Abstract:
An input power stabilizing circuit, which is disposed between a DC power source and an apparatus to which the DC power source is supplied, and which prevents a capacitor in the input power stabilizing circuit from flowing a backward current as many as possible when the output side of the DC power source became a short circuit momentarily, and which can reduce the loss of the power as many as possible at a normal operating time, is provided. The input power stabilizing circuit provides a current detecting means which detects the backward current from the capacitor in an input power supply line and a current braking means which brakes a current line connecting the apparatus with the DC power source. When the momentary short circuit occurs, the current line is broken by working the current detecting means and the current braking means. With this, the backward current from the capacitor is made to be a minimum value in the input power stabilizing circuit.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an input power stabilizing circuit, in which a backward current discharged from a capacitor in the input power stabilizing circuit is prevented as many as possible, at the time when an input power supply line had some trouble such as a momentary short circuit.  
           [0002]    Description of the Related Art  
           [0003]    Recently, the power consumption of apparatuses has been increased, and solutions have been required to find at the time when troubles occur by outside causes. One of the troubles is that an input power supply line becomes a short circuit momentarily. A diode is generally used in an input power stabilizing circuit as a solution to prevent a backward current from flowing in the input power stabilizing circuit at the time when the input power supply line has some trouble such as a momentary short circuit.  
           [0004]    [0004]FIG. 1 is a circuit diagram in which a conventional input power stabilizing circuit is connected to a direct current (DC) power source and a load. As shown in FIG. 1, a DC power source  1  is connected to a load  2  via an input power stabilizing circuit  15 . The input power stabilizing circuit  15  provides a capacitor  3 , an inductor  16 , and a diode  14 . A DC voltage from the DC power source  1  is charged in the capacitor  3 , and the capacitor  3  supplies the charged voltage to the load  2  when the impedance in the load  2  was changed. The inductor  16  filters out noise from the current inputted from the DC power source  1 . When an input power supply line between “a” and “b” terminals becomes a short circuit, the diode  14  breaks a backward current from the “b” terminal to the “d” terminal, which was discharged from the capacitor  3 .  
           [0005]    At an input power stabilizing circuit used a diode, when a large current flew, heating caused by the large current becomes a big problem. This problem is explained by using the circuit diagram shown in FIG. 1. Since a current always flows in the diode  14 , electric power being the product of forward voltage and forward current of the diode  14  is always consumed. This electric power is wasteful and also causes big heating in the input power stabilizing circuit  15  when the load  2  needs a large current. Consequently, there is a problem that a structure radiating the heat in the input power stabilizing circuit  15  becomes a big size and its manufacturing cost becomes high.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to provide an input power stabilizing circuit, disposed between a DC power source and an apparatus that works by the DC power source, can prevent a backward current from flowing from a capacitor in the input power stabilizing circuit as many as possible when the DC power source has some trouble such as that the DC input terminals becomes a short circuit momentarily, and also can reduce the power consumption of the input power stabilizing circuit as much as possible at the normal operating time of the input power stabilizing circuit. Moreover, the input power stabilizing circuit of the present invention largely reduces the amount of heat generating in the circuit, and its heat radiating structure is made to be a small size and also its manufacturing cost is made to be low.  
           [0007]    According to a first aspect of the present invention, for achieving the object mentioned above, there is provided an input power stabilizing circuit, which is disposed between a DC power source and a load to which the DC power source is supplied. The input power stabilizing circiut provides a voltage storing means which stores a voltage supplied from the DC power source and supplies the stored voltage to the load when a trouble occurred at the side of the DC power source and stabilizes the voltage input to the load, a current detecting means which detects a backward current from the voltage storing means in an input power supply line through which a current from the DC power source to the load is supplied, and a current braking means which brakes a current line connecting the load with the DC power source, when the backward current was detected by the current detecting means.  
           [0008]    According to a second aspect of the present invention, in the first aspect, the current detecting means provides a current transformer whose primary side is connected to the input power supply line, and a first transistor whose gate is made to be on/off by a voltage generated at the secondary side of the current transformer.  
