CN114157135B - PWM-PFM seamless switching controller with hysteresis function and control method thereof - Google Patents

Abstract

The invention provides a PWM-PFM seamless switching controller with hysteresis function and a control method thereof, and relates to the technical field of integrated circuits. The switching controller in the system includes a current detection device, which is used to detect load current and generate start requests and left and right switching requests; the left threshold switching controller and the right threshold switching controller are used to detect switching requests and circuit start responses, and generate actual switching signals. ; Switching controller, used to implement PWM/PFM switching, obtain control signals, and generate PWM and PFM shutdown requests; PWM and PFM controller, used to generate PWM and PFM control signals, and generate start-up response signals in time. The present invention proposes a method of using three load characteristic values of switching point, left threshold and right threshold to generate actual switching signals, realizing hysteretic switching of PWM and PFM, avoiding repeated switching of PWM and PFM, and at the same time extracting the target control before switching. mode to avoid large voltage drops due to slow start-up of the circuit and achieve seamless switching of PWM/PFM.

Description

PWM-PFM seamless switching controller with hysteresis function and its control method

Technical field

The present invention relates to the field of integrated circuit technology, and in particular to a PWM-PFM seamless switching controller with hysteresis function and a control method thereof.

Background technique

In DC-DC switching power supplies, pulse width modulation (PWM) and pulse frequency modulation (PFM) are two commonly used modulation modes. PWM fixes the switching frequency and controls the opening of the power tube in the DC-DC system by adjusting the duty cycle. time, and then adjust the output voltage. PFM fixes the switching time, and controls the switching frequency of the power tube by adjusting the off time to adjust the output voltage.

PWM and PFM modulation modes have their own advantages and disadvantages. At light load, PFM has higher conversion efficiency due to variable switching frequency, but its output ripple and response speed and other system performance are weaker than PWM within the full load range. , PWM performs well at heavy load, but at light load, due to its higher switching frequency, switching loss and conduction loss account for a larger proportion, and its conversion efficiency at light load is extremely low, limiting Application of PWM controlled DC-DC switching power supply in light load range.

In order to solve the problem of extremely low conversion efficiency of PWM control mode at light load, a dual-mode control DC-DC system using PWM and PFM came into being. In this mode, the system is controlled by PFM at light load and the system is controlled by PFM at heavy load. Controlled by PWM, the advantages of the two control modes are fully utilized to achieve high conversion efficiency of the system within the full load range. In order to realize the combination of PWM and PFM, a PWM/PFM switching controller is indispensable. However, the existing PWM/PFM switching controller has a simple structure and uses a single switching point to realize switching between PWM and PFM. The output voltage is relatively small during switching. There is a possibility of repeated switching between PWM and PFM due to large fluctuations and the system is working near the switching point, which brings a relatively large test to the stability of the system.

Contents of the invention

In view of the shortcomings of the existing technology, the present invention provides a PWM-PFM seamless switching controller with hysteresis function and a control method thereof. It can output the corresponding start signal and left and right switching signals according to the three load characteristic values of left threshold, switching middle value and right threshold, realize hysteretic switching of PWM and PFM, and ensure that the output voltage will not generate a large voltage during the switching process fluctuation.

On the one hand, a PWM-PFM seamless switching controller with hysteresis function includes: a current detection device, a starting circuit, a left switching controller, a right switching controller, a PWM controller, a PFM controller, and a switching controller.

The output port of the current detection device includes a first output port to a third output port, the input port of the switching controller includes a first input port to a fourth input port, and the left switching controller and the right switching controller have The input port includes a first input port and a second input port; the first output port of the current detection device is connected to the first input port of the left switching controller, and the second output port of the current detection device is connected to the startup circuit. The input port is connected, and the third output port of the current detection device is connected with the first input port of the right switching controller;

The output port of the startup circuit includes a first output port and a second output port; wherein the first output port of the startup circuit is connected to the first input port of the PWM controller, and the second output port of the startup circuit is connected to the The first input port of the PFM controller is connected;

