Patent Publication Number: US-10333400-B2

Title: Boost DC-DC converter including a switching element

Description:
RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2016-243695 filed on Dec. 15, 2016, the entire content of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a boost DC-DC converter and a method of using the same. 
     2. Description of the Related Art 
     A boost DC-DC converter having an input terminal and an output terminal has been known (for example, refer to Japanese Unexamined Patent Application No. 2009-254110). 
       FIG. 3  is a schematic circuit diagram of a conventional boost DC-DC converter  300 . In an example of  FIG. 3 , an output terminal  314  of the boost DC-DC converter  300  is connected to a ground terminal via a load  400 . The boost DC-DC converter  300  boosts input power input from an input terminal  301  and supplies the boosted power to the load  400 . 
     In the example of  FIG. 3 , the boost DC-DC converter  300  generates the boosted power having higher voltage than that of the input power from the input power supplied to the input terminal  301 , and the boost DC-DC converter  300  outputs the generated boosted power from the output terminal  314 . 
     The boost DC-DC converter  300  includes a coil  302 , an N-channel MOS transistor  305 , a diode  303 , a diode  304 , a diode  321 , an output capacitor  311 , a resistor  312 , a resistor  313 , and a control circuit  307 . 
     One terminal of the coil  302  is connected to the input terminal  301 . The N-channel MOS transistor  305  switches current which flows from the other terminal of the coil  302  to a ground terminal. The diode  303  rectifies the current output from the other terminal of the coil  302  and outputs the boosted power. An N-type terminal of the diode  303  is connected to the output terminal  314 . The N-type terminal of the diode  303  is connected to a ground terminal via the output capacitor  311 . The N-type terminal of the diode  303  is connected to a ground terminal via the resistor  312  and the resistor  313 . The N-type terminal of the diode  303  is connected to a power source terminal  309  of the control circuit  307  via the diode  321 . 
     The diode  304  rectifies the current input from the input terminal  301 , and the diode  304  outputs the input power to the power source terminal  309  of the control circuit  307  as an operation power source of the control circuit  307 . The other terminal of the coil  302  and a drain of the N-channel MOS transistor  305  are connected to each other. 
     The control circuit  307  includes a switching signal output terminal  308 , the power source terminal  309 , and a feedback terminal  310 . The switching signal output terminal  308  outputs a switching signal for driving the N-channel MOS transistor  305  to the gate of the N-channel MOS transistor  305 . The source of the N-channel MOS transistor  305  is connected to the ground terminal. The N-type terminal of the diode  303  is connected to the feedback terminal  310  via the resistor  312 . The control circuit  307  controls the boosted power by controlling the N-channel MOS transistor  305  based on the input of the feedback terminal  310 . 
     In the example of  FIG. 3 , when input power is supplied to the input terminal  301 , the input power is input to the power source terminal  309  of the control circuit  307  via the diode  304 . The control circuit  307  starts an operation by the input power supplied to the power source terminal  309 . Specifically, the control circuit  307  outputs the switching signal from the switching signal output terminal  308 , and switches the N-channel MOS transistor  305 . 
     When the control circuit  307  switches on the N-channel MOS transistor  305 , power is stored in the coil  302 . When the control circuit  307  switches off the N-channel MOS transistor  305 , the power stored in the coil  302  is output to the output terminal  314  via the diode  303 . The boost DC-DC converter  300  generates the boosted power and outputs the boosted power from the output terminal  314  by repeating power accumulation and power discharge performed by the coil  302 . 
     In the example of  FIG. 3 , when the boosted power is generated at the output terminal  314 , the boosted power is supplied to the power source terminal  309  of the control circuit  307  via the diode  321 . Accordingly, the control circuit  307  which generated the boosted power using the input power as the operation power source, generates the boosted power using the boosted power as the operation power source. 
     The voltage of the output terminal  314  is divided by the resistor  312  and the resistor  313 , and is input to the feedback terminal  310  of the control circuit  307 . The control circuit  307  controls the switching of the N-channel MOS transistor  305  such that the voltage of the feedback terminal  310  becomes a predetermined value, thereby controlling the voltage of the output terminal  314  to a desired value. 
     In the example of  FIG. 3 , the diode  304  is provided to use the input voltage to operate the control circuit  307  with a small loss of voltage, thereby reducing a value of the input voltage required to activate the control circuit  307  compared to a case without the diode  304 . And the diode  321  is provided to use the boosted power having higher voltage than that of the input power as the operation power source of the control circuit  307  after the control circuit  307  is activated, thereby increasing power conversion capability. 
