Abstract:
A voltage control circuit includes a voltage step-up device that steps up an applied voltage to a stepped-up voltage, an electronic device to which the stepped-up voltage is applied, a current monitor that monitors a supplied current that is supplied to the electronic device, based on the stepped-up voltage, a step-up controller that controls the stepped-up voltage to be a predetermined target voltage, based on the supplied current, and a warning provider that provides a warning when the current monitor can not monitor the supplied current.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a voltage control circuit for an endoscope, and especially relates to a voltage control circuit including a voltage step-up circuit for a light source for illuminating a subject, and so on.  
         [0003]     2. Description of the Related Art  
         [0004]     A light source for illuminating a subject is sometimes provide at a tip of a scope of an endoscope, for observing a dark subject inside a body. As a light source, an LED is known. In the case where a battery for driving the light source is used, a voltage step-up circuit is also generally used. This is because a high voltage is required for stabilizing the current supplied to an LED especially if the battery voltage has changed, or for increasing the current supplied to the LED for increasing brightness of the illuminating light. Further, the amount of current supplied to the LED for illumination is controlled by monitoring and feeding back the current.  
         [0005]     Generally, in the case where an LED for illumination is provided at the tip of a scope of a portable endoscope, the voltage control circuit for the voltage step-up circuit is located apart from the LED. When a portable endoscope is manufactured, each of the voltage control circuit and the LED is built separately, and after being built, they are connected to each other. Therefore, a disconnection between the circuit and the LED, such as a soldering error on lead wires, may occur. Further, the tip of a scope is required to be small and the space for installing the LED is small, therefore, a connecting error when installing the LED may also occur.  
         [0006]     When an error occurs with the LED for illuminating a subject, such as a disconnection error, feeding back the current becomes impossible and the step up circuit becomes uncontrollable. Therefore, a large excess voltage being much higher than the required level, may be generated. In this case, peripheral elements may be broken when the excess voltage level is higher than the tolerance level of the elements.  
       SUMMARY OF THE INVENTION  
       [0007]     Therefore, an object of the present invention is to provide a voltage control circuit that can provide a warning on a display to inform of an error and identify the cause of the error to a user, when a step-up circuit becomes uncontrollable.  
         [0008]     A voltage control circuit according to the present invention, includes a voltage step-up device that steps up an applied voltage to a stepped-up voltage, an electronic device to which the stepped-up voltage is applied, a current monitor that monitors a supplied current that is supplied to the electronic device, based on the stepped-up voltage, a step-up controller that controls the stepped-up voltage to be a predetermined target voltage, based on the supplied current, and a warning provider that provides a warning when the current monitor can not monitor the supplied current.  
         [0009]     An endoscope according to the present invention, includes a voltage step-up device that steps up an applied voltage to a stepped-up voltage, an electronic device to which the stepped-up voltage is applied, a current monitor that monitors a supplied current that is supplied to the electronic device, based on the stepped-up voltage, a step-up controller that controls the stepped-up voltage to be a predetermined target voltage, based on the supplied current, and a warning provider that provides a warning when the current monitor can not monitor the supplied current. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The present invention will be better understood from the description of the preferred embodiments of the invention set forth below together with the accompanying drawings, in which:  
         [0011]      FIG. 1  is a block diagram of a fiber scope of a portable endoscope of the first embodiment;  
         [0012]      FIG. 2  is a block diagram of a voltage control circuit provided in a light driving circuit of the first embodiment;  
         [0013]      FIG. 3  is a graph representing a relation between the amount of current flowing to a voltage-warning LED and the amount of voltage output from a DC/DC converter;  
         [0014]      FIG. 4  is a block diagram of a voltage control circuit of the second embodiment;  
         [0015]      FIG. 5  is a block diagram of an auxiliary voltage-control circuit having a voltage warning display function;  
         [0016]      FIG. 6  is a block diagram of a voltage control circuit of a comparative example;  
         [0017]      FIG. 7  is a graph representing the change in the applied voltage from a battery over time;  
         [0018]      FIG. 8  is a graph representing the change in the output voltage from a power source control circuit over time;  
         [0019]      FIG. 9  is a graph representing an operation state of an n-channel FET in a display driving circuit;  
         [0020]      FIG. 10  is a graph representing the change in brightness of light emitted by the voltage-warning LED of the comparative example in  FIG. 6 ;  
         [0021]      FIG. 11  is a graph representing the change in brightness of light emitted by the voltage-warning LED in the auxiliary voltage-control circuit;  
         [0022]      FIG. 12  is a graph representing the change in brightness of light emitted by the voltage-warning LED due to trouble in the voltage stepping up control process and a decrease in the applied voltage; and  
         [0023]      FIG. 13  is a block diagram of a voltage control circuit including an exclusive power source for the voltage-warning LED. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]     Hereinafter, the preferred embodiments of the present invention are described with reference to the attached drawings.  
