Wave trough opening control method, control device and switching power supply

Abstract

The invention provides a trough opening control method, a control device and a switching power supply. The control method comprises the following steps: generating a first clock signal according to a frequency conversion control signal of a switching tube; delaying the first clock signal for a first delay time to obtain a second clock signal; acquiring an overturning signal, wherein the overturning signal represents the moment when the drain-source voltage of the main switch passes through a set value in the process of changing from large to small during resonance; judging whether an overturning signal is detected in the first delay time or not: if yes, delaying the overturning signal acquired for the first time in the first delay time by a second delay time to obtain a third clock signal, controlling the switch tube to be conducted by using the third clock signal, and the arrival of the third clock signal is earlier than that of the second clock signal; and if not, using the second clock signal to control the switch tube to be switched on. According to the invention, smooth transition of opening and closing of the trough opening function during CCM / DCM mode switching can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to a valley switching control method, a control device and a switching power supply. Background Art

[0002] In a traditional flyback or boost converter circuit (the present invention also refers to "converter circuit" as "converter" or "system"), after the main switch tube is turned off, the inductor current will be demagnetized. If the inductor current has not dropped to zero before the main switch tube is turned on next time, then it works in CCM mode at this time, and the converter excitation inductance will not resonate with the output junction capacitance Coss of the main switch tube. At this time, when the main switch is turned on, it is generally hard turned on, which will cause large switching losses. If the inductor current drops to zero before the main switch tube is turned on next time, it works in DCM mode at this time, and the converter excitation inductance will resonate with the output junction capacitance Coss of the main switch tube. At this time, the voltage across the main switch tube will resonate with a certain voltage point as the center point, and its resonance period is determined by the inductance of the converter excitation inductance and the capacitance of the output junction capacitance Coss of the main switch tube.

[0003] When entering the DCM mode, the voltage across the main switch tube will resonate with a certain voltage point as the center point. At this time, if it is turned on near the bottom of the resonance, the voltage across the main switch tube is low, which can reduce the junction capacitance loss during switching. If the voltage across the main switch tube resonates to 0, turning it on at this time will achieve zero voltage turning on, without turning on loss, greatly improving the efficiency of the system. Currently, in the DCM mode, the turning on of the main switch tube is generally random, so its turning on point may be when the voltage across the main switch tube resonates to the peak. Therefore, it is necessary to propose a strategy that can accurately control the turning on of the main switch tube near the trough to improve the working efficiency of the system.

[0004] In addition, the existing commonly used valley opening method requires the judgment of the system's working mode, such as detecting that the system is working in DCM mode, and then turning on the valley opening function, which results in poor natural transition stability of valley opening during CCM / DCM switching. Summary of the invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a valley switching control method, a control device and a switching power supply, which are applicable to various converters and can achieve a smooth transition of turning on and off the valley switching function when switching between CCM / DCM modes.

[0006] As a first aspect of the present invention, the technical solution of the embodiment of the valley opening control method provided is as follows:

[0007] A valley switching control method is used to control the conduction of a switch tube in a converter, which comprises the following steps:

[0008] Generate a first clock signal according to the frequency conversion control signal of the switch tube;

[0009] Delaying the first clock signal by a first delay time to obtain a second clock signal;

[0010] Acquire a flip signal, wherein the flip signal represents the moment when the drain-source voltage of the main switch changes from large to small during resonance and passes through a set value;

[0011] Determine whether the flip signal is detected within the first delay time: if yes, delay the flip signal first obtained within the first delay time by a second delay time to obtain a third clock signal, and use the third clock signal to control the conduction of the switch tube, and the arrival of the third clock signal is earlier than the second clock signal; if no, use the second clock signal to control the conduction of the switch tube.

[0012] Preferably, the first delay time is ≤ the resonance period of the drain-source voltage of the switching tube.

[0013] Preferably, the second delay time is ≤ half of the switching tube drain-source voltage resonance period.

[0014] Preferably, the frequency conversion control signal of the switch tube is: an output voltage feedback signal of the converter; or a function signal related to the input voltage of the converter; or a function signal related to the output voltage feedback signal of the converter.

