Bootstrap circuit for driving MOS tube and LLC converter thereof

Abstract

The invention discloses a bootstrap circuit for driving an MOS tube and an LLC converter thereof, and the bootstrap circuit comprises a bootstrap module which comprises a driving chip and a bootstrap capacitor, and the output end of the driving chip is connected to the grid electrode of the MOS tube to be driven through the bootstrap capacitor; the voltage clamping branch is connected between a node between the bootstrap capacitor and the grid electrode of the MOS tube and a reference ground; wherein the voltage clamping branch is configured to be switched on when the driving chip outputs a low level, so as to provide a negative voltage at the grid electrode of the MOS tube. A voltage clamping branch is additionally arranged on the basis of a bootstrap module, and two core problems of level shift and negative voltage turn-off of high-voltage side driving are solved at the same time through an extremely simple passive circuit structure; an isolation transformer with a large size is completely omitted, the problems of cost and complexity caused by an existing complex active clamping loop are solved, and the design requirements for miniaturization and low cost of a power supply product are met.

Description

Technical Field

[0001] This invention relates to the field of power electronic drive technology, and in particular to a bootstrap circuit for driving MOSFETs and its LLC converter. Background Technology

[0002] In power conversion circuits such as on-board chargers for new energy vehicles, LLC resonant converters are widely used due to their high efficiency. The upper-arm MOSFETs in these circuits have source potentials that float between the high-voltage bus voltage and the reference ground, requiring a solution to the floating-ground drive problem in their drive circuit. The traditional solution is to use an isolation transformer, employing electromagnetic isolation to allow the reference ground of the drive signal to float with the MOSFET's source potential, thereby ensuring an effective gate-source voltage difference. For example... Figure 1 , 2 As shown, Figure 1 One end of the transformer, GND_GBH_AC, is connected to Figure 2 In the LLC circuit, when the source voltage of the MOSFET changes, the other end of the transformer, VCC16_GBH_AC, is affected by the primary side and will automatically follow the change of GND_GBH_AC. That is, as long as GND_GBH_AC is within a reasonable voltage range, VCC16_GBH_AC will always be 16V higher than it; thus, the gate-source voltage of the MOSFET is maintained at a voltage difference of 16V, keeping the MOSFET in the on state.

[0003] However, isolation transformer solutions suffer from large size and high cost, and are typically unable to provide negative voltage turn-off. During the turn-off period of a MOSFET, without negative voltage, the gate charge release rate is slow, which can easily lead to false turn-on due to the Miller effect, threatening circuit reliability.

[0004] To overcome the shortcomings of isolation transformers, existing technologies have developed driving schemes that use passive devices such as capacitors and Zener diodes to generate negative voltage. For example, Chinese invention patent CN111555596B discloses a SiCMOSFET gate crosstalk suppression driving circuit with adjustable negative voltage. This circuit generates a turn-off negative voltage through a parallel capacitor (C1) and a Zener diode (Z1), and uses this negative voltage to automatically turn on the Miller clamp circuit composed of two n-MOSFETs (S1, S2), thereby providing a low-impedance bypass for crosstalk current and suppressing gate voltage spikes.

[0005] While this type of solution eliminates the isolation transformer and achieves negative voltage drive, its circuit structure remains relatively complex. To achieve crosstalk suppression, it includes additional clamping switches (S1, S2), multiple diodes (D1, D2), and voltage divider capacitors (C2) and bleeder resistors (R1) forming the RCD circuit. Although this complex topology is functionally complete, its cost advantage is not significant in applications with stringent cost and size requirements, where the switching frequency and voltage change rate (dv / dt) are not extremely high.

[0006] Therefore, there is still a need in the field for a simpler, lower-cost MOSFET driving solution that can effectively achieve negative voltage turn-off, so as to better meet the design requirements of miniaturization and low cost of power supply products while ensuring basic reliability. Summary of the Invention

[0007] In a first aspect, to solve the above-mentioned technical problems, a bootstrap circuit for driving a MOS transistor is provided, comprising: The bootstrap module includes a driver chip and a bootstrap capacitor. The output terminal of the driver chip is connected to the gate of the MOS transistor to be driven through the bootstrap capacitor. A voltage clamping branch is connected between the node between the bootstrap capacitor and the gate of the MOS transistor and the reference ground. The voltage clamping branch is configured to be turned on when the driver chip outputs a low level, so as to provide a negative voltage to the gate of the MOS transistor.

[0008] Furthermore, the voltage clamping branch includes a Zener diode and a current-limiting resistor connected in series. The cathode of the Zener diode is connected to the node between the bootstrap capacitor and the current-limiting resistor, and the anode is connected to the reference ground; The end of the current-limiting resistor furthest from the Zener diode is connected to the gate of the MOS transistor; When the driver chip outputs a low level, the Zener diode is turned on to generate a negative voltage at the node, which then acts on the gate of the MOS transistor through the current-limiting resistor.

[0009] Furthermore, the power supply terminal of the driver chip receives a first voltage, and the voltage regulation value of the Zener diode is less than the first voltage.

