JP2005094890A - Switching power circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power circuit, which effectively protects a switching element from input overvoltage, and its protection method. <P>SOLUTION: An input voltage monitoring circuit 9, which detects input overvoltage, is provided on the primary side of a transformer, and also breaking switches 15A and 15B for compulsively stopping the switching action of switching elements 12 and 14 are provided on the same primary side. As compared with a conventional DC-DC converter, this system performs the protective action to the input voltage at an extremely high speed, so this protects circuit elements from input overvoltage without fail. High reliability is obtained even in such a severe application that an input overvoltage state occurs frequently, for example, in a two-battery type vehicle. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a switching power supply circuit including a switching element, and more particularly to a switching power supply circuit having a function of protecting a switching element and the like from an input overvoltage.

  A hybrid vehicle using a combination of an engine and a motor as a power source is known. This type of automobile is usually often configured as a two-battery vehicle including a high-voltage battery connected to a motor and a low-voltage battery arranged on the low-voltage side via a transformer. The high-voltage battery assists the engine by driving a motor during vehicle acceleration, and is charged by a regenerative action of the motor (functioning as a generator) during vehicle deceleration. On the other hand, the low voltage battery is used as a power source for a control circuit of a vehicle.

  In the two battery type vehicle as described above, power is supplied from the high voltage battery to the low voltage battery using a DC-DC converter. This DC-DC converter converts a DC input voltage into an AC voltage by an inverter circuit composed of switching elements, then steps down the AC voltage with a transformer, and converts the output voltage of the transformer into a DC voltage again with a rectifier circuit or the like. It has the function to do. When this DC-DC converter is applied to the above-described two-battery type vehicle, the output voltage of the high-voltage battery (that is, the DC input voltage to the inverter circuit) is generated by charging the high-voltage battery by motor regeneration during vehicle deceleration. There is a possibility that the switching element of the inverter circuit will rapidly increase beyond the withstand voltage, and as a result, a malfunction may occur in these switching elements.

  For this reason, conventionally, in a DC-DC converter mounted on a two-battery type vehicle, the circuit can be protected by stopping the operation of the inverter circuit when the DC input voltage of the inverter circuit exceeds a predetermined value. Has been done.

  For example, FIG. 1 of Patent Document 1 includes an inverter circuit that converts an input DC voltage from a high-voltage battery into an AC voltage, a transformer that transforms the AC voltage, a rectifier that rectifies the output voltage of the transformer, and an output of the rectifier circuit. A DC-DC converter is described that includes a smoothing circuit that smoothes the voltage and supplies power to the low-voltage battery, and a controller that is supplied with power from the low-voltage battery side and controls switching of the inverter circuit (hereinafter referred to as the first). This is called a DC-DC converter of the system). The controller determines that the input DC voltage is an overvoltage and turns off both the upper arm switching element and the lower arm switching element of the inverter circuit when the DC voltage input to the inverter circuit exceeds a predetermined value. In this case, the controller determines that the input DC voltage is an overvoltage based on the input voltage or the output voltage of the rectifier. Although not shown in FIG. 1 of Patent Document 1, in order for the secondary-side controller to stop the switching element of the primary-side inverter circuit, a switching signal is transmitted from the controller to the inverter circuit. It needs to be performed via an insulating circuit such as a transformer.

  And in said patent document 1, since the input overvoltage to an inverter circuit is determined based on the voltage of the secondary side of a transformer (especially any part from the secondary coil of a transformer to a smoothing circuit), it is simple. There is a description that the input overvoltage can be detected by the circuit configuration.

