JP4617977B2 - Voltage converter - Google Patents

Description

  The present invention relates to a voltage converter, and more particularly to a voltage converter that performs voltage conversion by repeatedly storing and releasing energy in a reactor.

Japanese Patent Laying-Open No. 2003-284328 (Patent Document 1) discloses a DC / DC converter for vehicle use. This DC / DC converter is provided with a protective field effect transistor that is normally in a conducting state and disconnects the circuit in an emergency.
JP 2003-284328 A JP 2000-354363 A JP 2000-333445 A Japanese Patent Laid-Open No. 2001-231251 JP 2003-70238 A JP 2001-128369 A

  FIG. 16 is a circuit diagram showing a configuration of a conventional DC / DC converter.

  Referring to FIG. 16, this DC / DC converter is connected between a high-voltage side DC power source 501 and a low-voltage side DC power source 506, and performs a step-down operation from power source 501 to power source 506, and from power source 506 to power source 501. Boost operation is possible.

  The DC / DC converter includes field effect transistors (hereinafter referred to as MOSFETs) 502 and 503 having a metal-oxide-semiconductor (MOS) structure, and a reactor 504.

  The MOSFETs 502 and 503 are connected in series between the positive electrode of the power source 501 and the ground. The reactor 504 is connected between the connection point of the MOSFETs 502 and 503 and the positive electrode of the power source 506. MOSFETs 502 and 503 have body diodes 507 and 508, respectively, so that the direction from the source to the drain is the forward direction because the source and the substrate are connected. The body diode is a diode formed parasitically in the MOSFET.

  Generally, in a DC / DC converter, soft start control is performed in order to protect a circuit from an excessive inrush current to a smoothing capacitor or the like in which charge is not accumulated at the time of starting. The soft start control is to gradually increase the voltage or decrease the voltage by shortening the period in which energy is stored in the reactor 504 for a certain period from the start of the operation.

  FIG. 17 is an operation waveform diagram for explaining soft start control when the step-down operation of the DC / DC converter shown in FIG. 16 is started.

  The MOSFETs 502 and 503 in FIG. 16 are subjected to synchronous control so that when one of the MOSFETs 502 and 503 performs a step-up or step-down operation, the other enters a non-conductive state. This is because it is less loss because the conduction resistance is lower when the commutation current is made to be conducted simultaneously than when the commutation current is made to flow only by the body diode.

  Referring to FIGS. 16 and 17, first, at time t1 to t2, gate signal G502 applied to the gate of MOSFET 502 is activated, and gate signal applied to the gate of MOSFET 503 is inactivated. At this time, the current IL flowing through the reactor 504 increases, and energy corresponding to the coil current is accumulated in the reactor 504.

  When the gate signal G502 is deactivated at time t2 and the gate signal G503 is activated, the current flowing into the power source 506 in the order of the power source 501, the MOSFET 502, and the reactor 504 is interrupted. At time t2 to t2A, the current flows from the MOSFET 503 through the reactor 504 to the power source 506. Then, the energy stored in reactor 504 becomes 0 at time t2A, and reactor current IL becomes 0.

  Thereafter, similarly, at time t3 to t4 and t5 to t6, the MOSFET 502 is conducted and energy is accumulated in the reactor 504, and at time t4 to t4A and t6 to t7, the reactor energy is released.

  As shown in FIG. 17, the soft start control of the DC / DC converter is performed by gradually increasing the activation period of the gate signal G502.

  However, if synchronous control is performed on the MOSFET 503 during this soft start control, the conduction time of the MOSFET 503 becomes longer than the period during which energy is released from the reactor.

  For example, the MOSFET 503 is in a conductive state between times t2 and t3. At this time, as indicated by the broken line in FIG. 17, the energy accumulated in the reactor 504 is after the time t2A to t3 has been released, so the reactor current IL once becomes 0, and thereafter the power source 506 Overcurrent IL flows through the path indicated by the arrow 16.

  Then, the reverse energy is accumulated in the reactor 504, so that the step-down operation may not be started well. This is a problem particularly in a configuration in which a power source such as a battery is connected to the load side.

  FIG. 18 is a circuit diagram illustrating a study example of a DC / DC converter.

  The circuit diagram shown in FIG. 18 differs from the configuration shown in FIG. 16 in that a current sensor 510 is provided between the reactor 504 and the power source 506, but the configuration is the same as that of FIG. The explanation will not be repeated.

  In order to solve the problem described with reference to FIG. 17, it is conceivable that the reactor current is monitored by the current sensor 510 to determine the timing for starting the synchronous control of the MOSFETs 502 and 503. However, if a sensor that uses a shunt resistor, for example, is arranged as the current sensor 510, power loss always occurs in this portion. Further, in a DC / DC converter that handles a large current and a large power, this current sensor becomes a considerably large component, which causes problems such as an increase in size of the device, an increase in cost, and a decrease in efficiency.

