JP2011166946A - Dc/dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC/DC converter that is low cost and highly reliable. <P>SOLUTION: The DC/DC converter includes: an input voltage detection circuit 35 which detects an input voltage Vi of an input terminal 13 and converts the voltage Vi to an input voltage signal Vid by a first A/D converter 43; an output voltage detection circuit 37 which detects an output voltage Vo of an output terminal 19 and converts the voltage Vo to an output voltage signal Vod by a second A/D converter 49; a current detection circuit 29 which detects a current I flowing through the terminal 19 and converts the current I to an current signal Id by a third A/D converter 53; an arithmetic circuit 55 which calculates and outputs an control signal Ctd to control matching at least either of the signal Vid, signal Vod, or signal Id to a predetermined target value; a D/A converter 61 which converts the signal Ctd to a control voltage Ct; and a PWM circuit 63 which outputs an on-off signal SW of a first switching element 23 and a second switching element 25 from the control voltage Ct. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a DC / DC converter that converts an input DC voltage into another voltage value and outputs the voltage value.

  In recent years, a configuration using a microcomputer as a control means for controlling the voltage of a DC / DC converter has been proposed in, for example, Patent Document 1. FIG. 2 is a block circuit diagram of such a DC / DC converter.

  In FIG. 2, a pair of connection terminals 101 to which a DC voltage is input is connected to a primary coil 105 of a transformer via four field effect transistors (hereinafter referred to as FETs 103). The transformer includes a first secondary coil 107 and a second secondary coil 109, which are connected to two output electrolytic capacitors 111 connected in series via four diodes 110. Has been. A resistance element 112 is connected in parallel to both ends of the output electrolytic capacitor 111 connected in series, and is also connected to a pair of other connection terminals 113, from which a converted voltage is output.

  With this configuration, the main operation of the DC / DC converter of FIG. 2 is as follows. First, the DC voltage input from the pair of connection terminals 101 is converted to AC by an on / off operation by the four FETs 103 and applied to the primary coil 105. As a result, an AC voltage is generated from the first secondary coil 107 and the second secondary coil 109, and this is rectified by the four diodes 110, and DC converted by the output electrolytic capacitor 111 and the resistance element 112. The output voltage is output from the pair of other connection terminals 113.

  In this DC / DC converter, a microcomputer 115 is used as a control means for controlling an output voltage by an on / off operation by four FETs 103. The microcomputer 115 has a function of reading a voltage (output voltage) of a pair of other connection terminals 113 and outputting a control pulse for controlling on / off of the four FETs 103. The schematic configuration and operation are as follows.

  The output voltage is input to an A / D converter 117 in the microcomputer 115 and is digitally converted. This converted signal is input to one of the comparison means 121 via the input register 119. The value of the target value register 123 is input to the other side of the comparison unit 121. The output of the comparison unit 121 is input to one of the output control units 127 via the determination result register 125. Since the control pulse generating means 129 is connected to the other side of the output control means 127, the output control means 127 outputs a digital signal for generating the control pulse. This digital signal is input to the D / A converter 133 via the output register 131. The D / A converter 133 converts the digital signal into the analog control pulse. The control pulse thus obtained is output to four FETs 103, and the FET 103 performs an on / off operation in accordance with the control pulses.

  Specific operation will be described below. A value obtained by digitally converting the output voltage by the A / D converter 117 is input to the input register 119. When this value is larger than the value of the target value register 123, the output from the D / A converter 133 is stopped. As a result, the operation of the four FETs 103 is also stopped, and the output voltage is lowered. As a result, when the value of the input register 119 becomes smaller than the value of the target value register 123, the control pulse is output from the D / A converter 133, and the four FETs 103 perform the on / off operation. As a result, the output voltage increases. By repeating such an operation, the output voltage can be stabilized.

JP 2004-297939 A

  According to the DC / DC converter, the microcomputer 115 can surely stabilize the output voltage. However, in order to further stabilize the output voltage, the PWM signal resolution that is the resolution in the on / off ratio of the control pulse is set. The PWM control may be performed finely by increasing the value. Here, in order to increase the PWM signal resolution, it is necessary to increase the clock frequency of the microcomputer 115 to increase the resolution on the time axis. Therefore, it is necessary to use a DSP (Digital Signal Processor) that can handle a high clock frequency, including the above-described conventional DC / DC converter. However, the DSP has a problem that it is expensive even if it is suitable for a power supply.

  An object of the present invention is to solve the above-described conventional problems, and to provide a DC / DC converter that realizes high resolution at low cost and can stabilize an output voltage.

