Bootstrap drive circuit, control method and switching power supply

Abstract

The invention discloses a bootstrap driving circuit, a control method and a switching power supply, and the bootstrap driving circuit comprises a first switching tube, a first diode, a first inductor, a driving circuit, a second diode, a first capacitor, a third diode and a second switching tube. The second switch tube pulls down the voltage of the connection point of the first switch tube and the first diode, so that the driving circuit charges the first capacitor through the second diode, and the bootstrap power supply process is achieved. According to the invention, the problem of bootstrap power supply of the main switching tube of the BUCK circuit when the switching power supply works in the Buck mode, the Buck-Boost mode and the Boost mode respectively is solved, the cost can be reduced, the efficiency can be improved, and the working reliability of the switching power supply product is greatly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronic converters, and in particular to a bootstrap drive circuit, a control method and a switching power supply. Background Art

[0002] like Figure 1 The figure shows a conventional Buck circuit and its driver circuit. Typically, the upper tube drive power supply of the Buck circuit needs to be completed through bootstrap power supply. Specifically, the Buck circuit is composed of the Buck upper tube Q1, the Buck lower tube Q2, and the inductor L. In the driver circuit, the HIN terminal is the input terminal of the Buck upper tube drive signal, the HO terminal is the output terminal of the Buck upper tube drive, the LIN terminal is the input terminal of the Buck lower tube drive signal, the LO terminal is the output terminal of the Buck lower tube drive, and the VCC is the power supply terminal of the driver circuit, which is connected to the bootstrap diode D b The anode of the upper tube is connected to the bootstrap capacitor C. b One end and the bootstrap diode D b The cathode of the Buck converter is VS, and VS is the reference ground terminal of the Buck converter. It should be noted that the names of the drive circuit ports mentioned in the present invention may be slightly different in different circuits, and the actual function of each port shall prevail. In the Buck converter, Q1 and Q2 are complementary and turned on. When Q2 is turned on, the inductor L is freewheeling. At this time, the midpoint SW connected to Q1 and Q2 is pulled low, and the drive power supply Vdd is fed to the bootstrap capacitor C through the bootstrap diode D. b After Q2 is turned off, the bootstrap capacitor C b To power Q1, Q1 conducts to excite the inductor L. To bootstrap capacitor C b To be able to charge in time, Q2 needs to be turned on for a sufficient time to pull down the SW voltage to achieve bootstrap power supply.

[0003] In the application scenario where the freewheeling current of the BUCK lower tube is not large, Q2 is often a diode, such as Figure 2 As shown, this can save the drive circuit, reduce losses and reduce costs. When Q2 uses a diode, when the output load is light, the inductor current is very small and is not enough to pull down SW. The bootstrap capacitor C of Q1 b When the voltage across both ends is less than the undervoltage threshold, the upper tube Q1 will not work.

[0004] like Figure 3 As shown, the Chinese patent application with publication number CN114221549A discloses a cascade circuit and a control method thereof, specifically relating to a buck-boost cascade circuit. When the above circuit operates in BOOST mode, Q1 is always on and Q2 is not conducting. If the driving power supply of Q1 adopts a bootstrap power supply method, since the lower tube Q2 is always not conducting, the bootstrap capacitor cannot be charged, resulting in Q1 not being able to be always on.

[0005] Usually, in order to solve the problem of bootstrap power supply, an isolated power supply method is used to power the driver of the upper tube. However, this power supply method requires an additional isolated power supply circuit, which increases the cost and volume. Summary of the Invention

[0006] In view of this, the present invention provides a bootstrap drive circuit, a control method and a switching power supply to solve the power supply problem of the BUCK upper tube in the step-down and step-up / step-down circuits, reduce costs and improve the reliability of the switching power supply.