     However, in the conventional boost DC-DC converter as described above, when the voltage of the input power is lower than a minimum operation voltage of the control circuit, the control circuit cannot start operation, neither start boost operation. 
     When the voltage of the input power is low, the voltage of the boosted power also becomes low. A power conversion amount thus decreases. When a load of large power consumption is connected to the output terminal, the conventional boost DC-DC converter, thus, cannot raise the voltage of the output terminal to a desired voltage and fails to activate the load since the boosted power falls short of the power consumption of the load at the activation from an input power having a low voltage. 
     The conventional boost DC-DC converter should have a configuration having a very large conversion capability to activate the load from the input power having a low voltage when the load of large power consumption is connected to the output terminal, resulting in increase of a size of the entire DC-DC converter and also increase of a power conversion loss. 
     An object of the present invention is to provide a boost DC-DC converter in which a boost operation can be started even when voltage of input power becomes low, and a method of using the same. 
     SUMMARY OF THE INVENTION 
     In order to achieve the above described object, the present invention adopts the following aspects. 
     (1) According to an aspect of the present invention, there is provided a boost DC-DC converter including: an input terminal; an output terminal; a first boost circuit configured to generate, from an input power to the input terminal, a first boosted power having a higher voltage than a voltage of the input power, and outputs the generated first boosted power from the output terminal; a second boost circuit configured to generate, from the input power, a second boosted power having a higher voltage than the voltage of the input power; and a storage capacitor configured to store the second boosted power as a storage power, and supply the storage power to the first boost circuit as an operation power source of the first boost circuit, the first boost circuit being configured to start a boost operation with the storage power as the operation power source when a voltage of the storage power is equal to or higher than a minimum operation voltage of the first boost circuit. 
     (2) In the boost DC-DC converter according to the above (1), the following configuration may be configured: the first boost circuit includes a coil having a terminal connected to the input terminal, an N-channel MOS transistor configured to switch a current flowing from the other terminal of the coil to a ground terminal, a first rectifier configured to rectify a pulse current output from the other terminal to output the first boosted power, a second rectifier configured to connect to the first rectifier in parallel, and rectifies the pulse current to output a third boosted power, and a control circuit to which the third boosted power is input and configured to control the first boosted power by controlling the N-channel MOS transistor, wherein the first boost circuit is configured to perform the boost operation with the third boosted power as the operation power source when a voltage of the third boosted power is equal to or higher than the minimum operation voltage. 
     (3) According to another aspect of the present invention, there is provided a method of using the boost DC-DC converter according to the above (1), comprising: driving a load connected to the output terminal by the first boosted power output from the output terminal, wherein the first boosted power is equal to or higher than a power consumption of the load. 
     (4) According to further another aspect of the present invention, there is provided a method of using the boost DC-DC converter according to the above (2), comprising: driving a load connected to the output terminal by the first boosted power output from the output terminal, wherein the first boosted power is equal to or higher than a power consumption of the load. 
     According to the above-described aspects of the present invention, it is possible to provide a boost DC-DC converter in which a boost operation can be started even when the voltage of input power is low, and a method of using the same. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a  FIG. 1  is a schematic circuit diagram of a boost DC-DC converter according to the first embodiment of the present invention. 
         FIG. 2  is a diagram showing an example of an operation waveform of the boost DC-DC converter of the first embodiment. 
         FIG. 3  is a schematic circuit diagram of a conventional boost DC-DC converter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     Hereinafter, the first embodiment of a boost DC-DC converter  100  is described with reference to the drawings. 
       FIG. 1  is a schematic circuit diagram of the boost DC-DC converter  100  according to the first embodiment. In the example of  FIG. 1 , an output terminal  114  of the boost DC-DC converter  100  according to the first embodiment is connected to a load  200 . More specifically, the output terminal  114  is connected to a ground terminal via the load  200 . In this example, the load  200  is a wireless communication module. In this case, the boost DC-DC converter  100  boosts input power input from an input terminal  101  and supplies the boosted input power to the wireless communication module. In another example, the load  200  other than the wireless communication module may be connected to the output terminal  114  of the boost DC-DC converter  100 . 
