Conversion circuit and bootstrap voltage control method thereof

Abstract

The present invention discloses a conversion circuit for converting input power into output power. The conversion circuit includes a switching circuit, a bootstrap circuit, and a control module. The switching circuit includes a power inductor, a first switch, and a second switch, which are connected to the midpoint of the switching circuit. The bootstrap circuit receives input power and provides a bootstrap voltage to drive the first switch. When the bootstrap voltage falls below a lower bootstrap threshold, the control module turns on the bootstrap circuit and the second switch to increase the bootstrap voltage. When the inductor current at the midpoint of the switching circuit increases in the reverse direction to a reverse threshold, the control module turns off the bootstrap circuit and the second switch.

Description

Technical Field

[0001] The present invention relates to a conversion circuit and a control method thereof, and in particular to a conversion circuit with bootstrap voltage control and a bootstrap voltage control method thereof. Background Art

[0002] Due to the rapid growth of the information industry in recent years, power supplies have played a crucial role, especially with the increasing power requirements of large-scale information equipment. Consequently, the output power of power supplies has also increased due to load demands. The circuitry primarily responsible for power conversion within a power supply is called the conversion circuit. This circuit converts input power into output power, providing a stable voltage to supply the load. The conversion circuit typically includes several switches and at least one power inductor. An internal controller controls the switching of these switches, causing the power inductor to store and release energy, thereby controlling the conversion circuit's conversion of input power into output power.

[0003] In a conversion circuit, several switches typically have at least one reference potential point that is not the circuit's ground point. To ensure that the controller's signal can successfully drive this switch, a bootstrap voltage is typically provided to boost the voltage at the switch's control terminal, enabling the controller to successfully drive the switch into conduction. However, the element capable of storing the bootstrap voltage can only be charged when a charging path is established between the element and the input power supply. Therefore, when the conversion circuit is lightly loaded or unloaded, the element may lack a charging path for an extended period, causing the bootstrap voltage to gradually deplete. If the stored energy is naturally depleted to the point where it can no longer drive the switch, the conversion circuit may become unstable or even fail.

[0004] On the other hand, if the bootstrap voltage storage device is charged too quickly, some switches within the converter circuit can accidentally turn on due to the short switching time. This can cause the input power to be directly connected to ground through the switch conduction, resulting in excessive current and damage to the switch. Conversely, if the bootstrap voltage storage device is charged for too long, the output power of the converter circuit can be consumed too low by the charging path, causing the output power voltage to drop too low. Therefore, whether the bootstrap voltage storage device is charged too quickly or too long, it will adversely affect the converter circuit.

[0005] Therefore, how to design a conversion circuit with bootstrap voltage control and its bootstrap voltage control method to control the charging time of the element storing the bootstrap voltage is a major research topic that the inventors of this case want to conduct. Summary of the Invention

[0006] To address the aforementioned issues, the present invention provides a conversion circuit with bootstrap voltage control to overcome the problems of the prior art. The conversion circuit of the present invention converts an input power source and provides an output power source at an output node, and the conversion circuit includes a switching circuit, a bootstrap circuit, and a control module. The switching circuit is coupled between the input power source and the output node, and includes a power inductor, a first switch, and a second switch, wherein the power inductor, the first switch, and the second switch are connected to the midpoint of the switching circuit. The bootstrap circuit receives input power and provides a bootstrap voltage to drive the first switch. The control module is configured to provide a first control signal to control the first switch and a second control signal to control the second switch. When the bootstrap voltage is lower than a lower bootstrap threshold, the control module turns on the bootstrap circuit and the second switch to increase the bootstrap voltage. When the inductor current at the midpoint of the switching circuit increases in the reverse direction to a reverse threshold, the control module turns off the bootstrap circuit and the second switch.

[0007] To address the aforementioned issues, the present invention provides a bootstrap voltage control method for a conversion circuit to overcome the problems of the prior art. The conversion circuit of the present invention converts an input power supply into an output power supply, and the conversion circuit includes a switching circuit and a bootstrap circuit. The switching circuit includes a first switch and a second switch, and the bootstrap voltage control method includes the following steps: (a) providing a first control signal to control the first switch based on feedback from the output power supply, and providing a second control signal to control the second switch. (b) The bootstrap circuit receives input power and provides a bootstrap voltage to drive the first switch. (c) detecting the bootstrap voltage, and when the bootstrap voltage is lower than a lower bootstrap threshold, turning on the bootstrap circuit and the second switch to increase the bootstrap voltage. (d) detecting the inductor current at the midpoint of the switching circuit to which the first and second switches are connected, and when the inductor current increases in the reverse direction to a reverse threshold, turning off the bootstrap circuit and the second switch.

[0008] The primary purpose and function of the present invention is to control the bootstrap voltage to a value lower than a lower threshold, thereby energizing the bootstrap circuit and the second switch to generate a charging path for the bootstrap circuit. Furthermore, when the control module detects that the inductor current at the midpoint of the switching circuit has increased in the reverse direction and reached a reverse threshold, the bootstrap circuit and the second switch are deenergized, thereby terminating the charging path. This allows for controlling the charging time of the element storing the bootstrap voltage, thereby preventing damage to the switching circuit or excessively low output voltage caused by excessively long or short charging times.

