Abstract:
A power supply control circuit that automatically shuts off power supply to an electric apparatus comprises a photocoupler for inputting a remote control signal, a switching circuit having a press-button switch provided toward an output end of the photocoupler and a power supply that is momentarily activated by shorting the switching circuit. Accordingly, a self-holding circuit is provided that maintains the active mode of the remote control signal for the photocoupler.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims priority of Japanese Application No. 2002-177120, filed on Jun. 18, 2002, the complete disclosure of which is hereby incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    a) Field of the Invention  
           [0003]    The present invention relates to a power supply control circuit that activates or shuts down power supply to a variety of electronic terminals in a secondary circuit.  
           [0004]    b) Description of the Related Art  
           [0005]    A known representative power supply control circuit is installed in a copier or similar electronic apparatus to automatically shut down power supply, thereby saving power consumption.  
           [0006]    To control power supply in a power system in a general automatic power supply shutdown function, a power supply and a control circuit are separately provided such that the circuit in the control system can continue to operate after power supply is shutdown.  
           [0007]    A control circuit in a power supply is described herein with reference to FIG. 5.  
           [0008]    Power supply control circuit  100  illustrated in FIG. 5 is generic wherein AC current within a range of 85-264 V is input from a commercial power supply at terminal  101  at 50 Hz or 60 Hz. Then, this AC current is transformed to a given voltage (e.g. 24 V DC current) by transformer  102  to be output at terminal  103  to supply power to a power system and the like.  
           [0009]    Controller  104  controls each circuit in transformer  102 . Controller  104  is actuated as photocoupler  106  receives a remote control signal from remote signal control circuit  105 . In other words, in photocoupler  106 , light emitting diode  106   a  converts the remote control signal into light, which is then converted back to an electric signal again through phototransistor  106   b.  It is this electric signal that actuates controller  104 .  
           [0010]    Problems Addressed by the Present Invention  
           [0011]    Nonetheless, to configure a conventional power supply control circuit  100  in such a way that circuit  105  or the like in a control system does not shutdown even though the power supply circuit of a power system is disconnected, it is essential that circuit  105  of the control system, for example, have a separate power supply for control circuit  105 .  
         OBJECT AND SUMMARY OF THE PRESENT INVENTION  
         [0012]    The primary object of the present invention is to provide a power supply control circuit that is capable of activating a power supply without using an external power supply and of automatically shutting off a power supply, thereby saving power consumption. Yet another object of the present invention is to provide a power supply control circuit that is further capable of shutting off the power supply before a given period time expires. Yet another object of the present invention is to provide a power supply control circuit that is capable of further shutting off the power source when an electronic apparatus enters an abnormal state.  
           [0013]    To achieve the above objectives, the power supply control circuit in accordance with the invention is a power supply control circuit that automatically shuts off power supply in an electric apparatus. The power supply control circuit comprises: a photocoupler for inputting a remote control signal; a switching circuit having a press-button switch provided toward the output end of the photocoupler; and a power supply that is momentarily activated by shorting the switching circuit. A self-holding circuit that maintains the active state of the remote control signal for the photocoupler is thus provided. This circuit allows the remote control signal to be sent to the photocoupler being maintained in the active state such that an output from the power supply is maintained for a given period of time after opening the switching circuit. The circuit inverts the remote control signal to a negative cycle after a given period of time elapses.  
           [0014]    Manual pressing of a button (e.g. press-button switch) turns the switch on only momentarily such that the power supply momentarily short circuits while the remote control signal from the photocoupler is maintained in an active mode. The remote control signal continues to be active for a given period time after the switching circuit is opened, and the remote control signal is inverted to a negative cycle after a given period time elapses. The power supply is thus automatically shut off and the need for an external power supply is eliminated. Subsequently, power consumption is saved.  
           [0015]    The present invention further has the power supply control circuit mentioned above which further comprises an automatic reversing switch that inverts the remote control signal to a negative cycle before a given period time elapses.  
           [0016]    For this reason, at any point in time before the given period time elapses, turning on the automatic inversion switch inverts the remote control signal to a negative cycle. A power supply can thus automatically be shut off during the period starting from opening of a switch circuit to any time before a given period time elapses.  