The input ports of the PWM controller and the PFM controller include a first input port and a second input port, and the output ports include a first output port and a second output port; wherein the first output port of the PWM controller and the right The second input port of the switching controller is connected, the second output port of the PWM controller is connected with the first input port of the switching controller, and the first output port of the PFM controller is connected with the third input port of the left switching controller. The two input ports are connected, and the second output port of the PFM controller is connected to the second input port of the switching controller;

The output port of the right switching controller is connected to the third input port of the switching controller, while the output port of the right switching controller is connected to the second input port of the PFM controller, and the output port of the left switching controller is connected to the switching controller. The fourth input port of the controller is connected, and the output port of the left switching controller is connected to the second input port of the PWM controller. The output port of the switching controller is the control signal;

The current detection device is composed of a first comparator, a second comparator, and a third comparator. The non-inverting terminal of the first comparator is connected to the left threshold voltage VREFL, and the inverting terminal of the first comparator is connected to the voltage representing the current magnitude. The voltage signal VH is connected, and the output terminal of the first comparator is the first output port of the current detection device. The non-inverting terminal of the second comparator is connected to VH, the inverting terminal of the second comparator is connected to the switching threshold voltage VREFM, the output terminal of the second comparator is the second output port of the current detection device, and the third comparator The non-inverting terminal is connected to VH, the inverting terminal of the third comparator is connected to the right threshold voltage VREFR, and the output port of the third comparator is the third output port of the current detection device.

The startup circuit includes a first inverter, a first D flip-flop, and a second D flip-flop. The input port of the first inverter is the first input of the startup circuit, and the output port of the first inverter is the same as the first inverter. The clock port Clk terminal of the second D flip-flop is connected, the reset port R of the second D flip-flop is connected with the PFM shutdown signal of the output port of the left switching controller, and the data terminal D of the second D flip-flop is connected with the power supply VDD. Connected, the output terminal Q of the second D flip-flop is the second output port of the startup circuit, and the clock port Clk of the first D flip-flop is connected to the input port of the first inverter, which is the first input of the startup circuit. The data D terminal of the first D flip-flop is connected to the power supply VDD, the reset port R of the first D flip-flop is connected to the PWM shutdown signal of the output port of the right switching controller, and the output terminal Q of the first D flip-flop is start The first output port of the circuit.

The left switching controller is composed of an AND gate. The first input port of the AND gate is the first input of the left switching controller. The second input of the AND gate is the second input of the left switching controller. The output of the AND gate is the left switching controller. Switch the output port of the controller to generate a PFM shutdown signal;

The right switching controller is composed of an AND gate, the first input port of the AND gate is the first input of the right switching controller, the second input of the AND gate is the second input of the right switching controller, and the output of the AND gate is the right switching controller. Switch the output port of the controller to generate a PWM shutdown signal.

The switching controller includes a two-choice data selector and an RS flip-flop. The R terminal of the RS flip-flop is the third input port of the switching controller, and the S terminal of the RS flip-flop is the fourth input port of the switching controller. , the Q terminal of the RS flip-flop is connected to the control port of the two-choice data selector, the 0-terminal of the two-choice data selector is the first input port of the switching controller, and the 1-terminal of the two-choice data selector is the switching The second input port of the controller is input, and the output of the two-choice data selector is the output of the switching controller.

On the other hand, a PWM-PFM seamless switching control method with hysteresis function is implemented based on the aforementioned PWM-PFM seamless switching controller with hysteresis function, including the following steps:

Step 1. The current detection device starts working and detects the relationship between the left switching threshold VREFL, the switching median VREFM, the right switching threshold VREFR and the voltage signal VH that represents the load current.

