aspect of the invention, the threshold setting resistor is connected in parallel to the series circuit including the current control circuit and the light emitting element. Therefore, when the light emitting element is energized, a part of the energizing current flowing in the energizing path of the light emitting element is shunted by the threshold setting resistor, and the light output of the light emitting element is transferred to the photoelectric conversion element. The current of the communication line required for driving can be set high, and the noise resistance of the photocoupler PC is improved.

Even if such a threshold setting resistor is provided, the current is supplied to the light emitting element through the current control circuit, so that the peak current and the hold current are controlled by this current control. It can be set individually by adjusting the resistance values of the energizing current control resistor and the peak current limiting resistor in the circuit. Therefore, according to the present invention, the peak current and the hold current can be simplified even in the data transmission device with the threshold setting resistor, which has conventionally been extremely difficult to individually set the peak current and the hold current. You will be able to adjust to.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a CD-RO in which image / sound data is stored.
Based on the driver device 2 that reads data from M and the image / sound data read by this driver device 2, C
In an AV (audio-visual) device for an automobile, which comprises a reproducing device 4 for displaying an image on a display device such as an RT or a liquid crystal display or for producing sound from a speaker, between the driver device 2 and the reproducing device 4. FIG. 3 is an electric circuit diagram showing a configuration of a data transmission device of an embodiment, which is used to perform data transmission in.

As shown in FIG. 1, in the data transmission apparatus of the present embodiment, as in the conventional apparatus shown in FIG. 2, the reproducing apparatus 4 serving as the receiving side device is provided with a photo diode including a light emitting diode Df and a phototransistor Trf. A coupler 10 is provided, and the reproducing device 4 and the driver device 2 serving as a receiving side device are connected by a pair of positive and negative communication lines L1 and L2 for energizing the light emitting diode Df.

In the driver device 2, the resistor R1 and the speed-up capacitor C are connected to the positive side communication line L1 connected to the anode side of the light emitting diode Df.
The power supply voltage Vcc is constantly applied through the parallel circuit with 1.
The negative electrode side communication line L2 connected to the cathode side of the light emitting diode Df is connected to the transistor T via a resistor R3.
The collector of r1 is connected.

The transistor Tr1 is a grounding transistor whose emitter is grounded, and the control signal from the transmission circuit 6 is input to its base. The transmission circuit 6 is
The image / sound data read from the CD-ROM by a reading pickup (not shown) is taken in as transmission data, and the transistor Tr1 is turned on according to this transmission data.
-Turn it OFF to switch between energization and de-energization of the light emitting diode Df.

As a result, on the reproducing device 4 side, the light emitting diode Df blinks according to the image / audio data read from the CD-ROM on the driver device 2 side, and the phototransistor Trf receives a current according to the blinking state. Flows. When a current flows through the phototransistor Trf,
The reception circuit 8 reproduces the image / sound data according to the current, and outputs this as reception data to a demodulation circuit (not shown) for demodulating a display signal or a sound signal.

On the other hand, in the reproducing device 4, a resistor RB for limiting a current supply is connected in series to a current path connecting the anode side of the light emitting diode Df and the positive side communication line L1, and this resistor RB is connected to this resistor RB. Has a series circuit of a speed-up capacitor C2 and a resistor RA connected in parallel. Further, between the energization path connecting the cathode side of the light emitting diode Df and the negative side communication line L2, and the energization path connecting the resistor RB and the positive side communication line L2,
It is connected with a resistor R4 for setting the threshold.

In the data transmission apparatus of this embodiment having the above-described structure, the resistor R1, the communication line L1, the resistor RB, and the light emitting diode Df are maintained for a while after the transistor Tr1 is held in the ON state. , The communication line L2, the resistor R3, and the transistor Tr1 provide a current i to the light emitting diode Df, and a resistor R4 has a bypass current bypassing the resistor RB and the light emitting diode Df. Therefore, the current i (= hold current iH) flowing through the light emitting diode Df at this time is determined by the resistance values of these respective portions.

On the other hand, the transistor Tr1 is switched from OFF to ON.
Immediately after being switched to (in other words, the light emitting diode Df
Immediately after the start of energization, the current i flowing through the light emitting diode Df gradually increases with a time constant determined by the resistance value of each part and the stray capacitance of the energizing path of the light emitting diode Df (in particular, the communication lines L1 and L2). The speed-up capacitors C1 and C2 are added to the resistors R1 and RB.
As shown in FIG. 3, the rising characteristic of the current i becomes steep by the speed-up capacitors C1 and C2, and the light-emitting diode Df has the following characteristics.
A peak current iP larger than the hold current iH in the normal state temporarily flows.

If the peak current iP becomes too high, the light emitting diode Df is deteriorated and eventually destroyed. Therefore, the peak current iP must be limited to the maximum allowable current of the light emitting diode Df or less. In the embodiment, since the resistor RA is connected in series to the speed-up capacitor C2 provided on the reproducing device 4 side, the peak current iP is limited by the resistor RA.

