Power converter control using pass-through and switching modes

Abstract

The invention relates to power converter control using pass-through and switching modes. Systems and methods for operating a power converter of a device are described. A controller of the power converter may determine a battery voltage of a battery of the device, and determine whether the battery voltage satisfies a threshold voltage. In response to determining that the battery voltage satisfies the threshold voltage, the controller may cause the power converter to operate in a pass-through mode in which the power converter provides a load voltage to the load that is equal to the battery voltage. Alternatively, in response to determining that the battery voltage does not meet the threshold voltage, the controller may cause the power converter to operate in a switching mode, where the power converter provides a load voltage equal to the threshold voltage. By using the pass-through mode when the battery voltage satisfies the threshold voltage, the battery life of the device can be saved.

Description

Technical Field

[0001] The present disclosure generally relates to semiconductor devices. More specifically, the present disclosure relates to controlling a power converter to optimize the battery life of a device. Background Art

[0002] An electrical load is typically capable of operating at a range of input voltages (e.g., below the nominal input voltage). For example, a heating element may have a nominal input voltage of 4.5 volts, but be capable of operating at an input voltage far less than 4.5 volts (although at lower power). Powering such a load constantly at the high end of its operating range can provide benefits (e.g., increased heat in the case of a heating element), however this typically comes at the expense of battery life (e.g., due to switching losses when the input voltage is higher than the battery voltage). Summary of the Invention

[0003] A method of controlling a power converter is described herein. The method includes determining the battery voltage of a battery of a device, and selecting a direct - through mode or a switching (boost) mode for the power converter of the device based on whether the battery voltage meets a threshold voltage. The method further includes configuring the power converter to operate in the direct - through mode or the switching mode based on the selection. In the direct - through mode, the power converter is configured to generate a load voltage to a load, the load voltage being equal to the battery voltage. In the switching mode, the power converter is configured to provide a load voltage equal to the threshold voltage.

[0004] A semiconductor device is described herein. The semiconductor device includes a controller configured to determine the battery voltage of a battery of the device and to determine whether the battery voltage meets a threshold voltage. In response to determining that the battery voltage meets the threshold voltage, the controller is configured to cause the power converter of the device to operate in the direct - through mode, wherein the power converter provides a load voltage equal to the battery voltage to a load. In response to determining that the battery voltage does not meet the threshold voltage, the controller is configured to cause the power converter to operate in the switching mode, wherein the power converter provides a load voltage equal to the threshold voltage.

[0005] A system is described herein. The system includes: a battery; a load configured to receive a load voltage between a fully - charged battery voltage and a lower voltage; a power converter connected between the battery and the load; and a controller. The controller is configured to determine the voltage of the battery and to determine whether the voltage meets a threshold voltage. In response to determining that the voltage meets the threshold voltage, the controller is configured to cause the power converter to operate in the direct - through mode, wherein the power converter provides a load voltage equal to the battery voltage to the load. In response to determining that the voltage does not meet the threshold voltage, the controller is configured to cause the power converter to operate in the switching mode, wherein the power converter provides a load voltage equal to the threshold voltage.

[0006] The foregoing abstract is merely illustrative and is not intended to be limiting in any way. In addition to the above - described illustrative aspects, embodiments, and features, other aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description. In the drawings, like reference numerals indicate like or functionally similar elements. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 Illustrates an example system configured to implement power converter control using a direct - through mode and a switching mode.

[0008] Figure 2 Illustrates an example of a power converter implemented as a buck - boost power converter Figure 1 of.

[0009] Figure 3 Illustrates an example of a power converter implemented as a boost power converter Figure 1 of.

[0010] Figure 4 Illustrates an example of power converter control using a direct - through mode and a switching mode, where the threshold voltage is equal to the battery threshold voltage.

[0011] Figure 5 Illustrates an example flow for implementing power converter control using a direct - through mode and a switching mode.

[0012] Figure 6 Illustrates an example method of power converter control using a direct - through mode and a switching mode. DETAILED DESCRIPTION

[0013] Figure 1 Illustrates an example of a system 100 configured to implement power converter control using a direct - through mode and a switching mode. The system 100 can consist of a device (e.g., an electronic cigarette, a heated object or article, a mobile device, any battery - powered device having a heater). The system 100 includes: a battery 102 configured to supply a battery voltage 104; a load 106 configured to receive a load voltage 108; and a power converter 110 (e.g., a buck converter, a buck - boost converter, a boost converter) configured to convert the battery voltage 104 into the load voltage 108.

