Semiconductor switch

Abstract

The invention relates to a semiconductor switch which is formed using a plurality of circuit modules connected in series. The circuit modules each comprise a first transistor (M3) having a source connection (source 3), a control connection (Gate3) and a low-potential connection, and a second transistor (Q2) having a source connection, a control connection and a low-potential connection. Here, the source connection of the second transistor (Q2) is connected to the control connection (Gate3) of the first transistor (M3), and the low potential connection of the second transistor (Q2) is connected to the source connection (Source3) of the first transistor (M3). A driver (V2) is also provided, which is connected to the control connections of the second transistors (Q1, Q2, Q3, Q4, Q5, Q6) of the respective circuit modules. For a subset of the plurality of circuit modules, means for reducing the control joint voltage of the first transistor are introduced in the respective connections to the driver. This measure makes it possible to better set the maximum short-circuit current or to achieve a more controlled process when the semiconductor switch according to the invention is defective.

Description

Technical Field

[0001] The present invention relates to a semiconductor switch. Background Art

[0002] Advances in the development of semiconductor components have led to new switch concepts that can replace traditional low-voltage switches, which are typically electromechanical. These new concepts involve, for example, circuit breakers or motor starters, but can also be used to switch higher currents, such as with circuit breakers. The term SSCB (solid-state circuit breaker) is also common for circuit breakers and circuit breakers.

[0003] The fast response time of semiconductor components is crucial here, as it prevents damage due to overload. This means the switch interrupts the current flow before the semiconductor components can be damaged. However, due to the higher sensitivity of semiconductor components compared to conventional switching elements, it is possible for the semiconductor-based switching mechanism to become damaged and the switch to no longer function properly.

[0004] An effective possibility for realizing a semiconductor switch with relatively low conduction losses is to implement the semiconductor switch as a series circuit of transistors (for example MOSFETs or IGBTs). Summary of the Invention

[0005] The technical problem to be solved by the present invention is to improve a switch formed by a series circuit of transistors.

[0006] This object is achieved by claim 1. Advantageous developments are specified in the dependent claims.

[0007] The present invention is based on a semiconductor switch having a plurality of circuit modules connected in series. Each of these circuit modules comprises a first transistor having a source connection, a control connection, and a low-potential connection, wherein the source connection is a source connection or an emitter connection, the control connection is a gate connection or a base connection, and the low-potential connection is a drain connection or a collector connection. Furthermore, each of these circuit modules comprises a second transistor having a source connection, a control connection, and a low-potential connection, wherein the source connection is connected to the control connection of the first transistor, and the low-potential connection is connected to the source connection of the first transistor (M3).

[0008] The semiconductor switch forms a driver which is connected via a connection to the control connection of the second transistor of the respective circuit module.

[0009] To carry out the optimization described in detail below, for a subset of the circuit modules (for example, one circuit module or two circuit modules), a device (for example, a Zener diode) for reducing the control connection voltage of the corresponding first transistor is introduced in the corresponding connection to the driver.

[0010] The first transistor can be a unipolar transistor, such as a MOSFET. However, it can also be implemented using a bipolar transistor, such as an IGBT (Insulated-Gate Bipolar Transistor) with an antiparallel protective diode (integrated or as an external freewheeling diode). In the case of a unipolar transistor, the control connection voltage would then be the gate-source voltage (hereinafter also referred to as the gate voltage); in the case of a bipolar transistor, the control connection voltage would then be the base-emitter voltage. In the case of an IGBT (bipolar transistor with an insulated gate electrode), which has an insulated gate of the voltage-controlled component (such as a MOSFET) in combination with the bipolar output characteristic of the bipolar transistor, the gate-emitter voltage would then be the gate-emitter voltage.

[0011] The improvements sought with this approach relate to the following:

[0012] 1. Without a device for reducing the control terminal voltage, the current limit depends on the drive voltage, which can lead to increased design complexity in applications. As described below within the scope of the exemplary embodiments, by selectively selecting a circuit module for the targeted introduction of a device for reducing the control terminal voltage, the reverse voltage that develops in the event of a short circuit can be set, thereby enabling the value of the maximum short-circuit current to be adjusted.