           [0017]    Another form of the invention has the power supply control circuit mentioned above which further comprises an abnormality detection circuit for detecting an abnormality in the electronic apparatus to invert the remote control signal to a negative cycle upon detection of an abnormality in the electronic apparatus.  
           [0018]    When the abnormality detection circuit detects an abnormality in the electronic apparatus, it inverts the remote control signal to a negative cycle. The power supply is thus automatically shut off when an abnormality is present in the electronic apparatus. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    In the drawings:  
         [0020]    [0020]FIG. 1 is a schematic circuit block diagram illustrating Embodiment 1 of the power control circuit of the present invention;  
         [0021]    [0021]FIG. 2 is a detailed circuit block diagram illustrating Embodiment 1 of the power control circuit of the present invention;  
         [0022]    [0022]FIG. 3 is a diagram illustrating the remote signal control circuit;  
         [0023]    [0023]FIG. 4 is a timing chart for the remote signal control circuit; and  
         [0024]    [0024]FIG. 5 is a schematic circuit block diagram illustrating a power supply control circuit of conventional technology. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0025]    The configuration of the present invention is described in detail herein with reference to drawings illustrating an embodiment.  
         [0026]    FIGS.  1 - 4  describe an embodiment of the power supply control circuit of the present invention.  
         [0027]    [0027]FIG. 1 illustrates a power supply control circuit  10  that outputs DC secondary power with AC primary power supply by the switching method. The main configuration of the circuit comprises: a photocoupler  11 ; a press button switching circuit  13  provided toward the output end of photocoupler  11 ; and a latch-in circuit  14  (FIG. 3) that maintains the active mode of the remote control signal from photocoupler  11  utilizing the power supply activated by means of momentarily short circuiting switching circuit  13 . The power supply output is thus maintained for a given period time after switching circuit  13  is opened, and after a given period time elapses, the remote control signal is inverted to a negative cycle.  
         [0028]    In the power supply control circuit  10 , AC current within a range of 85-264 V is input from a commercial power supply at input terminal 15 at 50 Hz or 60 Hz. Then, transformer (hereinafter referred to as “voltage converter”)  16  converts the AC current to a given voltage and rectifies the same to output DC current (e.g. 24V) at terminal  17  to a power system and the like.  
         [0029]    Controller  18  controls voltage converter  16 . Controller  18  is actuated as a remote control signal from remote signal control circuit  19  (FIG. 3) having a 5V external power supply is input to photocoupler  11 . In other words, photocoupler  11  converts the remote control signal to light by light emitting diode  11   a  and converts the light back to an electrical signal by phototransistor  11   b.  It is this electrical signal that actuates controller  18 . Switching circuit  13  is connected to the terminal of photo-transistor  11   b.  A press-button switch  12  is provided in the middle of switching circuit  13 . Power supply control circuit  10  is configured in the manner illustrated in FIG. 2 for example: DC current, that is rectified through noise filter  21 , rectifier  22 , entry current prevention unit  23 , booster chalk  24 , current detection resistor  25 , inverter  26 , controller  27 , and rectifier  28 , is boosted by transformer  16  such that the boosted AC current is converted to DC current by rectifier  33  to be output at terminal  17 . Controller  18  controls transformer  16  utilizing inverter  32  based on: (1) a current detecting signal from current detector  29 , which is of the numerical value of DC current input at transformer  16 ; (2) another signal from excess voltage protection unit  34  is derived from monitoring whether the output at terminal  17  is the excess voltage; and (3) another signal from controller  35  derived from monitoring whether the DC current output at terminal  17  is in shortage. Signals from excess voltage protection unit  34  and controller  35  are input to controller  18  via photocouplers  36  and  37  respectively. Note that in FIG. 2, Reference Symbol  15  is an input terminal and Reference Symbol  20  is a fuse.  
         [0030]    In the power supply control circuit  10 , as an incoming remote control signal from remote signal control circuit  19  having a 5V external power supply is input to photocoupler  11 , controller  18  is actuated. Power supply control circuit  10  actuates controller  18  even though a remote control signal is not sent as long as an operator presses button switch  12  to short circuit the output end of photocoupler  11 . The press-button switch  12  is attached to an operation panel.  
