Abstract:
A tertiary coil is provided in a DC/DC converter. An electric current is generated in the tertiary coil due to on an alternating-current voltage produced in the tertiary coil. An electrical current supplying circuit supplies the electric current generated in the tertiary coil to a load when supplementary power must be supplied to the load.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1) Field of the Invention  
         [0002]     The present invention relates to a DC/DC converter.  
         [0003]     2) Description of the Related Art  
         [0004]     A conventional DC/DC converter, that monitors an output voltage and regenerates the output voltage in a primary condenser to reduce damage to a power source, is disclosed in Japanese Patent Application Laid-Open Publication No. 2001-103746 (see pages 2-3, and FIG. 1). Further, a conventional technology, in which an excitation current is sent through a secondary coil to cause a magnetic flux density of a choker coil to become smaller when a load increases and an output voltage decreases, is disclosed in Japanese Patent Application Laid-Open Publication No. 2003-189613 (see pages 5-6, and FIG. 1).  
         [0005]     A circuit configuration of a conventional DC/DC converter is illustrated in  FIG. 5 . The output characteristics of this conventional DC/DC converter are illustrated in  FIGS. 6A and 6B .  FIG. 7  is a diagram of the load characteristics of a power source. These figures are used to explain a conventional DC/DC converter.  
         [0006]     As shown in  FIG. 5 , the conventional DC/DC converter includes a condenser C 1  that is connected at both ends to a direct-current (DC) input voltage Vin; a primary coil N 1  of a transformer that is connected to one end of a DC input voltage Vin; and a switching transistor TR 1  that is connected in tandem to the primary coil. The switching transistor TR 1  is a FET (field-effect transistor), for example. The other end of the primary coil N 1  is connected to a drain of the switching transistor TR 1 ; and the source of the switching transistor TR 1  is connected to the other end of the DC input voltage Vin.  
         [0007]     The conventional DC/DC converter also includes a secondary coil N 2  of a transformer T; and rectifier diodes D 1  and D 2  that are connected to the secondary coil N 2 . A choke coil L 1  is used for smoothing; and is connected to a cathode of the diode D 1 . A condenser C 2  is used for smoothing; and is connected between the other end of the choke coil L 1  and the other end of the common line. Output voltage Vo is taken out from both ends of the condenser C 2 . Condensers Co 1  to Con are connected in parallel between output lines. There is a load  1  that is connected to an output edge.  
         [0008]     Resistors R 2  and R 3  divide the output voltage Vo. An IC circuit  2  activates a photocoupler PC that receives voltage of the divider point by use of the resistors R 2  and R 3 . The photocoupler PC is configured from a photodiode D 3  and a phototransistor TR 2 . The positive voltage of the output voltage is connected to an anode of the photodiode D 3  via a resistor R 4 ; and the photodiode D 3  is connected to an IC circuit  2  on the cathode-side of the photodiode D 3 . The collector and emitter of the phototransistor TR 2 , that configures the photocoupler PC, are inside a controlling circuit  3 . The controlling circuit  3  provides “on” or “off” controlling signals to a gate of the switching transistor TR 1  which is a switching FET (field-effect transistor). Operations of a circuit configured in this manner are explained below.  
         [0009]     The switching transistor TR 1  switches the DC voltage Vin in accordance with the switching pulse provided by the controlling circuit  3 . The secondary coil N 2  of a transistor T 2  generates a high-frequency alternating-current. This high-frequency alternating-current is converted into a DC voltage by the rectifier diodes D 1  and D 2 ; and then further converted into smooth DC voltage by smoothing circuits consisting of the choke coil L 1  and the condenser C 2 . This DC voltage becomes an output Vo from the DC/DC converter.  
