Switching converter and light load mode detection circuit and method thereof

Abstract

The present application discloses a switching converter and its light load mode detection circuit and method. The light load mode detection circuit includes a threshold voltage generation module, a comparator, a duty cycle detection module and an output module. The threshold voltage generation module is used to generate a threshold voltage according to the input voltage, the comparator is used to compare the output voltage with the threshold voltage to generate a comparison signal, the duty cycle detection module is used to generate a duty cycle detection signal according to the switch control signal of the power tube, and the output module is used to generate a light load indication signal according to the comparison signal, the duty cycle detection signal and the overvoltage protection signal to control the switching converter to switch between light load mode and normal mode, which not only ensures stable mode switching, but also has extremely low static power consumption, which is conducive to improving the efficiency of the switching converter in the light load state and realizing an ultra-low power switching converter.

Description

Technical Field

[0001] The present invention relates to the field of electronic technology, and more particularly to a switching converter and a light-load mode detection circuit and method thereof. Background Art

[0002] With the growing demand for power electronics and the advancement of semiconductor technology, power management chips are becoming increasingly popular in portable computers, mobile phones, personal digital assistants, and other portable and non-portable electronic devices. Switching converters in switching power supplies are widely used due to their high conversion efficiency, high output current, low quiescent current, and wide output load range. In portable devices, the efficiency of the switching converter under light loads largely determines the standby time of the portable product system. Therefore, in recent years, the design of low-power, high-efficiency switching converters has become a research hotspot for portable devices.

[0003] The power consumption of a switching converter generally consists of three parts: conduction loss, switching loss, and static loss of the chip's internal analog circuits. Conduction loss primarily refers to the energy consumed by current flowing through the on-resistance of the power transistor, increasing with the chip's load current. Switching loss is the dynamic loss generated by the charging and discharging of the power transistor's gate capacitance during each operating cycle. Static loss is the consumption of the chip's internal analog circuits during operation. Both switching and static losses are independent of the chip's load current. Therefore, conduction loss is the primary loss when the chip is heavily loaded, while switching and static losses constitute the primary losses of the converter when lightly loaded. Since the efficiency of a portable device in standby mode primarily depends on the power consumption of the switching converter under light load, improving the efficiency of the switching converter under light load can effectively extend the battery life of portable devices.

[0004] like Figure 1 FIG. 1 shows a circuit diagram of a switching converter according to the prior art. Figure 1 As shown, switching converter 100 includes a main circuit and a control circuit integrated into the same integrated circuit chip. The control circuit includes an error amplifier EA, a logic and drive circuit 110, a current limiting protection circuit 120, a current backfeed protection circuit 130, and a light-load mode detection circuit 140. The main circuit includes discrete components such as power transistor MD1, rectifier transistor MD2, inductor Lx, output capacitor Cout, and resistors R1 and R2.

[0005] like Figure 1As shown, the light-load mode detection circuit 140 determines whether the load terminal of the switching converter 100 is in a light-load state by detecting the load current of the converter. When the switching converter 100 is operating in a light-load state, the light-load mode detection circuit 140 shuts down most of the operating circuits in the switching converter 100, such as the current limiting protection circuit 120 and the current backfeed protection circuit 130, while both the switching transistors MD1 and MD2 are turned off. This reduces the quiescent current of the entire converter, ensuring that the chip can operate normally and maintain low power consumption under light-load conditions. However, the switching converter 100 of the prior art has a disadvantage: when the input voltage Vin and the output voltage Vout are very close, the switching transistor MD1 will be in a constant-on state. At this time, it becomes very difficult to monitor the load current and ensure a sufficiently low quiescent current, making it impossible to achieve effective ultra-low power consumption. Summary of the Invention

[0006] In view of the above problems, an object of the present invention is to provide a switching converter and a light-load mode and method thereof, which can achieve stable mode switching when the input voltage and the output voltage are very close.