  An object of the present invention is to provide a voltage converter that is small, highly efficient, and has improved circuit protection performance.

  In summary, the present invention provides a voltage converter, which includes a reactor, and performs voltage conversion by repeatedly storing energy in the reactor and discharging energy from the reactor, between the first and second power supplies. A conversion unit to be connected, a connection unit provided on a path from the first power source to the second power source via the reactor, and a control unit for conducting and blocking the path, and a control for controlling the conversion unit and the connection unit A part. The control unit performs a soft start operation that gradually increases the amount of energy per cycle stored in the reactor at the start of operation, and sets the connection unit in synchronization with the cycle in which energy is stored and released in the reactor during the soft start operation. Control.

  Preferably, the conversion unit further includes first and second switching elements, and the connection unit includes a third switching element. In the soft start operation, the control unit causes the first and second switching elements to conduct complementarily and causes the third switching element to operate so as to prevent reverse current from the output.

  Preferably, the conversion unit further includes a main switching element that conducts when energy is stored in the reactor, and the control unit synchronizes the connection unit in synchronism with a time when the main switching element transitions from the non-conduction state to the conduction state. Conduct.

  More preferably, the control unit makes the connection unit non-conductive in synchronization with a time when the main switching element is changed from the conductive state to the non-conductive state.

  More preferably, the control unit makes the connection unit non-conductive in synchronization with a time when the release of energy from the reactor is completed after the main switching element is changed from the conductive state to the non-conductive state.

  Preferably, the conversion unit further includes a main switching element that conducts when energy is stored in the reactor, and a sub-switching element that conducts when energy is discharged from the reactor. The control unit causes the connection unit to conduct in synchronization with the timing at which the sub switching element transitions from the conductive state to the non-conductive state.

  More preferably, the control unit makes the connection unit non-conductive in synchronization with a time when the release of energy from the reactor is completed after the sub switching element is changed from the non-conductive state to the conductive state.

  Preferably, the connection portion includes a switching element with a current detection function.

  According to the present invention, during the soft start operation of the connection unit that connects the conversion unit that performs power conversion to the output-side power source or the input-side power source, by controlling in synchronization with one cycle of reactor energy storage and discharge, In normal operation, low-loss step-down operation can be realized, and current is prevented from flowing back from the output-side power source to the converter during the soft-start operation.

  It is also possible to protect the internal circuit of the voltage converter in the event of an abnormality (such as when the high-side power supply is grounded during normal times).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a circuit diagram showing a configuration of voltage converter 20 according to Embodiment 1 of the present invention.

  Referring to FIG. 1, voltage converter 20 is connected between high-voltage power supply 1 and low-voltage power supply 6 and performs a step-down operation from high-voltage power supply 1 to low-voltage power supply 6. Although not particularly limited, it can be used, for example, when charging a low voltage battery for auxiliary equipment from a high voltage battery for driving a motor for vehicle propulsion in a vehicle such as a hybrid vehicle.

  Voltage converter 20 incorporates reactor 4, and converts converter 20D that performs voltage conversion by repeatedly storing energy in reactor 4 and releasing energy from reactor 4, and reactor 4 of converter 20D from DC power supply 1. Provided on a path that leads to the power supply 6 via, a connection MOSFET 5 that conducts and cuts off this path, and a control unit 13 that controls the conversion unit 20D and the MOSFET 5 are provided.

  Voltage converter 20 further includes a smoothing capacitor 10 that smoothes the voltage output from conversion unit 20D, and a voltage that monitors the voltage of the positive electrode of power supply 1 and outputs voltage V signal 1 to control unit 13. The sensor 11 includes a voltage sensor 12 that monitors the voltage of the positive electrode of the power supply 6 and outputs a voltage signal V6 to the control unit 13.

  Conversion unit 20D includes MOSFETs 2 and 3 that are directly connected between the positive electrode of power supply 1 and the ground node, and reactor 4 that is connected at one end to node N1 that is a connection node of MOSFETs 2 and 3. The other end of reactor 4 is connected to output node N2 of conversion unit 20D.

  MOSFETs 2, 3, and 5 are all N-channel MOSFETs. Each of the MOSFETs 2, 3, and 5 has a back gate portion coupled to an electrode at one end. In this specification, the electrode coupled to the back gate portion is referred to as a source for convenience of explanation. Since these connections are made, MOSFETs 2, 3, and 5 each include body diodes 7, 8, and 9 whose forward direction is from the source to the drain, as will be described in detail later with reference to FIG. .

  The control unit 13 receives the voltage signals V1 and V6 and the current signal I5 indicating the current flowing through the MOSFET 5, and controls the gate signals G2, G3 and G5 in response thereto. Gate signals G2, G3, and G5 are gate signals applied to the gates of MOSFETs 2, 3, and 5, respectively. Here, the current signal I5 is given from the MOSFET 5.

