Series Power Supply

Abstract

To provide a series power supply capable of suppressing a large increase in output voltage even if a short circuit occurs in a transistor on the lowest potential side among the transistors.SOLUTION: An emergency power supply 50 as a series power supply includes: a series connection of first and second switches 51 and 52 that connect the positive electrode of a high voltage power supply 10 and a control circuit Dr; a drive circuit that drives each of the switches 51 and 52 so that a source voltage of each of the switches 51 and 52 is equal to or lower than a withstand voltage of the control circuit Dr. The drive circuit includes a resistor 61 and first and second Zener diodes 71 and 72. Each of the switches 51 and 52 has a withstand voltage equal to or higher than the output voltage of the high-voltage power supply 10.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to series power supplies.

Background Art

[0002] Conventionally, as described in Patent Document 1, there has been known a series power supply that steps down the output voltage of a DC power supply and supplies the stepped-down voltage to a powered component. The series power supply includes a series-connected body of a plurality of transistors, resistors respectively corresponding to the plurality of transistors, and a Zener diode. The Zener diode is provided corresponding to the transistor on the lowest potential side among the transistors.

Prior Art Literature

Patent Literature

[0003]

Patent Document 1

Summary of Invention

Problem to be Solved by the Invention

[0004] A short-circuit failure may occur in the lowest potential side transistor among the transistors. In this case, the output voltage of the series power supply greatly increases, and there is a concern that the output voltage of the series power supply will exceed the withstand voltage of the powered component. If the output voltage exceeds the withstand voltage of the powered component, there is a concern that a secondary failure of the powered component will occur.

[0005] A main object of the present disclosure is to provide a series power supply that can suppress a large increase in output voltage even when a short-circuit failure occurs in the lowest potential side transistor among the transistors.

Means for Solving the Problem

[0006] The present disclosure relates to a series power supply that steps down an output voltage of a DC power supply and supplies the stepped-down voltage to a powered component, A series connection of multiple transistors connecting the positive terminal side of the DC power supply and the power supply target, A drive circuit drives each transistor such that the voltage at the low-potential terminal of each transistor is less than or equal to the withstand voltage of the power supply unit, Equipped with, Each of the transistors has a voltage rating equal to or greater than the output voltage of the DC power supply.

[0007] Each transistor is driven by a drive circuit so that the voltage at the low-potential terminal of each transistor is below the withstand voltage of the powered component. Therefore, even if a short-circuit failure occurs in the lowest-potential transistor, the voltage at the low-potential terminal of the transistor adjacent to the high-potential side of the lowest-potential transistor can be kept below the withstand voltage of the powered component, thereby suppressing a large rise in the output voltage of the series power supply. This suppresses the occurrence of dependent failures in the powered component.

[0008] If a short circuit occurs in some transistors, such as the lowest-potential transistor, the remaining transistors that are not short-circuited must take on the output voltage of the DC power supply. In other words, the voltage between the high-potential and low-potential terminals of the transistors that are not short-circuited will rise.

[0009] Here, each transistor in this disclosure has a withstand voltage greater than or equal to the output voltage of the DC power supply. Therefore, even if a short-circuit failure occurs in some transistors, the voltage between the high-potential and low-potential terminals of the remaining transistors that have not experienced a short-circuit failure can be prevented from exceeding the withstand voltage of the remaining transistors. [Brief explanation of the drawing]

[0010] [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 the emergency power supply according to the second embodiment. [Figure 6] This diagram shows the current flow path in the first switch when a short circuit occurs between the drain and source, and when a short circuit occurs between the source and gate. [Figure 7] Circuit diagram of the emergency power supply according to the third embodiment. [Figure 8] Circuit diagram of the emergency power supply according to the fourth embodiment. [Modes for carrying out the invention]

[0011] 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.

[0012] <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.

[0013] 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.

[0014] The inverter 20 includes upper and lower arm switches SW for three phases. A first end of a winding 31 of a rotating electric machine 30 is connected to a connection point between the upper arm switch SW and the lower arm switch SW of each phase. A second end of the winding 31 of each phase is connected at a neutral point. The switch SW of the present embodiment is an N-channel MOSFET, and 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, it is only required that a freewheeling diode is anti-parallel connected to the IGBT. Further, the connection mode of the windings 31 is not limited to star connection, and may be delta connection.

[0015] The inverter 20 includes a control circuit Dr. The control circuits Dr are individually provided corresponding to each switch SW, and each switch SW is driven by the control circuit Dr. Accordingly, in each phase of the inverter 20, the upper arm switch SW and the lower arm switch SW are alternately turned on.

