Series Power Supply

Abstract

To provide a series power supply which can suppress continuous supply of overcurrent from a series power supply to a power supply target.SOLUTION: A series power supply 50 includes: first and second switches 51 and 52; a lowest potential diode 70 which electrically connects a gate of the second switch 52 and a ground; a high potential side resistor 61 which electrically connects a gate of the first switch 51 and a positive electrode side of a high voltage power supply 10; and a low potential side resistor 62 which electrically connects the gates of the first and second switches 51 and 52. A cathode of the lowest potential diode 70 is electrically connected to the gate of the second switch 52. The series power supply 50 includes a fuse 81 and a target diode 91 as pull-out parts for pulling out a gate charge of the first switch 51 when overcurrent flows in the first switch 51.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a series power supply.

Background Art

[0002] Conventionally, as described in, for example, Patent Document 1, a series power supply that steps down the output voltage of a DC power supply and supplies it to a power supply target unit is known. The series power supply includes a series connection of a plurality of transistors, a resistor corresponding to each transistor, and a Zener diode. The Zener diode is provided corresponding to the transistor on the lowest potential side among each transistor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A short circuit failure may occur in the transistor on the lowest potential side among each transistor. In this case, the output voltage of the series power supply greatly increases, and an overcurrent continues to be supplied from the series power supply to the power supply target unit. As a result, there is a concern that a failure may occur in the power supply target unit.

[0005] A main object of the present disclosure is to provide a series power supply that can suppress the continuous supply of an overcurrent from the series power supply to the power supply target unit even when a short circuit failure occurs in the transistor on the lowest potential side among each transistor.

Means for Solving the Problems

[0006] In the series power supply that steps down the output voltage of a DC power supply and supplies it to a power supply target unit, Multiple transistors that constitute a path for electrically connecting the positive terminal side of the DC power supply and the power supply target, The lowest potential diode is a Zener diode that electrically connects the gate and ground of the lowest potential transistor, which is the lowest potential transistor among the aforementioned transistors, A high-potential side resistor is a resistor that electrically connects the gate of the transistor with the highest potential among the aforementioned transistors and the positive terminal side of the DC power supply, In each of the aforementioned transistors, a low-potential side resistor is a resistor that electrically connects the gates of electrically adjacent transistors, Equipped with, The cathode of the lowest potential diode is electrically connected to the gate of the lowest potential transistor. The device includes an extraction unit that is electrically connected to the gate of a target transistor, which is at least one of the transistors other than the lowest potential transistor, and which extracts the gate charge of the target transistor when an overcurrent flows through the target transistor.

[0007] The series power supply of this disclosure comprises multiple transistors, a minimum potential diode, a high potential side resistor, and a low potential side resistor to step down the output voltage of a DC power supply and supply it to the powered unit.

[0008] In this case, if a short-circuit failure occurs in the lowest-potential transistor, which is the transistor with the lowest potential among all the transistors, an overcurrent will flow through the path that electrically connects the positive terminal of the DC power supply to the powered unit. In this case, the pull-out section pulls out the gate charge of the target transistor. This makes it possible to switch the target transistor to the off state or limit the current flowing to the target transistor. As a result, it is possible to suppress the continuous supply of overcurrent from the series power supply to the powered unit. [Brief explanation of the drawing]

[0009] [Figure 1] Overall configuration diagram of the control system according to the first embodiment. [Figure 2] Circuit diagram for emergency power supply. [Figure 3] Circuit diagram of Comparative Example 1. [Figure 4] Circuit diagram of Comparative Example 2. [Figure 5] Circuit diagram of an emergency power supply according to a modified example of the first embodiment. [Figure 6] Circuit diagram of the emergency power supply according to the second embodiment. [Figure 7] Circuit diagram of an emergency power supply according to a modified example of the second embodiment. [Figure 8] Circuit diagram of the emergency power supply according to the third embodiment. [Figure 9] Circuit diagram of the emergency power supply according to the fourth embodiment. [Modes for carrying out the invention]

[0010] Multiple embodiments will be described with reference to the drawings. In multiple embodiments, functionally and / or structurally corresponding and / or related parts may be given the same reference numeral, or reference numerals that differ by hundreds or more digits. For corresponding and / or related parts, refer to the descriptions of other embodiments.

[0011] <First Embodiment> The first embodiment of the series power supply described herein will be described below with reference to the drawings. The series power supply of this embodiment is applied to an inverter control system.

