Bootstrap device and buck-boost converter
By designing a first bootstrap circuit and a second bootstrap circuit that directly determine charging based on changes in the switching voltage and source terminal voltage in the bootstrap device, the problem of low charging efficiency of bootstrap capacitors in the prior art is solved, and efficient bootstrap capacitor charging is achieved.
Patent Information
- Application Number
- CN202311419972.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-10-30
- Publication Date
- 2025-05-02
AI Technical Summary
Existing bootstrap devices cannot efficiently charge the bootstrap capacitor, and require the periodic pull-down transistor source voltage of the external control circuit to be charged.
A bootstrap device is designed, including a first bootstrap circuit and a second bootstrap circuit. By directly determining whether to charge according to the change in the switching voltage, the source voltage of the transistor and the voltage difference between the bootstrap voltage, thereby avoiding the intervention of the external control circuit.
It realizes efficient charging of bootstrap capacitors, avoids periodic pull-down operations of external control circuits, and improves the charging efficiency of bootstrap devices.
Smart Images
Figure CN119921570A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to a device and a converter, in particular to a bootstrap device and a buck-boost converter. Background Art
[0002] See also Figure 1 The conventional buck-boost converter 1 includes four transistors 11, 12, 13, 14, and four pre-drivers 15, 16, 17, 18. When the buck-boost converter 1 operates in a buck mode, the transistors 11 and 13 are controlled by the pre-drivers 15 and 16 to switch between conduction and non-conduction, the transistor 12 is controlled by the pre-driver 17 to be continuously conducted, and the transistor 14 is controlled by the pre-driver 18 to be continuously non-conducted. When the buck-boost converter 1 operates in a boost mode, the transistor 11 is controlled by the pre-driver 15 to be continuously conducted, the transistor 13 is controlled by the pre-driver 16 to be continuously non-conducted, and the transistors 12 and 14 are controlled by the pre-drivers 17 and 18 to switch between conduction and non-conduction.
[0003] When operating in the buck mode or boost mode, the drain voltages of the transistors 11 and 12 are respectively the input voltage V in And the output voltage V out , which is a relatively high voltage in the circuit. If transistors 11 and 12 are to be fully turned on during operation, each of transistors 11 and 12 must have a sufficient gate-source voltage, that is, the gate-source voltage of each of transistors 11 and 12 must be higher than its own drain voltage. Therefore, a bootstrap voltage V higher than the drain voltage must be prepared. bst1 、V bst2 to provide the pre-drivers 15 and 17, so that the voltage of the control signal generated by the pre-drivers 15 and 17 for controlling the conduction of the transistors 11 and 12 can be higher than the corresponding drain voltage, and is used to generate the bootstrap voltage V bst1 、V bst2 The bootstrap device is Figure 1 As shown in symbol 2.
[0004] The existing bootstrap device 2 includes a linear regulator 21 for generating a regulated voltage, two bootstrap capacitors C bs1 , C bs2 And other components. Bootstrap capacitor C bs1 A bootstrap voltage V bst1 and a second end coupled to the source terminal n1 of the transistor 11. The bootstrap capacitor C bs2 A bootstrap voltage V bst2and a second end coupled to the source terminal n2 of the transistor 12. When the buck-boost converter 1 operates in the buck mode, the bootstrap capacitor C bs2 It must receive the current from the regulated voltage of the linear regulator 21 for charging in order to continuously provide sufficient bootstrap voltage V bst2 The pre-driver 17 is used to control the transistor 12 to be continuously turned on. However, due to the bootstrap capacitor C bs2 The second end of is coupled to the source terminal n2 of the transistor 12. In the buck mode, the voltage of the source terminal n2 of the transistor 12 is equal to the output voltage V out , and let the bootstrap capacitor C bs2 The voltage on the first terminal (i.e., the bootstrap voltage V bst2 ) is clamped to the voltage level V out '(That is, at this time V bst2 =V out '=V Cbs2 +V out , where V Cbs2 Represents the bootstrap capacitor C bs2 The cross voltage) leads to the bootstrap capacitor C bs2 Unable to receive the regulated voltage (V LVDD ) current to charge (so the regulated voltage is less than the bootstrap capacitor C bs2 The voltage on the first terminal, i.e. V LVDD <V bst2 (=V out ')), therefore, the voltage of the source terminal n2 of the transistor 12 must be periodically pulled down by an external control circuit to make the bootstrap capacitor C bs2 The voltage at the first end is V out 'Clamp back to the original bootstrap voltage V bst2 (At this time, the bootstrap capacitor C bs2 The voltage at the first end is less than the voltage level V out ', that is, V bst2 <V out '). When the regulated voltage (V LVDD ) is greater than the bootstrap capacitor C bs2 The voltage at the first end (i.e., V LVDD >V bst2 ), then the bootstrap capacitor C bs2 The current of the regulated voltage from the linear regulator 21 can be received for charging. Similarly, when the buck-boost converter 1 operates in the boost mode, the voltage of the source terminal n1 of the transistor 11 must be periodically pulled down by the external control circuit to make the bootstrap capacitor C bs1 The voltage at the first end is from the input voltage V in The voltage level (V in) clamps back to the original bootstrap voltage V bst1 When the regulated voltage (V LVDD ) is greater than the bootstrap capacitor C bs1 The voltage at the first end (i.e., V LVDD >V bst1 ), then the bootstrap capacitor C bs1 The current of the regulated voltage from the linear regulator 21 can be received for charging, so that sufficient bootstrap voltage V can be continuously provided. bst1 The pre-driver 15 is used to control the transistor 11 to be continuously turned on. Therefore, the existing bootstrap device 2 cannot provide the bootstrap capacitor C efficiently. bs1 , C bs2 Charging current. Summary of the invention
[0005] Therefore, the purpose of the present invention is to provide a bootstrap device that can charge the bootstrap capacitor more efficiently, so as to solve the problem that the existing bootstrap device cannot charge the bootstrap capacitor more efficiently because the voltage at one end of the bootstrap capacitor must be pulled down by an external control circuit before charging.
