Semiconductor devices and power converters

Abstract

To provide a semiconductor device constituted by connecting a plurality of power transistors in series which can reduce conduction loss in reverse conduction operation, and a power conversion device using the same.SOLUTION: A signal independent from a gate drive circuit of a first gate drive circuit 3 is input to a drive circuit 5 from a second gate drive circuit 4, when a switching element QN1 of a first stage is in an off state and is reverse conduction operated, switching elements QN2 and QN3 of second and subsequent stages are controlled to be in on states.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a semiconductor device and a power conversion device, and particularly to a technology effective when applied to a high-voltage element configured by connecting a plurality of low-voltage elements in series.

Background Art

[0002] In the development of power semiconductor devices, it is an important issue to realize a device that has a high breakdown voltage, a low on-resistance, and a small switching loss.

[0003] Normally, a power transistor has a drift region disposed between a body region and a drain region. The doping concentration of the drift region is lower than that of the drain region.

[0004] The on-resistance of a conventional power transistor depends on the length of the drift region in the direction of current flow and the doping concentration of the drift region. The on-resistance decreases when the length of the drift region is shortened or the doping concentration of the drift region is increased.

[0005] However, there is a problem that when the length of the drift region is shortened or the doping concentration of the drift region is increased, the breakdown voltage of the device decreases.

[0006] As a method for reducing the on-resistance of a power transistor having a predetermined breakdown voltage, a technique of providing a compensation region doped complementarily to the drift region, a technique of providing a field plate that is insulated from the drift region by a dielectric and connected to, for example, the gate or source terminal of a transistor in the drift region, etc. are well known.

[0007] In these types of power transistors, the compensation zone or the field plate partially secures the doping charges in the drift region by depletion when the device is in the off state, enabling high-concentration doping in the drift region and making it possible to reduce the on-resistance without reducing the breakdown voltage.

[0008] However, the output capacity of these devices tends to be large.

[0009] As background technology for this field, for example, there is technology like that described in Patent Document 1.

[0010] Patent Document 1 discloses a semiconductor device that can improve breakdown voltage and reduce output capacitance by autonomously controlling multiple power transistors in a cascode connection.

[0011] The technology described in Patent Document 1 offers not only performance advantages for power transistors, such as improved breakdown voltage, reduced on-resistance, and reduced switching losses, but also the advantage of simplified design, as the breakdown voltage can be changed by varying the number of cascode connection stages. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] U.S. Patent Application Publication No. 2012 / 0175635 [Overview of the project] [Problems that the invention aims to solve]

[0013] However, the technology disclosed in Patent Document 1 above has the following problems because it uses a cascode connection that connects the gate electrode to the source electrode of the previous stage.

[0014] (Problem 1) Since the second and subsequent power transistors must be normally-on type power transistors that conduct at a gate voltage of 0V, the degree of freedom in the design and manufacturing process of the power transistors is reduced. Also, when the power transistor is turned on (conducts), the gate-source voltage cannot be made above 0V, which presents a problem in that the channel resistance cannot be made sufficiently small. Furthermore, when the power transistor is reverse-conducted during freewheeling operation, the gate-source voltage is close to 0V, which also presents a problem in that the channel resistance cannot be made sufficiently small.

[0015] (Problem 2) In Patent Document 1, the breakdown voltage of the second and subsequent power transistors is limited by the breakdown voltage of the gate oxide film, and the breakdown voltage of individual power transistors is usually limited to about 20V. Furthermore, in order to obtain a higher breakdown voltage, it is necessary to increase the number of stages in the cascode connection, but as the number of stages increases, the number of power transistor channels and the number of contacts in series connecting the power transistors also increases, which leads to the problem of increased parasitic resistance.

[0016] (Problem 3) Reliability is reduced because multiple power transistors are connected in series. For example, in Patent Document 1, if the source-drain connection of even one of the power transistors connected in series is destroyed, all power transistors in the subsequent stages after the destroyed power transistor cannot be turned off, resulting in a significant decrease in breakdown voltage.

[0017] Therefore, to address the above-mentioned problem 1, it is desirable to realize a semiconductor device having a circuit configuration in which the second and subsequent power transistors among multiple power transistors connected in series can be autonomously controlled in conjunction with the first-stage power transistor, even if they are normally off type, that is, a circuit configuration in which a positive gate-source voltage can be applied to the second and subsequent power transistors when the first-stage power transistor is ON. Furthermore, in order to reduce conduction losses during reverse conduction operation, it is desirable to realize a semiconductor device having a circuit configuration in which a positive gate-source voltage can always be applied to the second and subsequent power transistors during reverse conduction operation.

[0018] Furthermore, in response to the above-mentioned problem 2, it is desirable to realize a semiconductor device in which the breakdown voltage of the second and subsequent power transistors is not limited by the breakdown voltage of the gate oxide film. In addition, it is important to appropriately design the ratio of parasitic resistances such as channel resistance and contact resistance within the resistive components of the power transistors, so that the number of series-connected power transistors from the second stage onward can be freely designed for a given target breakdown voltage.

[0019] Furthermore, to address the above-mentioned problem 3, it is desirable to realize a semiconductor device in which, even if some of the power transistors connected in series experience a source-drain breakdown voltage failure (short circuit), the other power transistors can be turned off, and the overall breakdown voltage of the series of power transistors connected in series does not decrease significantly.

