Cooling structure of power module

Abstract

The power module includes a first substrate, a first electronic component on a main surface of the first substrate, a second electronic component above the first electronic component, and a heat sink located above the first electronic component. The first electronic component and the second electronic component are thermally connected, and the first electronic component and the heat sink are thermally connected. In a top view of the power module, at least a portion of one of the first electronic components overlaps at least a portion of one of the second electronic components, and at least a portion of the one of the first electronic components overlaps a portion of the heat sink. In a side view of the power module, the second electronic component does not overlap any portion of the heat sink.

Description

Technical Field

[0001] The present invention relates to a power module. More specifically, the present invention relates to cooling a heat-generating power element in a power module, thereby improving the performance of the power module.

Background Art

[0002] Known power modules include heat-generating components such as power elements of the power module. The heat-generating components are usually separated from other more heat-sensitive components at positions where cavities / gaps are provided to enable temperature isolation and heat dissipation of the heat-generating components. For example, since an inductor may have a low thermal conductivity, an inductor near a heat-generating component can be a problem. Also, a part of the heat generated by the heat-generating component is usually transmitted through the substrate to a heat sink that can be connected to a carbon sheet.

[0003] For example, Patent Document 1 teaches a power conversion device 101 including a pair of circuit boards 10A and 10B including a heat-generating power component 14 and an inductive component 24 as shown in FIG. 1. A conductive body 23 is provided between the pair of circuit boards 10A and 10B, and heat dissipation plates 40A and 40B are provided adjacent to the pair of circuit boards 10A and 10B, respectively. Heat is transmitted from the pair of circuit boards 10A and 10B to the conductive body 23 through a heat dissipation terminal block 50. A heat sink 3 is attached to the conductive body 23 to assist in removing heat from the conductive body 23. The heat-generating power component 14 is separated from the inductive component 24 and is disposed in an open gap between the pair of circuit boards 10A and 10B, attempting to dissipate a part of the heat generated by the heat-generating power component 14 to the surrounding air.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

[0005] However, these arrangements in known power modules require a large space, which is undesirable when miniaturization of the power module is required. Furthermore, if heat-generating power components must be located near inductive components, the cooling efficiency decreases due to the low thermal conductivity of the inductive components. Reduced cooling efficiency prevents the heat-generating power components from operating at high currents. [Means for solving the problem]

[0006] To solve the above problems, a preferred embodiment of the present invention provides a power supply module that can be miniaturized while providing sufficient cooling to generate a large current. A preferred embodiment of the present invention provides a power supply module comprising a first substrate, a first electronic component on the main surface of the first substrate, a second electronic component above the first electronic component, and a heat sink located above the first electronic component. The first electronic component and the second electronic component are thermally connected, and the first electronic component and the heat sink are thermally connected. In a top view of the power supply module, at least a portion of one of the first electronic components overlaps with at least a portion of one of the second electronic components, and at least a portion of one of the first electronic components overlaps with a portion of the heat sink. In a side view of the power supply module, the second electronic component does not overlap with any portion of the heat sink.

[0007] The first electronic component may include a power element. The power module may further include a third electronic component on the main surface of the first circuit board. The third electronic component may include a capacitor.

[0008] The power module may further include a first thermal conductive material between a first electronic component and a second electronic component. The first thermal conductive material may include a first carbon sheet. The power module may further include a second thermal conductive material between the first electronic component and a heat sink. The second thermal conductive material may include a second carbon sheet. The first and second thermal conductive materials may define a single layer.

[0009] The second electronic component may include an inductor. The top surface of the heatsink may be located above the top surface of the inductor. The heatsink may be electrically and thermally conductive. The top surface of the second electronic component and / or the top surface of the heatsink may be at least partially molded within the housing.

[0010] A preferred embodiment of the present invention also provides a power supply module comprising a first substrate, a first electronic component and a second electronic component on the main surface of the first substrate, a second substrate above the first and second electronic components, a third electronic component on the main surface of the second substrate, a fourth electronic component above the third electronic component, and a heat sink above the third electronic component. The third electronic component and the fourth electronic component are thermally connected, and the third electronic component and the heat sink are thermally connected. In a top view of the power supply module, at least a portion of one of the third electronic components overlaps with a portion of one of the fourth electronic components and the power supply module, and at least a portion of one of the third electronic components overlaps with a portion of the heat sink. In a side view of the power supply module, the fourth electronic component does not overlap with any portion of the heat sink.