  In order to solve the above-described conventional problems, the DC / DC converter according to the present invention performs on / off control of a plurality of switching elements electrically connected to an input terminal to which an input voltage (Vi) is input. In a DC / DC converter that outputs an output voltage (Vo) from an output terminal electrically connected to an element, a first A / D converter that is electrically connected to the input terminal and detects the input voltage (Vi) An input voltage detection circuit that converts the input voltage signal (Vid) to output, or an output voltage signal (Vo) that is electrically connected to the output terminal, detects the output voltage (Vo), and is output by the second A / D converter. Vod) is output by the output voltage detection circuit or the current (I) flowing through the DC / DC converter is detected by the third A / D converter. A current detection circuit that converts the current signal into a current signal (Id) and outputs the current signal, and is electrically connected to at least one of the first A / D converter, the second A / D converter, and the third A / D converter; An arithmetic circuit that obtains and outputs a control signal (Ctd) for controlling the voltage signal (Vid), the output voltage signal (Vod), or the current signal (Id) so as to coincide with a predetermined target value; A D / A converter that is electrically connected to the arithmetic circuit and converts the control signal (Ctd) into a control voltage (Ct); and is electrically connected between the D / A converter and the switching element; And a PWM circuit that outputs an on / off signal (SW) of the switching element from the control voltage (Ct).

  According to the present invention, the PWM circuit (circuit that generates an on / off signal) that requires high-speed response is an analog circuit with excellent response, and the other control circuit is a digital circuit. The high-speed response is not so necessary. Therefore, since a general-purpose microcomputer having a low operating frequency can be applied to the digital circuit portion, it is possible to realize a DC / DC converter that can secure high resolution at low cost and can stabilize the output voltage. .

1 is a block circuit diagram of a DC / DC converter according to an embodiment of the present invention. Block diagram of a conventional DC / DC converter

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 is a block circuit diagram of a DC / DC converter according to an embodiment of the present invention. In FIG. 1, thick lines indicate power system wirings, and thin lines indicate signal system wirings.

  In FIG. 1, a positive electrode of a DC voltage source 15 having an input voltage Vi is electrically connected to an input terminal 13 of a DC / DC converter 11. Note that the negative electrode of the DC voltage source 15 is connected to the ground and is also electrically connected to the ground terminal 17 of the DC / DC converter 11. Therefore, the input voltage Vi is input to the DC / DC converter 11.

  On the other hand, a load 21 is electrically connected to the output terminal 19 of the DC / DC converter 11. The ground of the load 21 is electrically connected to the ground terminal 17. Therefore, the output voltage Vo output from the output terminal 19 of the DC / DC converter 11 is applied to the load 21.

  Next, the internal configuration of the DC / DC converter 11 will be described. The input terminal 13 is electrically connected to the first switching element 23. Here, the first switching element 23 is an FET that can be controlled on and off from the outside. A second switching element 25 is electrically connected between the first switching element 23 and the ground. Here, the second switching element 25 is also composed of an FET, like the first switching element 23. With such a configuration, a plurality of switching elements (first switching element 23 and second switching element 25) in FIG. 1 are electrically connected to the input terminal 13 in total.

  One end of an inductor 27 is electrically connected to a connection point between the first switching element 23 and the second switching element 25. The other end of the inductor 27 is electrically connected to the output terminal 19 via a shunt resistor 31 that is a component of the current detection circuit 29 that detects and outputs the current I flowing through the output terminal 19. A smoothing capacitor 33 for smoothing the output voltage Vo is electrically connected between the output terminal 19 and the ground.

  In order to control the output voltage Vo, the DC / DC converter 11 includes an input voltage detection circuit 35 that is electrically connected to the input terminal 13 and detects and outputs the input voltage Vi, in addition to the current detection circuit 29. And an output voltage detection circuit 37 that is electrically connected to the output terminal 19 and detects and outputs the output voltage Vo.

  Here, detailed configurations of the input voltage detection circuit 35, the output voltage detection circuit 37, and the current detection circuit 29 will be described.

  First, the input voltage detection circuit 35 includes an input voltage detection resistor 39 composed of two series resistors connected between the input terminal 13 and the ground terminal 17, and a connection point between the two input voltage detection resistors 39. And a first A / D converter 43 connected to the output of the voltage follower circuit 41. Therefore, the first A / D converter 43 outputs an input voltage signal Vid (digital signal) converted according to the input voltage Vi.

  The voltage follower circuit 41 is used for impedance conversion between the input voltage detection resistor 39 and the first A / D converter 43. This is because the input impedance of the first A / D converter 43 is the input voltage detection resistor. It may not be sufficient if it is sufficiently larger than the resistance value of 39.

  Next, the configuration of the output voltage detection circuit 37 is substantially the same as that of the input voltage detection circuit 35. That is, an output voltage detection resistor 45 composed of two series resistors connected between the output terminal 19 and the ground terminal 17, and a voltage follower circuit connected to the connection point of the two output voltage detection resistors 45. 47 and a second A / D converter 49 connected to the output of the voltage follower circuit 47. Therefore, the second A / D converter 49 outputs an output voltage signal Vod (digital signal) converted according to the output voltage Vo.

  As with the voltage follower circuit 41, the voltage follower circuit 47 is also used to perform impedance conversion between the output voltage detection resistor 45 and the second A / D converter 49. This is because the second A / D converter is used. The 49 input impedance may not be sufficiently larger than the resistance value of the output voltage detection resistor 45.

  Next, the current detection circuit 29 includes a differential amplifier 51 connected to both ends of the shunt resistor 31 and a third A / D converter 53 connected to the output of the differential amplifier 51. Accordingly, the third A / D converter 53 outputs a current signal Id (digital signal) converted according to the current I.