[0020] Therefore, the object of the present invention is to provide a highly reliable semiconductor device and a power conversion device using the same, which is configured by connecting a plurality of power transistors in series, in which normally off type power transistors can be used for each power transistor, and in which conduction losses during reverse conduction operation can be reduced by always applying a positive gate-source voltage to the gates of the second and subsequent power transistors, and even if the source-drain of some power transistors fails to withstand voltage, the withstand voltage of the semiconductor device as a whole does not drop significantly. [Means for solving the problem]

[0021] To solve the above problems, the present invention provides a semiconductor device comprising, for example, a plurality of switching elements connected in series in multiple stages, and a drive circuit for driving the plurality of switching elements, wherein when m is an integer of 3 or more, the plurality of switching elements connected in series in multiple stages have switching elements from the 1st stage to the mth stage connected in series with each other, the drive circuit has a plurality of elements from the 1st stage to the m-1th stage for driving the next stage of the switching elements, a gate drive signal that controls the on / off state of the 1st stage switching element is input to the gate of the 1st stage switching element from a first gate drive circuit, and the 1st stage of the drive circuit The element receives a signal independent of the gate drive signal from a second gate drive circuit for driving the second and subsequent switching elements, and the drive circuit controls the plurality of switching elements such that when the first-stage switching element is ON, the second and subsequent switching elements are also turned ON in conjunction; when the first-stage switching element is OFF and in a voltage blocking state, the second and subsequent switching elements are also turned OFF and in a voltage blocking state in conjunction; and when the first-stage switching element is OFF and in reverse conduction operation, the second and subsequent switching elements are turned ON.

[0022] Furthermore, the power conversion device of the present invention is characterized by using the above-described semiconductor device as a switching element. [Effects of the Invention]

[0023] According to the present invention, a semiconductor device is configured by connecting a plurality of power transistors in series, wherein normally-off power transistors can be used for each power transistor, and furthermore, a positive gate-source voltage can always be applied to the gates of the second and subsequent power transistors during reverse conduction operation to reduce conduction losses during reverse conduction operation, and even if the source-drain voltage of some power transistors fails to withstand, the overall withstand voltage of the semiconductor device does not drop significantly, thus realizing a highly reliable semiconductor device and a power conversion device using the same.

Brief Description of the Drawings

[0024] [Figure 1] It is a circuit diagram showing the configuration of the semiconductor device of Example 1. [Figure 2] It is a circuit diagram showing the configuration of the semiconductor device of Example 2. [Figure 3] It is a circuit diagram showing the configuration of the semiconductor device of Example 3. [Figure 4] It is a circuit diagram showing the configuration of the semiconductor device of Example 4. [[ID=E17]] [Figure 5] It is a circuit diagram showing the configuration of the semiconductor device of Example 5. [Figure 6] It is a circuit diagram showing the configuration of the semiconductor device of Example 6. [Figure 7] It is a circuit diagram showing the configuration of the semiconductor device of Example 7.

Modes for Carrying Out the Invention

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each figure and each embodiment, the same or similar components are denoted by the same reference numerals, and redundant descriptions are omitted. s

Embodiment

[0026] FIG. 1 is a circuit diagram showing the configuration of the semiconductor device of Example 1.

[0027] As shown in FIG. 1, the semiconductor device 10 of Example 1 includes a plurality of switching elements QN1, QN2, QN3 connected in series in multiple stages, and a drive circuit 5 for driving the plurality of switching elements QN1, QN2, QN3. Further, the semiconductor device 10 has a source terminal 1 and a drain terminal 2. [[ID=D45]]

[0028] It should be noted that there seems to be an error in the original text where "[[ID=E17]]" is likely a mislabeled "". This has been corrected in the translation for consistency.Figure 1 shows an example in which MOSFETs are used as power transistors (elements used in multiple switching elements QN1, QN2, QN3 and the drive circuit 5) that constitute the semiconductor device 10. However, IGBTs (Insulated Gate Bipolar Transistors) may be used as power transistors for multiple switching elements QN1, QN2, QN3 connected in series in multiple stages, or HEMTs (High Electron Mobility Transistors) made of materials such as gallium nitride (GaN) may be used. When using IGBTs as switching elements QN1, QN2, QN3, a diode connected in antiparallel to the IGBT may be added to the configuration. Also, when using IGBTs, source terminal 1 may be read as emitter terminal and drain terminal 2 may be read as collector terminal.

[0029] The semiconductor device 10 is connected to a first gate drive circuit 3 and a second gate drive circuit 4. Here, the example is given where the first gate drive circuit 3 and the second gate drive circuit 4 are provided outside the semiconductor device 10, but the explanation is not limited to this configuration, and the semiconductor device 10 may be configured to have one or both of the first gate drive circuit 3 and the second gate drive circuit 4 built into it.

[0030] Figure 1 shows an example of three stages of switching elements QN1, QN2, and QN3 connected in series in multiple stages, but it is not limited to this. When m is an integer of 3 or more, a configuration with switching elements from the 1st to the mth stage connected in series is also possible. In this case, source terminal 1 is connected to the source (s, hereafter the same) of the 1st stage switching element QN1, drain terminal 2 is connected to the drain (d, hereafter the same) of the mth stage switching element QNm (QN3 if m=3), and the sources of the 2nd and subsequent stages of switching elements are connected to the drains of the preceding switching elements. There is no prerequisite for using two stages (m=2) in series, but it is preferable to have three or more stages (m≧3) as this is suitable for high voltage resistance.

[0031] Multiple switching elements QN1, QN2, and QN3 are transistors having a first conductivity type, and in Example 1, the first conductivity type is described as an n-type example.

[0032] In Example 1, of the multiple switching elements QN1, QN2, and QN3, at least the second and subsequent switching elements QN2 and QN3 use normally-off transistors. The first-stage switching element QN1 may be either a normally-off or normally-on type.

[0033] The drive circuit 5 has multiple elements from the 1st stage to the m-1th stage for driving the next stage switching elements QN2 to QNm.

[0034] As shown in Figure 1, the drive circuit 5 of Embodiment 1 has normally-off transistors AP1, AP2, BP1, and BP2 having a second conductivity type. Transistors AP1 and BP1 constitute the first stage elements, and transistors AP2 and BP2 constitute the second stage elements.