  FIG. 13 of Patent Document 1 shows an inverter circuit, a step-down transformer, a rectifier circuit, a choke coil, an input overvoltage detection circuit, a controller, an input side smoothing capacitor, an output side smoothing capacitor, and a low voltage battery. A DC-DC converter having a constant voltage circuit that supplies the controller with a constant voltage and supplies it to the controller as a power supply voltage is described (hereinafter referred to as a second-system DC-DC converter). The input overvoltage detection circuit is used to determine whether or not the voltage of the high voltage battery exceeds a predetermined value in order to turn off the switching element of the inverter circuit and ensure its withstand voltage, and divides the voltage of the high voltage battery. A resistor voltage divider circuit, a constant voltage circuit that generates a predetermined threshold voltage, a comparator that compares the output voltage of the resistor voltage divider circuit with the threshold voltage from the constant voltage circuit, and the output of the comparator A photocoupler circuit for output isolation, and a control power supply voltage forming circuit for forming a DC power supply voltage that is input / output isolated from the voltage of the low-voltage battery and applying it as a power supply voltage to the comparator and the photocoupler circuit Yes. Although not shown in FIG. 13 of Patent Document 1, in order for the secondary-side controller to stop the switching element of the primary-side inverter circuit, a switching signal is transmitted from the controller to the inverter circuit. It needs to be performed via an insulating circuit such as a transformer.

And in said patent document 1, when a controller detects an input overvoltage based on the comparator output supplied via a photocoupler circuit, there exists description that the switching element of an inverter circuit can be turned off.
JP 2003-33015 A

  However, in the DC-DC converter of the first system, the controller detects an input overvoltage based on the secondary side voltage, and stops the primary side switching element via the insulation circuit (transformer). Therefore, the detection of the input overvoltage depends on the performance of the controller. When the controller is slow, the input overvoltage detection delay is significant. There is also a transmission delay in the insulation circuit. For this reason, it has been difficult to quickly stop the operation of the inverter circuit following the sudden rise in the input DC voltage to the inverter circuit. In particular, the pulse voltage output from the secondary side of the transformer is integrated by the waveform shaping circuit in order to detect the input overvoltage on the secondary side. It was difficult to perform good protection control.

  In the second type DC-DC converter, the input overvoltage is detected based on the primary side voltage, but the control for stopping the operation of the inverter circuit is performed by the controller arranged on the secondary side. For this reason, a photocoupler is required for signal transmission (detection of input overvoltage) from the primary side to the secondary side, and signal transmission from the secondary side to the primary side via an insulation circuit such as a transformer ( Since a delay occurs in the switching signal stop), it is difficult to transmit the signal sufficiently quickly.

  As described above, in the conventional DC-DC converter, the time delay of the voltage detection processing that occurs in the controller on the secondary side and the signal transmission that occurs in the insulating circuit provided in the switching signal transmission path from the secondary side to the primary side. Since the time delay is so large that it cannot be ignored, it is difficult to speed up the protection operation for protecting the switching element from the input overvoltage, and the circuit protection cannot be effectively performed in practice.

  The present invention has been made in view of such problems, and an object thereof is to provide a switching power supply circuit capable of effectively protecting a switching element from an input overvoltage.

  The switching power supply circuit of the present invention includes a transformer for transforming AC voltage and four switching elements, and is arranged on the primary side of the transformer. The switching operation of the switching element converts the DC input voltage into AC voltage and supplies it to the transformer. A first conversion circuit that is arranged on the secondary side of the transformer, a second conversion circuit that converts the AC output voltage of the transformer to a DC output voltage, and an input that is arranged on the primary side of the transformer and monitors the DC input voltage A voltage conversion circuit, and a first conversion circuit disposed on a primary side of the transformer and stopping a switching operation of at least two of the four switching elements when the input voltage monitoring circuit detects an input overvoltage state And a current interruption circuit for interrupting the current flowing through the.

  Here, the “transformer” may be either a step-down transformer or a step-up transformer. The “input overvoltage state” refers to a state in which the DC input voltage exceeds a preset allowable voltage level.

  In the switching power supply circuit of the present invention, the DC input voltage is monitored on the primary side of the transformer. When an overvoltage state of the DC input voltage is detected, the current interrupt circuit arranged on the primary side of the transformer is activated, and the switching operation of at least two of the four switching elements is stopped. As a result, the current flowing through the first conversion circuit is cut off, and a surge voltage exceeding the withstand voltage of the circuit element is prevented from flowing through the first and second conversion circuits. An overvoltage state of the DC input voltage is detected on the primary side of the transformer, and a current interrupt circuit provided on the same primary side is directly driven (without going through an insulating circuit) based on the detection result. Therefore, the time from the occurrence of the overvoltage state to the start of the protection operation is shortened.

