Patent Publication Number: US-10784774-B2

Title: Switching power supply device

Description:
FIELD OF THE INVENTION 
     The present invention relates to an electronic device equipped with a power converter and a current detector that is disposed at at least one position out of a primary-side position and a secondary-side position of the power converter and detects a current flowing at the disposed position(s). 
     DESCRIPTION OF THE RELATED ART 
     As one example of this type of electronic device, a motor driving apparatus disclosed in Patent Literature 1 (see Japanese Laid-open Patent Publication No. 2010-17080 (Pages 4, 5 and FIGS. 1 to 4) is known. This motor driving apparatus includes a rectifier circuit that inputs an alternating current (hereinafter “AC”) power supply, a first capacitor (or “smoothing capacitor”) that is connected across the output terminals of the rectifier circuit, and a three-phase inverter as a power converter that is connected in parallel to the first capacitor, and is configured so as to be capable of supplying the output of the three-phase inverter to a motor. This motor driving apparatus is additionally equipped with a second capacitor that is connected in parallel to an input side of the three-phase inverter, a current detector that is connected between the first capacitor and the second capacitor, and a snubber circuit (a series circuit produced by connecting a resistor and a third capacitor) connected in parallel to the first capacitor closer to the power supply (i.e., closer to the rectifier circuit) than the current detector. 
     Since this motor driving apparatus is provided with a snubber circuit as described above, unlike a configuration that is not provided with a snubber circuit, it is possible to significantly shorten transient states that occur in the current flowing (on a direct current (hereinafter “DC”) link) between the output of the rectifier circuit and the input of the three-phase inverter during switching of the three-phase inverter, which means that it is possible to greatly shorten the period during which the current flowing on the DC link cannot be measured (i.e., to shorten the waiting time until convergence of a transient state). 
     SUMMARY OF THE INVENTION 
     With the motor driving device described above as an electronic device, when increasing the capacitance of the capacitor (or “third capacitor”) that constructs the snubber circuit to enhance the functioning of the snubber circuit, it is necessary to either replace the third capacitor with a capacitor that has the same withstand voltage as the existing third capacitor (that is, a withstand voltage that exceeds the DC voltage supplied from the rectifier circuit to the DC link) but has a larger capacitance than the third capacitor, or to connect a capacitor with the same withstand voltage as the third capacitor in parallel to the third capacitor. 
     However, for typical capacitors, when the withstand voltage is the same, there is a tendency for the external dimensions to increase as the capacitance increases. This means that for the motor driving apparatus described above, there is the problem of an unavoidable increase in the mounting area of the capacitor(s) disposed on the DC link with both of the methods described above (i.e., when the existing capacitor is replaced with a different capacitor with a larger capacitance, and when another capacitor is connected in parallel to the existing capacitor). As other tendencies of typical capacitors, when the external dimensions are the same, it is possible to increase the capacitance as the withstand voltage falls, and when the capacitance is the same, it is possible to reduce the external dimensions as the withstand voltage falls. This means that for the motor driving apparatus described above, since it is difficult to use a low withstand-voltage capacitor (with a withstand voltage that is lower than the DC voltage supplied from the rectifier circuit) which would make it possible to increase capacitance while maintaining the same external dimensions, the only remaining option is to increase the capacitance of the capacitor in the snubber circuit described above to which a DC voltage is directly applied from the rectifier circuit. As a result, there is the problem that it is difficult to efficiently increase the capacitance of the capacitor of the snubber circuit while extensively suppressing any increase in mounting area. 
     The present invention was conceived in view of the problem described above and has a principal object of providing an electronic device where it is possible to efficiently increase the capacitance of the capacitor (s) in a snubber circuit while extensively suppressing increases in the mounting area of the capacitor(s) in the snubber circuit. 
     To achieve the stated object, an electronic device according to the present invention comprises: a power converter; and a current detector that is disposed at at least one position out of a primary-side position and a secondary-side position for the power converter and detects a current flowing at the at least one position, wherein a snubber circuit including a capacitor is directly connected in parallel to both ends of the current detector. 