[0016] The control system includes a low-voltage power supply 12, an insulated power supply 40, and an emergency power supply 50. The low-voltage power supply 12 is a chargeable and dischargeable storage 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, 1 / 10 or less of the output voltage of the high-voltage power supply 10.

[0017] The control system is provided with a low-voltage region and a high-voltage region 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 electric machine 30, and the emergency power supply 50 are provided in the high-voltage region. The insulated power supply 40 is provided across the low-voltage region and the high-voltage region.

[0018] The insulated power supply 40 supplies, to each control circuit Dr, power generated using the low-voltage power supply 12 as a power supply source. FIG. 1 shows an example in which power is supplied from the insulated power supply 40 to the control circuits Dr corresponding to the lower arm switches SW. Each control circuit Dr is operable when supplied with power.

[0019] Power supply to each control circuit Dr is normally performed by the insulated power supply 40. On the other hand, when power supply by the insulated power supply 40 becomes impossible, power supply to each control circuit Dr is performed by the emergency power supply 50 instead of the insulated power supply 40. For example, when the control system is mounted on a vehicle, the situation in which power supply by the insulated power supply 40 becomes impossible is when the vehicle collides. Even when power supply by the insulated power supply 40 becomes impossible, the emergency power supply 50 functions as a backup power supply, and the operation of each control circuit Dr can be continued.

[0020] 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 FIG. 2, the emergency power supply 50 includes a first switch 51, a second switch 52, a resistor 61, a first Zener diode 71, and a second Zener diode 72. The resistor 61, the first Zener diode 71, and the second Zener diode 72 constitute a drive circuit for the first and second switches 51 and 52. In the present embodiment, the first switch 51 and the second switch 52 are voltage-controlled semiconductor switching elements, specifically N-channel MOSFETs. The first switch 51, the second switch 52, the resistor 61, the first Zener diode 71, and the second Zener diode 72 are provided, for example, on a control board.

[0021] The positive electrode side of the high-voltage power supply 10 is connected to the drain, which is the high-potential side terminal of the first switch 51. The drain of the second switch 52 is connected to the source, which is the low-potential side terminal of the first switch 51. The source of the second switch 52 is connected to each control circuit Dr. 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] In the present embodiment, the resistor 61 is a series connection body of a plurality of (for example, more than ten) resistors. The resistor 61 is, for example, a chip resistor. The reason why a plurality of resistors 61 are provided is to secure an insulation distance between both ends of the resistor 61 and prevent creeping discharge on the control board.

[0023] The first end of the series connection of the multiple resistors 61 is connected to the drain of the first switch 51 and the positive terminal of the high-voltage power supply 10. The second end of the series connection of the multiple resistors 61 is connected to the cathode of the first Zener diode 71 and the gate, which is the control terminal of the first switch 51. The anode of the first Zener diode 71 is connected to the gate, which is the control terminal of the second switch 52 and the cathode of the second Zener diode 72. The anode of the second Zener diode 72 is connected to the ground in the high-voltage region. The negative terminal of the high-voltage power supply 10 is also connected to the ground in the high-voltage region.

[0024] 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 "VD2-Vth2". VD2 is the breakdown voltage of the second Zener diode 72. Vth2 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 Vth2, the second switch 52 turns on, and when the gate voltage of the second switch 52 falls below the threshold voltage Vth2, the second switch 52 turns off.

[0025] The source voltage Vs1 of the first switch 51 is controlled to a target voltage of "VD1 + VD2 - Vth1". VD1 is the breakdown voltage of the first Zener diode 71. Vth1 is the threshold voltage of the first switch 51.

[0026] In this embodiment, the breakdown voltages VD1 and VD2 of each Zener diode 71 and 72, and the threshold voltage Vth1 of the first switch 51 are set so that the source voltage Vs1 of the first switch 51 is less than or equal to the withstand voltage of the control circuit Dr, which is the "power supply target". Similarly, the breakdown voltage VD2 of the second Zener diode 72 and the threshold voltage Vth2 of the second switch 52 are set so that the source voltage Vs2 of the second switch 52 is less than or equal to the withstand voltage of the control circuit Dr. The reason why each source voltage Vs1 and Vs2 is controlled to be less than or equal to the withstand voltage of the control circuit Dr is to suppress the occurrence of dependent failures of the control circuit Dr in the event of a short-circuit failure of the second switch 52.