         [0025]     As shown in  FIG. 1 , at the tip of a fiber scope  10 , first and second LEDs  14  and  16  for illuminating a subject S, and first and second lighting lenses  18  and  19  are provided. The first and second LEDs  14  and  16  emit illuminating light on the subject S when provided with power from a battery  12 , under the control of a light driving circuit  20 . Illuminating light reflected from the surface of the subject S as reflected light, enters the eyes of a user via an objective lens  22 , an imaging guide  24 , and an eyepiece lens  26 . The subject S is observed by a user.  
         [0026]     A voltage-warning light  28  is provided on the surface of the body of the fiber scope  10  that a user holds. A voltage-warning LED (not shown) is included in the voltage-warning light  28 . The voltage-warning LED emits light to inform a user of trouble occurring in the control process for stepping up the applied voltage from the battery  12 , in the light driving circuit  20 . For example, when it is impossible to carry out the control process for stepping up the applied voltage from the battery  12  due to a disconnection at the first LED  14  or the second LED  16  which should be connected to the light driving circuit  20 , so that the applied voltage is stepped up by an abnormally large amount, the voltage-warning LED automatically emits light.  
         [0027]     As shown in  FIG. 2 , in the light driving circuit  20 , a voltage control circuit  25  including a power-source control circuit  30 , illuminating elements  50 , and an auxiliary voltage-control circuit  60 , are provided. In the power-source control circuit  30 , a DC/DC converter and a power switch  38  are provided. The DC/DC converter includes the step-up DC/DC converter IC  32 , a capacitor  40 , a transistor  42 , a coil  44 , a first resistor  45 , a shottky diode  46 , and a smoothing capacitor  48 . In the illuminating elements  50 , the first and second LEDs  14  and  16  are provided.  
         [0028]     When the applied voltage from the battery  12  is stepped up to the stepped-up voltage by the DC/DC converter and the stepped-up voltage is applied to the first and second LEDs  14  and  16 , current flows to the first and second LEDs  14  and  16 , so that the first and second LEDs  14  and  16  illuminate light. The current is monitored by the first resistor  45  which is connected to a first articulation point  39 , and the DC/DC converter IC  32  operates so that a constant current flows to the first articulation point  39 .  
         [0029]     That is, when the power switch  38  is turned on, a voltage is applied to a third terminal  32 C of the DC/DC converter IC  32  via a second articulation point  41 . The DC/DC converter IC  32  supplies a pulse base current to the transistor  42  connected to a fifth terminal  32 E of the DC/DC converter IC  32 . The repeating frequency of the active period of the driving voltage which is applied to the transistor  42  by the DC/DC converter IC  32  via the fifth terminal  32 E, that is, the repeating frequency at the fifth terminal being in a high state, is changeable according to the voltage at the first articulation point  39 , detected by the first terminal  32 A.  