[0007] According to a first aspect of an embodiment of the present invention, a light load mode detection circuit of a switching converter is provided, wherein the switching converter includes a power tube and a rectifier tube connected in series, wherein the power tube and the rectifier tube are used to control the transmission of electric energy from an input end to an output end so as to convert an input voltage into an output voltage, wherein the light load mode detection circuit includes: a threshold voltage generation module for generating a threshold voltage based on the input voltage; a comparator for comparing the output voltage with the threshold voltage to generate a comparison signal; a duty cycle detection module for generating a duty cycle detection signal based on a switching control signal of the power tube; and an output module for generating a light load indication signal based on the comparison signal, the duty cycle detection signal and an overvoltage protection signal to control the switching converter to switch between a light load mode and a normal mode.

[0008] Optionally, when the switching converter operates in normal mode, the output module is configured to: when the duty cycle detection signal is valid, when the comparison signal indicates that the output voltage is greater than a first threshold voltage, generate a valid light load indication signal to control the switching converter to switch from normal mode to light load mode; and when the switching converter operates in light load mode, the output module is configured to: when the comparison signal indicates that the output voltage is less than a second threshold voltage or the overvoltage protection signal is valid, generate an invalid light load indication signal to control the switching converter to switch from light load mode to normal mode.

[0009] Optionally, the second threshold voltage is lower than the first threshold voltage.

[0010] Optionally, the output module includes: an AND gate circuit, a first input terminal receiving the comparison signal, a second input terminal receiving the inverted signal of the overvoltage protection signal, a third input terminal receiving the duty cycle detection signal, and an output terminal outputting the light load indication signal.

[0011] Optionally, the duty cycle detection module is configured to output a valid duty cycle detection signal when the high level time of the switch control signal of the power tube is greater than a preset time.

[0012] Optionally, the threshold voltage generating circuit includes: a first resistor, a second resistor and a current source connected in series between the input voltage and ground, the intermediate node between the first resistor and the current source being used to provide the threshold voltage; and a first transistor, the first end of the first transistor being connected to the first end of the first resistor, the second end of the first transistor being connected to the second end of the first resistor, and the control end of the first transistor receiving the comparison signal.

[0013] Optionally, the first transistor is a P-type MOSFET.

[0014] According to a second aspect of an embodiment of the present invention, a switching converter is provided, comprising: a main circuit, comprising a power tube and a rectifier tube connected in series, the power tube and the rectifier tube being used to control the transmission of electrical energy from an input end to an output end so as to convert an input voltage into an output voltage; and the above-mentioned light load mode detection circuit.

[0015] According to a third aspect of an embodiment of the present invention, a light load mode detection method for a switching converter is provided, wherein the switching converter includes a power tube and a rectifier tube connected in series, and the power tube and the rectifier tube are used to control the transmission of electric energy from an input end to an output end to convert an input voltage into an output voltage, wherein the light load mode detection method: generates a threshold voltage based on the input voltage; compares the output voltage with the threshold voltage to generate a comparison signal; generates a duty cycle detection signal based on a switching control signal of the power tube; and generates a light load indication signal based on the comparison signal, the duty cycle detection signal and the overvoltage protection signal to control the switching converter to switch between light load mode and normal mode.

[0016] Optionally, generating a light load indication signal based on the comparison signal, the duty cycle detection signal and the overvoltage protection signal to control the switching converter to switch between the light load mode and the normal mode includes: when the switching converter operates in the normal mode, generating a valid light load indication signal when the duty cycle detection signal is valid and the comparison signal indicates that the output voltage is greater than a first threshold voltage, to control the switching converter to switch from the normal mode to the light load mode; and when the switching converter operates in the light load mode, generating an invalid light load indication signal when the comparison signal indicates that the output voltage is less than a second threshold voltage or the overvoltage protection signal is valid, to control the switching converter to switch from the light load mode to the normal mode.

[0017] Optionally, generating a duty cycle detection signal according to the switch control signal of the power tube includes: outputting a valid duty cycle detection signal when the high level time of the switch control signal of the power tube is greater than a preset time.

[0018] The switching converter and the light-load mode detection circuit and method thereof according to the embodiments of the present invention have the following beneficial effects.