         [0010]     The output voltage Vo is monitored by divider circuits that use the resistors R 2  and R 3 ; and the monitored output voltage enters the IC circuit  2 . The IC circuit  2  activates, in accordance with the output voltage Vo, the photodiode D 3 ; and, depending on the electrical current that is flowing at that time, the photodiode D 3  emits light. This emitted light is conveyed to the phototransistor TR 2 ; and causes an electrical current to flow in the phototransistor TR 2 . In this manner, the controlling circuit  3  is provided with a controlling signal in accordance with the output voltage Vo. When the output voltage Vo is low, the switching transistor TR 1  that receives the output of the controlling circuit  3  is in an “on” state for a longer period of time. But when the output voltage Vo is high, the switching transistor TR 1  is in an “on” for a shorter period of time. As a result, the value of the output voltage Vo remains constant due to this PWM (pulse-width modulation) control by the controlling circuit  3 .  
         [0011]      FIGS. 6A and 6B  are diagrams of the output fluctuation characteristics of the conventional DC/DC converter.  FIG. 6A  is a diagram of a change in an output electrical current and  FIG. 6B  is a diagram of a fluctuation of an output voltage. For example, the initial output electrical current is lo. At a time t 1 , the output electrical current rapidly changes from I 1  to I 2  (as illustrated in  FIG. 6A ). Concurrently, the output voltage Vo rapidly decreases from Vo 1  by an amount of Vd 1 , as illustrated in  FIG. 6B  The time period of the decrease, from time t 1  until the time when output voltage falls by the amount of Vd 1 , is a time Td 1 . Later, the output voltage Vo partially recovers up to a level Vo 2 . The differences of voltages Vo 1  to Vo 2  is ΔV, which is in accordance with the characteristics of the power source.  
         [0012]      FIG. 7  is a diagram of the load characteristics of a power source. In  FIG. 7 , the vertical axis is the output voltage Vo, the horizontal axis is a load lo. As the load current lo increases, the output voltage Vo decreases. The output voltage when the load current is lo is I 1  is Vo 1 . The output voltage when the load current is I 2  is Vo 2 . A voltage differential ΔV is generated between Vo 1  and Vo 2 . The differential ΔV of the characteristics of  FIGS. 6A and 6B  are due to this kind of reason.  
         [0013]     Recent electronic devices use mainly the DC/DC converter illustrated in  FIG. 5  to increase efficiency, but since the DC/DC converters cannot, from an operating viewpoint, keep pace with high-speed responses of an LSI, there is a large voltage fluctuation when the load suddenly changes and there are problems such as an occurrence of a malfunction of the LSI and the like. An output line in  FIG. 5  is connected to large-capacity condensers Co 1  to Con to respond to the sudden changes of load. However, there is a problem that taking this type of configuration requires large-capacity condensers, which makes the configuration high-priced and packaging space of the configuration larger.  
       SUMMARY OF THE INVENTION  
       [0014]     It is an object of the present invention to at least solve the problems in the conventional technology.  
         [0015]     A DC/DC converter according to an aspect of the present invention includes a transformer having a primary coil, a secondary coil, and a tertiary coil, wherein a direct-current voltage is input to a primary coil of a transformer, switching of the direct-current voltage is performed to generate an alternating-current voltage in a secondary coil, and an electric current based on the alternating-current voltage is supplied to a load; and an electrical current supplying circuit that supplies to the load an electrical current based on an alternating-current voltage generated in the tertiary coil. The electrical current supplying circuit is configured to supply the electrical current to the load when excessively large power is required by the load.  
         [0016]     The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a block diagram of a DC/DC converter according to an embodiment of the present invention;  
         [0018]      FIG. 2  is an exemplary circuit diagram of the DC/DC converter shown in  FIG. 1 ;  
         [0019]      FIG. 3  is a flowchart of an operation performed by the DC/DC converter shown in  FIG. 1 ;  
         [0020]      FIG. 4A  is a diagram of a change in an output electrical current of the DC/DC converter shown in  FIG. 1 ;  
         [0021]      FIG. 4B  is a diagram of a fluctuation of an output voltage of the DC/DC converter shown in  FIG. 1 ;  
         [0022]      FIG. 5  is a circuit diagram of a conventional DC/DC converter;  
         [0023]      FIG. 6A  is a diagram of a change in an output electrical current of the conventional DC/DC converter shown in  FIG. 5 ;  
         [0024]      FIG. 6B  is a diagram of a fluctuation of an output voltage of the conventional DC/DC converter shown in  FIG. 5 ; and  
         [0025]      FIG. 7  is a diagram of load characteristics of a power source. 
