Self-adaptive zero current detection circuit, switching power supply and method

Abstract

The invention relates to a self-adaptive zero current detection circuit, a switching power supply and a method, the detection circuit comprises a dead time detection module, a self-adaptive threshold generation module and a comparator module, the dead time detection module is used for detecting the sequence of a voltage zero-crossing time point of a switching node and defined dead time, and the self-adaptive threshold generation module is used for generating a self-adaptive threshold value; outputting a detection signal; the adaptive threshold is used for generating a corresponding turn-off threshold voltage according to the detection signal; and the comparator module is used for receiving the voltage of the switch node and the turn-off threshold voltage, comparing the voltage with the turn-off threshold voltage, and outputting a down tube turn-off signal after delaying for a preset time length when the voltage of the switch node is higher than the turn-off threshold voltage. By accurately tracking a real zero current point and designing a dynamic turn-off threshold voltage, the lower tube is turned off when infinitely approaching the real zero current, so that the follow current or negative current conduction loss of the body diode is reduced to the maximum extent, and the system efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of switching power supply technology, and relates to a current zero-crossing detection and lower transistor turn-off control technology for a buck converter, specifically an adaptive zero current detection circuit, a switching power supply, and a method. Background Technology

[0002] A BUCK converter converts the input voltage to a lower output voltage by controlling the alternating conduction of two switching transistors, the upper and lower transistors. When the upper transistor is turned off, the lower transistor provides a freewheeling path for the inductor current. The lower transistor must be turned off in time when the inductor current approaches zero. If the lower transistor is not turned off in time, it will cause reverse current in the output, resulting in additional losses and reduced system efficiency.

[0003] Figure 1 This is a circuit diagram for zero-current detection using the fixed threshold voltage comparison method, which is commonly used in existing technologies. For example... Figure 1 As shown, the fixed threshold comparison method works by detecting the voltage Vsw of the switching node SW and comparing it with a fixed negative threshold voltage Vth_fixed. When Vsw rises and crosses Vth_fixed, the comparator output flips, generating a signal to turn off the lower transistor. This method has a significant drawback: 1) Reliability at the expense of efficiency: To prevent current backflow under worst-case conditions such as component parameter distribution and delay, Vth_fixed must be set conservatively enough. This results in the lower transistor being turned off before the actual current IL reaches zero, with the remaining current IL = The current is forced to flow through the body diode of the lower tube, which is a freewheeling current. This is the on-resistance of the lower diode. The large forward voltage drop of the body diode generates additional conduction losses and reverse recovery losses, severely limiting the improvement of system efficiency under light load.

[0004] 2) Strong system dependence: The inductor current slope (di / dt=-Vout / L) is determined by system parameters (input voltage, output voltage, inductance value). Figure 2 This is a schematic diagram illustrating the generation of negative current using a fixed threshold voltage comparison method at different current slopes. For example... Figure 2 As shown, fixed threshold d. Under different inductor current slopes, the actual current value corresponding to the turn-off point varies greatly. Under a steep current drop, the lower transistor will be turned off too late, resulting in a larger negative current and more severe efficiency loss.

[0005] 3) Poor performance consistency: The turn-off current IL is subject to a fixed threshold. d and the on-resistance of the lower transistor Process deviations can lead to inconsistent system efficiency across different chips or at different temperatures, making it difficult to guarantee mass production yield and performance limits.

[0006] It should be noted that the information disclosed in the background section above is only used to enhance the understanding of the background of this disclosure, and therefore may include information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention discloses an adaptive zero-current detection circuit, a switching power supply, and a method.

[0008] The technical solutions adopted in the embodiments of the present invention are as follows: An adaptive zero-current detection circuit includes: Dead time detection module, which is used to detect the order of the voltage zero-crossing time of the switching node and the defined dead time, and outputs a detection signal; An adaptive threshold generation module is connected to the output of the dead time detection module and is used to generate a corresponding turn-off threshold voltage based on the detection signal. The comparator module has a first input terminal and a second input terminal. The first input terminal is connected to the switching node, and the second input terminal is connected to the output terminal of the adaptive threshold generation module. It is used to receive the voltage of the switching node and the turn-off threshold voltage and compare them. When the voltage of the switching node is higher than the turn-off threshold voltage, it outputs the lower transistor turn-off signal after a preset delay.