  Although FIG. 1 shows a configuration in which the current detection circuit 29 is electrically connected to the output terminal 19, the present invention is not limited to this. For example, the current detection circuit 29 may be electrically connected to the input terminal 13. The second switching element 25 may be electrically connected. At any of these positions, a current signal Id reflecting the current I flowing in the power system wiring of the DC / DC converter 11 is obtained.

  The first A / D converter 43, the second A / D converter 49, and the third A / D converter 53 are all those having a conversion bit number of 10 bits. However, the number of conversion bits is not limited to 10 bits, and may be determined according to the required stabilization accuracy of the output voltage Vo.

  The first A / D converter 43, the second A / D converter 49, and the third A / D converter 53 are electrically connected to the arithmetic circuit 55. Further, a memory 57 is electrically connected to the arithmetic circuit 55. Therefore, the arithmetic circuit 55 reads the input voltage signal Vid, the output voltage signal Vod, and the current signal Id output from the first A / D converter 43, the second A / D converter 49, and the third A / D converter 53, and stores them in the memory 57. The first switching element 23 and the second switching element 25 are turned on / off by the software and data thus set so that at least one of the input voltage signal Vid, the output voltage signal Vod, and the current signal Id matches a predetermined target value. The control signal Ctd for controlling the output is obtained and output. The memory 57 has a configuration in which the software and data can be rewritten with the memory data signal mem via the arithmetic circuit 55 by a communication data signal data from an external circuit (not shown). Further, the predetermined target value is stored in advance in the memory 57 when the DC voltage source 15 or the load 21 is relatively stable, and the operating state of the DC voltage source 15 or the load 21 varies greatly. Is input from the external circuit to the arithmetic circuit 55 by the communication data signal data so that the DC / DC converter 11 is optimally operated accordingly.

  Here, in this embodiment, the arithmetic circuit 55, the first A / D converter 43, the second A / D converter 49, the third A / D converter 53, and the memory 57 are all built in a one-chip microcomputer 59. did. As a result, the number of circuit components and the mounting area can be reduced, and the cost can be reduced. Further, with this configuration, the first A / D converter 43 in the input voltage detection circuit 35 is built in the microcomputer 59. Similarly, the second A / D converter 49 in the output voltage detection circuit 37 and the third A / D converter 53 in the current detection circuit 29 are also built in the microcomputer 59.

  Since the control signal Ctd obtained by the arithmetic circuit 55 is a digital signal, it is converted into an analog signal (control voltage Ct) for generating an on / off signal SW for turning on and off the first switching element 23 and the second switching element 25. There is a need. Therefore, a D / A converter 61 is electrically connected to the arithmetic circuit 55. Thereby, the control signal Ctd output from the arithmetic circuit 55 is converted into the control voltage Ct by the D / A converter 61. The number of conversion bits of the D / A converter 61 is set to 10 bits, which is the same as that of the first A / D converter 43 and the like. Thereby, it is possible to reduce a decrease in accuracy due to a small number of any of the converted bits. If the conversion bit number of the first A / D converter 43 or the like is determined to be other than 10 bits, the D / A converter 61 may be matched with the conversion bit number. Further, for example, when only the number of conversion bits of the D / A converter 61 is high, there is no problem in accuracy, but if the number of conversion bits in the input system such as the first A / D converter 43 is only 10 bits, it is more than that. It is not meaningful to use an expensive D / A converter 61 having the number of conversion bits. Accordingly, the number of conversion bits of the D / A converter 61 is 10 bits, which is the same as the number of conversion bits of the first A / D converter 43, and the necessary and sufficient number of conversion bits is obtained. For these reasons, it is possible to stabilize the output voltage Vo at a low cost by using the same number of conversion bits.

  A PWM circuit 63 that generates an on / off signal SW is electrically connected between the D / A converter 61 and the first switching element 23 and the second switching element 25. Specifically, the output of the D / A converter 61 is connected to one input terminal of a comparison circuit 65 built in the PWM circuit 63. On the other hand, the PWM circuit 63 incorporates a triangular wave generation circuit 67 as an oscillation circuit, and its output is electrically connected to the other input terminal of the comparison circuit 65. Accordingly, the control circuit Ct and the triangular wave signal Tri output from the triangular wave generation circuit 67 are input to the comparison circuit 65. As a result, the comparison circuit 65 outputs a pulse-like on / off signal SW corresponding to the control voltage Ct from the result of comparing the two.

  Although the triangular wave generating circuit 67 is used as the oscillation circuit in the PWM circuit 63 in the first embodiment, this may be a sawtooth wave generating circuit. Whichever waveform is used, the on / off signal SW can be obtained with high accuracy. In addition, other waveforms that change periodically such as a sine wave can be used as the waveform. However, from the viewpoint of accuracy in the time ratio of the on / off signal SW, the above-described triangular wave or sawtooth wave is more controlled. Since the linearity of the control voltage Ct with respect to the signal Ctd is good, the control voltage Ct is stable and high accuracy can be achieved. Therefore, it is desirable to use a triangular wave or a sawtooth wave. For these reasons, the PWM circuit 63 is composed of an oscillation circuit (triangular wave generation circuit 67) that generates a triangular wave or a sawtooth wave, and a comparison circuit 65, so that the circuit configuration is simple, inexpensive, and highly accurate. A signal SW can be obtained.

