JP3012708B2 - Photocoupler output circuit and photocoupler - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photocoupler used for transmitting various signals.

[0002]

2. Description of the Related Art As is well known, a photocoupler is an electronic component in which an electro-optical conversion element and an opto-electric conversion element are enclosed in the same package. Semiconductor elements such as phototransistors and photodiodes are used for the photoelectric conversion elements. FIGS. 5A and 5B show examples in which a two-pole type or three-pole type phototransistor is used, and FIG. 5C shows an example in which a photodiode is used. Since the output current is small, an amplifying transistor may be incorporated as shown in the figure.

When a photocoupler is used, the operation of a semiconductor element used as an optical-electrical conversion element is switching by ON / OFF. In general, when a transistor is used for switching, the operation at ON is performed in a saturation region. The circuit on the output side is configured as described above. However, when the transistor is operated in the saturation region, a large amount of excess carriers are generated in the base, and the turn-on time and the turn-off time (hereinafter, simply referred to as on-time and off-time), especially the off-time, have a characteristic. In order to reduce the load, it is most desirable to select the load current to be the maximum value in the active region and operate in the region just before the saturation.
However, it is actually difficult to select the load current to such a value and operate just before the saturation state because of variations in characteristics, etc., and when operating in the saturation region, the off-time becomes long, and When operated in the active region, there arises a problem that an amount of generated heat increases and an output signal decreases.

Although the phototransistor type photocoupler is relatively inexpensive, it is not suitable for applications requiring a high transmission speed for pulse signal transmission or the like because of the above-mentioned problems. A photodiode type with an amplifying transistor which is expensive but has a short off-time is often used.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem and has an object to shorten the off-time of a photocoupler.

[0006]

According to a first aspect of the present invention, a transistor for amplifying an output signal is connected to an output terminal of a photocoupler, and a photo-electric conversion element of the photocoupler is provided. While operating in the active region, each of the base and collector of the amplification transistor
The same type of excess carrier absorption diodes are connected. In the second invention, a photodiode is used as the photoelectric conversion element, and in a photocoupler having a built-in amplification transistor, the same type of excess carrier absorption diode is provided in each of the base and the collector of the amplification transistor. The connected circuit is enclosed in one package together with the photodiode.

[0007]

In the first aspect of the present invention, the semiconductor element used as the photoelectric conversion element is operated in the active region, so that the off time is shortened. Also, if the base current of the transistor is too large, the collector voltage becomes too low and the transistor operates in the saturation region, and as described above, excess carriers remain in the base, which causes the off time to be extended. In this case, the collector current flows through the diode for absorbing excess carriers, and the excess carriers are absorbed. As a result, a decrease in the collector voltage can be stopped before entering the saturation region, and no excess carriers are generated. For this reason, the amplifying transistor can also be operated in the active region, so that the time required for the OFF operation is greatly reduced as a whole, and an amplified output signal can be obtained.

In the second invention, the built-in amplification transistor can be operated in the active region,
By taking into account the characteristics of the photodiode, which has a shorter off-time than the phototransistor from the beginning, a photocoupler that requires less time for the off-operation and can be handled as a single electronic component can be obtained.

[0009]

Next, an embodiment will be described. FIG. 1 shows light-
This is an example of a photocoupler using a two-pole type phototransistor corresponding to FIG. 5A as an electric conversion element. (a) In the figure, 1a is a photocoupler, 2
Is a light emitting diode, 3a is a phototransistor, R1 is a load resistor connected in series with the phototransistor 3a,
Reference numeral 4 denotes an amplifying transistor, R2 denotes a load resistance of the transistor 4, D1 and D2 denote the same kind of excess carrier absorbing diodes connected to the base and the collector of the transistor 4, and 5 denotes a signal output terminal. The resistance value of the load resistor R1 is selected so that the phototransistor 3a does not malfunction due to noise. The diodes D1 and D2 are connected between the base and the collector of the transistor 4 with the polarities shown in the figure.