[0019] The light load mode detection circuit includes a threshold voltage generation module, a comparator, a duty cycle detection module, and an output module. The threshold voltage generation module is used to generate a threshold voltage according to the input voltage, the comparator is used to compare the output voltage with the threshold voltage to generate a comparison signal, the duty cycle detection module is used to generate a duty cycle detection signal according to the switch control signal of the power tube, and the output module is used to generate a light load indication signal according to the comparison signal, the duty cycle detection signal, and the overvoltage protection signal to control the switching of the switching converter between the light load mode and the normal mode. The light load mode detection circuit of the embodiment of the present invention only needs to keep the comparator and the overvoltage protection module working in the light load mode to monitor when to exit the light load mode, which can ensure that the quiescent current is sufficiently low in the light load mode, facilitate the realization of extremely low quiescent power consumption, and is beneficial to improving the efficiency of the switching converter in the light load state, thereby realizing an ultra-low power consumption switching converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0021] Figure 1 A circuit diagram of a switching converter according to the prior art is shown;

[0022] Figure 2 A circuit diagram of a switching converter according to an embodiment of the present invention is shown;

[0023] Figure 3 Show Figure 2 A circuit diagram of a light load mode detection circuit in FIG.

[0024] Figure 4a and Figure 4b Schematic waveform diagrams of the switching converter under light load and heavy load according to the embodiment of the present invention are shown respectively. DETAILED DESCRIPTION

[0025] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, identical elements are represented by identical or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0026] It should be understood that in the following description, a "circuit" may include a single or multiple combined hardware circuits, programmable circuits, state machine circuits, and / or elements capable of storing instructions executed by a programmable circuit. When an element or circuit is said to be "connected to" another element or an element / circuit is said to be "connected" between two nodes, it may be directly coupled or connected to the other element or there may be an intermediate element, and the connection between the elements may be physical, logical, or a combination thereof. Conversely, when an element is said to be "directly coupled to" or "directly connected to" another element, it means that there are no intermediate elements between the two.

[0027] In the present application, a switch tube is a transistor that operates in a switching mode to provide a current path, including one selected from a bipolar transistor or a field-effect transistor. The first end and the second end of the switch tube are respectively a high potential end and a low potential end on the current path, and the control end is used to receive a drive signal to control the on and off of the switch tube. MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) includes a first end, a second end and a control end. When the MOSFET is in the on state, current flows from the first end to the second end. The first end, the second end and the control end of the P-type MOSFET are respectively the source, the drain and the gate, and the first end, the second end and the control end of the N-type MOSFET are respectively the drain, the source and the gate. The present invention is further described below with reference to the accompanying drawings and embodiments.

[0028] Figure 2 FIG. 1 shows a circuit diagram of a switching converter according to an embodiment of the present invention. Figure 2 As shown, switching converter 200 includes a main circuit and a control circuit integrated in the same integrated circuit chip.

[0029] The main circuit of switching converter 200 includes a power transistor MD1 and a freewheeling transistor MD2 connected in series between an input terminal and a ground terminal. An inductor Lx is connected between the intermediate node between the power transistor MD1 and the freewheeling transistor MD2 and the output terminal. An output capacitor Cout is connected between the output terminal and the ground terminal. The input terminal of the main circuit receives an input voltage Vin, and the output terminal provides an output voltage Vout. The power transistor MD1 and the freewheeling transistor MD2 are, for example, referred to as a high-side switch and a low-side switch, respectively. The control circuit of switching converter 200 is used to provide a switching control signal to the power transistor MD1 and the rectifier transistor MD2. This switching control signal is a drive signal generated based on a pulse-width modulation signal. During each switching cycle, the power transistor MD1 and the rectifier transistor MD2 are alternately turned on and off, causing the inductor Lx to alternately store and supply electrical energy. When the power tube MD1 is turned on and the rectifier tube MD2 is turned off, the inductor Lx starts to store electric energy. When the power tube MD1 is turned off and the rectifier tube MD2 is turned on, the inductor Lx starts to supply electric energy to the output capacitor Cout, so that the output voltage Vout is stable.

[0030] In the embodiment of the present invention, the power transistor MD1 and the rectifier transistor MD2 may be various types of transistors, such as P-type MOSFET, N-type MOSFET, NPN Darlington transistor, NPN bipolar transistor, PNP bipolar transistor, etc.

[0031] The control circuit includes an error amplifier EA, a logic and driving circuit 210 , a current limiting protection circuit 220 , a current backflow protection circuit 230 and a light load mode detection circuit 240 .