[0015] Preferably, the greater the voltage value of the frequency conversion control signal is, the higher the frequency of the first clock signal is.

[0016] Preferably, the flip signal is directly acquired by sampling the voltage across the drain and source of the switch tube and comparing it with a set threshold.

[0017] Preferably, the flip signal is indirectly acquired by sampling the main inductor current flowing through the converter and comparing it with a set threshold.

[0018] As a second aspect of the present invention, the technical solution of the embodiment of the trough opening control device provided is as follows:

[0019] A valley switching control device is used to control the conduction of a switch tube in a converter, and includes the following modules:

[0020] An internal clock generating module, configured to generate a first clock signal according to the frequency conversion control signal of the switch tube;

[0021] A delay module, configured to delay the first clock signal by a first delay time to obtain a second clock signal;

[0022] A valley detection module is configured to obtain a flip signal, wherein the flip signal represents a moment when the drain-source voltage of the main switch passes through a set value during a process of changing from large to small during resonance;

[0023] The valley switching module is configured to determine whether the flip signal is detected within the first delay time: if yes, delay the flip signal first obtained within the first delay time by a second delay time to obtain a third clock signal, and use the third clock signal to control the conduction of the switch tube, and the arrival of the third clock signal is earlier than the second clock signal; if no, use the second clock signal to control the conduction of the switch tube.

[0024] As a third aspect of the present invention, an embodiment of a valley opening control method is provided as follows:

[0025] A switching power supply includes a converter, the converter includes a switching tube, wherein: the switching power supply also includes the valley switching control device described in any one of the second aspects above, and the valley switching control device is used to control the switching tube to be turned on.

[0026] The beneficial effect of the present invention is that different clock signals are selected to control the conduction of the switch tube according to whether a flip signal is detected within the first delay time, so as to realize valley-jumping to turn on the switch tube, thereby eliminating the need to additionally judge whether the converter is working in CCM mode or DCM mode, and realizing a smooth transition of turning on and off the valley-turning function during CCM / DCM mode switching, so that the switching power supply has not only high efficiency but also high stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A circuit schematic diagram of a flyback converter;

[0028] Figure 2a for Figure 1 The working waveform of the circuit when it works in CCM mode without valley switching control;

[0029] Figure 2b for Figure 1 The working waveform of the circuit when it works in DCM mode without valley switching control;

[0030] Figure 3 A specific principle block diagram of the trough opening control device of the second embodiment of the present invention;

[0031] Figure 4 This is a specific timing diagram of the switching power supply according to the third embodiment of the present invention when implementing valley switching control. DETAILED DESCRIPTION

[0032] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application may be combined with each other.

[0033] The present invention is further described in detail below by specific embodiments in conjunction with the accompanying drawings. In the following embodiments, many details are described to enable the present application to be better understood. However, those skilled in the art can easily recognize that some of the features can be omitted in different situations, or can be replaced by other elements, materials, methods.

[0034] Further, it should be understood that the present disclosure can have various changes in different embodiments, all of which do not depart from the scope of the present disclosure, and the descriptions and drawings therein are essentially intended to illustrate these changes rather than to limit the present disclosure.

[0035] Furthermore, the serial numbers assigned to the components herein, such as "first", "second", etc., are only used to distinguish the objects described and do not have any order or technical meaning. The "connection" and "coupling" mentioned in this application, unless otherwise specified, include direct and indirect connections (couplings).

[0036] The control strategy of the present invention can effectively solve the problem of current consistency of power transmission in each loop when using staggered CCM control when there are tolerances in the converter circuit system components, thereby ensuring the safety and reliability of the entire converter circuit system.

[0037] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the present invention can be embodied in a variety of forms without departing from the spirit or nature of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

[0038] The control method, control device and switching power supply of the present invention are introduced below by taking a flyback converter as an example. It should be noted that the present invention is applicable to various converter circuit systems, and the converter circuit given in this specification is only an example and should not limit the protection scope of the present invention.