[0009] In order to further understand the techniques, means and effects adopted by the present invention to achieve the intended objectives, please refer to the following detailed description of the present invention and the accompanying drawings. It is believed that the objectives, features and characteristics of the present invention can be understood in depth and in detail. However, the accompanying drawings are provided for reference and illustration only and are not intended to limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The circuit architecture diagram of the conversion circuit with bootstrap voltage control of the present invention is as follows:

[0011] Figure 2A This is a circuit diagram of the buck converter circuit of the present invention:

[0012] Figure 2B This is a circuit diagram of the boost converter circuit of the present invention:

[0013] Figure 3A Detailed circuit diagram of the first embodiment of the converter circuit with bootstrap voltage control according to the present invention:

[0014] Figure 3B This is a circuit block diagram of a control module applicable to the first embodiment of the conversion circuit of the present invention:

[0015] Figure 3C This is a flow chart of a bootstrap voltage control method applicable to the first embodiment of the conversion circuit of the present invention:

[0016] Figure 4A Detailed circuit diagram of the second embodiment of the converter circuit with bootstrap voltage control according to the present invention:

[0017] Figure 4B This is a circuit block diagram of a control module applicable to the second embodiment of the conversion circuit of the present invention:

[0018] Figure 4C This is a flow chart of the bootstrap voltage control method applicable to the second embodiment of the conversion circuit of the present invention:

[0019] Figure 4D FIG. 4 is a flow chart of a bootstrap voltage control method applicable to a second embodiment of a conversion circuit according to the present invention.

[0020] Wherein, the reference numerals:

[0021] 100, 100'...conversion circuit

[0022] 1…Switching circuit

[0023] L…Power inductor

[0024] Q1…First switch

[0025] Q2…Second switch

[0026] LX…switching circuit midpoint

[0027] 2…Bootstrap circuit

[0028] 22…Bootstrap switch

[0029] 24…Bootstrap capacitor

[0030] 26… Voltage Regulator

[0031] 3.3'...Control module

[0032] 32…Voltage detection unit

[0033] 34…Current detection unit

[0034] 36…Control unit

[0035] 362…Current comparison unit

[0036] 364…Pulse Width Modulation Unit

[0037] 38…Threshold adjustment module

[0038] 382…timing unit

[0039] 384…Zero current pulse counting unit

[0040] 386…Threshold adjustment unit

[0041] 4…Drive circuit

[0042] OUT…output node

[0043] 200...load

[0044] Vin…Input power

[0045] Vo…output power

[0046] Vcc…Input power

[0047] Vboost…bootstrap voltage

[0048] Ii1~Ii3…Inductor current

[0049] Sc1…first control signal

[0050] Sc2…Second control signal

[0051] Sv…voltage signal

[0052] Si…current signal

[0053] S1~S5…The first to fifth signals

[0054] Lc…Charging path

[0055] TD…Scheduled time period

[0056] NOC1~NOC3…bootstrap lower threshold

[0057] (S100)~(S400)…steps

[0058] A~C…dashed line DETAILED DESCRIPTION

[0059] The technical content and detailed description of the present invention are described below with reference to the accompanying drawings:

[0060] See also Figure 1 This is a circuit diagram of a converter circuit with bootstrap voltage control according to the present invention. The converter circuit 100 receives an input power source Vin and is coupled to a load 200. The converter circuit 100 converts the input power source Vin into an output power source Vo, which is then provided from an output node OUT to power the load 200. The converter circuit 100 includes a switching circuit 1, a bootstrap circuit 2, and a control module 3. The switching circuit 1 is coupled between the input power source Vin and the output node OUT. The switching circuit 1 includes a power inductor L, a first switch Q1, and a second switch Q2. The power inductor L, the first switch Q1, and the second switch Q2 are connected to a switching circuit midpoint LX. The bootstrap circuit 2 receives input power Vcc and, based on the input power Vcc, provides a bootstrap voltage Vboost to drive the first switch Q1. Specifically, the reference potential of the first switch Q1 is primarily the voltage at the switching circuit midpoint LX, not ground. Therefore, the bootstrap voltage Vboost is required to increase the voltage at the control terminal of the first switch Q1 to successfully turn on the first switch Q1.

[0061] The control module 3 is coupled to the first switch Q1 and the second switch Q2, and is used to control the switching of the switching circuit 1 based on the feedback of the output power Vo to adjust and stabilize the voltage value of the output power Vo. Specifically, the control module 3 is used to provide a first control signal Sc1 based on the feedback of the output power Vo to control the first switch Q1, and to provide a second control signal Sc2 based on the feedback of the output power Vo to control the second switch Q2. The structure of the switching circuit 1 will vary depending on whether it is a buck converter or a boost converter. For details, please refer to Figure 2A The circuit structure diagram of the buck converter circuit of the present invention is shown in FIG. Figure 2B The circuit structure diagram of the boost converter circuit of the present invention is shown in FIG. Figure 1 .exist Figure 2A In the embodiment, the first switch Q1 is coupled between the input power source Vin and the midpoint LX of the switching circuit, and the power inductor L is coupled between the output node OUT and the midpoint LX of the switching circuit. Figure 2B In the embodiment of the present invention, the first switch Q1 is coupled between the output node OUT and the midpoint LX of the switching circuit, and the power inductor L is coupled between the input power source Vin and the midpoint LX of the switching circuit. Therefore, a feature of the present invention is that the bootstrap voltage control method of the bootstrap circuit 2 is applicable to any converter circuit having the bootstrap circuit 2.