When VREFR>VH>VREFM, the second output of the current detection device is high, and the PWM controller is started at this time;

When VH>VREFR, the third output of the current detection device is high. At this time, it switches from PFM mode to PWM mode, that is, the RS flip-flop output Q terminal inside the switching controller jumps from 1 to 0, and one of the two data is selected. The controller selects the output 0 terminal, that is, switches the first input port signal of the controller, that is, outputs the PWM control signal;

When VREFL<VH<VREFM, the second output of the current detection device is low, and the PFM controller is started at this time;

When VH<VREFL, the first output of the current detection device is high. At this time, it switches from PWM mode to PFM mode, that is, the RS flip-flop output Q terminal inside the switching controller jumps from 0 to 1, and one of the two data is selected. The controller selects output 1 terminal, that is, switches the second input port signal of the controller, that is, outputs the PFM control signal;

Step 2. Adjust the system working status according to changes in load current to achieve PWM-PFM seamless switching control method;

The adjustments mentioned are specifically:

When the load is light load, that is, VH<VREFL, the PFM controller works, the PWM controller is turned off, and the two-to-one data selector selects 1 input channel;

When the load is heavy load, that is, VH>VREFR, the PFM controller is turned off, the PWM controller works, and the data selector selects the 0 input channel;

When the load is between the left switching threshold VREFL and the right switching threshold VREFR, the system retains the initial working state;

When the load changes from light load to heavy load, the following steps are included:

Step S1: When the load gradually increases and VH is greater than VREFM, the second output of the current detection device is logic 1, then the load current is greater than the switching median value, and the PWM controller starts;

Step S2: The PWM controller starts to start. After the startup is completed, a start response signal is generated and transmitted to the right switching controller, and the PWM control signal is output to the 0 input channel of the switching controller;

Step S3: When the load gradually increases and VH is greater than VREFR, the output of the right switching controller is logic 1. This signal is also a PFM shutdown signal and is transmitted to the PFM controller to turn off the PFM controller;

Step S4. The RS flip-flop of the switching controller receives the reset signal, and the output signal generated is logic 0. That is, the mode selection signal received by the two-select-one data selector in the switching controller is logic 0, and the 0 input channel is selected and the output PWM control signal to complete the conversion from PFM mode to PWM mode;

When the load changes from heavy load to light load, the following steps are included:

Step D1. When the load gradually decreases so that VH is less than VREFM, the second output of the current detection device is logic 0, then the load current is less than the switching median value, and the PFM controller starts;

Step D2: The PFM controller starts to start. After the startup is completed, a start response signal is generated and transmitted to the left switching controller, and the PFM control signal is output to the 1 input channel of the switching controller;

Step D3. When the load gradually decreases and VH is less than VREFL, the output of the left switching controller is logic 1. This signal is also a PWM shutdown signal and is transmitted to the PWM controller to turn off the PWM controller;

Step D4. The RS flip-flop of the switching controller receives the setting signal, and the generated output signal is logic 1. That is, the mode selection signal received by the two-select-one data selector in the switching controller is logic 1, and the 1 input channel is selected. Output the PFM control signal to complete the conversion from PWM mode to PFM mode.

The beneficial effects produced by adopting the above technical solutions are:

The present invention proposes a PWM-PFM seamless switching controller with hysteresis function and a control method thereof. In the existing PWM/PFM switching controller, a left threshold, switching median, right threshold and left and right switching are added. controller, when the load current is greater than the switching median value, the PWM controller starts to start, but does not complete the switching. When the load current is greater than the right threshold and the PWM controller generates a start response, the PFM to PWM switching is completed. When the load current is less than After switching the median value, the PFM controller starts to start, but does not complete the switching. When the load current is less than the left threshold and the PFM controller generates a start response, the switching from PWM to PFM is completed. However, the existing technology completes the switching immediately after receiving the switching signal. At this time, the startup of the PWM/PFM controller has not yet been completed. The control signal output by the PWM/PFM controller is not the expected control signal, resulting in large fluctuations in the system output voltage. By setting up the left and right switching thresholds and the PWM/PFM start response signal, the present invention delays the mode switching and reserves enough time for the start of the PWM/PFM controller, thereby ensuring the accuracy of the system control signal and realizing Seamless and hysteretic switching between PWM and PFM modes.

Description of the drawings

Figure 1 is a schematic diagram of the overall structure of the switching controller of the present invention;

Figure 2 is an overall circuit diagram of the switching controller of the present invention;

Figure 3 is a working flow chart of the switching controller of the present invention;

Figure 4 is a specific circuit diagram of the switching controller in the embodiment of the present invention.

Detailed ways

Specific implementations of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the invention but are not intended to limit the scope of the invention.