[0006] Therefore, the bootstrap device of the present invention is suitable for a buck-boost converter, which generates a DC output voltage according to a DC input voltage and includes a first transistor and a second transistor as a high-side switch. The bootstrap device includes a first bootstrap circuit and a second bootstrap circuit.
[0007] The first bootstrap circuit is used to generate a first bootstrap voltage to control the gate voltage of the first transistor to be greater than a first reference voltage, and receives a DC input voltage, a DC output voltage and a second bootstrap voltage, and is coupled to the source terminal of the first transistor. The first bootstrap circuit determines whether to charge according to at least one of the DC input voltage, the DC output voltage and the second bootstrap voltage according to whether the change of the voltage difference between the first switching voltage, the voltage level of the source terminal of the first transistor and the first bootstrap voltage is greater than a critical voltage, so that the first bootstrap voltage is maintained at a gate voltage greater than the first reference voltage that can be used to control the gate voltage of the first transistor.
[0008] The second bootstrap circuit receives a DC input voltage and a DC output voltage, is coupled to the first bootstrap circuit to receive the first bootstrap voltage, and is coupled to the source terminal of the second transistor. The second bootstrap circuit is used to generate a second bootstrap voltage to control the gate voltage of the second transistor to be greater than a second reference voltage, and output the second bootstrap voltage to the first bootstrap circuit. The second bootstrap circuit determines whether to charge according to at least one of the DC input voltage, the DC output voltage, and the first bootstrap voltage based on whether the change in the second switching voltage, the voltage level of the source terminal of the second transistor, and the voltage difference between the second bootstrap voltage is greater than a critical voltage, so that the second bootstrap voltage is maintained at a level that can be used to control the gate voltage of the second transistor to be greater than the second reference voltage.
[0009] In some embodiments, the first bootstrap circuit includes: a bootstrap transistor having a first terminal, a second terminal outputting a first bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor is used as the first switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the first transistor; a clamp circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, wherein the clamp circuit is used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, which is used to receive a DC input voltage and is coupled to the first terminal of the bootstrap transistor, and can generate a first voltage according to the DC input voltage. A charging current is output to the first end of the bootstrap transistor; a second charging circuit is used to receive the DC output voltage and is coupled to the first end of the bootstrap transistor, and can generate a second charging current according to the DC output voltage and output it to the first end of the bootstrap transistor; a third charging circuit is used to receive the second bootstrap voltage and is coupled to the first end of the bootstrap transistor, and can generate a third charging current according to the second bootstrap voltage and output it to the first end of the bootstrap transistor; and a driving unit is coupled to the control end of the bootstrap transistor and is used to receive the DC input voltage, the DC output voltage and the second bootstrap voltage, and provide a driving current to the control end of the bootstrap transistor accordingly.
[0010] In some embodiments, the first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, the anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the second bootstrap voltage, and the cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
[0011] In some embodiments, the driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, the first driving circuit, the second driving circuit and the third driving circuit respectively receive a DC input voltage, a DC output voltage and a second bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
[0012] In some embodiments, each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of a DC input voltage, a DC output voltage and a second bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.
[0013] In some embodiments, the second bootstrap circuit includes: a bootstrap transistor having a first terminal, a second terminal outputting a second bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor is used as the second switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the second transistor; a clamp circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, wherein the clamp circuit is used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, which is used to receive a DC input voltage and is coupled to the first terminal of the bootstrap transistor, and can generate a first voltage according to the DC input voltage. A charging current is output to the first end of the bootstrap transistor; a second charging circuit is used to receive the DC output voltage and is coupled to the first end of the bootstrap transistor, and can generate a second charging current according to the DC output voltage and output it to the first end of the bootstrap transistor; a third charging circuit is used to receive the first bootstrap voltage and is coupled to the first end of the bootstrap transistor, and can generate a third charging current according to the first bootstrap voltage and output it to the first end of the bootstrap transistor; and a driving unit is coupled to the control end of the bootstrap transistor and is used to receive the DC input voltage, the DC output voltage and the first bootstrap voltage, and provide a driving current to the control end of the bootstrap transistor accordingly.
[0014] In some embodiments, the first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, the anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the first bootstrap voltage, and the cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
[0015] In some embodiments, the driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, the first driving circuit, the second driving circuit and the third driving circuit respectively receive a DC input voltage, a DC output voltage and a first bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
[0016] In some embodiments, each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of a DC input voltage, a DC output voltage and a first bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.
[0017] The buck-boost converter of the present invention comprises a first transistor, a second transistor, a third transistor and a fourth transistor, the bootstrap device as described above, and a pre-driving circuit.
[0018] The first transistor has a drain terminal for receiving a DC input voltage, a source terminal, and a gate terminal. The second transistor has a drain terminal for outputting a DC output voltage, a source terminal, and a gate terminal. The third transistor has a drain terminal coupled to the source terminal of the first transistor, a grounded source terminal, and a gate terminal. The fourth transistor has a drain terminal coupled to the source terminal of the second transistor, a grounded source terminal, and a gate terminal.
[0019] The pre-driving circuit is coupled to the gate terminals of the first transistor, the second transistor, the third transistor and the fourth transistor, and is used to control the first transistor, the second transistor, the third transistor and the fourth transistor to be turned on or off, and is coupled to the bootstrap device to receive the first bootstrap voltage and the second bootstrap voltage, and controls the gate voltage of the first transistor to be greater than the first reference voltage according to the first bootstrap voltage, and controls the gate voltage of the second transistor to be greater than the second reference voltage according to the second bootstrap voltage.