         [0030]     That is, when the voltage at the first articulation point  39  is lower than a set voltage, the repeating frequency of the voltage from the fifth terminal  32 E at the base terminal of the transistor  42 , being in a high state is shortened, so that the frequency of the transistor  42  being in an on state, becomes high. On the other hand, when the voltage at the first articulation point  39  is higher than a set voltage, the repeating frequency of the voltage from the fifth terminal  32 E at the base terminal of the transistor  42 , being in a high state is lengthened, so that the frequency of the transistor  42  being in an on state becomes low. As a result of this, the voltage at the first articulation point  39 , that is, the stepped-up voltage applied to the first and second LEDs  14  and  16  is kept at almost a constant voltage (target voltage).  
         [0031]     The coil  44  which functions as a step up inductor is provided between the second articulation point  41  and the third articulation point  43 , the shottky diode  46  is provided between the third articulation point  43  and the first LED  14 , to prevent reverse current, and the smoothing capacitor  48  is provided to smooth the current.  
         [0032]     In the auxiliary voltage-control circuit  60 , the voltage-warning LED  34 , a second resistor  58 , and a zener diode  62  are provided in case the stepping up process is not properly controlled due to trouble with the DC/DC converter and so on. For example, when a disconnection occurs at the first LED  14  or the second LED  16 , current to the first resistor  45  stops flowing, and the voltage at the first articulation point  39  becomes undetectable by the first terminal  32 A, so that the voltage applied by the DC/DC converter IC  32  may become abnormally high. Therefore, in a voltage control circuit where an auxiliary voltage-control function is not provided, such as a comparative circuit explained later, a higher voltage than the target voltage (hereinafter an excess voltage) is output from the power-source control circuit  30 , and each element may be broken.  
         [0033]     On the other hand, in the auxiliary voltage-control circuit  60  having the zener diode  62 , the excess voltage is applied to the zener diode  62  via the second resistor  58 . When the excess voltage being higher than the predetermined zener voltage is applied to the zener diode  62 , additional current is drawn from the output side of the power-source control circuit  30  and flows to the zener diode  62 . That is, the additional current flows to the zener diode  62  from the output side of the power-source control circuit  30 . As a result of this, generation of an excess voltage stepped up to be much higher than the zener voltage is prevented, and the voltage-warning LED  34  emits light.  
         [0034]      FIG. 3  represents a relation between the amount of current flowing to the voltage-warning LED  34  and the amount of voltage output from the DC/DC converter, when a disconnection at the first LED  14  or the second LED  16  and so on occurs, the voltage at the first articulation point  39  becomes undetectable by the first terminal  32 A.  
         [0035]     The plurality of points plotted on the broken line in  FIG. 3 , represent measured values of the current flowing to the voltage-warning LED  34  and the output voltage from the DC/DC converter. The asymptotic curve (solid line) in  FIG. 3  approaches these points smoothly. The amount of current flowing to the voltage-warning LED  34  is calculated by subtracting the zener voltage drop at the zener diode  62  and the forward voltage to the voltage-warning LED  34  from the output voltage of the DC/DC converter, and dividing the subtracted result by the resistance value of the second resistor  58 .  
         [0036]     The level of the output voltage from the DC/DC converter, is extremely large when only a small current flows to the voltage-warning LED  34 , the second resistor  58 , and the zener diode  62 . However, when a slightly larger amount of current flows through these elements, the output voltage from the DC/DC converter drops by a large amount. That is, the second resistor  58  and the zener diode  62  prevent the generation of an excess voltage that is much larger than the target voltage.  
         [0037]     As mentioned above, in the voltage control circuit  25  of this embodiment, in the case where the stepping up of voltage by the power-source control circuit  30  becomes uncontrollable, generation of excess voltage is prevented, and a user is informed of the trouble in the voltage stepping up control process when the voltage-warning LED  34  starts to emit light.  
         [0038]     The voltage control circuit  25  of this embodiment, can be provided in fixed type endoscopes using a commercial power source, not only in the fiber scope  10  which is portable and uses the battery  12 .  
         [0039]     Hereinafter, the second embodiment is explained. In  FIGS. 4 and 5 , showing the second embodiment, the components that are the same as those in the first embodiment have the same reference numerals as those in the first embodiment.  