[0011] The first electronic component may include a capacitor. The second electronic component may include conductive connection pins. The power module may further include a fifth electronic component provided on the main surface of the second substrate. The fifth electronic component may include a capacitor. The power module may further include a sixth electronic component provided on another main surface of the second substrate opposite to the main surface of the second substrate on which the third electronic component is provided. The sixth electronic component may include a capacitor.

[0012] The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings. [Brief explanation of the drawing]

[0013] [Figure 1] An example of a known power supply module is shown. [Figure 2] A cross-sectional block diagram of a power supply module according to a first preferred embodiment of the present invention is shown. [Figure 3] A perspective view of the power module with the housing removed, according to a first preferred embodiment of the present invention, is shown. [Figure 4] A cross-sectional block diagram of a power module according to a second preferred embodiment of the present invention is shown. [Figure 5] A perspective view of the power module with the housing removed, according to a second preferred embodiment of the present invention, is shown. [Figure 6] A perspective view of a power module with the housing, heat sink, and one of the second substrates removed, according to a second preferred embodiment of the present invention, is shown. [Figure 7] A cross-sectional block diagram of a power supply module according to a modified version of a second preferred embodiment of the present invention is shown. [Figure 8] An example of a circuit diagram of a power supply module according to a third preferred embodiment of the present invention is shown. [Figure 9] A perspective view of a power supply module according to a fourth preferred embodiment of the present invention is shown. [Figure 10] The top view of a power module according to the fourth preferred embodiment of the present invention is shown. [Figure 11] The exploded view of the power module of FIG. 9 is shown. [Figure 12] The perspective view of the power module of FIG. 9 without a heat sink is shown. [Figure 13] The top view of the power module of FIG. 9 without a heat sink is shown. [Figure 14] The simulated heat map of a power module according to the fifth preferred embodiment of the present invention is shown. [Figure 15] The power module used to create the simulated heat map of FIG. 14 is shown.

Mode for Carrying Out the Invention

[0014] First Preferred Embodiment The power module according to the first preferred embodiment of the present invention will be described with reference to FIGS. 2 and 3. FIG. 2 is a cross-sectional block diagram showing an example of the arrangement of components of the power module 1 according to the first preferred embodiment of the present invention. FIG. 3 is a perspective view of an example of the power module 1 according to the first preferred embodiment of the present invention, in which the housing is removed to show the possible arrangement of the components of the power module 1.

[0015] As shown in FIG. 2, the power module 1 can include a first substrate 10, a heat conduction layer 20 (which can include at least one material layer), a housing 30, a first electronic component 11, a second electronic component 12, a third electronic component 13, and a heat sink 18.

[0016] At least one first electronic component 11 and one third electronic component 13 are provided on the main surface of the first substrate 11. Multiple first electronic components 11 and multiple third electronic components 13 may be provided on the main surface of the first substrate 11. The first electronic component 11 can be a high-heat generating element. For example, the first electronic component 11 can be a power element such as a transistor, operational amplifier, inverter, or diode. The third electronic component 13 can be a small, low-heat generating element. For example, the third electronic component 13 can be a capacitor such as a surface-mount chip capacitor.

[0017] The heat sink 18 may be a single heat sink, or it may be divided into multiple heat sinks that are in thermal contact with each other or not. The heat sink 18 can be made of a heat-conducting material such as a metal containing Al, Cu, brass, or an alloy of at least one of Al, Cu, and brass. The heat sink 18 can be manufactured by machining, pressing, die casting, etc. The heat sink 18 can be fixed to the product using adhesive, solder, etc. The heat sink 18 may be provided with protrusions, which can be used to fix the heat sink 18 in place by hooking the protrusions onto the edge of the substrate. Fixing the heat sink 18 to the edge of the substrate and bonding the heat sink can be done at the same location.

[0018] A thermal interface material (TIM) can be interposed between the heatsink 18 and the first electronic component 11. A thermal conductive layer 20 can be provided on the upper surface of the first electronic component 11. Depending on the application, the thermal conductive layer 20 may have a thermal conductivity lower than, higher than, or the same as that of the first substrate 10. The thermal conductive layer may include at least one material or layer, or two or more materials or layers bonded together. The at least one material or layer may include, for example, one or more types of carbon sheets.