  FIG. 2 is a circuit diagram showing a detailed structure of MOSFET 5 in FIG.

  Referring to FIG. 2, MOSFET 5 is a MOSFET with a current sense function, and includes MOSFETs 51 to 54 formed on the same semiconductor substrate 50, a resistor 55, and a voltage sensor 56 that measures a voltage across the resistor 55. . Note that the resistor 55 and the voltage sensor 56 may be provided outside the MOSFET 5.

  The MOSFET 5 is a power MOSFET capable of flowing a large current, and has a configuration having a large number of MOSFETs 51 to 53 connected in parallel. In addition, a MOSFET 54 whose drain and gate are commonly connected to the MOSFETs 51 to 53 and whose source is separated is provided.

  However, since the MOSFETs 51 to 54 are formed on the same substrate and the shape of each transistor cell is substantially the same, it can be considered that the values of flowing currents are substantially equal. A current flowing through the MOSFET 54 can be detected by connecting a shunt resistor 55 in series with the MOSFET 54 and measuring the voltage across this terminal. A value obtained by multiplying the current value by the number of transistors is a current value I5 flowing between the source and drain of the MOSFET 5.

  Since the current is small, the resistance 55 can be made smaller than the shunt resistance used in the current sensor 510 shown in FIG. 18, and the heat loss can also be reduced. By using such a MOSFET with a sense function, the entire device can be reduced in size and efficiency.

  FIG. 3 is an operation waveform diagram for explaining the operation at the time of soft start of the voltage converter 20 shown in FIG.

  Referring to FIGS. 1 and 3, gate signals G2, G3, and G5 are gate signals applied to the gates of MOSFETs 2, 3, and 5, respectively. The current signal I5 is a signal indicating the current flowing through the MOSFET 5.

  FIG. 3 shows the soft start operation until time t9. That is, the gate signal G2 is activated and the MOSFET 2 is in a conducting state between times t1 to t2, t3 to t4, t5 to t6, and t7 to t8. It turns out that the width | variety used as this conduction | electrical_connection state is gradually widened.

  The MOSFET 3 is synchronously controlled so as to be conductive when the MOSFET 2 is in a non-conductive state. At this time, the MOSFET 5 that connects the conversion unit 20D of FIG. 1 to the power source 6 is also subjected to conduction control in the same manner as the MOSFET 2 until time t9.

  By doing so, it is possible to prevent an overcurrent flowing from the power source 6 through the reactor 4 to the ground node via the MOSFET 3 during the period in which the MOSFET 3 is conducting.

  The controller 13 controls the gate signal G5 in the same manner as the gate signal G2 until time t9. At time t9, the gate signal G5 is fixed at the H level in response to the current signal I5 indicating the current flowing through the MOSFET 5 reaching the predetermined threshold value IT0. As a result, after time t9, the MOSFET 2 is controlled to conduct at a duty ratio corresponding to the potential difference between the power source 1 and the power source 6, and the MOSFET 3 is synchronously controlled to conduct in a complementary state.

  That is, the configuration shown in FIG. 1 and the control shown by the waveform of FIG. 3 will be described in summary. Conversion unit 20D incorporates reactor 4, and stores energy in reactor 4 and releases energy from reactor 4. Voltage conversion is performed by repeating. The MOSFET 5 is provided on a path from the power source 1 to the power source 6 via the reactor 4 and corresponds to a connection part that conducts and cuts off the path. Control unit 13 controls converter 20D and MOSFET 5.

  The controller 13 performs a soft start operation that gradually increases the amount of energy per cycle stored in the reactor 4 at the start of the operation. The control unit 13 controls the MOSFET 5 in synchronization with a cycle in which energy is stored and released in the reactor 4 during the soft start operation.

  During the soft start operation, conversion unit 20D includes MOSFET 2 that is a main switching element that conducts when energy is stored in reactor 4. Then, the control unit 13 causes the MOSFET 5 to conduct in synchronization with the time when the MOSFET 2 transitions from the non-conducting state to the conducting state. Furthermore, the control unit 13 makes the MOSFET 5 non-conductive in synchronization with the time when the MOSFET 2 is changed from the conductive state to the non-conductive state.

  After the soft start operation is completed, the MOSFET 5 is fixed to a conductive state.

  By performing such control on the MOSFET 5, in a normal operation, a low-loss step-down operation can be realized by synchronous control. During the soft start operation, a current flows backward from the output-side power source to the conversion unit 20D. Is prevented.

  FIG. 4 is a diagram showing a configuration of voltage converter 20A used in the first modification of the first embodiment.