[0032] The error amplifier EA compares the feedback voltage VFB of the output voltage Vout with the reference voltage Vref to generate an error signal Verr. For example, the switching converter 200 includes a resistor divider network consisting of resistors R1 and R2. Resistors R1 and R2 are connected in series between the output terminal of the switching converter and ground. The intermediate node between the resistors R1 and R2 is used to output the feedback voltage VFB.

[0033] The logic and drive circuit 210 is used to implement the system's logic control functions. It generates a pulse-width modulation signal based on the error signal Verr and the clock signal OSC, and converts the pulse-width modulation signal into switch control signals Hgate and Lgate to control the conduction states of the power transistor MD1 and the rectifier transistor MD2, respectively. For example, the logic and drive circuit 220 outputs the control signal Hgate for switching control of the power transistor MD1 to the control terminal of the power transistor MD1, and outputs the control signal Lgate for switching control of the rectifier transistor MD2 to the control terminal of the rectifier transistor MD2.

[0034] The current-limiting protection circuit 220 is used to limit the current flowing through the power transistor MD1 and provide short-circuit protection. In one embodiment, the current-limiting protection circuit 230 compares the current flowing through the power transistor MD1 with a current-limiting threshold. When the current exceeds the current-limiting threshold, the current-limiting protection circuit 230 outputs a current-limiting protection signal LIM to the logic and driver circuit 220, causing the logic and driver circuit 210 to stop operating. When the logic and driver circuit 210 stops operating, the switch control signal Hgate is high, disconnecting the power transistor MD1 and stopping the output current from being supplied to the output terminal. This reduces the risk of damage to the chip and downstream loads in the event of a short circuit at the chip's output terminal.

[0035] The current backfeed protection circuit 230 is used to detect whether the inductor current drops to zero during the inductor freewheeling phase. When the current of the rectifier tube MD2 drops close to zero, the current backfeed protection circuit 230 outputs a backfeed protection signal REV. The logic and drive circuit 210 outputs a switch control signal Lgate to a low level based on the backfeed protection signal REV, turning off the rectifier tube MD2 to prevent current backflow in the inductor.

[0036] Light-load mode detection circuit 240 is configured to determine whether the load terminal of switching converter 200 is in a light-load state and, based on the determination result, output a light-load indication signal DPSM to control switching converter 200 to operate in a light-load mode or a normal mode. For example, light-load mode detection circuit 250 determines whether the load terminal of switching converter 200 is in a light-load state by detecting the duty cycle of switching control signal Hgate and the voltage difference between input voltage Vin and output voltage Vout. When the switching converter 200 operates in a light-load state, the light-load mode detection circuit 240 outputs a valid light-load indication signal DPSM (i.e., the light-load indication signal DPSM is at a logic high level), controlling the switching converter 200 to enter the light-load mode. At this time, most of the operating circuits in the switching converter 200 are shut down, such as the current limiting protection circuit 220 and the current backfeed protection circuit 230. Only the UVLO (Undervoltage-Lockout module), BG (Bandgap voltage reference module), OTP (Over-temperature protection module), and OVP (Over Voltage Protection module) (not shown) are retained. The quiescent current of the entire converter is reduced accordingly, ensuring that the chip can operate normally and maintain low power consumption under light-load conditions.

[0037] Figure 3 Show Figure 2 The circuit diagram of the light load mode detection circuit in FIG. Figure 3As shown, the light load mode detection circuit 240 includes a threshold voltage generation module 241, a comparator 242, a duty cycle detection module 243, and an output module 244. The threshold voltage generation module 241 is used to generate a threshold voltage Va based on the input voltage Vin. The comparator 242 compares the output voltage Vout with the threshold voltage Va to generate a comparison signal V1. The duty cycle detection module 243 receives the switching control signal Hgate of the power transistor MD1 and generates a duty cycle detection signal V2 based on the switching control signal Hgate. The output module 244 generates a light load indication signal DPSM based on the comparison signal V1, the duty cycle detection signal V2, and the overvoltage protection signal OVP. The light load indication signal DPSM is used to control the switching converter to switch between light load mode and normal mode.