[0020] In some embodiments, the first bootstrap circuit includes: a bootstrap transistor having a first terminal, a second terminal outputting a first bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor is used as the first switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the first transistor; a clamp circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, wherein the clamp circuit is used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, which is used to receive a DC input voltage and is coupled to the first terminal of the bootstrap transistor, and can generate a first voltage according to the DC input voltage. A charging current is output to the first end of the bootstrap transistor; a second charging circuit is used to receive the DC output voltage and is coupled to the first end of the bootstrap transistor, and can generate a second charging current according to the DC output voltage and output it to the first end of the bootstrap transistor; a third charging circuit is used to receive the second bootstrap voltage and is coupled to the first end of the bootstrap transistor, and can generate a third charging current according to the second bootstrap voltage and output it to the first end of the bootstrap transistor; and a driving unit is coupled to the control end of the bootstrap transistor and is used to receive the DC input voltage, the DC output voltage and the second bootstrap voltage, and provide a driving current to the control end of the bootstrap transistor accordingly.
[0021] In some embodiments, the first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, the anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the second bootstrap voltage, and the cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
[0022] In some embodiments, the driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, the first driving circuit, the second driving circuit and the third driving circuit respectively receive a DC input voltage, a DC output voltage and a second bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
[0023] In some embodiments, each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of a DC input voltage, a DC output voltage and a second bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.
[0024] In some embodiments, the second bootstrap circuit includes: a bootstrap transistor having a first terminal, a second terminal outputting a second bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor is used as the second switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the second transistor; a clamp circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, wherein the clamp circuit is used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, which is used to receive a DC input voltage and is coupled to the first terminal of the bootstrap transistor, and can generate a first voltage according to the DC input voltage. A charging current is output to the first end of the bootstrap transistor; a second charging circuit is used to receive the DC output voltage and is coupled to the first end of the bootstrap transistor, and can generate a second charging current according to the DC output voltage and output it to the first end of the bootstrap transistor; a third charging circuit is used to receive the first bootstrap voltage and is coupled to the first end of the bootstrap transistor, and can generate a third charging current according to the first bootstrap voltage and output it to the first end of the bootstrap transistor; and a driving unit is coupled to the control end of the bootstrap transistor and is used to receive the DC input voltage, the DC output voltage and the first bootstrap voltage, and provide a driving current to the control end of the bootstrap transistor accordingly.
[0025] In some embodiments, the first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, the anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the first bootstrap voltage, and the cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
[0026] In some embodiments, the driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, the first driving circuit, the second driving circuit and the third driving circuit respectively receive a DC input voltage, a DC output voltage and a first bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
[0027] In some embodiments, each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of a DC input voltage, a DC output voltage and a first bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.
[0028] Thus, the first bootstrap circuit of the present invention can directly determine whether to charge according to at least one of the DC input voltage, the DC output voltage and the second bootstrap voltage according to whether the change of the first switching voltage, the voltage level of the source terminal of the first transistor and the voltage difference between the first bootstrap voltage is greater than the critical voltage, and the second bootstrap circuit can directly determine whether to charge according to at least one of the DC input voltage, the DC output voltage and the first bootstrap voltage according to whether the change of the second switching voltage, the voltage level of the source terminal of the second transistor and the voltage difference between the second bootstrap voltage is greater than the critical voltage. Therefore, there is no need for the existing bootstrap device to require an external control circuit to periodically pull down the voltage of the source terminal of the transistor before charging the bootstrap capacitor, thereby enabling the bootstrap device of the present invention to achieve a more efficient effect of charging the bootstrap capacitor. BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Figure 1 is a circuit block diagram illustrating an existing bootstrap device for a buck-boost converter.
[0030] Figure 2 is a circuit block diagram illustrating an embodiment of a buck-boost converter utilizing the bootstrap device of the present invention.
[0031] Figure 3 is a circuit block diagram illustrating a first bootstrap circuit of the embodiment.
[0032] Figure 4 is a circuit block diagram illustrating a second bootstrap circuit of the embodiment.
[0033] Reference numerals
[0034] 1 Buck-Boost Converter
[0035] 11~14 Transistors
[0036] 15~18 Pre-driver
[0037] 2 Bootstrap Devices
[0038] 21 Linear Regulator
[0039] 3 Bootstrap Devices
[0040] 31 First bootstrap circuit
[0041] 310 Bootstrap Transistor
[0042] 311 Bootstrap Capacitor
[0043] 312 Clamping Circuit
[0044] 313~315 First to third charging circuits
[0045] 316 Driver Unit
[0046] 317~319 First to third driving circuits
[0047] 32 Second bootstrap circuit
[0048] 320 Bootstrap Transistor
[0049] 321 Bootstrap Capacitor
[0050] 322 Clamping Circuit
[0051] 323~325 First to third charging circuits
[0052] 326 Drive Unit
[0053] 327~329 First to third driving circuits
[0054] 4 Buck-Boost Converter
[0055] 41~44 The first to fourth transistors
[0056] 45~48 1st to 4th pre-driver
[0057] 49 Inductor
[0058] C1 External control signal
[0059] C2 External control signal
[0060] C bs1 , C bs2 Bootstrap Capacitor
[0061] D1, D2, D3, D4 Schottky diodes
[0062] Source terminals of n1 and n2 transistors
[0063] N1 Source terminal of the first transistor
[0064] N2 The source terminal of the second transistor
[0065] S1, S2 current source
[0066] V bst1 Bootstrap Voltage
[0067] V bst2 Bootstrap Voltage
[0068] V BST1 First bootstrap voltage
[0069] V BST2 Second bootstrap voltage
[0070] V Cbs2 The voltage across the bootstrap capacitor
[0071] V D1 Schottky diode voltage
[0072] V D3 Schottky diode voltage
[0073] V in Input voltage
[0074] V IN DC input voltage
[0075] V LVDD Regulated voltage
[0076] V out Output voltage
[0077] V OUT DC output voltage
[0078] V S1 First switching voltage
[0079] V S2 The second switching voltage
[0080] V X1 The drain-source voltage across the bootstrap transistor
[0081] V X2 The drain-source voltage across the bootstrap transistor DETAILED DESCRIPTION
[0082] The present invention will be described in detail through the following embodiments and drawings to help those skilled in the art understand the purpose, features and effects of the present invention. It should be noted that certain terms are used throughout the specification to refer to specific components. As recognized by those skilled in the art, manufacturers can refer to components by different names. In the following description and patent scope, the terms "including" and "comprising" are used in an open manner and should not be interpreted as closed terms such as "consisting of..." In addition, the term "coupled" is intended to indicate an indirect or direct electrical connection. Therefore, if one device is coupled to another device, this connection can be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. In addition, in the content described in the present invention, terms such as "first", "second" and "third" are used to distinguish between components, rather than to limit the components themselves or to indicate a specific order of components.