     The boost DC-DC converter  100  of the first embodiment includes a first boost circuit  100   a , a second boost circuit  115 , and a storage capacitor  116 . The first boost circuit  100   a  generates the first boosted power having higher voltage than voltage of the input power from the input power input to the input terminal  101 , and the first boost circuit  100   a  outputs the generated first boosted power from the output terminal  114 . The second boost circuit  115  generates the second boosted power having higher voltage than voltage of the input power from the input power input to the input terminal  101 , and the second boost circuit  115  outputs the generated second boosted power from an output terminal  120  of the second boost circuit  115 . The storage capacitor  116  stores the second boosted power generated by the second boost circuit  115  as storage power. The storage capacitor  116  supplies the stored storage power to a power source terminal  109  of a control circuit  107  of the first boost circuit  100   a  as an operation power source of the control circuit  107  of the first boost circuit  100   a.    
     In the example of  FIG. 1 , the first boost circuit  100   a  includes a coil  102 , an N-channel MOS transistor  105 , a diode  103  which serves as first rectifier, a diode  104  which serves as second rectifier, a smoothing capacitor  106 , an output capacitor  111 , a resistor  112  and a resistor  113  which configure a bleeder resistor, and a control circuit  107 . 
     In the example of  FIG. 1 , the N-channel MOS transistor  105  is applied to the boost DC-DC converter  100 . However, the present invention is not limited to this configuration only. In another example, instead of the N-channel MOS transistor  105 , an arbitrary switching element (not shown) may be applied to the boost DC-DC converter  100 . 
     In the example of  FIG. 1 , one terminal (left one shown in  FIG. 1 ) of the coil  102  is connected to the input terminal  101 . The N-channel MOS transistor  105  switches current which flows from the other terminal (right one shown in  FIG. 1 ) of the coil  102  to a ground terminal. The diode  103  rectifies a pulse current output from the other terminal of the coil  102  and the diode  103  outputs the first boosted power. The other terminal of the coil  102  and a P-type terminal of the diode  103  are connected to each other. An N-type terminal of the diode  103  is connected to the output terminal  114 . The N-type terminal of the diode  103  is connected to a ground terminal via the output capacitor  111 . The N-type terminal of the diode  103  is connected to a ground terminal via the resistor  112  and the resistor  113  forming the bleeder resistor. 
     The diode  104  is connected to the other terminal of the coil  102  so as to be in parallel with the diode  103 . The diode  104  outputs third boosted power obtained by rectifying the pulse current output from the other terminal of the coil  102  to the power source terminal  109  of the control circuit  107  as the operation power source of the control circuit  107 . The other terminal of the coil  102  and a P-type terminal of the diode  104  are connected to each other. An N-type terminal of the diode  104  is connected to the power source terminal  109 . The N-type terminal of the diode  104  is connected to a ground terminal via the smoothing capacitor  106 . The other terminal of the coil  102  and the drain of the N-channel MOS transistor  105  are connected to each other. 
     In the example of  FIG. 1 , the control circuit  107  includes a switching signal output terminal  108 , the power source terminal  109 , and a feedback terminal  110 . The switching signal output terminal  108  outputs a switching signal for driving the N-channel MOS transistor  105  to the gate of the N-channel MOS transistor  105 . The gate of the N-channel MOS transistor  105  is connected to the switching signal output terminal  108 . The source of the N-channel MOS transistor  105  is connected to a ground terminal. The N-type terminal of the diode  103  is connected to the feedback terminal  110  via the resistor  112  forming a portion of the bleeder resistor. The control circuit  107  controls the first boosted power by controlling the N-channel MOS transistor  105  based on the input of the feedback terminal  110 . 
     In the example of  FIG. 1 , the boost DC-DC converter  100  includes switching element  117 . The second boost circuit  115  includes an input terminal  118 , a switching signal output terminal  119 , and an output terminal  120 . The input terminal  118  of the second boost circuit  115  is connected to the input terminal  101 . The output terminal  120  is connected to a ground terminal via the storage capacitor  116 . The output terminal  120  is connected to the power source terminal  109  of the control circuit  107  of the first boost circuit  100   a  via the switching element  117 . The N-type terminal of the diode  104  is connected to a ground terminal via the switching element  117  and the storage capacitor  116 . The N-type terminal of the diode  104  is connected to the output terminal  120  of the second boost circuit  115  via the switching element  117 . The switching signal output terminal  119  of the second boost circuit  115  is connected to the switching element  117 . The switching signal output terminal  119  outputs a switching signal for driving the switching element  117  to the switching element  117 . In this example of  FIG. 1 , the switching element  117  is a switching device such as the N-channel MOS transistor. 