  4, control unit 13 and voltage sensors 11 and 12 are the same as those shown in FIG. 1, and therefore illustration and description thereof will not be repeated. The voltage converter 20A shown in FIG. 4 is different in that the smoothing capacitor 10 connected to the node N2 in FIG. 1 is replaced with a capacitor 10A connected to a connection node between the MOSFET 5 and the power supply 6. . Since the voltage converter 20 shown in FIG. 1 and voltage converter 20A in FIG. 4 are the same for other configurations, description thereof will not be repeated.

  FIG. 5 is an operation waveform diagram for explaining the control of voltage converter 20A shown in FIG.

  Referring to FIG. 5, gate signals G2, G3, and G5 applied to MOSFETs 2, 3, and 5 are controlled in the same manner as described with reference to FIG. 3, and therefore description thereof will not be repeated.

  Here, since the capacitor 10A is connected to the output side of the voltage converter 20A, the same current as the current flowing through the reactor 4 flows through the MOSFET 5. Therefore, a triangular wave is observed so that the current signal I5 flows through the reactor.

  That is, the energy accumulated in the reactor 4 at the time t1 to t2 is released from the reactor 4 at the time t2 to t2A. Similarly, energy is accumulated in reactor 4 from time t3 to t4, and energy is released from reactor 4 from time t4 to t4A.

  Similarly, energy is accumulated in reactor 4 at times t5 to t6, t7 to t8, t9 to t10, and t11 to t12, and energy is released from reactor 4 at times t6 to t6A, times t8 to t9, and t10 to t11. .

  FIG. 6 is a diagram showing the structure per cell of the power MOSFET.

  Referring to FIG. 6, low-concentration n-type impurity region 64 is formed on high-concentration n-type impurity region 62 connected to the drain terminal, and p-type impurity region is formed on n-type impurity region 64. 66, and an n-type impurity region 68 having a high concentration is formed inside the p-type impurity region 66.

  A gate oxide film 70 and a gate electrode 72 are formed on the n-type impurity region 64, the p-type impurity region 66, and the n-type impurity region 68, and a source electrode 74 made of a metal layer is further formed thereon. .

  Such unit cells are repeatedly provided in order to pass a large number of currents. That is, the gate electrode 72 has a mesh shape in which a large number of holes are provided in order to provide a large number of source contacts. The source electrode 74 is connected to an n-type impurity region 68 serving as a source region and a p-type impurity region 66 serving as a back gate region.

  In the MOSFET having such a configuration, a body diode is formed between the p-type impurity region 66 and the n-type impurity region 64 at a portion indicated by a diode symbol in FIG.

  5, at time t1 to t2, t3 to t4, t5 to t6, and t7 to t8 when the gate signal G5 is activated, the source current ISD2 mainly flows from the source S to the drain D as shown in FIG. .

  In the period t2 to t2A, t4 to t4A, t6 to t6A, and t8 to t9 during which the energy of the reactor 4 is released, the gate signal G5 is inactivated, so that the current ISD2 in FIG. Only ISD1 flows.

  In FIG. 5, the control unit observes the current signal I5, so that the gate signal G5 is fixed at the active level after time t9 when the minimum current value Imin in one cycle becomes 0 or more. As a result, after time t9, the current ISD2 having a lower conduction resistance than the current ISD1 in FIG. 6 mainly flows and the conduction loss is reduced. From time t1 to t9, the current IL indicated by the arrow in FIG. Overcurrent can be prevented.

  FIG. 7 is an operation waveform diagram for illustrating control performed in the second modification of the first embodiment.

  In FIG. 7, gate signals G2, G3 and current I5 are similar to those shown in FIG. 5, and therefore description thereof will not be repeated. The operation waveform diagram of FIG. 7 is characterized in that the waveform of the gate signal G5 is different from the gate signal G5 shown in FIG.

  That is, the control unit activates the gate signal G5 in synchronization with the activation of the gate signal G2 until the soft start period time t8. Then, the current signal I5 is monitored and the gate signal G5 is deactivated in synchronization with the current signal I5 becoming zero.

  By performing such control, the conduction resistance of the MOSFET 5 is lowered even when the energy accumulated in the reactor 4 at the time of soft start is released. That is, the current ISD2 in FIG. 6 also flows at times t2 to t2A, t4 to t4A, and t6 to t6A, and the loss is reduced.

  The soft start control is ended in response to the maximum value of the current signal I5 exceeding the threshold value IT1 at time t8, and thereafter the MOSFET 5 is fixed to the conductive state. Note that the same control can be performed by continuing to monitor the current signal I5 after time t8 and keeping the MOSFET 5 conductive unless the current signal I5 falls below zero.

  In other words, in FIG. 7, during the soft start control, the control unit causes the MOSFET 5 to conduct in synchronization with the time when the MOSFET 2 transitions from the non-conducting state to the conducting state. And a control part makes MOSFET5 non-conductive in synchronism with the time when discharge | release of the energy from the reactor 4 is completed after making MOSFET2 change from a conductive state to a non-conductive state.