  The four switching elements are arranged on the upstream side and the downstream side of the transformer, respectively, and form the first current path so that the direction of the current flowing through the transformer is the first current direction. And a third current path that is arranged on the upstream side and the downstream side of the transformer and that forms a second current path so that a direction of a current flowing through the transformer is a second current direction opposite to the first current direction. The fourth switching element is preferably included.

  The current cutoff circuit preferably operates to stop the switching operation of the second and fourth switching elements when the input voltage monitoring circuit detects an input overvoltage state, but the first and second current paths As long as both can be cut off, the switching operation of the switching element may be stopped by another combination. For example, the switching operations of the first and third switching elements may be stopped. Alternatively, the switching operation of the first and fourth switching elements or the switching operation of the second and third switching elements may be stopped. Alternatively, all the switching operations of the four switching elements may be stopped.

  The switching power supply circuit of the present invention is particularly suitably applied to a vehicle including a high voltage battery and a low voltage battery. In this case, it is preferable that the DC input voltage input to the first conversion circuit is supplied from the high voltage battery and the DC output voltage output from the second conversion circuit is supplied to the low voltage battery. Especially when the high-voltage battery is connected to the motor, and the high-voltage battery is charged by the regenerative operation of the motor and the current is supplied from the high-voltage battery to the motor. It is preferably applied.

  According to the switching power supply circuit of the present invention, the overvoltage state of the DC input voltage is detected on the primary side of the transformer, and on the basis of the detection result, the current cutoff circuit provided on the same primary side is directly ( Since the drive is performed (without going through an insulating circuit), the time from the occurrence of the overvoltage state to the start of the protection operation is shortened. Therefore, the circuit element can be reliably protected from the surge voltage when the overvoltage is applied.

  Hereinafter, the best mode for carrying out the present invention (hereinafter simply referred to as an embodiment) will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 shows a configuration of a switching power supply circuit according to an embodiment of the present invention.

  The switching power supply circuit of the present embodiment functions as a DC-DC converter that converts the first DC voltage output from the high-voltage battery BH into a lower second DC voltage and supplies it to the low-voltage battery BL. is there. This switching power supply circuit includes an inverter circuit 1 provided between a primary high voltage line L1H and a primary low voltage line L1L, a transformer 2 having a primary coil 21 and secondary coils 22, 23, The rectifier circuit 3 provided on the secondary side of the transformer 2, the choke coil 4 provided on the secondary power supply line L2, the control circuit 5 for controlling the switching operation of the inverter circuit 1, the inverter circuit 1 and the control circuit 5 and an insulating circuit portion 6 provided between the two. The high voltage battery BH and the inverter circuit 1 are located on the primary side of the transformer 2, and the rectifier circuit 3, the choke coil 4, the control circuit 5, and the low voltage battery BL are located on the secondary side of the transformer 2. The low voltage battery BL is provided between the secondary power supply line L2 and the ground. This switching power supply circuit also includes an input-side smoothing capacitor 7 provided in parallel with the inverter circuit 1 between the primary-side high-voltage line L1H and the primary-side low-voltage line L1L, and the secondary-side power supply line L2 and ground. An output-side smoothing capacitor 8 provided in parallel with the low-voltage battery BL is provided between them to smooth voltage disturbance due to the operation of a switching element (described later) in the inverter circuit 1.

  The inverter circuit 1 is a single-phase inverter circuit that converts a first DC voltage output from the high-voltage battery BH into a single-phase AC voltage (almost rectangular-wave AC voltage). To a specific example. The inverter circuit 1 includes four switching elements 11, 12, 13, and 14 that are driven by switching signals 51 to 54 output from the control circuit 5. As the switching element, for example, a MOS (Metal-Oxide-Semiconductor) transistor or an IGBT (Insulated Gate Bipolar Transistor) is used. However, the switching element is not limited to these. .