     In this example, as the second boost circuit  115 , a flying capacitor boost circuit, a charge pump boost circuit incorporating a boost capacitor, or the like can be used. 
     In the boost DC-DC converter  100  of the first embodiment, when the voltage of the storage power stored in the storage capacitor  116  is equal to or higher than the minimum operation voltage of the first boost circuit  100   a , the first boost circuit  100   a  starts a boost operation with the storage power as the operation power source. 
     In the example of  FIG. 1 , when the voltage of the storage power is equal to or higher than the minimum operation voltage of the control circuit  107  of the first boost circuit  100   a , the second boost circuit  115  turns on the switching element  117 . As a result, the storage power is supplied to the control circuit  107 , and thus, the control circuit  107  enters a state in which the control circuit  107  can switch the N-channel MOS transistor  105  with the storage power as the operation power source. Next, the control circuit  107  starts switching of the N-channel MOS transistor  105 . Thus, the first boost circuit  100   a  starts the boost operation. 
     When the voltage of the third boosted power output from the diode  104  is equal to or higher than the minimum operation voltage, the control circuit  107  enters a state in which the control circuit  107  can switch the N-channel MOS transistor  105  by using the third boosted power supplied to the control circuit  107 . When the voltage of the third boosted power is equal to or higher than the minimum operation voltage, the first boost circuit  100   a  performs the boost operation with the third boosted power as the operation power source. 
       FIG. 2  is a diagram showing an example of an operation waveform of the boost DC-DC converter  100  of the first embodiment. A horizontal axis in  FIG. 2  indicates time. A vertical axis in (A) of  FIG. 2  indicates the voltage of the input terminal  101 . A vertical axis in (B) of  FIG. 2  indicates the voltage of the power source terminal  109  of the control circuit  107 . A vertical axis in (C) of  FIG. 2  indicates the voltage of the output terminal  114 . A vertical axis in (D) of  FIG. 2  indicates the voltage of the storage power stored by the storage capacitor  116 . A vertical axis in (E) of  FIG. 2  indicates the voltage of the third boosted power output from the diode  104  of the first boost circuit  100   a.    
     In the example of  FIG. 2 , at time t 1 , the input power is supplied to the input terminal  101  and the voltage of the input terminal  101  becomes a value V 1 . The input power supplied to the input terminal  101  is supplied to the input terminal  118  of the second boost circuit  115 . The second boost circuit  115  generates the second boosted power having a value V 4  which is a higher voltage than the value V 1  of the voltage of the input power, from the input power. The second boost circuit  115  outputs the second boosted power to the output terminal  120 . The second boosted power output from the output terminal  120  is stored in the storage capacitor  116  as the storage power. Accordingly, after time t 1 , the voltage of the storage power gradually increases. The second boost circuit  115  monitors the voltage (the voltage of the storage power stored in the storage capacitor  116 ) of the output terminal  120 . 
     At time t 1 , the first boost circuit  100   a  has not yet started the boost operation. Accordingly, the value of the first boosted power generated by the first boost circuit  100   a  becomes zero. The value of the voltage of the third boosted power output from the diode  104  becomes zero. 
     At time t 1 , a value Vout 1  of the voltage of the output terminal  114  is lower than the value V 1  of the voltage of the input terminal  101  by a forward voltage drop in the diode  103 . 
     At time t 1 , the second boost circuit  115  does not turn on the switching element  117 . At time t 1 , the switching element  117  is in a turned-off state. Accordingly, the second boosted power generated by the second boost circuit  115  is not supplied to the power source terminal  109  of the control circuit  107 . As a result, a value V 2  of the voltage in the power source terminal  109  of the control circuit  107  is lower than the value V 1  of the voltage of the input terminal  101  by a forward voltage drop in the diode  104 . 
     In the example of  FIGS. 1 and 2 , the forward voltage drop in the diode  104  is smaller than the forward voltage drop in the diode  103 . Accordingly, the value V 2  of the voltage of the power source terminal  109  of the control circuit  107  is higher than the Vout 1  of the voltage of the output terminal  114  at time t 1 . 
