Switching control circuit and switching power supply

Abstract

This invention proposes a switch control circuit and a switching power supply. The switch control circuit controls the switching transistor in the switching power supply and includes a judgment circuit, a charging / discharging circuit, and a valley-level conduction signal generation circuit. The input of the judgment circuit is coupled to a detection signal terminal to obtain a detection signal characterizing the drain-source voltage of the switching transistor. The judgment circuit performs zero-crossing detection on the detection signal and generates a valley-level signal. The input of the charging / discharging circuit is coupled to the output of the judgment circuit, and the output of the charging / discharging circuit outputs a charging / discharging voltage. The first input of the valley-level conduction signal generation circuit is coupled to the output of the charging / discharging circuit, and the second input of the valley-level conduction signal generation circuit is coupled to a preset voltage terminal to obtain a preset voltage. The output of the valley-level conduction signal generation circuit outputs a valley-level conduction signal. This invention provides a switch control circuit and a switching power supply that can promptly achieve valley-level conduction and exhibits good system stability.

Description

Technical Field

[0001] This utility model belongs to the field of power electronics, and relates to a switching power supply technology, particularly a switching control circuit and a switching power supply. Background Technology

[0002] Switching power supplies are widely used due to their advantages such as high efficiency and energy saving, small size and light weight, stable output, multiple protection functions, and wide input voltage range. These advantages enable switching power supplies to perform well in various application scenarios and meet the power requirements of modern electronic devices.

[0003] In switching power supplies, to improve system efficiency or optimize EMI performance, the system switching frequency is limited. Common methods include direct frequency limiting and valley-locked algorithms. The principle of valley-locked algorithms is as follows (see appendix). Figure 1 As shown, as the load decreases, the on-time Ton decreases, requiring a reduction in the switching frequency, and the system operates in DCM mode (i.e., discontinuous mode). In actual DCM mode operation, as... Figure 2 As shown, as the number of valleys gradually increases, the resonant energy gradually weakens, which may cause the switching power supply to no longer be able to detect the valleys. This could lead to a Tswmax operating state, i.e., an excessively long turn-off time in DCM mode, causing abrupt changes in the switching cycle and resulting in system instability. Figure 2 As shown, when the switching transistor in the switching power supply needs to be turned on at the third valley of its drain-source voltage VDS, the third valley becomes difficult to detect because the VDS oscillates and decays continuously. This can lead to situations where the switching transistor cannot be effectively turned on, causing the cycle to extend to Tswmax. Furthermore, the valley-locking algorithm suffers from instability when the number of valleys in the switching power supply is large.

[0004] In view of this, a new structure is needed to solve at least some of the above problems. Utility Model Content

[0005] In view of one or more problems in the prior art, this utility model proposes a switch control circuit and a switching power supply.

[0006] According to one aspect of this utility model, a switch control circuit is disclosed, which is used to control the switching transistor in a switching power supply. The switch control circuit includes:

[0007] The judgment circuit has its input terminal coupled to the detection signal terminal to obtain the detection signal characterizing the drain-source voltage of the switching transistor, which is used to perform zero-crossing detection on the detection signal and generate a valley signal.

[0008] A charging / discharging circuit, whose input is coupled to the output of a judgment circuit, and whose output outputs a charging / discharging voltage; and

[0009] The valley conduction signal generation circuit has a first input terminal coupled to the output terminal of the charging and discharging circuit, a second input terminal coupled to a preset voltage terminal to obtain a preset voltage, and an output terminal that outputs a valley conduction signal.

[0010] In one embodiment, the determining circuit includes:

[0011] The zero-crossing detection circuit has its input terminal coupled to the detection signal terminal to obtain the detection signal, and its output terminal outputs the zero-crossing detection signal.

[0012] A period detection circuit, whose input is coupled to the output of a zero-crossing detection circuit, outputs a period detection signal; and

[0013] The valley signal generation circuit has its input terminals coupled to the output terminals of the zero-crossing detection circuit and the period detection circuit, respectively, and its output terminal outputs the valley signal.

[0014] In one embodiment, the input terminal of the charging and discharging circuit is coupled to the output terminal of the zero-crossing detection circuit, and the charging and discharging circuit is used to charge and discharge according to the zero-crossing detection signal.

[0015] In one embodiment, the charging and discharging circuit includes:

[0016] The first switch has its control terminal coupled to the judgment circuit and its second terminal coupled to ground.

[0017] A first capacitor, the first terminal of which is coupled to the first terminal of a first switch, and the second terminal of which is coupled to ground; and

[0018] The first current source has its first end coupled to the first end of the first capacitor and its second end coupled to ground.