[0038] The light-load mode detection circuit of this embodiment operates as follows: when the switching converter operates in normal mode, the duty cycle detection module 243 generates a valid duty cycle detection signal V2 (i.e., the duty cycle detection signal V2 is at a logic high level) after the high level duration of the switching control signal Hgate exceeds a preset time. Simultaneously, the output module 244 is configured to output a valid light-load indication signal DPSM (i.e., the light-load indication signal DPSM is at a logic high level) when the comparison signal V1 indicates that the output voltage Vout increases to a first threshold voltage Va1, thereby controlling the switching converter to switch from normal mode to light-load mode. When the switching converter operates in light-load mode, the output module 244 is configured to output a deactivated light-load indication signal DPSM (i.e., the light-load indication signal DPSM is at a logic low level) when the comparison signal V1 indicates that the output voltage Vout decreases to a second threshold voltage Va2, or when the overvoltage protection signal OVP is active, thereby controlling the switching converter to switch from light-load mode to normal mode.

[0039] Furthermore, the output module 244 is implemented, for example, by an AND gate circuit AND1, wherein the first input end of the AND gate circuit AND1 receives the comparison signal V1, the second input end receives the inverted signal of the overvoltage protection signal OVP, the third input end receives the duty cycle detection signal V2, and the output end is used to output the light load indication signal DPSM.

[0040] Furthermore, the light-load mode detection circuit 240 further includes an inverter INV1 , an input terminal of the inverter INV1 receiving the overvoltage protection signal OVP, and an output terminal connected to the second input terminal of the AND gate circuit AND1 to provide an inverted signal of the overvoltage protection signal.

[0041] Furthermore, the threshold voltage generation module 241 includes a resistor Rhys connected in series between the input voltage Vin and ground, a resistor R3, a current source I1, and a transistor P1 connected in parallel between the two ends of the resistor Rhys. The control terminal of the transistor P1 is connected to the output terminal of the comparator 242. The resistor Rhys is used to set the hysteresis of the mode determination to avoid the problem of critical point oscillation. The transistor P1 is, for example, a P-type MOSFET. When the comparison signal V1 is at a logic high level, the transistor P1 is turned off, and when the comparison signal V1 is at a logic low level, the transistor P1 is turned on. Furthermore, the threshold voltage Va is used to represent the critical switching point between the light load mode and the normal mode of the switching converter of this embodiment. When the switching converter operates in the normal mode, the comparison signal V1 is at a logic low level, and the transistor P1 is turned on. At this time, the first threshold voltage Va1 = Vin-I1×R3, where I1 represents the current of the constant current source I1. When the switching converter operates in the light-load mode, the comparison signal V1 is at a logic high level, and the transistor P1 is turned off. At this time, the second threshold voltage Va2 = Vin-(I1×R3+Rhys).

[0042] As can be seen from the above, the critical switching point at which the switching converter of this embodiment switches from normal mode to light load mode is Vout = Vin - I1 × R3. Furthermore, when the duty cycle of the switching control signal Hgate is 100%, Vout = Vin - Iload × Rds, where Iload represents the load current and Rds represents the on-resistance of the power transistor MD1. Therefore, the load current at the critical switching point is Iload = (I1 × R3) / Rds. Assuming I1 = 0.5 uA, R3 = 200 Kohm, and Rds = 500 mohm, the load current at the critical switching point of this embodiment is Iload = 200 mA. That is, when the load current is less than 200 mA, the switching converter will switch from normal mode to light load mode. When the load current is greater than 200 mA, the switching converter will not switch to light load mode even if the duty cycle of the switching control signal Hgate is 100%.

[0043] Figure 4a and Figure 4b Schematic waveform diagrams of the switching converter under light load and heavy load are shown respectively. Figure 4a and Figure 4bFigure 2 shows the voltage waveforms of the input voltage Vin, output voltage Vout, and light-load indication signal DPSM, respectively. Under light-load conditions, as the input voltage Vin decreases, the voltage difference between the output voltage Vout and the input voltage Vin falls below a predetermined value, causing the light-load indication signal DPSM to flip from a logic-low level to a logic-high level, controlling the switching converter to switch from normal mode to light-load mode. Under heavy-load conditions, because the voltage difference between the output voltage Vout and the input voltage Vin exceeds the predetermined value, the light-load indication signal DPSM remains at a logic-low level, and the switching converter does not switch to light-load mode.