[0012] As shown in Figure 1, the control system includes a high-voltage power supply 10 as a DC power source, an inverter 20, and a rotating electric machine 30. The high-voltage power supply 10 is a rechargeable battery, such as a lithium-ion battery or a nickel-metal hydride battery. The rotating electric machine 30 is connected to the high-voltage power supply 10 via the inverter 20. A smoothing capacitor 11 is provided between the high-voltage power supply 10 and the inverter 20. The rotating electric machine 30 is, for example, a permanent magnet field type or a wound field type synchronous machine.

[0013] The inverter 20 includes upper and lower arm switches SW for three phases. The first ends of the windings 31 of the rotating electrical machine 30 are connected to the connection points of the upper and lower arm switches SW of each phase. The second ends of the windings 31 of each phase are connected at the neutral point. The switch SW in this embodiment is an N-channel MOSFET. The switch SW has a body diode. Note that the switch SW included in the inverter 20 may be, for example, an IGBT instead of a MOSFET. In this case, a freewheel diode may be connected in antiparallel to the IGBT. Also, the connection mode of the windings 31 is not limited to the star connection and may be a delta connection.

[0014] The inverter 20 includes a control circuit Dr (corresponding to the "power supply target unit"). The control circuit Dr is provided individually corresponding to each switch SW. Each switch SW is driven by the control circuit Dr. Thereby, in each phase of the inverter 20, the upper arm switch SW and the lower arm switch SW are alternately turned on.

[0015] The control system includes a low-voltage power supply 12, an isolation power supply 40, and an emergency power supply 50. The low-voltage power supply 12 is a rechargeable battery having an output voltage (specifically, a rated voltage) lower than that of the high-voltage power supply 10, and is, for example, a lead-acid battery. The output voltage of the low-voltage power supply 12 is, for example, a voltage of 1 / 10 or less of the output voltage of the high-voltage power supply 10.

[0016] The control system is provided with a low-voltage region and a high-voltage region that is electrically insulated from the low-voltage region. The low-voltage power supply 12 is provided in the low-voltage region. The high-voltage power supply 10, the inverter 20, the rotating electrical machine 30, and the emergency power supply 50 are provided in the high-voltage region. The isolation power supply 40 is provided across the low-voltage region and the high-voltage region.

[0017] The isolation power supply 40 supplies the power generated using the low-voltage power supply 12 as a power supply source to each control circuit Dr. FIG. 1 shows an example in which power is supplied from the isolation power supply 40 to the control circuit Dr corresponding to each lower arm switch SW. Each control circuit Dr is operable by being supplied with power.

[0018] Normally, each control circuit Dr is powered by an isolated power supply 40. However, if power supply from the isolated power supply 40 becomes impossible, power to each control circuit Dr is supplied by an emergency power supply 50 instead. For example, if the control system is installed in a vehicle, the situation in which power supply from the isolated power supply 40 becomes impossible is during a vehicle collision. Even if power supply from the isolated power supply 40 becomes impossible, the emergency power supply 50 functions as a backup power supply, allowing each control circuit Dr to continue operating.

[0019] The emergency power supply 50 is a series power supply that steps down the output voltage of the high-voltage power supply 10 and supplies the stepped-down DC voltage to each control circuit Dr. As shown in Figure 2, the emergency power supply 50 includes a first switch 51, a second switch 52, a high-potential side resistor 61, a low-potential side resistor 62, a lowest-potential diode 70, a fuse 81, and a target diode 91. In this embodiment, the first switch 51 and the second switch 52 are voltage-controlled semiconductor switching elements, specifically N-channel MOSFETs. The lowest-potential diode 70 and the target diode 91 are Zener diodes. The first switch 51, the second switch 52, the high-potential side resistor 61, the low-potential side resistor 62, the lowest-potential diode 70, the fuse 81, and the target diode 91 are provided, for example, on a control board. In this embodiment, the second switch 52 corresponds to the "target transistor".

[0020] The positive terminal of the high-voltage power supply 10 is connected to the drain, which is the high-potential terminal of the first switch 51. The first terminal of the fuse 81 is connected to the source, which is the low-potential terminal of the first switch 51. The drain of the second switch 52 is connected to the second terminal of the fuse 81. The first switch 51 and the second switch 52 are connected by a single fuse 81. In this embodiment, the fuse 81 is a microfuse.

