WO2020015391A1

WO2020015391A1 - Control method for improving output precision of switching power supply

Info

Publication number: WO2020015391A1
Application number: PCT/CN2019/081814
Authority: WO
Inventors: 徐申; 于利民; 陶蓉蓉; 陈威宇; 孙伟锋; 陆生礼; 时龙兴
Original assignee: 东南大学
Priority date: 2018-07-17
Filing date: 2019-04-08
Publication date: 2020-01-23
Also published as: CN109004840B; CN109004840A

Abstract

A control method for improving the output precision of a switching power supply, the control method being based on a control system composed of a sampling module, a precision control module, an error calculation module, a PID module and a PWM module, wherein the control system is connected to a controlled switching power supply to form a closed loop. Mode switching is controlled by means of detecting an output voltage, wherein when the output voltage exceeds an upper limit voltage, a circuit is enabled to enter a DCM mode by means of mode switching, thereby reducing input energy and stabilizing the output voltage within an adjustment range; and when the output voltage is lower than a lower limit voltage, the circuit is enabled to enter a CCM mode by means of mode switching, thereby increasing the input energy and quickly restoring the output voltage to the adjustment range. During normal adjustment, a change in the output voltage is limited between the upper limit voltage and the lower limit voltage, such that a voltage output ripple is reduced, and the precision is improved.

Description

Control method for improving output accuracy of switching power supply

Technical field

The invention relates to a switching power supply, in particular to a control method for improving the output accuracy of a switching power supply, which can reduce the output ripple of the switching power supply and improve the output accuracy of the switching power supply.

Background technique

The switching power supply is generally used as a power source for various types of electric equipment, and converts an unadjusted AC or DC input voltage into an adjusted AC or DC output voltage. Because the switching power supply needs to adapt to different working conditions, the output precision performance requirements of the power supply are getting higher and higher. As the process size is gradually reduced, the withstand voltage of the devices in the chip is also reduced. If the power supply voltage is too large at this time, it is easy to cause the chip device to apply too much voltage or consume too much power to damage, and the power supply voltage is too low As a result, the performance of some devices may be degraded or even inoperable. When the output voltage accuracy is not high and the ripple is large, it will affect the performance of the chip. For example, the digital voltmeter requires an extremely accurate stable power supply inside to ensure the voltage / digital conversion accuracy. Another example is that the power supply in the oscilloscope must be stable to ensure the accuracy of the light spot's deflection sensitivity and scan time.

In today's power management, high power efficiency has become a necessary performance. Many high-voltage power supplies (such as flyback converters with input mains voltage) use high-efficiency soft switching technology to turn on when the drain voltage of the primary power tube drops to zero. Although this technology achieves high efficiency, because its actual on-time is different from the on-time calculated by the system theory, the output voltage ripple caused by this circuit is larger than that of a non-valley on-circuit. At the same time, in a SOC (System On Chip) system, different modules need different current capabilities. Even if the same module works at different times, its current requirements are different. This brings the current that the power chip supplies to these modules is not fixed. When the current provided by the power supply just makes the power supply work in the critical region of continuous conduction mode (CCM) and discontinuous conduction mode (DCM), and the power supply is discontinuous Structured circuit, the circuit works under CCM, there is a hysteresis between the output energy obtained and the amount of increase of the inductor current, and in DCM, because all the energy is transmitted to the output terminal in the current cycle, the output energy and the inductor current increase There is no hysteresis between the quantities. If the power supply enters DCM after working multiple CCMs, and then enters CCM after passing multiple DCMs, the output voltage ripple will be large and the output accuracy will be very low.

In addition, for the power chip with too low adjustment accuracy, when the chip works at the boundary between DCM and CCM, a load region will also appear, the output voltage ripple is large, and the accuracy is low.

Therefore, due to the increasingly high output accuracy requirements and the low output accuracy caused by the soft switching control method, a control method to improve the output voltage accuracy is proposed. It has a good effect on reducing voltage overshoot and undervoltage and reducing output ripple, and it is necessary to improve the output accuracy performance of the circuit.

The applicant's earlier application, "A Control Method for Improving the Dynamic Response of a Switching Power Supply," addresses when the system output load is switched (such as switching from heavy load to light load or light load to heavy load). The problem of undershoot or undershoot is proposed by a dynamic fast recovery algorithm, so that the output voltage can be restored to the normal adjustment range within the shortest possible time, thereby reducing the output voltage overshoot or undershoot, which is a dynamic adjustment. The system uses a valley bottom The conduction mode makes the actual switching period and the theoretically calculated switching period may differ by a maximum of half a resonance period, so the current on the inductor will be unstable compared to a non-valley-switched power supply system. At the same time, the power supply of this structure belongs to the output current interruption. Continuing structure, this structure has the zero point on the right plane, which will bring the phase delay of the compensation loop, and finally cause the problem of large output voltage ripple under the condition of stable output load.