[0014] System 100 also includes a controller 112 configured to control the power converter 110 to operate in a direct-through mode 114 (PTM) or a switching mode 116. In the direct-through mode 114, the load voltage 108 output by the power converter 110 is approximately equal to the battery voltage 104 (with slight losses through the power converter 110). Additionally, in the direct-through mode 114, the switches in the power converter 110 may not experience switching. In the switching mode 116, the load voltage 108 output by the power converter 110 may be equal to the threshold voltage 118. Additionally, in the switching mode 116, the switches in the power converter 110 may switch in a specific sequence to regulate the load voltage 108 at the threshold level 118.

[0015] The battery 102 may be rechargeable and may have a corresponding fully charged voltage (e.g., corresponding to a fully charged state), a corresponding threshold voltage (e.g., a nominal voltage, the voltage at which the battery voltage 104 starts to rapidly decline during discharge), and a low voltage (e.g., the lowest battery voltage supplied by the battery 102). For example, the battery 102 may have a fully charged voltage of approximately 4.2 volts, a threshold / nominal voltage of 3.7 volts, and a low voltage of 2.5 volts to 3 volts.

[0016] The load 106 may be any type of electrical component with a variable input voltage. For example, the load 106 may be a heating element configured to operate with an input voltage between 3.7 volts (or less than 3.7 volts) and 4.5 volts. A higher load voltage 108 will cause the heating element to obtain more power (e.g., heat up faster). Conventional techniques typically power such a load at the high end of the input voltage range, which requires operating the power converter in the switching mode throughout the entire discharge cycle of the battery (assuming the battery voltage is always low). Compared to the techniques discussed herein, this results in a shorter battery life.

[0017] To determine whether the power converter 110 should operate in the direct-through mode 114 or the switching mode 116, the controller 112 may compare the battery voltage 104 with the threshold voltage 118. The threshold voltage 118 may be somewhere between the fully charged voltage and the low voltage. For example, the threshold voltage 118 may correspond to the threshold voltage of the battery 102. In some cases, the load 106 may have an input voltage requirement higher than the threshold voltage of the battery 102. In those cases, the threshold voltage 118 may be equal to the lowest input voltage accepted by the load 106 (but still lower than the fully charged battery voltage).

[0018] In one embodiment, if the battery voltage 104 meets the threshold voltage 118 (e.g., is greater than the threshold voltage 118, is greater than or equal to the threshold voltage 118), the controller 112 may control the power converter 110 to operate in the direct-through mode 114. If the battery voltage 104 does not meet the threshold voltage 118 (e.g., is less than the threshold voltage 118, is less than or equal to the threshold voltage 118), the controller 112 may control the power converter 110 to operate in the switching mode 116. For battery discharge starting from a battery voltage 104 higher than the threshold voltage 118, the controller 112 may control the power converter 110 to operate in the direct-through mode 114 until the battery voltage 104 drops below the threshold voltage 118. From this point until the battery voltage 104 reaches a range of low voltages of the battery 102 (e.g., a range of low voltages below the threshold voltage 118), the controller 112 may cause the power converter 110 to operate in the switching mode 116. Thus, the load voltage 108 supplied to the load 106 may be maintained at the threshold voltage 118.

[0019] In one embodiment, the controller 112 may use other inputs (e.g., in addition to the battery voltage 104) to determine whether the power converter 110 should operate in the direct-through mode 114 or the switching mode 116. For example, the controller 112 may receive a user mode indication 120 (e.g., normal mode, battery saving mode) and / or an auxiliary power indication 122 (e.g., whether the system 100 has an auxiliary power supply, whether it is plugged in). If the user mode indication 120 indicates the normal mode, the controller 112 may cause the power converter 110 to operate in the switching mode 116 regardless of the battery voltage 104. Similarly, if the auxiliary power indication 122 indicates that the system 100 has an auxiliary power supply (e.g., is plugged in, has a universal serial bus (USB) power supply), the controller 112 may cause the power converter 110 to operate in the switching mode 116 regardless of the battery voltage 104.