[0035] The gate (g, hereafter denoted as such) of the first-stage switching element QN1 is input from the first gate drive circuit 3 to control the on / off state of the first-stage switching element QN1.

[0036] The first-stage elements AP1 and BP1 of the drive circuit 5 receive signals that are independent of the gate drive signals of the first gate drive circuit 3, and are used to drive the second and subsequent switching elements QN2 and QN3 from the second gate drive circuit 4.

[0037] The drive circuit 5 controls the multiple switching elements QN2 and QN3 such that when the first-stage switching element QN1 is ON, the second and subsequent switching elements QN2 and QN3 are also turned ON in conjunction; when the first-stage switching element QN1 is OFF and in a voltage blocking state, the second and subsequent switching elements QN2 and QN3 are also turned OFF and in a voltage blocking state in conjunction; and when the first-stage switching element QN1 is OFF and in reverse conduction operation, the second and subsequent switching elements QN2 and QN3 are turned ON.

[0038] According to the semiconductor device 10 of Embodiment 1, a signal independent of the gate drive signal of the first gate drive circuit 3 is input from the second gate drive circuit 4 to the drive circuit 5. When the first-stage switching element QN1 is in the off state and in reverse conduction operation, the second and subsequent switching elements QN2 and QN3 are controlled to be in the on state. As a result, even during reverse conduction operation, current flows through the channels of the second and subsequent switching elements QN2 and QN3 in the on state. Therefore, voltage drops due to the freewheeling diodes (diodes built into the MOSFET or diodes connected in antiparallel to the IGBT) of the second and subsequent switching elements QN2 and QN3 can be avoided, and conduction losses during reverse conduction operation can be reduced.

[0039] Regarding the signal from the second gate drive circuit 4, it is desirable that an ON signal be input from the second gate drive circuit 4 when at least the first-stage switching element QN1 is ON or in reverse conduction operation. Alternatively, an ON signal may be always input from the second gate drive circuit 4 when the multiple switching elements QN1, QN2, and QN3 are operating normally. For example, a constant voltage source can be used as the second gate drive circuit 4. By using a constant voltage source, the second gate drive circuit 4 can be made into a simpler configuration.

[0040] Next, we will describe a specific example of the configuration of the drive circuit 5 in the semiconductor device 10 of Embodiment 1.

[0041] The drive circuit 5 has a first element consisting of normally-off transistors AP1 and AP2 having a second conductivity type, from the first stage to the (m-1)th stage, and a second element consisting of normally-off transistors BP1 and BP2 having a second conductivity type, from the first stage to the (m-1)th stage. Here, m=3, so it is from the first stage to the second stage, but in the following explanation, we will also consider the case where m is 4 or greater.

[0042] The first element of the first stage, transistor AP1, has a signal input from the second gate drive circuit 4 to its drain, its gate is connected to the source of the next stage switching element QN2, and its source is connected to the gate of the next stage switching element QN2.

[0043] The second element of the first stage, transistor BP1, has its drain connected to the source of the next stage switching element QN1, and its gate receives a signal from the second gate drive circuit 4, with its source connected to the gate of the next stage switching element QN2.

[0044] The first element, transistor AP2, from the second stage to the (m-1)th stage, has its drain connected to the gate of the switching element QN2 in the same stage, its gate connected to the source of the switching element QN3 in the next stage, and its source connected to the gate of the switching element QN3 in the next stage.

[0045] The second element from the second stage to the (m-1) stage, transistor BP2, has its drain connected to the source of the next stage switching element QN3, its gate connected to the gate of the same stage switching element QN2, and its source connected to the gate of the next stage switching element QN3.

[0046] Next, an example of the operation of the semiconductor device 10 of Example 1 will be described.

[0047] Here, we assume that the drain-source breakdown voltage of the switching elements QN1, QN2, and QN3, and the transistors AP1, AP2, BP1, and BP2 is 20V, and that these are connected to operate as a single semiconductor device 10. Therefore, the gate of the semiconductor device 10 is the gate of the first-stage switching element QN1, the source is the source of the first-stage transistor QN1, and the drain is the drain of the final, third-stage switching element QN3.

[0048] Furthermore, the second gate drive circuit 4 outputs an ON signal (for example, a +15V signal relative to the potential of source terminal 1) at least when the semiconductor device 10 is conducting (on state) or in reverse conducting state. In Embodiment 1, as an example, a constant voltage source that always outputs an ON signal of +15V relative to the potential of source terminal 1 is used.

[0049] First, let's explain the behavior during blocking.

[0050] As an example of operation during blocking, we will explain using the case where a voltage is applied to the drain terminal 2 and the first gate drive circuit 3 outputs an off signal (for example, 0V or less).

[0051] The off signal from the first gate drive circuit 3 turns off the switching element QN1, and the drain potential of the switching element QN1 rises. When the drain potential of the switching element QN1 rises to 15V or higher, the transistor AP1 turns off, and then the transistor BP1 turns on. Consequently, the gate and source of the switching element QN2 become at the same potential, the switching element QN2 turns off, and the drain voltage of the switching element QN2 rises.

[0052] Similarly, transistor AP2 turns off, and transistor BP2 turns on. Consequently, the gate and source of switching element QN3 become at the same potential, switching element QN3 turns off, and the drain voltage of switching element QN3 rises.

[0053] Through the series of operations described above, the switching elements QN1, QN2, and QN3 connected in series, and the transistors AP1 and AP2 connected in series, are simultaneously turned off, resulting in high voltage withstand performance.

[0054] Next, we will explain the operation when the circuit is connected.

