Bootstrap capacitor charging circuit and charging method

Abstract

The present invention proposes a bootstrap capacitor charging circuit and a charging method, wherein the charging circuit comprises a unidirectional conduction circuit and a current limiting circuit, wherein the unidirectional conduction circuit and the current limiting circuit are connected in series; the supply voltage charges the bootstrap capacitor through the charging circuit, and the current limiting circuit limits the charging current of the bootstrap capacitor; the bootstrap capacitor is used to supply power to a driving circuit of an upper tube of a switching power supply, and the upper tube of the switching power supply receives an input voltage. The present invention prevents the charging current of the bootstrap capacitor from flowing through a body diode in the unidirectional conduction circuit, thereby avoiding the influence caused by the parasitic effect of the body diode.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to a bootstrap capacitor charging circuit and a charging method. Background Art

[0002] Figure 1 The schematic diagram of the switching power supply in the prior art is shown. The power supply voltage VDD supplies power to the switching power supply driving circuit through two MOS tubes connected in series. However, when the synchronous rectifier tube M1 is turned on, the voltage at SW will be pulled down to less than zero, so that the voltage at the high potential end of the bootstrap capacitor C0 is pulled down, so that the voltage difference between the input end and the positive electrode of the bootstrap capacitor C0 is large, causing the main switch tube M2 to have leakage current flowing through its body diode. Due to the parasitic effect of the body diode, the leakage current flowing through the body diode will affect the circuit performance. Summary of the invention

[0003] The object of the present invention is to provide a bootstrap capacitor charging circuit and charging method for preventing leakage current from flowing through a body diode, so as to solve the problem of parasitic effects caused by leakage current flowing through a body diode in the prior art.

[0004] To achieve the above object, the present invention provides a bootstrap capacitor charging circuit, comprising a unidirectional conduction circuit and a current limiting circuit, wherein the unidirectional conduction circuit and the current limiting circuit are connected in series; the supply voltage charges the bootstrap capacitor through the charging circuit, and the current limiting circuit limits the charging current of the bootstrap capacitor;

[0005] Optionally, when the upper tube of the switching power supply is turned off, the current limiting circuit is turned off, and when the turn-off time reaches the first time, the current limiting circuit is turned on.

[0006] Optionally, when the upper tube of the switching power supply is turned off, the current limiting circuit is turned off; when the voltage at the high potential end of the bootstrap capacitor or the voltage at the low potential end thereof reaches a corresponding threshold, the current limiting circuit is turned on.

[0007] Optionally, the current limiting circuit includes a switch tube, which is connected to the unidirectional conduction circuit; when the upper tube of the switching power supply is turned off, the switch tube is turned off, and when the shutdown time reaches a first time, the switch tube is turned on.

[0008] Optionally, the unidirectional conduction circuit includes two MOS tubes, and the body diodes of the two MOS tubes are connected in reverse series.

[0009] Optionally, the two MOS tubes are both PMOS tubes.

[0010] Optionally, the two MOS tubes are both NMOS tubes.

[0011] Optionally, of the two MOS tubes, one is an NMOS tube and the other is a PMOS tube.

[0012] The present invention also provides a bootstrap capacitor charging method, which is based on a unidirectional conduction circuit and a current limiting circuit, wherein the unidirectional conduction circuit and the current limiting circuit are connected in series; the supply voltage charges the bootstrap capacitor through the unidirectional conduction circuit and the current limiting circuit, and the current limiting circuit limits the charging current of the bootstrap capacitor.

[0013] Optionally, when the upper tube of the switching power supply is turned off, the current limiting circuit is turned off, and when the turn-off time reaches the first time, the current limiting circuit is turned on.

[0014] Compared with the prior art, the present invention has the following advantages: the present invention is based on a unidirectional conduction circuit and a current limiting circuit, the unidirectional conduction circuit and the current limiting circuit are connected in series; the power supply voltage charges the bootstrap capacitor through the unidirectional conduction circuit and the current limiting circuit, and the current limiting circuit limits the charging current of the bootstrap capacitor. When the upper tube of the switching power supply is turned off, the current limiting circuit is turned off, and when the off time reaches the first time or the voltage at one end of the bootstrap capacitor reaches the corresponding threshold voltage, the current limiting circuit is turned on. The present invention can prevent the charging current of the bootstrap capacitor from flowing through the body diode in the unidirectional conduction circuit, thereby avoiding the influence of the parasitic effect of the body diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the schematic diagram of the switching power supply in the prior art;

[0016] Figure 2 This is a schematic diagram of the bootstrap capacitor charging circuit of the present invention;

[0017] Figure 3 This is a schematic diagram of a second real-time example of a unidirectional conduction circuit of the present invention;

[0018] Figure 4 This is a schematic diagram of a third real-time example of a unidirectional conduction circuit of the present invention;

[0019] Figure 5 This is a schematic diagram of a fourth embodiment of a unidirectional conduction circuit of the present invention; DETAILED DESCRIPTION