  Then, the current is detected by the MOSFET 5 when control for connecting the conversion unit for performing voltage conversion to the power source is performed, and the soft start control is shifted to the normal control when a certain threshold value is exceeded. During normal control, MOSFET 5 is fixed in a conductive state. When the DC / DC converter is not operating, MOSFET 5 is fixed in a non-conductive state.

  Thus, by providing the MOSFET 5 as a connection portion and performing the above-described control during the soft start control, normally, the ground via the power supply reactor on the high side (output side for boosting and input side for stepping down) is provided. Since the MOSFET 5 can also include the function of detecting the output current, the voltage converter that is smaller, lighter and more efficient than the prior art and has a protection function can be realized.

[Embodiment 2]
The control described in the first embodiment can also be applied to the step-up DC / DC converter.

  FIG. 8 is a circuit diagram showing a configuration of a boost converter 80 which is a voltage converter according to the second embodiment.

  Referring to FIG. 8, boost converter 80 is connected between a low voltage power supply 81 connected to the input side and a high voltage power supply 86 connected to the output side. Boost converter 80 includes a conversion unit 80D and a connection unit 85 that conducts and cuts off a connection path between the conversion unit 80D and the power supply 86 on the output side. Connection unit 85 includes MOSFETs 85A and 85B.

  Conversion unit 80D includes a reactor 84, a MOSFET 82, and a MOSFET 83. Reactor 84 and MOSFET 82 are connected in series between power supply 81 on the input side and the ground node. MOSFET 83 is connected between a connection node between reactor 84 and MOSFET 82 and a connection portion 85 provided on the output side.

  Body diodes 87, 88 and 89 are parasitic diodes which can be formed by internally connecting the source and back gate in MOSFETs 82, 83 and 85, respectively.

  MOSFETs 85A and 85B have both the source and back gate connected to node N3. A gate voltage is applied to the gates of the MOSFETs 85A and 85B with reference to the potential of the node N3.

  At least one of the MOSFETs 85A and 85B has a configuration similar to that of the MOSFET 5 described in FIG. Details of the configuration have been described with reference to FIG.

  In such a configuration, the MOSFET 82 is turned on to store energy in the reactor 84, and then the MOSFET 82 is turned off and the MOSFET 83 is turned on. In synchronization with this cycle, the connecting portion 85 is also conducted.

  In other words, conversion unit 80 </ b> D is a reactor 84, MOSFET 82, which is a main switching element that conducts when energy is stored in reactor 84, and a sub-switching element that conducts when energy is discharged from reactor 84. MOSFET 83 is included.

  Although not shown, the control unit that controls the conversion unit 80D and the connection unit 85 causes the connection unit 85 to conduct in synchronization with the time when the sub-switching element (MOSFET 83) transitions from the non-conduction state to the conduction state.

  And a control part makes the connection part 85 non-conductive in synchronism with the time when discharge | release of the energy from the reactor 84 is completed, after making a subswitching element (MOSFET83) change from a non-conduction state to a conduction | electrical_connection state.

  The conduction of the MOSFET 83 and the connection portion 85 is synchronized at the time of soft start, and when the current flowing through the connection path of the connection portion 85 becomes a predetermined condition, the soft start control is terminated and the connection portion 85 is fixed to the conduction state. To do. By performing such control, the step-up DC / DC converter can be downsized and the protection function can be enhanced.

  FIG. 9 is a circuit diagram showing a modification of the second embodiment.

  The DC / DC converter 90 shown in FIG. 9 is also a step-up DC / DC converter connected between a low-voltage power supply 91 on the input side and a high-voltage power supply 96 on the output side. In the configuration shown in FIG. 9, the conversion unit 90D is directly connected to the output-side power supply 96, and a connection unit 95 is provided between the input-side low-voltage power supply and the conversion unit 90D. Connection unit 95 includes MOSFETs 95A and 95B.

  MOSFETs 95A and 95B have both the source and back gate connected to node N4. A gate voltage is applied to the gates of the MOSFETs 95A and 95B with reference to the potential of the node N4.

  The configuration of the conversion unit 90D is the same as the configuration of the conversion unit 80D in FIG. That is, the reactor 94 and the MOSFET 92 are connected in series, and the MOSFET 93 is connected between the connection node and the output node. As described above, the present invention can also be applied to a configuration in which the power shut-off connecting portion 95 is provided on the path connecting the reactor 94 to the power source on the input side.

  During the soft start control, the control unit causes the connection unit 95 to conduct in synchronization with the timing at which the MOSFET 92 is transitioned from the non-conducting state to the conducting state. And a control part makes the connection part 95 non-conductive in synchronism with the time when discharge | release of the energy from the reactor 94 is completed, after changing MOSFET92 from a conduction | electrical_connection state to a non-conduction state.