  The on / off signal SW output from the PWM circuit 63 is input to the first switching element 23 through the first drive circuit 68, and the on / off signal SW inverted through the inversion circuit 69 is supplied to the second switching circuit 23 through the second drive circuit 71. Input to the switching element 25. As a result, the first switching element 23 and the second switching element 25 repeat the on / off operation alternately according to the pulse waveform of the on / off signal SW.

  The triangular wave generation circuit 67 is electrically connected to the arithmetic circuit 55. Therefore, the arithmetic circuit 55 outputs the triangular wave control signal Trd to the triangular wave generation circuit 67, thereby controlling the oscillation frequency and the time ratio limit of the triangular wave signal Tri.

  The first drive circuit 68 and the second drive circuit 71 are circuits for directly driving the first switching element 23 and the second switching element 25 in response to the on / off signal SW, respectively. Connected. Therefore, the arithmetic circuit 55 outputs the first drive signal IO1, so that the first switching element 23 performs an on / off operation according to the on / off signal SW, or turns off the first switching element 23 regardless of the on / off signal SW. You can control what to do. Similarly, the arithmetic circuit 55 outputs the second drive signal IO2, so that the second switching element 25 performs an on / off operation according to the on / off signal SW, or turns off the second switching element 25 regardless of the on / off signal SW. You can control what to do.

  Next, the operation of such a DC / DC converter 11 will be described.

  First, a basic operation of supplying a stable output voltage Vo to the load 21 by controlling the output voltage Vo to reach the reference output voltage value Vrd that is the predetermined target value will be described.

  The arithmetic circuit 55 outputs a triangular wave control signal Trd having predetermined frequency information to the triangular wave generating circuit 67 in order to activate the DC / DC converter 11. Thereby, the triangular wave generating circuit 67 outputs the triangular wave having the predetermined frequency as the triangular wave signal Tri. In the present embodiment, the predetermined frequency is 100 kHz. Therefore, the ON / OFF cycle of the first switching element 23 and the second switching element 25 is 10 μsec. With this predetermined frequency, even if the voltage fluctuation of the input voltage Vi occurs in the DC voltage source 15, the response that can sufficiently supply a stable voltage to the load 21 by adjusting the output voltage Vo is obtained.

  When starting the DC / DC converter 11, soft start is performed to gradually increase the time ratio of the on / off period of the first switching element 23 or the second switching element 25 from zero. In this case, when the first switching element 23 is used as a reference, the time ratio is increased from 0, and when the second switching element 25 is used as a reference, the inverter 69 is passed through, so that the time ratio is decreased from 1. The arithmetic circuit 55 is programmed to change the control signal Ctd. During this control, the arithmetic circuit 55 turns off either the first drive signal IO1 or the second drive signal IO2 to keep the first switching element 23 or the second switching element 25 for a certain period. Turn off. As a result, the possibility of backflow of the current I can be reduced. As described above, the software in the arithmetic circuit 55 can easily realize the functions of the soft start control and the reduction of the possibility of backflow.

  As another starting method, since the input voltage Vi and the output voltage Vo are detected by the input voltage detection circuit 35 and the output voltage detection circuit 37, respectively, the initial value of the control signal Ctd output from the arithmetic circuit 55 is used. The duty ratio may be determined to be Vo / Vi. Thereby, the increase in the current I immediately after the start of the DC / DC converter 11 can be reduced.

  After startup, in order to stabilize the output voltage Vo to the load 21, the arithmetic circuit 55 outputs an output voltage signal Vod obtained by digitizing the current output voltage Vo from the second A / D converter 49 of the output voltage detection circuit 37. Is read. The arithmetic circuit 55 calculates the control signal Ctd and outputs it to the D / A converter 61 so that the value of the output voltage signal Vod reaches the reference output voltage value Vrd stored in the memory 57 in advance. The D / A converter 61 converts the control signal Ctd into a control voltage Ct and outputs it to the comparison circuit 65 of the PWM circuit 63. As a result, the on / off signal SW is generated from the triangular wave signal Tri and the control voltage Ct by the analog PWM circuit 63, and the on / off operation of the first switching element 23 and the second switching element 25 is performed. The output voltage Vo is stabilized by repeating such an operation and performing feedback control. At this time, the accuracy of the output voltage Vo is greatly influenced by the resolution of the on / off signal SW. Then, the resolution of the on / off signal SW was set to 0.1%. Therefore, the resolution of 10 n (nano) seconds is required for the above 10 μs on / off period, but the analog PWM circuit 63 can sufficiently ensure the resolution.