[0021] Each control circuit Dr is connected to the source of the second switch 52. The source voltage of the second switch 52 is supplied to each control circuit Dr as the output voltage of the emergency power supply 50.

[0022] The first terminal of the high-potential resistor 61 is connected to the drain of the first switch 51 and the positive terminal of the high-voltage power supply 10. The second terminal of the high-potential resistor 61 is connected to the first terminal of the low-potential resistor 62 and the gate, which is the control terminal of the first switch 51. The second terminal of the low-potential resistor 62 is connected to the cathode of the lowest-potential diode 70. The anode of the lowest-potential diode 70 is connected to the ground in the high-voltage region. The cathode of the lowest-potential diode 70 is connected to the gate of the second switch 52. The negative terminal of the high-voltage power supply 10 is also connected to the ground in the high-voltage region.

[0023] In this embodiment, each resistor 61, 62 may be composed of, for example, a series connection of multiple (e.g., a dozen or so) resistors. The resistors are, for example, chip resistors. Multiple resistors are provided to ensure sufficient insulation distance between the ends of each resistor 61, 62 and to prevent surface discharge on the control board.

[0024] The cathode of the target diode 91 is connected to the gate of the first switch 51. The anode of the target diode 91 is connected to the second terminal of the fuse 81 and the drain of the second switch 52.

[0025] The source voltage of the second switch 52 becomes the output voltage of the emergency power supply 50. The source voltage Vs2 of the second switch 52 is controlled to a target voltage of "VD-Vth". VD is the breakdown voltage of the lowest potential diode 70. Vth is the threshold voltage of the second switch 52. When the gate voltage of the second switch 52 becomes greater than or equal to the threshold voltage Vth, the second switch 52 turns on, and when the gate voltage of the second switch 52 falls below the threshold voltage Vth, the second switch 52 turns off.

[0026] The source voltage Vs1 of the first switch 51 is controlled so that "Vs1 ​​≈ VD + R2 / (R1 + R2) × VH". R1 is the resistance value of the high-potential side resistor 61, and R2 is the resistance value of the low-potential side resistor 62. VH is the output voltage of the high-voltage power supply 10.

[0027] The first switch 51 and the second switch 52 have a voltage withstand capability equal to or higher than the output voltage (specifically, the rated voltage) of the high-voltage power supply 10. This is to prevent the remaining switches, which are not short-circuited, from failing due to the output voltage of the high-voltage power supply 10 in the event of a short-circuit failure in either switch 51 or 52.

[0028] The fuse 81 and the target diode 91 correspond to the "pull-out section" and are configured to quickly interrupt the overcurrent flowing from the high-voltage power supply 10 to the emergency power supply 50 in the event of a short-circuit failure of the second switch 52.

[0029] If the second switch 52 short-circuits, the source voltage Vs1 of the first switch 51 becomes about half the voltage of the high-voltage power supply 10, causing an overcurrent to flow through the fuse 81. As a result, the fuse 81 blows, electrically disconnecting the source of the first switch 51 and the drain of the second switch 52. This interrupts the flow of overcurrent through the first switch 51.

[0030] When fuse 81 blows, current flows from the high-voltage power supply 10 to the second switch 52 via the high-potential resistor 61 and the target diode 91. At this time, the high-potential resistor 61 prevents overcurrent from flowing through the target diode 91.

[0031] When current flows from the high-voltage power supply 10 to the second switch 52 via the high-potential resistor 61 and the target diode 91, a voltage drop occurs in the target diode 91. In this case, the gate charge of the first switch 51 is drawn out to the second switch 52 side via the target diode 91, and the gate voltage of the first switch 51 decreases. As a result, the first switch 51 is switched to the off state. Consequently, the voltage across the fuse 81 is clamped to the breakdown voltage of the target diode 91, and the output voltage of the high-voltage power supply 10 is applied between the drain and source of the first switch 51. However, the first switch 51 does not fail because it has a withstand voltage greater than or equal to the output voltage of the high-voltage power supply 10.

[0032] Here, the fuse 81 has a breakdown voltage lower than the output voltage of the high-voltage power supply 10. The breakdown voltage of the fuse 81 is the upper limit of the voltage across the fuse 81 that prevents the fuse 81 from re-conducting due to dielectric breakdown when the fuse 81 is blown. The fuse 81 has such a breakdown voltage in order to reduce its size. On the other hand, the target diode 91 has a breakdown voltage that is the same as the breakdown voltage of the fuse 81, or a breakdown voltage that is lower than the breakdown voltage of the fuse 81. This makes it possible to keep the voltage across the fuse 81 below the breakdown voltage of the fuse 81. As a result, when the fuse 81 is blown, it is possible to prevent the occurrence of arc discharge across the fuse 81 and prevent the fuse 81 from re-conducting.