[0062] See also Figure 3A This is a detailed circuit diagram of the first embodiment of the converter circuit with bootstrap voltage control according to the present invention. Figures 1-2B . In order to easily illustrate the features of the present invention, this embodiment is illustrated by a buck converter circuit 100. The converter circuit 100 further includes a drive circuit 4, which is coupled between the control module 3 and the switching circuit 1, and receives the bootstrap voltage Vboost provided by the bootstrap circuit 2 as the power supply of the drive circuit 4. Therefore, the drive circuit 4 can drive the first switch Q1 to be turned on in response to the first control signal Sc1 being a first level. The bootstrap circuit 2 includes a bootstrap switch 22 and a bootstrap capacitor 24, and the bootstrap switch 22 receives input power Vcc. The bootstrap capacitor 24 is coupled between the bootstrap switch 22 and the midpoint LX of the switching circuit, and stores the input power Vcc based on the conduction of the bootstrap switch 22 to provide the bootstrap voltage Vboost.

[0063] When the bootstrap switch 22 is on, the input power Vcc charges the bootstrap capacitor 24 through the bootstrap switch 22. Conversely, when the bootstrap switch 22 is off, the input power Vcc cannot charge the bootstrap capacitor 24 through the bootstrap switch 22. Alternatively, the bootstrap circuit 2 may optionally include a voltage regulator 26. When the bootstrap circuit 2 does not include the voltage regulator 26, the source of the input power Vcc may be an external device (not shown). When the bootstrap circuit 2 includes the voltage regulator 26, the voltage regulator 26 receives the input power Vin and is coupled to the bootstrap switch 22. The voltage regulator 26 may be, for example, but not limited to, a linear regulator that converts the input power Vin into the input power Vcc. It is worth noting that in one embodiment of the present invention, the internal structure of the bootstrap circuit 2 is merely one of many implementations, and the preferred embodiment is not limited thereto. Any bootstrap circuit 2 structure that can provide power through a bootstrap method to enable the normal operation of the associated circuitry controlling the conduction of the high-bridge switch (i.e., the first switch Q1) is included within the scope of this embodiment.

[0064] The control module 3 is used to detect the magnitude of the bootstrap voltage Vboost on the bootstrap capacitor 24 and the magnitude of the inductor current Ii at the midpoint LX of the switching circuit. When the control module 3 determines that the bootstrap voltage Vboost is lower than the bootstrap lower threshold, it indicates that the energy stored in the bootstrap capacitor 24 is insufficient, potentially causing the driver circuit 4 to enter undervoltage lockout (UVLO), preventing the driver circuit 4 from successfully driving the first switch Q1 to conduct, resulting in failure of the entire converter circuit 100. This situation typically occurs when the load 200 is lightly loaded or no-load, and the converter circuit 100 is operating in discontinuous conduction mode (DCM), or even a low-power mode such as burst mode, pulse skip mode, or off-time modulation (hereinafter collectively referred to as DCM).

[0065] Because the conversion circuit 100 is operated in a discontinuous conduction mode, the interval between the two turns on and off of the second switch Q2 is long. During the long off-circuit period of the second switch Q2, the bootstrap capacitor 24 cannot be charged for a long time. Therefore, it is easy to cause insufficient bootstrap voltage Vboost. Therefore, when the bootstrap voltage Vboost is lower than the bootstrap lower threshold, the control module 3 turns on the bootstrap switch 22 and the second switch Q2 of the bootstrap circuit 2 to form a charging path Lc from the input power Vcc, the bootstrap switch 22, the bootstrap capacitor 24, the switching circuit midpoint LX, the second switch Q2 to the ground point, so that the bootstrap capacitor 24 is charged and the bootstrap voltage Vboost is pulled up, thereby preventing the bootstrap voltage Vboost from being too low and entering undervoltage lockout.

[0066] On the other hand, due to the establishment of the charging path Lc, the output power Vo at the output node is fed back to the second switch Q2 through the power inductor L, so the inductor current Ii gradually decreases from its original positive value (flowing from the switching circuit midpoint LX to the output node) to a negative value, and the voltage of the output power Vo gradually decreases. In order to (1) prevent the second switch Q2 from being on for too short a period of time to charge the bootstrap capacitor 24, causing the first switch Q1 and the second switch Q2 to malfunction and turn on simultaneously, and (2) prevent the charging path Lc from being established for too long, causing the reverse negative inductor current Ii to be too low, causing the voltage of the output power Vo to be pulled too low; therefore, the control module 3 must adjust the time when the second switch Q2 is turned off to stop charging the bootstrap capacitor 24. Specifically, after the charging path Lc is established, the control module 3 also detects the magnitude of the inductor current Ii at the switching circuit midpoint LX. When the inductor current Ii at the midpoint LX of the switching circuit increases in the reverse direction to reach the reverse threshold, the control module 3 turns off the bootstrap switch 22 and the second switch Q2 of the bootstrap circuit 2 to cut off the charging path Lc.

[0067] When the inductor current Ii at the switching circuit midpoint LX increases in the reverse direction to the reverse threshold, the control module 3 also detects the bootstrap voltage Vboost on the bootstrap capacitor 24 to confirm whether the bootstrap voltage Vboost has been effectively pulled up to above the lower bootstrap threshold or is still below the lower bootstrap threshold. If the bootstrap voltage Vboost is still below the lower bootstrap threshold, it indicates that there may be a path abnormality, a short circuit, or component damage in the conversion circuit 100, causing energy from the bootstrap capacitor 24 to leak through a hidden path. Therefore, when the control module 3 determines that the bootstrap voltage Vboost is below the lower bootstrap threshold, the control module 3 determines that the conversion circuit 100 has failed. When the bootstrap voltage Vboost is above the lower bootstrap threshold, it indicates that the bootstrap capacitor 24 is normal and subsequent operations can continue. Therefore, the control module 3 switches the switching circuit 1 until the output power supply Vo increases in the forward direction to exceed a predetermined voltage, allowing the load 200 to continue to operate normally based on the voltage of the output power supply Vo. It is worth noting that in one embodiment of the present invention, the bootstrap lower threshold may be a hysteresis range. For example, but not limited to, when the bootstrap voltage Vboost falls below the bootstrap lower threshold of 3V, charging of the bootstrap capacitor 24 may be triggered. Charging may be stopped only after the bootstrap voltage Vboost reaches 5V. The predetermined voltage of the output power supply Vo may also be similarly determined and will not be further described here.

