Switching Power Supply Main Power Transistor Drive Circuit

Abstract

The present invention provides a driving circuit for a main power transistor of a switching power supply. The main power transistor is a PMOS transistor. The driving circuit includes a pull-down circuit and a clamping circuit. The first end of the pull-down circuit is connected to the control end of the power transistor, and its second end is grounded. By controlling the conduction of the pull-down circuit, the power transistor is driven to conduct fully. The first end of the clamping circuit receives a supply voltage, and its second end is connected to the control end of the power transistor. When the clamping circuit conducts, the voltage at the control end of the power transistor is clamped at a desired voltage. The present invention can quickly drive the power transistor with high working efficiency.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and particularly to a driving circuit for the main power transistor of a switching power supply. Background Art

[0002] In the prior art, a PMOS transistor is often used as the main power transistor of a switching power supply. Figure 1 Illustrates the driving circuit of the PMOS main power transistor in the prior art. In the prior art, the main power transistor is driven to conduct by controlling the switch M1 to conduct, and the main power transistor is driven to turn off by controlling the switch M2 to conduct. However, only by pulling down the main power transistor through the switch M1, the conduction speed of the main power transistor is not fast enough; secondly, the main power transistor cannot be controlled to conduct fully. Summary of the Invention

[0003] The object of the present invention is to provide a driving circuit for the main power transistor of a switching power supply that is efficient and can quickly drive the power transistor, so as to solve the problems in the prior art that the conduction speed of the power transistor is not fast enough and it cannot conduct fully.

[0004] To achieve the above object, the present invention provides a driving circuit for the main power transistor of a switching power supply. The main power transistor is a PMOS transistor, and it is characterized in that: the driving circuit includes a pull-down circuit and a clamping circuit. The first end of the pull-down circuit is connected to the control end of the power transistor, and its second end is grounded. By controlling the pull-down circuit to conduct, the power transistor is driven to conduct fully; the first end of the clamping circuit receives the supply voltage, and its second end is connected to the control end of the power transistor; when the main power transistor conducts fully, the clamping circuit conducts, and the clamping circuit clamps the voltage of the control end of the power transistor at the desired voltage.

[0005] Optionally, the pull-down circuit includes a first switch transistor and a second switch transistor. The first end of the first switch transistor is connected to the control end of the power transistor, and its second end is grounded; the first end of the second switch transistor is connected to the control end of the main power transistor, and its second end is grounded; by controlling the first switch transistor and the second switch transistor to conduct, the power transistor is driven to conduct fully.

[0006] Optionally, after the clamping circuit conducts, the second switch transistor is controlled to turn off.

[0007] Optionally, the driving circuit further includes a third switch transistor. The first end of the third switch transistor receives the supply voltage, and the second end of the third switch transistor is connected to the control end of the power transistor; by controlling the third switch transistor to conduct, the power transistor is controlled to turn off.

[0008] Optionally, the drive circuit further includes a first resistor, a first current source, and a fourth switching transistor. The first end of the first resistor receives a supply voltage, and its second end is connected to the control end of the main power transistor. The first current source and the fourth switching transistor are connected in series and then connected to the control end of the power transistor. During the conduction stage of the main power transistor, the first current source and the fourth switching transistor are turned on.

[0009] Compared with the prior art, the present invention has the following advantages: The drive circuit includes a pull-down circuit and a clamping circuit. The first end of the pull-down circuit is connected to the control end of the power transistor, and its second end is grounded. By controlling the conduction of the pull-down circuit, the power transistor is driven to fully conduct. The first end of the clamping circuit receives a supply voltage, and its second end is connected to the control end of the power transistor. When the clamping circuit conducts, the voltage at the control end of the power transistor is clamped at a desired voltage. The present invention can quickly drive the power transistor with high working efficiency. Description of the Drawings

[0010] Figure 1 is a schematic diagram of a drive circuit for the main power transistor of a switching power supply in the prior art;

[0011] Figure 2 is a schematic diagram of a drive circuit for the main power transistor of a switching power supply according to the present invention; Detailed Embodiments

[0012] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any alternatives, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0013] For the public to have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention. However, those skilled in the art can fully understand the present invention without the description of these details.

