CN117081369A - Switching power supply and bootstrap power supply circuit thereof - Google Patents

Abstract

A switching power supply and its bootstrap power supply circuit are provided. The switching power supply includes a half-bridge driver circuit. The bootstrap power supply circuit includes a bootstrap power supply enhancement circuit, an internal low-voltage power supply, and a bootstrap capacitor. When the upper power switch tube and the lower power switch tube of the half-bridge drive circuit are both in the off state, the bootstrap power supply enhancement circuit uses the system input voltage of the switching power supply to charge the bootstrap capacitor. When the upper power switch of the half-bridge drive circuit is in the off state and the lower power switch is in the on state, the internal supply voltage generated by the internal low-voltage power supply charges the bootstrap capacitor.

Description

Switching power supply and its bootstrap power supply circuit

Technical field

The present invention relates to the field of circuits, and more specifically to a switching power supply and a bootstrap power supply circuit thereof.

Background technique

Switching power supply, also known as switching power supply and switching converter, is a type of power supply. The function of the switching power supply is to convert a level of voltage into what the user needs through different forms of architecture (for example, fly-back architecture, buck architecture, or boost architecture, etc.) voltage or current.

Contents of the invention

According to a bootstrap power supply circuit used in a switching power supply according to an embodiment of the present invention, the switching power supply includes a half-bridge drive circuit, and the bootstrap power supply circuit includes a bootstrap power supply enhancement circuit, an internal low-voltage power supply, and a bootstrap capacitor. When the upper power switch tube and the lower power switch tube of the half-bridge drive circuit are both in the off state, the bootstrap power supply enhancement circuit uses the system input voltage of the switching power supply to charge the bootstrap capacitor. When the upper power switch of the half-bridge drive circuit is in the off state and the lower power switch is in the on state, the internal supply voltage generated by the internal low-voltage power supply charges the bootstrap capacitor.

A switching power supply according to an embodiment of the present invention includes a bootstrap power supply circuit as described above.

Description of the drawings

The present invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, in which:

Figure 1 shows a system schematic diagram of a DC/DC switching power supply according to an embodiment of the present invention.

FIG. 2 shows a schematic diagram of an example circuit implementation of the bootstrap powered enhancement circuit shown in FIG. 1 .

Detailed ways

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The present invention is in no way limited to any specific configurations and algorithms set forth below, but covers any modifications, substitutions and improvements of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

Most direct current to direct current (DC/DC) switching power supplies choose N-type metal oxide semiconductor field effect transistors (MOSFETs) as the power switch tubes to form a half-bridge drive circuit, but N-type MOSFETs as power switch tubes require a bootstrap power supply circuit . The traditional bootstrap power supply circuit can only stabilize the voltage on the bootstrap capacitor by charging the bootstrap capacitor through the internal low-voltage power supply when the lower power switch is in the on state. However, the DC/DC switching power supply will work in sleep mode for a long time when the system load is very light. At this time, neither the upper power switch tube nor the lower power switch tube is working (that is, both are in the off state). The half-bridge drive circuit The midpoint voltage of the half-bridge is equal to the system output voltage. The internal low-voltage power supply cannot charge the bootstrap capacitor. The internal device leakage causes the voltage on the bootstrap capacitor to decrease. The DC/DC switching power supply will not be able to turn on the power switch normally after exiting the sleep mode. . In view of this, a switching power supply and a bootstrap power supply circuit thereof according to embodiments of the present invention are proposed.

The following describes the working principle of the switching power supply and its bootstrap power supply circuit according to the embodiment of the present invention, taking the DC/DC switching power supply and its bootstrap power supply circuit as an example with reference to the accompanying drawings.

Figure 1 shows a system schematic diagram of a DC/DC switching power supply according to an embodiment of the present invention. As shown in Figure 1, a DC/DC switching power supply 100 according to an embodiment of the present invention includes an upper power switch NMO, a lower power switch NM1, and a bootstrap power supply circuit 102, where the upper power switch NMO and the lower power switch The transistor NM1 forms a half-bridge drive circuit, and the bootstrap power supply circuit 102 includes a bootstrap power supply enhancement circuit 1022, an internal low-voltage power supply 1024, and a bootstrap capacitor C. When the upper power switch NM0 and the lower power switch NM1 are both in the off state (that is, when the DC/DC switching power supply 100 is operating in the sleep mode), the bootstrap power supply enhancement circuit 1022 utilizes the power of the DC/DC switching power supply 100 The system input voltage VIN charges the bootstrap capacitor C. When the upper power switch NM0 is in the off state and the lower power switch NM1 is in the on state (that is, when the DC/DC switching power supply 100 is operating in the non-sleep mode), the internal supply voltage PVCC generated by the internal low-voltage power supply 1024 Charge the bootstrap capacitor C. In this way, the voltage on the bootstrap capacitor C can be kept stable, so that the DC/DC switching power supply 100 can still turn on the upper power switch NM0 normally after exiting the sleep mode. In other words, when the DC/DC switching power supply 100 is working in the sleep mode, by using the system input voltage VIN to charge the bootstrap capacitor C, it solves the problem that the voltage on the bootstrap capacitor C is too low in the light load mode and causes the power switch to turn on. NM0 not working problem.