[0055] As an example of operation during conduction, we will explain using a state in which a voltage is applied to the drain terminal 2 via a load (not shown) and the first gate drive circuit 3 outputs an ON signal (for example, 15V).

[0056] The ON signal from the first gate drive circuit 3 turns on the switching element QN1, and the drain potential of the switching element QN1 decreases. Consequently, transistor AP1 turns on and transistor BP1 turns off. Then, the charge supplied from the second gate drive circuit 4 accumulates at the gate of the switching element QN2, turning on the switching element QN2, and the drain potential of the switching element QN2 decreases.

[0057] Similarly, transistor AP2 turns ON and transistor BP2 turns OFF. As a result, the charge supplied from the second gate drive circuit 4 is accumulated on the gate of switching element QN3, switching element QN3 turns ON, and the potential at drain terminal 2 decreases.

[0058] Through the series of operations described above, the series-connected switching elements QN1, QN2, and QN3 are turned on in conjunction, allowing current to conduct.

[0059] Next, we will explain the operation during reverse conduction.

[0060] As an example of operation during reverse conduction, we will explain using the example of the reverse conduction operation that occurs when the inverter is recirculating, where current flows from the source to the drain, and where the first gate drive circuit 3 is outputting an off signal (for example, 0V or less).

[0061] The switching element QN1 is in the off state due to the off signal from the first gate drive circuit 3, and current flows from the source to the drain via the freewheeling diode (in this case, the PN diode built into the switching element QN1).

[0062] At this time, the drain potential of switching element QN1 is lower than the source potential, so transistor AP1 is ON and transistor BP1 is OFF. Therefore, the charge supplied from the second gate drive circuit 4 is stored at the gate of switching element QN2, switching element QN2 is ON, and current flows from source to drain through the channel of switching element QN2.

[0063] Similarly, since the drain potential of switching element QN2 is lower than the source potential, transistor AP2 is ON and transistor BP2 is OFF. Therefore, the charge supplied from the second gate drive circuit 4 is stored at the gate of switching element QN3, switching element QN3 is ON, and current flows from source to drain through the channel of switching element QN3.

[0064] The above series of operations allows current to be reversed from source terminal 1 to drain terminal 2. At this time, the second and subsequent switching elements QN2 and QN3, which are connected in series, are in the ON state, and current flows through the channel. This avoids the voltage drop caused by the freewheeling diodes of the second and subsequent switching elements QN2 and QN3 (in this case, the PN diodes built into the switching elements QN2 and QN3), thereby reducing conduction losses during reverse conduction operation.

[0065] As another example of operation during reverse conduction, we will explain using the case where the first gate drive circuit 3 is outputting an ON signal (for example, 15V).

[0066] The switching element QN1 is turned on by the ON signal from the first gate drive circuit 3, and current flows from source to drain through the channel of switching element QN1. Similarly, in switching elements QN2 and QN3, current flows from source to drain through the channel as described above.

[0067] The above series of operations allows current to be reversed from source terminal 1 to drain terminal 2. At this time, the series-connected switching elements QN1, QN2, and QN3 are in the ON state, and current flows through the channel, so the voltage drop due to the freewheeling diodes of the switching elements QN1, QN2, and QN3 (in this case, the PN diodes built into the switching elements QN1, QN2, and QN3) can be avoided, and conduction losses during reverse conduction operation can be reduced.

[0068] Next, we will explain the operation that occurs when a short circuit occurs between the drain and source of some switching elements.

[0069] As an example of the operation when a short-circuit failure occurs in a switching element, we will explain using the example of a situation where a short circuit occurs between the drain and source of switching element QN2, and a voltage is applied to the drain terminal 2, and the first gate drive circuit 3 is outputting an off signal (for example, 0V or less).

[0070] As described above, the off signal from the first gate drive circuit 3 turns off the switching element QN1 and transistor AP1, and turns on transistor BP1. However, since the drain-source of switching element QN2 is short-circuited, the potential difference between the drain and source of switching element QN2 is small. Nevertheless, if this potential difference is several volts or more (greater than or equal to the absolute value of the gate threshold voltage of transistor BP2 + the built-in potential of the PN diode built into transistor BP2), transistor BP2 will turn on, the gate-source of switching element QN3 will be at the same potential, and switching element QN3 will be turned off.

[0071] Even if the drain-source potential difference of switching element QN2 is smaller than the aforementioned potential, if the absolute value of the gate threshold voltage of switching element QN3 is greater than the absolute value of the gate threshold voltage of transistor BP2, switching element QN3 will be in the off state. Therefore, it is desirable to configure the system so that the absolute value of the gate threshold of the second element is greater than the absolute value of the gate threshold of the next switching element.

[0072] Furthermore, as another example of the operation when a short-circuit failure occurs in the switching element, we will explain using the case where a voltage is applied to the drain terminal 2 via a load (not shown) and the gate drive circuit 3 outputs an ON signal (e.g., 15V).

[0073] Even if the drain-source of switching element QN2 is short-circuited, when conduction is maintained, the voltage applied between the drain-source of switching elements QN1, QN2, and QN3 is the same as during normal operation, and they can operate as normal.

[0074] Furthermore, it can operate in the same way as under normal conditions even when reverse conduction is occurring.

[0075] As a result, even when the drain-source of switching element QN2 is short-circuited, the next switching element QN3 (and all subsequent switching elements if there are many in series) can be turned off. Therefore, compared to normal operation, the degradation of the voltage withstand performance is limited to only the portion that switching element QN2 is originally responsible for. Furthermore, conduction and reverse conduction operations can be performed as in normal operation.

[0076] Therefore, even if some of the switching elements in the semiconductor device 10 short-circuit, the entire semiconductor device 10 can continue to operate.