[0033] According to the embodiment described above, in the event of a short-circuit failure in the second switch 52, the output current of the emergency power supply 50 can be quickly interrupted. Furthermore, this configuration for quickly interrupting the current can be achieved using a small and inexpensive fuse 81, rather than a large and expensive high-voltage fuse.

[0034] In contrast, the following disadvantages arise in the cases of Comparative Examples 1 and 2, which are described below. Figure 3 shows the emergency power supply of Comparative Example 1. The emergency power supply of Comparative Example 1 includes a switch 151, a resistor 161, a minimum potential diode 170, and several fuses 181 (three are shown as examples). Each fuse 181 is a microfuse. The switch 151, resistor 161, minimum potential diode 170, and each fuse 181 are mounted on a control board.

[0035] Because microfuses are small, the gap between the fuse ends is narrow. Therefore, arc discharge is likely to occur in the gap even at relatively low voltages. For this reason, in Comparative Example 1, multiple fuses 181 are provided. However, in this case, the mounting area of ​​fuses 181 on the control board increases.

[0036] Figure 4 shows the emergency power supply of Comparative Example 2. The emergency power supply of Comparative Example 2 includes a switch 151, a resistor 161, a minimum potential diode 170, and a high-voltage fuse 182. The switch 151, resistor 161, minimum potential diode 170, and high-voltage fuse 182 are provided on the control board.

[0037] The high-voltage fuse 182 has a wide gap to prevent re-conduction due to arc discharge after blowing. As a result, the size of the high-voltage fuse 182 is large, and the mounting area of ​​the high-voltage fuse 182 on the control board increases.

[0038] <Modified form of the first embodiment> The number of switches electrically connecting the high-voltage power supply 10 and the control circuit Dr is not limited to two, but may be three or more. Figure 5 shows an example in which three switches are provided. In the configuration shown in Figure 5, the fuse 81 will be referred to as the first fuse, the target diode 91 as the first target diode, and the low-potential side resistor 62 as the first low-potential side resistor.

[0039] As shown in Figure 5, the emergency power supply 50 further comprises a third switch 53, a second fuse 82, a second target diode 92, and a second low-potential side resistor 63. In this embodiment, the third switch 53 is an N-channel MOSFET and corresponds to the "target transistor". The first fuse 81 and the first target diode 91 are provided separately in correspondence with the first switch 51, and the second fuse 82 and the second target diode 92 are provided separately in correspondence with the second switch 52.

[0040] Incidentally, it is not necessary to provide a fuse and a corresponding diode for either of the first and second switches 51 and 52.

[0041] The higher-level control unit of the control circuit Dr may determine that an abnormality has occurred in the emergency power supply 50 if it determines that the power supply from the emergency power supply 50 to the control circuit Dr has been stopped.

[0042] <Second Embodiment> The second embodiment will now be described, focusing on the differences from the first embodiment, with reference to the drawings. As shown in Figure 6, in the emergency power supply 150 of this embodiment, the configuration for extracting charge from the gate of the first switch 51 when an overcurrent flows between the drain and source of the first switch 51 has been changed.

[0043] The emergency power supply 150 includes a detection resistor 100 and a discharge transistor 101 as extraction components. In this embodiment, the discharge transistor 101 is an NPN type bipolar transistor.

[0044] The source of the first switch 51 is connected to the first terminal of the detection resistor 100. The drain of the second switch 52 is connected to the second terminal of the detection resistor 100. The first terminal of the detection resistor 100 is connected to the base, which is the control terminal of the discharge transistor 101. The gate of the first switch 51 is connected to the collector, which is the first terminal of the discharge transistor 101. The second terminal of the detection resistor 100 is connected to the emitter, which is the second terminal of the discharge transistor 101. The discharge transistor 101 is turned ON when the voltage difference Vbe between the base and emitter becomes greater than or equal to the threshold voltage Vdth of the discharge transistor 101, and is turned OFF when the voltage difference Vbe becomes less than the threshold voltage Vdth.