[0019] At least one second electronic component 12 and a heat sink 18 are provided on the main surface of the thermal conductive layer 20. Multiple second electronic components 12 and heat sinks 18 may be provided on the thermal conductive layer 20. The second electronic component 12 can be a large, low-heat generating element. For example, the second electronic component 12 can be an inductor that has a lower thermal conductivity than the heat sink 18. The first electronic element 11 and the second electronic element 12 may be larger than the third electronic element 13. By arranging low-heat generating elements such as inductors and heat sinks on the same layer, stacking large electronic elements such as power elements and inductors in a top view, and stacking high-heat generating elements such as power elements and heat sinks in a top view, it is possible to achieve miniaturization (e.g., reduction of mounting area) while providing sufficient thermal coupling between high-heat generating elements and heat sinks.

[0020] Another TIM can be interposed between each part of the first electronic component 11 that overlaps with the lower part of the second electronic component 12. The thermal resistance can be high even when thermally coupled to the second electronic component 12. Therefore, a thermal conductive layer 20 can be interposed between the lower parts of the first electronic component and the second electronic component to facilitate heat dissipation to the heat sink 18.

[0021] The first electronic component 11, the second electronic component 12, and the heatsink 18 can be arranged such that (i) when viewed from the top surface of the power module 1, a portion of the first electronic component 11 and the heatsink 18 overlap each other, and (ii) when viewed from the top surface of the power module 1, a portion of the first electronic component 11 and the second electronic component 12 overlap each other. Alternatively, the first electronic component 11, the second electronic component 12, and the heatsink 18 may be arranged such that (i) when viewed from the top surface of the power module 1, a portion of one of the first electronic components 11 and the heatsink 18 overlap each other, and (ii) when viewed from the top surface of the power module 1, a portion of the first electronic component 11 and a portion of the second electronic component 12 overlap each other. The first electronic component 11 (or more) and the heatsink 18 can overlap to any degree. These arrangements and the thermal conductive layer 20 ensure that both the first electronic component 11 and the second electronic component 12 are efficiently thermally connected to the heat sink 18. Although inductors typically have low thermal conductivity, the inclusion of the thermal conductive layer 20 provides a path for heat to transfer from the second electronic component 12 to the heat sink 18. This efficient thermal connection results in an improved cooling effect, which in turn improves the performance of the power module 1 and enables a higher current output.

[0022] Additionally, the first electronic component 11 and the third electronic component 13 may or may not overlap each other when viewed from the side of the power module 1, depending on the specific application. The second electronic component 12 and the heat sink 18 may or may not overlap each other when viewed from the side of the power module 1, depending on the specific application.

[0023] In a top view of the power module 1, the first electronic component 11, the second electronic component 12, and the heat sink 18 can be stacked on top of each other, thereby reducing the surface area of ​​the first substrate 10, and thus enabling miniaturization of the power module 1.

[0024] The heatsink 18 can be made of a material that has both thermal and electrical conductivity. Suitable materials for the heatsink 18 include, for example, copper, aluminum, or other suitable materials. The upper surface of the heatsink 18 can be positioned above the upper surface of the second electronic component 12. This arrangement allows heat to dissipate more easily to the outside of the power module 1 by defining a gap between the housing 30, which contacts the upper surface of the heatsink 18 but not the second electronic component 12, and the second electronic component 12. Furthermore, this arrangement makes it easier to avoid failures caused by short circuits or electrostatic discharge between the housing 30 and the second electronic component 12. The housing 30 can be made of, for example, aluminum, steel, copper, brass, or other suitable materials.

[0025] To further facilitate heat dissipation, the thermal conductivity between the housing 30, the second electronic component 12, and the heat sink 18 can be increased by molding or embedding at least partially the upper surface of the second electronic component 12 and / or the upper surface of the heat sink 18 into a part of the housing 30.