  The switching element 11 is provided between one end 21A of the primary coil 21 of the transformer 2 and the primary high voltage line L1H, and the switching element 12 includes the other end 21B of the primary coil 21 and the primary low voltage line L1L. It is provided between. The switching element 13 is provided between the other end 21B of the primary side coil 21 of the transformer 2 and the primary side high voltage line L1H, and the switching element 14 includes one end 21A of the primary side coil 21 and the primary side low voltage line L1L. It is provided between. Here, each of the switching elements 11 to 14 corresponds to a specific example of “first to fourth switching elements” in the present invention.

  When the switching elements 11 and 12 are turned on, the current flows in the first current path from the primary high voltage line L1H to the primary low voltage line L1L through the switching element 11, the primary coil 21 and the switching element 12 in order. When the switching elements 13 and 14 are turned on, the second current that reaches the primary low-voltage line L1L from the primary high-voltage line L1H through the switching element 13, the primary coil 21 and the switching element 14 in order. Current flows through the path. Therefore, the switching elements 11 and 13 are always located on the high voltage side (upstream side) of the primary coil 21 on the current path, and the switching elements 12 and 14 are always on the low voltage side (downstream) of the primary coil 21 on the current path. Side). Therefore, in the following description, the switching elements 11 and 13 are collectively referred to as high-voltage side switching elements, and the switching elements 12 and 14 are collectively referred to as low-voltage side switching elements as appropriate.

  The transformer 2 steps down the AC voltage converted by the inverter circuit 1 and outputs AC voltages that are 180 degrees out of phase from the pair of secondary coils 22 and 23. In this case, the degree of step-down is determined by the turn ratio of the primary side coil 21 and the secondary side coils 22 and 23. A connection point C between the secondary coil 22 and the secondary coil 23 is grounded.

  The rectifier circuit 3 is a single-phase full-wave rectifier circuit composed of a pair of diodes 31 and 32, and corresponds to a specific example of “second conversion circuit” in the present invention. One end of the diode 31 is connected to one end 22 </ b> A of the secondary side coil 22 of the transformer 2, and one end of the diode 32 is connected to one end 23 </ b> A of the secondary side coil 23. The other ends of the diodes 31 and 32 are connected to each other and connected to one end of the choke coil 4. This rectifier circuit 3 rectifies each half-wave period of the AC voltage output from the transformer 2 individually by diodes 31 and 32 to obtain a DC voltage.

  The choke coil 4 and the output-side smoothing capacitor 8 smooth the DC voltage obtained by the rectifier circuit 3, and supply the obtained DC voltage to the low-voltage battery BL as a second DC voltage.

  The control circuit 5 operates using the second DC voltage output from the low-voltage battery BL as a power supply voltage, and outputs switching signals 51 to 54.

  The insulating circuit unit 6 includes insulating circuits 61 to 64 each made of a transformer or the like. The insulating circuits 61 to 64 have a function of transmitting the switching signals 51 to 54 output from the control circuit 5 to the inverter circuit 1 while isolating the primary side and the secondary side of the transformer 2. The switching signals 51 to 54 transmitted to the secondary side via the insulating circuit unit 6 are respectively applied to control terminals (here, gates) of the switching elements 11 to 14 of the inverter circuit 1, and each switching element is turned on / off ( (Open / close) operation is controlled.

  The switching power supply circuit of the present embodiment further includes an input voltage monitoring circuit 9 and cutoff switches 15A and 15B on the primary side of the transformer 2.

  The input voltage monitoring circuit 9 includes voltage dividing resistors 91 and 92, a comparator 93, and a constant voltage circuit 94. The voltage dividing resistors 91 and 92 are arranged in series between the primary high voltage line L1H and the primary low voltage line L1L. From the connection point D of the voltage dividing resistors 91 and 92, a divided voltage VD corresponding to the ratio of both resistance values is output. The constant voltage circuit 94 operates using the high voltage battery BH as a power source and outputs a constant reference voltage VR. The comparator 93 compares the divided voltage VD from the voltage dividing resistors 91 and 92 with the reference voltage VR from the constant voltage circuit 94, and according to the result (specifically, the divided voltage VD exceeds the reference voltage VR). And a switching cutoff signal 95 is output. The comparator 93 operates with a voltage Va generated from the high voltage battery BH as a power supply voltage.