[0045] The emergency power supply 150 is equipped with a limiting diode 102. The limiting diode 102 is a Zener diode. The cathode of the limiting diode 102 is connected to the source of the second switch 52, and the anode of the limiting diode 102 is connected to the ground in the high-voltage region.

[0046] The detection resistor 100 and the discharge transistor 101 are configured to continue supplying power to the control circuit Dr while limiting the current flowing from the high-voltage power supply 10 to the emergency power supply 50 to less than or equal to the rated current of the first switch 51 and the second switch 52 in the event of a short-circuit failure of the second switch 52.

[0047] If a short circuit occurs in the second switch 52, the current flowing from the high-voltage power supply 10 to the first switch 51, the detection resistor 100, and the second switch 52 increases. When RD is the resistance value of the detection resistor 100, when the current flowing through the detection resistor 100 reaches "Vdth / RD", the voltage difference Vbe between the base and emitter of the discharge transistor 101 becomes greater than or equal to the threshold voltage Vdth, and the discharge transistor 101 is switched to the ON state. As a result, charge is drawn from the gate of the first switch 51 through the discharge transistor 101. Consequently, the gate voltage of the first switch 51 decreases, and the current flowing through the detection resistor 100 is maintained at "Vdth / RD".

[0048] Here, the limiting diode 102 has a breakdown voltage below the withstand voltage of the control circuit Dr. Therefore, the voltage applied from the emergency power supply 150 to the control circuit Dr is kept below the withstand voltage of the control circuit Dr. This suppresses the occurrence of failures in the control circuit Dr.

[0049] According to the embodiment described above, even if a short-circuit failure occurs in the second switch 52, power can be continued from the emergency power supply 150 to the control circuit Dr while preventing overcurrent from flowing to the first switch 51, etc.

[0050] <Modified form of the second embodiment> The discharge transistor is not limited to an NPN bipolar transistor; for example, it may be an N-channel MOSFET as shown in Figure 7. The gate, which is the control terminal of the discharge transistor 103, is connected to the first end of the detection resistor 100. The drain, which is the first terminal of the discharge transistor 103, is connected to the gate of the first switch 51. The source, which is the second terminal of the discharge transistor 103, is connected to the second end of the detection resistor 100. The discharge transistor 103 is turned ON when the voltage difference Vgs between the gate and the source becomes greater than or equal to the threshold voltage of the discharge transistor 103, and is turned OFF when the voltage difference Vgs becomes less than the threshold voltage.

[0051] According to the configuration shown in Figure 7, when a short-circuit failure occurs in the second switch 52, the current flowing through the detection resistor 100 is maintained at "Vdth2 / RD". Vdth2 is the threshold voltage of the discharge transistor 103.

[0052] <Third Embodiment> The third embodiment will now be described, focusing on the differences from the second embodiment, with reference to the drawings. As shown in Figure 8, the emergency power supply 190 includes a second detection resistor 111, a resistor 112, and a notification transistor 113 as a detection circuit to detect when a short circuit failure occurs in the second switch 52 and an overcurrent flows to the first switch 51. In this embodiment, the notification transistor 113 is an NPN type bipolar transistor. In this embodiment, the detection resistor 100 will be referred to as the first detection resistor.

[0053] The first terminal of the second detection resistor 111 is connected to the anode of the limiting diode 102 and the base, which is the control terminal of the notification transistor 113. The second terminal of the second detection resistor 111 is connected to the ground in the high-voltage region.

[0054] The first terminal of resistor 112 is connected to the source of the second switch 52 and the cathode of the limiting diode 102. The second terminal of resistor 112 is connected to the collector, which is the first terminal of notification transistor 113. The emitter, which is the second terminal of notification transistor 113, is connected to the second terminal of second detection resistor 111. The voltage at the second terminal of resistor 112 is transmitted to the higher-level control device 120 as a notification signal Sg.

[0055] The notification transistor 113 is turned ON when the voltage difference VA between the emitter and base becomes greater than or equal to the threshold voltage Veth of the notification transistor 113, and is turned OFF when the voltage difference VA falls below the threshold voltage Veth.

[0056] If a short circuit occurs in the second switch 52, the current flowing from the high-voltage power supply 10 to the second detection resistor 111 via the first switch 51, the first detection resistor 100, and the second switch 52 increases. If RE is the resistance value of the second detection resistor 111, when the current flowing through the second detection resistor 111 reaches "Veth / RE", the notification transistor 113 is switched to the ON state. As a result, the logic of the notification signal Sg inverts from H to L. When the higher-level control device 120 determines that the logic of the notification signal Sg has inverted to L, it determines that an abnormality has occurred in the emergency power supply 190 and performs a process to stop the power supply from the high-voltage power supply 10 to the emergency power supply 190. The power supply stop process can be, for example, a process to switch the switch (e.g., relay) connecting the high-voltage power supply 10 and the emergency power supply 190 to the OFF state.