[0019] In one embodiment, the determining circuit includes:

[0020] A first OR gate, wherein a first input receives a switch control signal and a second input receives a second valley signal; and

[0021] The trigger circuit has a set terminal that receives the first valley signal, a reset terminal that is coupled to the output of the first OR gate, and a second output terminal that is coupled to the control terminal of the first switch.

[0022] In one embodiment, the valley conduction signal generation circuit includes a comparator circuit, the first input terminal of which is coupled to the output terminal of the charge-discharge circuit, and the second input terminal of which is coupled to a preset voltage terminal.

[0023] In one embodiment, the valley conduction signal generation circuit further includes a second OR gate, the first input of which is coupled to the output of the comparison circuit, and the second input of which is used to receive the second valley signal.

[0024] In one embodiment, the switch control circuit further includes a switch control signal generation circuit, the input terminal of which is coupled to the output terminal of the valley conduction signal generation circuit, and the output terminal of the switch control signal generation circuit outputs a switch control signal to control the switch transistor.

[0025] In one embodiment, the determination circuit includes a valley signal generation circuit that generates a valley signal; the valley conduction signal generation circuit includes a quasi-valley signal generation circuit that generates a quasi-valley signal; the input terminal of the valley conduction signal generation circuit is coupled to the output terminal of the valley signal generation circuit, and the output terminal of the valley conduction signal generation circuit outputs a valley conduction signal.

[0026] According to another aspect of the present invention, a switching power supply is disclosed, the switching power supply including a switching control circuit as described in any of the preceding claims, the switching control circuit being used to generate a switching control signal to control the operating state of the switching transistor.

[0027] This invention proposes a switch control circuit and a switching power supply. The switch control circuit controls the switching transistor in the switching power supply and includes a judgment circuit, a charging / discharging circuit, and a valley-level conduction signal generation circuit. The input of the judgment circuit is coupled to a detection signal terminal to obtain a detection signal characterizing the drain-source voltage of the switching transistor. The judgment circuit performs zero-crossing detection on the detection signal and generates a valley signal. The input of the charging / discharging circuit is coupled to the output of the judgment circuit, and the output of the charging / discharging circuit outputs a charging / discharging voltage. The first input of the valley-level conduction signal generation circuit is coupled to the output of the charging / discharging circuit, and the second input of the valley-level conduction signal generation circuit is coupled to a preset voltage terminal to obtain a preset voltage. The output of the valley-level conduction signal generation circuit outputs a valley-level conduction signal. This invention provides a switch control circuit and a switching power supply that can promptly achieve valley-level conduction and exhibits good system stability. Specifically, when a true valley-level is not detected or is inaccurately detected, the switch control circuit can generate a quasi-valley to replace the unobtainable true valley, thus ensuring timely switching of the switching transistor. Attached Figure Description

[0028] The accompanying drawings are provided to further illustrate the present invention and, together with the description, serve to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings:

[0029] Figure 1 A schematic diagram of the signal waveform of a prior art switching power supply is shown;

[0030] Figure 2 A schematic diagram of the signal waveform of another prior art switching power supply is shown;

[0031] Figure 3A schematic diagram of the circuit structure of a switch control circuit according to an embodiment of the present invention is shown;

[0032] Figure 4 A schematic diagram of the circuit structure of a switch control circuit according to another embodiment of the present invention is shown;

[0033] Figure 5 A schematic diagram of the signal waveform of a switching power supply according to an embodiment of the present invention is shown. Detailed Implementation

[0034] To further understand this utility model, preferred embodiments of this utility model are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this utility model, and not for limiting the scope of the claims of this utility model.

[0035] The description in this section pertains to only a few typical embodiments, and this utility model is not limited to the scope of the embodiments described. Combinations of different embodiments, substitution of some technical features in different embodiments, and substitution of the same or similar prior art with some technical features in the embodiments are also within the scope of the description and protection of this utility model.

[0036] The terms "coupled" or "connected" in this specification include both direct and indirect connections. Indirect connections are connections made through an intermediate medium, such as a conductor or electrical medium that may contain parasitic inductance or capacitance. Connections can also be made through intermediate circuits or components described in the embodiments of this specification. Indirect connections may also include connections made through other active or passive devices that achieve the same or similar functions, such as connections through switches, signal amplification circuits, follower circuits, or other circuits or components. "Multiple" or "more" indicates two or more. For the switching state of a switching transistor, "on" and "conduct" are synonyms. Furthermore, in this invention, terms such as "first" and "second" are primarily used to distinguish one technical feature from another, and do not necessarily require or imply any actual relationship or order between these technical features.