[0013] 2. Different levels of stress are placed on the individual first transistors of the semiconductor switch circuit module. In the event of a rapid current increase due to a short circuit, the external transistors (closer to the connection terminals) are less stressed because the current quickly commutates to the load-removing network. The transistor directly supplied by the driver also remains in the linear or ohmic characteristic region, placing less stress on it. One of the transistors shifts its operating point into the blocking region, placing a greater stress on it. (Depending on the transistor type, the designations used here for regions, which are common for MOSFET transistors, may differ; for example, the saturation region and active region may be used for IGBTs; however, the principle applies generally, and the problem is independent of the transistor type.) Which transistor in the circuit is in this unfavorable state is unclear and depends on the specific boundary conditions. However, for durability and simplified maintainability in terms of resource conservation, it is important that the individual transistors experience a higher thermal load, which in turn results in a significantly lower mean time between failures (MTBF). This ensures that if a defect occurs in a semiconductor switch, it is highly likely that one of the power semiconductors is defective. Therefore, a "sacrificial transistor" (a single transistor or a module containing a transistor) is provided for quick and easy replacement (e.g., particularly easy to access, pluggable, marked for easy identification, etc.). This can be achieved by selectively reducing the control connection voltage of semiconductor switches formed using identical circuit modules.

[0014] In another embodiment of the semiconductor switch according to the present invention, the increased loading of the first transistors of a subset of the switching modules having the device for reducing the control connection voltage is compensated by using a first transistor that is different from the other first transistors. Preferably, for predetermined operating conditions (e.g., rated current) of the semiconductor switch, the first transistors of the subset are designed to have a comparable service life or MTBF under the predetermined operating conditions as the other first transistors.

[0015] In one embodiment of the semiconductor switch according to the present invention, the semiconductor switch has an even number of circuit modules, wherein the first half of the circuit modules are connected in series one after another with the same conduction direction, and the second half of the circuit modules are connected in series one after another with opposite conduction directions. Two of the circuit modules are then connected one after another with opposite conduction directions, and a device for reducing the control connection voltage of the first transistor is incorporated into the respective connection to the driver for one circuit module in the first half of the circuit modules and one circuit module in the second half of the circuit modules. The positions of the two circuit modules correspond to each other with respect to the number of circuit modules between them and the circuit module with the corresponding conduction direction adjacent to the circuit module with the opposite conduction direction. The semiconductor switch is then preferably designed with respect to the arrangement of the device for reducing the control connection voltage of the circuit modules in a mirror-symmetrical manner with respect to a line defined by the connection of the two switch modules with different conduction directions.

[0016] There are various design variations for the circuit module. For example, as mentioned above, the first transistor can be a unipolar transistor, such as a MOSFET. However, it can also be implemented using a bipolar transistor, such as an IGBT (insulated gate bipolar transistor) with an antiparallel protective diode (integrated or as an external freewheeling diode).

[0017] According to one embodiment of the circuit module, the connection to the driver is formed by means of a conductor section, in which a blocking diode in the direction of the driver is incorporated.

[0018] According to one configuration of the circuit module, the control terminal and the source terminal of the second transistor are connected to one another, and a blocking diode in the direction of the control terminal is arranged between the control terminal and the source terminal of the second transistor.

[0019] According to one configuration of the circuit module, the control connection and the low potential connection of the second transistor are connected to one another, and a resistor (preferably an ohmic resistor) is arranged between the control connection and the low potential connection of the second transistor.

[0020] According to one embodiment of the circuit module, a voltage limiting device is provided in parallel with the first transistor. A capacitive resistor may also be provided in parallel with the first transistor.

[0021] According to a first design alternative of the circuit module, the control terminal and the source terminal of the first transistor are connected to one another, and a blocking diode in the direction of the control terminal is arranged between the control terminal and the source terminal of the first transistor. This diode is an optional feature and can be implemented, for example, by a Zener diode that limits the maximum control terminal voltage.

[0022] For example, protection diodes and voltage limiting devices can be selectively provided only for circuit modules required for the specific design of the semiconductor switch. For example, the second transistor can be omitted for the circuit module with the shortest distance from the driver, or for a symmetrically constructed semiconductor switch, for both circuit modules with the shortest distance from the driver.