  On the other hand, as shown in the conventional configuration of FIG. 2, consider the case where all of the control pulses (corresponding to the on / off signal SW of FIG. 1) are digitally processed by a microcomputer. When the control pulse is generated at the same frequency (100 kHz) as in the present embodiment, the necessary accuracy is 10 ns as described above, so the frequency necessary for generating the control pulse to ensure this accuracy. Is at least 100 MHz which is the inverse of 10 ns. Actually, since the microcomputer not only generates the control pulse but also needs to perform processing such as voltage reading and comparison with a target value, the operating clock frequency of the microcomputer needs to be higher than 100 MHz. There is. In order to cope with such a high frequency, when all the controls are digitized, it is understood that an expensive microcomputer such as the DSP needs to be used.

  Therefore, in the basic operation of the DC / DC converter 11 in the present embodiment, the part from the comparison between the output voltage Vo and the reference output voltage value Vrd to the part that outputs the control signal Ctd is digitized, and high accuracy (= high frequency). Since the PWM circuit 63 that is required is an analog circuit, the microcomputer 59 is not required to have such a high frequency, and a general-purpose microcomputer with an operation clock frequency of about 10 MHz can be used. As a result, the cost of the microcomputer 59 can be significantly reduced.

  Next, the safety ensuring operation of the DC / DC converter 11 in the present embodiment will be described. First, the input voltage Vi is detected by the input voltage detection circuit 35 to monitor whether or not the voltage of the DC voltage source 15 has reached an overvoltage. Specifically, the input voltage signal Vid output from the first A / D converter 43 of the input voltage detection circuit 35 is input to the arithmetic circuit 55. The arithmetic circuit 55 compares the overvoltage value Vmd (corresponding to the predetermined target value) stored in the memory 57 with the value of the input voltage signal Vid. If the value of the input voltage signal Vid exceeds the overvoltage value Vmd, the DC In order to protect the components of the DC / DC converter 11 and the load 21, the first drive signal IO1 and the second drive signal IO2 are output so as to stop the operation of the DC / DC converter 11. Here, although the FET is used for the first switching element 23, the anode side of the parasitic diode (not shown) is connected to be the input terminal 13. Further, an FET is used for the second switching element 25, and the parasitic diode (not shown) is connected so that the anode side is grounded. Therefore, when the first switching element 23 and the second switching element 25 are turned off by the first drive signal IO1 and the second drive signal IO2, it is possible to reduce the possibility that an overvoltage is applied to the subsequent stage from the first switching element 23.

  In addition, although the control which turns off the 1st switching element 23 and the 2nd switching element 25 was demonstrated here, it is not limited to this control, The 1st switching element 23 and the 2nd switching element 25 are not turned off. It is also possible to suppress an increase in the input voltage Vi by the control signal Ctd. In this case, the arithmetic circuit 55 performs control so that the input voltage signal Vid matches the predetermined target value in preference to the control for the output voltage Vo. As a result, the input voltage Vi can be controlled so as not to reach an overvoltage.

  Next, whether or not an overcurrent flows is monitored by detecting the current I flowing through the output terminal 19 by the current detection circuit 29. Specifically, the current signal Id output from the third A / D converter 53 of the current detection circuit 29 is input to the arithmetic circuit 55. The arithmetic circuit 55 compares the overcurrent value Imd (corresponding to the predetermined target value) stored in the memory 57 with the value of the current signal Id. If the value of the current signal Id exceeds the overcurrent value Imd, the DC In order to protect the components of the DC / DC converter 11 and the load 21, the first drive signal IO1 and the second drive signal IO2 are output so as to stop the operation of the DC / DC converter 11. The subsequent operation is the same as the overvoltage monitoring operation described above. With such an operation, the first switching element 23 and the second switching element 25 are turned off, so that the possibility that an overcurrent flows to the subsequent stage can be reduced.

  Here, the control for turning off the first switching element 23 and the second switching element 25 has been described. However, the control is not limited to this control, and the first switching element 23 and the second switching element are not limited to this control. Similar to the operation of suppressing the increase of the input voltage Vi by the control signal Ctd without turning off the switching element 25, the current I is limited by the control signal Ctd without turning off the first switching element 23 and the second switching element 25. It can be carried out. In this case, the arithmetic circuit 55 performs control so that the current signal Id matches the predetermined target value in preference to the control for the output voltage Vo. As a result, the current I can be controlled so as not to reach an overcurrent.

  From the above, the safety ensuring operation by monitoring overvoltage or overcurrent has a higher priority than the feedback control in which the output voltage Vo reaches the reference output voltage value Vrd. Therefore, if an overvoltage or overcurrent is detected, the stabilization of the output voltage Vo by the feedback control is interrupted and the operation of the DC / DC converter 11 is stopped, or the input voltage signal Vid matches the overvoltage value Vmd. Thus, the DC / DC converter 11 is controlled to ensure safety so that the current signal Id matches the overcurrent value Imd. When an overvoltage or overcurrent is detected, the arithmetic circuit 55 notifies the external circuit of the occurrence of the overvoltage or overcurrent by the communication data signal data. As a result, the external circuit can perform control corresponding to overvoltage or overcurrent and provide a warning to the user.