  That is, during the soft start control, the MOSFET 92 and the connection portion 95 are made conductive in synchronization, and the connection portion 95 is made non-conductive in synchronization when the current flowing through the connection portion 95 becomes zero. After the soft start control is finished, the connecting portion 95 may be fixed in a conductive state.

[Embodiment 3]
In the third embodiment, the present invention is also applied to a DC / DC converter capable of bidirectionally increasing and decreasing the voltage.

  FIG. 10 is a circuit diagram showing a configuration of DC / DC converter 100 that can be used in the bi-directional step-up / step-down step used in the third embodiment.

  Referring to FIG. 10, DC / DC converter 100 is connected between DC power supply 101 and DC power supply 106.

  The voltage of the DC power supply 101 may be higher or lower than the voltage of the DC power supply 106 depending on the state of the system. Although not limited thereto, for example, when the DC / DC converter 100 is mounted and used in a dual power supply vehicle system or the like, the DC power supplies 101 and 106 correspond to batteries.

  DC / DC converter 100 includes MOSFETs 102 and 103 connected in series between a positive electrode of DC power supply 101 and a ground node, and MOSFETs 105 and 110 connected in series between a positive electrode of DC power supply 106 and a ground node. And reactor 104. Reactor 104 is connected between a connection node of MOSFETs 102 and 103 and a connection node of MOSFETs 105 and 110.

  As the MOSFET 102 and the MOSFET 105, a MOSFET with a current detection function as described in FIG. 2 is used. When the MOSFETs 102 and 103 are switched to perform step-up / step-down, the MOSFET 110 is fixed in a non-conductive state, and the MOSFET 105 is operated as a connection unit that connects the conversion unit to a power source.

  Conversely, when the MOSFETs 105 and 110 are switched to perform the step-up / step-down operation, the MOSFET 103 is controlled to be in a non-conductive state, and the MOSFET 102 functions as a connection unit that connects the voltage conversion unit to the power source.

  FIG. 11 is an operation waveform diagram for explaining the control when the step-down operation is performed from power supply 101 to 106.

  Referring to FIGS. 10 and 11, gate signals G102, G103, G105 and G110 are gate signals applied to MOSFETs 102, 103, 105 and 110, respectively. A current signal I105 is a current signal indicating a current flowing through the MOSFET 105.

  When performing step-down operation from the power source 101 to the power source 106, a control unit (not shown) of the DC / DC converter 100 keeps the gate signal G110 in an inactive state and controls the MOSFET 105 in synchronization with the MOSFET 102 at the time of soft start. When the normal operation is started, the MOSFET 105 is fixed to the conductive state.

  Regarding the control of gate signals G102, G103 and G105 and current signal I105, the control corresponding to gate signals G2, G3 and G5 and current signal I5 in FIG. 5 is performed, respectively, and therefore the description made in FIG. 5 will not be repeated.

  That is, as shown by the waveform in FIG. 11, during the soft start control, the control unit causes the MOSFET 105 to conduct in synchronization with the time when the MOSFET 102 transitions from the non-conducting state to the conducting state. Then, the control unit makes the MOSFET 105 non-conductive in synchronization with the time when the MOSFET 102 is changed from the conductive state to the non-conductive state. When shifting to the normal operation, the MOSFET 105 is fixed in a conductive state.

  Also, it is possible to control the MOSFET 105 to be non-conductive in synchronization with the time when the MOSFET 102 transitions from the conductive state to the non-conductive state and the release of the energy charged in the reactor 104 is completed.

  FIG. 12 is an operation waveform diagram when the step-down operation is performed from the power supply 106 to the power supply 101.

  10 and 12, when the step-down operation is performed from power supply 106 to power supply 101, MOSFET 103 is controlled to be in a non-conductive state, and conduction cutoff control is performed between the conversion unit in which MOSFET 102 performs voltage conversion and the power supply. It operates as a connection unit for performing

  In the waveforms shown in FIG. 12, the gate signals G102 and G103 are controlled in the same manner as the gate signals G105 and G110 in FIG. 11, respectively, and the gate signals G105 and G110 in FIG. Controls similar to those in G102 and G103 are performed. In this case, control is performed based on a current signal I102 indicating a current flowing in the MOSFET 102 instead of the current signal I105 in FIG. The contents of each control are the same as in FIG. 11, and the description will not be repeated.

  That is, as shown in the waveform of FIG. 12, during the soft start control, the control unit causes the MOSFET 102 to conduct in synchronization with the time when the MOSFET 105 transitions from the non-conducting state to the conducting state. Then, the control unit makes the MOSFET 102 non-conductive in synchronization with the time when the MOSFET 105 is changed from the conductive state to the non-conductive state. When shifting to the normal operation, the MOSFET 102 is fixed to the conductive state.