[0037] One embodiment of this utility model discloses a switch control circuit used to control the switching transistor in a switching power supply. The switching transistor can be internally or externally placed in the switch control circuit, depending on the specific circuit requirements. Figure 3As shown, in one embodiment, the switch control circuit includes a judgment circuit 10, a charging / discharging circuit 20, and a valley conduction signal generation circuit 30. The input terminal of the judgment circuit 10 is coupled to a detection signal terminal to obtain a detection signal characterizing the drain-source voltage of the switching transistor. In one embodiment, the detection signal is positively correlated with the drain-source voltage of the switching transistor. In another embodiment, the detection signal is proportional to the drain-source voltage of the switching transistor. The judgment circuit 10 performs zero-crossing detection on the detection signal to obtain a zero-crossing detection signal, and generates a valley signal based on the zero-crossing detection signal, which corresponds to the true valley of the drain-source voltage of the switching transistor. The input terminal of the charging / discharging circuit 20 is coupled to the output terminal of the judgment circuit 10, and the output terminal of the charging / discharging circuit 20 outputs a charging / discharging voltage. The charging / discharging circuit 20 performs charging and discharging based on the zero-crossing detection signal. In a specific embodiment, when the zero-crossing detection signal is at a first level (e.g., a high level), the charging / discharging circuit 20 begins charging. When the charging / discharging voltage of the charging / discharging circuit 20 reaches a preset value, the charging / discharging circuit ends the charging process and resets the charging / discharging voltage to zero. At the end of the charging process, the valley-level conduction signal generation circuit controls the quasi-valley signal to be at a first level (e.g., high level). The first input terminal of the valley-level conduction signal generation circuit 30 is coupled to the output terminal of the charge / discharge circuit 20, and the second input terminal of the valley-level conduction signal generation circuit 30 is coupled to a preset voltage terminal to obtain a preset voltage. The output terminal of the valley-level conduction signal generation circuit 30 outputs a valley-level conduction signal. In one embodiment, the switch control circuit further includes a switch control signal generation circuit. The input terminal of the switch control signal generation circuit is coupled to the output terminal of the valley-level conduction signal generation circuit, and the output terminal of the switch control signal generation circuit outputs a switch control signal to control the switching transistor. The switch control signal controls the valley-level conduction switching transistor based on the valley-level conduction signal.

[0038] In one embodiment, the determination circuit includes a zero-crossing detection circuit, a period detection circuit, and a valley signal generation circuit. The input of the zero-crossing detection circuit is coupled to a detection signal terminal to obtain a detection signal. The zero-crossing detection circuit performs zero-crossing detection on the detection signal and generates a zero-crossing detection signal. When the detection signal decreases from a positive value to a negative value at the zero-crossing moment, the zero-crossing detection signal becomes a first level (e.g., a high level). The output of the zero-crossing detection circuit outputs the zero-crossing detection signal. The input of the period detection circuit is coupled to the output of the zero-crossing detection circuit. The period detection circuit determines each oscillation period of the drain-source voltage of the switching transistor based on the zero-crossing detection signal. The output of the period detection circuit outputs a period detection signal, which characterizes each oscillation period of the drain-source voltage of the switching transistor. The input of the valley signal generation circuit is coupled to the outputs of the zero-crossing detection circuit and the period detection circuit, respectively. The output of the valley signal generation circuit outputs a valley signal. In one embodiment, the true valley can be obtained by delaying the zero-crossing moment of the detection signal by a quarter of the current oscillation period of the drain-source voltage of the switching transistor. In one embodiment, the input terminal of the charging and discharging circuit is coupled to the output terminal of the zero-crossing detection circuit, and the charging and discharging circuit is used to charge and discharge according to the zero-crossing detection signal.

[0039] In one embodiment, the switch control circuit includes a judgment circuit, a charging / discharging circuit, and a valley-level conduction signal generation circuit. The input terminal of the charging / discharging circuit is coupled to the output terminal of the judgment circuit. The input terminal of the valley-level conduction signal generation circuit is coupled to the output terminal of the charging / discharging circuit. Figure 4 As shown, the judgment circuit includes a first OR gate and an RS trigger circuit. The first input terminal of the first OR gate receives the switch control signal Gate, and the second input terminal of the first OR gate receives the second valley signal RV2. The set terminal S of the RS trigger circuit receives the first valley signal RV1, the reset terminal of the RS trigger circuit is coupled to the output terminal of the first OR gate, and the second output terminal QN of the RS trigger circuit is coupled to the control terminal of the first switch S1. In one embodiment, the valley signal includes a first valley signal and a second valley signal. Both the first valley signal and the second valley signal are true valleys, that is, valley signals obtained by the switch control circuit based on the zero-crossing detection signal.