On the one hand, a PWM-PFM seamless switching controller with hysteresis function, as shown in Figure 1 and Figure 2, includes: current detection device, starting circuit, left switching controller, right switching controller, PWM controller, PFM controller, and switching controller.

The output port of the current detection device includes a first output port to a third output port, the input port of the switching controller includes a first input port to a fourth input port, and the left switching controller and the right switching controller have The input port includes a first input port and a second input port; the first output port of the current detection device is connected to the first input port of the left switching controller, and the second output port of the current detection device is connected to the startup circuit. The input port is connected, and the third output port of the current detection device is connected with the first input port of the right switching controller;

The output port of the startup circuit includes a first output port and a second output port; wherein the first output port of the startup circuit is connected to the first input port of the PWM controller, and the second output port of the startup circuit is connected to the The first input port of the PFM controller is connected;

The input ports of the PWM controller and the PFM controller include a first input port and a second input port, and the output ports include a first output port and a second output port; wherein the first output port of the PWM controller and the right The second input port of the switching controller is connected, the second output port of the PWM controller is connected with the first input port of the switching controller, and the first output port of the PFM controller is connected with the third input port of the left switching controller. The two input ports are connected, and the second output port of the PFM controller is connected to the second input port of the switching controller;

The output port of the right switching controller is connected to the third input port of the switching controller, while the output port of the right switching controller is connected to the second input port of the PFM controller, and the output port of the left switching controller is connected to the switching controller. The fourth input port of the controller is connected, and the output port of the left switching controller is connected to the second input port of the PWM controller. The output port of the switching controller is the control signal;

The current detection device is composed of a first comparator, a second comparator, and a third comparator. The non-inverting terminal of the first comparator is connected to the left threshold voltage VREFL, and the inverting terminal of the first comparator is connected to the voltage representing the current magnitude. The voltage signal VH is connected, and the output terminal of the first comparator is the first output port of the current detection device. The non-inverting terminal of the second comparator is connected to VH, the inverting terminal of the second comparator is connected to the switching threshold voltage VREFM, the output terminal of the second comparator is the second output port of the current detection device, and the third comparator The non-inverting terminal is connected to VH, the inverting terminal of the third comparator is connected to the right threshold voltage VREFR, and the output port of the third comparator is the third output port of the current detection device.

The startup circuit includes a first inverter, a first D flip-flop, and a second D flip-flop. The input port of the first inverter is the first input of the startup circuit, and the output port of the first inverter is the same as the first inverter. The clock port Clk terminal of the second D flip-flop is connected, the reset port R of the second D flip-flop is connected with the PFM shutdown signal of the output port of the left switching controller, and the data terminal D of the second D flip-flop is connected with the power supply VDD. Connected, the output terminal Q of the second D flip-flop is the second output port of the startup circuit, and the clock port Clk of the first D flip-flop is connected to the input port of the first inverter, which is the first input of the startup circuit. The data D terminal of the first D flip-flop is connected to the power supply VDD, the reset port R of the first D flip-flop is connected to the PWM shutdown signal of the output port of the right switching controller, and the output terminal Q of the first D flip-flop is start The first output port of the circuit.

The left switching controller is composed of an AND gate. The first input port of the AND gate is the first input of the left switching controller. The second input of the AND gate is the second input of the left switching controller. The output of the AND gate is the left switching controller. Switch the output port of the controller to generate a PFM shutdown signal;

The right switching controller is composed of an AND gate, the first input port of the AND gate is the first input of the right switching controller, the second input of the AND gate is the second input of the right switching controller, and the output of the AND gate is the right switching controller. Switch the output port of the controller to generate a PWM shutdown signal.

The switching controller includes a two-choice data selector and an RS flip-flop. The R terminal of the RS flip-flop is the third input port of the switching controller, and the S terminal of the RS flip-flop is the fourth input port of the switching controller. , the Q terminal of the RS flip-flop is connected to the control port of the two-choice data selector, the 0-terminal of the two-choice data selector is the first input port of the switching controller, and the 1-terminal of the two-choice data selector is the switching The second input port of the controller is input, and the output of the two-choice data selector is the output of the switching controller.