     
    
     DETAILED DESCRIPTION  
       [0026]     Exemplary embodiments of a DC/DC converter according to the present invention are explained below in reference to the accompanying drawings.  
         [0027]      FIG. 1  is a block diagram of a DC/DC converter according to an embodiment of the present invention.  FIG. 2  is an exemplary circuit diaagram of the DC/DC converter shown in  FIG. 1 . In the figures, dentical items have been provided with identical reference numerals. In the figures, a configuration, in which an input of a direct-current voltage Vin, a rectification and a smoothing of an alternating-current voltage induced in a secondary coil N 2  of a transformer T to acquire a direct-current voltage, and a PWM control of a primary switching transistor TR 1  to stabilize the acquired direct-current voltage Vo are performed, is completely identical to the conventional circuit illustrated in  FIG. 5 .  
         [0028]     In other words, the output voltage Vo is monitored by a divided resistance from resistors R 2  and R 3 , this monitored voltage is input to an IC circuit, and a photodiode D 3  of a photocoupler PC is activated by a signal in accordance with the monitored voltage. This electrical current activates a controlling circuit  3 , which controls a time that a switching transistor TR 1  is “on”. As a result, when the output voltage Vo decreases, the time that the switching transistor TR 1  is “on” is lengthened; and when the output voltage Vo increases, the time that the switching transistor TR 1  is “on” is shortened. This PWM control keeps the output voltage Vo constant.  
         [0029]     An electrical current supplying circuit  10  supplies electrical current, as the need arises, to a power line L; and is the circuit that characterizes the present invention. An output detecting circuit # 2   11  monitors the output voltage Vo. The electrical current supplying circuit is controlled in accordance with the detection results of this output detecting circuit # 2   11  to supplement the electrical current supplied to the load  1 . In the electrical current supplying circuit  10 , there is a tertiary coil N 3  of the transformer T, a rectifying diode D 4  which is connected to the tertiary coil N 3 , and a smoothing condenser C 3  that is connected to a cathode of the rectifying diode D 4 . An output of a rectifying circuit  5  and a smoothing circuit  6  that are configured from the rectifying diode D 4  and the smoothing condenser C 3  is Vc. This voltage Vc is connected to an emitter of an electrical current supplying transistor TR 3  via a resistor R 5 . The collector of the electrical current supplying transistor TR 3  is connected to the power line L.  
         [0030]     In the output detecting circuit # 2   11 , there are resistors R 6  and R 7  that monitor electrical output voltages. There is an electrical potential at the divider point between these resistors R 6  and R 7  which are connected to a positive (+) input of an operational amplifier OP. A tandem circuit of a diode D 5  and a resistor R 7  is connected between the positive input of the operational amplifier OP and the output to configure a recovery circuit. The output of the output detecting circuit # 2   11  is connected to a base of the electrical current supplying transistor TR 3  via a resistor R 8 . A reference voltage Es is impressed on the negative (−) input of the operational amplifier OP.  
         [0031]     There is a primary controlling circuit that controls the output circuit of the output voltage Vo; and a secondary controlling circuit that controls the electrical current supplying circuit  10 . The correspondences between  FIG. 1  and  FIG. 2  are as follows. The rectifying circuit  5  of  FIG. 1  corresponds to the circuit formed by diodes D 1  and D 2  of  FIG. 2 . The smoothing circuit  6  of  FIG. 1  corresponds to the circuit of a choke coil L 1  and a condenser C 2  of  FIG. 2 . The output detecting circuit # 1   7  of  FIG. 1  corresponds to the circuit formed from the resistors R 2 , R 3 , and R 4 , the photocoupler PC, and the IC circuit IC. The controlling circuit  8  of  FIG. 1  corresponds to the controlling circuit  3  of  FIG. 2 . The following is an explanation of operations of circuits configured in this manner.  