[0083] See also Figure 2 , illustrating a buck-boost converter 4 including a bootstrap device 3 of the present invention. The buck-boost converter 4 is configured to generate a voltage according to a DC input voltage V IN Generates a DC output voltage V OUT The buck-boost converter 4 further includes first to fourth transistors 41, 42, 43, 44, first to fourth pre-drivers 45, 46, 47, 48, and an inductor 49. The first to fourth pre-drivers 45, 46, 47, 48 serve as pre-driving circuits. The buck-boost converter 4 can operate in a buck mode, a boost mode, and a buck-boost mode, and the operation method is similar to that of the buck-boost converter 1 (see Figure 1 ), which is well known to those skilled in the art, so it will not be described here. The bootstrap device 3 generates the first and second bootstrap voltages V BST1 、V BST2 , used to increase the voltage level of the gate terminals of the first and second transistors 41 and 42.
[0084] The first transistor 41 has a gate for receiving a DC input voltage V IN The second transistor 42 has a drain terminal, a source terminal N1, and a gate terminal. OUTThe third transistor 43 has a drain terminal coupled to the source terminal N1 of the first transistor 41, a source terminal grounded, and a gate terminal. The fourth transistor 44 has a drain terminal coupled to the source terminal N2 of the second transistor 42, a source terminal grounded, and a gate terminal. In the present embodiment, the first to fourth transistors 41, 42, 43, 44 are each an N-type metal oxide semi-conductor field effect transistor. The first and second transistors 41, 42 serve as upper switches, and the third and fourth transistors 43, 44 serve as lower switches. The inductor 49 is coupled between the source terminal N1 of the first transistor 41 and the source terminal N2 of the second transistor 42.
[0085] The output terminals of the first to fourth pre-drivers 45, 46, 47, 48 are respectively coupled to the gate terminals of the first to fourth transistors 41, 42, 43, 44, and are used to control the first to fourth transistors 41, 42, 43, 44 to be turned on or off according to the operation mode (i.e., buck mode, boost mode, or buck-boost mode) of the buck-boost converter 4. The first pre-driver 45 receives the external control signal C1, and is also coupled to the bootstrap device 3 to receive the first bootstrap voltage V BST1 , and is coupled to the source terminal N1 of the first transistor 41. The first pre-driver 45 is connected to the first bootstrap voltage V BST1 and the source voltage of the first transistor 41, adjusting the gate voltage of the first transistor 41 (i.e., raising the voltage level of the gate terminal of the first transistor 41), so that when the buck-boost converter 4 operates in the boost mode, the gate voltage of the first transistor 41 is controlled to be continuously greater than the first reference voltage (i.e., the sum of the source voltage of the first transistor 41 and the first threshold voltage), so that the first transistor 41 is controlled by the first pre-driver 45 to be continuously turned on. The second pre-driver 46 controls the first transistor 41 to be turned on continuously according to the external control signal C2, the second bootstrap voltage V BST2 and the source voltage of the second transistor 42, regulating the gate voltage of the second transistor 42 (i.e., raising the voltage level of the gate terminal of the second transistor 42), so as to control the gate voltage of the second transistor 42 to be continuously greater than the second reference voltage (i.e., the sum of the source voltage of the second transistor 42 and the second threshold voltage) when the buck-boost converter 4 operates in the buck mode, so that the second transistor 42 is controlled by the second pre-driver 46 and is continuously turned on.
[0086] It should be noted that the present invention focuses on how the bootstrap device 3 can more efficiently and continuously provide the stable first and second bootstrap voltages V BST1 、V BST2, respectively, to increase the voltage level of the gate terminal of the first and second transistors 41, 42, so as to solve the problems mentioned in the prior art. Therefore, the configuration of the first to fourth pre-drivers 45, 46, 47, 48 of this embodiment and the operation of determining when to switch the first to fourth transistors 41, 42, 43, 44 from conducting to non-conducting are well known to those skilled in the art, and are not described here for the sake of brevity. Please note that the bootstrap device 3 disclosed in the present invention is not limited to applications such as Figure 2 A buck-boost converter 4 is shown.
[0087] The bootstrap device 3 includes a first bootstrap circuit 31 and a second bootstrap circuit 32 .
[0088] The first bootstrap circuit 31 is used to generate a first bootstrap voltage V BST1 , to control the gate voltage of the first transistor 41 to be greater than the first reference voltage, and to receive the DC input voltage V IN , DC output voltage V OUT and the second bootstrap voltage V BST2 , and is coupled to the source terminal N1 of the first transistor 41. The first bootstrap circuit 31 is connected to the source terminal N1 of the first transistor 41 according to the first switching voltage V S1 , the voltage level of the source terminal N1 of the first transistor 41 and the first bootstrap voltage V BST1 Whether the voltage difference between the two is greater than the threshold voltage Vt of the bootstrap transistor 310 is determined according to the DC input voltage V IN , DC output voltage V OUT and the second bootstrap voltage V BST2 At least one of them is charged so that the first bootstrap voltage V BST1 The gate voltage of the first transistor 41 is maintained to be greater than the first reference voltage. BST1 As the first transistor 41 is turned on, the first bootstrap circuit 31 needs to be charged to make the first bootstrap voltage V BST1 Keep at a certain voltage.