[0010] Furthermore, the first voltage is 3.3V-17V.

[0011] Furthermore, the current-limiting resistor is configured to suppress the oscillation of the MOS transistor gate.

[0012] Furthermore, the input terminal of the driver chip is used to receive pulse signals from the microcontroller unit.

[0013] Preferably, the driver chip is model IR2110.

[0014] In a second aspect, the present invention provides an LLC converter including a half-bridge or full-bridge circuit, the half-bridge or full-bridge circuit including an upper bridge arm MOSFET and a lower bridge arm MOSFET, the upper bridge arm MOSFET being driven by the bootstrap circuit.

[0015] Compared with the prior art, the embodiments of the present invention have the following beneficial effects: This invention solves the two core problems of high-voltage side drive level shifting and negative voltage shutdown by adding a voltage clamping branch to the bootstrap module, with an extremely simple passive circuit structure. It not only completely eliminates the bulky isolation transformer, but also avoids the cost and complexity problems caused by existing complex active clamping circuits, thus meeting the design requirements of miniaturization and low cost of power supply products. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a circuit diagram of an existing isolation transformer solution. Figure 2 This is a schematic diagram of an LLC circuit in the prior art; Figure 3 This is a circuit schematic diagram of the bootstrap capacitor scheme disclosed in this invention; Figure 4 This is a waveform diagram of the output terminal OUTB of the driver chip U1 of the present invention.

[0018] In the diagram: 10, Bootstrap module; 20, Voltage clamping branch. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 3The present invention aims to provide a bootstrap circuit for driving a MOSFET, mainly including a bootstrap module 10 and a voltage clamping branch 20, specifically: The bootstrap module 10 includes a driver chip U1 and a bootstrap capacitor C14. The output of the driver chip U1 is connected to the gate of the MOS transistor to be driven through the bootstrap capacitor C14. The input of the driver chip U1 is used to receive pulse signals from the microcontroller unit. Preferably, the driver chip is an IR2110.

[0021] Voltage clamping branch 20 is connected between the node between bootstrap capacitor C14 and the gate of the MOSFET and the reference ground. Voltage clamping branch 20 is configured to conduct when the driver chip U1 outputs a low level, thereby providing a negative voltage at the gate of the MOSFET.

[0022] In a further embodiment, the voltage clamping branch 20 includes a Zener diode ZD1 and a current-limiting resistor R4 connected in series. The cathode of the Zener diode ZD1 is connected to the node between the bootstrap capacitor C14 and the current-limiting resistor R4 (denoted as node A), and the anode is connected to the floating ground GND_GBH_AC through the current-limiting resistor R4. Node A is ultimately connected to the MOSFET to be driven (i.e.,...) through the current-limiting resistor R4. Figure 2 The gate LLC_GBH of Q1 in the middle.

[0023] In a further embodiment, the end of the current-limiting resistor R4 furthest from the Zener diode ZD1 is connected to the gate of the MOSFET. When the driver chip U1 outputs a low level, the Zener diode ZD1 is turned on, generating a negative voltage at node A, which is then applied to the gate of the MOSFET through the current-limiting resistor R4. The current-limiting resistor R4 is configured to suppress oscillations at the MOSFET gate.

[0024] In this scheme, the power supply terminal of the driver chip U1 receives a first voltage, and the voltage regulation value of the Zener diode ZD1 is less than the first voltage. The first voltage is 3.3V-17V.

[0025] This solution uses a driver chip U1, a bootstrap capacitor C14, a Zener diode ZD1, and a current-limiting resistor R4 to form a driver circuit. Figure 3 LLC_GBH is connected to the gate of the MOSFET; the low-level reference ground of driver chip U1 is connected to the floating ground GND_GBH_AC. This floating ground GND_GBH_AC is... Figure 2 The source of the upper bridge arm MOSFET Q1 in the LLC circuit shown is shown. The power supply terminal VCC17_AC_D of the driver chip U1 receives a fixed power supply voltage. The input terminal INB of the driver chip U1 is used to receive pulse control signals from the microcontroller unit (MCU) (not shown in the figure). The output terminal OUTB of the driver chip U1 is used to output a drive square wave with the same frequency as the input signal.

[0026] This can be understood as follows: when the INB port of the driver chip U1 receives a pulse signal from the MCU, the OUTB output terminal of the driver chip U1 will output a pulse signal of the same frequency; among them, the high-level output of the square wave signal is the VCC17_AC_D port voltage, i.e., 17V, and the low-level output of the square wave signal is GND_GBH_AC.

[0027] If there is no bootstrap capacitor C14, then when Figure 2 When Q1 is turned on, the source voltage becomes 400V, the gate voltage becomes lower than the source voltage, Q1 will turn off, and the circuit cannot perform its normal function.

[0028] With the addition of bootstrap capacitor C14, when the source voltage becomes 400V, due to the characteristic that the voltage across the capacitor cannot change abruptly, the voltage across the output terminal OUTB of the driver chip U1 connected to bootstrap capacitor C14 will rise to 400V, so that the voltage difference between the gate and source of Q1 is normal.