On the other hand, a PWM-PFM seamless switching control method with hysteresis function is implemented based on the aforementioned PWM-PFM seamless switching controller with hysteresis function, as shown in Figure 3, including the following steps:

Step 1. The current detection device starts working and detects the relationship between the left switching threshold VREFL, the switching median VREFM, the right switching threshold VREFR and the voltage signal VH that represents the load current.

When VREFR>VH>VREFM, the second output of the current detection device is high, and the PWM controller is started at this time;

When VH>VREFR, the third output of the current detection device is high. At this time, it switches from PFM mode to PWM mode, that is, the RS flip-flop output Q terminal inside the switching controller jumps from 1 to 0, and one of the two data is selected. The controller selects the output 0 terminal, that is, switches the first input port signal of the controller, that is, outputs the PWM control signal;

When VREFL<VH<VREFM, the second output of the current detection device is low, and the PFM controller is started at this time;

When VH<VREFL, the first output of the current detection device is high. At this time, it switches from PWM mode to PFM mode, that is, the RS flip-flop output Q terminal inside the switching controller jumps from 0 to 1, and one of the two data is selected. The controller selects output 1 terminal, that is, switches the second input port signal of the controller, that is, outputs the PFM control signal;

Step 2. Adjust the system working status according to changes in load current to achieve PWM-PFM seamless switching control method;

The adjustments mentioned are specifically:

When the load is light load, that is, VH<VREFL, the PFM controller works, the PWM controller is turned off, and the two-to-one data selector selects 1 input channel;

When the load is heavy load, that is, VH>VREFR, the PFM controller is turned off, the PWM controller works, and the data selector selects the 0 input channel;

When the load is between the left switching threshold VREFL and the right switching threshold VREFR, the system retains the initial working state;

When the load changes from light load to heavy load, the following steps are included:

Step S1: When the load gradually increases and VH is greater than VREFM, the second output of the current detection device is logic 1, then the load current is greater than the switching median value, and the PWM controller starts;

Step S2: The PWM controller starts to start. After the startup is completed, a start response signal is generated and transmitted to the right switching controller, and the PWM control signal is output to the 0 input channel of the switching controller;

Step S3: When the load gradually increases and VH is greater than VREFR, the output of the right switching controller is logic 1. This signal is also a PFM shutdown signal and is transmitted to the PFM controller to turn off the PFM controller;

Step S4. The RS flip-flop of the switching controller receives the reset signal, and the output signal generated is logic 0. That is, the mode selection signal received by the two-select-one data selector in the switching controller is logic 0, and the 0 input channel is selected and the output PWM control signal to complete the conversion from PFM mode to PWM mode;

When the load changes from heavy load to light load, the following steps are included:

Step D1. When the load gradually decreases so that VH is less than VREFM, the second output of the current detection device is logic 0, then the load current is less than the switching median value, and the PFM controller starts;

Step D2: The PFM controller starts to start. After the startup is completed, a start response signal is generated and transmitted to the left switching controller, and the PFM control signal is output to the 1 input channel of the switching controller;

Step D3. When the load gradually decreases and VH is less than VREFL, the output of the left switching controller is logic 1. This signal is also a PWM shutdown signal and is transmitted to the PWM controller to turn off the PWM controller;

Step D4. The RS flip-flop of the switching controller receives the setting signal, and the generated output signal is logic 1. That is, the mode selection signal received by the two-select-one data selector in the switching controller is logic 1, and the 1 input channel is selected. Output the PFM control signal to complete the conversion from PWM mode to PFM mode.

Figure 4 shows a specific embodiment of the present invention, including a current detection device, a starting circuit, a left switching controller, a right switching controller, a PWM controller, a PFM controller, and a switching controller.

The current detection device is used to determine the relationship between the reference voltage left switching threshold VREFL, the right switching threshold VREFR, the switching median VREFM and the voltage value VH that represents the load current, and change the state of the output voltage according to the relationship between the voltages, thereby determining The subsequent working status of the system. If VH>VREFM, the second output of the current detection device is high, starting the PWM controller; if VH>VREFR, the third output of the current detection device is high, and the modulation mode switches from PFM mode to PWM mode; if VH<VREFM, the current detection device The second output of the device is low, starting the PFM controller; if VH<VREFL, the first output of the current detection device is high, and the modulation mode switches from PWM mode to PFM mode.