[0020] In one or more embodiments, the controller 112 can be implemented in software, hardware, or some combination thereof. The controller can consist of semiconductor devices (e.g., microcontrollers, processors, control units). Additionally, the controller 112 can be part of another controller (e.g., a central processing unit (CPU), a main controller) of the device. The controller 112 can be configured to directly control the power converter 110 or control the power converter 110 via a driver (not shown). For example, the controller 112 can be configured to provide a control signal (e.g., a pulse width modulation (PWM) control signal) to the power converter 110 or the driver. The driver can be part of the power converter or can be separate from the power converter 110. The driver can be configured to receive a control signal from the controller 112 and drive the switches within the power converter 110.

[0021] In one embodiment, the controller 112 can also be configured to execute at least one control loop to determine whether to operate the power converter 110 in a direct conduction mode 114 or a switching mode 116 to supply the load voltage 108 to the load 106. In one aspect, the control loop can be implemented by at least one analog and / or digital component of the controller 112 (e.g., software and / or firmware executed by the controller 112). To execute the control loop, a quantitative measurement (e.g., the battery voltage 104) can be input into the corresponding control loop (along with the user mode indication 120 and / or the auxiliary power indication 122, if implemented). The controller 112 can perform a comparison of the quantitative measurement with a reference value (e.g., a threshold voltage 118). The controller 112 can use the comparison result to determine whether to operate the power converter 110 in the direct conduction mode 114 or the switching mode 116, as discussed above and below.

[0022] In one or more embodiments, the controller 112 can also include components such as a digital-to-analog converter (DAC), a comparator, a mixer, a memory device (e.g., a register), and other electronic components. The controller 112 can include a memory device that is configured to store various predetermined values (e.g., a digital representation of the battery voltage 104, a digital representation of the threshold voltage 118, a digital representation of the user mode indication 120, a digital representation of the auxiliary power indication 122) that can be used by the control loop. For example, registers in the controller 112 can store the predetermined values (e.g., the battery voltage 104), which can then be converted to analog signals by a DAC in the controller 112. The analog signals can be provided as reference values to the control loop, where the reference values are input into a comparator of the controller 112.

[0023] Figure 2FIG. illustrates an example of a power converter 110 implemented as a buck - boost power converter. The power converter 110 may include a plurality of switches 200 (e.g., 200 - 1, 200 - 2, 200 - 3, and 200 - 4) and an inductor 202. When the power converter 110 is implemented as a buck - boost power converter, the controller 112 may control the power converter 110 to convert an input voltage (e.g., the battery voltage 104) into an output voltage (e.g., the load voltage 108), which may be less than or greater than the input voltage. The switches 200 may be metal - oxide - semiconductor field - effect transistors (MOSFETs) or other types of switches. The switches 200 are controlled (directly or indirectly) via the controller 112.

[0024] In this configuration, for the direct - through mode 114, the controller 112 may turn on the switches 200 - 1 and 200 - 3 and turn off the switches 200 - 2 and 200 - 4. In other words, half of the switches 200 are in the on state (i.e., the high - side switches), and half of the switches 200 are in the off state (i.e., the low - side switches). Thus, power flows from the battery voltage 104 through the switch 200 - 3, the inductor 202, and the switch 200 - 1 to the load voltage 108. The direct - through mode 114 may enable the load voltage 108 to be close to the battery voltage 104 without causing switching losses. The load voltage 108 in this configuration can be expressed as:

[0025] V load =V bat -I load (DCR[[ID=1)3]] ind +R DS,ON,sw1 +R DS,ON,sw3 ) (1)

[0026] Where V load is the load voltage 108, V bat is the battery voltage 104, I load is the current consumption of the load 106, DCR ind is the resistance of the inductor 202, R DS,ON,sw1 is the resistance of the switch 200 - 1 in the on state, and R DS,ON,sw3 is the resistance of the switch 200 - 3 in the on state.

[0027] In this configuration, for switching mode 116, the controller 112 can control switches 200-1 and 200-2 to alternately switch between conducting and non-conducting states, switch 200-3 will be in the conducting state (e.g., keep switch 200-3 conducting), and switch 200-4 will be in the non-conducting state (e.g., keep switch 200-4 off). Through the timing of the switching, the controller 112 can control the power converter 110 to regulate the load voltage 108 and output it at the threshold voltage 118.