  The cutoff switches 15A and 15B correspond to a specific example of the “current cutoff circuit” in the present invention, and are respectively disposed between the gates of the low-voltage side switching elements 12 and 14 and the primary-side low-voltage line L1L. ing. The cutoff switches 15A and 15B are turned on (closed) when the switching cutoff signal 95 is given from the comparator 93, and short between the gates of the low-voltage side switching elements 12 and 14 and the primary-side low-voltage line L1L. By doing so, the switching operation of the low voltage side switching elements 12, 14 is forcibly stopped.

  Next, the operation of the switching power supply circuit having the above configuration will be described.

  The control circuit 5 arranged on the secondary side is converted into electric power supplied from the low-voltage battery BL arranged on the secondary side, or voltage converted from the high-voltage battery BH on the primary side by the transformer 2, and the power line on the secondary side It operates based on the power supplied via L2, and outputs switching signals 51-54. The switching signals 51 to 54 are transmitted to the primary side via the insulating circuit unit 6 and applied to the respective gates of the switching elements 11 to 14 of the inverter circuit 1.

  The inverter circuit 1 generates an AC voltage by switching the DC voltage output from the high voltage battery BH based on the switching signals 51 to 54 from the control circuit 5 and applies the AC voltage to the transformer 2. Specifically, when the switching elements 11 and 12 of the inverter circuit 1 are in the on state, the primary low voltage line passes through the switching element 11, the primary coil 21 and the switching element 12 in order from the primary high voltage line L 1 H. A current flows through the first current path reaching L1L. On the other hand, when the switching elements 13 and 14 are in the ON state, the second current that reaches the primary low-voltage line L1L from the primary high-voltage line L1H through the switching element 13, the primary coil 21 and the switching element 14 in order. Current flows through the path. As a result, a substantially rectangular AC voltage is applied to the primary coil 21 of the transformer 2.

  In response to the AC voltage applied to the primary coil 21, an AC voltage having a voltage lower than the primary voltage is generated in the secondary coils 22 and 23 of the transformer 2. The pair of diodes 31 and 32 of the rectifier circuit 3 performs single-phase full-wave rectification in which the half-wave periods of the AC voltage output from the transformer 2 are individually rectified by the diodes 31 and 32, respectively. Thereby, a DC voltage is obtained. This DC voltage is further smoothed by the choke coil 4 and used for charging the low voltage battery BL.

  The comparator 93 of the input voltage monitoring circuit 9 compares the divided voltage VD at the connection point D of the voltage dividing resistors 91 and 92 with the reference voltage VR from the constant voltage circuit 94, and if the divided voltage VD exceeds the reference voltage VR. The input overvoltage is determined, and the switching cutoff signal 95 is output. This switching cutoff signal 95 changes the cutoff switches 15A and 15B to the closed state. As a result, the gates of the low-voltage side switching elements 12 and 14 are connected to the primary-side low-voltage line L1L and become low potential (low-voltage side ground level), so that the low-voltage side switching elements 12 and 14 stop switching operation and are turned off. It is held in the (open) state. As a result, the first and second current paths are both cut off, and no current flows through the inverter circuit 1. As a result, the transformer 2 cannot supply power to the secondary side, and no surge voltage is generated in the switching elements 11 to 14 of the inverter circuit 1. Therefore, even if the output voltage of the high voltage battery BH rises to near the breakdown voltage of the switching elements 11 to 14, it is possible to avoid damage to these elements. Further, on the secondary side of the transformer 2, a surge voltage exceeding the withstand voltage of the diodes 31 and 32 of the rectifier circuit 3 is not generated with switching, so that these diodes are also protected.

  Here, the high speed of the input overvoltage detection operation in the input voltage monitoring circuit 9 will be considered. In the present embodiment, since the input voltage monitoring circuit 9 is disposed on the primary side, detection can be performed at a higher speed than, for example, a conventional DC-DC converter. The reason is as follows.