[0023] According to a second design alternative of the circuit module, the circuit module is formed with a third transistor, wherein the third transistor is of the same type as the first transistor, and the first and third transistors are directly connected to one another with their source connections (i.e., they are practically arranged in opposite directions). In this design, the source connection of the second transistor is connected to the control connections of the first and third transistors, and the low potential terminal of the second transistor is connected to the connection of the source connections of the first and third transistors. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Below, the present invention will be described in more detail within the scope of the embodiment according to the accompanying drawings. In the accompanying drawings:

[0025] 1a and 1b show a circuit module for forming a semiconductor switch according to the present invention,

[0026] Figure 2 shows the construction of a semiconductor switch formed using the circuit module according to FIG. 1 a and FIG. 1 b ,

[0027] Figure 3 Shown according to Figure 2 semiconductor switch, wherein, according to the invention, a Zener diode for selected circuit modules is introduced in connection with the driver,

[0028] FIG4a and FIG4b show the following graphs, which show the graphs with Figure 3 The shift of the operating point of the circuit module or the reduction of the on-resistance of the introduced Zener diode, and

[0029] FIG5a and FIG5b show the following tables, which show that in the case of a short circuit, Figure 3 The Zener diode introduced is based on Figure 2 and Figure 3 The influence of the semiconductor switches on the build-up of the cut-off voltage in the circuit module. DETAILED DESCRIPTION

[0030] The present invention is based on a semiconductor switch formed using series-connected circuit modules. Figures 1a and 1b illustrate an implementation of such a circuit module. The module includes a MOSFET M3 having a source terminal Source3, a gate terminal Gate3, and a drain terminal, and a PNP bipolar transistor Q2 having an emitter terminal, a base terminal, and a collector terminal. The emitter terminal is connected to the gate terminal Gate3 of MOSFET M3, and the collector terminal is connected to the source terminal Source3 of MOSFET M3. The gate terminal Gate3 and the source terminal Source3 of MOSFET M3 are interconnected, and a diode D5 (preferably a Zener diode) is arranged between these terminals, which blocks the flow in the direction of the gate terminal Gate3. The base terminal and the emitter terminal of the PNP bipolar transistor Q2 are interconnected, and a diode D4 is arranged in this connection, which blocks the flow in the direction of the base terminal. The base terminal of the PNP bipolar transistor Q2 is also connected to its collector terminal, with a resistor R5 connected in this connection.

[0031] Furthermore, a connection is provided between the base terminal of the PNP bipolar transistor Q2 and the driver V2. This can be achieved from Figure 2 Seen in Figure 2 , a semiconductor switch formed by modules connected in series is shown, which has a driver V2. The driver V2 is connected to the PNP bipolar transistors Q1-Q6 of six circuit modules connected in series. Here, diodes D1, D6, D7, D12, D14 and D16 are also introduced accordingly between the driver V2 and the base connections of the PNP bipolar transistors Q1-Q6, which are cut off in the direction of the driver V2. Fuses S1-S6 are also provided accordingly between the driver V2 and the diodes D1, D6, D7, D12, D14 and D16. In this switch geometry, the semiconductor switch is formed by an even number of modules, wherein the first half of the circuit modules are connected in series with the same conduction direction, and the second half of the circuit modules are connected in series with opposite conduction directions. The semiconductor circuit modules are shown twice in FIG1a and FIG1b, wherein the conduction directions are different. That is, according to Figure 2 The semiconductor switch is composed half of the module according to FIG1a and half of the module according to FIG1b. In this case, the Zener diodes D5 and D18 in FIG1a and FIG1b are optional. Figure 2In the middle of the circuit, two modules with opposite conduction directions are connected in series. Driver V2 is connected to the source connection of the two circuit modules connected in opposite conduction directions and, via this connection and resistor R11, to ground. Resistors R2 and R6 are provided between this connection and the base connections of the PNP bipolar transistors of the two circuit modules, respectively. Furthermore, resistor R1 is provided between the positive terminal of driver V2 and the connection of one of the circuit modules with the same conduction direction. Furthermore, these circuit modules are each connected in parallel with capacitors C1-C6 and voltage limiting devices U1-U6 (e.g., in the form of suppression diodes or varistors). These voltage limiting devices U1-U6 of the circuit modules are optional components. Also shown is voltage V1 and load R3, which is powered by this voltage.

[0032] About the basis Figure 2 The following two points are important for the semiconductor switch structure:

[0033] On the one hand, it is a circuit for alternating current flow (AC or DC with two current flow directions). For unipolar current flow, only half of the circuit shown would be needed (ie a module with transistors with only one conduction direction).