[0007] The present invention provides a bootstrap drive circuit, the technical solution is as follows:

[0008] In a first aspect, the present invention provides a bootstrap drive circuit for use in a switching power supply. The bootstrap drive circuit includes a first switching transistor, a first diode, a first inductor, a drive circuit, a second diode, a first capacitor, a third diode, and a second switching transistor. The first terminal of the first switching transistor is connected to a power supply terminal, the second terminal of the first switching transistor is respectively connected to the cathode of the first diode and the first terminal of the first inductor. The first output terminal of the drive circuit is connected to the control terminal of the first switching transistor. The upper tube driving power supply reference ground terminal of the drive circuit is connected to the second terminal of the first switching transistor. The power supply terminal of the drive circuit is respectively connected to the driving power supply terminal and the anode of the second diode. The cathode of the second diode is respectively connected to the upper tube driving power supply terminal of the drive circuit and the first terminal of the first capacitor. The anode of the third diode is connected to the second terminal of the first switching transistor. The cathode of the third diode is connected to the first terminal of the second switching transistor. The second terminal of the second switching transistor and the anode of the first diode are both connected to ground. The second output terminal of the drive circuit is connected to the control terminal of the second switching transistor. The first input terminal of the drive circuit is connected to a first driving signal for driving the first switching transistor. The second input terminal of the drive circuit is connected to a second driving signal for driving the second switching transistor.

[0009] The second switch tube pulls down the voltage of the connection point between the first switch tube and the first diode, so that the driving circuit charges the first capacitor through the second diode.

[0010] Optionally, the second end output of the first inductor is connected to a switching power supply circuit.

[0011] Optionally, the switching power supply circuit includes any one of a full-bridge circuit, a push-pull circuit, a half-bridge circuit, an isolated circuit or a non-isolated circuit, or a combination of multiple circuits.

[0012] In a second aspect, the present invention further provides a control method for the bootstrap drive circuit according to the first aspect, the control method comprising:

[0013] When it is determined that the switching power supply operates in the Boost mode, controlling the first switching tube to be continuously turned on and turned off according to a set period interval, and controlling the second switching tube to be complementary to the first switching tube to be turned on;

[0014] When it is determined that the switching power supply operates in Buck mode or Buck-Boost mode, the second switching tube is controlled to be complementary to the first switching tube when the inductor current is in discontinuous mode; and the second switching tube is controlled to remain off when the inductor current is in continuous mode.

[0015] Optionally, the set period is less than 50us.

[0016] Optionally, the turn-off time of the first switch tube is greater than 100ns.

[0017] In a third aspect, the present invention further provides a switching power supply, which includes the bootstrap drive circuit as described in the first aspect.

[0018] The beneficial effects of the present invention are:

[0019] 1. The present invention solves the power supply problem of the first switching tube by adding a second switching tube and a third diode, so that the switching power supply operates in the Boost mode, the DCM mode of the Buck mode, and the DCM mode of the Buck-Boost mode. Only a few auxiliary components are added, which reduces the cost and improves the reliability of the switching power supply.

[0020] 2. When the switching power supply of the present invention operates in the CCM mode of the Buck mode and the CCM mode of the Buck-Boost mode, the second switch tube is not turned on, thereby reducing loss and improving efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the existing Buck circuit and its bootstrap power supply circuit diagram;

[0022] Figure 2 This is a bootstrap power supply circuit diagram of an existing Buck circuit with a diode as the lower tube;

[0023] Figure 3 This is a schematic diagram of a cascade circuit in publication number CN114221549A;

[0024] Figure 4 A circuit diagram of a bootstrap drive circuit according to the present invention;

[0025] Figure 5 This is a schematic diagram of a BUCK circuit used in a first embodiment of a bootstrap drive circuit of the present invention;

[0026] Figure 6This is a schematic diagram of a four-tube BUCK-BOOST circuit in a first embodiment of a bootstrap drive circuit according to the present invention;

[0027] Figure 7 This is a circuit schematic diagram of a second embodiment of a bootstrap drive circuit of the present invention. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of this application.