     According to the above electronic device, since the snubber circuit which includes a capacitor is directly connected in parallel to both ends of the current detector where the produced voltage drop between both ends is extremely low, it is possible for the snubber circuit to sufficiently suppress transient states which may occur in the current flowing at the at least one position described above due to the inductance component present between the two ends of the current detector. By using this configuration, since it is possible to use a low withstand-voltage capacitor as the capacitor in the snubber circuit and capacitors typically have a tendency where it is possible to reduce the external dimensions in keeping with a fall in the withstand voltage for the same capacitance, it is possible here to maintain the required capacitance but still greatly reduce the external dimensions of the capacitor(s) in the snubber circuit(s), which means that it is possible to greatly reduce the mounting area of the capacitors. Capacitors typically have another tendency where when the external dimensions are the same, it is possible to increase the capacitance as the withstand voltage falls, which means that it is possible to efficiently increase the capacitances of the capacitors while greatly suppressing an increase in the mounting area of the capacitors in the snubber circuits. 
     Also, in the electronic device according to the present invention, the snubber circuit is constructed of a series circuit with the capacitor and a resistor. According to the above electronic device, since it is possible to cause rapid attenuation in the amplitude in a transient state which may occur in the current flowing at the at least one position described above, it is possible to greatly reduce the time spent in the transient state. 
     Further, in the electronic device according to the present invention, the capacitor is a high dielectric constant multilayer ceramic capacitor. According to the above electronic device, even when a high dielectric constant multilayer ceramic capacitor that has a DC bias characteristic such that the electrostatic capacitance gradually decreases as the applied DC voltage increases is used in the snubber circuit, it is possible to use the capacitor in a region where the applied DC voltage is low, that is, in a region where the electrostatic capacitance is high. 
     Also, in the electronic device according to the present invention, the current detector is disposed between a smoothing capacitor, which is disposed at the at least one position, and the power converter, and the snubber circuit is directly connected in parallel to the current detector. According to the above electronic device, since the current detector and the snubber circuit are directly connected in parallel at an appropriate position on at least one of the primary side and the secondary side of the electronic device, it is possible to sufficiently suppress transient states that may occur in the current flowing due to the inductance component present between both ends of the current detector more effectively. 
     It should be noted that the disclosure of the present invention relates to a content of Japanese Patent Application 2017-135150 that was filed on 11 Jul. 2017 and the entire content of which is herein incorporated by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other objects and features of the present invention will be explained in more detail below with reference to the attached drawings, wherein: 
         FIG. 1  is a block diagram depicting the configuration of an electronic device  1 ; 
         FIG. 2  is a circuit diagram of one example of a snubber circuit  9  ( 10 ); and 
         FIG. 3  is a circuit diagram of another example of a snubber circuit  9  ( 10 ). 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of an electronic device will now be described with reference to the attached drawings. 
     First, the configuration of an electronic device  1  as one example of an “electronic device” for the present invention will be described with reference to  FIG. 1 . As one example, the electronic device  1  is a switching power supply device and includes a pair of input terminals  2   a  and  2   b , an input smoothing capacitor  3 , a power converter  4 , an output smoothing capacitor  5 , a pair of output terminals  6   a  and  6   b , a first current detector  7 , a second current detector  8 , a first snubber circuit  9 , and a second snubber circuit  10 , and is configured so as to be capable of converting a voltage V 1  across both ends of the input smoothing capacitor  3  to an output voltage V 2  at the power converter  4  and outputting the output voltage V 2  from the pair of output terminals  6   a  and  6   b  to a load LD. 