  The reference output voltage value Vrd, the overvoltage value Vmd, and the overcurrent value Imd, which are the predetermined target values, are all stored in the memory 57, but the memory 57 can be rewritten by the memory data signal mem. Therefore, when the specifications of the DC voltage source 15 and the load 21 are changed, the arithmetic circuit 55 that has received the communication data signal data from the external circuit outputs the memory data signal mem to the memory 57, so that the reference The output voltage value Vrd, the overvoltage value Vmd, and the overcurrent value Imd can be rewritten. As a result, it is possible to easily and inexpensively change the specifications without changing parts in the hardware of the DC / DC converter 11. Furthermore, since the DC / DC converters 11 having various specifications can be created by simply rewriting data with the same hardware, a variety of products can be manufactured at low cost.

  The arithmetic circuit 55 may be configured to limit the value of the control signal Ctd by software so as to provide an upper limit value or a lower limit value. Thereby, for example, when the upper limit value is provided, the control signal Ctd does not become a value equal to or higher than the upper limit value, so that the upper limit is controlled with respect to the time ratio of the on / off signal SW. As a result, since the maximum value of the duty ratio is not 1, the possibility that the first switching element 23 remains on, for example, can be reduced. Therefore, the possibility that the overcurrent continues to flow from the DC voltage source 15 to the load 21 can be reduced.

  On the other hand, when a lower limit is provided for the value of the control signal Ctd, the lower limit is controlled with respect to the time ratio of the on / off signal SW. As a result, since the minimum value of the duty ratio does not become 0, for example, in the second switching element 25 in which the on / off state is inverted by the inverting circuit 69, the possibility of being kept on can be reduced. . Therefore, since the possibility that the both ends of the load 21 continue to be short-circuited can be reduced, for example, when the power storage element is used as the load 21, the possibility that a large current continues to flow due to the short-circuit is reduced.

  Furthermore, both the upper limit value and the lower limit value may be provided for the value of the control signal Ctd. In this case, since the possibility that both the first switching element 23 and the second switching element 25 remain on is reduced, the possibility of both the overcurrent and the short circuit can be reduced.

  For these reasons, by providing at least one of an upper limit value and a lower limit value for the control signal Ctd by the arithmetic circuit 55, it is possible to control at least one of the upper limit and the lower limit in the time ratio of the on / off signal SW. The safety ensuring operation can be further enhanced.

  With the above configuration and operation, as the control circuit of the DC / DC converter 11, the PWM circuit 63 having excellent high-speed response is an analog circuit, and the other circuits are digital circuits. A general-purpose microcomputer 59 having a low level can be applied. Therefore, it is possible to realize the DC / DC converter 11 that can secure high resolution at low cost and can stabilize the output voltage.

  In this embodiment, the input voltage detection circuit 35 and the current detection circuit 29 are used for ensuring safety, but this is when the voltage stability of the DC voltage source 15 is ensured and no overvoltage occurs ( For example, when an overcurrent prevention function is built in the DC voltage source 15, the input voltage detection circuit 35 and the current detection circuit 29 may be omitted. In addition, when the voltage stability of the DC voltage source 15 is ensured but no overcurrent countermeasure is taken, only the current detection circuit 29 is used, but the overcurrent countermeasure is taken, but the voltage stability is secured. If not, only the input voltage detection circuit 35 may be provided. If the input voltage detection circuit 35 or the current detection circuit 29 is not provided, at least one of the first A / D converter 43 and the third A / D converter 53 is not incorporated in the microcomputer 59 accordingly. Become.

  In the present embodiment, when the DC / DC converter 11 is used as a constant current source, only the current detection circuit 29 may be provided, and both the input voltage detection circuit 35 and the output voltage detection circuit 37 may be omitted. In this case, the arithmetic circuit 55 performs an operation of outputting the control signal Ctd so that the value of the current signal Id detected by the current detection circuit 29 reaches the reference current value Ird. As a result, a constant current is supplied to the load 21. However, in the case of such a configuration, since both the input voltage detection circuit 35 and the output voltage detection circuit 37 are not provided, the DC voltage source 15 is applied with a specification that is stable without reaching an overvoltage, and a load is applied. The load 21 needs to be configured such that the load 21 does not reach overvoltage or overvoltage detection. Therefore, even when used as the constant current source, depending on the specifications and configuration of the DC voltage source 15 and the load 21, the input voltage detection circuit 35, the output voltage detection circuit 37, or both may be provided. In this case, the priority of the control is to determine whether the input voltage signal Vid from the input voltage detection circuit 35 or the output voltage signal Vod from the output voltage detection circuit 37 has reached an overvoltage, and constant current control is performed. The priority of operation is the next point.