[0029] refer to Figure 4 An embodiment of the present invention provides a bootstrap drive circuit for use in a switching power supply. The bootstrap drive circuit includes a first switch tube Q1, a first diode D1, a first inductor L1, a drive circuit, a second diode D2, a first capacitor C1, a third diode D3, and a second switch tube Q2. The first end of the first switch tube Q1 is connected to a power supply terminal Vin, and the second end of the first switch tube Q1 is respectively connected to the cathode of the first diode D1 and the first end of the first inductor L1. The first output end of the drive circuit is connected to the control end of the first switch tube Q1, the reference ground end VS of the drive circuit is connected to the second end of the first switch tube, and the power supply end VCC of the drive circuit is respectively connected to the drive power supply end Vdd and the first end of the first inductor L1. An anode of a second diode D2 and a cathode of the second diode D2 are connected to the upper tube driving power supply terminal VB of the driving circuit and the first end of the first capacitor C1, respectively; an anode of the third diode D3 is connected to the second end of the first switching tube Q1, and a cathode of the third diode D3 is connected to the first end of the second switching tube Q2; the second end of the second switching tube Q2 and the anode of the first diode D1 are both connected to the ground; a second output end of the driving circuit is connected to the control end of the second switching tube Q2; a first input end of the driving circuit is connected to a first driving signal for driving the first switching tube Q1; and a second input end of the driving circuit is connected to a second driving signal for driving the second switching tube Q2;

[0030] The second switch tube Q2 pulls down the voltage at the connection point between the first switch tube Q1 and the first diode D1 , so that the driving circuit charges the first capacitor C1 through the second diode D2 .

[0031] The driving circuit may be implemented by a driving IC.

[0032] In one embodiment, the first inductive switching power supply circuit may be any one of a full-bridge circuit, a push-pull circuit, a half-bridge circuit, an isolated circuit, or a non-isolated circuit, or a combination of multiple circuits.

[0033] In addition, an embodiment of the present invention further provides a control method applied to a bootstrap drive circuit, comprising:

[0034] When it is determined that the switching power supply operates in the Boost mode, controlling the first switching tube to be continuously turned on and turned off according to a set period interval, and controlling the second switching tube to be complementary to the first switching tube to be turned on;

[0035] When it is determined that the switching power supply operates in Buck mode or Buck-Boost mode, the second switch tube is controlled to be complementary to the first switch tube in a discontinuous current mode (DCM) of the inductor; and the second switch tube is controlled to remain off in a continuous current mode (CCM) of the inductor.

[0036] In one embodiment, the set period is less than 50 us.

[0037] In one embodiment, the turn-off time of the first switch tube is greater than 100 ns.

[0038] First embodiment

[0039] This embodiment Figure 5 As shown, a bootstrap drive circuit is applied to a Buck circuit, including: a first switch tube Q1, a first diode D1, a first inductor L1, a drive circuit, a second diode D2, a first capacitor C1, a third diode D3, and a second switch tube Q2; the drain of the first switch tube Q1 is connected to +Vin, the source of the first switch tube Q1 is connected to the cathode of the first diode D1 and one end of the first inductor L1, and the other end of the first inductor L1 is connected to the output +Vo; the anode of the first diode D1 is connected to GND; the HO end of the drive circuit is connected to the gate of the first switch tube Q1, and the VS end of the drive circuit is connected to the source of the first switch tube Q1; the drive power supply Vdd is connected to the VCC end of the drive circuit and the anode of the second diode D2, the cathode of the second diode D2 is connected to the VB end of the drive circuit and one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the VS end of the drive circuit. The anode of the third diode D3 is connected to the source of the first switch tube Q1 and the cathode of the first diode D1. The cathode of the third diode D3 is connected to the drain of the second switch tube Q2. The source of the second switch tube Q2 is connected to GND. The LO terminal of the drive circuit is connected to the gate of the second switch tube Q2. The HIN terminal of the drive circuit is connected to the first drive signal PWM1 of the first switch tube Q1. The LIN terminal of the drive circuit is connected to the second drive signal PWM2 of the second switch tube Q2.