[0028] Figure 3 FIG. illustrates an example of the power converter 110 implemented as a boost power converter. When the power converter 110 is implemented as a boost power converter, the controller 112 can control the power converter 110 to convert an input voltage (e.g., battery voltage 104) into an output voltage (e.g., load voltage 108), and the output voltage can be greater than the input voltage.

[0029] In this configuration, for direct-through mode 114, the controller 112 can keep switch 200-1 in the conducting state and switch 200-2 in the non-conducting state. In other words, half of the switches 200 are in the conducting state (i.e., high-side switches), and half of the switches 200 are in the non-conducting state (i.e., low-side switches). Thus, power flows from the battery voltage 104 through the inductor 202 and switch 200-1 to the load voltage 108. Doing so enables the load voltage 108 to approach the battery voltage 104 without incurring switching losses. The load voltage 108 in this configuration can be expressed as:

[0030] V load =V bat -I load (DCR ind +R DS,ON,sw1 ) (2)

[0031] In this configuration, for switching mode 116, the controller 112 can control switches 200-1 and 200-2 to alternately switch between the conducting state and the non-conducting state. Through the timing of the switching, the controller 112 can control the power converter 110 to regulate the load voltage 108 and output it at the threshold voltage 118.

[0032] Figure 4 FIG. 400 illustrates an example voltage of the battery 102 over time when discharging (assuming no auxiliary power source is attached) using the direct-through mode and the switching mode. In the illustrated example, the battery voltage 104 starts at the fully charged voltage 402 (e.g., 4.2 volts, the maximum voltage of a single lithium-ion battery), and the threshold voltage 118 is at the nominal voltage or threshold voltage of the battery 102 (e.g., 3.7 volts, the nominal voltage of a single lithium-ion battery).

[0033] At the start, the battery voltage 104 is higher than / meets the threshold voltage 118. Thus, the controller 112 can control the power converter 110 to operate in the direct-conduction mode 114. As discussed above, when the battery discharges from the fully charged voltage 402, the load voltage 108 in the direct-conduction mode 114 is slightly lower than the battery voltage 104.

[0034] The controller continues to operate the power converter 110 in the direct-conduction mode 114 until the battery voltage 104 meets or drops below the threshold voltage (e.g., at the transition point 404). At this point, since the battery voltage 104 is not higher than / does not meet the threshold voltage 118, the controller 112 can control the power converter 110 to switch to the switching mode 116. As described above, the power converter 110 generates the load voltage 108 at the threshold voltage 118 in the switching mode.

[0035] In the illustrated example, it is evident that the power converter 110 operates in the direct-conduction mode 114 for most of the discharge cycle. Since the direct-conduction mode 114 does not cause switching losses, the battery life can be improved as compared to constantly operating the power converter 110 in the switching mode 116 (e.g., generating a load voltage 108 higher than the fully charged voltage 402).

[0036] In some embodiments, the lower limit of the load voltage 108 can be higher than the threshold voltage of the battery 102. For example, in a system with a battery threshold of 3.7 volts, the load 106 may be able to accept a load voltage 108 of 3.9 volts. In this case, the threshold voltage 118 can be set to the minimum load voltage. The transition point 404 will bend further to the left along the battery voltage 104 curve, but the advantages can still be achieved (although less energy is saved due to the shorter time in the direct-conduction mode 114).

[0037] Conversely, the lower limit of the load voltage 108 can be lower than the threshold voltage of the battery 102. For example, for a 3.7-volt battery, the load 106 may be able to accept a load voltage 108 of 2 volts. In this case, the threshold voltage 118 can be set to the minimum load voltage (e.g., pushing the transition point 404 to the right along the battery voltage 104 curve). Although this can result in increased energy savings by allowing the power converter 110 to operate in the direct-conduction mode 114 for a longer time, it may be at the expense of the performance of the load 106 (e.g., unacceptable heating time in the case of a heater).

