Abstract:
An optocoupler having a driving traic and at least one normally-on driving element couple in series to the driving triac. A light emitting element turns on the driving triac at a time when a phase of a load current is at about 0°. The normally-on driving element is composed of either a MOSFET, or optionally a relay, and an associated element for turning off MOSFET, or relay, at a time when a phase of the load current is about 90°. The arrangement prevents an inrush current or commutation failure, and provides an optocoupler which can be turned off with prescribed timing. Alternative embodiments are disclosed for an optocoupler that can turn itself off when an abnormality occurs, for example, when an ambient temperature rises to an extremely high level.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optocoupler such as a solid-state relay, etc., and more particularly to an optocoupler capable of controlling an off-state thereof with a prescribed timing. 
     2. Description of the Related Art 
     A conventional solid-state relay  900 , as illustrated in FIG. 9, has a structure including: a light emitting element  901  (generally, a GaAs LED or a GaAlAs LED) which converts an electric signal into a light: a light receiving element  902  (generally, a phototriac) which converts a light into an electric signal; a driving triac  903  which is coupled to the light receiving element  902 : and a resistance element  904 . The driving triac  903  is also coupled to a load  905 . 
     When an input current is applied to the light emitting element  901 , the light receiving element  902  is activated and the light receiving element  902  drives the driving triac  903  so that the driving triac  903  is switched over to an on-state. 
     Once the triac  903  is turned on, even if the input current is turned off immediately afterward, the driving triac  903  maintains the on-state until a load current flowing therethrough reaches a zero value (which is a basic operation of solid-state relays). 
     One method for activating the solid-state relay  900  involves phase control. As illustrated in FIG. 10A, phase control is realized by adjusting the timing of turning on the driving triac  903  based on the timing of applying the input current, thereby controlling the load current. Arbitrary control of the load current is generally possible depending on the application timing of the input current (FIGS. 10A,  10 B and  10 C). 
     Now, consider the case where the load  905  must be activated with a half amount of electric power (FIG. 10B) as compared to that required for a full-phase on-driving mode. Activating the load  905  with the half amount of electric power in comparison to that of the full-phase on-driving mode may be achieved by setting the timing of the input current application, as illustrated in FIG. 10B, so as to occur at phase angles of 90° and 270° of a load current waveform. 
     As illustrated in FIG. 11, when the input current is applied, the load current is at a peak. Thus, a substantial inrush current may flow into the solid-state relay  900  immediately after the input current is applied, depending on the type of the load  905 , thereby adversely affecting the solid-state relay  900 . 
     Once the driving triac  903  is turned on, even if the input current is turned off immediately afterward, the driving triac  903  maintains an on-state until the load current flowing therethrough reaches a zero value. is As illustrated in FIG. 12, especially in the case of a load which gives rise to a load current whose phase is shifted with respect to the phase of a supply voltage, e.g., an inductive load, a steep voltage is applied to the triac  903  as the triac  903  is turned off. Accordingly, there is a possibility that commutation failure may occur. 
     As described above, the solid-state relay  900  has characteristics such that once the driving triac  903  is turned on, the driving triac  903  maintains the on-state until the load current flowing therethrough reaches a zero value. Therefore, the problems described above may arise depending on the application timing of the input current or the type of the load. 
     The conventional solid-state relay  900  is not provided with a function of compulsorily turning off the triac  903  when the ambient temperature rises to an extremely high level. At present. the product safety Is sought more than ever. Accordingly, it is desired that any solid-state relay be provided with a function of turning itself off when any abnormality occurs. 
     As described above, the solid-state relay  900  has characteristics such that once the driving triac  903  is turned on, the driving triac  903  maintains the on-state until the load current flowing therethrough reaches a zero value. Therefore problems such as an increase in the inrush current, commutation failure, etc., may arise depending on the application timing of the input current, the type of the load, etc. 
     SUMMARY OF THE INVENTION 
     An optocoupler of the present invention includes a driving triac and at least one normally-on driving element coupled in series to the driving triac, thereby accomplishing objects of the present invention. 