  First, in the conventional first-system DC-DC converter, the controller arranged on the secondary side detects the input overvoltage by integrating the pulsed AC voltage on the secondary side. This is because the delay is significant, but in the present embodiment, the DC voltage on the primary side is directly detected by the comparator 93.

  Secondly, in the conventional first-system DC-DC converter, the controller arranged on the secondary side fixes the switching signal to the output stop level, and this is transferred to the primary side via an insulation circuit (transformer). In this embodiment, only the result detected on the primary side is transmitted to the same primary side cut-off switches 15A and 15B. This is because there is no need to go through an insulation circuit and transmission delay hardly occurs. This also applies to the comparison with the conventional second type DC-DC converter. In the second type DC-DC converter, although the input overvoltage is detected on the primary side, the controller that actually stops the operation of the inverter circuit is the secondary side controller. That is, in the second type DC-DC converter, it is necessary to transmit a signal from the secondary side to the primary side (stop of the switching signal) via an insulation circuit such as a transformer, and there is a transmission delay that cannot be ignored. It happens.

  When the time from the start of the input DC voltage rise to the switching stop of the inverter circuit is estimated, in the first DC-DC converter, as described above, the delay due to the detection operation (integration process) on the secondary side And since the delay accompanying transmission from the secondary side to the primary side is large, several msec is required. Further, in the second type DC-DC converter, there is a delay accompanying transmission from the secondary side to the primary side, and therefore, several hundreds of microseconds are required. On the other hand, in the present embodiment, the main delay factor is only the delay derived from the comparison operation of the comparator 93, so that it can be suppressed to about several tens of microseconds.

  Thus, according to the switching power supply circuit of the present embodiment, the input voltage monitoring circuit 9 for detecting the input overvoltage is provided on the primary side of the transformer 2, and the switching operation of the switching elements 12 and 14 on the same primary side. Since the cutoff switches 15A and 15B for forcibly stopping the switching are provided, the protection operation against the input overvoltage can be performed at a very high speed as compared with the conventional DC-DC converter. Therefore, the circuit element can be reliably protected from the input overvoltage. In particular, high reliability can be obtained even in severe applications such as a two-battery type vehicle in which an input overvoltage state frequently occurs.

<Modification 1>
In the present embodiment, the cutoff switches 15A and 15B are arranged between the low-voltage side switching elements 12 and 14 and the primary-side low-voltage line L1L, respectively. Instead of this, for example, FIG. As shown in FIG. 5, the cutoff switches 15A and 15B may be disposed between the low-voltage side switching elements 12 and 14 and the insulating circuits 64 and 62, respectively. In FIG. 2, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted. In this case, the switching signals 54 and 52 are directly cut off by the cut-off switches 15A and 15B, so that the switching operation of the low-voltage side switching elements 12 and 14 is stopped. In this case, the same effect as in the case of the first embodiment can be obtained.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.

  FIG. 3 shows a configuration of a switching power supply circuit according to the second embodiment of the present invention. In this figure, the same components as those shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

  In the first embodiment, the switching operation of the low-voltage side switching elements 12 and 14 is stopped by the switching cutoff signal 95 from the input voltage monitoring circuit 9, but in the present embodiment, the high-voltage side switching element 11 is stopped. , 13 is stopped. In this case, since the ground level of the high voltage side switching elements 11 and 13 is different from the ground level of the low voltage side switching elements 12 and 14, the switching cutoff signal 95 is the same as in the first embodiment. It is not possible to directly control the high-voltage side switching elements 11 and 13 using the cutoff switches 15A and 15B that are opened and closed by.

  Therefore, in the present embodiment, the switching operation of the high-voltage side switching elements 13 and 11 is stopped using the photocouplers 16A and 16B that can transmit only the signal contents while isolating the signal level. . Specifically, the phototransistor of the photocoupler 16A is disposed between the gate and drain of the high voltage side switching element 13, and the photodiode of the photocoupler 16A is driven by the switching cutoff signal 95. Similarly, the phototransistor of the photocoupler 16B is disposed between the gate and the drain of the high voltage side switching element 11, and the photodiode of the photocoupler 16B is driven by the switching cutoff signal 95. Other configurations are the same as those of the first embodiment (FIG. 1). In practice, a buffer circuit (not shown) is provided on the output side of the comparator 93.