[0077] As described above, the semiconductor device of Embodiment 1 is a semiconductor device configured by connecting multiple power transistors in series, in which normally-off power transistors can be used for each power transistor, and furthermore, a positive gate-source voltage can always be applied to the gates of the second and subsequent power transistors during reverse conduction operation to reduce conduction losses during reverse conduction operation, and even if the source-drain of some power transistors fails to withstand voltage, the overall withstand voltage of the semiconductor device does not drop significantly, thus realizing a highly reliable semiconductor device. [Examples]

[0078] Figure 2 is a circuit diagram showing the configuration of the semiconductor device of Example 2.

[0079] Example 2 is a modification of Example 1, and the difference from Example 1 is that the first element in the first stage of the drive circuit 5 is replaced with a diode D1. When the first conductivity type is n type, the anode (a, hereafter denoted by the symbol) of diode D1 receives the signal from the second gate drive circuit 4, and the cathode (k, hereafter denoted by the symbol) is connected to the gate of the second stage switching element QN2. A feature of Example 2 is that the turn-off operation, which transitions from the on state to the off state, is fast. Other than this, the configuration and effects are the same as in Example 1, so we will explain the differences from Example 1 and omit redundant explanations.

[0080] First, as an example of operation during conduction, we will explain a state in which a voltage is applied to the drain terminal 2 via a load (not shown), and the first gate drive circuit 3 outputs an ON signal (for example, 15V).

[0081] The ON signal from the first gate drive circuit 3 turns on the switching element QN1, and the drain potential of the switching element QN1 is low. Therefore, the output (15V) of the second gate drive circuit is input to the gate of the switching element QN2 via the diode D1, turning on the switching element QN2 and lowering the drain voltage of the switching element QN2. From this point onward, as in Embodiment 1, the switching element QN3 also turns on, and as a result, the semiconductor device 10 turns on.

[0082] Next, as an example of operation during blocking, we will explain the operation in which the output of the first gate drive circuit 3 changes from an ON signal to an OFF signal (for example, below 0V).

[0083] First, the switching element QN1 turns off due to the off signal from the first gate drive circuit 3, causing the drain potential of switching element QN1 to rise. Then, due to capacitive coupling, the gate potential of switching element QN2 rises relative to the source terminal 1. In the configuration of Embodiment 1, the gate potential of switching element QN2 was maintained at 15V relative to the source terminal 1 by discharging charge to the second gate drive circuit 4 via the ON transistor AP1. However, in Embodiment 2, since diode D1 is connected, discharge to the second gate drive circuit 4 is prevented, and a positive potential difference is generated between the cathode and anode of diode D1, turning on transistor BP1. Consequently, the gate charge of switching element QN2 flows into the drain of switching element QN1, accelerating the rise in the drain potential of switching element QN1. The subsequent operation is the same as in Embodiment 1.

[0084] According to Example 2, the acceleration of the drain potential rise of the switching element QN1 speeds up the turn-off operation of the semiconductor device 10 as a whole. [Examples]

[0085] Figure 3 is a circuit diagram showing the configuration of the semiconductor device of Example 3.

[0086] Example 3 is a modification of Example 1, and the difference from Example 1 is that the drains of the second elements, transistors BP1 and BP2, from the first stage to the m-1 stage, are connected to the sources of the switching elements QN1 and QN2 in the same stage. A feature of Example 3 is that the switching elements QN2 and QN3 from the second stage onward may be normally-off or normally-on types, or a mixture of both. Since the configuration and effects are the same as in Example 1, we will focus on explaining the differences from Example 1 and omit redundant explanations.

[0087] First, as an example of operation during blocking, we will explain the situation where a voltage is applied to the drain terminal 2 and the first gate drive circuit 3 outputs an off signal (for example, 0V or less).

[0088] The switching element QN1 is in the off state due to the off signal from the first gate drive circuit 3, and the drain potential of switching element QN1 rises. When the drain potential of switching element QN1 rises to 15V or higher, transistor AP1 turns off, and then transistor BP1 turns on. Therefore, the gate and source terminals 1 of switching element QN2 become at the same potential, and a negative voltage of the same magnitude as the voltage applied between the drain and source of switching element QN1 is applied between the gate and source of switching element QN2, causing switching element QN2 to turn off and its drain voltage to rise.

[0089] Similarly, transistor AP2 turns off, and transistor BP2 turns on. Consequently, the gate of switching element QN3 and the source of switching element QN2 are at the same potential, and a negative voltage equal in magnitude to the voltage applied between the drain and source of switching element QN2 is applied between the gate and source of switching element QN3. As a result, switching element QN3 turns off, and the drain voltage of switching element QN3 rises.

[0090] According to Example 3, a negative voltage can be applied between the gate and source of the switching elements QN2 and QN3, making it possible to turn off the switching elements QN2 and QN3 even if they are normally off types.

[0091] The configuration of Example 3 may also be applied to Example 2. [Examples]

[0092] Figure 4 is a circuit diagram showing the configuration of the semiconductor device of Example 4.

[0093] Example 4 is a modification of Example 1, and the difference from Example 1 is that p-type is used as the first conductivity type and n-type as the second conductivity type. Therefore, the switching elements QP1, QP2, and QP3 are composed of p-type transistors, and the transistors AN1, AN2, BN1, and AN2 are composed of n-type transistors. Consequently, the drain terminal 2 has a lower potential than the source terminal 1. The basic circuit configuration of Example 4 is the same as that of Example 1, except that the conductivity types are swapped. Since the configuration and effects are the same as those of Example 1, we will explain the differences from Example 1 and omit redundant explanations.

[0094] The first gate drive circuit 3 receives, for example, -15V as an ON signal and, for example, 0V or higher as an OFF signal. The second gate drive circuit 4 can be a constant voltage source that always receives an ON signal of -15V relative to the potential of the source terminal 1, but as in Embodiment 1, it is not limited to this.