[0009] A further technical solution is that the dead time detection circuit includes: The first comparator receives the voltage of the switching node at its non-inverting input terminal and receives 0V voltage at its inverting input terminal, and outputs a zero-crossing signal of the switching node voltage. A dead-zone pulse generator is provided, wherein the input terminal of the dead-zone pulse generator is connected to the output terminal of the comparator module, and the dead-zone pulse generator generates and outputs a dead-zone pulse signal based on the lower transistor turn-off signal output by the comparator module. The D flip-flop has its CLK input connected to the output of a first comparator and its D input connected to the output of a dead-time pulse generator. It is used to trigger when the voltage of the switching node crosses zero, and its Q output is a detection signal determined based on the trigger time and the dead-time pulse signal.

[0010] A further technical solution is that the adaptive threshold generation module includes: An up-and-down counter, the input of which is connected to the Q terminal of a D flip-flop, is used to count pulses of the detection signal and output the pulse count result; A digital-to-analog converter, the input of which is connected to the output of an upper and lower counter, is used to generate a turn-off threshold voltage based on the pulse counting result.

[0011] A switching power supply includes an upper transistor, a lower transistor, an upper transistor drive control module, a lower transistor drive control module, and an inductor. A switching node is provided between the upper transistor and the lower transistor. The switching power supply includes the aforementioned adaptive zero-current detection circuit. The output terminal of the comparator module is connected to the input terminal of the lower transistor drive control module and is used to send a lower transistor turn-off signal to the lower transistor drive control module.

[0012] An adaptive zero-current detection method is applied to the switching power supply, the method comprising the following steps: During the inductor current decrease phase, the sequential changes of the voltage zero-crossing time and dead time of the switching node are detected to obtain a detection signal representing the sequential changes in time. An adaptive shutdown threshold is generated based on the detected signal. : When the voltage zero-crossing point of the switching node occurs within the dead time, Get bigger; When the voltage zero-crossing point of the switching node occurs outside the dead time, Get smaller; Real-time comparison of voltage at switching nodes With adaptive shutdown threshold when After a preset delay, the lower tube is turned off.

[0013] A further technical solution involves determining the real-time voltage of the switching node within the comparator module. Dynamic threshold generated by the adaptive threshold generation module The size of the comparator module and its output are simultaneously input to the lower transistor drive control module and the dead-time pulse generator. when At this time, the lower tube drive control module controls the lower tube to maintain its current conducting state; when When the down-tube drive control module issues a down-tube turn-off command, the down-tube turn-off command takes effect after a dead-time pulse signal duration.

[0014] A further technical solution is that the dead-zone pulse signal is a custom pulse signal with a fixed width that is synchronized with the lower tube turn-off signal.

[0015] A further technical solution is that the D trigger performs the following judgment process: If the output signal of the first comparator falls within the dead-time pulse signal, the dead-time pulse signal is still at a high level, the D terminal of the D flip-flop samples D=1, and the Q terminal outputs a high level. If the output signal of the first comparator falls outside the dead-time pulse signal, the dead-time pulse signal becomes low, the D terminal of the D flip-flop samples D=0, and the Q terminal outputs a low level.

[0016] The beneficial effects of the embodiments of the present invention are as follows: This invention proposes an adaptive zero-current detection circuit and method. By adding a dead-time detection module, an adaptive threshold generation module, and a comparator module, the turn-off threshold is adaptively adjusted according to the zero-crossing time of the switching node. This reduces the dependence on a fixed threshold, improves the accuracy of current zero-crossing judgment, and ensures that the lower transistor is turned off when the inductor current is close to zero under different system applications. It reduces the conduction time of the body diode, preventing the lower transistor from turning off too early, and reduces the conduction time of the negative current, preventing the lower transistor from turning off too late. This effectively avoids premature or late turn-off caused by a fixed threshold setting, significantly reduces reverse current loss, improves system efficiency and product consistency, and has better robustness to process differences and system parameter changes. It can solve the problem of inaccurate turn-off timing and low system efficiency caused by using a fixed threshold for zero-current detection in the prior art. Attached Figure Description

[0017] Figure 1 This is a circuit diagram for zero-current detection using the fixed threshold voltage comparison method, which is commonly used in existing technologies.

[0018] Figure 2 This is a schematic diagram illustrating the generation of negative current using a fixed threshold voltage comparison method at different current slopes.