     The optocoupler may be a solid-state relay. 
     The driving element may include a MOSFET. 
     The driving element may include a mechanical relay. 
     A timing of turning off the driving element may be synchronized with a phase point substantially corresponding to 0 V level of a supply voltage on an output side of the optocoupler. 
     The driving element may include a light emitting element for controlling the MOSFET. The optocoupler may further include a temperature detecting means coupled to the light emitting element. 
     The driving element may further include a light emitting element for controlling the MOSFET. The optocoupler may further include a resistance element coupled in series to the light emitting element and the resistance element may have a negative temperature coefficient. 
     The driving element may further include a first light emitting element for controlling the MOSFET. The optocoupler may include a second light emitting element corresponding to the driving triac and an integrated circuit coupled to the first light emitting element and the second light emitting element. The integrated circuit may have a delay function. 
     There may be more than one driving triac. 
     According to one aspect of the present invention, when a solid-state relay is turned on, an input current is applied to a light emitting diode so as to activate a driving triac. When the solid-state relay is turned off afterward, a trigger pulse is applied to a normally-on driving element. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay. 
     According to another aspect of the present invention, when the solid-state relay is turned on, an input current is applied to a light emitting diode associated with the light receiving element/driving triac, so as to activate the driving triac. When the solid state relay is turned off afterward at a predetermined time, an input current is applied to the light emitting diode associated with the MOSFET so as to turn off the normally-on MOSFET. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay. 
     According to still another aspect of the present invention, when the solid-state relay is turned on, an input current is applied to a light emitting diode so as to activate the driving triac. When the solid-state relay is turned off afterward at a predetermined time, a trigger pulse is applied to a normally-on mechanical relay. Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay. 
     According to still another aspect of the present invention, it is possible to prevent a steep voltage from being applied to the solid-state relay in the off-state. Accordingly, it is possible to prevent commutation failure from occurring. 
     According to still another aspect of the invention, by preconditioning the solid-state relay so,that an input current will flow into the light emitting diode (which controls the MOSFET) when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, the normally-on MOSFET is turned off, thereby compulsorily turning off the device. Accordingly, it is possible to prevent an abnormal operation of the device at high temperatures, for example. 
     According to still another aspect of the present invention, by preconditioning the solid-state relay so that an input current sufficient to turn off the normally-on MOSFET will flow into the light emitting diode (which controls the MOSFET) by reducing a-resistance value of the resistance element having a negative temperature coefficient when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, the normally-on MOSFET is turned off, thereby compulsorily turning off the device. Accordingly, it is possible to prevent an abnormal operation of the device at high temperatures, for example. 
     According to still another aspect of the present invention, when a phase control is performed, the solid-state relay can maintain a stable on state during the time delay provided by an integrated circuit. Accordingly, It is possible to facilitate the design of the device by using the integrated circuit. 
     According to still another aspect of the present Invention, there is provided an optocoupler which is characterized by including a plurality of normally-on driving elements coupled in series to a driving triac. 
     For example, as shown in FIG. 7, two normally-on driving elements  105  may be coupled in series to the driving triac  103 . In this case, one of the normally-on driving elements  105  may be dedicated to the “off-controlling” of the device (the term “off-controlling” as used herein refers to controlling of an off-state of a device, i.e., turning off a device) and the other may be dedicated to the compulsory shutting off of the device operation when the device is abnormally heated, for example. 
     As a result, it is possible to realize a device which is capable of being controlled so as to be on/off with a predetermined timing and, moreover, it is possible to compulsorily turn of f the solid-state relay  700  when the solid-state relay  700  is abnormally heated, for example. 
     Effects of the present invention will be described below. 
     According to the present invention, there is provided an optocoupler such as a solid-state relay, etc., which can not only be turned on, but also turned off with a predetermined timing. As a result, even in the case of driving the load with a prescribed electric power, it is possible to prescribe the timings of turning on/off the solid-state relay for minimizing an inrush current and preventing commutation failure by adjusting such prescribed timings of turning on/off while performing phase control. 