[0027] If the second switch 52 short-circuits, the output voltage of the emergency power supply 50 becomes the source voltage Vs1 of the first switch 51. The source voltage Vs1 is below the withstand voltage of the control circuit Dr. Therefore, even if a short-circuit occurs in the second switch 52, the occurrence of a dependent failure in the control circuit Dr can be suppressed.

[0028] In this embodiment, the first switch 51 and the second switch 52 have a withstand voltage 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 have not experienced a short-circuit failure, from failing due to the output voltage of the high-voltage power supply 10 in the event of a short-circuit failure in either of the switches 51 or 52.

[0029] In contrast, in the case of Comparative Examples 1 and 2, described below, the reliability of the emergency power supply decreases when a short-circuit failure occurs.

[0030] 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, and a Zener diode 171. For convenience, in Figure 3, the resistor 161 is shown as a single resistor circuit symbol.

[0031] In Comparative Example 1, the source voltage Vs of switch 151 is controlled so that "Vs ≈ VD - Vth". VD is the breakdown voltage of Zener diode 171. Vth is the threshold voltage of switch 151.

[0032] In Comparative Example 1, if a short-circuit failure occurs in switch 151, the output voltage of the high-voltage power supply 10 is directly applied to the control circuit Dr. As a result, a dependent failure occurs in the control circuit Dr.

[0033] Figure 4 shows the emergency power supply of Comparative Example 2. The emergency power supply of Comparative Example 2 includes a first switch 151, a second switch 152, a first resistor 161, a second resistor 162, and a Zener diode 171. For convenience, in Figure 4, resistors 161 and 162 are shown as a single resistor circuit symbol.

[0034] The source voltage Vs1 of the first switch 151 is controlled so that "Vs1 ​​≈ VD + R2 / (R1 + R2) × VH". R1 is the resistance value of the first resistor 161, and R2 is the resistance value of the second resistor 162. VH is the output voltage of the high-voltage power supply 10.

[0035] In Comparative Example 2, if a short-circuit failure occurs in the first switch 151, the source voltage Vs2 of the second switch 152 is controlled to "VD-Vth2". Vth2 is the threshold voltage of the second switch 152. Since the source voltage Vs2 is below the withstand voltage of the control circuit Dr, a dependent failure of the control circuit Dr does not occur.

[0036] On the other hand, if a short circuit occurs in the second switch 152, the source voltage Vs1 of the first switch 151 becomes about half the voltage of the high-voltage power supply 10. In this case, the source voltage Vs1 exceeds the withstand voltage of the control circuit Dr, causing a dependent failure of the control circuit Dr.

[0037] As described above, in this embodiment, each switch 51, 52 is driven such that the source voltage of each switch 51, 52 is less than or equal to the withstand voltage of the control circuit Dr. Therefore, even if a short-circuit failure occurs in the second switch 52 (corresponding to the "lowest potential transistor") which is on the lowest potential side of each switch 51, 52, the source voltage of the first switch 51 adjacent to the high potential side of the second switch 52 can be kept below the withstand voltage of the control circuit Dr, thereby suppressing a large rise in the output voltage of the emergency power supply 50. This suppresses the occurrence of dependent failures of the control circuit Dr.

[0038] Furthermore, each switch 51, 52 has a withstand voltage greater than or equal to the output voltage of the high-voltage power supply 10. Therefore, even if a short-circuit failure occurs in, for example, the second switch 52 among the switches 51, 52, the drain-source voltage of the remaining first switch 51, which is not short-circuited, can be prevented from exceeding the withstand voltage of the drain-source voltage of the first switch 51.

[0039] <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 5, in the emergency power supply 55 of this embodiment, the gates of the first switch 51 and the second switch 52 are connected to separate reference voltage generation circuits.

[0040] The emergency power supply 55 includes a first resistor 61, a first Zener diode 71, and a second Zener diode 72 as a reference voltage generation circuit connected to the gate of the first switch 51. The emergency power supply 55 also includes a second resistor 62 and a third Zener diode 73 as a reference voltage generation circuit connected to the gate of the second switch 52. In this embodiment, the breakdown voltages of each Zener diode 71 to 73 are the same. The sum of the breakdown voltages of the first Zener diode 71 and the second Zener diode 72 is higher than the breakdown voltage of the third Zener diode 73.

[0041] The cathode of the first Zener diode 71 is connected to the gate of the first switch 51. The anode of the first Zener diode 71 is connected to the cathode of the second Zener diode 72. The anode of the second Zener diode 72 is connected to the ground in the high-voltage region.