Therefore, according to the data transmission apparatus of this embodiment, the transistor Tr1 is switched from OFF to ON and the rising characteristic of the conduction current i of the light emitting diode Df immediately after the conduction of the light emitting diode Df is started is speeded up by the capacitor. Not only can it be made steep by C1 and C2, but the peak current iP generated at that time can be adjusted by the resistor R
It can be arbitrarily set by the resistance value of A. Also,
The hold current iH can be arbitrarily set by adjusting the resistance value of the resistor RB.

Therefore, it is possible to extremely easily perform the adjustment work for setting the hold current iH to the optimum value while suppressing the peak current iP within the normal operable range of the light emitting diode Df. Current i
To set H individually, it is not necessary to reexamine the entire transmission device as in the conventional device.

Further, the rise characteristic of the current i immediately after the start of energization of the light emitting diode Df is changed in accordance with the change of the power supply voltage Vcc or the path length of the energizing path of the light emitting diode Df (particularly the communication lines L1, L2). If you do, or
Even if the current characteristics of the photocoupler used differ, the peak current iP and the hold current iH can be individually set according to the characteristics, and the rising characteristics of the conduction current of the light emitting diode Df can be optimally set. Therefore, according to this embodiment, even a system in which the data transmission path or the photocoupler itself is different can be easily diverted.

Further, according to the present embodiment, since the resistor RA capable of adjusting the peak current iP is provided on the reproducing device 4 side, when the peak current iP and the hold current iH are actually adjusted, the reproduction is performed. It suffices to adjust the resistance values of the resistors RA and RB on the device 4 side, and the adjustment work can be performed more easily.

Furthermore, in the present embodiment, a circuit as the current control circuit composed of a speed-up capacitor C2, a resistor RA and a resistor RB, and a light emitting diode Df.
In series circuit with, resistor R4 for threshold setting
Are connected in parallel, a part of the current supplied from the driver device 2 side is shunted by the resistor R4 when the light emitting diode Df is energized, and the noise resistance of the photocoupler PC is improved. Even if such a threshold setting resistor R4 is provided, the peak current iP and the hold current iH can be individually set by adjusting the resistance values of the resistors RA and RB.

Although one embodiment of the present invention has been described above, the present invention is not limited to such an embodiment and can take various modes. For example, in the present embodiment, the data transmission apparatus including the threshold setting resistor R4 for shunting the current flowing through the light emitting diode Df has been described. However, such a threshold setting resistor R4 is provided. Even in the case of a non-existent system, the same effects as described above can be obtained by applying the present invention.
Further, in the present embodiment, the case where the present invention is applied to the AV device for the automobile, which includes the driver device 2 and the reproducing device 4, has been described. However, the present invention uses the photocoupler to transmit data between two devices. As long as it is a device that performs the above, it can be applied not only to automobiles but also to any device.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of a data transmission device according to an embodiment.

FIG. 2 is an electric circuit diagram showing a configuration of a conventional data transmission device.

FIG. 3 is an explanatory diagram illustrating a peak current and a hold current that flow when a light emitting diode forming a photocoupler is energized.

[Explanation of symbols]

2 ... Driver device 4 ... Reproducing device 6 ... Transmission circuit
8 ... Receiving circuit 10 ... Photo coupler Df ... Light emitting diode (light emitting element) Trf ... Photo transistor (photoelectric conversion element) Tr1 ...
Transistors R1, RB, R3 ... Resistors (for energizing current limiting) C1, C2 ... Speed-up capacitors RA ... Resistors (for peak current limiting) R4 ... Resistors (for threshold setting)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01L 31/12 F H03H 11/02 A 8628-5J H03K 17/78 E

Claims (3)

[Claims] 1. A photocoupler comprising a light emitting element and a photoelectric conversion element for receiving light from the light emitting element and converting the light into an electric signal is provided in a receiving side device, and the light emitting element is provided in the transmitting side device. A data transmission device for transmitting transmission data from a transmitting side device to a receiving side device by connecting / disconnecting the energization path of the light emitting element in accordance with the transmission data, the light emitting element being connected in series to the energization path of the light emitting element. The device is provided with one or more energization current limiting resistors for limiting the current when the element is energized to a predetermined operating current, and is connected in parallel to at least one of the energization current limiting resistors, and when the light emitting element energization is started. Is provided with a speed-up capacitor for making the rising of the energization current steep, and further, at least one of the speed-up capacitors is connected in series, and the peak current immediately after the energization of the light emitting element is started. A data transmission device comprising a peak current limiting resistor for limiting a predetermined current. 2. The light emitting device in the receiving side device, comprising a current control circuit in which a series circuit of the speed-up capacitor and the peak current limiting resistor and the energization current limiting resistor are connected in parallel. The data transmission device according to claim 1, wherein the data transmission device is provided in an energization path of the element. 3. The data transmission device according to claim 2, wherein a threshold setting resistor is connected in parallel to a series circuit composed of the current control circuit and the light emitting element.