[0068] See also Figure 3B This is a block diagram of the control module circuit of the first embodiment of the conversion circuit of the present invention, and is also referred to in conjunction with FIG. Figures 1 to 3AThe control module 3 includes a voltage detection unit 32, a current detection unit 34, and a control unit 36. The voltage detection unit 32 is coupled to the bootstrap capacitor 24 of the bootstrap circuit 2 to detect the bootstrap voltage Vboost on the bootstrap capacitor 24 and provide a voltage signal Sv. The current detection unit 34 is coupled to the midpoint LX of the switching circuit and is used to detect the inductor current Ii flowing through the midpoint LX of the switching circuit and provide a current signal Si. The control unit 36 ​​is coupled to the voltage detection unit 32, the current detection unit 34, and the switching circuit 1, and provides a first control signal Sc1 and a second control signal Sc2 based on the feedback of the output power supply Vo, so as to adjust and stabilize the voltage value of the output power supply Vo through the first control signal Sc1 and the second control signal Sc2. The control unit 36 ​​also obtains the magnitude of the bootstrap voltage Vboost by receiving the voltage signal Sv, and obtains the magnitude of the inductor current Ii by receiving the current signal Si, so as to control the bootstrap switch 22, the first switch Q1, and the second switch Q2 of the bootstrap circuit based on the bootstrap voltage Vboost and the inductor current Ii. The control unit 36 ​​includes a current comparison unit 362 and a pulse width modulation unit 364. The current comparison unit 362 is coupled to the current detection unit 34 and the pulse width modulation unit 364, and the pulse width modulation unit 364 is coupled to the voltage detection unit 32 and the switching circuit 1. The current comparison unit 362 is used to determine whether the inductor current Ii is lower than the reverse threshold and provide a first signal S1 to the pulse width modulation unit 364, so that the pulse width modulation unit 364 performs pulse width modulation accordingly to provide a first control signal Sc1 and a second control signal Sc2.

[0069] See also Figure 3C This is a flowchart of the bootstrap voltage control method of the first embodiment of the conversion circuit according to the present invention, and is also referred to in conjunction with FIG. Figures 1 to 3BThe bootstrap voltage control method primarily adjusts the bootstrap voltage Vboost of the bootstrap capacitor 24 to prevent the driver circuit 4 from accidentally entering undervoltage lockout. It also prevents the switching between the first switch Q1 and the second switch Q2 from being too short when charging the bootstrap capacitor 24, and prevents the charging path Lc from being established too long. Therefore, the control unit 36 ​​provides a first control signal Sc1 to control the first switch Q1 and a second control signal Sc2 to control the second switch Q2 based on feedback from the output power source Vo. At this time, the bootstrap circuit 2 also receives input power Vcc and provides a bootstrap voltage Vboost to drive the first switch Q1, allowing the driver circuit 4 to control the first switch Q1 based on the high-level first control signal Sc1. Next, the converter circuit 100 is detected to determine whether it is operating in discontinuous conduction mode (S100). If the converter circuit 100 is operating in discontinuous conduction mode (which can be detected by the control unit 36), it is determined whether the bootstrap voltage is below the bootstrap lower threshold (S120). Otherwise, the process returns to step (S100) and continues testing. In step (S120), the control unit 36 ​​determines the magnitude of the bootstrap voltage Vboost via the voltage signal Sv. When the bootstrap voltage Vboost falls below the lower threshold, the control unit 36 ​​controls the second switch Q2 to conduct (S140). Otherwise, the process returns to step (S100) for continued detection. In step (S140), the control unit 36 ​​controls the second switch Q2 to conduct by providing a second control signal Sc2, thereby generating a charging path Lc for charging the bootstrap capacitor 24. Whether the bootstrap switch 22 of the bootstrap circuit 2 is controlled to conduct depends on the internal circuit structure of the bootstrap circuit 2.

[0070] Next, the control unit 36 ​​determines whether the inductor current Ii has increased in the reverse direction to a reverse threshold (S160). The control unit 36 ​​determines the magnitude of the inductor current Ii via the current signal Si. If the inductor current Ii has not increased in the reverse direction to the reverse threshold, the control unit 36 ​​returns to step (S140) to continuously turn on the second switch Q2. When the inductor current Ii has increased in the reverse direction to the reverse threshold, the control unit 36 ​​determines whether the bootstrap voltage Vboost is still below the bootstrap lower threshold (S180). If the bootstrap voltage Vboost is above the bootstrap lower threshold, the control unit 36 ​​determines that the bootstrap voltage Vboost is temporarily sufficient and that the converter circuit 100 does not experience any path abnormalities, short circuits, or component damage. The control unit 36 ​​then returns to step (S100) to continuously confirm whether the converter circuit 100 is still operating in discontinuous conduction mode. At this point, the control unit 36 ​​also controls the switching circuit 1 to switch until the output power Vo increases in the forward direction to exceed a predetermined voltage. When the inductor current Ii has increased in the reverse direction to the reverse threshold and the bootstrap voltage Vboost is still lower than the bootstrap lower threshold, it means that the conversion circuit 100 may have a path abnormality, a short circuit, or a damaged component, causing the energy of the bootstrap capacitor 24 to leak through a hidden path. Therefore, it is determined that the conversion circuit has failed (S200).