[0095] The operation of Example 4 is the same as that of Example 1, except for the difference in the conductive type, so the explanation will be omitted.

[0096] According to Example 4, the same effect as in Example 1 can be obtained even if p-type is used as the first conductivity type and n-type as the second conductivity type.

[0097] The configuration of Example 3 may also be applied to Example 4. [Examples]

[0098] Figure 5 is a circuit diagram showing the configuration of the semiconductor device of Example 5.

[0099] Example 5 is a modification of Example 4, and is a combination of Example 4 and Example 2. The difference from Example 4 is that, as with Example 2, the first element of the first stage of the drive circuit 5 is replaced with a diode D1. The difference from Example 2 is that, since the first conductivity type is p-type, the diode D1 has a signal from the second gate drive circuit 4 input to its cathode, and its anode is connected to the gate of the second stage switching element QP2. The characteristic of Example 5 is that, as with Example 2, the turn-off operation from the on state to the off state is fast. Other than this, the configuration and effects are the same as in Example 4, so redundant explanations are omitted.

[0100] The configuration of Example 3 may also be applied to Example 5. [Examples]

[0101] Figure 6 is a circuit diagram showing the configuration of the semiconductor device of Example 6.

[0102] Example 6 is a modification of Example 1, and the differences from Example 1 are that the switching elements QHN1, QHN2, and QHN3 of the semiconductor device 20 have a higher breakdown voltage than the switching elements QN1, QN2, and QN3 of Example 1, for example, QN3 with a breakdown voltage of 20V, for example, switching elements with a breakdown voltage of 100V are used, and the drive circuit 5 has, as a third element, transistors CP1 and CP2 with a breakdown voltage of 80V. In Example 1, in the blocking state, the voltage from the gate of switching element QN2 to switching element QN3, the voltage from the source to the drain of transistor AP2, and the voltage from the gate to the source of transistor BP2 are all equal, so the drain-source breakdown voltage of the switching elements is limited by the gate-source breakdown voltage of transistor BP2 (generally about 20V). In contrast, this embodiment 6 is characterized in that the voltage that can be applied between the drain and source of the switching elements QHN1, QHN2, and QHN3 is not limited by the gate-source breakdown voltage of the second elements of the drive circuit 5, transistors BP1 and BP2. Other than this, the configuration and effects are the same as in embodiment 1, so we will focus on explaining the differences from embodiment 1 and omit redundant explanations.

[0103] The semiconductor device 20 of Example 6 is basically the same as the semiconductor device 10 of Example 1, but the drive circuit 5 has normally-off transistors CP1 and CP2 having a second conductivity type as third elements from the 1st stage to the m-1th stage. The third elements from the 1st stage to the (m-1)th stage, transistors CP1 and CP2, have their gates connected to the sources of the next stage switching elements QN2 and QN3. The third element from the 2nd stage to the (m-1)th stage, transistor CP2, has its drain connected to the gate of the same stage switching element QHN2. The first element from the 2nd stage to the (m-1)th stage, transistor AP2, has its drain connected to the gate of the same stage switching element QHN2 via the third element transistor CP2. The third element of the 1st stage, transistor CP1, has a signal from the second gate drive circuit 4 input to its drain. The first element of the 1st stage, transistor AP1, has a signal from the second gate drive circuit 4 input via the third element transistor CP1 of the 1st stage. The second element of the 1st stage, transistor BP1, has a signal from the second gate drive circuit 4 input to its gate via the third element transistor CP1 of the 1st stage.

[0104] In the case where the first element of the first stage is transistor AP1, as in Embodiment 1, the drain of transistor AP1 is connected to the second gate drive circuit 4 via transistor CP1, which is the third element of the same stage, and a signal from the second gate drive circuit 4 is input.

[0105] Furthermore, Embodiment 6 may be combined with Embodiment 2. In the case where the first element of the first stage is a diode D1, as in Embodiment 2, the anode of diode D1 is connected to the second gate drive circuit 4 via a transistor CP1, which is the third element of the same stage, so that a signal from the second gate drive circuit 4 is input.

[0106] In Example 6, the breakdown voltage of the switching elements QHN1, QHN2, and QHN3 was set to 100V, for example, but switching elements with any breakdown voltage may be used. Also, the breakdown voltage of the third element, transistors CP1 and CP2, was set to 80V, for example, but transistors with any breakdown voltage may be used.

[0107] Next, an example of the operation of the semiconductor device 20 in Example 6 will be described.

[0108] The blocking operation is the same as in Example 1, except that transistors CP1 and CP2 turn off at the same time as transistors AP1 and AP2, respectively. As a result, the series-connected switching elements QHN1, QHN2, and QHN3 and the series-connected transistors CP1, AP1, CP2, and AP2 turn off in conjunction, resulting in high voltage withstand performance.

[0109] In Example 6, the breakdown voltages of the switching elements QHN1, QHN2, and QHN3 are each 100 V, and the breakdown voltages of the transistors CP1 and CP2 are each 80 V, resulting in a high breakdown voltage of 300 V for the semiconductor device 20.

[0110] The operation during conduction is the same as in Example 1, except that transistors CP1 and CP2 turn on at the same timing as transistors AP1 and AP2, respectively.

[0111] The operation during reverse conduction is the same as in Example 1, except that transistors CP1 and CP2 turn on at the same timing as transistors AP1 and AP2, respectively.

[0112] The operation when a short-circuit failure occurs in the switching element is the same as in Example 1, except that transistors CP1 and CP2 turn off at the same timing as transistors AP1 and AP2, respectively.