         [0032]     The main power supplying circuit supplies power to the load  1  by use of the stabilizing operations previously described. When the output voltage Vo is held at a predetermined value, the output detecting circuit # 2   11  does not operate. In other words, when the output voltage Vo is a predetermined value, the electrical potential of the divider point between the resistors R 6  and R 7  is higher than the reference voltage Es. Accordingly, the output of the operational amplifier OP becomes positive, and the reverse bias of the electrical current supplying transistor TR 3  of the electrical current supplying circuit  10  is maintained. Therefore, a supplementary electrical current Is does not flow.  
         [0033]     If the load  1  drastically changes and the output voltage Vo decreases, this change is detected by the output detecting circuit # 2   11 . Then, the electrical potential at the divider point between the resistors R 6  and R 7  becomes lower, and the difference between the electrical potential and the reference voltage Es, which the operational amplifier OP outputs, decreases. As a result, the electrical current in the electrical current supplying transistor TR 3  receives a forward bias; and electrical current flows in the electrical current supplying transistor TR 3 . This flowing electrical current is Is, which supplements the load current that flows to the load  1  through the power line L. In other words, when there is an output electrical current lo from the main power circuit, lo′=lo when electrical current is not supplied from the electrical current supplying circuit  10 . But if the load  1  suddenly changes and an excessively large electrical current is needed, lo′+ls=lo, and the supplementary electrical current Is from the electrical current supplying circuit  10  becomes a portion of the load current and flows to the load  1 .  
         [0034]     In this manner, by mean of the present invention, large-capacity condensers are not equipped on the power line L, and it is possible to respond to changes in the load.  
         [0035]     Also, by means of the present invention, it is possible to perform stabilization control of the output voltage at the primary controlling circuit; and to perform electrical current supplying control when the load suddenly changes.  
         [0036]      FIG. 3  is a diagram that illustrates an operational flow of the present invention.  
         [0037]      FIG. 4A  is a diagram of a change in an output electrical current of a circuit according to the present invention.  
         [0038]      FIG. 4B  is a diagram of a fluctuation of an output voltage of a circuit according to the present invention.  
         [0039]     An explanation is given below while comparing  FIG. 3 ,  FIG. 4A , and  FIG. 4B . First, the electrical current of an LSI, which is a load, suddenly increases (I 1 →I 2 ) as illustrated in  FIG. 4A  (step S 1 ). As a result, the output voltage Vo 1  of an OBP (on-board power source) decreases, as illustrated in  FIG. 4B  (step S 2 ). This decrease of voltage is detected by a secondary controlling circuit (refer to  FIG. 2 ) (step S 3 ). The detected voltage is Vs. The secondary controlling circuit of the operational amplifier OP starts operations (step S 4 ). As a result, the electrical current supplying transistor TR 3  of the electrical current supplying circuit  10  goes “on”.  
         [0040]     When the electrical current supplying transistor TR 3  goes “on”, the supplementary electrical current Is is supplied from the supplementary power source (electrical current supplying circuit  10 ) (step S 6 ). Concurrently, the output voltage Vo rises until the detected voltage Vs of the secondary controlling circuit (step S 7 ). When the output voltage Vo rises, the secondary controlling circuit becomes inactive, and the operational amplifier OP becomes “off” (step S 8 ). Then, the electrical current supplying transistor TR 3  becomes “off”; and the electrical current supply from the supplementary power source (electrical current supplying circuit  10 ) stops (step S 9 ). Next, when the output voltage Vo decreases (step S 10 ), the secondary controlling circuit responds, and output voltage rises again and becomes a normal output voltage Vo 2  that is stable (step S 11 ).  
         [0041]     In  FIG. 4B , the decreased portion Vd 2  of the output voltage becomes a value far smaller that the decreased portion Vd 1  of the output voltage of the conventional circuit illustrated in  FIG. 6A . Moreover, the time of the decreased output voltage Td 2  is also shorter than the time of the decreased output voltage Td 1  of the conventional circuit illustrated in  FIG. 6A . Further, in  FIG. 4B  and  FIG. 6A , the hunting (surging) of the output voltage with Vs as the center is based on the transient state.  
         [0042]     The present invention has an effect of detecting a decrease of output voltage to a load, and making an electrical current supplying circuit quickly supply a supplementary current to the load. Therefore, a capacity condenser for supplementary charge storage, which has a high price and consumes much package space, is not required.  
         [0043]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.