[0034] On the other hand, the modules close to the driver can, in principle, be designed to be switched on without transistors Q5 or Q6. Components D13, D14, D17, and R17, or D15, D16, D18, and R10, can then be omitted, so that these modules consist solely of MOSFETs M1 or M4. However, to switch off all components connected in series as simultaneously as possible, or to achieve symmetry in the turn-off behavior, it is advantageous to design these two modules in a manner similar to the other modules.

[0035] For simplicity, the following describes the operation of a switch with unipolar current flow, which has only Figure 2 , which is half of the circuit module shown in FIG (ie the module having transistors with only one conducting direction).

[0036] Given a suitable selection of the operating voltage, the circuit shown here has an inherent short-circuit current limitation, since a corresponding voltage drop occurs across the components connected in series, depending on the load current.

[0037] Zener diodes D19 and D20 are respectively introduced in the gate paths of the MOSFETs M2 and M5 in the series circuit. These Zener diodes D19 and D20 selectively reduce the gate voltage of these MOSFETs and operate them close to the blocking region.

[0038] Now, if the driver V2 has an output voltage of 15V and the MOSFETs M2 and M5 have zener diodes D19 and D20 connected in series with a voltage of 8V, then all MOSFETs except MOSFETs M2 and M5 are operated at their rated gate voltage of 15V and thus have the smallest possible on-resistance RDSon. This is shown in Figures 4a and 4b. Figure 4a shows the voltage V between the drain and source. DS The current flowing through a typical MOSFET is related to the current flowing through the MOSFET. When the MOSFET reaches saturation, the current almost stops increasing with the voltage V DS The relationship between current and voltage is initially essentially linear (which is equivalent to having essentially constant resistance) before increasing with the rise of . The time it takes to reach saturation depends on the gate voltage V GS The results for different gate voltages V GS =5V, 6V, 7V, 8V and 10V. The boundary between the ohmic region and the blocking region is also plotted, which changes with the gate voltage V GS The increase in drain-source voltage V DS Now, if, for example, a load current of approximately 250 A flows, then for a MOSFET operated at its nominal gate voltage of 15 V, this corresponds to a drain-source voltage V of approximately 0.7 V, plotted in region 1 in FIG. 4 a . DS On the contrary, the gate voltage V GS =7V operation of MOSFETs M2 and M5 at a drain-source voltage of approximately 1.2V V DS The corresponding on-resistance (region 1 and region 2) is given in Figure 4b. GS =15V, the on-resistance of the MOSFET is about 2.8mΩ, while for GS =7V operation of MOSFET M2 and M5, the on-resistance is about 4.8mΩ.

[0039] MOSFETs M2 and M5 operate at a gate voltage of only 7V and therefore generally have higher losses, resulting in higher operating temperatures and longer temperature cycles. This reduces their service life and MTBF (mean time between failures). This means they fail earlier than MOSFETs operated at higher gate voltages. By reducing the gate voltage with a Zener diode, it is possible to determine which MOSFET experiences wear-induced interference. This type of MOSFET is also referred to below as the sacrificial MOSFET.

[0040] This measure increases the total on-resistance of the entire switch (approximately 2 mΩ per sacrificial MOSFET in Figure 4b). However, this increase in on-resistance RDSon is negligible and has a negligible impact on the switch's performance characteristics. While only the two switch modules in the series circuit (with MOSFETs M2 and M5) are operated with a slightly increased RDSon, the other MOSFETs, now operating ideally, compensate for this increase. Therefore, in this example, the RDSon of the six series-connected MOSFETs increases from 6 x 3.6 mΩ = 21.6 mΩ to 5 x 3.6 mΩ + 4.0 mΩ = 22.0 mΩ. However, since the other five MOSFETs operate at 15V, their RDSon also decreases slightly, even though this is not explicitly indicated in Figures 4a and 4b. Thus, it is possible to achieve exactly the same result without even a slight reduction in the total on-resistance or total RDSon. Regardless, this change is smaller than the dissipation value for this parameter given in the data sheet and can be ignored.

[0041] The sacrificial MOSFET now always operates with a significantly lower gate voltage than the other MOSFETs in the series circuit. This has the following consequences:

[0042] a. The MOSFET now changes to the active region at a predetermined current that can be read in the data sheet and a reverse voltage builds up.