[0040] In one embodiment, such as Figure 4 As shown, the charging and discharging circuit includes a first switch S1, a first capacitor C1, and a first current source I1. The control terminal of the first switch S1 is coupled to the second output terminal QN of the judgment circuit. The first terminal of the first switch S1 is coupled to the first terminal of the first capacitor C1, and the second terminal of the first switch S1 is coupled to ground. The first terminal of the first capacitor C1 is coupled to the first terminal of the first switch S1, and the second terminal of the first capacitor C1 is coupled to ground. The first current source I1 is used to provide a first current.

[0041] In one embodiment, such as Figure 4 As shown, the valley conduction signal generation circuit includes a comparator circuit U1 and a second OR gate. The comparator circuit has a first input terminal coupled to the output terminal of the charge / discharge circuit to receive the charge / discharge voltage, and a second input terminal coupled to a preset voltage terminal to receive a preset voltage V1. The first input terminal of the second OR gate is coupled to the output terminal of the comparator circuit U1, and the second input terminal of the second OR gate is used to receive the second valley signal RV2.

[0042] In another embodiment, the determination circuit includes a valley signal generation circuit that generates a valley signal. The valley conduction signal generation circuit includes a quasi-valley signal generation circuit that generates a quasi-valley signal. The input terminal of the valley conduction signal generation circuit is coupled to its output terminal, and the valley conduction signal generation circuit generates a valley conduction signal based on the valley signal and the quasi-valley signal. The valley signal is obtained based on a zero-crossing detection signal. The quasi-valley signal is a valley signal obtained based on a charging / discharging circuit, not the actual valley. The output terminal of the valley conduction signal generation circuit outputs a valley conduction signal.

[0043] In one embodiment, such as Figure 5 As shown, the PWM signal is the switching control signal for the switching transistor. When the PWM signal is at the first level (e.g., high level), the switching control circuit controls the switching transistor to be in the on state. When the PWM signal is at the second level (e.g., low level), the switching control circuit controls the switching transistor to be in the off state. The VDS signal is the drain-source voltage of the switching transistor. The ZCT signal is the zero-crossing detection signal. The Valley signal is the oscillation period signal, and the time period t1-t2 can be regarded as the first oscillation period. Generally, the third oscillation period after the second oscillation period is difficult to obtain. The QuasiValley Counter signal can correspond to the charging and discharging voltage. The QuasiValley signal is the quasi-valley signal. The QRValley signal represents the various oscillation periods obtained by the switching control circuit, which include the actual oscillation period and the quasi-oscillation period inferred by the switching control circuit. In one embodiment, the switching control circuit can obtain the first valley, which is the actual valley. In this embodiment, the switching control circuit cannot obtain the actual second valley. Based on this invention, a second valley is obtained at time t4, which is considered a quasi-valley; a third valley is obtained at time t5, which is also considered a quasi-valley. If the system is set to turn on the switch at the third valley, then the switch will turn on at the third valley (i.e., time t5), thereby ensuring timely switching and effectively solving the problem of instability in existing switching power supply systems.

[0044] This utility model also discloses a switching power supply, which includes a switching control circuit as described in any of the preceding embodiments. The switching control circuit includes a switching transistor and is used to generate a switching control signal to control the operating state of the switching transistor. The operating state of the switching transistor includes an on state and an off state. In another embodiment, the switching power supply includes a switching control circuit and a switching transistor. The output terminal of the switching control circuit is coupled to the control terminal of the switching transistor, and the switching control circuit is used to generate a switching control signal to control the operating state of the switching transistor. In one embodiment of this utility model, the switching control circuit can be configured to select one of the following valleys (first valley, second valley, third valley, fourth valley, etc.) for valley conduction according to the needs of the specific circuit. In one embodiment, the first valley and the second valley are both real valleys, and the third valley, fourth valley, etc. are quasi-valleys. In another embodiment, the first valley is a real valley, and the second valley, third valley, fourth valley, etc. are quasi-valleys. Other achievable embodiments are not described in detail here. Those skilled in the art can set specific circuit structures and signal settings based on the circuit implementation principle of this utility model.

[0045] This invention proposes a switch control circuit and a switching power supply that can promptly activate the switching transistor at the valley bottom, resulting in good system stability. Specifically, when the actual valley bottom cannot be detected or is detected inaccurately, the switch control circuit can generate a quasi-valley bottom to replace the unobtainable actual valley bottom, thereby ensuring timely activation of the switching transistor.