[0019] Figure 3 This is a circuit block diagram of the adaptive zero-current detection circuit proposed in Embodiment 1 of the present invention.

[0020] Figure 4 This is a circuit diagram of an example of the adaptive zero-current detection circuit proposed in Embodiment 1 of the present invention.

[0021] Figure 5 The waveform diagram is obtained using an adaptive zero-current detection method proposed in Embodiment 3 of this invention. Detailed Implementation

[0022] The specific embodiments of the present invention will now be described with reference to the accompanying drawings.

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the device proposed by this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are in a very simplified form and use non-precise proportions, only for the purpose of conveniently and clearly illustrating the embodiments of this invention. Please refer to the accompanying drawings to make the objectives, features, and advantages of this invention more apparent and understandable. It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the implementation conditions of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0024] Example 1 Figure 3 This is a circuit block diagram of an adaptive zero-current detection circuit proposed in an embodiment of the present invention. Figure 3 As shown, the adaptive zero-current detection circuit in this embodiment includes: a dead-time detection module, an adaptive threshold generation module, and a comparator module. The dead-time detection module is used to detect the order of the zero-crossing time of the voltage at the switching node SW with the defined dead time.

[0025] The adaptive threshold generation module is connected to the dead-time detection module and is used to dynamically generate an adaptive turn-off threshold voltage Vth_adaptive based on the detection time sequence. The absolute value of this adaptive threshold Vth_adaptive is related to the zero-crossing time of the voltage at the switching node SW and the defined dead time sequence.

[0026] The comparator module has its first input connected to the switching node SW and its second input receiving the turn-off threshold voltage Vth_adaptive of the adaptive switch. It is used to compare the switching node voltage Vsw with Vth_adaptive, and outputs the lower transistor turn-off signal after a time delay when Vsw is higher than Vth_adaptive.

[0027] Furthermore, Figure 4 This is a circuit diagram of an example of the adaptive zero-current detection circuit proposed in Embodiment 1 of the present invention. Figure 4 As shown, the dead time detection module includes: The first comparator receives the voltage of the switching node at its non-inverting input and receives 0V voltage at its inverting input, and outputs a zero-crossing signal of the switching node voltage. The first comparator is a zero comparator. By comparing the real-time voltage of the switching node SW with 0V, the instant when the inductor current truly crosses zero can be accurately detected.

[0028] The dead-zone pulse generator has its input connected to the output of the comparator module. The dead-zone pulse generator generates and outputs a dead-zone pulse signal based on the lower transistor turn-off signal output by the comparator module.

[0029] The D flip-flop has its CLK input connected to the output of the first comparator and its D input connected to the output of the dead-time pulse generator. It is used to trigger when the voltage of the switching node crosses zero. The Q output is a detection signal determined by the trigger time and the dead-time pulse signal.

[0030] Furthermore, such as Figure 4 As shown, the adaptive threshold generation module includes: The upper and lower counters are connected to the Q terminal of a D flip-flop and are used to count pulses of the detection signal and output the pulse count result. The digital-to-analog converter has its input connected to the output of the upper and lower counters, and is used to generate the turn-off threshold voltage based on the pulse counting results.

[0031] The adaptive zero-current detection circuit proposed in this embodiment accurately tracks the true zero-current point by designing a dead-time detection module, an adaptive threshold generation module, and a comparator module. It compares the true zero-current point with the time sequence of the dead-time pulse signal generated based on the actual lower diode drive signal. Based on the comparison result, a dynamic turn-off threshold voltage is generated, causing the lower diode to be turned off when it is infinitely close to the true zero current. This minimizes the losses caused by the freewheeling or negative current conduction of the body diode, improves system efficiency, and can adapt to different operating conditions. It fundamentally solves the problems caused by the use of fixed threshold control for lower diode turn-off in existing technologies.

[0032] Example 2 This embodiment proposes a switching power supply, including an upper transistor, a lower transistor, an upper transistor drive control module, a lower transistor drive control module, and an inductor. A switching node is provided between the upper transistor and the lower transistor. The switching power supply includes the adaptive zero-current detection circuit proposed in Embodiment 1. The output terminal of the comparator module is connected to the input terminal of the lower transistor drive control module and is used to send a lower transistor turn-off signal to the lower transistor drive control module.