     As one example, a rectifier circuit  52  that rectifies (full-wave rectification or half-wave rectification) and outputs the AC voltage outputted from an AC power supply  51  is connected to the pair of the input terminals  2   a  and  2   b . The input smoothing capacitor  3  (hereinafter also referred to simply as the “smoothing capacitor  3 ”) is a smoothing capacitor disposed at a “primary-side position”, described later, for the power converter  4 . As one example, the smoothing capacitor  3  is constructed of an electrolytic capacitor, for which capacitors with a large capacitance value and a high withstand voltage are easy to obtain, and is connected between the input terminals  2   a  and  2   b . With this configuration, the smoothing capacitor  3  smoothes the DC voltage (pulse voltage) outputted from the rectifier circuit  52 . By doing so, the voltage V 1  across both ends of the smoothing capacitor  3  is outputted via a pair of input power lines L 1  and L 2  (hereinafter also referred to simply as the “power lines L 1  and L 2 ”) to the power converter  4  as a DC voltage on which a ripple component is superimposed. 
     As one example, the power converter  4  includes a switch  21  and a rectifier  22  and converts the voltage V 1  across both ends inputted across both input terminals  4   a  and  4   b  via the input power lines L 1  and L 2  to the DC voltage V 3  which is outputted across output terminals  4   c  and  4   d . As one example in the present embodiment, the input terminal  2   a  and the input terminal  4   a  are connected by one power line L 1  and the input terminal  2   b  and the input terminal  4   b  are connected by another power line L 2  (the power line L 2  on which a parallel circuit composed of the first current detector  7  and the first snubber circuit  9  is disposed). The switch  21  includes one or two or more switching elements, not illustrated, that perform an on/off operation based on a driving signal supplied from a control circuit, not illustrated, and is configured as an inverter that outputs an AC pulse voltage by switching the voltage V 1  inputted across the input terminals  4   a  and  4   b . The rectifier  22  includes rectifier elements, such as one or two or more diodes, not illustrated, and rectifies the AC pulse voltage outputted from the switch  21  to generate the DC voltage V 3  which is outputted across the output terminals  4   c  and  4   d . The DC voltage V 3  is supplied via a pair of output power lines L 3  and L 4  (hereinafter also referred to simply as the “power lines L 3  and L 4 ”) to the pair of output terminals  6   a  and  6   b . As one example in the present embodiment, the output terminal  4   c  and the output terminal  6   a  are connected by one power line L 3  and the output terminal  4   d  and the output terminal  6   b  are connected by another power line L 4  (the power line L 4  on which a parallel circuit composed of the second current detector  8  and the second snubber circuit  10  is disposed). 
     The output smoothing capacitor  5  (hereinafter also referred to simply as the “smoothing capacitor  5 ”) is a smoothing capacitor disposed at a “secondary-side position”, described later, for the power converter  4 . As one example, the smoothing capacitor  5  is an electrolytic capacitor, for which capacitors with a large capacitance value and a high withstand voltage are easy to obtain, and is connected between the output terminals  6   a  and  6   b . With this configuration, the smoothing capacitor  5  smoothes the DC voltage (pulse voltage) outputted from the rectifier  22  of the power converter  4 . By doing so, the output voltage V 2  is outputted across the output terminals  6   a  and  6   b  as a DC voltage on which a ripple component is superimposed. 
     The first current detector  7  (hereinafter also referred to simply as the “current detector  7 ”) is disposed on one of the power lines L 1  and L 2  (that is, at a position on the primary side (hereinafter “primary-side position”) for the power converter  4 ). Although the current detector  7  is disposed on the power line L 2  positioned on a reference potential side of the voltage V 1  as one example in the present embodiment, the current detector  7  may be disposed on the power line L 1 . The current detector  7  detects the current (or “input current”) I 1  inputted into the power converter  4 , generates a detection signal, not illustrated, whose voltage value changes in proportion to a current value of the current I 1 , and outputs to the control circuit, not illustrated, mentioned above. 