[0038] Accordingly, the threshold voltage 118 can be set based on various factors (e.g., the desired energy savings, the desired minimum load voltage, the load type). For applications that typically desire a relatively high load voltage 108 (e.g., an intermittent heater), the battery threshold can constitute a good value for the threshold voltage 118. This is because most of the discharge cycle can be spent in the direct-through mode 114 while still achieving a relatively high load voltage.

[0039] Figure 5 An example logic flow 500 for implementing power converter control using the direct-through mode and the switching mode is illustrated. The example logic flow 500 can be implemented by the controller 112. The example logic flow 500 can include one or more operations, actions, or functions illustrated in one or more of blocks 502, 504, and / or 506. Although illustrated as discrete blocks, depending on the desired implementation, the individual blocks can be split into additional blocks, combined into fewer blocks, eliminated, executed in a different order, or executed in parallel.

[0040] Optionally, at decision 502, it can be determined whether the device has an auxiliary power source. For example, it can be determined whether the auxiliary power source indication 122 indicates that an external power source is connected to the system 100 (e.g., in addition to the battery 102). If an external power source is connected (e.g., "yes" from decision 502), the power converter 110 can operate in the switching mode 116. If no external power source is connected (e.g., "no" from decision 502), the example logic flow 500 can proceed to decision 504.

[0041] Optionally, at decision 504, it can be determined whether the device is in a power-saving mode. For example, it can be determined whether the user mode indication 120 indicates that the system 100 will operate in the power-saving mode. If it is determined that the system 100 does not operate in the power-saving mode (e.g., normal mode or "no" from decision 504), the power converter 110 can be operated in the switching mode 116. If it is determined that the system 100 operates in the power-saving mode (e.g., "yes" from decision 504), the example logic flow 500 can proceed to decision 506.

[0042] At decision 506, it can be determined whether the battery voltage meets the threshold voltage. For example, it can be determined whether the battery voltage 104 meets the threshold voltage 118. If the battery voltage 104 meets the threshold voltage 118 (e.g., greater than the threshold voltage 118, or greater than or equal to the threshold voltage 118), the power converter 110 can be operated in the direct-through mode 114. If the battery voltage 104 does not meet the threshold voltage 118 (e.g., less than the threshold voltage 118, or less than or equal to the threshold voltage 118), the power converter 110 can be operated in the switching mode 116.

[0043] Figure 6 Illustrated is an example method 600 for implementing power converter control using a direct mode and a switching mode. The example method 600 can be implemented by a controller 112. The example method 600 can include one or more operations, actions, or functions illustrated in one or more of blocks 602, 604, and / or 606. Although illustrated as discrete blocks, depending on the desired implementation, each block can be split into additional blocks, combined into fewer blocks, eliminated, executed in a different order, or executed in parallel.

[0044] At 602, determine the battery voltage of the device battery. For example, the controller 112 can determine the battery voltage 104.

[0045] At 604, based on whether the battery voltage meets a threshold voltage, select a direct mode or a switching mode for the power converter of the device. For example, the controller 112 can compare the battery voltage 104 with the threshold voltage 118. If the battery voltage 104 meets the threshold voltage 118 (e.g., is greater than the threshold voltage 118, or is greater than or equal to the threshold voltage 118), then the controller 112 can select the direct mode 114. Conversely, if the battery voltage 104 does not meet the threshold voltage 118 (e.g., is less than the threshold voltage 118, or is less than or equal to the threshold voltage 118), then the controller 112 can select the switching mode 116.

[0046] At 606, based on the selection, configure the power converter to operate in the direct mode or the switching mode. For example, by configuring the switch 200 (or causing the configuration of the switch 200) to operate as discussed above, the controller 112 can cause the power converter 110 to operate in the direct mode 114 or the switching mode 116.

[0047] The flowcharts and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagram can represent a module, segment, or portion of instructions, which includes one or more executable instructions for implementing a particular logical function. In some alternative implementations, the functions noted in the blocks may not occur in the order noted in the figures. For example, depending on the functionality involved, two blocks shown in succession may in fact be implemented substantially simultaneously, or the blocks may sometimes be implemented in the reverse order. It should also be noted that each block in the block diagrams and / or flowchart illustrations, and combinations of blocks in the block diagrams and / or flowchart illustrations, can be implemented by a special purpose hardware-based system that performs the specified functions or actions, or by a combination of special purpose hardware and computer instructions.