[0026] Figure 3 shows a perspective view of an example of a power module 1 with the housing removed, according to a first preferred embodiment of the present invention. The housing is not shown in Figure 3. Here, a first electronic component 11 (power element) and a third electronic component 13 (chip capacitor) are provided on the main surface of the first substrate 10. A thermal conductive layer 20 (not visible in Figure 3 as it is overlapped with other components) is provided on the upper surface of the first electronic component 11, and the thermal conductive layer 20 is in contact with the lower surface of the second electronic component 12 (inductor) and the heat sink 18.

[0027] Second Preferred Embodiment A power supply module according to a second preferred embodiment of the present invention will be described with reference to Figures 4 to 7. Figure 4 is a cross-sectional block view showing an example of the arrangement of components of the power supply module 2 according to a second preferred embodiment of the present invention. Figure 5 is a perspective view of an example of the power supply module 2 according to a second preferred embodiment of the present invention, with the housing removed to show possible arrangements of components of the power supply module 2. The housing is not shown in Figure 5. Figure 6 is another perspective view of an example of the power supply module 2 according to a second preferred embodiment of the present invention, with one of the first substrates 10 removed to show possible arrangements of components of the power supply module 2. The housing is not shown in Figure 6.

[0028] As shown in Figure 4, the power supply module 2 according to the second preferred embodiment differs from the power supply module 1 according to the first preferred embodiment in that the first substrate 10 and the second substrate 100 are stacked on top of each other. The first substrate 10 can be stacked on top of the second substrate 100. The first substrate 10 may be a single substrate, or it may include two or more first substrates 10, as shown in Figures 5 and 6. Other components of the power supply module 2 according to the second preferred embodiment can be the same as those of the power supply module 1 according to the first preferred embodiment, and for simplicity, the description of the identical parts will be omitted.

[0029] In the second preferred embodiment, the first substrate 10, first electronic component 11, second electronic component 12, third electronic component 13, heat sink 18, thermal conductive layer 20, and housing 30 can be arranged in the same or similar manner as in the first preferred embodiment. The first substrate 10 can be mounted on the second substrate 100 with the fourth electronic component 14 and fifth electronic component 15 between the first substrate 10 and the second substrate 100. The fourth electronic component 14 may include a small, low-heat generating element, such as a capacitor, and the fifth electronic component 15 may include, for example, contact pins or other suitable connectors connecting the first substrate 10 and the second substrate 100.

[0030] The power module 2 may include a multilayer substrate defined by a first substrate 10 and a second substrate 100. The first substrate 10 includes at least one third electronic component 13 provided on the main surface of the first substrate 10. The second substrate 200 includes at least one fifth electronic component 15 provided on the main surface of the second substrate 200. This arrangement allows for miniaturization of the power module 2, particularly when additional chip capacitors are used in the power module 2.

[0031] The first substrate 10 may include at least one first electronic component 11 and one third electronic component 13 on its main surface, and at least one second electronic component 12 and a heat sink 18 are provided on the main surface of the heat conductive layer 20 on the first electronic component 11. Similar to the power module 1, in the power module 2, the first electronic component 11, the second electronic component 12 and the heat sink 18 may be arranged such that (i) when viewed from the top surface of the power module 2, the portion of the first electronic component 11 and the heat sink 18 overlap each other, and (ii) when viewed from the top surface of the power module 2, the portion of the first electronic component 11 and the second electronic component 12 overlap each other. Alternatively, the first electronic component 11, the second electronic component 12, and the heat sink 18 may be arranged such that (i) when viewed from the top surface of the power module 2, a portion of the first electronic component 11 and the heat sink 18 overlap each other, and (ii) when viewed from the top surface of the power module 2, a portion of the first electronic component 11 and a portion of the second electronic component 12 overlap each other.

[0032] The power module 2 includes a laminated substrate defined by the first substrate 10 and the second substrate 100, which allows for the inclusion of additional components in a smaller mounting area. On the other hand, the specific arrangement of the power module 2 provides efficient thermal connectivity, resulting in improved cooling, which in turn improves the performance of the power module 2 and enables a higher current output.

[0033] Figure 7 shows a modified form of the power module 2A in which a sixth electronic component 16 can be provided on the underside of the first substrate 10. This configuration allows for further miniaturization while maintaining improved cooling.