[0020] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0021] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0022] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportions, in order to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0023] like Figure 2 As shown, the schematic diagram of the bootstrap capacitor charging circuit of the present invention is illustrated, including a current limiting circuit and a unidirectional conduction circuit, the current limiting circuit and the unidirectional conduction circuit are connected, and the power supply voltage VDD charges the bootstrap capacitor C0 of the switching power supply through the current limiting circuit and the unidirectional conduction circuit. The current limiting circuit includes a switch tube M0, a drive circuit U01 and a timing circuit U02. When the upper tube of the switching power supply is turned off, the voltage at the high potential end of the bootstrap capacitor is pulled down, and the conduction voltage drop of the unidirectional conduction circuit increases. Due to the influence of the parasitic capacitance of the unidirectional conduction circuit, parasitic oscillations will occur for a period of time. Therefore, when the upper tube of the switching power supply is turned off, the switch tube M0 is controlled to be turned off. When the off time reaches the first time or the voltage at one end of the bootstrap capacitor reaches the corresponding threshold, the switch tube M0 is controlled to be turned on.

[0024] The unidirectional conduction circuit in this embodiment includes two NMOS tubes M1 and M2. The body diodes of the two NMOS tubes are connected in reverse series. The drain of one NMOS tube M1 is connected to the gates of the two NMOS tubes. The drain of the NMOS tube M1 is the positive electrode of the unidirectional conduction circuit, and the drain of the other NMOS tube M2 is the negative electrode of the unidirectional conduction circuit.

[0025] like Figure 3 As shown, a schematic diagram of a second embodiment of a unidirectional conduction circuit of the present invention is illustrated, comprising two PMOS tubes M1 and M2 with body diodes connected in series, wherein the drain of one PMOS tube M2 is connected to the gates of the two PMOS tubes, the drain of the PMOS tube M2 is the negative electrode of the unidirectional conduction circuit, and the drain of the other MOS tube M1 is the positive electrode of the unidirectional conduction circuit.

[0026] like Figure 4 As shown, a schematic diagram of a third embodiment of a unidirectional conduction circuit of the present invention is illustrated, comprising a PMOS tube M1 and an NMOS tube M2, the body diodes of the two MOS tubes are connected in reverse series, the drain of the PMOS tube M1 is connected to the gate of the NMOS tube M2, the gate of the PMOS tube M1 is connected to its drain and the source of the NMOS tube M2, the source of the PMOS tube M1 is the positive electrode of the unidirectional conduction circuit, and the drain of the NMOS tube M2 is the negative electrode of the unidirectional conduction circuit.

[0027] like Figure 5As shown, a schematic diagram of a fourth embodiment of a unidirectional conduction circuit of the present invention is illustrated, comprising a PMOS tube M1 and an NMOS tube M2, the body diodes of the two MOS tubes are connected in reverse series, the gate of the PMOS tube M1 is connected to the source of the NMOS tube M2, the source of the PMOS tube M1 is connected to the gate and drain of the NMOS tube M2, the drain of the PMOS tube M1 is the positive electrode of the unidirectional conduction circuit, and the source of the NMOS tube M2 is the negative electrode of the unidirectional conduction circuit.

[0028] It is considered by ordinary technicians that replacement and integration can be made between the embodiments. If there is any content not explicitly recorded in one embodiment, reference can be made to another embodiment that is recorded.

[0029] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A bootstrap capacitor charging circuit, characterized in that: It comprises a unidirectional conduction circuit and a current limiting circuit, the unidirectional conduction circuit and the current limiting circuit are connected in series; the power supply voltage charges the bootstrap capacitor through the charging circuit, and the current limiting circuit limits the charging current of the bootstrap capacitor; the bootstrap capacitor is used to supply power to the driving circuit of the upper tube of the switching power supply, and the upper tube of the switching power supply receives the input voltage; When the upper tube of the switching power supply is turned off, the current limiting circuit is turned off, and when the off time reaches the first time, or when the high potential end voltage or the low potential end voltage of the bootstrap capacitor reaches the corresponding threshold, the current limiting circuit is turned on.

2. The bootstrap capacitor charging circuit according to claim 1, characterized in that: The current limiting circuit includes a switch tube, which is connected to the unidirectional conduction circuit; when the upper tube of the switching power supply is turned off, the switch tube is turned off, and when the turn-off time reaches a first time, the switch tube is turned on.

3. The bootstrap capacitor charging circuit according to claim 1, characterized in that: The unidirectional conduction circuit includes two MOS tubes, and the body diodes of the two MOS tubes are connected in reverse series.

4. The bootstrap capacitor charging circuit according to claim 3, characterized in that: The two MOS tubes are both PMOS tubes.

5. The bootstrap capacitor charging circuit according to claim 3, characterized in that: The two MOS tubes are both NMOS tubes.

6. The bootstrap capacitor charging circuit according to claim 3, characterized in that: Of the two MOS tubes, one is an NMOS tube and the other is a PMOS tube.

Images