  Moreover, in this Embodiment, it is good also as a structure used as a charging / discharging circuit of the said electrical storage element by using an electrical storage element as the load 21, and making the DC / DC converter 11 into a bidirectional | two-way structure. Thereby, when the voltage fluctuation of the DC voltage source 15 is large, it is possible to stabilize the voltage of the DC voltage source 15 by charging / discharging the electric power corresponding to the fluctuation to the power storage element. As a specific example of such an application, for example, in a vehicle, the DC voltage source 15 is a battery, the electric storage element is an electric double layer capacitor, and an electrical component is connected in parallel with the DC voltage source 15, thereby The structure which stabilizes the battery voltage which is fluctuate | varied with the electric power usage condition of goods, and the electric power generation amount of the generator of the said vehicle with the electric power of the said electric double layer capacitor is mentioned. Since the control in this configuration is an operation of stabilizing the input voltage Vi of the DC voltage source 15, the arithmetic circuit 55 is a reference in which the input voltage signal Vid output from the input voltage detection circuit 35 is stored in the memory 57 in advance. The control signal Ctd is output so as to reach the input voltage value Vsd. Here, in FIG. 1, since the DC voltage source 15 side is defined as an input, in the case of stabilization of the battery voltage, it is expressed as control with respect to the input voltage Vi, but actually, the storage element (load 21 side). Becomes the input, and the battery (DC voltage source 15 side) becomes the output. Therefore, even when the DC / DC converter 11 is applied to the vehicle, the arithmetic circuit 55 substantially obtains the control signal Ctd for controlling the output voltage Vo (corresponding to the input voltage Vi in FIG. 1). Output. However, in order to avoid the complexity of notation, the following description will be made using the symbols shown in FIG.

  In the configuration applied to the vehicle, the arithmetic circuit 55 compares the current signal Id output from the current detection circuit 29 with the overcurrent value Imd for overcurrent monitoring, and performs control so as not to exceed the overcurrent value Imd. At the same time, the output voltage signal Vod output from the output voltage detection circuit 37 is compared with the upper limit voltage value Vud stored in the memory 57 in order to avoid overcharging of the power storage element so as not to exceed the upper limit voltage value Vud. Is controlling. Therefore, in this case, the control priority for the current I and the output voltage Vo is high, and the control priority for the input voltage Vi is the next point.

  In the above control, the input voltage Vi may not be controlled during a period when the voltage fluctuation of the DC voltage source 15 (the battery) is small. Thereby, the DC / DC converter 11 can be a charging circuit that charges the storage element with a constant current and a constant voltage.

  In addition, the above-described configuration for stabilizing the battery voltage for a vehicle can be used as an emergency backup power source in the event of a power failure. In this case, since it is generally necessary to store a large amount of power, a large number of the storage elements are required. In such a configuration, voltage variations of the respective storage elements occur, and thus the voltage variations are adjusted by a balance circuit. At this time, since the voltages of the respective storage elements are measured, the voltages of all the storage elements (corresponding to the output voltage Vo) can be known from the balance circuit. Therefore, in the case of such a configuration, the output voltage detection circuit 37 may not be provided in the DC / DC converter 11. Furthermore, when the maximum value of the current I at the time of backup in an emergency is determined, the circuit component of the DC / DC converter 11 is designed so that it can sufficiently cope with the maximum value. A configuration in which the current detection circuit 29 is not particularly provided may be employed.

  From the above, the DC / DC converter 11 may be provided with at least one of the input voltage detection circuit 35, the output voltage detection circuit 37, and the current detection circuit 29 according to various applications. Accordingly, at least one of the first A / D converter 43, the second A / D converter 49, and the third A / D converter 53 is electrically connected to the arithmetic circuit 55, and the input voltage signal Vid, the output voltage signal Vod, or the current signal Id. The control signal Ctd for controlling to match at least one of the predetermined target value with the predetermined target value is obtained and output. In this case, since the control target and priority of the DC / DC converter 11 change depending on the application, the predetermined target value for at least one of the input voltage signal Vid, the output voltage signal Vod, and the current signal Id is obtained from the external circuit. The configuration may be such that the communication data signal data is received and updated as appropriate, or the software that controls the operation of the arithmetic circuit 55 stored in the memory 57 and the predetermined target value may be rewritten from the external circuit.

  The arithmetic circuit 55 determines the current target value Idt so that the input voltage signal Vid or the output voltage signal Vod matches the predetermined target value, and controls the current signal Id to match the current target value Idt. The control signal Ctd may be obtained and output. Specifically, first, the arithmetic circuit 55 obtains a difference between the input voltage signal Vid and the output voltage signal Vod so as to match the predetermined target value. Next, the obtained difference is amplified, and the current target value Idt is determined so as to reduce the difference between the two. Next, the difference between the current target value Idt and the current signal Id is amplified, and the control signal Ctd is obtained so as to reduce these differences, so that the current signal Id matches the current target value Idt. / DC converter 11 is controlled. With such an operation, the DC / DC converter 11 can always reliably control the current I even when the input voltage Vi or the output voltage Vo is controlled, so that more stable control can be realized.

  In the present embodiment, the first A / D converter 43, the second A / D converter 49, and the third A / D converter 53 are all incorporated in the microcomputer 59. However, at least one of these is shown. It may be configured to be externally attached to the microcomputer 59. In this case, since the number of built-in A / D converters that are small or not built in can be used as the microcomputer 59, the cost of the microcomputer 59 can be reduced. However, since an external A / D converter is required, the number of external A / D converters can be determined as appropriate in consideration of the total cost.