[0040] This embodiment provides a control method for a bootstrap drive circuit, and the technical solution is as follows:

[0041] When the Buck circuit operates in DCM mode, the first switch Q1 and the second switch Q2 are complementary and conductive. While the second switch Q2 is on, it pulls down the midpoint between the first switch Q1 and the first diode D1. The drive power supply Vdd passes through the second diode D2 to charge the first capacitor C1. The first capacitor C1 provides the drive power for the first switch Q1, thereby turning on the first switch Q1. In CCM mode, the second switch Q2 is not conductive. After the first switch Q1 is turned off, the current in the first inductor L1 is relatively large, sufficient to pull down the midpoint between the first switch Q1 and the first diode D1. The drive power supply Vdd passes through the second diode D2 to charge the first capacitor C1, achieving a bootstrap power supply process. This eliminates the need for the second switch Q2 to turn on, reduces losses, and improves the efficiency of the switching power supply in the Buck CCM mode.

[0042] In this embodiment Figure 5 Based on the Buck circuit shown in the figure, a four-tube Buck-Boost circuit is formed by cascading half-bridge circuits. Figure 6 As shown, a bootstrap drive circuit is applied to a switching power supply, including: a first switching tube Q1, a first diode D1, a first inductor L1, a switching power supply circuit, a drive circuit, a second diode D2, a first capacitor C1, a third diode D3, and the second switching tube Q2; the drain of the first switching tube Q1 is connected to +Vin, the source of the first switching tube Q1 is connected to the cathode of the first diode D1 and one end of the first inductor L1, the other end of the first inductor L1 is connected to the input end of the switching power supply circuit, and the output end of the switching power supply circuit is connected to +Vo and -Vo; the anode of the first diode D1 is connected to GND; the HO end of the drive circuit is connected to the gate of the first switching tube Q1, and the VS end of the drive circuit is connected to the source of the first switching tube Q1; the drive power supply Vdd is connected to the VCC end of the drive circuit and the anode of the second diode D2, the cathode of the second diode D2 is connected to the VB end of the drive circuit and one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the VS end of the drive circuit. The anode of the third diode D3 is connected to the source of the first switch tube Q1 and the cathode of the first diode D1. The cathode of the third diode D3 is connected to the drain of the second switch tube Q2. The source of the second switch tube Q2 is connected to GND. The LO terminal of the drive circuit is connected to the gate of the second switch tube Q2. The HIN terminal of the drive circuit is connected to the drive signal PWM1 of the first switch tube Q1. The LIN terminal of the drive circuit is connected to the drive signal PWM2 of the second switch tube Q2.

[0043] The switching power supply circuit is a half-bridge circuit consisting of switching tubes Q3 and Q4. The drain of Q3 is connected to the +Vo terminal of the switching power supply circuit, the source of switching tube Q3 is connected to the drain of switching tube Q4 and the Vbus terminal of the switching power supply, and the source of switching tube Q4 is connected to the -Vo terminal of the switching power supply circuit, which is connected to the GND terminal. The first switching tube Q1, the first diode D1, the first inductor L1, the opening tube Q3, and the switching tube Q4 form a four-tube Buck-Boost circuit.

[0044] This embodiment provides a control method for a bootstrap drive circuit, and the technical solution is as follows:

[0045] When the switching power supply operates in Boost mode, switches Q3 and Q4 are alternately turned on. The first switch Q1 is turned on for a long time and then turned off once every 42 μs. The first switch Q1 and the second switch Q2 are then turned on in a complementary manner. That is, after the first switch Q1 is turned off, the second switch Q2 is turned on. The second switch Q2 is turned on for 150 ns, pulling down the midpoint between the first switch Q1 and the first diode D1. The driving power supply Vdd passes through the second diode D2 to charge the first capacitor C1. The first capacitor provides the driving power supply for the first switch Q1, achieving a long-term conduction of the first switch Q1. The auxiliary components, the third diode D3 and the second switch, added in this embodiment have relatively low rated currents, allowing the use of low-current, small-package components, reducing costs and improving the reliability of the switching power supply.