[0071] See also Figure 4A This is a detailed circuit diagram of the second embodiment of the conversion circuit with bootstrap voltage control of the present invention, and is also referred to in conjunction with Figures 1~3C The conversion circuit 100 of this embodiment is Figure 3A The difference between the converter circuit 100 and the control module 3' is that the control module 3' further includes a threshold adjustment module 38. The threshold adjustment module 38 is primarily used to adjust the reverse threshold to reduce the drop in output power Vo caused by negative inductor current Ii, thereby reducing the number of switching cycles required by the switching circuit 1 to increase the output power Vo in a positive direction to above a predetermined voltage. Specifically, when the inductor current Ii increases in the reverse direction to the reverse threshold, the voltage of the output power Vo will fall below the predetermined voltage. To prevent the output power Vo from being too low and failing to meet the requirements of the load 200, the voltage of the output power Vo must be increased in a positive direction to above the predetermined voltage. To achieve this, the control module 3' must control the switching circuit 1 to switch at least once to increase the output power Vo. However, if the inductor current Ii increases in the reverse direction too much, the voltage of the output power Vo will often drop too low. The control module 3' must control the switching circuit 1 to switch several times to increase the output power Vo in a positive direction to above the predetermined voltage, resulting in additional power consumption.

[0072] Therefore, the threshold adjustment module 38 is configured to gradually increase the reverse threshold to reduce the number of switching cycles of the switching circuit 1. This ensures that, after the inductor current Ii increases in the reverse direction to the reverse threshold, the control module 3' only needs to control the switching circuit 1 to switch once in order to increase the output power Vo in the forward direction above a predetermined voltage. Furthermore, the threshold adjustment module 38 is coupled to the control unit 36 ​​and measures a predetermined period of time based on the bootstrap voltage Vboost falling below the bootstrap lower threshold. During the predetermined period of time, the threshold adjustment module 38 counts the number of times the first switch Q1 conducts and adjusts the reverse threshold based on this number of times the first switch Q1 conducts, gradually increasing the reverse threshold to reduce the number of times the first switch Q1 conducts (corresponding to the number of times the switching circuit 1 switches).

[0073] See also Figure 4B This is a block diagram of a control module circuit applicable to the second embodiment of the conversion circuit of the present invention, and is also referred to in conjunction with FIG. Figures 1 to 4A The control module 3' of this embodiment is Figure 3BThe control module 3 of the embodiment differs in that the threshold adjustment module 38 includes a timing unit 382, ​​a zero-current pulse counting unit 384, and a threshold adjustment unit 386. The timing unit 382 is coupled to the control unit 36 ​​and, based on a second signal S2 indicating that the bootstrap voltage Vboost is below the bootstrap lower threshold, begins timing a predetermined period of time to provide a third signal S3 corresponding to the predetermined period of time. The zero-current pulse counting unit 384 is coupled to the timing unit 382 and the current comparison unit 362 and is configured to count, within a predetermined period of time, the number of at least one zero-current pulse applied when the first switch Q1 is turned on to restore the inductor current Ii to a positive value or zero.

[0074] Specifically, the zero-current pulse counting unit 384 receives the third signal S3 to determine the counting period and the first signal S1 to determine whether the inductor current Ii has fallen below the reverse threshold. The zero-current pulse counting unit 384 then receives the current signal Si to determine the magnitude of the inductor current Ii. When the inductor current Ii reaches zero, it generates a zero-current pulse and provides a fourth signal S4 corresponding to the number of zero-current pulses to the threshold adjustment unit 386. The number of times the first switch Q1 is turned on is related to the number of zero-current pulses. When the first switch Q1 is turned on / off, the inductor current Ii increases or decreases due to the on / off switching of the first switch Q1, causing the inductor current Ii to reach zero. The threshold adjustment unit 386 is coupled to the zero-current pulse counting unit 384 and the current comparison unit 362, and obtains the number of zero-current pulses based on the fourth signal S4. The threshold adjustment unit 386 determines whether to continue adjusting the reverse threshold based on the number of zero-current pulses. If it is determined that the reverse threshold needs to be further reduced toward zero, the fifth signal S5 corresponding to the reduced reverse threshold is provided to the current comparison unit 362, so that the current comparison unit 362 uses the reduced reverse threshold as the current reverse threshold.

[0075] Furthermore, when the threshold adjustment unit 386 detects that the current number of zero-crossing current pulses is less than or equal to the pulse count threshold preset by the threshold adjustment unit 386, the threshold adjustment unit 386 retains the current reverse threshold without modifying the currently stored reverse threshold and provides a fifth signal S5 corresponding to the current reverse threshold to the current comparison unit 362. The threshold adjustment module 38 uses this as the bootstrap voltage Vboost pull-up operation to indicate that the bootstrap voltage Vboost is again below the bootstrap lower threshold in the next cycle. When the threshold adjustment unit 386 detects that the current number of zero-crossing current pulses is greater than the pulse count threshold preset by the threshold adjustment unit 386, the threshold adjustment unit 386 replaces the original reverse threshold with the reduced reverse threshold and provides a fifth signal S5 corresponding to the reduced reverse threshold to the current comparison unit 362. The threshold adjustment unit 386 also temporarily stores the original reverse threshold before reduction as a successfully calibrated value for subsequent reverse threshold adjustments.