           [0009]    According to a third aspect of the present invention, in the second aspect, the current detecting means further provides a diode which rectifies the voltage generated at the secondary side of the current transformer, a capacitor which smoothes the voltage rectified at the diode, and a first voltage divider which divides the voltage smoothed at the capacitor and takes out a first designated voltage. And the first transistor becomes “on” when the voltage divided at the first voltage divider is applied to the gate of the first transistor, and this “on” state of the first transistor is sent to the current braking means.  
           [0010]    According to a fourth aspect of the present invention, in the third aspect, the current braking means provides a second voltage divider which divides a voltage inputted from the DC power source and takes out a second designated voltage, and a second transistor which is disposed in the current line connecting the load with the DC power source, and the gate of the second transistor is made to be on/off by the voltage taken out from the second voltage divider. And the second transistor is made to be “off” when the voltage from the second voltage divider has not been applied to the gate of the second transistor, and the current line is broken.  
           [0011]    According to a fifth aspect of the present invention, in the fourth aspect, the first transistor makes both ends of one of resistors, of which the second voltage divider is composed, short, and stops applying the voltage from the second voltage divider to the gate of the second transistor.  
           [0012]    According to a sixth aspect of the present invention, in the first aspect, the input power stabilizing circuit further provides an inductor, which delays the backward current from the voltage storing means, in the input power supply line.  
           [0013]    According to a seventh aspect of the present invention, in the second aspect, the current detecting means provides plural current transformers in the input power supply line in parallel, and detects the backward current from the voltage storing means.  
           [0014]    According to an eighth aspect of the present invention, in the second aspect, the current detecting means provides plural current transformers in the input power supply line in series, and detects the backward current from the voltage storing means.  
           [0015]    According to a ninth aspect of the present invention, in the first aspect, the voltage storing means discharges the backward current to the input power supply line, when output ends of the DC power source became a short circuit. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The objects and features of the present invention will become more apparent from the consideration of the following detailed description taken in conjunction with the accompanying drawings in which:  
         [0017]    [0017]FIG. 1 is a circuit diagram in which a conventional input power stabilizing circuit is connected to a DC power source and a load;  
         [0018]    [0018]FIG. 2 is a circuit diagram in which an input power stabilizing circuit at a first embodiment of the present inventions is connected to a DC power source and a load;  
         [0019]    [0019]FIG. 3 is a circuit diagram showing a backward current detecting section in an input power stabilizing circuit at a second embodiment of the present invention; and  
         [0020]    [0020]FIG. 4 is a circuit diagram showing a backward current detecting section in an input power stabilizing circuit at a third embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    Referring now to the drawings, embodiments of the present invention are explained in detail. In the embodiments of the present invention, the reference number of each function has the same number that the conventional example has, when the function at the embodiments of the present invention is almost equal to the conventional example. And the input power stabilizing circuit at the embodiments of the present invention has also the same reference number, but its structure is different from that at the conventional example.  
         [0022]    [0022]FIG. 2 is a circuit diagram in which an input power stabilizing circuit at the first embodiment of the present inventions is connected to a DC power source and a load. As shown in FIG. 2, a DC power source  1  is connected to a load  2  via an input power stabilizing circuit  15  at the first embodiment of the present invention. The input power stabilizing circuit  15  provides a first capacitor  3 , a current transformer  4 , first and second transistors  5  and  6 , a second capacitor  7 , a diode  8 , first, second, third, fourth, and fifth resistors  9 ,  10 ,  11 ,  12 , and  13 , an inductor  16 , and a parasitic diode  17 .  
         [0023]    The first capacitor  3  charges a DC voltage from the DC power source  1 , and supplies the charged voltage to the load  2  when the impedance in the load  2  was changed.  