The startup circuit is used to receive the second output of the current detection and generate corresponding startup signals of the PWM controller and the PFM controller according to its status. If the second output state of the current detection device is high, a PWM controller start signal is generated. If the second output state of the current detection device is low, a PFM controller start signal is generated. At the same time, the startup circuit receives the PFM shutdown signal and the PWM shutdown signal and generates the shutdown signals of the PWM and PFM controllers in time.

The left switching controller and the right switching controller receive the first output and the second output of the current detection device respectively, and generate actual PWM and PFM switching signals according to their states. And after completing the switching, the PWM turn-off signal and the PFM turn-off signal are generated in time.

The switching controller is used to receive the PWM and PFM switching signals, and select the PWM control signal and the PFM signal according to the switching signal to complete the actual switching of the two modulation modes.

The PWM controller is used to generate a PWM control signal, including an error amplifier, a voltage comparator, a first inverter, and a second inverter. The non-inverting end of the error amplifier is connected to the reference voltage VREF, and the inverting end of the error amplifier is connected to the reference voltage VREF. The feedback signal is connected, the output of the error amplifier is connected to the non-inverting terminal of the voltage comparator, at the same time, the output of the error amplifier is connected to the input terminal of the first inverter, and the output of the first inverter is connected to the input of the second inverter. Connected, the output of the second inverter is the first output of the PWM controller, that is, the PWM start completion signal. The inverting end of the voltage comparator is connected to the triangle wave modulation signal VM, and the output of the voltage comparator is the second output of the PWM controller, that is, the PWM signal.

The PFM controller is used to generate PFM signals, including a voltage comparator, a D flip-flop, and an AND gate. The non-inverting end of the voltage comparator is connected to the reference voltage VREF, the inverting end of the voltage comparator is connected to the feedback signal, the output end of the voltage comparator is connected to the data input D end of the D flip-flop, and the output of the voltage comparator is PFM. The first output of the controller is the PFM startup completion signal. The clock terminal of the D flip-flop is connected to the clock signal. The output Q terminal of the D flip-flop is connected to the first input of the AND gate. The second input of the AND gate is connected to the clock signal. , the output of the AND gate is the second output of the PFM controller, which is the PFM signal.

The working process after the circuit is powered on is as follows:

After the circuit is powered on, it first obtains the voltage signal VH that represents the current size, and determines the relationship between VH and VREFM. If VH>VREFM, the second output of the current detection device is high, the startup circuit generates a PWM startup signal, and the PWM controller starts. , but the system does not complete the switching between PWM and PFM at this time. After the PWM controller starts, it will output the PWM start completion signal. If VH>VREFR, and the PWM start completion signal is high, the right switching controller generates the PWM switching signal. After receiving the signal, the switching controller selects to output the PWM signal to complete the PFM and PWM switching.

If VH<VREFM, the second output of the current detection device is low, the startup circuit generates a PFM startup signal, and the PFM controller starts to startup, but at this time the system does not complete the switching between PWM and PFM. After the PFM controller is started, it will output the PFM start completion signal. If VH < VREFL, and the PFM start completion signal is high, the left switching controller generates the PFM switching signal. After receiving the signal, the switching controller selects to output the PFM signal, completing two Mode switching.

After hysteresis switching is generated with the help of three comparison thresholds, the modulation mode of the system in the switching interval (between VREFL and VREFR) is determined by the modulation mode of the system before entering the switching interval. If the load changes from light load to heavy load, the system is in the switching interval. The modulation mode is PFM modulation mode. If the load changes from heavy load to light load, the modulation mode of the system in the switching interval is PWM modulation mode. The introduction of the hysteresis interval solves the problem of frequent switching between the two modes near a single switching point, making the dual-mode control system more stable.