[0043] b. Since once the voltage has been built up for a MOSFET determined by the integration of a Zener diode, all MOSFETs in the series circuit operating via this MOSFET (between the MOSFET with the Zener diode and the load connection, or further away from the driver ground than this MOSFET or the circuit module with the Zener diode) are forced together into the active region, the total reverse voltage can be set specifically.

[0044] In other words, a "sacrificial MOSFET" is implemented, which generates greater losses than the other MOSFETs during normal operation but ensures that all other MOSFETs can operate in a loss-optimized manner at this operating point. Compared to short-circuit current limiting without a Zener diode, the individual MOSFETs no longer enter the blocking region one after another, with a gradual increase in reverse voltage. Instead, the sacrificial MOSFET only predetermines the drain current that leads to saturation through its output characteristic curve. As a result, short-circuit current limiting becomes voltage-independent. However, a 10% higher loss in the sacrificial MOSFET also results in a 10% higher chip temperature, which manifests as larger temperature fluctuations during load changes. As a result, this MOSFET ages faster than the other MOSFETs installed in the series circuit (this can be quantified using the so-called raindrop model, where large temperature changes lead to faster aging, but many small temperature changes contribute to component aging; see "Lifetime calculation for power modules, application and theory of models and counting methods," K. Mainka, M. Thoben, O. Schilling, Engineering Proceedings of the 2011 14th European Conference on Power Electronics and Applications. Lifetime calculation for power modules, application and theory of models and counting methods). Higher temperatures also increase the likelihood of failure of the sacrificial MOSFET. This single MOSFET is also subject to significant stress in the event of a short circuit or overload. All the lower MOSFETs (i.e., the MOSFET between the driver's reference potential and the sacrificial MOSFET) are always operated in the ohmic range, resulting in optimal power loss. When the sacrificial MOSFET is saturated, all MOSFETs between the sacrificial MOSFET and the load connection are switched off, i.e., the circuit portion that blocks both positive and negative voltages (i.e., the MOSFETs that are further from the driver than the sacrificial MOSFET). This is because, due to the transition into the blocking region, a voltage builds up on the drain-source line of the sacrificial MOSFET, causing the gate voltage of this MOSFET to become zero. In other words, at these MOSFETs, the gate voltage falls below the threshold voltage, which corresponds to the "off" state.Therefore, during the transition to short-circuit current limiting, only the sacrificial MOSFET has the full load current at the full drain-source voltage, which only means an additional thermal load for this MOSFET and likewise leads to faster aging of this MOSFET.

[0045] Alternatively, there is the possibility of deliberately overdesigning the sacrificial MOSFET (e.g. with a lower on-resistance RDSon) so that it achieves the same MTBF time as the rest of the circuit. As a result, the circuit will no longer consist of one type of MOSFET, but of two.

[0046] Figures 5a and 5b show examples of calculations for the expected gate voltages of the individual MOSFETs. The tables shown in these figures are again based on the use of MOSFETs with an on-resistance RDSon of 3.9 mΩ (in the linear range), such as the MOSFET IPT039N15N5 from Infineon. In the table of Figure 5a, the drive voltage is 11 V, while in the table of Figure 5b, the drive voltage is 15 V. In this case, the individual MOSFETs or switching modules are numbered consecutively in the first column. The list corresponds to the increasing distance from the driver, that is, the data in the first row corresponds to the MOSFET closest to the driver (e.g. Figure 3 The data in the second row corresponds to the next MOSFET (e.g. Figure 3 MOSFET M2 in ), etc. Columns 2-5 list the gate voltage U for different load currents (50A, 100A, 200A, and 400A). GS In the last row, the total rated on-resistance RDSon of the MOSFET is listed according to the quantity (i.e., multiply the on-resistance RDSon of 3.9mΩ by the quantity in the first column, e.g. 2*3.9mΩ=7.8mΩ, 3*3.9mΩ=11.7mΩ, etc.).