         [0024]    The current transformer  4  detects a backward current in the input power supply line. Since a current I 1  is generally flowing from the “a” terminal to the “c” terminal at the primary side of the current transformer  4 , the current transformer  4  is in a magnetic saturation state. Consequently, a current is not generated at the secondary side of the current transformer  4 .  
         [0025]    The diode  8  rectifies a voltage generated at the secondary side of the current transformer  4 . The second capacitor  7  holds the peak value of the voltage rectified at the diode  8  and smoothes the voltage.  
         [0026]    The second resistor  10  and the third resistor  11  are connected in series, and work as a voltage divider. A voltage being a desiring ratio of the voltage rectified and smoothed at the diode  8  and the second capacitor  7  is taken out at the tap between the second resistor  10  and the third resistor  11 .  
         [0027]    The voltage divided at the voltage divider (the second and third resistors  10  and  11 ) is applied to the gate of the first transistor  5 . Since a voltage is not being applied to the gate of the first transistor  5  at a normal operating time, the first transistor  5  keeps an “off” state.  
         [0028]    The fourth resistor  12  and the fifth resistor  13  are connected in series, and also work as a voltage divider. A voltage being a desiring ratio of the voltage Vin is taken out at the tap between the fourth resistor  12  and the fifth resistor  13 .  
         [0029]    The voltage divided at the voltage divider (the fourth and fifth resistors  12  and  13 ) is applied to the gate of the second transistor  6 . Since a voltage is being applied to the gate of the second transistor  6  at a normal operating time, the second transistor  6  keeps an “on” state.  
         [0030]    The inductor  16  shows an inductance value equivalent to the inductance value from the terminal “a” to the terminal “c”, and filters out noise from the current inputted from the DC power source  1 . The inductor  16  also works to delay the backward current from the first capacitor  3 . Therefore, the characteristics of the inductor  16  are decided based on the time from that the current transformer  4  detected the backward current to that the second transistor  6  is made to be “off”.  
         [0031]    The parasitic diode  17  works to supply the inputted voltage to the load  2 , irrespective of that the second transistor  6  is “on” or “off”. However, at the normal operating time, the inputted current flows through the second transistor  6  and does not flow through the parasitic diode  17 .  
         [0032]    At the embodiments of the present invention, a field effect transistor (FET) is used for both of the first and second transistors  5  and  6 , by the following reason. It is desirable that the time, from that the current transformer  4  detected the backward current to that the second transistor  6  is made to be “off”, is made to be zero as much as possible, in order to make the backward current discharged from the first capacitor  3  be a minimum value. Therefore, in order to make the time be the minimum value, the FET is the most suitable, because the FET can realize a high speed switching by controlling the voltage of the gate. However, a transistor using for the first and second transistors  5  and  6  is not limited to the FET, a bipolar transistor can be used for the first and second transistors  5  and  6 .  
         [0033]    Next, operation of the input power stabilizing circuit at the first embodiment of the present invention is explained. A case that the input terminals “a” and “b” of the input power stabilizing circuit  15  became a short circuit momentarily is explained.  
         [0034]    First, when the terminals “a” and “b” became a short circuit, electric charges, charged in the first capacitor  3 , starts to flow to the input side terminal “a” via the current transformer  4 .  
         [0035]    During a time that the current transformer  4  becomes a magnetic saturation state in the backward direction, the voltage of Ve is generated at the first resistor  9  at the secondary side of the current transformer  4  at the tap “e”, by this backward current from the first capacitor  3 . This generated voltage Ve is rectified at the diode  8  and is smoothed at the second capacitor  7 . This smoothed voltage is divided at the voltage divider (the second and third resistors  10  and  11 ), and the divided voltage is applied to the gate of the first transistor  5 . When the first transistor  5  becomes “on” by the gate voltage, the both ends of the fifth resistor  13  becomes a short circuit.  
         [0036]    The voltage, which the voltage Vin was divided by the voltage divider (the fourth and fifth resistors  12  and  13 ), has been applied to the gate of the second transistor  6 . When the both ends of the fifth resistor  13  became the short circuit by the first transistor  5 , the gate voltage of the second transistor  6  becomes zero, and the second transistor  6  becomes “off”.  