[0089] The second bootstrap circuit 32 receives the DC input voltage V IN And DC output voltage V OUT , and coupled to the first bootstrap circuit 31 to receive the first bootstrap voltage V BST1 , and is coupled to the source terminal N2 of the second transistor 42. The second bootstrap circuit 32 is used to generate a second bootstrap voltage V BST2 , to control the gate voltage of the second transistor 42 to be greater than the second reference voltage, and to increase the second bootstrap voltage V BST2 The second bootstrap circuit 32 outputs the second switching voltage VS2 , the voltage level of the source terminal N2 of the second transistor 42 and the second bootstrap voltage V BST2 Whether the voltage difference between the two is greater than the threshold voltage Vt of the bootstrap transistor 320 is determined according to the DC input voltage V IN , DC output voltage V OUT and the first bootstrap voltage V BST1 At least one of them is charged so that the second bootstrap voltage V BST2 The gate voltage of the second transistor 42 is maintained to be greater than the second reference voltage. BST2 As the second transistor 42 is turned on, the second bootstrap circuit 32 needs to be charged to make the second bootstrap voltage V BST2 Keep at a certain voltage.
[0090] Further reading Figure 3 , is a schematic diagram of a first bootstrap circuit 31 according to an embodiment of the present invention. The first bootstrap circuit 31 includes a bootstrap transistor 310, a bootstrap capacitor 311, a clamp circuit 312, first to third charging circuits 313, 314, 315, and a driving unit 316.
[0091] The bootstrap transistor 310 has a first terminal, an output first bootstrap voltage V BST1 The voltage level of the control terminal of the bootstrap transistor 310 is used as the first switching voltage V S1 The bootstrap transistor 310 is an N-type metal oxide semi-conductor field effect transistor, wherein the drain, source and gate serve as the first terminal, the second terminal and the control terminal of the bootstrap transistor 310 respectively. The bootstrap capacitor 311 is coupled between the second terminal of the bootstrap transistor 310 and the source terminal N1 of the first transistor 41. The first bootstrap voltage V BST1 is the floating voltage.
[0092] The clamp circuit 312 is coupled between the control terminal of the bootstrap transistor 310 and the second terminal of the bootstrap capacitor 311. The clamp circuit 312 is used to maintain a potential difference between the second terminal of the bootstrap capacitor 311 and the control terminal of the bootstrap transistor 310. Since the voltage of the second terminal of the bootstrap capacitor 311 is not constant, the first switching voltage V S1 The clamp circuit 312 may be a product known to a person skilled in the art in the art to which the present invention belongs, and may include, for example, a plurality of clamp transistors, wherein each of the plurality of clamp transistors is implemented by a diode-type transistor. For example, the gate terminal and the drain terminal of each of the plurality of clamp transistors are coupled to each other, and the plurality of clamp transistors are connected in series.
[0093] The first charging circuit 313 is used to receive a DC input voltage V IN, and coupled to the first end of the bootstrap transistor 310, and can be based on the DC input voltage V IN Generates a first charging current and outputs it to the first terminal of the bootstrap transistor 310. The second charging circuit 314 is used to receive the DC output voltage V OUT , and coupled to the first end of the bootstrap transistor 310, and can output the DC output voltage V OUT Generate a second charging current and output it to the first terminal of the bootstrap transistor 310. The third charging circuit 315 is used to receive the second bootstrap voltage V BST2 , and is coupled to the first end of the bootstrap transistor 310, and can be based on the second bootstrap voltage V BST2 A third charging current is generated and output to the first terminal of the bootstrap transistor 310. In this embodiment, each of the first to third charging circuits 313, 314, 315 has a Schottky diode D1, but is not limited thereto. In each of the first to third charging circuits 313, 314, 315, the anode of the Schottky diode D1 is used to receive the DC input voltage V IN , DC output voltage V OUT and the second bootstrap voltage V BST2 and a cathode of the Schottky diode D1 is coupled to a first terminal of the bootstrap transistor 310 .
[0094] The driving unit 316 is coupled to the control terminal of the bootstrap transistor 310 and is used to receive a DC input voltage V IN , DC output voltage V OUT and the second bootstrap voltage V BST2 , and accordingly provide a driving current to the control terminal of the bootstrap transistor 310. The driving unit 316 includes first to third driving circuits 317, 318, 319. The first to third driving circuits 317, 318, 319 receive a DC input voltage V IN , DC output voltage V OUT and the second bootstrap voltage V BST2 , and the first to third driving circuits 317, 318, 319 are coupled to the control terminal of the bootstrap transistor 310. Each of the first to third driving circuits 317, 318, 319 has a current source S1 and a Schottky diode D2 connected in series. In each of the first to third driving circuits 317, 318, 319, the current source S1 is used to receive the DC input voltage V IN , DC output voltage V OUT and the second bootstrap voltage V BST2 An anode of the Schottky diode D2 is coupled to the current source S1 , and a cathode of the Schottky diode D2 is coupled to the control terminal of the bootstrap transistor 310 .
[0095] According to the first bootstrap circuit 31 disclosed in this embodiment, the bootstrap capacitor 311 can be charged in the following state: S1 The voltage value V1 obtained by subtracting the voltage level of the source terminal N1 of the first transistor 41 from the first bootstrap voltage V BST1 When the voltage V2 obtained by subtracting the voltage level of the source terminal N1 of the first transistor 41 is greater than the threshold voltage Vt of the bootstrap transistor 310 (ie, V1-V2>Vt), the bootstrap transistor 310 is turned on. IN Subtract the corresponding voltage across the Schottky diode D1, V D1 and minus the drain-source voltage V of the bootstrap transistor 310 X1 Greater than the first bootstrap voltage V BST1 When (i.e., V IN -V D1 -V X1 >V BST1 ), the first charging current charges the bootstrap capacitor 311; when the DC output voltage V OUT Subtract the corresponding voltage across the Schottky diode D1, V D1 and minus the drain-source voltage V of the bootstrap transistor 310 X1 Greater than the first bootstrap voltage V BST1 When (i.e., V OUT -V D1 -V X1 >V BST1 ), the second charging current charges the bootstrap capacitor 311; when the second bootstrap voltage V BST2 Subtract the corresponding voltage across the Schottky diode D1, V D1 and minus the drain-source voltage V of the bootstrap transistor 310 X1 Greater than the first bootstrap voltage V BST1 When (i.e., V BST2 -V D1 -V X1 >V BST1 ), the third charging current charges the bootstrap capacitor 311, so that the first bootstrap voltage V BST1 The gate voltage for controlling the first transistor 41 is maintained to be greater than the first reference voltage.