[0039] like Figure 1The figure shows a circuit schematic diagram of a flyback converter, wherein 101 is an input voltage source, 102 is a resistor of an RCD absorption circuit, 103 is a capacitor of the RCD absorption circuit, 104 is a diode of the RCD absorption circuit; 105 is a drain-source junction capacitor Coss of a main switch tube, 106 is a main switch tube SM, 107 is a control signal Q1 for controlling the on and off of the main switch tube, 108 is a primary leakage inductance Lk of a transformer TX1, 109 is a primary magnetizing inductance Lm of a transformer TX1; and the secondary circuit includes a synchronous rectifier switch tube SR, an output capacitor Co and an output load RL.

[0040] Figure 2a for Figure 1 The circuit works in CCM mode without valley switching control. Figure 2b for Figure 1 The working waveform of the circuit when it works in DCM mode without valley switching control is as follows: Figure 2a As shown, since the converter works in CCM mode, the main switch tube SM is in a hard-on state, and valley-on cannot be achieved at this time; however, Figure 2b As shown, since the converter works in DCM mode, when the excitation current drops to 0, the drain-source junction capacitance Coss of the main switch tube SM will resonate with the primary excitation inductance Lm and the primary leakage inductance Lk, and the resonant center point voltage is Vin. At this time, the main switch tube control signal Q1 controls the main switch tube to turn on. Since no specific valley turning-on control strategy is added, the turning-on time is random, and valley turning-on may occur (such as at time T4), but valley turning-on is not achieved when turning on at times T5 and T6. Therefore, the working efficiency of the converter circuit system will be greatly reduced, especially in high-frequency applications.

[0041] It should be noted that although the background technology and the above analysis are all based on the main switch tube, in some topologies, in addition to the main switch tube, there are other switch tubes, such as the clamp switch tube in the active clamp flyback circuit. The present invention can also be used to achieve valley opening control of the clamp tube. Therefore, the control method and control device of the present invention are universal and are not only applicable to the main switch tube, but also to non-main switch tubes.

[0042] First embodiment

[0043] This embodiment provides a valley switching control method for controlling the conduction of a switch tube in a converter, which includes the following steps:

[0044] Generate a first clock signal according to the frequency conversion control signal of the switch tube;

[0045] Delaying the first clock signal by a first delay time to obtain a second clock signal;

[0046] Obtaining a flip signal, the flip signal represents the moment when the drain-source voltage of the main switch changes from large to small during resonance and passes through a set value;

[0047] Determine whether a flip signal is detected within the first delay time: if yes, delay the flip signal first obtained within the first delay time by the second delay time to obtain a third clock signal, and use the third clock signal to control the switch tube to be turned on, and the arrival of the third clock signal is earlier than the second clock signal; if no, use the second clock signal to control the switch tube to be turned on.

[0048] The valley switching control method of this embodiment selects different clock signals to control the conduction of the switch tube according to whether the flip signal is detected within the first delay time, thereby realizing valley skipping to switch on the switch tube. Therefore, there is no need to additionally judge whether the converter is working in CCM mode or DCM mode, and valley switching in DCM mode and valley switching in CCM / DCM mode can be realized smoothly, so that the switching power supply has not only high efficiency but also high stability.

[0049] As a specific implementation manner, the first delay time is ≤ one switching tube drain-source voltage resonance period, which can ensure accurate detection of the flip signal while ensuring that the time interval between the flip signal and the second clock signal is as small as possible.

[0050] As a specific implementation manner, the second delay time is ≤ half of the drain-source voltage resonance period of the switch tube, which can achieve finding the valley conduction moment under the shortest time delay.

[0051] As a specific implementation, the frequency conversion control signal of the switch tube is: the output voltage feedback signal of the converter; or a function signal related to the input voltage of the converter; or a function signal related to the output voltage feedback signal of the converter.

[0052] As a specific implementation method, the larger the voltage value of the frequency conversion control signal is, the higher the frequency of the first clock signal is, so as to achieve high-efficiency operation under all working conditions.

[0053] As a specific implementation method, the flip signal is obtained by sampling the voltage across the drain and source of the switch tube and comparing it with a set threshold.

[0054] As a specific implementation manner, the flip signal is indirectly obtained by sampling the main inductor current flowing through the converter and comparing it with a set threshold.

