Patent Publication Number: US-2006017391-A1

Title: Power control photocoupler and electronic device in which the power control photocoupler is used

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2004-213142 filed in Japan on Jul. 21, 2004, the entire contents of which are hereby incorporated by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to photocouplers for controlling AC (alternating current), and to electronic devices in which such photocouplers are used.  
      2. Description of the Related Art  
       FIG. 7  is a circuit diagram showing an example of a conventional apparatus for controlling a load.  
      The circuit shown in  FIG. 7  is an example of a conventional load control apparatus that is constituted by using an AC current power source, and a power control element. The load control apparatus will be described here using an example in which a solid-state relay is used. It should be noted that a solid-state relay means a non-contact semiconductor relay that uses a power semiconductor device such as a gate control bidirectional triode thyristor or a reverse-blocking triode thyristor, characterized in that once the relay is turned ON, the ON-state is maintained until the current flowing through the switching portion becomes 0, even if a control signal for controlling ON/OFF is not applied.  
      A solid-state relay  110  shown in  FIG. 7  is composed of a light emitting element  111  that converts electric signals into light (principally a gallium-arsenic LED (light emitting diode) or a gallium-aluminum-arsenic LED), a light receiving element  112  that converts light into electric signals (principally a photo-gate control-type bidirectional triode thyristor that conducts electricity when light hits the gate), and a power control element  113  (principally a gate control-type bidirectional triode thyristor). The light receiving element  112  conducts current when the light emitting element  111  emits light due to a control current I flowing through the light emitting element  111  and a current control resistor  120  that is in series with the light emitting element  111 ; a trigger current flows through the gate of the power control element  113 ; and the power control element  113  fires. Thus, current flows through a load  130  and the load  130  is activated.  
      Since an alternating current  140  is flowing on the output side, the current soon approaches 0 A, however if there is no input signal at this time, then since the current that flows through the thyristor portion (the light receiving element  112  and the power control element  113 ) is 0 A, the light receiving element  112  and the power control element  113  are OFF.  
      The alternating current is thus turned ON and OFF by an optical input signal.  
      Furthermore, with advances in energy savings in all kinds of devices in recent years, attention has also turned to the electrical power that is consumed by the load, and there is increasing demand for load control of alternating current loads at low power consumption. For example, JP 2001-111398A (referred hereafter as Patent Reference 1) proposes a spike voltage suppression circuit for semiconductor two-way switches that can suppress spike voltages generated in both directions in semiconductor two-way switches, by connecting a Zener diode and a reverse series diode circuit between the gates and the collectors of the transistors of a semiconductor two-way switch in which the transistors are connected in reverse series or reverse parallel.  
      However, in load control with conventional solid-state relays, although the alternating current could be turned ON and OFF, the alternating current itself could not be controlled.  
      With the spike voltage control circuit for semiconductor two-way switches disclosed in Patent Reference 1 serving as another example of a conventional load control device, a circuit that is configured with a two-way switch is proposed. However, since delicate drive control is difficult, depending on the condition of the load, and an input signal is usually supplied from a small-signal circuit such as a microprocessor, it has been necessary to prevent malfunction due to switching noise and the like from the load by separating the direct current small-signal circuit and the alternating current large circuit. Therefore, it is necessary to insulate with light.  
     SUMMARY OF THE INVENTION  
      The present invention has been achieved with consideration of the above-described facts, and it is an object thereof to provide delicate drive control of a load signal, a power control photocoupler that can reduce power consumption, and electronic devices in which the power control photocoupler is used.  
      In order to solve the above-noted problems, the power control photocoupler of the present invention is a power control photocoupler for controlling an alternating current load connected to a secondary side based on a signal from a microcomputer connected to a primary side, and is characterized by being provided with a photocoupler portion for outputting an input signal from the primary side to the secondary side, and a control portion for controlling the alternating current load based on the output from the photocoupler portion.  
      With such a configuration, it is possible to reduce the current consumed when controlling the alternating current output.  
      With such a power control photocoupler, in the present invention, the control portion may contain a two-way switch composed of a combination of an IGBT (insulated gate bipolar transistors) and a diode.  
      The control portion may also use an FET (field-effect transistors) instead of the IGBT.  
      In any configuration of the control portion described above, the drive of the load signal can be controlled more delicately.  
      Furthermore, the diode of the control portion may also be composed of an FRD (fast recovery diode).  
      A frequency modulation circuit may also be provided as the primary side pre-circuit of the photocoupler portion. In this configuration, changes to the frequency due to changes in application and load capacity can be carried out easily as desired.  
      The secondary side frequency signal may be fed back into the frequency modulation circuit. In this case, the power consumed by the load may be controlled more delicately.  
      Furthermore, an oscillating circuit may be provided in the frequency modulation circuit so as to produce a PWM (pulse width modulation) waveform based on the secondary side frequency signal that is fed back. In this configuration, the power consumed by the load can be controlled even more delicately.  