[0096] Further reading Figure 4 , is a schematic diagram of a second bootstrap circuit 32 according to an embodiment of the present invention. The second bootstrap circuit 32 includes a bootstrap transistor 320, a bootstrap capacitor 321, a clamp circuit 322, first to third charging circuits 323, 324, 325, and a driving unit 326.
[0097] The bootstrap transistor 320 has a first terminal, an output second bootstrap voltage V BST2The voltage level of the control terminal of the bootstrap transistor 320 is used as the second switching voltage V S2 The bootstrap transistor 320 is an N-type metal oxide semi-conductor field effect transistor, wherein the drain, source and gate serve as the first terminal, the second terminal and the control terminal of the bootstrap transistor 320 respectively. The bootstrap capacitor 321 is coupled between the second terminal of the bootstrap transistor 320 and the source terminal N2 of the second transistor 42. The second bootstrap voltage V BST2 is the floating voltage.
[0098] The clamp circuit 322 is coupled between the control terminal of the bootstrap transistor 320 and the second terminal of the bootstrap capacitor 321. The clamp circuit 322 is used to maintain a potential difference between the second terminal of the bootstrap capacitor 321 and the control terminal of the bootstrap transistor 320. Since the voltage of the second terminal of the bootstrap capacitor 321 is not constant, the second switching voltage V S2 The clamp circuit 322 may be a product known to a person skilled in the art of the present invention, and may include, for example, a plurality of clamp transistors, wherein each of the plurality of clamp transistors is implemented by a diode-type transistor. For example, the gate terminal and the drain terminal of each of the plurality of clamp transistors are coupled to each other, and the plurality of clamp transistors are connected in series.
[0099] The first charging circuit 323 is used to receive a DC input voltage V IN , and coupled to the first end of the bootstrap transistor 320, and can be based on the DC input voltage V IN Generate another first charging current and output it to the first terminal of the bootstrap transistor 320. The second charging circuit 324 is used to receive the DC output voltage V OUT , and coupled to the first end of the bootstrap transistor 320, and can output the DC output voltage V OUT Generate another second charging current and output it to the first terminal of the bootstrap transistor 320. The third charging circuit 325 is used to receive the first bootstrap voltage V BST1 , and is coupled to the first end of the bootstrap transistor 320, and can be based on the first bootstrap voltage V BST1 Another third charging current is generated and output to the first terminal of the bootstrap transistor 320. In this embodiment, each of the first to third charging circuits 323, 324, 325 has a Schottky diode D3, but is not limited thereto. In each of the first to third charging circuits 323, 324, 325, the anode of the Schottky diode D3 is used to receive the DC input voltage V IN , DC output voltage V OUT and the second bootstrap voltage V BST1 and a cathode of the Schottky diode D1 is coupled to a first terminal of the bootstrap transistor 320 .
[0100] The driving unit 326 is coupled to the control terminal of the bootstrap transistor 320 and is used to receive the DC input voltage V IN , DC output voltage V OUT and the first bootstrap voltage V BST1 , and accordingly provide a driving current to the control terminal of the bootstrap transistor 320. The driving unit 326 includes first to third driving circuits 327, 328, 329. The first to third driving circuits 327, 328, 329 receive a DC input voltage V IN , DC output voltage V OUT and the first bootstrap voltage V BST1 , and the first to third driving circuits 327, 328, 329 are coupled to the control terminal of the bootstrap transistor 320. Each of the first to third driving circuits 327, 328, 329 has a current source S2 and a Schottky diode D4 connected in series. In each of the first to third driving circuits 327, 328, 329, the current source S2 is used to receive the DC input voltage V IN , DC output voltage V OUT and the first bootstrap voltage V BST1 An anode of the Schottky diode D4 is coupled to the current source S2 , and a cathode of the Schottky diode D4 is coupled to the control terminal of the bootstrap transistor 320 .
[0101] According to the second bootstrap circuit 32 disclosed in this embodiment, the bootstrap capacitor 321 can be charged in the following state: S2 The voltage value V3 obtained by subtracting the voltage level of the source terminal N2 of the second transistor 42 and the second bootstrap voltage V BST2 When the voltage value V4 obtained by subtracting the voltage level of the source terminal N2 of the second transistor 42 is greater than the critical voltage Vt of the bootstrap transistor 320 (ie, V3-V4>Vt), the bootstrap transistor 320 is turned on. IN Subtract the corresponding voltage across the Schottky diode D3, V D3 and minus the drain-source voltage V of the bootstrap transistor 320 X2 Greater than the second bootstrap voltage V BST2 When (i.e., V IN -V D3 -V X2 >V BST2 ), another first charging current charges the bootstrap capacitor 321; when the DC output voltage V OUT Subtract the corresponding voltage across the Schottky diode D3, V D3 and minus the drain-source voltage V of the bootstrap transistor 320 X2 Greater than the second bootstrap voltage V BST2 When (i.e., V OUT -VD3 -V X2 >V BST2 ), another second charging current charges the bootstrap capacitor 321; when the first bootstrap voltage V BST1 Subtract the corresponding voltage across the Schottky diode D3, V D3 and minus the drain-source voltage V of the bootstrap transistor 320 X2 Greater than the second bootstrap voltage V BST2 When (i.e., V BST1 -V D3 -V X2 >V BST2 ), another third charging current charges the bootstrap capacitor 321, so that the second bootstrap voltage V BST2 The gate voltage for controlling the second transistor 42 is maintained to be greater than the second reference voltage.