[0057] Here, "Veth / RE" is a value smaller than "Vdth / RD" as described in the second embodiment, and is higher than the upper limit of the voltage range across the second detection resistor 111 that can take place when the emergency power supply 190 is functioning normally. Since "Veth / RE" < "Vdth / RD", the current flowing through the first switch 51 can be reduced while notifying the higher-level control device 120 that an abnormality has occurred in the emergency power supply 190.

[0058] <Modified form of the third embodiment> The notification transistor is not limited to an NPN bipolar transistor, but may also be, for example, an N-channel MOSFET. In this case, the gate, which is the control terminal of the notification transistor, is connected to the anode of the limiting diode 102 and the first end of the second detection resistor 111. The drain, which is the first terminal of the notification transistor, is connected to the second end of the resistor 112. The source, which is the second terminal of the notification transistor, is connected to the second end of the second detection resistor 111.

[0059] <Fourth Embodiment> The fourth embodiment will now be described, focusing on the differences from the third embodiment, with reference to the drawings. As shown in Figure 9, the emergency power supply 200 includes a second detection resistor 131, a resistor 132, a protection diode 130, and a notification transistor 133 as a detection circuit to detect when a short circuit occurs in the second switch 52 and an overcurrent flows to the first switch 51. In this embodiment, the notification transistor 133 is a PNP type bipolar transistor. The protection diode 130 is a Zener diode. In this embodiment, the detection resistor 100 will be referred to as the first detection resistor.

[0060] The first terminal of the second detection resistor 131 is connected to the cathode of the protection diode 130 and to the emitter, which is the first terminal of the notification transistor 133. The anode of the protection diode 130 is connected to the source of the second switch 52. The protection diode 130 is a switch intended to protect the gate and source of the second switch 52.

[0061] The second terminal of the second detection resistor 131 is connected to the cathode of the lowest potential diode 70 and to the base, which is the control terminal of the notification transistor 133. The anode of the lowest potential diode 70 is connected to the ground in the high-voltage region.

[0062] The collector, which is the second terminal of the notification transistor 133, is connected to the first terminal of resistor 132. The second terminal of resistor 132 is connected to the ground in the high-voltage region. The voltage at the first terminal of resistor 132 is transmitted to the higher-level control device 120 as a notification signal Sg.

[0063] The notification transistor 133 is turned ON when the voltage difference VB between the emitter and base becomes greater than or equal to the threshold voltage Vfth of the notification transistor 133, and is turned OFF when the voltage difference VB falls below the threshold voltage Vfth.

[0064] If a short-circuit failure occurs in the second switch 52, the current flowing from the high-voltage power supply 10 to the second detection resistor 131 via the first switch 51, the first detection resistor 100, the second switch 52, and the protection diode 130 increases. If RF is the resistance value of the second detection resistor 131, when the current flowing through the second detection resistor 131 reaches "Vfth / RF", the notification transistor 133 is switched to the ON state. As a result, the logic of the notification signal Sg inverts from H to L. When the higher-level control device 120 determines that the logic of the notification signal Sg has inverted to L, it determines that an abnormality has occurred in the emergency power supply 200 and, similar to the third embodiment, performs the process of stopping the power supply from the high-voltage power supply 10 to the emergency power supply 200.

[0065] Here, "Vfth / RF" is a value smaller than "Vdth / RD" as described in the second embodiment, and is higher than the upper limit of the voltage range that the second detection resistor 131 can take when the emergency power supply 200 is functioning normally. Since "Vfth / RF" < "Vdth / RD", it is possible to shorten the period during which a large current flows through the first switch 51 while notifying the higher-level control device 120 that an abnormality has occurred in the emergency power supply 200.

[0066] <Other Embodiments> Furthermore, each of the above embodiments may be implemented with the following modifications.