[0034] In the modified version of the second embodiment, the first substrate 10, the second substrate 100, the first electronic component 11, the second electronic component 12, the third electronic component 13, the fourth electronic component 14, the fifth electronic component 15, the heat sink 18, the thermal conductive layer 20, and the housing 30 can be arranged in the same or similar manner as in the second embodiment. A sixth electronic component can be added to the lower surface of the first substrate 10. The sixth electronic component 15 can be a small, low-heat generating element, such as a capacitor.

[0035] Third Preferred Embodiment Figure 8 shows a circuit diagram of a power supply module according to a third preferred embodiment of the present invention. This circuit diagram can be implemented in power supply modules according to other preferred embodiments, including the first and second preferred embodiments described above, and the fourth and fifth preferred embodiments described later. The circuit diagram in Figure 8 is merely an example, and power supply modules of other preferred embodiments may implement other power supply circuits or topologies.

[0036] The circuit diagram includes an input voltage V1, an input capacitor Cin, power stages 1, 2, 3, and 4, inductors L1, L2, L3, and L4, an output capacitor Cout, and a load I1. The input voltage V1 is connected to the input capacitor Cin. Power stages 1, 2, 3, and 4 are connected to the input capacitor Cin. Figure 8 shows four power stages, but any number of power stages may be used. Each power stage 1, 2, 3, and 4 includes drivers that drive two power switches Q1 and Q2, Q3 and Q4, Q5 and Q6, Q7 and Q8. Different topologies may have a different number of power switches in each stage. Each power stage 1, 2, 3, and 4 can be connected to the corresponding inductors L1, L2, L3, and L4. The number of inductors may correspond to the number of power stages. Inductors L1, L2, L3, and L4 can be coupled as shown in Figure 8. Inductors can be coupled by sharing a common core, for example, as shown in Figure 6. In some applications, the inductors do not need to be coupled. Inductors L1, L2, L3, and L4 are connected to the output capacitor Cout. Load I1 is connected to the output capacitor Cout.

[0037] Various components in the circuit diagram can be located in different areas of the power supply module. For example, the components of power stages 1, 2, 3, and 4, including the driver and power switches Q1 and Q2, Q3 and Q4, Q5 and Q6, Q7 and Q8, can be the first electronic component 11 on the first substrate 10; the inductors L1, L2, L3, and L4 can be the second electronic component 12 located above the first electronic component 11 and at least partially overlapping it; the input capacitor Cin and output capacitor Cout can be the third electronic component 13 on the first substrate 10, or the fifth electronic component 15 and sixth electronic component 16 between the first substrate 10 and the second substrate 100, as shown in Figure 8. A fourth electronic component 14 can be used to connect electronic components located on different substrates.

[0038] Fourth Preferred Embodiment Figures 9 to 13 show a power supply module 2 according to a fourth preferred embodiment of the present invention. The power supply module 2 in Figures 9 to 13 is similar to the power supply module 2 of the second preferred embodiment, but includes eight first substrates 10 on a second substrate 100. Figures 9 and 10 show a power supply module 2 without a housing but including a single heatsink 18. Figure 11 is an exploded view showing the heatsink 18 above the first substrates 10. Figures 12 and 13 show a power supply module 2 without the heatsink 18. Note that in Figure 12, one of the first substrates 10 is not shown, and the inductors on two of the other first substrates 10 are not shown.

[0039] Above the first substrate 10 are a heat sink 18, a first electronic component 11, a second electronic component 12, and a third electronic component 13. As shown in Figures 9 and 10, a single heat sink 18 can be located on all eight first substrates 10, and each of the first substrates 10 may contain a separate first electronic component 11, a second electronic component 12, and a third electronic component 13. A fourth electronic component 14 can connect different first substrates 10 to the second substrate 100. A fifth electronic component 15 (e.g., a capacitor), and possibly a sixth electronic component (e.g., a capacitor) (not shown in Figures 9 to 13) can be located between a corresponding one of the first substrates 10 and the second substrate 100.

[0040] As shown in Figures 9 to 13, the second substrate 100 may include one or more areas that are not covered by the corresponding first substrate 10. Additional electronic components may be included in these uncovered areas. The additional electronic components may, for example, control the first electronic component 11. For example, if the first electronic component includes a power stage having a power switch and a driver for the power switch, the additional electronic component may include a controller that transmits control signals to the driver of the power stage.