         [0040]     In the voltage control circuit  25  of the second embodiment, a voltage warning display function and a display driving circuit  36  are provided in the auxiliary voltage-control circuit  60 , and this is the difference to the first embodiment. The display driving circuit  36  is provided to further make the voltage-warning LED  34  emit light when the applied voltage from the battery  12  has decreased due to long-term usage and so on, and for warning a user of the drop in the applied voltage.  
         [0041]     Next, the operation of the display driving circuit  36  is explained (see  FIG. 5 ). In the display driving circuit  36 , a standard voltage generating circuit  52  is provided. The standard voltage generating circuit  52 , for example, generates a standard voltage of 2.3 (V). The applied voltage input by the battery  12  is divided by resistors, and the divided voltage and the standard voltage are input to the comparator  54 . In the comparator  54 , these input voltages are compared and it is judged whether the applied voltage from the battery  12  is smaller than the standard voltage of 2.3 (V) or not.  
         [0042]     When it is judged that the divided voltage according to the applied voltage from the battery  12  is smaller than the standard voltage, the high state voltage is applied to the gate of the n-channel FET  56  by the comparator  54 . Therefore, when the divided voltage from the battery  12  is smaller than the standard voltage, the voltage at the output terminal of the comparator  54  becomes high, the gate voltage of the n-channel FET  56  also becomes high, and current flows between the drain and source. As a result of this, the current flows to the voltage-warning LED  34  connected to the n-channel FET  56  via the second resistor  58 , and the voltage-warning LED  34  emits light to inform a user that the residual quantity of the battery  12  is smaller than the predetermined level.  
         [0043]     As mentioned above, due to the auxiliary voltage-control circuit  60  having the voltage warning display function, the voltage-warning LED  34  emits light, not only when the output voltage from the DC/DC converter is large excess because control of the voltage stepping up process by the power-source control circuit  30  becomes impossible, similarly to the first embodiment, but also when the applied voltage from the battery  12  has decreased.  
         [0044]     In this embodiment, when the output voltage of the battery  12  is decreased, as long as the power-source control circuit  30  functions, current is supplied to the voltage-warning LED  34  based on the stepped up voltage. That is, current based on the output voltage of the battery  12  is not supplied to the voltage-warning LED  34 , but current based on voltage stepped up under the control of the power-source control circuit  30 , is supplied via the second resistor  58 .  
         [0045]     As mentioned above, when the applied voltage from the battery  12  is decreased, sufficient current is supplied to the voltage-warning LED  34  to light it brightly, based on the stepped up voltage via the second resistor  58 , as long as the power-source control circuit  30  operates. Therefore, the voltage-warning light  28  can clearly inform a user that the output voltage of the battery  12  has decreased. Note that in this embodiment, the DC/DC converter operates when a voltage higher than 2.0(V) is applied from the battery  12 .  
         [0046]     On the other hand, in a voltage control circuit  27  of a comparative example shown in  FIG. 6 , while the illuminating elements  50  are driven by the stepped up voltage generated by the power-source control circuit  30  from the applied voltage from the battery  12 , the voltage-warning LED  34  is directly connected to the battery  12  via the second resister  58  and emits light using the current generated by the applied voltage from the battery  12  and the second resister  58 . Therefore, brightness of the light emitted by the voltage-warning LED  34  decreases in accordance with the decreased residual quantity of the battery  12 . As a result of this, when the voltage-warning LED  34  emits light to warn that the residual quantity of the battery  12  has decreased, the amount of the current flowing through the voltage-warning LED  34  is small. Therefore, brightness of the light emitted by the voltage-warning LED  34  is low, so that the warning display may not be recognized by a user.  
         [0047]     Note that in the comparative example in  FIG. 6 , a zener diode  63  is provided between an output terminal at the hot side of the smoothing capacitor  48  and the first articulation point  39 , as an excessive voltage protection circuit for protecting the power-source control circuit  30  from an excessive voltage generated by an open load due to the disconnection of the illuminating elements  50 .  