     Moreover, when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, it is possible to compulsorily turn off the device, thereby preventing an abnormal operation of the device when the device is heated, for example. 
     Thus, the invention described herein makes possible the advantages of: (1) providing an optocoupler capable of preventing an increase in an inrush current or commutation failure; (2) providing an optocoupler which can be turned off with a prescribed timing; and (3) providing an optocoupler capable of compulsorily turning itself off when any abnormality occurs, e.g., when an ambient temperature rises to an extremely high level. 
     These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram of a solid-state relay according to an embodiment of the present invention wherein a normally-on driving element is coupled in series to a driving triac. 
     FIG. 2 is a structural diagram of a solid-state relay according to an embodiment of the present invention wherein a normally-on driving element is a MOSFET. 
     FIG. 3 is a structural diagram of a solid-state relay according to an embodiment of the present invention wherein a normally-on driving element is a mechanical relay. 
     FIG. 4 is a structural diagram of a solid-state relay according to an embodiment of the present invention wherein a temperature detecting circuit is provided in association with a light emitting diode which controls a MOSFET. 
     FIG. 5 is a structural diagram of a solid-state relay according to an embodiment of the present invention wherein a resistance element having a negative temperature coefficient is coupled in series to a light emitting diode. 
     FIG. 6 is a structural diagram of a solid-state relay according to an embodiment of the present invention wherein a light emitting diode associated with a driving triac is coupled to a light emitting diode associated with a normally-on driving element via an IC having a delay function, 
     FIG. 7 is a structural diagram of a solid-state relay according to an embodiment of the present invention wherein a plurality of normally-on driving elements are coupled in series to a driving triac. 
     FIGS. 8A and 8B are graphs illustrating phase-controlled waveforms of a solid-state relay, according to an embodiment of the present invention, capable of preventing at increase in an inrush current and a commutation failure when a load is activated in a phase control mode. 
     FIG. 9 is a structural diagram of a conventional solid-state relay. 
     FIGS. 10A,  10 B and  10 C are graphs illustrating phase-controlled waveforms of a conventional solid-state relay. 
     FIG. 11 is a graph illustrating an inrush current waveform in a phase control mode of a conventional solid-state relay. 
     FIG. 12 is a graph illustrating a commutation failure waveform of a conventional solid-state relay. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A solid-state relay  100  according to an embodiment of the present Invention is illustrated in FIG.  1 . The solid-state relay  100  includes: a light emitting diode  101 : a light receiving element (phototriac)  102 : a driving triac  103 ; a resistance  104 : and a normally-on driving element  105  coupled in series to the driving triac  103 . 
     Now, a case will be considered in which, an inductive load  106  which gives rise to a load current whose phase is shifted substantially by 90° with respect to a supply voltage is coupled to the solid-state relay  100 , the load being driven with an electric power which is half of that required in a full-phase on-driving mode, 
     First, phase control which may be performed in a conventional solid-state relay  900  (FIG. 9) will be described. As illustrated in FIG. 8A, input currents are applied to a light emitting element  902  at respective times t 1 , t 2 , t 3  and t 4  approximately corresponding to 90° phase points of a current waveform, so as to activate the solid-state relay  900 . 
     A load current LI 1  approximately has its peak values at times t 1 , t 2 , t 3  and t 4 . Accordingly, a substantial inrush current may occur at each of these times, thereby adversely affecting the device. Moreover, a supply voltage DV 1  approximately has its peak values at the off-points, i.e., at t 81 , t 82 , t 83  and t 84 , so that a commutation failure may be caused in the solid-state relay  900  due to its (dv/dt)c characteristics. 
     Next, referring to FIG. 8B, an operation of the solid-state relay  100  (FIG. 1) according to an embodiment of the present invention will be described, in which the load  106  is activated with a half amount of electric power in comparison to that of a full-phase on-driving mode. 