[0076] On the other hand, if during the reverse threshold reduction process, the inductor current Ii reversely increases to the reduced reverse threshold, and the bootstrap voltage Vboost is still below the lower bootstrap threshold, and the previously successfully adjusted value already exists, this means that the previous reverse threshold can still increase the bootstrap voltage Vboost above the lower bootstrap threshold. However, the current reduction in the reverse threshold results in a shorter charging time for the bootstrap capacitor 24, preventing the bootstrap voltage Vboost from effectively increasing above the lower bootstrap threshold. Therefore, the reverse threshold used this time after the reduction is invalid. Therefore, the threshold adjustment unit 386 replaces the reverse threshold with the stored successfully adjusted value (i.e., restoring the previously used reverse threshold, which can generally be considered as lowering the reverse threshold by a predetermined value away from zero).

[0077] It's worth noting that the pulse count threshold can preferably be set to correspond to the number of times the first switch Q1 is turned on only once during the counting period corresponding to the third signal S3. That is, the inductor current Ii will touch zero twice as the first switch Q1 switches from off, on, and off. However, this is not a limitation; the pulse count threshold can be adjusted upward based on actual needs.

[0078] See also Figure 4C This is a flowchart of the bootstrap voltage control method for the second embodiment of the conversion circuit according to the present invention, and is also referred to in conjunction with FIG. Figures 1 to 4B . Figure 4C The bootstrap voltage control method and Figure 3CThe bootstrap voltage control method differs in that it includes, between step (S120) and step (S140), the start of a predetermined time period (S130) and an additional reverse threshold adjustment loop. Specifically, in step (S130), when the bootstrap voltage Vboost falls below the bootstrap lower threshold, the threshold adjustment module 38 of the control module 3' begins timing the predetermined time period, preparing to count the number of zero crossings of the inductor current Ii during the predetermined time period. Then, if the determination in step (S180) is negative, the threshold adjustment loop is entered. Furthermore, if the determination in step (S180) is negative, the threshold adjustment module 38 stores the current reverse threshold as a successfully adjusted value and controls the switching circuit 1 to begin switching (S300). The purpose of controlling the switching circuit 1 to begin switching is to turn on the first switch Q1 to apply at least one zero-crossing current pulse, restoring the inductor current Ii to a positive value or zero, thereby causing the output power Vo to increase in a positive direction, thereby preventing the output power Vo from being too low and affecting the operation of the load 200. As the output power Vo increases in a positive direction and exceeds a predetermined voltage, the threshold adjustment module 38 of the control module 3' counts at least one zero-crossing current pulse when the inductor current reaches zero until the predetermined period ends (S320). The threshold adjustment module 38 generates a zero-crossing current pulse in response to the inductor current Ii reaching zero, and counts the number of zero-crossing current pulses. The number of zero-crossing current pulses is correlated to the number of times the first switch Q1 is turned on.

[0079] Then, determine whether the number of zero-crossing current pulses is greater than the pulse number threshold (S340). When it is known that the number of zero-crossing current pulses is greater than the pulse number threshold pre-set by the threshold adjustment module 38, the reverse threshold is raised by a preset value in the direction close to 0 (S360), so that the original reverse threshold is replaced by the reduced reverse threshold (the reverse threshold minus the preset value) (S100). When it is known that the number of zero-crossing current pulses is less than or equal to the pulse number threshold pre-set by the threshold adjustment module 38, the threshold adjustment module 38 continues to use the current reverse threshold and returns to step (S100). It is worth mentioning that in one embodiment of the present invention, the above-mentioned "threshold adjustment module 38 stores the current reverse threshold as a successfully adjusted value" is not limited to being executed in step 300, and it can be executed in any one of steps (S300) to (S360).

[0080] On the other hand, if the judgment in step (S180) is yes, then it is determined whether there is a previous successful calibration value (S380). If the judgment result is no, then it is determined that the conversion circuit has failed (S200). On the contrary, if the judgment result is yes, it means that the previous reverse threshold reduction can still increase the bootstrap voltage Vboost to above the bootstrap lower threshold, but the current reverse threshold reduction makes the charging time of the bootstrap capacitor 24 too short, and the reverse threshold used this time is an invalid calibration value. Therefore, the threshold adjustment module 38 replaces the reverse threshold with the stored successful calibration value (S400) and returns to step (S100). In other words, the reverse threshold used last time can generally be regarded as lowering the reverse threshold by a preset value away from 0.

[0081] See also Figure 4D This is a flowchart of the bootstrap voltage control method for the second embodiment of the conversion circuit according to the present invention, and is also referred to in conjunction with FIG. Figures 1 to 4B .exist Figure 4D In this example, TD represents a predetermined time period, and Ii1-Ii3 represent the inductor currents (or current signals corresponding to the inductor currents Ii1-Ii3). The inductor currents Ii1-Ii3 represent the inductor currents Ii1-Ii3 during different cycles, each of which is initiated when the bootstrap voltage Vboost transitions from above the bootstrap lower threshold to below the bootstrap lower thresholds NOC1-NOC3. Assuming that the control module 3' presets a pulse count threshold corresponding to one conduction of the first switch Q1, i.e., the control module 3' presets a pulse count threshold of two, the reverse threshold is adjusted.