[0055] Second embodiment

[0056] This embodiment provides a valley switching control device for controlling the conduction of a switch tube in a converter, which includes the following modules:

[0057] An internal clock generation module is configured to generate a first clock signal according to a frequency conversion control signal of the switch tube;

[0058] A delay module, configured to delay the first clock signal by a first delay time to obtain a second clock signal;

[0059] A valley detection module is configured to obtain a flip signal, where the flip signal represents a moment when the drain-source voltage of the main switch changes from large to small during resonance and passes through a set value;

[0060] The valley opening module is configured to determine whether a flip signal is detected within the first delay time: if yes, the flip signal first obtained within the first delay time is delayed by the second delay time to obtain a third clock signal, and the third clock signal is used to control the switch tube to be turned on, and the arrival of the third clock signal is earlier than the second clock signal; if no, the second clock signal is used to control the switch tube to be turned on.

[0061] Figure 3 This is a specific principle block diagram of the trough opening control device of the second embodiment of the present invention, and the specific working process is as follows:

[0062] Step 1: Generate a first clock signal 301 from a frequency conversion control signal, wherein a common frequency conversion control signal is a voltage loop feedback signal (i.e., an output voltage feedback signal), or a function signal defined according to an input voltage, an output voltage feedback signal, etc. Generally, the greater the voltage of the frequency conversion control signal, the higher the frequency of the first clock signal;

[0063] Step 2: Delay the first clock signal 301 by a first delay time 302 to obtain a second clock signal 303, wherein the first delay time is set within a resonant cycle, such as in a flyback converter. If it is a boost circuit,

[0064] Step 3: Input the first clock signal 301 to the S terminal of the trigger, and input and output the second clock signal 303 to the R terminal of the trigger, so the Q terminal output 304 of the trigger is set high when the first clock signal arrives, and is set low when the second clock signal arrives, so the time when the Q terminal output 304 of the trigger is high level is the first delay time;

[0065] Step 4: Connect the trigger Q-end output 304 and the flip signal 305 to the two ends of an AND gate respectively, where the flip signal 305 is a detection signal that can characterize the valley. Generally, for example, in a boost circuit and a flyback circuit, the voltage V-coss at both ends of the main switch tube in the DCM mode is equal to the resonant center point voltage Vin, so the flip signal 305 can be obtained by comparing the size of V-coss and the input voltage Vin.

[0066] Step 5: After the signal output by the AND gate passes through the second delay time 306, a third clock signal 307 is obtained, the third clock signal is input to one end of the OR gate, and the second clock signal is input to the other end of the OR gate, and the output of the OR gate is used as a triggering turn-on signal 308 that finally triggers the main switch to turn on. The second delay time 306 needs to be less than half the resonant cycle time, and the specific time can be adjusted according to the actual application situation.

[0067] The smooth transition of the valley switching function when switching between CCM and DCM modes is as follows: when in CCM mode, since there is no first flip signal within the first delay time, the AND gate output is always at a low level, so the trigger switching signal is the second clock signal; when entering DCM mode, if the first flip signal is detected within the first delay time, the first flip signal will be before the second clock. Since the moment when the V-coss resonant voltage is equal to Vin is not the valley moment, the first flip signal needs to be delayed by the second delay time as the final trigger switching signal to achieve valley switching.

[0068] Third embodiment

[0069] This embodiment provides a switching power supply, including a converter, the converter including a switching tube, wherein: the switching power supply also includes any valley switching control device in the second aspect above, the valley switching control device is used to control the switching tube to be turned on.

[0070] Figure 4 FIG. 1 is a specific timing diagram of the switching power supply of the third embodiment of the present invention when implementing valley switching control. Figure 4 As shown, the time length between T1→T2 is the first delay time, the first clock signal obtains the second clock signal after the first delay time, at T3, the Q1 signal controls the main switch tube to be disconnected, at this time the drain-source voltage V-coss of the main switch tube will rise, at T4, the magnetizing inductance Lm is demagnetized to 0, at T5, the drain-source voltage V-coss of the main switch tube passes through the center value during the change from large to small during resonance, which is the first flip signal, because it is not within the first delay range at this time, so the AND gate output is a low level, and the first delay time begins at T6, and the second flip signal appears at T7. At this time, the second flip signal is subjected to the second delay time, where the second delay time is one quarter of the resonance cycle corresponding to the valley moment, and T8 is the third clock signal obtained by the second flip signal after the second delay time. Since the third clock signal will arrive earlier than the second clock signal, the third clock signal can be used as the opening trigger signal of the main switch tube to achieve valley opening.