[0046] Those skilled in the art should know that the logic controls such as "high level" and "low level", "set" and "reset", "AND gate" and "OR gate", "non-inverting input" and "inverting input" in the logic control involved in the specification or drawings can be interchanged or changed, and the same function or purpose as the above embodiment can be achieved by adjusting the subsequent logic control.

[0047] The description and application of this utility model herein are illustrative and not intended to limit the scope of the utility model to the above embodiments. The effects or advantages described in the specification may not be apparent in actual experimental examples due to uncertainties in specific conditions or parameters or other factors, and such descriptions are not intended to limit the scope of the utility model. Variations and modifications to the embodiments disclosed herein are possible, and various substitutions and equivalent components of the embodiments are well known to those skilled in the art. It should be clear to those skilled in the art that this utility model can be implemented in other forms, structures, arrangements, proportions, and with other components, materials, and parts without departing from the spirit or essential characteristics of the utility model. Other variations and modifications can be made to the embodiments disclosed herein without departing from the scope and spirit of the utility model.

Claims

1. A switching control circuit for controlling a switching transistor in a switching power supply, characterized in that, The switch control circuit includes: The judgment circuit has its input terminal coupled to the detection signal terminal to obtain the detection signal characterizing the drain-source voltage of the switching transistor, which is used to perform zero-crossing detection on the detection signal and generate a valley signal. A charging / discharging circuit, whose input is coupled to the output of a judgment circuit, and whose output outputs a charging / discharging voltage; and The valley conduction signal generation circuit has a first input terminal coupled to the output terminal of the charging and discharging circuit, a second input terminal coupled to a preset voltage terminal to obtain a preset voltage, and an output terminal that outputs a valley conduction signal.

2. The switch control circuit of claim 1, wherein The determination circuit includes: The zero-crossing detection circuit has its input terminal coupled to the detection signal terminal to obtain the detection signal, and its output terminal outputs the zero-crossing detection signal. A period detection circuit, whose input is coupled to the output of a zero-crossing detection circuit, outputs a period detection signal; and The valley signal generation circuit has its input terminals coupled to the output terminals of the zero-crossing detection circuit and the period detection circuit, respectively, and its output terminal outputs the valley signal.

3. The switch control circuit of claim 2, wherein The input terminal of the charging and discharging circuit is coupled to the output terminal of the zero-crossing detection circuit, and the charging and discharging circuit is used to charge and discharge according to the zero-crossing detection signal.

4. The switch control circuit of claim 1, wherein The charging and discharging circuit includes: The first switch has its control terminal coupled to the judgment circuit and its second terminal coupled to ground. A first capacitor, the first terminal of which is coupled to the first terminal of a first switch, and the second terminal of which is coupled to ground; and The first current source has its first end coupled to the first end of the first capacitor and its second end coupled to ground.

5. The switch control circuit of claim 4, wherein, The determination circuit includes: A first OR gate, wherein a first input receives a switch control signal and a second input receives a second valley signal; and The trigger circuit has a set terminal that receives the first valley signal, a reset terminal that is coupled to the output of the first OR gate, and a second output terminal that is coupled to the control terminal of the first switch.

6. The switch control circuit of claim 1, wherein The valley bottom conduction signal generation circuit includes a comparator circuit. The first input terminal of the comparator circuit is coupled to the output terminal of the charge-discharge circuit, and the second input terminal of the comparator circuit is coupled to a preset voltage terminal.

7. The switch control circuit of claim 6, wherein The valley bottom conduction signal generation circuit also includes a second OR gate, the first input of which is coupled to the output of the comparison circuit, and the second input of which is used to receive the second valley bottom signal.

8. The switch control circuit of claim 1, wherein The switch control circuit also includes a switch control signal generation circuit. The input terminal of the switch control signal generation circuit is coupled to the output terminal of the valley conduction signal generation circuit. The output terminal of the switch control signal generation circuit outputs a switch control signal to control the switch transistor.

9. The switch control circuit of claim 1, wherein, The judgment circuit includes a valley bottom signal generation circuit, which generates a valley bottom signal; the valley bottom conduction signal generation circuit includes a quasi-valley bottom signal generation circuit, which generates a quasi-valley bottom signal; the input terminal of the valley bottom conduction signal generation circuit is coupled to the output terminal of the valley bottom signal generation circuit, and the output terminal of the valley bottom conduction signal generation circuit outputs a valley bottom conduction signal.

10. A switching power supply, characterized in that, The switching power supply includes a switching control circuit as described in any one of claims 1-9, wherein the switching control circuit is used to generate a switching control signal to control the operating state of the switching transistor.

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