[0046] When the switching power supply operates in Buck or Buck-Boost mode, in DCM mode, the first switch Q1 and the second switch Q2 are complementary and conductive. During the conduction period, the second switch Q2 pulls down the midpoint between the first switch Q1 and the first diode D1, driving the power supply Vdd through the second diode D2 to charge the first capacitor C1. The first capacitor C1 provides the driving power supply for the first switch Q1, thereby turning on the first switch Q1. In CCM mode, the second switch Q2 is not conductive. After the first switch Q1 is turned off, the current in the first inductor L1 is relatively large, sufficient to pull down the midpoint between the first switch Q1 and the first diode D1. The power supply Vdd is driven through the second diode D2 to charge the first capacitor C1, thus achieving a bootstrap power supply process. This eliminates the need for the second switch Q2 to turn on, reduces losses, and improves the efficiency of the switching power supply in the Buck CCM mode.

[0047] Second embodiment

[0048] like Figure 7, which is a specific schematic diagram of this embodiment, a bootstrap drive circuit is applied to a switching power supply, including: a first switching tube Q1, a first diode D1, a first inductor L1, a switching power supply circuit, a drive circuit, a second diode D2, a first capacitor C1, a third diode D3, and a second switching tube Q2; the drain of the first switching tube Q1 is connected to +Vin, the source of the first switching tube Q1 is connected to the cathode of the first diode D1 and one end of the first inductor L1, the other end of the first inductor L1 is connected to the input end of the switching power supply circuit, and the output end of the switching power supply circuit is connected to +Vo and -Vo; the anode of the first diode D1 is connected to GND; the HO end of the drive circuit is connected to the gate of the first switching tube Q1, and the VS end of the drive circuit is connected to the source of the first switching tube Q1; the drive power supply Vdd is connected to the VCC end of the drive circuit and the anode of the second diode D2, the cathode of the second diode D2 is connected to the VB end of the drive circuit and one end of the first capacitor C1, and the other end of the first capacitor C1 is connected to the VS end of the drive circuit. The anode of the third diode D3 is connected to the source of the first switch tube Q1 and the cathode of the first diode D1. The cathode of the third diode D3 is connected to the drain of the second switch tube Q2. The source of the second switch tube Q2 is connected to GND. The LO terminal of the drive circuit is connected to the gate of the second switch tube Q2. The HIN terminal of the drive circuit is connected to the drive signal PWM1 of the first switch tube Q1. The LIN terminal of the drive circuit is connected to the drive signal PWM2 of the second switch tube Q2.

[0049] The switching power supply circuit is an isolated full-bridge circuit, including a primary full-bridge composed of switch tubes Q3-Q6, a transformer, and a secondary full-bridge rectifier composed of switch tubes Q7-Q10. Specifically, the drains of the switch tubes Q3 and Q4 are commonly connected to the Vbus terminal of the switching power supply circuit, the sources of the switch tubes Q5 and Q6 are commonly connected to the GND terminal of the switching power supply circuit, the midpoint to which the switch tubes Q3 and Q5 are connected is connected to one end of the primary winding of the transformer, and the midpoint to which the switch tubes Q4 and Q6 are connected is connected to the other end of the primary winding of the transformer; the drains of the switch tubes Q7 and Q8 are commonly connected to the +Vo terminal of the switching power supply circuit, the sources of the switch tubes Q9 and Q10 are commonly connected to the -Vo terminal of the switching power supply circuit, the midpoint to which the switch tubes Q7 and Q9 are connected is connected to one end of the secondary winding of the transformer, and the midpoint to which the switch tubes Q8 and Q10 are connected is connected to the other end of the secondary winding of the transformer.

[0050] This embodiment provides a control method for a bootstrap drive circuit, and the technical solution is as follows:

[0051] When the switching power supply operates in Boost mode, the first switch Q1 is turned on for a long time, and the primary full-bridge switches Q3-Q6 are turned on together to excite the inductor L1. Furthermore, the first switch Q1 is turned off once every 42µs. The first switch Q1 and the second switch Q2 are then turned on in a complementary manner. That is, after the first switch Q1 is turned off, the second switch Q2 is turned on. The second switch Q2 is on for 150ns, pulling down the midpoint between the first switch Q1 and the first diode D1. The drive power supply Vdd passes through the second diode D2, charging the first capacitor C1. The first capacitor provides the drive power for the first switch Q1, ensuring that the first switch Q1 remains on for a long time. The auxiliary components, the third diode D3 and the second switch, added in this embodiment have relatively low rated currents, allowing the use of low-current, compact components, reducing costs and improving the reliability of the switching power supply.