  It is also possible to control the MOSFET 102 to be non-conductive in synchronization with the time when the MOSFET 105 transitions from the conductive state to the non-conductive state and the release of the energy charged in the reactor 104 is completed.

  FIG. 13 is an operation waveform diagram for explaining the operation when the boosting operation is performed from power supply 101 to power supply 106.

  Referring to FIGS. 10 and 13, when a boost operation is performed from power supply 101 toward power supply 106, MOSFET 102 functions as a connection unit that connects the voltage conversion unit to power supply 101. In this case, the MOSFET 103 is controlled to be in a non-conductive state. During the soft start control at times t1 to t2, t3 to t4, t5 to t6, and t7 to t8, the active pulse width of the gate signal G110 is controlled to gradually increase.

  In the meantime, the gate signal G105 is activated in response to the deactivation of the gate signal G110, and deactivated in response to the current I105 becoming zero. After the minimum value Imin of the current signal I105 becomes greater than 0, the gate signal G105 is deactivated in synchronization with the activation of the gate signal G110 after time t9.

  FIG. 14 is an operation waveform diagram for explaining an operation when a boosting operation is performed from power supply 106 to power supply 101.

  Referring to FIGS. 10 and 14, when a boost operation is performed from power supply 106 toward power supply 101, MOSFET 105 functions as a connection unit that connects the voltage conversion unit to power supply 106. In this case, the MOSFET 110 is controlled to be in a non-conductive state. During the soft start control at times t1 to t2, t3 to t4, t5 to t6, and t7 to t8, the active pulse width of the gate signal G103 is controlled to be gradually increased.

  In the meantime, the gate signal G102 is activated in response to the deactivation of the gate signal G110, and deactivated in response to the current I102 becoming zero. Then, after the minimum value Imin of the current signal I102 becomes greater than 0, the deactivation timing of the gate signal G102 is synchronized with the activation of the gate signal G103 after time t9.

  As described above, the present invention can also be applied to a DC / DC converter capable of step-up / step-down in both directions.

[Embodiment 4]
In the fourth embodiment, it is possible to apply the present invention by connecting a power source and a voltage conversion unit to each phase in a multi-phase DC / DC converter with a MOSFET that controls conduction and disconnection.

  FIG. 15 is a diagram illustrating an example of a multi-phase DC / DC converter.

  Referring to FIG. 15, multi-phase DC / DC converter 200 is connected between high-voltage side power supply 201 and low-voltage side power supply 206.

  DC / DC converter 200 includes conversion units 200 </ b> D and 210 </ b> D connected in parallel between power supply 201 and power supply 206. DC / DC converter 200 further includes MOSFET 205 provided on a path connecting converter 200D to power supply 206, and MOSFET 215 provided on a path connecting converter 210D to power supply 206.

  Conversion unit 200D includes MOSFETs 202 and 203 connected in series between the positive electrode of power supply 201 and the ground node, and reactor 204 connected at one end to the connection node of MOSFETs 202 and 203. The other end of the reactor 204 is connected to the MOSFET 205.

  Conversion unit 210D includes MOSFETs 212 and 213 connected in series between the positive electrode of power supply 201 and the ground node, and reactor 214 connected at one end to the connection node of MOSFETs 212 and 213. The other end of the reactor 214 is connected to the MOSFET 215.

  Body diodes 207, 208, and 209 are parasitic diodes formed by coupling the sources and back gates of MOSFETs 202, 203, and 205, respectively. The body diodes 217, 218, and 219 are parasitic diodes formed by coupling the sources and back gates of the MOSFETs 212, 213, and 215, respectively.

  As the MOSFETs 205 and 215, MOSFETs with a current sensing function as described in FIG. 2 are used. Thereby, a compact configuration can be realized.

  Control for conversion unit 200D and MOSFET 205 is the same as the control described in any of FIG. 3, FIG. 5, and FIG. The converter 210D and the MOSFET 210 are controlled in the same way as the step-down converter 200D and the MOSFET 205 with a phase shifted. By shifting the phase, the ripple of the current supplied from the power source 201 to the power source 206 can be reduced. In FIG. 15, the case where the number of phases is 2 has been described, but the number of phases may be larger.

  In FIG. 15, the multi-phase DC / DC converter including a plurality of step-down converters has been described. However, the present invention also applies to a multi-phase DC / DC converter including a plurality of step-up converters and bidirectional step-up / step-down converters. Can be applied.