The above description is only a description of the preferred embodiments of the present disclosure and the technical principles applied. Persons skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to technical solutions composed of specific combinations of the above technical features, and should also cover the above-mentioned technical solutions without departing from the above-mentioned inventive concept. Other technical solutions formed by any combination of technical features or their equivalent features. For example, a technical solution is formed by replacing the above features with technical features with similar functions disclosed in the embodiments of the present disclosure (but not limited to).

Claims (8)

1. A PWM-PFM seamless switching controller with hysteresis function, comprising: a current detection device, a starting circuit, a left switching controller, a right switching controller, a PWM controller, a PFM controller, and a switching controller;

the output ports of the current detection device comprise first to third output ports, the input ports of the switching controller comprise first to fourth input ports, and the input ports of the left and right switching controllers comprise first and second input ports; the first output port of the current detection device is connected with the first input port of the left switching controller, the second output port of the current detection device is connected with the input port of the starting circuit, and the third output port of the current detection device is connected with the first input port of the right switching controller;

the output port of the starting circuit comprises a first output port and a second output port; the first output port of the starting circuit is connected with the first input port of the PWM controller, and the second output port of the starting circuit is connected with the first input port of the PFM controller;

the input ports of the PWM controller and the PFM controller comprise a first input port and a second input port, and the output ports comprise a first output port and a second output port; the first output port of the PWM controller is connected with the second input port of the right switching controller, the second output port of the PWM controller is connected with the first input port of the switching controller, the first output port of the PFM controller is connected with the second input port of the left switching controller, and the second output port of the PFM controller is connected with the second input port of the switching controller;

the output port of the right switching controller is connected with the third input port of the switching controller, the output port of the right switching controller is connected with the second input port of the PFM controller, the output port of the left switching controller is connected with the fourth input port of the switching controller, the output port of the left switching controller is connected with the second input port of the PWM controller, and the output port of the switching controller is a control signal.

2. The PWM-PFM seamless switching controller with hysteresis function according to claim 1, wherein the current detecting device is composed of a first comparator, a second comparator and a third comparator, the in-phase end of the first comparator is connected with the left threshold voltage VREFL, the reverse phase end of the first comparator is connected with the voltage signal VH representing the current magnitude, and the output end of the first comparator is the first output port of the current detecting device; the non-inverting terminal of the second comparator is connected with VH, the inverting terminal of the second comparator is connected with the switching threshold voltage VREFM, the output terminal of the second comparator is a second output terminal of the current detection device, the non-inverting terminal of the third comparator is connected with VH, the inverting terminal of the third comparator is connected with the right threshold voltage VREFR, and the output terminal of the third comparator is a third output terminal of the current detection device.

3. The PWM-PFM seamless switching controller with hysteresis function according to claim 1, wherein the start-up circuit comprises a first inverter, a first D flip-flop, and a second D flip-flop, the input port of the first inverter is the first input of the start-up circuit, the output port of the first inverter is connected to the clock port Clk of the second D flip-flop, the reset port R of the second D flip-flop is connected to the PFM off signal of the output port of the left switching controller, the data port D of the second D flip-flop is connected to the power supply VDD, the output port Q of the second D flip-flop is the second output port of the start-up circuit, the clock port Clk of the first D flip-flop is the first input of the start-up circuit, the data D port of the first D flip-flop is connected to the power supply VDD, the reset port R of the first D flip-flop is connected to the PWM off signal of the output port of the right switching controller, and the output port Q of the first D flip-flop is the first output port of the start-up circuit.

4. The PWM-PFM seamless switching controller with hysteresis function according to claim 1, wherein the left switching controller is composed of an and gate, a first input port of the and gate is a first input of the left switching controller, a second input of the and gate is a second input of the left switching controller, an output of the and gate is an output port of the left switching controller, and a PFM off signal is generated;

the right switching controller is composed of an AND gate, a first input port of the AND gate is a first input of the right switching controller, a second input of the AND gate is a second input of the right switching controller, and an output of the AND gate is an output port of the right switching controller, so that a PWM (pulse width modulation) turn-off signal is generated.