[0033] Example 3 This third embodiment proposes an adaptive zero-current detection method, applied to the switching power supply described in embodiment two. The method includes the following steps: Step 1: During the inductor current decrease phase, detect the sequential changes in the zero-crossing time of the voltage at the switching node SW (Vsw>0V time point) and the time of the tdead pulse.

[0034] Step 2: Based on the detected temporal changes, generate an adaptive shutdown threshold Vth_adaptive: When the zero-crossing point of the SW voltage occurs within the tdead pulse time... Get bigger; When the zero-crossing point of the SW voltage occurs outside the tdead pulse time... It gets smaller.

[0035] Step 3: Real-time comparison of the switching node voltage Vsw with the adaptive threshold. ; Step 4, when Vsw> After a time delay of tdead pulse, the output signal is used to turn off the lower transistor.

[0036] Figure 5 The waveform diagram is obtained using the adaptive zero-current detection method proposed in Embodiment 3 of this invention. (Comparison) Figure 5 and Figure 2 As can be seen from the waveform diagram, the method in this embodiment designs the end point of the generated dead-time pulse signal to coincide with the zero-crossing time point of the switching node SW. Then, the turn-off threshold is designed to adaptively adjust with the zero-crossing time point of the switching node, which can reduce the dependence on a fixed threshold. After a delay of one dead-time pulse signal, the lower transistor turn-on control signal is output to ensure that the lower transistor is turned off when the inductor current is close to zero under different system applications, reducing the conduction time of the body diode and preventing the lower transistor from turning off too early, reducing the conduction time of the negative current and preventing the lower transistor from turning off too late.

[0037] The adaptive zero-current detection method in this embodiment aims for the ideal state where the zero-crossing time of the switching node SW coincides with the end point of the dead-zone pulse signal.

[0038] To achieve this ideal state, this embodiment determines the real-time voltage of the switching node SW in the comparator module. Dynamic threshold generated by the adaptive threshold generation module The magnitude of the value, the output of the comparator module, is simultaneously input to the lower transistor drive control module and the dead-time pulse generator. When the lower tube drive control module controls the lower tube to maintain its current conducting state; when When the down-tube drive control module issues a down-tube turn-off command, the command takes effect after a dead time tdead.

[0039] Furthermore, the dead-time pulse signal generated by the dead-time pulse generator is a pulse signal with a fixed width that is synchronized with the turn-off signal of the lower transistor, providing a stable judgment window for the subsequent D flip-flop. That is, the dead-time pulse signal provides a stable judgment window for the D flip-flop, and this judgment window serves as a unified benchmark for judging whether the turn-off timing is "early" or "late," enabling the adaptive logic of this invention to operate stably.

[0040] The judgment process for D trigger execution is as follows: Case A: If the output of the first comparator is b'1, which falls within the dead-zone pulse signal tdead pulse, the dead-zone pulse signal tdead pulse is still at a high level.

[0041] When the D input of the D flip-flop samples to D=1, the Q input outputs a high level ("1"). The high level output of the D flip-flop at this time indicates that the "zero-crossing event" of the switching node SW has occurred within the "dead zone".

[0042] Case B: If the output of the first comparator is b'1, which falls outside the dead-zone pulse signal tdead pulse, then the dead-zone pulse signal tdead pulse becomes low.

[0043] When the D input of the D flip-flop samples to D=0, the Q input outputs a low level ("0"). The low level output of the D flip-flop at this time indicates that the "zero-crossing event" of the switching node SW occurs after the "dead zone".

[0044] In this embodiment, the output of a high level "1" or a low level "0" at the Q terminal of the D flip-flop directly encodes the sequence of the two time points: "voltage zero crossing point" and "dead time end point".

[0045] It should be noted that in this embodiment, the dead-time pulse signal also implements the function of turn-off delay. Regardless of how the dynamic threshold output by the adaptive threshold generation module changes, the comparator module flips (i.e., determines...) The delay time from the final shut-off of the lower tube is fixed (i.e., tdead). This method can avoid the risk of control loop instability caused by variable delay and ensure the determinism of the system.

[0046] In this embodiment of the invention, by designing a dead-time pulse signal, an ideal window is defined into which the "zero-current point" should eventually fall. At the same time, the turn-off action of the lower transistor is delayed by one dead-time pulse, tdead, indicating that the system attempts to issue the instruction by advancing the turn-off time by tdead.