[0042] The cathode of the third Zener diode 73 is connected to the gate of the second switch 52. The anode of the third Zener diode 73 is connected to the ground in the high-voltage region.

[0043] In this embodiment, the first resistor 61 and the second resistor 62 are, as in the first embodiment, a series connection of a plurality (e.g., a dozen or so) of resistors. Each resistor is, for example, a chip resistor.

[0044] The first terminal of the series connection of the multiple first and second resistors 61 and 62 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 series connection of the multiple first resistors 61 is connected to the cathode of the first Zener diode 71 and the gate of the first switch 51. The second terminal of the series connection of the multiple second resistors 62 is connected to the cathode of the third Zener diode 73 and the gate of the second switch 52.

[0045] The source voltage Vs2 of the second switch 52 is controlled to the target voltage "VD3-Vth2". VD3 is the breakdown voltage of the third Zener diode 73. The breakdown voltages of each Zener diode 71-73 are set to the same value, for example.

[0046] The configuration of this embodiment is designed to suppress the occurrence of dependent failures in the first switch 51 when a short-circuit failure occurs between the gate and source, following a short-circuit failure between the drain and source. This will be explained below with reference to Figure 6.

[0047] Figure 6 shows the configuration of the first embodiment. In the configuration of Figure 6, if a short circuit occurs between the drain and source of the first switch 51, the high voltage of the high-voltage power supply 10 is applied between the gate and source of the first switch 51, which can cause a short circuit between the gate and source. In this case, short circuit failures can occur in the first Zener diode 71 and the second Zener diode 72. When a short circuit occurs in the first Zener diode 71, a large current flows from the high-voltage power supply 10 to ground through the first switch 51, the first Zener diode 71, and the second Zener diode 72. Subsequently, when the failure mode of the second Zener diode 72 transitions to an open circuit, the source voltage Vs2 of the second switch 52 rises significantly, and the source voltage Vs2 exceeds the withstand voltage of the control circuit Dr, causing a dependent failure of the control circuit Dr.

[0048] In contrast, according to this embodiment shown in Figure 5, even if, for example, a short circuit occurs between the drain and source of the first switch 51, followed by a short circuit between the gate and source, and then an open circuit occurs in either the first or second Zener diode 71, the operation of the second switch 52 is not affected. Therefore, the source voltage Vs2 of the second switch 52 can be kept below the withstand voltage of the control circuit Dr. Note that if a short circuit occurs in both the first and second Zener diodes 71 and 72, the output voltage of the emergency power supply 55 becomes 0.

[0049] <Modified form of the second embodiment> The Zener diode connected to the gate of the first switch 51 is not limited to two Zener diodes; for example, it may be one Zener diode. In this case, the breakdown voltage of the Zener diode connected to the gate of the first switch 51 should be set to a value higher than the breakdown voltage of the third Zener diode 73.

[0050] The reference voltage generation circuit connected to the gates of each switch 51, 52 is not limited to the one shown in Figure 5, but may also be, for example, a shunt regulator having a comparator, a bipolar transistor, and a resistor. In this case, a shunt regulator should be provided individually for each switch 51, 52, and the output of the shunt regulator should be connected to the gate of the switch.

[0051] <Third Embodiment> The third embodiment will now be described, focusing on the differences from the first embodiment, with reference to the drawings. As shown in Figure 7, the emergency power supply 56 of this embodiment includes a rectifier diode 80 and a discharge resistor 81. The rectifier diode 80 has a voltage withstand capability equal to the output voltage (specifically, the rated voltage) of the high-voltage power supply 10, or a voltage withstand capability higher than the output voltage (specifically, the rated voltage) of the high-voltage power supply 10. The rectifier diode 80 is provided in the electrical path connecting the gate of the first switch 51 (corresponding to the "highest potential transistor") and the cathode of the first Zener diode 71 (corresponding to the "highest potential diode"). The cathode of the rectifier diode 80 is connected to the gate of the first switch 51.

[0052] The source of the first switch 51 is connected to the gate of the first switch 51 via a discharge resistor 81. The discharge resistor 81 is a component that ensures a discharge path for the gate charge of the first switch 51 when the first switch 51 is functioning normally.

[0053] According to this embodiment, even if a short-circuit failure occurs between the gate and source of the first switch 51 due to a short-circuit failure between the drain and source, the rectifier diode 80 can prevent the flow of a large current. This prevents a large current from flowing through the first Zener diode 71 and the second Zener diode 72, protecting each Zener diode 71 and 72. As a result, the operation of the second switch 52 can continue, and the occurrence of a situation where the source voltage Vs2 of the second switch 52 exceeds the withstand voltage of the control circuit Dr can be suppressed.