As shown in Figure 1, the bootstrap capacitor C is connected between the half-bridge midpoint SW of the half-bridge drive circuit and the bootstrap capacitor connection node BST. In some embodiments, the bootstrap power supply enhancement circuit 102 may be connected to the bootstrap capacitor connection node BST via a first diode D1, and the internal low-voltage power supply 104 may be connected to the bootstrap capacitor connection node BST via a second diode D2.

As shown in Figure 1, the working process of the DC/DC switching power supply 100 can be divided into two stages: charging and freewheeling. During the charging phase, the upper power switch NM0 is in the on state and the lower power switch NM1 is in the off state. The system input voltage VIN supplies power to the output capacitor C _L and the system load R _L via the inductor L. During the freewheeling phase, the upper power switch NM0 is in the off state, the lower power switch NM1 is in the on state, and the inductor L and the output capacitor C _L supply power to the system load R _L.

FIG. 2 shows a schematic diagram of an example circuit implementation of the bootstrap power enhancement circuit 1022 shown in FIG. 1 . As shown in Figure 2, in some embodiments, the bootstrap power supply enhancement circuit 1022 includes a source follower structure circuit, which includes a power switch transistor PM1, a power switch transistor NM2, and a power switch transistor NM3, where, The gate of the power switch PM1 is connected to the half-bridge midpoint SW of the half-bridge drive circuit, the source of the power switch PM1 is connected to the source of the power switch NM2, and the gate of the power switch NM2 is connected to the power switch NM2. The drain of the power switch NM3 and the gate of the power switch NM3 are connected to the bootstrap capacitor connection node BST via the first diode D1.

As shown in Figure 2, in some embodiments, the bootstrap power supply enhancement circuit 1022 also includes a power switch PM2 and a power switch NM4, wherein the gate of the power switch PM2 is connected to the gate and source of the power switch PM1. The gate of the power switch NM3 is connected to the gate, the drain is connected to the drain of the power switch NM4, the source of the power switch NM4 is grounded, and the power switch NM4 is connected to both the upper power switch NM0 and the lower power switch NM1. In the off state, it is in the off state.

As shown in Figure 2, in some embodiments, when the DC/DC switching power supply 100 is working in the sleep mode, the working mode indication signal XSLEEP used to indicate whether the DC/DC switching power supply 100 is working in the sleep mode is low level, The power switch NM4 is in the off state, and the gate voltage V _{gate_NM3} of the power switch NM3 is:

V _{gate_NM3} =V _SW +V _{GS_PM1} +I×R ₁ +V _{GS_NM2}

Among them, V _SW represents the half-bridge midpoint voltage of the half-bridge drive circuit, V _{GS_PM1} represents the voltage difference between the gate and source of the power switch PM1 when it is in the conductive state, and V _{GS_NM2} represents the power switch NM2 in the conductive state. The voltage difference between its gate and source in the on state.

As shown in FIG. 2 , in some embodiments, when the DC/DC switching power supply 100 is operating in the sleep mode, since the upper power switch NM0 and the lower power switch NM1 do not have switching operations, internal device leakage causes the bootstrap capacitor C to rise. The voltage decreases. At this time, the bootstrap power supply enhancement circuit 1022 uses the system input voltage VIN to charge the bootstrap capacitor C so that the voltage on the bootstrap capacitor C reaches a steady state. The voltage V _BST at the node BST where the bootstrap capacitor is connected is:

V _BST =V _{gate_NM3} -V _{GS_NM3} -V _D1

Among them, V _{GS_NM3} represents the voltage difference between the gate and the source of the power switch NM3 when it is in the on state, and V _D1 represents the turn-on voltage of the first diode D1 (the first diode D1 is used to block Bootstrap capacitor C leaks to the input terminal of system input voltage VIN).

As shown in Figure 2, in some embodiments, when the DC/DC switching power supply 100 operates in the non-sleep mode, the working mode indication signal XSLEEP used to indicate whether the DC/DC switching power supply 100 operates in the sleep mode is high level. , the power switch NM4 is in the on state, and the gate voltage V _{gate_NM3} of the power switch NM3 is:

V _{gate_NM3} =V _SW +V _{GS_PM2}

Among them, V _{GS_PM2} represents the voltage difference between the gate and the source of the power switch PM2 when it is in the on state.