Summary of the invention

In order to overcome the limitations and deficiencies of the prior art, the present invention proposes a control method for improving the output accuracy of a switching power supply, which belongs to steady state regulation. In response to the problem that the system has a large output ripple and low accuracy under a stable output load, a corresponding method is proposed. The algorithm can limit the overshoot and undervoltage of the output voltage within a certain range, reduce the output ripple, improve the output accuracy, and will not cause system instability in multi-mode control, making the circuit's output accuracy performance better .

In order to achieve the above object, the technical solution adopted by the present invention is: a control method for improving the output accuracy of a switching power supply, which is characterized in that it is based on a control system composed of a sampling module, an accuracy control module, an error calculation module, a PID module, and a PWM module. The control system is connected with the controlled switching power supply to form a closed loop;

The sampling module includes a sampling circuit and a sampling calculation module. The sampling circuit obtains output voltage information through the output voltage division of the switching power supply. The sampling calculation module calculates the sampling voltage Vo corresponding to the output voltage information according to the output voltage information and outputs it to the error calculation module. And precision control module;

The accuracy control module includes a voltage monitoring module and a mode switching module. The voltage monitoring module receives the sampling voltage Vo output by the sampling module and is respectively set with the set sampling voltage Vo upper limit Vomax and the sampling voltage Vo lower limit Vomin according to the size of the sampling voltage Vo. The voltage relationship determines whether to use the mode switch and choose whether to use the CCM mode or the DCM mode. The voltage monitoring module includes two comparators and a logic unit, one of which is used to compare the setting of the sampling voltage Vo and the sampling voltage Vo. The value is between the limit value Vomax and the other comparator is used to compare the size between the sampling voltage Vo and the set lower limit value Vomin of the sampling voltage Vo. The outputs of the two comparators are respectively connected to the logic unit. The comparison result of the comparator outputs the mode selection result mode_F to the mode switching module. When Vo <Vomin, the logic unit outputs mode_F = 1, which is the CCM mode. When Vo> Vomax, the logic unit outputs mode_F = 0, which is the DCM mode. When Vo Between Vomin and Vref, the mode selection result mode_F keeps the currently selected mode unchanged; the mode switching module is connected The mode selection result output by the voltage detection module, mode_F, and the output voltage information Vsense obtained by the output voltage division are compared with the output voltage information Vsense and the zero-level signal GND to generate a signal ZCMP that reacts when the inductor current drops to zero. The signal ZCMP determines The signal that the power tube is turned on in DCM mode, and the internal clock Fclk is the signal that determines the power tube on in CCM mode. The power-off signal of the power tube in DCM mode and CCM mode is determined by the output signal V _{PI of the} PID module; ZCMP The signal and the internal clock Fclk pass a two-to-one logic combination gate circuit, and generate a mode switching result control signal mode_ctl to the PWM module according to different values of the mode selection result mode_F;

The error calculation module receives the sampling voltage Vo output from the sampling module, and subtracts the difference between the sampling voltage Vo with the reference voltage Vref to obtain the current sampling voltage error e1 and outputs it to the PID module. The PID module uses the proportional parameter Kp and the integration parameter according to the sampling voltage error e1. K _i , the differential parameter K _{d is} subjected to PID calculation, and the compensation result V _{PI is obtained and} output to the PWM module for determining the peak current value of the next cycle;

The PWM module includes a PWM unit and a driving unit. The input of the PWM unit is the mode switching result control signal mode_ctl output by the mode switching module and the compensation result V _PI output by the PID module. The switching cycle Ts and the peak current Ipeak are calculated and output through the driving unit. The duty cycle waveform realizes loop control on the gate of the power tube of the switching power supply. The mode switching result mode_ctl determines the power tube on, and the compensation result V _PI determines the power tube off.

The above process is repeated, and the output voltage of the switching power supply is sampled again, and the turning on and off of the power tube of the switching power supply is cyclically controlled to make the system more stable, thereby obtaining higher output accuracy.

When the sampling voltage Vo is lower than the lower limit voltage Vomin, the voltage detection module outputs a signal mode_F to control the mode switching module to make it a constant-frequency CCM mode. In this mode, the power tube conduction is determined by the rising edge of the internal clock. Shutdown is determined by the output signal V _{PI of the} PID module. The high input power of the system causes the sampling voltage Vo to quickly rise to the reference voltage Vref and maintains this mode of operation. The system will switch to DCM mode until the sampling voltage Vo is greater than the upper limit voltage Vomax. ;

When the sampling voltage Vo is larger than the upper limit voltage Vomax, the voltage detection module output signal mode_F controls the mode switching module to make it into DCM mode. In this mode, the power tube needs to be turned on after the inductor current becomes zero. The next valley of the source voltage Vds is turned on, and the power tube is turned off is determined by the output signal V _{PI of the} PID module. In this mode, the small input power of the system causes the sampling voltage Vo to quickly fall to the reference voltage Vref, and keeps the mode working until The sampling voltage Vo is lower than the lower limit voltage Vomin, and the system will switch to CCM mode.