[0048] The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present invention. As used herein, unless the context clearly dictates otherwise, the singular forms "a", "an" and "the" are also intended to include the plural forms. It should also be understood that when the terms "comprises" and / or "comprising" are used in this specification, it specifies the presence of the stated features, integers, steps, operations, elements, and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.

[0049] All structural, material, acts, and equivalents of the means or step plus function elements in the following claims, if any, are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The embodiments disclosed herein are presented for purposes of illustration and description, but are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. These embodiments were chosen and described in order to best explain the principles of the invention and its practical application and to enable others of ordinary skill in the art to understand the invention in various embodiments with various modifications suited to the particular use contemplated.

Claims

1. A method, comprising: Determining a battery voltage of a battery of a device; Selecting a direct - through mode or a switching mode for a power converter of the device based on whether the battery voltage meets a threshold voltage; And Configuring the power converter to operate in the direct - through mode or the switching mode based on the selection, wherein: In the direct - through mode, the power converter is configured to generate a load voltage to a load, the load voltage being equal to the battery voltage, and In the switching mode, the power converter is configured to provide the load voltage equal to the threshold voltage.

2. The method according to claim 1, wherein the threshold voltage corresponds to a nominal voltage of the battery.

3. The method according to claim 1, wherein the method is performed in response to determining that the device will operate in a power - saving mode.

4. The method according to claim 1, wherein the power converter is a buck - boost power converter.

5. The method according to claim 1, wherein the power converter is a boost power converter.

6. The method according to claim 1, wherein the selection includes selecting the direct - through mode in response to determining that the battery voltage meets the threshold voltage.

7. The method according to claim 1, wherein the selection includes selecting the switching mode in response to determining that the battery voltage does not meet the threshold voltage.

8. The method according to claim 1, wherein in the direct - through mode, at least one high - side switch in the power converter remains on, and at least one low - side switch in the power converter remains off.

9. The method according to claim 1, wherein the load includes a heating element.

10. The method according to claim 1, wherein the load is configured to accept a load voltage in a range from a fully - charged voltage corresponding to a fully - charged state of the battery to at least the threshold voltage.

11. A semiconductor device, comprising: A controller configured to: Determine a battery voltage of a battery of a device; Determine whether the battery voltage meets a threshold voltage; And In response to determining that the battery voltage meets the threshold voltage, cause the power converter of the device to operate in a direct - through mode, wherein the power converter provides a load voltage equal to the battery voltage to a load; or In response to determining that the battery voltage does not meet the threshold voltage, cause the power converter to operate in a switching mode, wherein the power converter provides the load voltage equal to the threshold voltage.

12. The controller according to claim 11, wherein the controller is further configured to: Determine whether the device is operating in a normal mode or a power - saving mode; and In response to determining that the device is operating in the normal mode, cause the power converter of the device to operate in the switching mode.

13. The controller according to claim 11, wherein the threshold voltage corresponds to a nominal voltage of the battery.

14. The controller according to claim 11, wherein the power converter is a buck-boost power converter.

15. The controller according to claim 11, wherein the power converter is a boost power converter.

16. The controller according to claim 11, wherein operating the power converter in the direct-conduction mode or the switching mode includes configuring the operation of two or four switches of the power converter.

17. The controller according to claim 11, wherein the load is configured to accept a load voltage in a range from a fully charged voltage to at least the threshold voltage.

18. A system, comprising: a battery; a load configured to accept a load voltage between a fully charged battery voltage and a lower voltage; a power converter connected between the battery and the load; and a controller configured to: determine a voltage of the battery; determine whether the voltage meets a threshold voltage; and in response to determining that the voltage meets the threshold voltage, operate the power converter in a direct-conduction mode, wherein the power converter provides the load voltage equal to the battery voltage to the load; or in response to determining that the voltage does not meet the threshold voltage, operate the power converter in a switching mode, wherein the power converter provides the load voltage equal to the threshold voltage.

19. The system according to claim 18, wherein: the power converter includes a plurality of switches; and one or more high-side switches in the power converter remain in an on state in the direct-conduction mode.

20. The system according to claim 18, wherein the threshold voltage corresponds to the lower voltage.

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