It should be noted that when the DC/DC switching power supply 100 is operating in the non-sleep mode, due to the large resistance of R1 and the combination with the gate parasitic capacitance of the power switch NM2, the gate voltage of the power switch NM2 cannot be increased. Closely following the change of the half-bridge midpoint voltage of the half-bridge drive circuit, the upper power switch NM0 is turned on, thereby generating a large current path between the bootstrap capacitor connection node BST and the input terminal of the system input voltage VIN, so a power switch is added. tube PM2 and NM4. When the DC/DC switching power supply 100 is operating in the non-sleep mode, the power switch NM4 is in a conductive state. Since the impedance of the power switch PM2 is small, the gate voltage of the power switch NM2 can closely follow the half-bridge driving circuit. The voltage at the bridge midpoint changes to avoid the above problems.

As shown in Figure 2, in some embodiments, the bootstrap power supply enhancement circuit 1022 also includes a first Zener diode ZD1, connected between the gate and source of the power switch NM3, to prevent the power switch NM3 from being damaged. The leakage causes the voltage at the bootstrap capacitor connection node BST to increase, and at the same time, the source potential of the power switch NM3 is clamped to prevent the voltage difference between the gate and the source of the power switch NM3 from being too large and causing damage to the power switch NM3. .

As shown in Figure 2, in some embodiments, the bootstrap power supply enhancement circuit 1022 also includes a second Zener diode ZD2, connected between the gate and the source of the power switch PM2, for clamping the power switch PM2 The source potential of the power switch PM2 is set to prevent the power switch PM2 from being damaged due to an excessive voltage difference between the gate and the source of the power switch PM2.

The present invention may be implemented in other specific forms without departing from its spirit and essential characteristics. For example, algorithms described in specific embodiments may be modified without departing from the basic spirit of the invention. The present embodiments are therefore to be considered in all respects as illustrative rather than restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and everything within the meaning and equivalents of the claims is All changes within the scope are therefore included in the scope of the invention.

Claims (7)

1. A bootstrap power supply circuit used in a switching power supply, wherein the switching power supply includes a half-bridge drive circuit, the bootstrap power supply circuit includes a bootstrap power supply enhancement circuit, an internal low-voltage power supply, and a bootstrap capacitor, and in: When the upper power switch tube and the lower power switch tube of the half-bridge drive circuit are both in the off state, the bootstrap power supply enhancement circuit uses the system input voltage of the switching power supply to charge the bootstrap capacitor, and When the upper power switch transistor of the half-bridge driving circuit is in the off state and the lower power switch transistor is in the on state, the internal supply voltage generated by the internal low-voltage power supply charges the bootstrap capacitor. 2. The bootstrap power supply circuit according to claim 1, wherein the bootstrap power supply enhancement circuit is connected to the bootstrap capacitor via a first diode and a bootstrap capacitor connection node, and the internal low voltage power supply is connected to the bootstrap capacitor via a first diode and a bootstrap capacitor connection node. A diode and the bootstrap capacitor connection node are connected to the bootstrap capacitor. 3. The bootstrap power supply circuit according to claim 2, wherein the bootstrap power supply enhancement circuit includes a source follower structure circuit, and the source follower structure circuit includes a first power switch tube and a second power switch tube. , and a third power switch, the gate of the first power switch is connected to the half-bridge midpoint of the half-bridge drive circuit, and the source of the first power switch is connected to the second power switch The source electrode of the tube, the gate electrode of the second power switch tube is connected to the drain electrode of the second power switch tube and the gate electrode of the third power switch tube, and the source electrode of the third power switch tube The bootstrap capacitor connection node is connected via the first diode. 4. The bootstrap power supply circuit according to claim 3, wherein the bootstrap power supply enhancement circuit further includes a fourth power switch tube and a fifth power switch tube, and the gate of the fourth power switch tube is connected to the The gate and source of the first power switch are connected to the gate and drain of the third power switch, and the source of the fifth power switch is connected to the drain of the fifth power switch. The fifth power switch tube is grounded, and the fifth power switch tube is in the off state when the upper power switch tube and the lower power switch tube of the half-bridge drive circuit are both in the off state. 5. The bootstrap power supply circuit according to claim 4, wherein the bootstrap power supply enhancement circuit further includes a first Zener diode connected between the gate and the source of the third power switch. 6. The bootstrap power supply circuit according to claim 4, wherein the bootstrap power supply enhancement circuit further includes a second Zener diode connected between the gate and the source of the fourth power switch. 7. A switching power supply, comprising the bootstrap power supply circuit according to any one of claims 1 to 6.