[0041] Fifth Preferred Embodiment Figure 14 shows a heatmap of a power module 3 according to a fifth preferred embodiment of the present invention shown in Figure 15. Power module 3 is similar to power module 2 of the second preferred embodiment, which includes a first substrate 10 on a second substrate 100. Above the first substrate 10 are a heat sink 18, a first electronic component 11 (e.g., a power element), a second electronic component 12 (e.g., an inductor), and a third electronic component 13 (e.g., a capacitor). A fourth electronic component 14 can connect the first substrate 10 and the second substrate 100. A fifth electronic component 15 (e.g., a capacitor) can be located between the first substrate 10 and the second substrate 100.

[0042] The heat map in Figure 14 shows that by placing both the second electronic component 12 and the heat sink 18 on top of the first electronic component 11, heat can be transferred from the first electronic component 11 and the second electronic component 12 to the heat sink 18.

[0043] The preferred embodiments and modified configurations described above can be appropriately combined with each other, and each combination can produce corresponding effects. It should be understood that the foregoing description is merely illustrative of the present invention. Those skilled in the art can devise various alternative and modified forms without departing from the present invention. Accordingly, the present invention is intended to encompass all such alternative, modified, and altered forms that fall within the scope of the appended claims.

Claims

1. A power module, The first substrate and A first electronic component on the main surface of the first substrate, The second electronic component is located above the first electronic component, A heatsink located above the first electronic component, A first thermally conductive material is provided between the first electronic component and the second electronic component, The first electronic component and the second electronic component are thermally connected. The first electronic component and the heat sink are thermally connected, In a top view of the power supply module, at least a portion of one of the first electronic components overlaps with at least a portion of one of the second electronic components. In the top view of the power module, at least a portion of the one first electronic component overlaps with a portion of the heat sink. In a side view of the power supply module, the second electronic component does not overlap with any part of the heat sink.

2. The power supply module according to claim 1, wherein the first electronic component includes a power element.

3. The power supply module according to claim 1, further comprising a third electronic component on the main surface of the first substrate.

4. The power supply module according to claim 3, wherein the third electronic component includes a capacitor.

5. The power module according to claim 1, wherein the first thermally conductive material includes a first carbon sheet.

6. The power supply module according to claim 1, further comprising a second thermally conductive material between the first electronic component and the heat sink.

7. The power module according to claim 6, wherein the second thermally conductive material includes a second carbon sheet.

8. The power supply module according to claim 6, wherein the first thermally conductive material and the second thermally conductive material define a single layer.

9. The power supply module according to any one of claims 1 to 4, wherein the second electronic component includes an inductor.

10. The power supply module according to claim 9, wherein the upper surface of the heat sink is located above the upper surface of the inductor.

11. The power supply module according to any one of claims 1 to 4, wherein the heat sink has electrical conductivity and thermal conductivity.

12. The power supply module according to any one of claims 1 to 4, wherein at least one of the upper surface of the second electronic component and the upper surface of the heat sink is at least partially molded within the housing.

13. A power module, A first substrate and a second substrate, wherein the first substrate is located above the second substrate, and the first and second substrates are... A first electronic component on the main surface of the first substrate, The second electronic component is located above the first electronic component, The fourth electronic component on the main surface of the second substrate, The heatsink above the first electronic component, A thermally conductive material between the first electronic component and the second electronic component, The first electronic component and the second electronic component are thermally connected. The first electronic component and the heat sink are thermally connected, In a top view of the power supply module, a portion of one of the first electronic components overlaps with a portion of one of the second electronic components. In the top view of the power module, at least a portion of the one first electronic component overlaps with a portion of the heat sink. In a side view of the power supply module, the second electronic component does not overlap with any part of the heat sink.

14. The power supply module according to claim 13, wherein the fourth electronic component includes a capacitor.

15. The power supply module according to claim 13, further comprising conductive connection pins for connecting the first substrate and the second substrate.

16. The power supply module according to any one of claims 13 to 15, further comprising a third electronic component provided on the main surface of the first substrate.

17. The power supply module according to claim 16, wherein the third electronic component includes a capacitor.

18. The power supply module according to any one of claims 13 to 15, further comprising a sixth electronic component provided on another main surface of the first substrate opposite to the main surface of the first substrate on which the first electronic component is provided.

19. The power supply module according to claim 18, wherein the sixth electronic component includes a capacitor.

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