         [0048]     As shown in  FIG. 7 , the applied voltage from the battery  12 , that is battery voltage, is 3.5 (V) at the start of use (the usage time “t”=0), and gets smaller with the passing of usage time “t”. In  FIGS. 8-13 , the situation where the applied voltage changes as shown in  FIG. 7 , is premised. When the applied voltage from the battery  12  is more than 2.0 (V), the DC/DC converter operates so that the output voltage from the DC/DC converter is constant, for example being 7.5 (V) (see  FIG. 8 ). When the amount of the applied voltage becomes smaller than 2.0 (V), the DC/DC converter does not operate because a voltage larger than 2.0 (V) is necessary for the operation of the DC/DC converter IC  32 . Therefore, applied voltage from the battery  12  is output via the coil  44 , the shottky diode  46 , and the second resistor  58 . At this time, in the auxiliary voltage-control circuit  60  having the warning display function, the voltage-warning LED  34  is switched on for emitting light, and therefore the voltage-warning LED  34  emits light.  
         [0049]     When the applied voltage is lower than the standard voltage of 2.3 (V) and higher than 2.0 (V), because the DC/DC converter operates, the n-channel FET  56  in the display driving circuit  36  is turned to be in the on state (see  FIG. 9 ). At this time, the output voltage at the output terminal “OUT” (see  FIG. 5 ) is decreased similarly to the applied voltage from the battery  12 . As a result of this, current corresponding to the decreased voltage is supplied to the voltage-warning LED  34 , so that the voltage-warning LED  34  emits light. In accordance with the decrease in the applied voltage from the battery  12  represented by FIGS.  7  to  9 , the change over time in brightness of light emitted by the voltage-warning LED  34 , in the auxiliary voltage-control circuit  60  having the voltage warning display function, is explained below.  
         [0050]     Both in  FIG. 10  representing the change in brightness of light emitted by the voltage-warning LED  34  directly using the power from the battery  12 , in a display circuit  61  of the comparative example (see  FIG. 6 ), and in  FIG. 11  representing the change in brightness of light emitted by the voltage-warning LED  34  in the auxiliary voltage-control circuit  60 , the chain line represents the change over time in the applied voltage from the battery  12 . When the applied voltage from the battery  12  is higher than the standard voltage of 2.3 (V), both in the display circuit  61  of the comparative example and in the auxiliary voltage-control circuit  60 , the voltage-warning LED  34  does not light. When the applied voltage gradually decreases, and becomes lower than the standard voltage of 2.3(V), in the display circuit  61 , brightness of light emitted by the voltage-warning LED  34  also gradually decreases from brightness level in proportion to the standard voltage of 2.3 (V) (hereinafter, level 1). This is because the current flowing to the voltage-warning LED  34 , that depends on the applied voltage from the battery  12  decreases.  
         [0051]     On the other hand, a stable voltage that is in proportion to the output voltage from the DC/DC converter and much higher than the standard voltage of 2.3 (V) is applied to the voltage-warning LED  34  in the auxiliary voltage-control circuit  60  having the voltage warning display function. Therefore, a large current can constantly be supplied, so that the voltage-warning LED  34  can emit light having a constant brightness level (see  FIG. 11 ).  
         [0052]     When the applied voltage from the battery  12  drops below 2.0 (V), the stepped-up voltage from the DC/DC converter stops, in both the auxiliary voltage-control circuit  60  having the voltage warning display function, and in the display circuit  61 , because the DC/DC converter does not operate. Therefore, brightness of light emitted by the voltage-warning LED  34  is at a level that is in proportion to the applied voltage 2.0 (V) through the coil  44 , the shottky diode  46 , the second resistor  58 , and so on (hereinafter, level 2). When the applied voltage from the battery  12  is further reduced and drops under 2.0 (V), brightness of light from the voltage-warning LED  34  also drops to a level below level 2, in accordance with the applied voltage.  