      With the electronic device according to the present invention, since the current consumed in the power control photocoupler can be reduced when controlling the alternating current output, as a result, it is possible to reduce the current consumed by the electronic device.  
      It should be noted that the power control optical element and the electronic device can be put to practical use in electronic devices such as fridges, air-conditioners and vending machines in which solenoid valves and fans are provided as the load. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is a circuit diagram showing Embodiment 1 of the power control photocoupler of the present invention.  
       FIG. 2  is an explanatory diagram showing a current path in a two-way switching portion of an alternating current that is output from the alternating current power source of  FIG. 1   
       FIG. 3  is an explanatory diagram showing an output current waveform of the alternating current power source of  FIG. 1 .  
       FIG. 4  is a circuit diagram showing Embodiment 2 of the power control photocoupler of the present invention.  
       FIG. 5  is an explanatory diagram showing an example of a current waveform used in the power control photocoupler shown in  FIG. 4 .  
       FIG. 6  is a circuit diagram showing another example of a two-way switch portion that constitutes the power control photocoupler of the present invention.  
       FIG. 7  is a circuit diagram showing an example of a conventional load control device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The embodiments of the present invention are described below with reference to the drawings.  
     Embodiment 1  
       FIG. 1  is a circuit diagram showing Embodiment 1 of the power control photocoupler of the present invention.  
      A power control photocoupler  10  of the present invention is constituted by an photocoupler portion that is provided with a light emitting diode  11 , an IGBT gate control portion  20  that is provided with a push-pull circuit, and a two-way switch circuit  30  for alternating current control.  
      The IGBT gate control portion  20  is constituted by a light receiving element  21  for receiving light that is output from the light emitting diode  11 , an amplifier (AMP)  26  connected to the light receiving element  21 , an interface  25  connected to the AMP  26 , and a push-pull circuit that is connected to the interface  25 . The push-pull circuit is constituted by two transistors (a first Tr  22  and a second Tr  23 ) and a resistor (RG  24 ). Furthermore, the emitter of the first Tr  22 , whose collector is connected to the control power source portion, and the emitter of the second Tr  23  whose collector is connected to an earth potential, are connected, and one terminal of the RG  24  is connected to the connection point of the set of emitters. Furthermore, one terminal of the interface  25 , whose other terminal is connected to the control portion power source, is connected to the bases of the first Tr 22  and the second Tr  23 .  
      The two-way switch portion  30  is constituted by two transistors (a first IGBT.  31  and a second IGBT  32 ) whose emitters are connected to each other, and two diodes (a first FRD  33  and a second FRD  34 ) whose anodes are connected to each other, wherein the other end of the RG  24  is connected to the gate terminal of the first -IGBT  31  and the second IGBT  32 . The collector of the first IGBT  31  is connected to the cathode of the first FRD  33 , and the collector of the second IGBT  32  is connected to the cathode of the second FRD  34 . The point at which the emitters of the first IGBT  31  and the second IGBT  32  are connected is connected by a signal line to the point at which the anodes of the first FRD  33  and the second FRD  34  are connected, and the collector of the second Tr  23  of the IGBT gate control portion  20  is connected to the point at which the emitters of the first IGBT  31  and the second IGBT  32  are connected. Moreover, the load  41  and the alternating current power source  42  are connected between the connection point of the collector of the first IGBT  31  and the cathode of the first FRD  33 , and the connection point of the collector of the second IGBT  32  and the cathode of the second FRD  34 . That is, in the present Embodiment 1, FRDs (fast recovery diodes) that have the same voltage resistance and response speed as IGBTs are used as the two diodes in the two-way switch portion  30 .  
      Because the circuit is configured in this way, provided that the signal received by the light emitting diode  11  is at a high level, the first Tr  22  is turned ON and the second Tr  23  is turned OFF, an electric charge is supplied to the gates of the first IGBT  31  and the second IGBT  32 , and the first IGBT  31  and the second IGBT  32  both turn ON. On the other hand, if the signal input to the light emitting diode  11  is at a low level, then the first Tr  22  is turned OFF and the second Tr  23  is turned ON, supply of the electric charge to the gate of the first IGBT  31  and the gate of the second IGBT  32  stops, and the first IGBT  31  and the second IGBT  32  both turn OFF.  
      ON/OFF actuation of the power control photocoupler  10  will be described next with reference to the drawings.  
       FIG. 2  is an explanatory diagram showing the current path of the alternating current that is output from the alternating current source  42  in the two-way switch portion  30 , and  FIG. 3  is an explanatory diagram showing an output current waveform of the alternating current source  42 .  