     It is assumed that input current pulses I 5 , I 6 , I 7  and I 8  for turning on the driving triac  103  are applied to the light emitting diode  101  at times t 5 , t 6 , t 7  and t 8 , respectively, approximately corresponding to 0° phase points of the load current phase and that trigger pulses TG 9 , TG 10  TG 11  and TG 12  for turning off the normally-on driving element  105  are applied to the normally-on driving element  105  at times t 9 , t 10 , t 11  and t 12 , respectively, approximately corresponding to 90° phase points. 
     Under such conditions, an inrush current can be prevented since the phase of a load current L 12  in the on-states, i.e., at times t 5 , t 6 , t 7  and t 8 . is approximately at 0°. Moreover, the phase of a supply voltage DV 2  is approximately at 0° in the off-states, i.e., at times t 9 , t 10 , t 11  and t 12 . Thus, no steep overvoltage is applied to the device, thereby preventing commutation failures. 
     Therefore, since the solid-state relay  100  is capable of turning itself off with a predetermined timing, it is possible to achieve a stable operation of the load  106 . 
     FIG. 2 illustrates a structure of a solid-state relay  200  according to an embodiment of the present invention in which a normally-on driving element  105 A includes a MOSFET  205 . Like reference numerals to those of the solid-state relay  100  according to the previous embodiment of the present invention discussed with reference to FIG. 1 denote like elements in the present embodiment, and will not be further described below. 
     The normally-on driving element  105 A, which is coupled in series to a driving triac  103 , includes a light emitting diode  101 A and the normally-on MOSFET  205 . 
     When the solid-state relay  200  is turned on, an input current is applied to a light emitting diode  101  associated with a light receiving element  102 /driving triac  103  so as to activate the driving triac  103 . When the solid-state relay  200  is turned off afterward at a predetermined time, an input current is applied to the light emitting diode  101 A associated with the MOSFET  205  so as to turn off the normally-on MOSFET  205 . 
     Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay  200 . 
     FIG. 3 illustrates a structure of a solid-state relay  300  according to an embodiment of the present invention in which a normally-on driving element  105 B is a mechanical relay. Like reference numerals to those of the solid-state relay  100  according to an embodiment of the present invention previously discussed with regard to FIG. 1 denote like elements, and will not further be described below. 
     The normally-on driving element  105 B coupled in series to a driving triac  103  includes a normally-on mechanical relay  305 . 
     When the solid-state relay  300  is turned on, an input current is applied to a light emitting diode  101  so as to activate the driving triac  103 . When the solid-state relay  300  is turned off afterward at a predetermined time, a trigger pulse is applied to the normally-on mechanical relay  305 , that is, an input current is applied to a coil  306  so as to turn off the normally-on mechanical relay  305 . 
     Therefore, it is possible to prescribe the timing for turning off, as well as turning on, the solid-state relay  300 . 
     FIG. 4 illustrates a structure of a solid-state relay  400  according to an embodiment of the present invention in which a temperature detecting circuit  406  is provided associated with a light emitting diode  101 A which controls a normally-on MOSFET  205 . Like reference numerals to those of the solid-state relay  100  according to the previous embodiment of the present invention discussed with regard to FIG. 1 denote like elements in the present embodiments, and will not be further described below. 
     A normally-on driving element  105 A, which is coupled in series to a driving triac  103 , includes the light emitting diode  101 A and the normally-on MOSFET  205 . The light emitting diode  101 A controls the MOSFET  205 . 
     The solid-state relay  400  further includes the temperature detecting circuit  406  coupled in series to the light emitting diode  101 A. 
     By preconditioning the solid-state relay  400  so that an input current will flow into the light emitting diode  101 A (which controls the normally-on, MOSFET  205 ) when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, the normally-on MOSFET  205  is turned off, thereby compulsorily turning off the solid-state relay  400 . Accordingly, it is possible to prevent an abnormal operation of the solid-state relay  400  at high temperatures, for example. 