     The second current detector  8  (hereinafter also referred to simply as the “current detector  8 ”) is disposed on one of the power lines L 3  and L 4  (that is, at a position on the secondary side (hereinafter “secondary-side position”) of the power converter  4 ). Although the current detector  8  is disposed on the power line L 4  positioned on a reference potential side of the output voltage V 2  as one example in the present embodiment, the current detector  8  may be disposed on the power line L 3 . The current detector  8  detects the current (or “output current”) I 2  outputted from the power converter  4 , generates a detection signal, not illustrated, whose voltage value changes in proportion to a current value of the current I 2 , and outputs to the control circuit, not illustrated, mentioned above. Although in the present embodiment, the current detectors  7  and  8  are constructed of current transformers where the voltage drops that occur at the respective primary windings disposed on the power lines L 2  and L 4  are extremely low, the present invention is not limited to this. As one example, instead of current transformers, the current detectors  7  and  8  can be constructed of resistors (so-called “shunt resistors”) with low resistance values such that the voltage drops that occur when the current I 1  and the current I 2  flow are negligible compared to the voltage V 1  and the output voltage V 2 . 
     Note that the control circuit controls the voltage value of the output voltage V 2  and the current value of the current I 2  by controlling the pulse width and the like of a driving signal supplied to the switching element described above of the power converter  4  based on detection signals outputted from the current detectors  7  and  8 , a detection signal indicating the voltage value of the voltage V 1  detected via a voltage detector, not illustrated, and a detection signal indicating the voltage value of the output voltage V 2  detected via a voltage detector, not illustrated. 
     The first snubber circuit  9  (hereinafter also referred to simply as the “snubber circuit  9 ”) is connected in parallel to both ends of the current detector  7  (i.e., to ends  7   a  and  7   b  connected to the power line L 2 ). More specifically, the snubber circuit  9  is connected in parallel to the current detector  7  by directly connecting one end  9   a  of the snubber circuit  9  to one end  7   a  of the current detector  7  and directly connecting another end  9   b  of the snubber circuit  9  to another end  7   b  of the current detector  7 . 
     The second snubber circuit  10  (hereinafter also referred to simply as the “snubber circuit  10 ”) is connected in parallel to both ends of the current detector  8  (i.e., to ends  8   a  and  8   b  connected to the power line L 4 ). More specifically, the snubber circuit  10  is connected in parallel to the current detector  8  by directly connecting one end  10   a  of the snubber circuit  10  to one end  8   a  of the current detector  8  and directly connecting another end  10   b  of the snubber circuit  10  to another end  8   b  of the current detector  8 . 
     More specifically, the snubber circuits  9  and  10  are each constructed as one snubber circuit out of a C snubber circuit constructed of only a capacitor  31  as depicted in  FIG. 2  and a RC snubber circuit constructed of a series circuit with a capacitor  31  and a resistor  32  as depicted in  FIG. 3 . That is, the snubber circuits  9  and  10  are both snubber circuits including a capacitor. Here, both of the snubber circuits  9  and  10  may be constructed of the snubber circuit depicted in  FIG. 2  (i.e, a C snubber circuit), both may be constructed of the snubber circuit depicted in  FIG. 3  (i.e., an RC snubber circuit), and the snubber circuits  9  and  10  may be constructed of respectively different snubber circuits (i.e., one C snubber circuit and one RC snubber circuit). 
     It has been confirmed that when the snubber circuits  9  and  10  are constructed of either of the C snubber circuit and the RC snubber circuit described above, and are disposed in the same configuration as the electronic device (motor driving apparatus) described in the background art (that is, when the snubber circuit  9  is connected in parallel to the smoothing capacitor  3  and the snubber circuit  10  is connected in parallel to the smoothing capacitor  5 ), a same level of functioning or higher is achieved. The reason for this is that although the transient state, which is caused by the switching of the voltage V 1  by the switch  21  of the power converter  4 , in the current I 1  that flows at the primary-side position (i.e., the DC link where the smoothing capacitor  3  is disposed) for the power converter  4  occurs due to various factors, the main factor is the inductance component present between both ends  7   a  and  7   b  of the current detector  7  (this inductance component is present even when the current detector is constructed of a resistor). In the same way, although a transient state occurs due to various factors in the current I 2  that flows at a secondary-side position for the power converter  4  (the DC link where the smoothing capacitor  5  is provided), the main factor is the inductance component present between both ends  8   a  and  8   b  of the current detector  8 . For this reason, the snubber circuits  9  and  10  are directly connected in parallel to the current detectors  7  and  8  that are the main factor for the transient states that occur in the currents, thereby making current loops very short (that is, current loops where the equivalent series impedance is extremely small), which makes it possible to sufficiently suppress the occurrence of transient states. 