      Since the alternating current source  42  is connected to the output side in the power control photocoupler  10  of the present embodiment, when the first IGBT  31  and the second IGBT  32  are both ON (that is to say, when the signal input to the light emitting diode  11  is at a high level), in the part of the output of the alternating current source  42  indicated by A in  FIG. 3 , a current A flows from one terminal  30   a  of the two-way switch portion  30 , via the first IGBT  31  and the second FRD  34 , to the other terminal  30   b,  and in the part of the output of the alternating current source  42  indicated by B in  FIG. 3 , a current B flows from the other terminal  30   b  via the second IGBT  32  and the first FRD  33  to the one terminal  30   a,  as shown in  FIG. 2 . As a result, it is possible to drive the load  41 . On the other hand, when the first IGBT  31  and the second IGBT  32  are both OFF (that is to say, when the input signal to the light emitting diode is at a low level, the power control photocoupler  10  is OFF, and current does not flow to the load  41 . That is to say, the alternating current can be turned ON/OFF by switching the input signal to the light emitting diode  11  between high and low. Consequently, it is possible to control the power consumed on the output side by modulating the control signal from the microcomputer  44  connected to the light emitting diode  11  via the resistor  43  into a pulse signal of a specific frequency before transmitting it to the light emitting diode  11 . More specifically, the total power consumed may be decreased by repeatedly turning the output side alternating current ON/OFF by transmitting the input signal to the light emitting diode  11  at a frequency that is higher (from hundreds of hertz to a few kilohertz) than the frequency of the output side alternating current (50 Hz or 60 Hz) to switch the first IGBT  31  and the second IGBT  32  ON/OFF at high speed.  
      With the power control photocoupler  10  of the present Embodiment 1, since the space between input and output is electrically insulated and the signal from the microcomputer can be directly connected, the power consumption can be reliably controlled without being affected by noise caused by fluctuating electric potential, for example, on the output side. Furthermore, changes to the frequency due to changes in application and load capacity can be carried out easily as desired.  
     Embodiment 2  
       FIG. 4  is a circuit diagram showing Embodiment 2 of the power control photocoupler  10  of the present invention.  
      The power control photocoupler  10  of Embodiment 2 of the present invention has a further feedback portion for detecting the frequency of the output alternating current and feeding it back to the power control photocoupler, and a frequency modulation circuit for creating a pulse width modulating waveform based on the frequency that was fed back, added onto the power control photocoupler shown in the above-noted Embodiment 1.  
      That is to say, as well as providing a frequency modulation circuit  12  between the light emitting diode  11  and the resistor  43 , a photocoupler  13  and a frequency detection circuit  14  for detecting the frequency of the alternating current are provided between a direct current line power source L 2  of the frequency modulation circuit  12 , and an alternating current power source line L 1  connected to the two output terminals of the two-way switch portion  30 . Since the alternating current power source line L 1  and the direct current power source line L 2  that connect the output and input sides of the power control photocoupler  10  are non-contactably connected via the photocoupler  13 , the power control photocoupler  10  is less affected by noise and the like, and its operation is reliable.  
      With the power control photocoupler  10  of the present Embodiment 2, it is possible to create a PWM control waveform that corresponds to the frequency of the output side alternating current by modulating the output (for example, a triangular waveform or the like) from an oscillating circuit  12   a  provided in the frequency modulating circuit  12 , based on the frequency that is fed back, and to use the waveform to control the light emitting diode  11 , thus the energy consumed by the load  41  can be controlled even more delicately.  
       FIG. 5  is an explanatory diagram showing an example of the current waveform used in the power control photocoupler  10  shown in  FIG. 4 . The solid line waveform in  FIG. 5  indicates a saw-tooth waveform that is output from the oscillating circuit  12   a,  the broken line waveform shows the current (output current) that is output from the direct current power source line L 2  to the frequency modulating circuit  12 , and the pulse waveform with the thick solid line shows the PWM control waveform.  
      Moreover, the strength of the operating load can be controlled by adjusting the frequency of the PWM control waveform and the duty ratio, and it is also possible to control the operating load by other parameters of the electronic devices provided with the load.  
      Another example of the two-way switch portion is described next.  
       FIG. 6  is a circuit diagram showing another example of the two-way switch portion that constitutes the power control photocoupler of the present invention  
      The above noted Embodiment 1 and Embodiment 2 have been described in which IGBTs are treated as the transistors constituting the two-way switch portion, however, depending on the voltage and the current, the same effect may be achieved by using FETs (a first FET  35  and a second FET  36 ) as a substitute for the IGBTs.  
      It is possible to reduce the current consumed when controlling alternating current output using the power control photocoupler  10  configured above, and more delicate control is possible by providing microcomputer control.  
      Furthermore, by mounting the power control photocoupler  10  having the configuration described above into an electronic device, the consumed current can be reduced by the power control photocoupler when controlling the alternating current power output, and as a result, the current consumed by the electronic device can be reduced.  
      The present invention can be embodied and practiced in other different forms without departing from the spirit and essential characteristics thereof. Therefore, the above-described embodiments are considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than by the foregoing description. All variations and modifications falling within the equivalency range of the appended claims are intended to be embraced therein.