[0102] In summary, since the bootstrap device 3 of the present invention can directly switch the first switching voltage V S1 , the voltage level of the source terminal N1 of the first transistor 41 and the first bootstrap voltage V BST1 The voltage difference between the two voltages changes at any time, and determines whether to IN , DC output voltage V OUT and the second bootstrap voltage V BST2 The bootstrap capacitor 311 is charged by at least one of the currents of the second switching voltage V S2 , the voltage level of the source terminal N2 of the second transistor 42 and the second bootstrap voltage V BST2 The voltage difference between the two voltages changes at any time, and determines whether to IN , DC output voltage V OUT and the first bootstrap voltage V BST1 The bootstrap capacitor 321 is charged by the current of at least one of the first bootstrap circuits 31 and 321. Therefore, it is not necessary for the external control circuit to periodically pull down the voltage of the source terminal of the transistor before charging the bootstrap capacitor as in the conventional bootstrap device. Thus, the bootstrap device 3 of the present invention has a more efficient effect of charging the bootstrap capacitors 311 and 321. In addition, the first bootstrap circuit 31 will charge the first bootstrap voltage V BST1 is provided to the second bootstrap circuit 32, and the second bootstrap circuit 32 converts the second bootstrap voltage V BST2 Provided to the first bootstrap circuit 31, the bootstrap device 3 of the present invention also has a charge sharing mechanism and can be used to charge the bootstrap capacitors 311 and 321, so that the first and second bootstrap voltages V BST1 、V BST2The voltage can be maintained at a certain level, thereby reducing the possibility of failure to charge the bootstrap capacitors 311 and 321 . Compared with the existing bootstrap devices, the bootstrap device 3 of the present invention also has better charging capability.
[0103] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that the embodiments are only used to describe the present invention and should not be interpreted as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to the embodiments should be considered to be within the scope of the present invention. Therefore, the scope of protection of the present invention shall be subject to the content defined in the claims.
Claims
1. A bootstrap device, suitable for a buck-boost converter, wherein the buck-boost converter generates a DC output voltage from a DC input voltage, and comprises a first transistor and a second transistor as a top switch, wherein: The bootstrap device comprises: a first bootstrap circuit for generating a first bootstrap voltage, receiving the DC input voltage, the DC output voltage and the second bootstrap voltage, and coupled to the source terminal of the first transistor, wherein the first bootstrap circuit determines whether to charge according to at least one of the DC input voltage, the DC output voltage and the second bootstrap voltage according to whether the change of the voltage difference among the first switching voltage, the voltage level of the source terminal of the first transistor and the first bootstrap voltage is greater than a critical voltage, so that the first bootstrap voltage is maintained at a gate voltage greater than a first reference voltage that can be used to control the first transistor; and A second bootstrap circuit receives the DC input voltage and the DC output voltage, and is coupled to the first bootstrap circuit to receive the first bootstrap voltage, and is coupled to the source terminal of the second transistor. The second bootstrap circuit is used to generate the second bootstrap voltage and output the second bootstrap voltage to the first bootstrap circuit. The second bootstrap circuit determines whether to charge according to at least one of the DC input voltage, the DC output voltage and the first bootstrap voltage based on whether the change in the second switching voltage, the voltage level of the source terminal of the second transistor and the voltage difference between the second bootstrap voltage is greater than the critical voltage, so that the second bootstrap voltage is maintained at a gate voltage greater than a second reference voltage that can be used to control the second transistor.
2. The bootstrap device according to claim 1, characterized in that The first bootstrap circuit comprises: A bootstrap transistor having a first terminal, a second terminal for outputting the first bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor serves as the first switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the first transistor; a clamping circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, the clamping circuit being used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, configured to receive the DC input voltage and coupled to the first end of the bootstrap transistor, and capable of generating a first charging current according to the DC input voltage and outputting the first charging current to the first end of the bootstrap transistor; a second charging circuit, for receiving the DC output voltage and coupled to the first end of the bootstrap transistor, and capable of generating a second charging current according to the DC output voltage and outputting the second charging current to the first end of the bootstrap transistor; a third charging circuit, configured to receive the second bootstrap voltage, coupled to the first end of the bootstrap transistor, and capable of generating a third charging current according to the second bootstrap voltage and outputting the third charging current to the first end of the bootstrap transistor; and The driving unit is coupled to the control end of the bootstrap transistor and is used for receiving the DC input voltage, the DC output voltage and the second bootstrap voltage, and providing a driving current to the control end of the bootstrap transistor accordingly.
3. The bootstrap device according to claim 2, characterized in that The first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, an anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the second bootstrap voltage, and a cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
4. The bootstrap device according to claim 2, characterized in that The driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, wherein the first driving circuit, the second driving circuit and the third driving circuit respectively receive the DC input voltage, the DC output voltage and the second bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
5. The bootstrap device according to claim 4, characterized in that Each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of the DC input voltage, the DC output voltage and the second bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.
6. The bootstrap device according to claim 1, characterized in that The second bootstrap circuit comprises: A bootstrap transistor having a first terminal, a second terminal for outputting the second bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor serves as the second switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the second transistor; a clamping circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, the clamping circuit being used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, configured to receive the DC input voltage and coupled to the first end of the bootstrap transistor, and capable of generating a first charging current according to the DC input voltage and outputting the first charging current to the first end of the bootstrap transistor; a second charging circuit, for receiving the DC output voltage and coupled to the first end of the bootstrap transistor, and capable of generating a second charging current according to the DC output voltage and outputting the second charging current to the first end of the bootstrap transistor; a third charging circuit, configured to receive the first bootstrap voltage and be coupled to the first end of the bootstrap transistor, and capable of generating a third charging current according to the first bootstrap voltage and outputting the third charging current to the first end of the bootstrap transistor; and The driving unit is coupled to the control end of the bootstrap transistor and is used for receiving the DC input voltage, the DC output voltage and the first bootstrap voltage, and providing a driving current to the control end of the bootstrap transistor accordingly.