[0029] When the output terminal OUTB of the driver chip U1 outputs a low level, the voltage across the bootstrap capacitor C14 cannot change abruptly. The side of the bootstrap capacitor C14 closest to the current limiting resistor R4 will become a negative voltage. Due to the presence of the Zener diode ZD1, the negative voltage on the left side of the current limiting resistor R4 is the Zener voltage value of the Zener diode ZD1.

[0030] In a specific example, the Zener diode is chosen to regulate a voltage of 3.3V.

[0031] When this solution is working normally, the waveform of the output terminal OUTB of the driver chip U1 is as follows: Figure 4 As shown.

[0032] The working principle of this solution is as follows: 1. High-level output stage (MOSFET turned on): When the INB terminal of driver chip U1 receives a high-level signal, its OUTB terminal outputs a high-level signal, with a voltage value approximately equal to the power supply voltage at VCC17_AC_D. Current charges the gate capacitance of the MOSFET, causing the gate voltage to exceed the source voltage, thus driving the MOSFET to conduct. During this period, because the voltage at the OUTB terminal of driver chip U1 is higher than the voltage at node A, the Zener diode ZD1 is in reverse cutoff and does not function. The bootstrap capacitor C14 is charged during this process, establishing a voltage difference across it.

[0033] 2. Low-level output and negative voltage generation stage (MOSFET off): When the INB terminal of driver chip U1 receives a low-level signal, its OUTB terminal outputs a low level. Ideally, its potential is pulled down to the floating ground GND_GBH_AC. Based on the characteristic that the voltage across a capacitor cannot change abruptly, when the potential at the OUTB terminal of driver chip U1 suddenly drops, the potential at node A will also drop synchronously. During the turn-off process of the MOSFET, its source potential GND_GBH_AC will jump to a high voltage due to circuit operation. This jump will further push the potential of node A to a negative value through the coupling of bootstrap capacitor C14. At this time, the negative voltage at node A will cause Zener diode ZD1 to conduct in the forward direction, thereby clamping the potential of node A at approximately -Vz (where Vz is the Zener voltage of Zener diode ZD1, for example, 3.3V). Therefore, the voltage applied to the gate LLC_GBH of the MOSFET is approximately -3.3V. This negative voltage ensures that the gate of the MOSFET is at a negative potential relative to the source, which can quickly discharge the gate charge, greatly accelerate the turn-off process of the MOSFET, and effectively suppress the risk of false turn-on caused by Miller capacitance.

[0034] The present invention also protects an LLC converter, including a half-bridge or full-bridge circuit, wherein the half-bridge or full-bridge circuit includes an upper bridge arm MOSFET and a lower bridge arm MOSFET, wherein the upper bridge arm MOSFET is driven by the aforementioned bootstrap circuit.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A bootstrap circuit for driving a MOS transistor, characterized by The application relates to a bootstrap circuit for driving a MOS tube, comprising: a bootstrap module (10) comprising a driving chip and a bootstrap capacitor, an output terminal of the driving chip being connected to a gate of a MOS tube to be driven through the bootstrap capacitor; a voltage clamping branch (20) connected between a node between the bootstrap capacitor and the gate of the MOS tube and a reference ground; wherein the voltage clamping branch (20) is configured to be turned on when the driving chip outputs a low level, so as to provide a negative voltage at the gate of the MOS tube.

2. The bootstrap circuit for driving a MOS transistor according to claim 1, wherein, The voltage clamping branch (20) comprises a voltage stabilizing tube and a current limiting resistor connected in series with each other; a cathode of the voltage stabilizing tube is connected to a node between the bootstrap capacitor and the current limiting resistor, and an anode of the voltage stabilizing tube is connected to the reference ground; one end of the current limiting resistor away from the voltage stabilizing tube is connected to the gate of the MOS tube; wherein when the driving chip outputs a low level, the voltage stabilizing tube is turned on to generate a negative voltage at the node and act on the gate of the MOS tube through the current limiting resistor.

3. The bootstrap circuit for driving a MOS transistor according to claim 2, wherein, A power supply terminal of the driving chip receives a first voltage, and a voltage stabilizing value of the voltage stabilizing tube is less than the first voltage.

4. The bootstrap circuit for driving a MOS transistor according to claim 3, wherein, The first voltage is 3.3V-17V.

5. The bootstrap circuit for driving a MOS transistor according to claim 2, wherein, The current limiting resistor is configured to suppress oscillation of the gate of the MOS tube.

6. The bootstrap circuit for driving a MOS transistor according to claim 1, wherein, An input terminal of the driving chip is used for receiving a pulse signal from a micro control unit.

7. The bootstrap circuit for driving a MOS transistor according to claim 1, wherein, The model of the driving chip is IR2110.

8. An LLC converter comprising a half bridge or full bridge circuit, the half bridge or full bridge circuit comprising an upper bridge MOSFET and a lower bridge MOSFET, characterized in that, The upper bridge arm MOS tube is driven by the bootstrap circuit in any one of claims 1 to 7.

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