[0047] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0048] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. An adaptive zero-current detection circuit, applied to a switching power supply including an upper transistor and a lower transistor, wherein a switching node is provided between the upper transistor and the lower transistor, characterized in that, The circuit includes: Dead time detection module, which is used to detect the order of the voltage zero-crossing time of the switching node and the defined dead time, and outputs a detection signal; An adaptive threshold generation module is connected to the output of the dead time detection module and is used to generate a corresponding turn-off threshold voltage based on the detection signal. The comparator module has a first input terminal and a second input terminal. The first input terminal is connected to the switching node, and the second input terminal is connected to the output terminal of the adaptive threshold generation module. It is used to receive the voltage of the switching node and the turn-off threshold voltage and compare them. When the voltage of the switching node is higher than the turn-off threshold voltage, it outputs the lower transistor turn-off signal after a preset delay.

2. The adaptive zero-current detection circuit as described in claim 1, characterized in that, The dead time detection circuit includes: The first comparator receives the voltage of the switching node at its non-inverting input terminal and receives a 0V voltage at its inverting input terminal, and outputs a zero-crossing signal of the switching node voltage. A dead-zone pulse generator is provided, wherein the input terminal of the dead-zone pulse generator is connected to the output terminal of the comparator module, and the dead-zone pulse generator generates and outputs a dead-zone pulse signal based on the lower transistor turn-off signal output by the comparator module. The D flip-flop has its CLK input connected to the output of a first comparator and its D input connected to the output of a dead-time pulse generator. It is used to trigger when the voltage of the switching node crosses zero, and its Q output is a detection signal determined based on the trigger time and the dead-time pulse signal.

3. The adaptive zero-current detection circuit as described in claim 2, characterized in that, The adaptive threshold generation module includes: An up-and-down counter, the input of which is connected to the Q terminal of a D flip-flop, is used to count pulses of the detection signal and output the pulse count result; A digital-to-analog converter, the input of which is connected to the output of an upper and lower counter, is used to generate a turn-off threshold voltage based on the pulse counting result.

4. A switching power supply, comprising an upper transistor, a lower transistor, an upper transistor drive control module, a lower transistor drive control module, and an inductor, wherein a switching node is provided between the upper transistor and the lower transistor, characterized in that: The switching power supply includes an adaptive zero-current detection circuit as described in any one of claims 1-3, wherein the output terminal of the comparator module is connected to the input terminal of the lower MOSFET drive control module, and is used to send a lower MOSFET turn-off signal to the lower MOSFET drive control module.

5. An adaptive zero-current detection method, applied to the switching power supply of claim 4, characterized in that, The method includes the following steps: During the inductor current decrease phase, the sequential changes of the voltage zero-crossing time and dead time of the switching node are detected to obtain a detection signal representing the sequential changes in time. An adaptive shutdown threshold is generated based on the detected signal. : When the voltage zero-crossing point of the switching node occurs within the dead time, Get bigger; When the voltage zero-crossing point of the switching node occurs outside the dead time, Get smaller; Real-time comparison of voltage at switching nodes With adaptive shutdown threshold ; when After a preset delay, the lower tube is turned off.

6. The adaptive zero-current detection method as described in claim 5, characterized in that: In the comparator module, the real-time voltage of the switching node is determined. Dynamic threshold generated by the adaptive threshold generation module The size of the comparator module and its output are simultaneously input to the lower transistor drive control module and the dead-time pulse generator. when At this time, the lower tube drive control module controls the lower tube to maintain its current conducting state; when When the down-tube drive control module issues a down-tube turn-off command, the down-tube turn-off command takes effect after a dead-time pulse signal duration.

7. The adaptive zero-current detection method as described in claim 6, characterized in that: The dead-zone pulse signal is a custom-defined pulse signal with a fixed width that is synchronized with the lower tube turn-off signal.

8. The adaptive zero-current detection method as described in claim 7, characterized in that, The D trigger performs the following judgment process: If the output signal of the first comparator falls within the dead-time pulse signal, the dead-time pulse signal is still at a high level, the D terminal of the D flip-flop samples D=1, and the Q terminal outputs a high level. If the output signal of the first comparator falls outside the dead-time pulse signal, the dead-time pulse signal becomes low, the D terminal of the D flip-flop samples D=0, and the Q terminal outputs a low level.

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