5. The PWM-PFM seamless switching controller with hysteresis function according to claim 1, wherein the switching controller comprises a second data selector and an RS flip-flop, the R end of the RS flip-flop is a third input port of the switching controller, the S end of the RS flip-flop is a fourth input port of the switching controller, the Q end of the RS flip-flop is connected with the control port of the second data selector, the 0 end of the second data selector is a first input port of the switching controller, the 1 end of the second data selector is a second input port of the switching controller, and the output of the second data selector is the output of the switching controller.

6. A PWM-PFM seamless switching control method with hysteresis function, based on the PWM-PFM seamless switching controller with hysteresis function of claim 1, characterized by comprising the following steps:

step 1, a current detection device starts to work, and detects the relation between a left switching threshold value VREFL, a switching median value VREFM and a right switching threshold value VREFR and a voltage signal VH representing the magnitude of load current;

and step 2, adjusting the working state of the system according to the change of the load current to realize the PWM-PFM seamless switching control method.

7. The method for seamless switching control of PWM-PFM with hysteresis according to claim 6, wherein the relationship in step 1 specifically includes:

when VREFR > VH > VREFM, the second output of the current detection device is high, at which time the PWM controller is started;

when VH > VREFR, the third output of the current detecting device is high, and the current detecting device is switched from PFM mode to PWM mode, i.e. the output Q end of the RS trigger in the switching controller jumps from 1 to 0, and the data selector selects the output 0 end, i.e. the first input port signal of the switching controller, i.e. the PWM control signal is output;

when VREFL < VH < VREFM, the second output of the current detection device is low, and the PFM controller is started;

when VH < VREFL, the first output of the current detecting device is high, and the PWM mode is switched to the PFM mode, i.e. the output Q end of the RS flip-flop in the switching controller jumps from 0 to 1, and the data selector selects the output 1 end, i.e. the second input port signal of the switching controller, i.e. the PFM control signal is output.

8. The method for seamless switching control of PWM-PFM with hysteresis according to claim 6, wherein the adjusting in step 2 specifically comprises:

when the load is light load, namely VH < VREFL, the PFM controller works, the PWM controller is closed, and the data selector selects the 1 input channel;

when the load is heavy, namely VH > VREFR, the PFM controller is closed, the PWM controller works, and the data selector selects 0 input channel;

when the load is between the left switching threshold VREFL and the right switching threshold VREFR, the system keeps an initial working state;

when the load is changed from light load to heavy load, the method comprises the following steps:

step S1, when the load is gradually increased so that VH is larger than VREFM, the second output of the current detection device is logic 1, and then the load current is larger than the switching median value, and the PWM controller is started;

step S2, starting the PWM controller, generating a starting response signal after starting, transmitting the starting response signal to the right switching controller, and outputting a PWM control signal to a 0 input channel of the switching controller;

step S3, when the load is gradually increased so that VH is larger than VREFR, the right switching controller outputs logic 1, and the signal is a PFM switching-off signal at the same time and is transmitted to the PFM controller so that the PFM controller is switched off;

step S4, the RS trigger of the switching controller receives the reset signal, the generated output signal is logic 0, namely, the mode selection signal received by the alternative data selector in the switching controller is logic 0, a 0 input channel is selected, a PWM control signal is output, and the conversion from the PFM mode to the PWM mode is completed;

when the load changes from heavy load to light load, the method comprises the following steps:

step D1, when the load is gradually reduced so that VH is smaller than VREFM, the second output of the current detection device is logic 0, then the load current is smaller than the switching median, and the PFM controller is started;

step D2, starting the PFM controller, generating a starting response signal after starting, transmitting the starting response signal to the left switching controller, and outputting a PFM control signal to a 1 input channel of the switching controller;

step D3, when the load is gradually reduced so that VH is smaller than VREFL, the left switching controller outputs logic 1, and the signal is a PWM off signal at the same time and is transmitted to the PWM controller so that the PWM controller is turned off;

and D4, receiving a setting signal by an RS trigger of the switching controller, wherein the generated output signal is logic 1, namely, a mode selection signal received by a data selector selected from the switching controller is logic 1, selecting 1 input channels, outputting a PFM control signal, and completing conversion from a PWM mode to a PFM mode.