7. The bootstrap device according to claim 6, characterized in that The first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, an anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the first bootstrap voltage, and a cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
8. The bootstrap device according to claim 6, characterized in that The driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, wherein the first driving circuit, the second driving circuit and the third driving circuit respectively receive the DC input voltage, the DC output voltage and the first bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
9. The bootstrap device according to claim 8, characterized in that Each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of the DC input voltage, the DC output voltage and the first bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.
10. A buck-boost converter, comprising: The first transistor has a drain terminal for receiving a DC input voltage, a source terminal, and a gate terminal; A second transistor having a drain terminal for outputting a DC output voltage, a source terminal, and a gate terminal; a third transistor having a drain terminal coupled to the source terminal of the first transistor, a source terminal connected to ground, and a gate terminal; a fourth transistor having a drain terminal coupled to the source terminal of the second transistor, a source terminal connected to the ground, and a gate terminal; The bootstrap device as claimed in claim 1; and A pre-driving circuit is coupled to the gate terminals of the first transistor, the second transistor, the third transistor and the fourth transistor, and is used to control the first transistor, the second transistor, the third transistor and the fourth transistor to be turned on or off, and is coupled to the bootstrap device to receive the first bootstrap voltage and the second bootstrap voltage, and controls the gate voltage of the first transistor to be greater than the first reference voltage according to the first bootstrap voltage, and controls the gate voltage of the second transistor to be greater than the second reference voltage according to the second bootstrap voltage.
11. The buck-boost converter according to claim 10, characterized in that The first bootstrap circuit comprises: A bootstrap transistor having a first terminal, a second terminal for outputting the first bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor serves as the first switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the first transistor; a clamping circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, the clamping circuit being used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, configured to receive the DC input voltage and coupled to the first end of the bootstrap transistor, and capable of generating a first charging current according to the DC input voltage and outputting the first charging current to the first end of the bootstrap transistor; a second charging circuit, for receiving the DC output voltage and coupled to the first end of the bootstrap transistor, and capable of generating a second charging current according to the DC output voltage and outputting the second charging current to the first end of the bootstrap transistor; a third charging circuit, configured to receive the second bootstrap voltage, coupled to the first end of the bootstrap transistor, and capable of generating a third charging current according to the second bootstrap voltage and outputting the third charging current to the first end of the bootstrap transistor; and The driving unit is coupled to the control end of the bootstrap transistor and is used for receiving the DC input voltage, the DC output voltage and the second bootstrap voltage, and providing a driving current to the control end of the bootstrap transistor accordingly.
12. The buck-boost converter according to claim 11, characterized in that The first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, an anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the second bootstrap voltage, and a cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
13. The buck-boost converter according to claim 11, wherein: The driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, wherein the first driving circuit, the second driving circuit and the third driving circuit respectively receive the DC input voltage, the DC output voltage and the second bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
14. The buck-boost converter according to claim 13, characterized in that Each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of the DC input voltage, the DC output voltage and the second bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.
15. The buck-boost converter according to claim 10, wherein: The second bootstrap circuit comprises: A bootstrap transistor having a first terminal, a second terminal for outputting the second bootstrap voltage, and a control terminal, wherein the voltage level of the control terminal of the bootstrap transistor serves as the second switching voltage; a bootstrap capacitor coupled between the second terminal of the bootstrap transistor and the source terminal of the second transistor; a clamping circuit coupled between the control terminal of the bootstrap transistor and the second terminal of the bootstrap capacitor, the clamping circuit being used to maintain a potential difference between the second terminal of the bootstrap capacitor and the control terminal of the bootstrap transistor; a first charging circuit, configured to receive the DC input voltage and coupled to the first end of the bootstrap transistor, and capable of generating a first charging current according to the DC input voltage and outputting the first charging current to the first end of the bootstrap transistor; a second charging circuit, for receiving the DC output voltage and coupled to the first end of the bootstrap transistor, and capable of generating a second charging current according to the DC output voltage and outputting the second charging current to the first end of the bootstrap transistor; a third charging circuit, configured to receive the first bootstrap voltage and be coupled to the first end of the bootstrap transistor, and capable of generating a third charging current according to the first bootstrap voltage and outputting the third charging current to the first end of the bootstrap transistor; and The driving unit is coupled to the control end of the bootstrap transistor and is used for receiving the DC input voltage, the DC output voltage and the first bootstrap voltage, and providing a driving current to the control end of the bootstrap transistor accordingly.
16. The buck-boost converter according to claim 15, characterized in that The first charging circuit, the second charging circuit and the third charging circuit each have a Schottky diode, an anode of the Schottky diode is used to receive a corresponding one of the DC input voltage, the DC output voltage and the first bootstrap voltage, and a cathode of the Schottky diode is coupled to the first end of the bootstrap transistor.
17. The buck-boost converter according to claim 15, wherein: The driving unit includes a first driving circuit, a second driving circuit and a third driving circuit, wherein the first driving circuit, the second driving circuit and the third driving circuit respectively receive the DC input voltage, the DC output voltage and the first bootstrap voltage, and the first driving circuit, the second driving circuit and the third driving circuit are coupled to the control end of the bootstrap transistor.
18. The buck-boost converter according to claim 17, characterized in that Each of the first driving circuit, the second driving circuit and the third driving circuit has a current source and a Schottky diode connected in series, the current source is used to receive a corresponding one of the DC input voltage, the DC output voltage and the first bootstrap voltage, the anode of the Schottky diode is coupled to the current source, and the cathode of the Schottky diode is coupled to the control end of the bootstrap transistor.