     Also, as described above, the snubber circuit  9  is connected in parallel between both ends  7   a  and  7   b  of the current detector  7  where the produced voltage drop is extremely low and the snubber circuit  10  is connected in parallel between both ends  8   a  and  8   b  of the current detector  8  where the produced voltage drop is extremely low. This means that when the snubber circuits  9  and  10  are constructed of either of the C snubber circuit and the RC snubber circuit described above, it is possible to use capacitors with an extremely low withstand voltage compared to the voltage V 1  and the output voltage V 2  as the included capacitors  31 . Accordingly, by comparing with an imaginary configuration where the snubber circuit  9  is connected in parallel to the smoothing capacitor  3  as in the electronic device described in the background art, the ability to use a capacitor  31  with a lower withstand voltage in the electronic device  1  makes it possible to greatly miniaturize the external dimensions when the capacitance of the capacitor  31  is set the same as before. In the same way, the snubber circuit  10  can also be constructed using a capacitor  31  with greatly reduced external dimensions. Compared to the electronic device described in the background art, circuit board layout for disposing the snubber circuits  9  and  10  also becomes easier. 
     In this way, according to the electronic device  1 , by directly connecting the snubber circuit  9 , which includes the capacitor  31 , in parallel to the two ends  7   a  and  7   b  of the current detector  7  that is disposed on one of the power lines L 1  and L 2  (in the present embodiment, the power line L 2 ) as a primary-side position for the power converter  4  and has an extremely low voltage drop between the two ends  7   a  and  7   b  and directly connecting the snubber circuit  10 , which includes the capacitor  31 , in parallel to the two ends  8   a  and  8   b  of the current detector  8  that is disposed on one of the power lines L 3  and L 4  (in the present embodiment, the power line L 4 ) as a secondary-side position for the power converter  4  and has an extremely low voltage drop between the two ends  8   a  and  8   b , it is possible for the snubber circuit  9  to sufficiently suppress transient states which may occur in the current I 1  due to the inductance component present between the two ends  7   a  and  7   b  of the current detector  7  and for the snubber circuit  10  to sufficiently suppress transient states which may occur in the current I 2  due to the inductance component present between the two ends  8   a  and  8   b  of the current detector  8 . 
     Also, according to the electronic device  1 , since it is possible to use low withstand-voltage capacitors as the capacitors  31  in the snubber circuits  9  and  10 , when the snubber circuit disposed at a primary-side position for the power converter  4  is constructed of only the snubber circuit  9  and the snubber circuit disposed at a secondary-side position of the power converter  4  is constructed of only the snubber circuit  10  as in the electronic device  1 , it is possible to construct all of the capacitors  31  in the snubber circuits  9  and  10  included in the electronic device  1  of low withstand-voltage capacitors. Since capacitors typically have a tendency where it is possible to reduce the external dimensions in keeping with a fall in the withstand voltage for the same capacitance, it is possible here to maintain the required capacitance but still greatly reduce the external dimensions of the capacitors  31 , which means that it is possible to greatly reduce the mounting area of the capacitors  31 . Capacitors typically have another tendency where when the external dimensions are the same, it is possible to increase the capacitance as the withstand voltage falls, which means that it is possible to efficiently increase the capacitances of the capacitors  31  while greatly suppressing an increase in the mounting area of the capacitors  31  in the snubber circuits  9  and  10 . 