[0054] Furthermore, according to this embodiment, the number of resistors 61 and the mounting area of ​​the resistors 61 on the control board can be reduced compared to the second embodiment.

[0055] <Modified form of the third embodiment> In the configuration shown in Figure 7, in addition to the rectifier diode 80 and discharge resistor 81 corresponding to the first switch 51, a rectifier diode 80 and discharge resistor 81 corresponding to the second switch 52 may also be provided.

[0056] <Fourth Embodiment> The fourth embodiment will now be described, focusing on the differences from the first embodiment, with reference to the drawings. As shown in Figure 8, the emergency power supply 57 of this embodiment includes a third Zener diode 91, a fourth Zener diode 92, a first rectifier diode 101, and a second rectifier diode 102. Each of the rectifier diodes 101 and 102 has a withstand voltage equal to the output voltage of the high-voltage power supply 10 (specifically, the rated voltage), or a withstand voltage higher than the output voltage of the high-voltage power supply 10 (specifically, the rated voltage).

[0057] The gate of the first switch 51 is connected to the anode of the first rectifier diode 101. The cathode of the first rectifier diode 101 is connected to the second terminal of a series connection of multiple resistors 61 and to the anode of the second rectifier diode 102. The cathode of the second rectifier diode 102 is connected to the cathode of the third Zener diode 91. The cathode of the third Zener diode 91 is connected to the gate of the second switch 52 and to the cathode of the fourth Zener diode 92. The anode of the fourth Zener diode 92 is connected to the ground in the high-voltage region.

[0058] In this embodiment, the electrical path from the second end of the series connection of resistors 61 to ground via the first rectifier diode 101 corresponds to the "first individual electrical path" corresponding to the first switch 51. Similarly, the electrical path from the second end of the series connection of resistors 61 to ground via the second rectifier diode 102 corresponds to the "second individual electrical path" corresponding to the second switch 52. The emergency power supply 57 is configured such that the resistance value of the first individual electrical path and the resistance value of the second individual electrical path are the same. This is to allow current to flow from the high-voltage power supply 10 through the resistors 61 to both the first and second individual electrical paths, thereby enabling the source voltage of each switch 51, 52 to be controlled to the target voltage. In this embodiment, the sum of the breakdown voltages of the first Zener diode 71 and the second Zener diode 72 is set to the same value as the sum of the breakdown voltages of the third Zener diode 91 and the fourth Zener diode 92, so that the resistance value of the first individual electrical path and the resistance value of the second individual electrical path are the same value. The forward voltage drop of the first rectifier diode 101 is set to the same value as the forward voltage drop of the second rectifier diode 102. In this embodiment, the breakdown voltages of each Zener diode 71, 72, 91, and 92 are the same.

[0059] The configuration of this embodiment is designed to suppress the occurrence of dependent failures in the first switch 51 or the second switch 52 when a short-circuit failure occurs between the drain and source, and subsequently a short-circuit failure occurs between the gate and source.

[0060] Even if a short circuit occurs between the drain and source of the first switch 51, followed by a short circuit between the gate and source, and then an open circuit occurs in the first or second Zener diode 71 or 72, the large current is blocked by the first rectifier diode 101. This prevents large currents from flowing through the third and fourth Zener diodes 91 and 92, and does not affect the operation of the second switch 52. As a result, the source voltage Vs2 of the second switch 52 can be kept below the withstand voltage of the control circuit Dr.

[0061] On the other hand, even if a short circuit occurs between the drain and source of the second switch 52, followed by a short circuit between the gate and source, and then an open circuit occurs in the third Zener diode 93, the large current is blocked by the second rectifier diode 102. Therefore, it is possible to prevent a large current from flowing through the first Zener diode 71 and the second Zener diode 72, and the operation of the first switch 51 is not affected. As a result, the source voltage Vs1 of the first switch 51 can be kept below the withstand voltage of the control circuit Dr.

[0062] Furthermore, if a short-circuit failure occurs in both the first Zener diode 71 and the second Zener diode 72, or if a short-circuit failure occurs in the fourth Zener diode 92, the output voltage of the emergency power supply 57 will become 0.

[0063] According to the embodiment described above, it is possible to reduce the number of resistors and the mounting area of ​​the resistors on the control board, while suppressing the decrease in reliability of the emergency power supply 57 that occurs when a short-circuit failure occurs in any of the switches 51 and 52.