[0044] Furthermore, the switching converter of the embodiment of the present invention responds to load and power steps when in light-load mode as follows: If a sudden load increase occurs while the switching converter is in light-load mode, the output voltage Vout will inevitably decrease, causing the output voltage Vout to fall below the second threshold voltage Va2. The light-load indication signal DPSM will flip from a logic high level to a logic low level, and the switching converter will directly exit light-load mode. If a sudden power increase occurs while the switching converter is in light-load mode, the output voltage Vout will inevitably increase along with the input voltage Vin until the overvoltage protection (OVP) is triggered. The light-load indication signal DPSM will also flip from a logic high level to a logic low level, and the switching converter will directly exit light-load mode. It can be seen that after entering light-load mode, the switching converter of the embodiment of the present invention maintains a constant on state in the power transistor. Only the comparator and overvoltage protection module in the light-load mode detection circuit need to remain operational to detect when to exit light-load mode. This ensures a sufficiently low quiescent current in light-load mode, facilitates extremely low quiescent power consumption, and improves the efficiency of the switching converter in light-load mode, achieving an ultra-low power switching converter.

[0045] In the above embodiment, although the Figure 2 A switching converter with a buck topology is described. However, it can be understood that the light-load mode detection circuit of the embodiment of the present invention can also be applied to switching converters with other topologies, including but not limited to buck, boost, buck-boost, non-inverting buck-boost, forward, and flyback topologies.

[0046] In summary, in the switching converter and its light load mode detection circuit and method according to the embodiments of the present invention, the light load mode detection circuit includes a threshold voltage generation module, a comparator, a duty cycle detection module, and an output module. The threshold voltage generation module is used to generate a threshold voltage based on the input voltage, the comparator is used to compare the output voltage with the threshold voltage to generate a comparison signal, the duty cycle detection module is used to generate a duty cycle detection signal based on the switching control signal of the power tube, and the output module is used to generate a light load indication signal based on the comparison signal, the duty cycle detection signal, and the overvoltage protection signal to control the switching of the switching converter between light load mode and normal mode. In the light load mode, the light load mode detection circuit according to the embodiments of the present invention only needs to keep the comparator and the overvoltage protection module in operation to monitor when to exit the light load mode. This ensures a sufficiently low quiescent current in the light load mode, facilitates extremely low quiescent power consumption, and is beneficial for improving the efficiency of the switching converter under light load conditions, thereby realizing an ultra-low power switching converter.

[0047] It should be noted that although the device is described herein as a certain N-channel or P-channel device, or a certain N-type or P-type doped region, it will be understood by those skilled in the art that complementary devices can also be realized according to the present invention. It will be understood by those skilled in the art that the conductivity type refers to the mechanism by which conduction occurs, such as conduction by holes or electrons, and therefore the conductivity type does not refer to the doping concentration but to the doping type, such as P-type or N-type. It will be understood by those skilled in the art that the terms "during", "when", and "when..." used in this article in relation to circuit operation are not strict terms indicating an action that occurs immediately upon the start of the start-up action, but rather that there may be some small but reasonable delay or delays between the action and the reaction initiated by the start-up action, such as various transmission delays. The terms "approximately" or "substantially" are used herein to mean that the element value has a parameter that is expected to be close to the stated value or position. However, as is well known in the art, there are always slight deviations that make it difficult for the value or position to be exactly the stated value. It has been well established in the art that a deviation of at least ten percent (10%) (or at least twenty percent (20%) for semiconductor doping concentrations) is a reasonable deviation from the desired goal of accuracy as described. When used in conjunction with a signal state, the actual voltage value or logic state of the signal (e.g., "" or "") depends on whether positive logic or negative logic is used.

[0048] In addition, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further limitations, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0049] The embodiments of the present invention are described above, but these embodiments do not describe all details in detail, nor do they limit the invention to specific embodiments. Obviously, many modifications and variations can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and modify and use it based on the present invention. The scope of protection of the present invention shall be based on the scope defined by the claims of the present invention.