[0082] Taking the inductor current Ii1 as the initial condition, when the control module 3' detects that the bootstrap voltage Vboost has fallen below the bootstrap lower threshold NOC1, the threshold adjustment module 38 of the control module 3' begins timing a predetermined period TD and controls the switching circuit 1 to switch until the output power Vo increases in the positive direction and exceeds the predetermined voltage. Therefore, the inductor current Ii begins to rise from the bootstrap lower threshold NOC1. After several switching cycles of the switching circuit 1, the output power Vo eventually increases in the positive direction and exceeds the predetermined voltage. Simultaneously, the control module 3' counts the number of zero crossings of the inductor current Ii1 during the predetermined period TD. During the predetermined period TD, the inductor current Ii1 touches zero six times, which infers that the first switch Q1 has turned on three times. Because the number of zero-current pulses (six) is greater than the pulse count threshold (two), the control module 3' replaces the original reverse threshold NOC1 with the reduced reverse threshold NOC2 and stores the original reverse threshold NOC1 as the successfully calibrated value.

[0083] Then, in the next cycle (indicated by dashed line A), control module 3' counts four zero-crossings of inductor current Ii2 during the predetermined period TD, still exceeding the pulse count threshold (two). Therefore, control module 3' replaces the original reverse-current threshold NOC2 with the reduced reverse-current threshold NOC3 and stores the original reverse-current threshold NOC2 as a successfully calibrated value. In the next cycle (indicated by dashed line B), control module 3' counts two zero-crossings of inductor current Ii3 during the predetermined period TD, equal to the pulse count threshold (two). Therefore, control module 3' continues to use the current reverse-current threshold NOC3 value stored in step 300, indicating a successful calibration.

[0084] Finally, assume that control module 3 previously stored reverse threshold NOC2 as a successfully calibrated value in the previous calibration cycle. In the next calibration cycle, the reverse threshold NOC3 decreases, causing the bootstrap voltage Vboost to fall below the lower threshold, leading to a failed adjustment. In this case, when the inductor current Ii3 increases in the reverse direction to the reverse threshold NOC3 in the next cycle, but the bootstrap voltage Vboost falls below the lower threshold, control module 3' determines whether a previously stored successfully calibrated value exists. Upon confirming the existence of a successfully calibrated value (i.e., the previous reverse threshold NOC2), control module 3' replaces the reverse threshold with the previously stored successfully calibrated value (i.e., the previous reverse threshold NOC2) (indicated by dashed line C).

[0085] However, the above description is merely a detailed description and drawings of preferred embodiments of the present invention. The features of the present invention are not limited thereto and are not intended to limit the present invention. The entire scope of the present invention shall be subject to the following patent application. All embodiments that conform to the spirit of the patent application and similar variations of the present invention shall be included in the scope of the present invention. Any changes or modifications that can be easily conceived by a person familiar with the art within the field of the present invention shall be covered by the following patent application.

Claims

1. A conversion circuit, characterized in that: The system converts an input power source to provide an output power source at an output node, comprising: a switching circuit coupled between the input power source and the output node, the switching circuit comprising a power inductor, a first switch, and a second switch, wherein the power inductor, the first switch, and the second switch are connected to a midpoint of the switching circuit; a bootstrap circuit receiving an input power and providing a bootstrap voltage to drive the first switch; and a control module for providing a first control signal to control the first switch and providing a second control signal to control the second switch; When the bootstrap voltage is lower than a bootstrap lower threshold and an inductor current at the midpoint of the switching circuit has not reversely increased to a reverse threshold, the control module continuously turns on the second switch, thereby conducting the bootstrap circuit and the second switch to increase the bootstrap voltage. When the inductor current reversely increases to the reverse threshold, the control module turns off the bootstrap circuit and the second switch and determines whether the increased bootstrap voltage is higher than the bootstrap lower threshold.

2. The conversion circuit according to claim 1, wherein: The conversion circuit further includes: A driving circuit is coupled between the control module and the switching circuit and receives the bootstrap voltage as a power source of the driving circuit to drive the first switch to conduct in response to the first control signal being at a first level.

3. The conversion circuit according to claim 1, wherein: When the inductor current increases in the reverse direction to the reverse threshold, the control module does not store a successful adjustment value, and the bootstrap voltage is lower than the bootstrap lower threshold, the control module determines that the conversion circuit is failed.

4. The conversion circuit according to claim 1, wherein: After the inductor current increases in the reverse direction to the reverse threshold, the control module controls the switching circuit to switch until the output power increases in the forward direction to exceed a predetermined voltage.

5. The conversion circuit according to claim 1, wherein: The control module includes: a voltage detection unit coupled to the bootstrap circuit and configured to detect the bootstrap voltage; a current detection unit coupled to the midpoint of the switching circuit and configured to detect the inductor current; a control unit coupled to the voltage detection unit, the current detection unit, and the switching circuit, and providing the first control signal and the second control signal based on feedback from the output power supply, and controlling the bootstrap circuit, the first switch, and the second switch based on the bootstrap voltage and the inductor current; the control unit comprising: A current comparison unit is coupled to the current detection unit and is used to determine whether the inductor current is lower than the reverse threshold.

6. The conversion circuit according to claim 1, wherein: The control module further includes: a threshold adjustment module, which counts a predetermined period of time when the bootstrap voltage is lower than the bootstrap lower threshold; The threshold adjustment module counts the number of times the first switch is turned on during the predetermined period and adjusts the reverse threshold based on the number of times. After the inductor current increases in the reverse direction to the reverse threshold, the threshold adjustment module stores the reverse threshold as a successfully adjusted value based on the fact that the bootstrap voltage is not lower than the bootstrap lower threshold.