[0047] At the gate voltage U shown GS Among the values of , those shown in larger font correspond to MOSFETs in the linear region, while those shown in smaller font correspond to MOSFETs in the blocking region. For these MOSFETs, the resistance increases accordingly (i.e., greater than 3.9 mΩ), as shown in Figure 4b. In practice, all MOSFETs with the gate voltage shown in smaller font will develop a reverse voltage. If the sum of the reverse voltages equals the drive voltage, equilibrium is established, and the current generated during a short circuit increases to zero. Therefore, the circuit actively and inherently limits the short-circuit current based on the applied drive voltage.

[0048] Figure 5a shows the values without a Zener diode (or sacrificial MOSFET); in Figure 5b, MOSFET 6 is configured as a sacrificial MOSFET. The basis is an RDSon of 3.9 mΩ and a gate signal of 15 V. It can be seen that at a current of 50 A, MOSFET 6 has a significantly lower gate voltage than MOSFET 7, yet it still operates in the linear region. At a current of 200 A, MOSFET 6 switches to the blocking region. According to Figure 4a, the MOSFET used with a gate voltage of 6.1 V cannot carry a drain current of 200 A. This means that it builds up a voltage, which reduces the gate voltages of all subsequent MOSFETs in the series circuit, causing them to also build up a reverse voltage. This means that MOSFETs 7 through 11 also switch to the active region. Therefore, the achievable reverse voltage at a current of 200 A is the sum of the individual reverse voltages of all MOSFETs, typically the limiting voltage of the overvoltage limiters installed in parallel. Now, if a Zener diode is placed in the gate path of MOSFET 7, the reverse voltage is reduced by the reverse voltage of a single MOSFET; if a Zener diode is placed in the gate path of MOSFET 5, the reverse voltage is increased by the reverse voltage of a single MOSFET. In other words, there are multiple possibilities for setting the required reverse voltage and maximum short-circuit current values.

Claims

1. A semiconductor switch having - a plurality of circuit modules connected in series, each of the circuit modules being formed with: - a first transistor (M3) having a source terminal (source3), a control terminal (Gate3) and a low potential terminal, wherein: - the source connection (source3) is a source connection or an emitter connection, the control connection (Gate3) is a gate connection or a base connection, and the low potential terminal connection is a drain connection or a collector connection, and - a second transistor (Q2) having a source connection, a control connection and a low potential terminal, wherein: - the source terminal is connected to the control terminal (Gate3) of the first transistor (M3), - the low potential terminal is connected to the source terminal (source3) of the first transistor (M3), and - the semiconductor switch has a driver (V2) which is connected via a connection to the control terminal of the second transistor (Q1, Q2, Q3, Q4, Q5, Q6) of the respective circuit module, In this case, for a subset of the plurality of circuit modules, a device for reducing the control connection voltage of the first transistor is introduced in the corresponding connection to the driver.

2. The semiconductor switch according to claim 1, It is characterized by: The device used to reduce the control terminal voltage is a Zener diode.

3. The semiconductor switch according to claim 1 or 2, It is characterized by: The subset consists of one or two circuit modules.

4. The semiconductor switch according to claim 1, It is characterized by: The first transistors of the circuit modules are designed identically.

5. The semiconductor switch according to claim 1, It is characterized by: The circuit modules of the subset of the plurality of circuit modules having the device for reducing the control connection voltage of the first transistor are designed to allow replacement of the module or the first transistor of the module in a simplified manner compared to the other circuit modules.

6. The semiconductor switch according to any one of claims 1 to 3, It is characterized by: The first transistors of a subset of the circuit blocks differ in design from the other first transistors.

7. The semiconductor switch according to claim 6, It is characterized by: - the operating conditions of the semiconductor switches are specified, and The first transistors of the subset are designed to have a comparable service life as the other first transistors under specified operating conditions.

8. The semiconductor switch according to claim 1, It is characterized by: - the semiconductor switch has an even number of circuit modules, - the first half of the circuit module is connected in series with the same conduction direction, and - The second half of the circuit module is connected in series in opposite conduction directions. - Two of the circuit modules are connected in sequence with opposite conduction directions, and - For one circuit module in the first half of the circuit modules and for one circuit module in the second half of the circuit modules, a device for reducing the control connection voltage of the first transistor is introduced in the corresponding connection to the driver, wherein the positions of the two circuit modules correspond to each other with respect to the number of circuit modules between them and the circuit module with the corresponding conduction direction, wherein the circuit module with the corresponding conduction direction is adjacent to the circuit module with the opposite conduction direction.

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