Claims

1. A light-load mode detection circuit for a switching converter, the switching converter comprising a power transistor and a rectifier transistor connected in series, the power transistor and the rectifier transistor being configured to control power transmission from an input terminal to an output terminal to convert an input voltage into an output voltage, wherein the light-load mode detection circuit comprises: A threshold voltage generating module, configured to generate a threshold voltage according to the input voltage; a comparator, configured to compare the output voltage with the threshold voltage to generate a comparison signal; A duty cycle detection module, configured to generate a duty cycle detection signal according to the switch control signal of the power tube; as well as an output module, configured to generate a light-load indication signal according to the comparison signal, the duty cycle detection signal, and the overvoltage protection signal, so as to control the switching converter to switch between a light-load mode and a normal mode, Wherein, when the switching converter operates in normal mode, the output module is configured to: when the duty cycle detection signal is valid, when the comparison signal indicates that the output voltage is greater than a first threshold voltage, generate a valid light load indication signal to control the switching converter to switch from normal mode to light load mode, and When the switching converter operates in light load mode, the output module is configured to generate an invalid light load indication signal when the comparison signal indicates that the output voltage is less than a second threshold voltage or the overvoltage protection signal is valid, so as to control the switching converter to switch from light load mode to normal mode.

2. The light load mode detection circuit according to claim 1, wherein: The second threshold voltage is lower than the first threshold voltage.

3. The light load mode detection circuit according to claim 1, wherein: The output module includes: The AND gate circuit has a first input terminal receiving the comparison signal, a second input terminal receiving the inverted signal of the overvoltage protection signal, a third input terminal receiving the duty cycle detection signal, and an output terminal outputting the light load indication signal.

4. The light load mode detection circuit according to claim 1, wherein: The duty cycle detection module is configured to output a valid duty cycle detection signal when the high level time of the switch control signal of the power tube is greater than a preset time.

5. The light load mode detection circuit according to claim 1, wherein: The threshold voltage generating circuit comprises: a first resistor, a second resistor, and a current source connected in series between the input voltage and ground, wherein an intermediate node between the first resistor and the current source is used to provide the threshold voltage; and A first transistor, wherein a first end of the first transistor is connected to the first end of the first resistor, a second end of the first transistor is connected to the second end of the first resistor, and a control end of the first transistor receives the comparison signal.

6. The light load mode detection circuit according to claim 5, wherein: The first transistor is a P-type MOSFET.

7. A switching converter, characterized in that: include: A main circuit includes a power tube and a rectifier tube connected in series, wherein the power tube and the rectifier tube are used to control the transmission of electric energy from the input end to the output end to convert the input voltage into the output voltage; as well as The light load mode detection circuit according to any one of claims 1 to 6.

8. A method for detecting a light-load mode of a switching converter, wherein the switching converter comprises a power transistor and a rectifier transistor connected in series, wherein the power transistor and the rectifier transistor are used to control the transmission of power from an input end to an output end to convert an input voltage into an output voltage, wherein: The light load mode detection method: generating a threshold voltage according to the input voltage; comparing the output voltage with the threshold voltage to generate a comparison signal; Generate a duty cycle detection signal according to the switch control signal of the power tube; as well as generating a light-load indication signal according to the comparison signal, the duty cycle detection signal, and the overvoltage protection signal to control the switching converter to switch between a light-load mode and a normal mode, The step of generating a light-load indication signal according to the comparison signal, the duty cycle detection signal, and the overvoltage protection signal to control the switching converter to switch between the light-load mode and the normal mode includes: When the switching converter operates in the normal mode, generating a valid light-load indication signal when the duty cycle detection signal is valid and the comparison signal indicates that the output voltage is greater than a first threshold voltage, so as to control the switching converter to switch from the normal mode to the light-load mode; and When the switching converter operates in light load mode, an invalid light load indication signal is generated when the comparison signal indicates that the output voltage is less than the second threshold voltage or the overvoltage protection signal is valid, so as to control the switching converter to switch from light load mode to normal mode.

9. The light load mode detection method according to claim 8, wherein: Generating a duty cycle detection signal according to the switch control signal of the power tube includes: When the high level time of the switch control signal of the power tube is greater than the preset time, a valid duty cycle detection signal is output.

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