In the configuration shown in the figure, when the light emitting diode 2 emits light, a current flows through the phototransistor 3a. The current is supplied from the transistor 4 through the diode D2, and the operation is performed in the active region. This current value is generally selected to be small so that the phototransistor 3a is not thermally damaged, and the OFF operation of the phototransistor 3a is shorter than in the case of the saturation region. Note that the stray capacitance of the base lead acts to increase the off-time, but the effect is relatively small. On the other hand, the transistor 4 can operate in the active region because the collector current flows through the diodes D1 and D2 and the excess carriers are absorbed, so that the off operation is faster than the simple on / off operation performed in the saturation region, and the load is increased. Since the output signal obtained by the resistor R1 is amplified, a large output signal can be obtained. Therefore, even a relatively inexpensive phototransistor-type photocoupler 1a can operate with a short off-time that can be used for high-speed transmission of a pulse signal or the like.

FIG. 2 shows an optical-electrical conversion element of FIG.
This is an embodiment in the case of a photocoupler using a three-pole type phototransistor corresponding to (b) and operating it as a photodiode by grounding the phototransistor.
1b is a photocoupler, 3b is a phototransistor, and other configurations are the same as those in FIG. In the configuration of FIG. 2 as well, the current value of the phototransistor 3b associated with the light emission of the light emitting diode 2 is smaller than the value in the saturation region, and the operation is performed in the active region. On the other hand, the transistor 4 operates in the active region because the collector current flows through the diodes D1 and D2, and excess carriers are absorbed. That is, since the phototransistor is used as a photodiode, the off-time is shortened, and the off-operation of the transistor 4 is also faster, so that the entire off-operation is greatly reduced, and high-speed transmission of a pulse signal or the like is achieved. This enables operation with a short off-time that can be used.

FIG. 3 shows an embodiment in which the present invention is applied to a photodiode type photocoupler having a built-in amplification transistor as shown in FIG. 5 (c), wherein 1c is a photocoupler, 6 is a photodiode, 7 Is a built-in amplifying transistor, and the configuration of an externally added output circuit is the same as that of FIG.

In the configuration shown in FIG. 3, the photodiode 6 has no delay in the off-time like the phototransistors 3a and 3b in FIGS. 1 and 2, but when the amplifying transistor 7 is operated in the saturation region, the off-time is reduced. Becomes longer. Therefore, in this embodiment, the resistance value of the load resistor R1 is selected so that the amplifying transistor 7 operates in the active region. Therefore, the off-time of the amplifying transistor 7 is shortened as compared with the operation in the saturation region. In addition, since the collector current of the transistor 4 of the additional circuit flows through the diodes D1 and D2, surplus carriers are absorbed, and the transistor 4 operates in the active region. Therefore, the off operation becomes faster, and an operation with a shorter off time can be performed.

Incidentally, in FIGS. 1 and 2, when the diodes D1 and D2 are not provided, the on-time is 3 seconds.
While the off time is about 15 to 30 μsec before and after μsec, in the embodiment in which the diodes D1 and D2 are provided, in the case of FIG.
In the case of FIG. 2, the on-time and the off-time are both about 0.02 μsec, which is significantly reduced. Further, in FIG. 3, when the diodes D1 and D2 are not provided, the on-time is about 0.5 μsec and the off-time is about 1 μsec, respectively.
In the embodiment provided with D2, the on-time was almost the same, but the off-time was reduced to about 0.1 μsec.

FIG. 1A and FIGS. 2 and 3 show examples in which the amplifying transistor 4 is of the PNP type. When the amplifying transistor 4 is of the NPN type, for example, FIG. The output circuit may be configured as shown in b), and the circuit configurations in FIGS. 2 and 3 may be configured in accordance with this. Of FIG.
In (b), D3 and D4 are the same kind of excess carrier absorbing diodes connected to the base and the collector of the transistor 4, and R3 is the base resistor.