[0064] <Other Embodiments> Furthermore, each of the above embodiments may be implemented with the following modifications.

[0065] In the fourth embodiment, the third Zener diode 91 may not be provided. In this case, the resistance value of the first individual electrical path including the first rectifier diode 101 and the resistance value of the second individual electrical path including the second rectifier diode 102 should be the same, for example, by setting the forward voltage drop of the second rectifier diode 102 to be greater than the forward voltage drop of the first rectifier diode 101.

[0066] The switch constituting the emergency power supply is not limited to an N-channel MOSFET; 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 may also be used.

[0067] The number of switches connected in series to constitute the emergency power supply is not limited to two; it may be three or more. In this case, the emergency power supply drive circuit should be configured such that the source voltage of each switch decreases as you move from the high-potential switch to the low-potential switch.

[0068] 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]

[0069] 10...High-voltage power supply, 50...Emergency power supply, 51...First switch, 52...Second switch, 61...Resistor, 71...First Zener diode, 72...Second Zener diode, Dr...Control circuit.

Claims

1. In a series power supply (50, 55-57) that steps down the output voltage of a DC power supply (10) and supplies it to a power supply target (Dr), A series connection of multiple transistors (51, 52) connecting the positive terminal side of the DC power supply and the power supply target, A drive circuit (61, 62, 71-73, 80, 81, 91, 92, 101, 102) drives each transistor so that the voltage at the low-potential terminal of each transistor is less than or equal to the withstand voltage of the power supply unit, Equipped with, Each of the transistors in the series power supply has a voltage rating greater than or equal to the output voltage of the DC power supply.

2. The aforementioned drive circuit is Resistor (61) and Zener diodes (71, 72) are provided individually in relation to each of the aforementioned transistors, Equipped with, Each of the Zener diodes has its cathode electrically connected to the gate of the transistor. Each of the Zener diodes is connected in series such that the anode of the higher-potential Zener diode and the cathode of the lower-potential Zener diode are electrically connected to each other. The anode of the Zener diode (72) with the lowest potential among the Zener diodes is electrically connected to ground. The first end of the resistor is electrically connected to the positive terminal side of the DC power supply. The series power supply (50, 56) according to claim 1, wherein the second end of the resistor is electrically connected to the cathode of the highest potential diode (71), which is the highest potential Zener diode among the Zener diodes.

3. The system includes a rectifier diode (80) provided in the path that electrically connects the gate of the highest potential transistor (51), which is the transistor with the highest potential among the aforementioned transistors, and the cathode of the highest potential diode. The series power supply (56) according to claim 2, wherein the cathode of the rectifier diode is electrically connected to the gate of the highest potential transistor.

4. The drive circuit has a reference voltage generation circuit (61, 62, 71-73) provided individually for each transistor, The series power supply (55) according to claim 1, wherein each reference voltage generation circuit generates a voltage to control the voltage at the low-potential terminal of the transistor corresponding to itself to a voltage below the withstand voltage of the power supply target, and supplies the generated voltage to the gate of the transistor.

5. Each of the above reference voltage generation circuits is: Zener diodes (71-73) and Resistors (61, 62) and It has, In each of the above reference voltage generation circuits, the first end of the resistor is electrically connected to the positive terminal side of the DC power supply. In each of the above reference voltage generation circuits, the second terminal of the resistor is electrically connected to the cathode of the Zener diode. The series power supply according to claim 4, wherein in each of the above reference voltage generation circuits, the anode of the Zener diode is electrically connected to ground.

6. The aforementioned drive circuit is Resistor (61) and Individual electrical paths (71, 72, 91, 92, 101, 102) are provided separately for each of the aforementioned transistors, It has, The first end of the resistor is electrically connected to the positive terminal side of the DC power supply. Each of the aforementioned individual electrical paths electrically connects the second end of the resistor to ground. Each of the aforementioned individual electrical circuits includes: Rectifier diodes (101, 102) and Zener diodes (71, 72, 92) generate a voltage to control the voltage at the low-potential terminal of the transistor to a voltage below the withstand voltage of the power supply target, and supply the generated voltage to the gate of the transistor. A system was established, In each of the individual electrical paths, the rectifier diode is provided such that its anode faces the second end of the resistor. The series power supply (57) according to claim 1, wherein in each of the individual electrical paths, the Zener diode is provided on the ground side of the rectifier diode.

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