         [0053]     As mentioned above, brightness of light emitted by the voltage-warning LED  34  in the display circuit  61  of the comparative example, becomes lower than level 1 to less than level 2, regardless of whether the DC/DC converter operates or not. On the other hand, brightness of light emitted by the voltage-warning LED  34  in the auxiliary voltage-control circuit  60  having the voltage warning display function, is much higher than level 1 until the end of the operation of the DC/DC converter.  
         [0054]     In this embodiment, as mentioned above, the voltage-warning LED  34  emits a bright light until just before the DC/DC converter stops operation, that is until the requirement for warning of a drop in the applied voltage from the battery  12  is the largest, so that the voltage-warning light  28  including the voltage-warning LED  34  can clearly inform a user of a decrease in the residual quantity of the battery  12 .  
         [0055]     In this embodiment, the DC/DC converter operates when a voltage higher than 2.0(V) is applied, therefore, the standard voltage is set to be 2.3 (V) which is slightly higher than 2.0(V). The level of the standard voltage can be modified according to the minimum required level of the applied voltage for the operation of the DC/DC converter and other circuits, which operate for stepping up voltage.  
         [0056]     In  FIG. 12 , when the applied voltage from the battery  12  represented by the chain line is higher than 2.3 (V), that is when the usage time “t”=0 to t 1 , the voltage-warning LED  34  emits light only when trouble occurs in the voltage step up control process. In this case, brightness of light emitted by the voltage-warning LED  34  is higher than that when the applied voltage is lower than 2.3 (V), that is when the usage time “t”&gt;t 1 . This is because current based on excess voltage larger than the voltage appropriately stepped up, temporally flows to the voltage-warning LED  34  when the applied voltage is not appropriately stepped up by the DC/DC converter IC  32  and so on.  
         [0057]     As mentioned above, in this embodiment, the voltage-warning light  28  can clearly warn a user not only of trouble in the control process for stepping up the voltage due to an open load in the illuminating elements  50  and so on, but also of a drop in the applied voltage from the battery  12 . Further, the structure of the auxiliary voltage-control circuit  60  can be simplified, because only the voltage-warning LED  34  as a single lighting element is provided for informing of trouble caused by a problem in the stepping up control process and a drop in the applied voltage from the battery  12 .  
         [0058]     In this embodiment, only the voltage-warning LED  34  is provided to inform of trouble in a control process for stepping up voltage, and a drop in the applied voltage, however, a plurality of lighting elements can be provided for informing of each respective problem. In this case, it is possible to inform a user which one of the voltage stepping up control process and the applied voltage drop, is the problem.  
         [0059]     In this embodiment, as shown in  FIG. 13 , an additional power source  35  for indication, that is an exclusive power source for the voltage-warning LED  34  to indicate a drop in the battery voltage, can be installed. In this case, when the applied voltage from the battery  12  becomes lower than 2.0 (V) and the DC/DC converter IC  32  does not operate, brightness of light emitted by the voltage-warning LED  34  is maintained to be higher than the above-mentioned level 1.  
         [0060]     In both the first and second embodiments, a lamp can be used instead of the first and second LED  14  and  16 , being light sources for illuminating a subject, or the voltage-warning LED  34 . Further, the number, arrangement, and so on of the light sources are not limited to those in the embodiments, for example, a single light source which emits bright light for illuminating a subject can be used, or two light sources can be arranged in parallel.  
         [0061]     The voltage control circuit  25  can be produced using conventional elements. For example, the DC/DC converter IC  32  can be the “TK11840L” produced by TOKO, INC.  
         [0062]     Finally, it will be understood by those skilled in the art that the foregoing description is of preferred embodiments of the apparatus, and that various changes and modifications may be made to the present invention without departing from scope thereof.  
         [0063]     The present disclosure relates to subject matter contained in Japanese Patent Application No.2005-117005 (filed on Apr. 14, 2005) which is expressly incorporated herein, by reference, in its entirety.