[0113] In Example 6, the breakdown voltage of the second-stage switching element QHN2 can be set to the sum of the breakdown voltage of the third element of the first stage, transistor CP1, and the breakdown voltage of the first element of the first stage, transistor AP1. The same applies to subsequent stages. Therefore, according to Example 6, the voltage that can be applied between the drain and source of the switching elements QHN1, QHN2, and QHN3 is not limited by the gate-source breakdown voltage of the second elements of the drive circuit 5, transistors BP1 and BP2. As a result, the source-drain breakdown voltage and gate-source breakdown voltage of each power transistor can be designed independently, enabling the realization of a semiconductor device with a high degree of design and manufacturing freedom.

[0114] Furthermore, the combination is not limited to Example 2; the configurations of Examples 3 to 5 may also be applied to Example 6. [Examples]

[0115] Figure 7 is a circuit diagram showing the configuration of the semiconductor device of Example 7.

[0116] Example 7 is a modification of Example 6. The difference from Example 6 is that the drive circuit 5 has diodes E1 and E2 connected in antiparallel to each other as the fourth elements from the 1st stage to the m-1st stage, and the transistors CP1 and CP2, which are the third elements from the 1st stage to the m-1st stage, are connected to the sources of the next stage switching elements QHN2 and QHN3 via the diodes E1 and E2, which are the fourth elements of the same stage and connected in antiparallel to each other. According to Example 7, the turn-off operation is faster than in Example 6. Since the configuration and effects are the same as in Example 6, we will explain the differences from Example 6 and omit redundant explanations.

[0117] The operation of Embodiment 7 will be explained using the example of when the output of the first gate drive circuit 3 changes from an ON signal (e.g., 15V) to an OFF signal (e.g., 0V or less).

[0118] The off signal from the first gate drive circuit 3 causes the switching element QHN1 to transition from the on state to the off state, and the potential of the drain of the switching element QHN1 rises. When the drain potential of the switching element QHN1 rises to 15V or higher, transistor AP1 first transitions from the on state to the off state, and then transistor BP1 transitions from the off state to the on state.

[0119] At this point, the gate voltage of transistor CP1 is lower than the gate voltage of transistor AP1 by the amount of the internal potential of diode E1, which is connected in antiparallel to it, so it has not yet transitioned to the off state. Therefore, the gate and source of switching element QHN2 become the same potential, and switching element QHN2 turns off. Furthermore, as the drain voltage of switching element QHN1 rises, transistor CP1 transitions from the on state to the off state.

[0120] Since switching element QHN2 has transitioned to the off state, the drain potential of switching element QHN2 rises, causing transistor AP2 to transition from the on state to the off state, and then transistor BP2 to transition from the off state to the on state.

[0121] At this point, the gate voltage of transistor CP2 is lower than the gate voltage of transistor AP2 by the amount of the internal potential of diode E2, which is connected in antiparallel to it, so it has not yet transitioned to the off state. Therefore, the gate and source of switching element QHN3 become the same potential, and switching element QHN3 turns off. Furthermore, as the drain voltage of switching element QHN2 rises, transistor CP2 transitions from the on state to the off state.

[0122] Since the switching element QHN3 has transitioned to the off state, the drain potential of the switching element QHN3 rises.

[0123] Through the series of operations described above, the series-connected switching elements QHN1, QHN2, and QHN3 and the series-connected transistors CP1, AP1, CP2, and AP2 are all turned off in conjunction, resulting in high voltage withstand performance.

[0124] In Example 7, as described above, transistor AP1 turns off earlier than transistor CP1, and transistor AP2 turns off earlier than transistor CP2. As a result, the source-drain voltage of transistors AP1 and AP2 rises more rapidly, and consequently, transistors BP1 and BP2 turn on faster. Because transistors BP1 and BP2 turn on faster, the charge accumulated on the gates of switching elements QHN2 and QHN3 is discharged more quickly, resulting in faster turn-off of switching elements QHN2 and QHN3.

[0125] In addition, the configurations of Examples 2 to 5 may be applied to Example 7, similar to Example 6. [Examples]

[0126] Example 8 is a modification of Examples 6 and 7. The difference from Example 6 is that in the drive circuit 5, the absolute value of the gate threshold of the third elements, transistors CP1 and CP2, from the 1st stage to the (m-1)th stage is smaller than the absolute value of the gate threshold of the first elements, transistors AP1 and AP2, in the same stage. The difference from Example 7 is that in Example 7, the timing at which the third elements, transistors CP1 and CP2, turn off is delayed compared to the first elements, transistors AP1 and AP2, by using diodes E1 and E2 connected in antiparallel to each other, whereas in Example 8, this is achieved by adjusting the absolute value of the gate threshold. According to Example 8, similar to Example 7, the turn-off operation is faster than in Example 6.

[0127] The circuit configuration of Example 8 is the same as that of Figure 6. Alternatively, the configuration of Example 8 may be applied to Example 7, and the absolute value of the gate threshold may be set to match that of Example 8 in the circuit configuration of Figure 7.

[0128] Since the rest of the configuration and effects are the same as in Example 6, we will omit any redundant explanations. [Examples]

[0129] Example 9 is an example of a power conversion device.

[0130] The semiconductor devices 10 and 20 described in any of Examples 1 to 8, or semiconductor devices obtained by appropriately combining and applying Examples 1 to 8, can be used as switching elements in a power conversion device. Since the configuration of the power conversion device is general, a detailed explanation will be omitted.