[0067] In the fourth embodiment, the notification transistor is not limited to a PNP bipolar transistor, but may be, for example, a P-channel MOSFET. In this case, the gate, which is the control terminal of the notification transistor, is connected to the cathode of the lowest potential diode 70 and the second end of the second detection resistor 131. The source, which is the first terminal of the notification transistor, is connected to the first end of the second detection resistor 131 and the cathode of the protection diode 130. The drain, which is the second terminal of the notification transistor, is connected to the first end of the resistor 132.

[0068] In the second to fourth embodiments, the number of switches constituting the path for electrically connecting the high-voltage power supply 10 and the control circuit Dr may be three or more.

[0069] The switch that constitutes the path for electrically connecting the high-voltage power supply 10 and the control circuit Dr is not limited to an N-channel MOSFET, but may also be, for example, an NPN bipolar transistor having a collector as the high-potential terminal, an emitter as the low-potential terminal, and a base as the control terminal.

[0070] The series power supply described herein is not limited to being implemented as an emergency power supply, but may also be implemented, for example, as a starting circuit for a flyback power supply whose primary side is a high-voltage power supply. [Explanation of Symbols]

[0071] 10...High-voltage power supply, 50...Emergency power supply, 51...First switch, 52...Second switch, 61...High-potential resistor, 62...Low-potential resistor, 70...Lowest potential diode, 81...Fuse, 91...Target diode, Dr...Control circuit.

Claims

1. In a series power supply (50, 150, 190, 200) that steps down the output voltage of a DC power supply (10) and supplies it to a power supply target (Dr), Multiple transistors (51, 52; 51-53) that constitute a path for electrically connecting the positive terminal side of the DC power supply and the power supply target, The lowest potential diode (70) is a Zener diode that electrically connects the gate and ground of the lowest potential transistor (52; 53), which is the lowest potential transistor among the aforementioned transistors, A high-potential side resistor (61) is a resistor that electrically connects the gate of the transistor (51) with the highest potential among the aforementioned transistors and the positive terminal side of the DC power supply, In each of the transistors, there are low-potential side resistors (62; 62, 63) which are resistors that electrically connect the gates of electrically adjacent transistors, Equipped with, The cathode of the lowest potential diode is electrically connected to the gate of the lowest potential transistor. A series power supply comprising a pull-out section (81, 91; 81, 82, 91, 92; 100, 101; 100, 103) which is electrically connected to the gate of a target transistor (51; 51, 52) which is at least one of the transistors other than the lowest potential transistor, and which pulls out the gate charge of the target transistor when an overcurrent flows through the target transistor.

2. The aforementioned extraction portion is, A fuse (81; 81, 82) electrically connects the low-potential terminal of the target transistor and the high-potential terminal of the transistor (52; 52, 53) adjacent to the low-potential side of the target transistor, A target diode (91; 91, 92) is a Zener diode that electrically connects the high-potential terminal of the target transistor adjacent to the low-potential side of the target transistor, and the gate of the target transistor, Equipped with, The series power supply (150) according to claim 1, wherein the cathode of the target diode is electrically connected to the gate of the target transistor.

3. The fuse has a voltage rating lower than the output voltage of the DC power supply. The series power supply according to claim 2, wherein the target diode has a breakdown voltage less than or equal to the withstand voltage of the fuse.

4. The aforementioned extraction portion is, A detection resistor (100) electrically connects the low-potential terminal of the target transistor (51) and the high-potential terminal of the transistor (52) adjacent to the low-potential side of the target transistor, Discharge transistors (101, 103), Equipped with, The control terminal of the discharge transistor is electrically connected to the high-potential side of both ends of the detection resistor. The first terminal of the discharge transistor is electrically connected to the gate of the target transistor. The second terminal of the discharge transistor is electrically connected to the low-potential side of both ends of the detection resistor. The series power supply (150) according to claim 1, wherein the discharge transistor is turned ON when the voltage difference between the control terminal and the second terminal becomes greater than or equal to a threshold voltage, and is turned OFF when the voltage difference becomes less than the threshold voltage.

5. The system includes a limiting diode (102), which is a Zener diode that electrically connects the low-potential terminal of the lowest-potential transistor to the ground. The cathode of the limiting diode is electrically connected to the low-potential terminal of the lowest-potential transistor. The series power supply according to claim 4, wherein the limiting diode has a breakdown voltage less than or equal to the withstand voltage of the power supply unit.

6. The series power supply (190, 200) according to claim 4, comprising a detection circuit (111-113; 130-133) provided between the low-potential terminal of the lowest-potential transistor and the ground for detecting when an overcurrent flows through the target transistor.

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