7. The conversion circuit according to claim 6, wherein: The threshold adjustment module includes: a timing unit for timing the predetermined period of time based on the bootstrap voltage being lower than the bootstrap lower threshold; a zero current pulse counting unit, coupled to the timing unit and configured to count the number of at least one zero current pulse when the inductor current reaches zero during the predetermined period based on the inductor current being lower than the reverse threshold; and a threshold adjustment unit coupled to the zero current pulse counting unit and configured to adjust the reverse threshold based on the number of the at least one zero current pulse; The number of times the first switch is turned on is related to the number of the at least one zero-current-crossing pulse.

8. The conversion circuit according to claim 7, wherein: When the number of the at least one zero-crossing current pulse is less than or equal to a pulse number threshold, the threshold adjustment unit continues to use the current reverse threshold.

9. The conversion circuit according to claim 7, wherein: When the number of the at least one zero-crossing current pulse is greater than a pulse number threshold, the threshold adjustment unit replaces the reverse threshold with a reduced reverse threshold.

10. The conversion circuit according to claim 9, wherein: When the inductor current increases in the reverse direction to the reverse threshold, the bootstrap voltage is lower than the bootstrap lower threshold, and the successful adjustment value already exists, the threshold adjustment unit replaces the reverse threshold with the successful adjustment value.

11. The conversion circuit according to claim 1, wherein: The bootstrap circuit includes: a bootstrap switch coupled to the input power; a bootstrap capacitor coupled between the bootstrap switch and a midpoint of the switching circuit, and storing the input electrical energy when the bootstrap switch is turned on to provide the bootstrap voltage; and a voltage regulator receiving the input power and coupled to the bootstrap switch; The voltage regulator is used to convert the input power into the input electrical energy.

12. A bootstrap voltage control method for a conversion circuit, characterized in that: The conversion circuit converts an input power supply into an output power supply, and the conversion circuit includes a switching circuit and a bootstrap circuit; the switching circuit includes a first switch and a second switch, and the bootstrap voltage control method includes the following steps: (a) providing a first control signal to control the first switch and providing a second control signal to control the second switch based on feedback from the output power; (b) the bootstrap circuit receives an input power and provides a bootstrap voltage to drive the first switch; (c) detecting the bootstrap voltage and an inductor current at a midpoint of a switching circuit commonly connected to the first switch and the second switch, and when the bootstrap voltage is lower than a bootstrap lower threshold and the inductor current has not reversely increased to a reverse threshold, continuously turning on the second switch to conduct the bootstrap circuit and the second switch to increase the bootstrap voltage; (d) When the inductor current increases in the reverse direction to the reverse threshold, the bootstrap circuit and the second switch are turned off, and it is determined whether the boosted bootstrap voltage is higher than the bootstrap lower threshold.

13. The bootstrap voltage control method according to claim 12, wherein: Step (c) comprises the following steps: (c1) confirming that the conversion circuit enters a discontinuous conduction mode; and (c2) In the discontinuous conduction mode, determining whether the bootstrap voltage is lower than the bootstrap lower threshold.

14. The bootstrap voltage control method according to claim 12, wherein: The step (d) further comprises the following steps: (d1) after the inductor current increases in the reverse direction to the reverse threshold, determining whether the bootstrap voltage is lower than the bootstrap lower threshold, and determining that the conversion circuit has failed based on the bootstrap voltage being lower than the bootstrap lower threshold; and (d2) The switching circuit is switched until the output power increases in a positive direction and exceeds a predetermined voltage.

15. The bootstrap voltage control method according to claim 12, wherein: The step (d) further comprises the following steps: (d1) after the inductor current increases in the reverse direction to the reverse threshold, determining whether the bootstrap voltage is lower than the bootstrap lower threshold, and determining whether to store a successful adjustment value based on the bootstrap voltage being lower than the bootstrap lower threshold; and (d2) When the successful calibration value is not stored, the conversion circuit is determined to be failed.

16. The bootstrap voltage control method according to claim 15, wherein: The step (d1) is followed by the following steps: (d11) after the inductor current increases in the reverse direction to the reverse threshold, storing the reverse threshold as the successfully adjusted value based on the bootstrap voltage not being lower than the bootstrap lower threshold; (d12) The switching circuit is switched until the output power increases in a positive direction exceeding a predetermined voltage.

17. The bootstrap voltage control method according to claim 15, wherein: It also includes the following steps: (e) timing a predetermined period of time based on the bootstrap voltage being lower than the bootstrap lower threshold; and (f) Counting the number of times the first switch is turned on during the predetermined period, and adjusting the reverse threshold based on the number of times.

18. The bootstrap voltage control method according to claim 17, wherein: Step (f) comprises the following steps: (f1) counting the number of at least one zero-crossing current pulses during the predetermined period of time when the inductor current reaches zero; (f2) when the number of the at least one zero-current-crossing pulse is greater than a pulse number threshold, replacing the reverse threshold with a reduced reverse threshold; and (f3) When the number of the at least one zero-crossing current pulse is less than or equal to the pulse number threshold, continue to use the current reverse threshold.

19. The bootstrap voltage control method according to claim 18, wherein: Step (f) further comprises the following steps: (f4) When the inductor current increases in the reverse direction to the reverse threshold, the bootstrap voltage is lower than the bootstrap lower threshold, and the successful adjustment value already exists, the reverse threshold is replaced by the successful adjustment value.

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