  In the present embodiment, when the photocouplers 16A and 16B are operated by the switching cutoff signal 95 output from the comparator 93 via a buffer circuit (not shown), the gates of the high-voltage side switching elements 13 and 11 are set to low potential ( Therefore, these two switching elements stop the switching operation and are held in the off (open) state. As a result, the two current paths (first and second current paths) in the inverter circuit 1 are cut off, so that no surge voltage is generated due to the switching operation, so that the switching elements 11 to 14, the diodes 31 and 32, etc. Circuit elements are protected. Even in this case, the same effect as in the case of the first embodiment in which the high-speed switching operation interruption process based on the high-speed input overvoltage detection is performed can be obtained.

<Modification 2>
For example, as shown in FIG. 4, the photocouplers 16A and 16B are arranged between the high voltage side switching elements 13 and 11 and the insulating circuits 64 and 62, respectively, and an inverter circuit (not shown) is provided on the output side of the comparator 93. May be provided. In FIG. 4, the same components as those shown in FIG. 3 are denoted by the same reference numerals, and description thereof is omitted. In this case, the photocouplers 16A and 16B are operated by the switching cut-off signal 95 output from the comparator 93 via the inverter circuit (not shown), and the switching signals 54 and 52 are cut off directly, respectively. The switching operation of the switching elements 13 and 11 is stopped and held in the off (open) state. In this case, the same effect as in the second embodiment can be obtained.

[Third Embodiment]
Next, a third embodiment of the present invention will be described.

  In the first and second embodiments, the switching operation is stopped by the switching cutoff signal 95 that is the output of the input voltage monitoring circuit 9 in the low-voltage side switching elements 12 and 14 or the high-voltage side switching elements 11 and 13. It was either.

  On the other hand, in the present embodiment, as shown in FIG. 5, one of the two low-voltage side switching elements (here, the low-voltage side switching element 14) and the two high-voltage side switching elements 11, Any one of 13 (here, the high voltage side switching element 11) is stopped. Since the low-voltage side switching element 14 and the high-voltage side switching element 11 are held in the off (open) state, the two current paths (first and second current paths) in the inverter circuit 1 are both cut off and the switching operation is performed. The accompanying surge voltage is eliminated and circuit elements such as the switching elements 11 to 14 and the diodes 31 and 32 are protected. Even in this case, the same effect as in the case of the first embodiment in which the high-speed switching operation interruption process based on the high-speed input overvoltage detection is performed can be obtained.

<Modification 3>
For example, as shown in FIG. 6, the photocoupler 16B is disposed between the high-voltage side switching element 11 and the insulating circuit 61, and the cutoff switch 15B is disposed between the high-voltage side switching element 14 and the insulating circuit 62. You may make it do. In FIG. 6, the same components as those shown in FIG. 5 are denoted by the same reference numerals, and the description thereof is omitted. In this case, the photocoupler 16B and the cutoff switch 15B are operated by the switching cutoff signal 95 output from the comparator 93 via the inverter circuit (not shown), and the switching signals 51 and 52 are directly cut off, respectively. The switching operation of the switching elements 11 and 14 is stopped and held in the off (open) state. In this case, the same effect as in the case of the third embodiment can be obtained.

  The low voltage side switching element 12 of the two low voltage side switching elements 12 and 14 and the high voltage side switching element 13 of the two high voltage side switching elements 11 and 13 are stopped and held in the off (open) state. You may make it do.

  Although the present invention has been described with reference to the embodiment and the examples, the present invention is not limited to these, and various modifications can be made. For example, in each of the above embodiments, in order to cut off the first and second current paths formed in the inverter circuit 1, either one of the switching elements on the first current path and the second current path Only two of the switching elements are held in the off (open) state, but the present invention is not limited to this, and all four switching elements may be in the off state. However, since it is not easy to obtain a photocoupler that can be applied to those used under harsh environmental conditions such as a two-battery vehicle, considering the above point, the first As shown in the embodiment (FIG. 1), a method that eliminates the use of a photocoupler (a method of stopping the operation of only the low-voltage side switching elements 12 and 14) is more preferable.