[0071] Furthermore, when the system frequency drops again, flip signals appear at T11, T12, and T13. However, since they are not within the first delay time, these flip signals are shielded. The first delay time begins at T14, a flip signal is detected at T15, and the third clock signal is obtained by passing the flip signal through the second delay time at T16. The valley opening can be achieved by triggering the opening at T16, and the valley jumping control strategy is implemented at the same time.

[0072] Furthermore, when the system frequency rises and enters the CCM mode, during the time T17→T18 or T20→T21, since the flip signal cannot be detected within the first delay time, the second clock signal is used as the trigger start signal to achieve a smooth transition of the valley start function on and off when switching between CCM / DCM modes.

[0073] Based on the control strategy of the present invention, the resonant valley switching control of the switch tubes in multiple circuits can be realized, and the smooth transition of the valley switching function on and off during CCM / DCM mode switching can be realized.

[0074] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the present invention can be embodied in a variety of forms without departing from the spirit or nature of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A valley switching control method for controlling the conduction of a switch tube in a converter, characterized in that: The steps include: Generate a first clock signal according to the frequency conversion control signal of the switch tube; Delaying the first clock signal by a first delay time to obtain a second clock signal; Acquire a flip signal, wherein the flip signal represents the moment when the drain-source voltage of the main switch changes from large to small during resonance and passes through a set value; Determine whether the flip signal is detected within the first delay time: if yes, delay the flip signal first obtained within the first delay time by a second delay time to obtain a third clock signal, and use the third clock signal to control the conduction of the switch tube, and the arrival of the third clock signal is earlier than the second clock signal; if no, use the second clock signal to control the conduction of the switch tube.

2. The valley opening control method according to claim 1, characterized in that: The first delay time is ≤ the drain-source voltage resonance period of the switch tube.

3. The valley opening control method according to claim 1, characterized in that: The second delay time is ≤ half of the switching tube drain-source voltage resonance period.

4. The valley opening control method according to claim 1, characterized in that: The frequency conversion control signal of the switch tube is: the output voltage feedback signal of the converter; or a function signal related to the input voltage of the converter; or a function signal related to the output voltage feedback signal of the converter.

5. The valley opening control method according to claim 1, characterized in that: The larger the voltage value of the frequency conversion control signal is, the higher the frequency of the first clock signal is.

6. The valley opening control method according to claim 1, characterized in that: The flip signal is directly obtained by sampling the voltage across the drain and source of the switch tube and comparing it with a set threshold.

7. The valley opening control method according to claim 1, characterized in that: The flip signal is indirectly obtained by sampling the main inductor current flowing through the converter and comparing it with a set threshold.

8. A valley switching control device for controlling the conduction of a switch tube in a converter, characterized in that: Includes the following modules: An internal clock generating module, configured to generate a first clock signal according to the frequency conversion control signal of the switch tube; A delay module, configured to delay the first clock signal by a first delay time to obtain a second clock signal; A valley detection module is configured to obtain a flip signal, wherein the flip signal represents a moment when the drain-source voltage of the main switch passes through a set value during a process of changing from large to small during resonance; The valley switching module is configured to determine whether the flip signal is detected within the first delay time: if yes, delay the flip signal first obtained within the first delay time by a second delay time to obtain a third clock signal, and use the third clock signal to control the conduction of the switch tube, and the arrival of the third clock signal is earlier than the second clock signal; if no, use the second clock signal to control the conduction of the switch tube.

9. A switching power supply, comprising a converter, wherein the converter comprises a switch tube, characterized in that: The switching power supply further comprises the valley switching control device as claimed in claim 8, and the valley switching control device is used to control the conduction of the switching tube.

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