     Also, according to the electronic device  1 , by using the configuration depicted in  FIG. 3  (that is, the RC snubber circuit that is composed of a series circuit with the capacitor  31  and the resistor  32 ) in the snubber circuits  9  and  10 , although the mounting area increases by an amount corresponding to the resistor  32  compared to the configuration depicted in  FIG. 2  that can achieve the greatest reduction in the overall mounting area of the snubber circuits  9  and  10 , it is possible, when a transient state with a low amplitude occurs in the current I 1  and the current I 2 , to cause rapid attenuation in this amplitude, which means that the time spent in the transient state can be greatly reduced. 
     Note that although in the electronic device  1  described above, a configuration is used where the snubber circuits disposed at the primary-side position and the secondary-side position for the power converter  4  are composed of the snubber circuit  9  which is directly connected in parallel to the current detector  7  and the snubber circuit  10  which is directly connected in parallel to the current detector  8 , the snubber circuits disposed at a primary-side position and a secondary-side position for the power converter  4  are not limited to this configuration. As one example, although not illustrated, it is possible for the electronic device  1  to use a configuration which is equipped with a snubber circuit connected in parallel to the smoothing capacitor  3  as in the electronic device (motor driving apparatus) described in the background art but additionally includes the snubber circuit  9  connected in parallel between both ends  7   a  and  7   b  of the current detector  7  to increase the overall capacitance of capacitors in snubber circuits at primary-side positions. Similarly, although not illustrated, it is possible for the electronic device  1  to use this primary-side configuration of snubber circuits on the secondary-side. That is, it is also possible to use a configuration which is equipped with a snubber circuit connected in parallel to the smoothing capacitor  5  but additionally includes the snubber circuit  10  connected in parallel between both ends  8   a  and  8   b  of the current detector  8  to increase the overall capacitance of capacitors in snubber circuits at secondary-side positions. 
     With the electronic device  1  of this configuration, by increasing the overall capacitance of the capacitors in the snubber circuits, it is possible, while further suppressing transient states that may occur in the current I 1  and the current I 2  flowing on the primary side positions and/or the secondary side positions of the power converter  4  with the overall snubber circuits, to extensively suppress the increase in the overall mounting area of the capacitors in the snubber circuits (i.e., increases in mounting area due to the capacitors  31  of the snubber circuits  9  and  10 ) through the use low withstand-voltage capacitors (i.e., capacitors that have small external dimensions even for the same capacitance). That is, it is possible to efficiently increase the overall capacitance of the capacitors in the snubber circuits while extensively suppressing any increase in the overall mounting area of the capacitors in the snubber circuits. 
     With the electronic device  1  described above, since the current detector  7  is disposed at a primary-side position for the power converter  4 , the current detector  8  is disposed at a secondary-side position for the power converter  4 , the snubber circuit  9  is connected in parallel to the current detector  7  and the snubber circuit  10  is connected in parallel to the second current detector  8 , depending on the method by which the control circuit controls the switch  21 , it is also possible to use a configuration where the current detector  7  is disposed at a primary-side position for the power converter  4  but a current detector is not disposed at a secondary-side position or conversely a configuration where the current detector  8  is disposed at a secondary-side position for the power converter  4  but a current detector is not disposed at a primary-side position. For an electronic device  1  of this configuration, it is possible to use a configuration where a snubber circuit is disposed at the one position where the current detector is disposed out of the primary-side position and the secondary-side position for the power converter  4 . 
     Also, when a high dielectric constant multilayer ceramic capacitor (that is, a capacitor with a DC bias characteristic such that the electrostatic capacitance gradually decreases as the applied DC voltage increases) is used as the capacitor  31  of the snubber circuit  9  and/or the snubber circuit  10 , since such capacitor will be used in a region where the applied DC voltage is low (that is, a region where the electrostatic capacitance is high), the configuration of the electronic device  1  described above (i.e., the configuration where snubber circuits are connected in parallel to the current detectors) is preferable.