     Subsequently, in the example of  FIG. 2 , at time t 2 , the voltage of the storage power reaches a minimum operation voltage VT of the control circuit  107  of the first boost circuit  100   a . At time  2 , when the storage power is supplied to the power source terminal  109  of the control circuit  107 , the control circuit  107  enters a state in which the control circuit  107  can output the switching signal to the N-channel MOS transistor  105 . In the example of  FIG. 2 , at time t 2 , the storage power has not yet supplied to the power source terminal  109  of the control circuit  107 . 
     Subsequently, in the example of  FIG. 2 , at time t 3 , the voltage of the storage power becomes equal to a value V 4  of the voltage of the second boosted power generated by the second boost circuit  115 . The value V 4  is higher than the minimum operation voltage VT. 
     At time t 3 , the second boost circuit  115  stops the boost operation and turns on the switching element  117 . Accordingly, the storage power is supplied to the power source terminal  109  of the control circuit  107  via the switching element  117 . As a result, the voltage of the power source terminal  109  of the control circuit  107  becomes higher than the minimum operation voltage VT. Accordingly, the control circuit  107  can switch the N-channel MOS transistor  105  with the storage power as the operation power source. The switching signal output terminal  108  of the control circuit  107  outputs the switching signal for driving the N-channel MOS transistor  105  to the gate of the N-channel MOS transistor  105 . 
     The example of  FIG. 2 , at time t 3 , the control circuit  107  starts the switching of the N-channel MOS transistor  105 . 
     More specifically, when the control circuit  107  turns on the N-channel MOS transistor  105 , power is stored in the coil  102 . When the control circuit  107  turns off the N-channel MOS transistor  105 , the power stored in the coil  102  is output to the output terminal  114  via the diode  103 . The first boost circuit  100   a  repeats power accumulation and power discharge performed by the coil  102  to generate the first boosted power. 
     At time t 3 , the first boost circuit  100   a  starts the boost operation of generating the first boosted power with the storage power as the operation power source. Accordingly, at time t 3 , the first boosted power becomes larger than zero. The first boosted power is output to the output terminal  114  via the diode  103 . Accordingly, the voltage of the output terminal  114  increases from the value Vout 1  to a value Vout 2 . 
     The voltage of the output terminal  114  is divided by the resistor  112  and the resistor  113  and is input to the feedback terminal  110  of the control circuit  107 . 
     After the boost operation of the first boost circuit  100   a  is started (after time t 3 ), the control circuit  107  controls the switching of the N-channel MOS transistor  105  such that the voltage of the feedback terminal  110  becomes a predetermined value. Accordingly, the control circuit  107  controls the voltage of the output terminal  114  to the desired value Vout 2 . 
     After time t 3 , a portion of the power stored in the coil  102  is output from the diode  104  to the power source terminal  109  of the control circuit  107  as the third boosted power. The value V 3  of the voltage of the power source terminal  109  is higher than the minimum operation voltage VT. 
     Accordingly, after time t 3 , the control circuit  107  switches the N-channel MOS transistor  105  with the third boosted power as the operation power source. The first boost circuit  100   a  performs the boost operation, which generates the first boosted power, with the third boosted power as the operation power source. 
     As described above, after time t 3 , the first boost circuit  100   a  performs the boost operation, which generates the first boosted power, with the third boosted power as the operation power source. Accordingly, the second boosted power is not required. Therefore, in the example of  FIG. 2 , after time t 3 , the second boost circuit  115  does not generate the second boosted power. 
     The turned-on state of the switching element  117  is maintained. Accordingly, the value of the voltage of the storage power becomes equal to the value V 3  of the voltage of the power source terminal  109 . 
     In the example of  FIGS. 1 and 2 , as described above, the forward voltage drop in the diode  104  is lower than the forward voltage drop in the diode  103 . Accordingly, the value V 3  of the voltage of the power source terminal  109  of the control circuit  107  after time t 3  is higher than the value Vout 2  of the voltage of the output terminal  114  after time t 3 . 
     As described above, in the boost DC-DC converter  100  of the first embodiment, when the voltage of the storage power is equal to or higher than the minimum operation voltage VT of the first boost circuit  100   a , the first boost circuit  100  starts the boost operation with the storage power as the operation power source. Accordingly, it is possible to start the boost operation of the first boost circuit  100   a  even when the voltage of the input power is low. The boost capability required in the second boost circuit  115  can be suppressed comparing with the example when the storage capacitor  116  is not provided. 