  In the present embodiment, the memory 57 is also built in the microcomputer 59, but this may be an external memory. As a result, the memory capacity can be increased arbitrarily, so that it is possible to collect memories necessary for circuits other than the DC / DC converter 11. As a result, depending on the number of memories and the total memory capacity at the time of providing a memory for each circuit, it may be possible to reduce the cost, so whether it is externally installed or built in considering the total cost May be determined as appropriate.

  In this embodiment, the D / A converter 61 is configured separately from the microcomputer 59, but it may be configured to be built in the microcomputer 59. In this case, since the 10-bit D / A converter 61 is used in this embodiment, a general-purpose microcomputer having a 10-bit built-in D / A converter is required. Therefore, the configuration may be determined in consideration of the total cost when using such a general-purpose microcomputer and when using a separate configuration.

  In the present embodiment, the arithmetic circuit 55 has various current voltage signals (input voltage signal Vid, output voltage signal Vod and current from the first A / D converter 43, the second A / D converter 49, and the third A / D converter 53). The signal Id) is read, but this may be performed by reading the current and voltage signals for a predetermined number of times determined in advance, for example, to obtain an average value. This improves the accuracy of the various current / voltage signals and stabilizes the output voltage Vo. Further, the past various current / voltage signals may be stored in the memory 57 and averaged with those values. Thereby, since the fluctuation | variation of the said various current voltage signals by single noise etc. can be suppressed, further high precision becomes possible and the stability of output voltage Vo improves. Note that the calculation method is not limited to the above average value, and if the required accuracy can be ensured, the median value or the mode value may be used, and the calculation method of averaging is not limited to a simple arithmetic average, For example, a method such as a weighted average that weights between the previous value and the current value may be used.

  In the present embodiment, two switching elements (the first switching element 23 and the second switching element 25) are used. However, the present invention is not limited to this, and four switching elements are used. A configuration of a step-up / step-down DC / DC converter may be employed.

  The DC / DC converter according to the present invention can secure high resolution at low cost and can stabilize the output voltage, so that it is particularly useful as a DC / DC converter for a vehicle that requires low cost and high stability at the same time. It is.

DESCRIPTION OF SYMBOLS 11 DC / DC converter 13 Input terminal 19 Output terminal 23 1st switching element 25 2nd switching element 29 Current detection circuit 35 Input voltage detection circuit 37 Output voltage detection circuit 43 1st A / D converter 49 2nd A / D converter 53 3rd A / D converter 55 Arithmetic circuit 57 Memory 59 Microcomputer 61 D / A converter 63 PWM circuit

Claims (7)

The output voltage (Vo) is output from the output terminal electrically connected to the switching element by performing on / off control of the plurality of switching elements electrically connected to the input terminal to which the input voltage (Vi) is input. In the DC / DC converter,
An input voltage detection circuit that is electrically connected to the input terminal, detects the input voltage (Vi), converts the input voltage (Vid) to a first A / D converter, and outputs the input voltage signal (Vid);
Or an output voltage detection circuit that is electrically connected to the output terminal, detects the output voltage (Vo), converts it to an output voltage signal (Vod) by a second A / D converter, and outputs the output voltage signal (Vod);
Or at least one of a current detection circuit that detects a current (I) flowing through the DC / DC converter, converts the current (I) into a current signal (Id) by a third A / D converter, and outputs the current signal (Id);
It is electrically connected to at least one of the first A / D converter, the second A / D converter, and the third A / D converter, and at least the input voltage signal (Vid), the output voltage signal (Vod), or the current signal (Id). An arithmetic circuit that obtains and outputs a control signal (Ctd) for controlling either one to match a predetermined target value;
A D / A converter electrically connected to the arithmetic circuit and converting the control signal (Ctd) into a control voltage (Ct);
A DC / DC converter comprising: a PWM circuit that is electrically connected between the D / A converter and the switching element and outputs an on / off signal (SW) of the switching element from the control voltage (Ct). The control circuit determines a current target value (Idt) so that the input voltage signal (Vid) or the output voltage signal (Vod) matches the predetermined target value, and the current signal (Id) is determined as the current 2. The DC / DC converter according to claim 1, wherein a control signal (Ctd) for controlling to match the target value (Idt) is obtained and output. The arithmetic circuit is configured to control at least one of an upper limit and a lower limit in a time ratio of the on / off signal (SW) by providing at least one of an upper limit value and a lower limit value for the control signal (Ctd). The DC / DC converter according to claim 1. The PWM circuit includes an oscillation circuit that generates a triangular wave or a sawtooth wave;
The comparison circuit according to claim 1, further comprising: a comparison circuit that is electrically connected to the oscillation circuit and obtains the on / off signal (SW) from a result of comparing the output of the oscillation circuit and the control voltage (Ct). DC / DC converter. 2. The DC / DC converter according to claim 1, wherein at least one of the arithmetic circuit and the first A / D converter, the second A / D converter, or the third A / D converter is built in a one-chip microcomputer. 2. The DC / DC converter according to claim 1, wherein the arithmetic circuit is electrically connected to a memory capable of rewriting software from outside. 2. The DC / DC converter according to claim 1, wherein the first A / D converter, the second A / D converter, the third A / D converter, and the D / A converter have the same number of conversion bits.

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