         [0031]    Next, remote signal control circuit  19  is described in detail herein with reference to FIG. 3. Remote signal control circuit  19  has a latch-in circuit utilizing a flip flop IC. A remote control signal is output at terminal “Q”. The “PR” terminal is fixed to “H” ( HIGH). A power supply monitoring signal (reset signal) is input at the “CLK” terminal, and the remote control signal is synchronized with the reset signal to prepare for operation. A Watchdog Timer (WDT) inputs an automatic reset signal in response to an abnormality. Further, the “CLR” terminal is connected to NOR circuit  39 . The remote control signal from the Central Processing Unit (CPU) (not illustrated) and the automatic reset signal sent by the WDT responding to an abnormality are input at the NOR circuit  39 . An automatic reset switch  12  is provided on an operation panel (not illustrated).  
         [0032]    Now, operation of remote signal control circuit  19  utilizing switching circuit  13  is described herein with reference to a circuit diagram illustrated in FIG. 3 and a timing chart illustrated in FIG. 4.  
         [0033]    Upon manual pressing of a press-button switch, photocoupler  11  short circuits at its output end to turn the remote signal into an active mode overriding the remote control signal; power supply is activated so as to supply power to the control circuit of the apparatus having power supply control circuit  14 . The CPU in the control circuit thus retains the active state of the remote signal. As the output end of photocoupler  11  short circuits, a remote control signal is output overriding the state of the remote control terminal. External power supply  38 , thus, supplies secondary power to power supply control circuit  10  such that the remote control signal is set to the HIGH level as the reset signal sets in the HIGH mode. Connecting (supplying) the remote control signal to the remote control terminal in the power supply allows the output from photocoupler  11  to be kept active.  
         [0034]    Even when the operator releases press button switch  12  afterwards, the output from photocoupler  11  is active. The secondary power supply thus continues to output (power), thereby allowing continued operation of the apparatus.  
         [0035]    Remote signal control circuit  19  has signal input terminals that invert the remote control signal to a LOW level. One of the terminals is for outputting a signal through the CPU: it outputs a signal to turn off the remote control signal when a given period time elapses or when an automatic inversion switch is pressed.  
         [0036]    Another terminal is for outputting a signal through a monitoring circuit to shut off power supply independent of the CPU in the apparatus when an abnormality is detected.  
         [0037]    As a signal through the CPU or a signal through monitoring circuit comes in, the remote control signal levels off to a LOW level, and photocoupler  11  is turned off, thereby shutting off the output from the secondary power supply.  
         [0038]    While the secondary power supply is leveling off, remote signal control circuit  19  maintains the remote control signal in a LOW mode and does not allow the remote control signal to be inverted to a HIGH mode even when the voltage applied to remote signal control circuit  19  is in the unstable operating region. This ensures stable shut off of the apparatus.  
         [0039]    In the stand by mode, power supply is maintained while the secondary power supply end is unloaded. This requires little current during the stand by mode, greatly enhancing the power consumption saving advantages of the apparatus.  
         [0040]    As described above, according to the power supply control circuit, as an operator presses a switch, a switching circuit momentarily short circuits to activate the power supply, which then maintains the active mode of the remote control signal from the photocoupler. The active mode is maintained only during a given period time after the switching circuit is opened. The remote control signal is inverted to a negative cycle as soon as the given period time elapses. The power supply can thus automatically be shut off without using an external power supply as long as a small number of circuit components are added to the conventional circuit, subsequently saving power consumption to a great extent.  
         [0041]    Moreover, the power supply control circuit has also been described having an automatic inversion switch that inverts the remote control signal to a negative cycle; the power supply can automatically be shut off during a period starting from opening of the switch circuit and any time before a given period time elapses.  
         [0042]    Further, the power supply control circuit has further been described such that, when the abnormality detection circuit detects an abnormality in the electronic apparatus, the remote control signal is inverted to a negative cycle. The power supply is thus automatically shut off when an abnormality is present in the electronic apparatus.  
         [0043]    While the foregoing description and drawings represent the present invention, it will be obvious to those skilled in the art that various changes may be made therein without departing from the true spirit and scope of the present invention.