     As described above, in the example of  FIG. 2 , after time t 3 , the second boost circuit  115  does not generate the second boosted power. Accordingly, it is possible to eliminate the necessity of controlling the second boost circuit  115  after time t 3  when the voltage of the third boosted power becomes the value V 3  equal to or higher than the minimum operation voltage VT. 
     As described above, in the example of  FIG. 1 , the output terminal  114  of the boost DC-DC converter  100  is connected to the load  200 . The first boosted power output from the output terminal  114  drives the load  200 . In the example of  FIG. 2 , after time t 3 , the first boosted power becomes a value equal to or higher than the power consumption of the load  200 . 
     In the example of  FIG. 2 , even when the power of the input power is low, the first boost circuit  100   a  can start the boost operation with the storage power having higher voltage than the voltage of the input power as the operation power source. When the boost operation is started (time t 3 ), the first boosted power (conversion power) exceeds the power consumption of the load  200 . The boost DC-DC converter  100  outputs the first boosted power (conversion power) exceeding the power consumption of the load  200  by the input of the input power having a lower voltage than the minimum operation voltage VT. In the boost DC-DC converter  100 , the size thereof is small and the conversion loss thus becomes lower. 
     The second boost circuit  115  needs to be a circuit which has a lower minimum operation voltage than that of the first boost circuit  100   a  and can boost even when the input voltage is low, and the power conversion capability of the second boost circuit  115  may be smaller than that of the first boost circuit  100   a . Accordingly, the size of the second boost circuit  115  can be decreased. 
     In the example of the conventional circuit of  FIG. 3 , the control circuit  307  switches the N-channel MOS transistor  305  with boosted power having voltage decreased by a forward voltage drop in the diode  303  and the diode  321  as an operation power source. On the other hand, in the example of the first embodiment of  FIG. 1 , the control circuit  107  switches the N-channel MOS transistor  105  with the third boosted power having the voltage decreased by only the forward voltage drop in the diode  104  as the operation power source. Accordingly, compared to the example of the conventional circuit of  FIG. 3 , in the example of the first embodiment of  FIG. 1 , it is possible to adopt a configuration in which the first boosted power (conversion power) is small, the size thereof can be decreased, and the conversion loss can be decreased. 
     In the example of  FIG. 2 , the second boosted power generated by the second boost circuit  115  is stored in the storage capacitor  116 . When the voltage of the storage power stored in the storage capacitor  116  is equal to or higher than the minimum operation voltage VT of the first boost circuit  100   a , the control circuit  107  starts the boost operation by the first boost circuit  100   a  with the storage power as the operation power source. Accordingly, unlike the example of the conventional circuit of  FIG. 3 , in the example of the first embodiment of  FIG. 2 , it is not necessary to drive the control circuit with the boosted power as the operation power source. In the example of the first embodiment of  FIG. 2 , even when the boost capability of the second boost circuit  115  is low, it is possible to drive the control circuit  107  by taking times to store electricity. Accordingly, it is possible to decrease the size of the second boost circuit  115 . 
     In the example of  FIG. 1 , the diode  103  is used as the first rectifier and the diode  104  is used as the second rectifier, the present invention is not limited to this configuration only. In another example, instead of the diode, an arbitrary element, a circuit, or the like having a rectification function may be used. 
     Second Embodiment 
     In a boost DC-DC converter  100  of the second embodiment is configured to be similar to the boost DC-DC converter  100  of the above-described first embodiment except for the following matters. Therefore, according to the boost DC-DC converter  100  of the second embodiment, advantageous effects similar to those of the boost DC-DC converter  100  of the first embodiment can be exerted. 
     As of  FIG. 1 , the first boost circuit  100   a  of the boost DC-DC converter  100  of the above-described first embodiment is a boost chopper type voltage conversion circuit. On the other hand, in the boost DC-DC converter  100  of the second embodiment, in this example, another arbitrary voltage conversion circuit (not shown) such as a charge pump type voltage conversion circuit can be used as the first boost circuit  100   a.    
     While preferred embodiments of the invention have been described and illustrated above, it should be understood that these are exemplary of the invention and are not to be considered as limiting. These embodiments and modifications can be performed in other various ways; therefore, additions, omissions, substitutions, and other modifications can be made without departing from the scope of the invention. These embodiments and modifications are included in the scope of the invention described in the claims and equivalence thereof. Furthermore, the embodiments and the modifications can be combined with each other.