     FIG. 5 illustrates a structure of a solid-state relay  500  according to an embodiment of the present invention, in which a resistance element  507  having a negative temperature coefficient is coupled in series to a light emitting diode  101 A. 
     A normally-on driving element  105 A coupled in series to a driving triac  103  includes the light emitting diode  101 A and a normally-on MOSFET  205 . The light emitting diode  101 A controls the normally-on MOSFET  205 . 
     The solid-state relay  500  further includes the resistance element  507  coupled in series to the light emitting diode  101 A. The resistance element  507  has a negative temperature coefficient. 
     By preconditioning the solid-state relay  500  so that an input current sufficient to turn off the normally-on MOSFET  205  will flow into the light emitting diode  101 A (which controls the normally-on MOSFET  205 ) by reducing a resistance value of the resistance element  507  having a negative temperature coefficient when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level, the normally-on MOSFET  205  is turned off, thereby compulsorily turning off the solid-state relay  500 . Accordingly, it is possible to prevent an abnormal operation of the solid-state relay  500  at high temperatures, for example. 
     FIG. 6 illustrates a structure of a solid-state relay  600  according to an embodiment of the present invention, in which a light emitting diode  101  associated with a driving triac  103  is coupled to a light emitting diode  101 A associated with a normally-on driving element  105 A via an IC  608  having a delay function. 
     The normally-on driving element  105 A coupled in series to the driving triac  103  includes the light emitting diode  101 A and a normally-on MOSFET  205 . The light emitting diode  101 A controls the normally-on MOSFET  205 . 
     The solid-state relay,  600  further includes the IC  608  coupled in series to the light emitting diode  101  and the light emitting diode  101 A. The IC  608  has a delay function. 
     Therefore, when a phase control is performed, the solid-state relay  600  can maintain a stable on-state during the time delay provided by the Integrated circuit  608 . Accordingly, it is possible to facilitate the design of the device by using the integrated circuit  608 . 
     FIG. 7 illustrates a structure of a solid-state relay  700  according to an embodiment of the present invention in which a plurality of normally-on driving elements  105  are coupled in series to a driving triac  103 . 
     The solid-state relay  700  includes the plurality of normally-on driving elements  105  coupled in series to the driving triac  103 . 
     For example, as shown in FIG. 7, two normally-on driving elements  105  may be coupled in series to the driving triac  103 . In this case, one of the normally-on driving elements  105  may be dedicated to the “off controlling” of the device, and the other may be dedicated to the compulsory shutting off of the device operation, at high temperatures, for example. 
     As a result, it is possible to realize a device which is capable of being controlled so as to be on/off with a predetermined timing and, moreover, it is possible to compulsorily turn off the solid-state relay  700  when the solid-state relay  700  is abnormally heated, for example. 
     Although the above embodiment illustrates an example in which two driving elements  105  are coupled together, the present invention is. not limited thereto. Three or more driving elements  105  may be coupled to the driving triac  103 . 
     Although the above-described embodiments of the present invention illustrate examples directed to the solid-state relays, the present invention is not limited thereto. The present invention is applicable to any optocoupler which incorporates a thyristor or triac as a driving element, e.g., a photothyristor, a phototriac coupler, etc. 
     As described above, the present invention provides an optocoupler capable of preventing an increase in inrush current or commutation failure. 
     The present invention further provides an optocoupler whose off-timing can be controlled. 
     The present invention further provides an optocoupler capable of compulsorily turning itself off when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level. 
     Accordingly, there is provided an optocoupler such as a solid-state relay, etc., which can be not only turned on, but also turned off, with a predetermined timing. Thus, when the optocoupler is employed for driving a load while performing a phase control, an increase in inrush current or commutation failure can be prevented. Moreover, it is possible to compulsorily turn off the device when an abnormality occurs, e.g., an ambient temperature rises to an extremely high level. 
     Various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, It in not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be broadly construed.