  Further, in each of the above embodiments, the description has been made on the assumption that it is applied to a two-battery type vehicle. However, the present invention can also be applied to other uses in which the input DC voltage to the inverter circuit may be excessive. Of course.

1 is a circuit diagram illustrating an overall configuration of a switching power supply circuit according to a first embodiment of the present invention. FIG. 6 is a circuit diagram illustrating a modification of the switching power supply circuit illustrated in FIG. 1. It is a circuit diagram showing the whole structure of the switching power supply circuit which concerns on the 2nd Embodiment of this invention. FIG. 4 is a circuit diagram illustrating a modification of the switching power supply circuit illustrated in FIG. 3. It is a circuit diagram showing the whole structure of the switching power supply circuit which concerns on the 3rd Embodiment of this invention. FIG. 6 is a circuit diagram illustrating a modification of the switching power supply circuit illustrated in FIG. 5.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Inverter circuit, 2 ... Transformer, 3 ... Rectifier circuit, 4 ... Choke coil, 5 ... Control circuit, 6 ... Insulation circuit part, 7 ... Input side smoothing capacitor, 8 ... Output side smoothing capacitor, 11-14 ... Switching element , 9 ... Input voltage monitoring circuit, 15A, 15B ... Cutoff switch, 16A, 16B ... Photocoupler, 91, 92 ... Voltage dividing resistor, 93 ... Comparator, 94 ... Constant voltage circuit, BH ... High voltage battery, BL ... Low voltage battery.

Claims (7)

A transformer that transforms AC voltage;
A first conversion circuit that includes four switching elements and is arranged on the primary side of the transformer, converts a DC input voltage into an AC voltage by a switching operation of the switching element, and supplies the AC voltage to the transformer;
A second conversion circuit disposed on the secondary side of the transformer and converting an AC output voltage of the transformer into a DC output voltage;
An input voltage monitoring circuit disposed on a primary side of the transformer and monitoring the DC input voltage;
When the input voltage monitoring circuit is disposed on the primary side of the transformer and detects an input overvoltage state, the switching operation of at least two switching elements of the four switching elements is stopped, whereby the first A switching power supply circuit comprising: a current cutoff circuit that cuts off a current flowing through the conversion circuit. The four switching elements are:
First and second switching elements disposed on the upstream side and the downstream side of the transformer, respectively, and forming a first current path so that a direction of a current flowing through the transformer is a first current direction;
A second current path is formed on each of the upstream side and the downstream side of the transformer, and forms a second current path so that the direction of the current flowing through the transformer is a second current direction opposite to the first current direction. The switching power supply circuit according to claim 1, comprising: 3 and a fourth switching element. 3. The switching power supply circuit according to claim 2, wherein the current cutoff circuit stops switching operations of the second and fourth switching elements when the input voltage monitoring circuit detects an input overvoltage state. 4. 3. The switching power supply circuit according to claim 2, wherein the current cutoff circuit stops switching operations of the first and third switching elements when the input voltage monitoring circuit detects an input overvoltage state. 4. The current interrupt circuit stops the switching operation of the first and fourth switching elements or the switching operation of the second and third switching elements when the input voltage monitoring circuit detects an input overvoltage state. The switching power supply circuit according to claim 2. 3. The switching power supply circuit according to claim 2, wherein the current cutoff circuit stops all switching operations of the four switching elements when the input voltage monitoring circuit detects an input overvoltage state. 4. A switching power supply circuit mounted on a vehicle including a first battery that outputs a higher DC voltage and a second battery that outputs a lower DC voltage,
The DC input voltage input to the first conversion circuit is supplied from the first battery, and the DC output voltage output from the second conversion circuit is supplied to the second battery. The switching power supply circuit according to claim 1, wherein the switching power supply circuit is characterized in that:

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