  As described above, during the soft start operation of the connection unit that connects the conversion unit that performs power conversion to the output-side power source or the input-side power source, by controlling in synchronization with one cycle of reactor energy storage and release, In normal operation, low-loss step-down operation can be realized, and current is prevented from flowing back from the output-side power source to the converter during the soft-start operation.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is the circuit diagram which showed the structure of the voltage converter 20 which concerns on Embodiment 1 of this invention. It is the circuit diagram which showed the detailed structure of MOSFET5 in FIG. FIG. 6 is an operation waveform diagram for explaining an operation at the time of soft start of the voltage converter 20 shown in FIG. 1. It is a figure showing composition of voltage converter 20A used in the 1st modification of Embodiment 1. FIG. 5 is an operation waveform diagram for describing control of voltage converter 20A shown in FIG. It is the figure which showed the structure per cell of power MOSFET. FIG. 10 is an operation waveform diagram for illustrating control performed in the second modification of the first embodiment. FIG. 5 is a circuit diagram showing a configuration of a boost converter 80 that is a voltage converter according to a second embodiment. FIG. 10 is a circuit diagram showing a modification of the second embodiment. FIG. 5 is a circuit diagram showing a configuration of a DC / DC converter 100 that can be used for bidirectional buck-boost in the third embodiment. FIG. 6 is an operation waveform diagram for illustrating control when performing a step-down operation from power supply 101 to 106; FIG. 6 is an operation waveform diagram when a step-down operation is performed from the power supply 106 to the power supply 101. FIG. 6 is an operation waveform diagram for explaining an operation when performing a boosting operation from power supply 101 to power supply 106; FIG. 6 is an operation waveform diagram for explaining an operation when a boosting operation is performed from power supply 106 toward power supply 101. It is the figure which showed an example of the multiphase type DC / DC converter. It is a circuit diagram which shows the structure of the conventional DC / DC converter. FIG. 17 is an operation waveform diagram for illustrating soft start control when starting the step-down operation of the DC / DC converter shown in FIG. 16. It is the circuit diagram which showed the example of examination of a DC / DC converter.

Explanation of symbols

  1, 6, 81, 86, 91, 96, 101, 106, 201, 206 Power supply, 2, 3, 5, 51-54, 82, 83, 85A, 85B, 92, 93, 95A, 95B, 102, 103 , 105, 110, 202, 203, 205, 212, 213, 215 MOSFET, 4, 84, 94, 104, 204, 214 reactor, 7, 8, 9, 87, 88, 207, 208, 209, 217, 218 , 219 body diode, 10, 10A capacitor, 11, 12, 56 voltage sensor, 13 control unit, 20D, 80D, 90D, 200D, 210D conversion unit, 20, 20A voltage converter, 50 semiconductor substrate, 55 resistor, 62, 64, 68 n-type impurity region, 66 p-type impurity region, 70 gate oxide film, 72 gate electrode, 74 source electrode, 0 boost converter, 85 and 95 connecting portion, 90,100,200 DC / DC converter, D drain, S source.

Claims (8)

A built-in reactor, performing voltage conversion by repeating the release of energy from the storage and the reactor of energy to the reactor, a conversion unit connected between the first and second power supplies,
A connecting portion that is provided on a path from the first power source to the second power source via the reactor, and that conducts and shuts off the path;
A control unit for controlling the conversion unit and the connection unit,
The control unit performs a soft start operation for gradually increasing the amount of energy per cycle stored in the reactor at the start of operation, and synchronizes with a cycle for storing and releasing energy in the reactor during the soft start operation. Control the connection part ,
The control unit is a voltage converter that controls the connection unit to be fixed in a conductive state after the soft start operation is completed . The converter is
Further comprising first and second switching elements;
The connecting portion is
Including a third switching element;
In the soft start operation, the control unit causes the first and second switching elements to conduct complementarily, and causes the third switching element to conduct when the first switching element is turned on. After the switching element becomes non-conductive, at least the third switching element is controlled to be non-conductive after the current flowing through the reactor becomes zero according to the conduction of the first switching element in the one cycle after the switching element becomes non-conductive. The voltage converter according to claim 1. The converter is
A main switching element that conducts when storing energy in the reactor;
The voltage converter according to claim 1, wherein the control unit conducts the connection unit in synchronization with a time when the main switching element transitions from a non-conduction state to a conduction state.   4. The voltage converter according to claim 3, wherein the control unit makes the connection unit non-conductive in synchronization with a time when the main switching element is changed from a conductive state to a non-conductive state.   The said control part makes the said connection part non-conductive in synchronism with the time when discharge | release of the energy from the said reactor is completed after making the main switching element change from a conductive state to a non-conductive state. Voltage converter. The converter is
A main switching element that conducts when storing energy in the reactor;
And a sub-switching element that conducts when discharging energy from the reactor,
2. The voltage converter according to claim 1, wherein the control unit conducts the connection unit in synchronization with a time at which the sub switching element is transitioned from a conduction state to a non-conduction state.   The said control part makes the said connection part non-conductive in synchronization with the time when discharge | release of the energy from the said reactor is completed after making the said subswitching element change from a non-conductive state to a conductive state. Voltage converter. The connecting portion is
The voltage converter according to claim 1, comprising a switching element with a current detection function.

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