         [0037]    By the operation mentioned above, the backward current from the terminal “b” to the terminal “d” is prevented by the “off” of the second transistor  6 , and the discharge from the first capacitor  3  becomes small enough.  
         [0038]    The length of the period, which the current transformer  4  becomes the magnetic saturation state in the backward direction, depends on the characteristics of the inductor  16 . When the trouble of the short circuit was solved, that is, the input voltage was recovered, the power is supplied to the load  2  via the parasitic diode  17 , irrespective of the “on” or “off” state of the second transistor  6 . However, soon after the recovery, the second transistor  6  becomes “on” and the current flows through the second transistor  6 .  
         [0039]    Further, when a backward voltage was applied to the input power stabilizing circuit  15 , caused by an error wiring at the input power supply line, the gate of the second transistor  6  becomes a reverse bias and keeps the “off” state. Therefore, the input power stabilizing circuit  15  also works as a protection circuit for a circuit following the input power stabilizing circuit  15 .  
         [0040]    Next, referring to the drawing, a second embodiment of the present invention is explained. FIG. 3 is a circuit diagram showing a backward current detecting section in an input power stabilizing circuit at the second embodiment of the present invention. As shown in FIG. 3, at the second embodiment, plural current transformers are provided in the input power stabilizing circuit. That is, at the second embodiment, a current transformer  4  and a current transformer  4 ′ are provided. The primary sides of the current transformers  4  and  4 ′ are connected in parallel, and the secondary sides of the current transformers  4  and  4 ′ are connected in series.  
         [0041]    At the second embodiment of the present invention, a large current can be detected, and even when a backward current flows in the current transformers  4  and  4 ′ unequally, the backward current can be detected by the total amount of the backward currents.  
         [0042]    Next, referring to the drawing, a third embodiment of the present invention is explained. FIG. 4 is a circuit diagram showing a backward current detecting section in an input power stabilizing circuit at the third embodiment of the present invention. As shown in FIG. 4, at the third embodiment, plural current transformers are also provided in the input power stabilizing circuit. That is, at the third embodiment, a current transformer  4  and a current transformer  4 ′ are provided, as the same as at the second embodiment. However, the connection between the current transformers  4  and  4 ′ is different from the second embodiment. That is, the primary sides of the current transformers  4  and  4 ′ are connected in series, and also the secondary sides of the current transformers  4  and  4 ′ are connected in series.  
         [0043]    At the third embodiment of the present invention, since the primary sides of the current transformers  4  and  4 ′ are connected in series, the detecting voltage can be made to be twice as many voltage as the first and second embodiments. And its current sensitivity can be made to be high simply. With this, even when the backward current discharged from the first capacitor  3  is very small, the voltage, to be applied to the gate of the first transistor  5 , is made to be a high value within the operation of the first transistor  5  is kept, by controlling the on/off of the gate of the first transistor  5 .  
         [0044]    As mentioned above, according to the present invention, when a backward current is detected at the input power supply line, the current line is made to be “off”. With this, a discharge from a capacitor in an input power stabilizing circuit, caused by such as a momentary short circuit of the input power supply line, can be made to be a minimum value.  
         [0045]    At the conventional input power stabilizing circuit used a diode, since a current is always flowing in the diode, electric power being the product of forward voltage and forward current of the diode is always consumed. This electric power is wasteful and causes big heating in the input power stabilizing circuit when a load current is large. Consequently, there was a problem that a structure radiating the heat becomes a big size and its manufacturing cost becomes high. However, according to the present invention, the loss is only caused by “on” resistance of a second transistor, and at the normal operating state, a current does not flow through a parasitic diode of the second transistor. Therefore, the amount of heating is reduced largely, compared with the case that the diode was used as mentioned at the conventional example, and its heat radiating structure can be made to be small and its manufacturing cost is made to be low at the present invention.  
         [0046]    While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by those embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.