[0014] In the following paragraphs, the present invention is described more specifically by way of example with reference to the accompanying drawings. It should be noted that the drawings are all in a relatively simplified form and use non-precise scales to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0015] Such as Figure 2As shown in the figure, the schematic diagram of the driving circuit of the main power transistor of the switching power supply according to the embodiment of the present invention is illustrated. The main power transistor of the present invention is a PMOS transistor. The driving circuit includes a pull-down circuit, a clamping circuit, and switching transistors M4, M3, a first current source I1, and a first resistor R1. The pull-down circuit includes a PMOS transistor M1 and an NMOS transistor M2. The source of the PMOS transistor M1 is connected to the control terminal of the main power transistor, and its drain is grounded. The drain of the NMOS transistor M2 is connected to the control terminal of the main power transistor, and its source is grounded. By driving the transistors M1 and M2 to conduct, the main power transistor is fully driven to conduct. The switching transistor M3 and the current source I1 are connected in series and then connected to the control terminal of the main power transistor. The current source I1 and the transistor M3 are always conducting when the main power transistor is turned on. The voltage I1*R1 on the first resistor R1 maintains the gate-source voltage VGS of the main power transistor. In order to ensure that the lowest level after the main power transistor is pulled down is controlled, the clamping circuit is connected to the control terminal of the main power transistor. The first end of the clamping circuit receives the supply voltage, and its second end is connected to the control terminal of the power transistor. When the clamping circuit conducts, the voltage of the control terminal of the power transistor is clamped at the desired voltage, and an enable signal EN is output to control the second switching transistor to turn off. After the main power transistor conducts, the enable signal EN controls the NMOS transistor M2 to turn off. The first end of the switching transistor M4 receives the input voltage, and its second end is connected to the control terminal of the main power transistor. By pulling down the switching transistor M4, the main power transistor is driven to turn off.

[0016] Although the embodiments are described and illustrated separately above, for the common technologies involved, in the view of those of ordinary skill in the art, substitutions and integrations can be made between the embodiments. For the content not clearly recorded in one of the embodiments, reference can be made to another embodiment with relevant records.

[0017] The above-described embodiments do not constitute a limitation on the protection scope of the technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principle of the above embodiments shall be included within the protection scope of the technical solution.

Claims

1. A driving circuit for the main power transistor of a switching power supply, where the main power transistor is a PMOS transistor, and it is characterized in that: The driving circuit includes a pull-down circuit and a clamping circuit. The first end of the pull-down circuit is connected to the control end of the power transistor, and its second end is grounded. By controlling the conduction of the pull-down circuit, the power transistor is driven to conduct fully. The first end of the clamping circuit receives the supply voltage, and its second end is connected to the control end of the power transistor. When the main power transistor conducts fully, the clamping circuit conducts, and the clamping circuit clamps the voltage at the control end of the power transistor to a desired voltage. The pull-down circuit includes a first switching transistor and a second switching transistor. The first end of the first switching transistor is connected to the control end of the power transistor, and its second end is grounded. The first end of the second switching transistor is connected to the control end of the main power transistor, and its second end is grounded. By controlling the conduction of the first switching transistor and the second switching transistor, the power transistor is driven to conduct fully. After the clamping circuit conducts, the second switching transistor is controlled to turn off. The driving circuit further includes a first resistor, a first current source, and a fourth switching transistor. The first end of the first resistor receives the supply voltage, and its second end is connected to the control end of the main power transistor. The first current source and the fourth switching transistor are connected in series and then connected to the control end of the power transistor. During the conduction stage of the main power transistor, the first current source and the fourth switching transistor conduct. The first switching transistor is a PMOS transistor, and the second switching transistor is an NMOS transistor.

2. The switching power supply main power tube drive circuit according to claim 1, wherein: The driving circuit further includes a third switching transistor. The first end of the third switching transistor receives the supply voltage, and the second end of the third switching transistor is connected to the control end of the power transistor. By controlling the conduction of the third switching transistor, the power transistor is controlled to turn off.

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