[0131] Although embodiments of the present invention have been described above, the present invention is not limited to the configurations described in the embodiments, and various modifications are possible within the scope of the technical idea of ​​the present invention. Furthermore, some or all of the configurations described in each embodiment may be combined and applied. [Explanation of Symbols]

[0132] 1…Source terminal 2…Drain terminal 3…First gate drive circuit 4…Second gate drive circuit 5…Drive circuit 10, 20… Semiconductor equipment AP1, AP2, AN1, AN2... Transistors (first element) BP1, BP2, BN1, BN2... Transistors (second element) CP1, CP2... Transistors (third element) D1... Diode (first element) E1, E2... Diodes connected in antiparallel to each other (the fourth element) QN1, QN2, QN3, QP1, QP2, QP3, QHN1, QHN2, QHN3… Switching elements

Claims

1. A semiconductor device comprising a plurality of switching elements connected in series in multiple stages, and a drive circuit for driving the plurality of switching elements, When m is an integer of 3 or more, the multiple switching elements connected in series in the multi-stage configuration have switching elements from the 1st stage to the mth stage connected in series with each other. The drive circuit has a plurality of elements from the first stage to the m-1 stage for driving the next stage switching element, A gate drive signal is input to the gate of the first stage switching element from the first gate drive circuit to control the on / off state of the first stage switching element. The first stage element of the drive circuit receives a signal that is independent of the gate drive signal and is used to drive the second and subsequent stages of the switching elements from the second gate drive circuit. The aforementioned drive circuit is When the first stage switching element is in the ON state, the second and subsequent stages of switching elements are also turned ON in conjunction. When the first stage switching element is in the off state and voltage blocking state, the second and subsequent stages of switching elements also turn off and enter a voltage blocking state in conjunction with it. When the first stage switching element is in the off state and conducting in reverse, the second and subsequent stages of switching elements are turned on. A semiconductor device characterized by controlling the plurality of switching elements.

2. In claim 1, A semiconductor device characterized in that an ON signal is input from the second gate drive circuit when at least the first stage of the switching element is ON or in reverse conduction operation.

3. In claim 2, A semiconductor device characterized in that an ON signal is always input from the second gate drive circuit while the plurality of switching elements are operating normally.

4. In claim 1, The plurality of switching elements are transistors having a first conductivity type, The semiconductor device is characterized in that the drive circuit has a normally-off transistor having at least a second conductivity type.

5. In claim 4, A semiconductor device characterized in that at least the second and subsequent switching elements are normally-off transistors.

6. In claim 4, A semiconductor device characterized in that at least the second and subsequent switching elements are normally-on type transistors.

7. In claim 4 A semiconductor device characterized in that the first conductivity type is n-type and the second conductivity type is p-type.

8. In claim 4 A semiconductor device characterized in that the first conductivity type is p-type and the second conductivity type is n-type.

9. In claim 4, The source terminal connected to the source of the first-stage switching element, It has a drain terminal connected to the drain of the m-th stage switching element, The source of the second and subsequent switching elements is connected to the drain of the preceding switching element. The aforementioned drive circuit is A first-stage element comprising a normally-off transistor or diode having the second conductivity type, The first elements, from the second stage to the (m-1) stage, are composed of normally-off transistors having the second conductivity type, It has a second element consisting of normally-off transistors having the second conductivity type, from the first stage to the (m-1)th stage, The first elements from the second stage to the m-1 stage are, The drain is connected to the gate of the switching element in the same stage. The gate is connected to the source of the next stage switching element, The source is connected to the gate of the next stage switching element. The second element from the second stage to the m-1 stage is The drain is connected to the source of the switching element in the next stage or the same stage. The gate is connected to the gate of the switching element in the same stage, The source is connected to the gate of the next stage switching element. The second element in the first stage is The drain is connected to the source of the switching element in the next stage or the same stage. The signal from the second gate drive circuit is input to the gate. The source is connected to the gate of the next stage switching element. A semiconductor device characterized by having the following features.

10. In claim 9, The first element of the first stage is a normally-off transistor having the second conductivity type, The signal from the second gate drive circuit is input to the drain. The gate is connected to the source of the next stage switching element, The source is connected to the gate of the next stage switching element. A semiconductor device characterized by having the following features.

11. In claim 9, The first element in the first stage is the diode, If the first conductivity type is n-type, the signal from the second gate drive circuit is input to the anode; if the first conductivity type is p-type, the signal is input to the cathode. If the first conductivity type is n-type, the cathode is connected to the gate of the second-stage switching element; if the first conductivity type is p-type, the anode is connected to the gate of the second-stage switching element. A semiconductor device characterized by having the following features.

12. In claim 9, A semiconductor device characterized in that the drains of the second elements from the first stage to the m-1 stage are connected to the source of the next stage switching element.

13. In claim 9, A semiconductor device characterized in that the drains of the second elements from the first stage to the m-1 stage are connected to the sources of the switching elements in the same stage.

14. In claim 9, The drive circuit has a third element consisting of a normally-off transistor having the second conductivity type, from the first stage to the (m-1)th stage. The third elements from the first stage to the m-1 stage have their gates connected to the source of the next stage switching element. The third elements from the second stage to the m-1 stage have drains connected to the gates of the switching elements in the same stage. The first elements from the second stage to the m-1 stage have drains connected to the gates of the switching elements in the same stage via the third element in the same stage. The third element in the first stage has the signal from the second gate drive circuit input to its drain. The first element of the first stage receives the signal from the second gate drive circuit via the third element of the first stage. The second element in the first stage receives the signal from the second gate drive circuit at its gate via the third element in the first stage. A semiconductor device characterized by having the following features.

15. In claim 14, The drive circuit has a fourth element consisting of a first stage to an m-1 stage, each composed of diodes connected in antiparallel to each other. A semiconductor device characterized in that the gates of the third elements from the first stage to the m-1 stage are connected to the source of the next stage switching element via the fourth element of the same stage.

16. In claim 14, A semiconductor device characterized in that the absolute value of the gate threshold of the third element from the first stage to the m-1 stage is smaller than the absolute value of the gate threshold of the first element in the same stage.

17. A power conversion device characterized by using a semiconductor device according to any one of claims 1 to 16 as a switching element.

Images