FIG. 4 is a diagram showing the connection of the embodiment of the second invention, in which a single photocoupler is constructed by applying the present invention to a photodiode type having a built-in amplifying transistor. That is, D5 and D6 are diodes for absorbing the same kind of excess carrier, 8 is a package, and the other is FIG.
Light emitting diode 2 and photodiode 6
Are arranged facing each other, diodes D5 and D6 are respectively connected between the base and the collector of the amplifying transistor 7 connected to the photodiode 6, as shown in FIG. Terminals 9a to
9 e is led out of the package 8 to constitute a photocoupler 1 d which is a single electronic component.

Conventionally, a diode for absorbing excess carriers cannot be connected to the built-in amplifying transistor itself. Therefore, it is necessary to reduce the off-time by providing an additional circuit as shown in FIG. For this reason, the effect of shortening the off-time was small for the parts cost required for the additional circuit as described above, but according to this embodiment, the additional circuit is not required, and mass production is not possible. In other words, the off-time can be reduced without substantially increasing the manufacturing cost.

[0018]

As is clear from the above embodiment, the first embodiment
In the invention, a semiconductor element used as a photoelectric conversion element is operated in an active region, and the same type of excess carrier absorption diode is connected to each of a base and a collector of an amplification transistor. . Therefore, the off-time of the photoelectric conversion element can be reduced, and the off-time can be shortened by operating the amplifying transistor in the active region. The operation speed of the transistor-type photocoupler can be increased, and high-speed operation of the entire circuit can be realized. Further, according to the present invention, it is possible to minimize the influence of the variation in the characteristics of the semiconductor element used as the photoelectric conversion element and the transistor for amplification and the influence of the temperature and the like, and to provide a highly reliable product. Becomes possible.

According to a second aspect of the present invention, there is provided a photodiode type photocoupler having a built-in amplification transistor.
A circuit in which the same type of excess carrier absorbing diode is connected to each of the base and collector of the amplifying transistor is enclosed in one package together with the photodiode. Accordingly, it is possible to further reduce the off-time of the photodiode type without an external additional circuit, and to obtain a photocoupler that can be easily handled as a single electronic component at a low cost.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing a configuration of an embodiment of the first invention.

FIG. 2 is a connection diagram showing a configuration of another embodiment.

FIG. 3 is a connection diagram showing a configuration of another embodiment.

FIG. 4 is a connection diagram showing a configuration of one embodiment of the second invention.

FIG. 5 is a connection diagram showing a configuration of a general photocoupler.

[Explanation of symbols]

 1a to 1d Photocoupler 2 Light emitting diode 3a, 3b Phototransistor 4,7 Amplification transistor 6 Photodiode 8 Package 9a to 9e Terminal R1 Load resistance D1 to D6 Excess carrier absorption diode

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-188020 (JP, A) JP-A-3-97236 (JP, U) Yasuo Suzuki and Takenao Higuchi, “Picture Circuit Circuit Encyclopedia”, No. 1st Edition, Ohmsha Co., Ltd., May 1980, p. 7-8 (58) Field surveyed (Int. Cl. ⁷ , DB name) H03K 17/78 H01L 31/12 H03H 11/02

Claims (2)

(57) [Claims] 1. An output signal amplifying transistor is connected to an output terminal of a photocoupler to operate an opto-electrical conversion element of the photocoupler in an active region, and a base and a collector of the amplifying transistor are respectively provided. An output circuit of a photocoupler, wherein diodes of the same kind for excess carrier absorption are respectively connected. 2. A photocoupler using a photodiode as an optical-electrical conversion element and incorporating an amplifying transistor, wherein the same type of excess carrier absorbing diode is connected to each of the base and the collector of the amplifying transistor. A photocoupler wherein a circuit is enclosed in one package together with the photodiode.