[0052] When the switching power supply operates in Buck or Buck-Boost mode, in DCM mode, the first switch Q1 and the second switch Q2 are complementary and conductive. During the conduction period, the second switch Q2 pulls down the midpoint between the first switch Q1 and the first diode D1, driving the power supply Vdd through the second diode D2 to charge the first capacitor C1. The first capacitor C1 provides the driving power supply for the first switch Q1, thereby turning on the first switch Q1. In CCM mode, the second switch Q2 is not conductive. After the first switch Q1 is turned off, the current in the first inductor L1 is relatively large, sufficient to pull down the midpoint between the first switch Q1 and the first diode D1. The power supply Vdd is driven through the second diode D2 to charge the first capacitor C1, thus achieving a bootstrap power supply process. This eliminates the need for the second switch Q2 to turn on, reduces losses, and improves the efficiency of the switching power supply in the Buck CCM mode.

[0053] In addition, an embodiment of the present invention further provides a switching power supply, which includes the bootstrap drive circuit in the above embodiment.

[0054] The above are merely preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be construed as limiting the present invention. Persons skilled in the art will appreciate that equivalent substitutions, improvements, and modifications may be made without departing from the spirit and scope of the present invention. These equivalent substitutions, improvements, and modifications should also be considered within the scope of protection of the present invention. Examples will not be used here for further elaboration; the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A bootstrap drive circuit, applied to a switching power supply, characterized in that: The bootstrap drive circuit includes a first switching transistor, a first diode, a first inductor, a drive circuit, a second diode, a first capacitor, a third diode, and a second switching transistor. The first terminal of the first switching transistor is connected to a power supply terminal, the second terminal of the first switching transistor is respectively connected to the cathode of the first diode and the first terminal of the first inductor. The first output terminal of the drive circuit is connected to the control terminal of the first switching transistor. The upper tube driving power supply reference ground terminal of the drive circuit is connected to the second terminal of the first switching transistor. The power supply terminal of the drive circuit is respectively connected to the driving power supply terminal and the anode of the second diode. The cathode of the second diode is respectively connected to the upper tube driving power supply terminal of the drive circuit and the first terminal of the first capacitor. The anode of the third diode is connected to the second terminal of the first switching transistor. The cathode of the third diode is connected to the first terminal of the second switching transistor. The second terminal of the second switching transistor and the anode of the first diode are both connected to the ground terminal. The second output terminal of the drive circuit is connected to the control terminal of the second switching transistor. The first input terminal of the drive circuit is connected to a first driving signal for driving the first switching transistor. The second input terminal of the drive circuit is connected to a second driving signal for driving the second switching transistor. The second switch tube pulls down the voltage of the connection point between the first switch tube and the first diode, so that the driving circuit charges the first capacitor through the second diode.

2. The bootstrap driving circuit according to claim 1, wherein: The second end output of the first inductor is connected to the switching power supply circuit.

3. The bootstrap driving circuit according to claim 2, wherein: The switching power supply circuit includes any one of a full-bridge circuit, a push-pull circuit, a half-bridge circuit, an isolated circuit or a non-isolated circuit, or a combination of multiple circuits.

4. A control method for the bootstrap drive circuit according to any one of claims 1 to 3, characterized in that: The control method includes: When it is determined that the switching power supply operates in the Boost mode, controlling the first switching tube to be continuously turned on and turned off according to a set period interval, and controlling the second switching tube to be complementary to the first switching tube to be turned on; When it is determined that the switching power supply operates in Buck mode or Buck-Boost mode, the second switching tube is controlled to be complementary to the first switching tube when the inductor current is in discontinuous mode; and the second switching tube is controlled to remain off when the inductor current is in continuous mode.

5. The control method according to claim 4, characterized in that: The set period is less than 50 us.

6. The control method according to claim 4, characterized in that: The turn-off time of the first switch tube is greater than 100 ns.

7. A switching power supply, characterized in that: The method comprises the bootstrap drive circuit according to any one of claims 1 to 3.

Images