The two comparators in the voltage monitoring module are COMP1 and COMP3. The positive end of COMP1 is connected to Vomax, the negative end is connected to Vo, the positive end of COMP3 is connected to Vo, the negative end is connected to Vomin, and the output signal of comparator COMP1 is SMAX and the output signal SMIN of the comparator COMP3 are connected to the logic unit, and the logic unit outputs the mode selection result mode_F.

The mode switching module includes a comparator COMP, an inverter INV, an AND gate AND and two NOR gates NOR1 and NOR2. A positive input terminal of the comparator COMP is connected to a zero-level signal GND, and a negative input terminal of the comparator COMP is connected. The output voltage information Vsense obtained by dividing the voltage, the output of the comparator COMP is connected to one input terminal of the NOR gate NOR1, or the other input terminal of the NOR gate NOR1 is connected to the mode selection result mode_F and one input terminal of the AND gate AND. The other input is connected to the output of the inverter INV, the input of the inverter INV is connected to the internal clock Fclk, the output of the AND gate is connected to one input of the NOR gate NOR2, or the other input of the NOR gate NOR2 is connected to OR The output of the NOR gate NOR1 or the NOR gate NOR2 output mode switching result control signal mode_ctl.

Advantages and significant effects of the present invention:

1. The control method for improving the output accuracy of the switching power supply according to the present invention can enable the circuit to immediately enter the DCM mode by switching the mode when the output voltage exceeds the upper limit voltage, reducing the input energy, thereby stabilizing the output within the adjustment range and reducing the output voltage. At the lower limit voltage, the mode is switched to make the circuit immediately enter the CCM mode, and the input energy is increased, so that the output voltage quickly returns to the adjustment range. In the normal mediation process, the change in output voltage is limited between the upper limit voltage and the lower limit voltage, the voltage output ripple is reduced, and the accuracy is improved.

2. The control method for improving the output accuracy of the switching power supply according to the present invention can compensate for the output ripple caused by the low adjustment accuracy and the large energy change in a single step by detecting the switching of the output voltage control mode when the circuit adjustment accuracy is low. Too big a problem.

3. The invention belongs to steady-state regulation. It adds a new algorithm on the basis of dynamic regulation, and its control method for improving dynamic response is still retained. A circuit for implementing the algorithm is shown in Figure 1c.

4. The present invention is suitable for various types of switching power supply circuit structures with intermittent output current and small load output, that is, the small load means that the average current of the inductor in the CCM mode and the average current of the DCM mode cannot differ too much.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1a is a block diagram of a system structure of the control method of the present invention; Fig. 1b is a block diagram of a voltage monitoring module in Fig. 1a; Fig. 1c is an implementation structure of a mode switching module in Fig. 1a;

FIG. 2 is an application schematic diagram of judging a switching mode according to Vo;

3 is an embodiment of a closed-loop circuit structure diagram of a single-tube resonant converter according to the present invention;

4 is a simulation diagram of the relationship between the output voltage, resonance voltage, and primary current of the structure of FIG. 3 in a steady state;

FIG. 5 is a test chart of the relationship between the output voltage ripple, the resonance voltage, and the primary current in the steady state of the structure of FIG. 3; FIG.

Figure 6 is the output voltage ripple under steady state when the patent algorithm is not used in the dynamic regulation patent;

Figure 7 shows the output voltage ripple under steady state when the algorithm of this patent is adopted in the dynamic adjustment patent.

detailed description

Referring to FIG. 1 a, the present invention is based on a control system including a sampling module, an accuracy control module, an error calculation module, a PID module, and a PWM module. The control system is connected to a controlled switching power supply to form a closed loop.

The sampling module includes a sampling circuit and a sampling calculation module. The sampling circuit obtains the output voltage information through the output voltage division. The sampling calculation module obtains the output voltage information through the sampling algorithm to reflect the sampling voltage Vo reflecting the current output voltage and outputs it to the accuracy control module. With the error calculation module, the sampling here can be direct sampling or indirect sampling, and the sampling result can be analog or digital.

The precision control module includes a voltage monitoring module and a mode switching module. The voltage monitoring module determines which mode is used according to the sampled voltage Vo. The voltage monitoring module receives the sampling voltage Vo output from the sampling module and judges whether the mode switching is adopted according to the magnitude of Vo and the set Vo upper limit Vomax and Vo lower limit Vomin. Vomin and Vomax are more acceptable than Vo. The range should be narrow, that is, leave a certain margin. Mode switching means that when the change of the sampling voltage Vo exceeds an acceptable range, the single-cycle energy transmission is changed by the mode conversion, so that the sampling voltage Vo is adjusted within the set range to achieve high-precision output. The mode switching here refers to switching between the CCM and DCM modes. The output of the mode switching module is mode_ctl.

As shown in Figure 1b, the voltage monitoring module includes two comparators COMP1 and COMP3 and a logic unit, which is used to judge which mode is used. The two comparators judge the sampling voltage Vo and the lower limit voltage Vomin, the sampling voltage Vo and the upper limit voltage Vomax, respectively, and the logic unit selects the result mode_F according to the comparator result output mode. mode_F is used as the input of the mode switching module. When mode_F = 1, it is the CCM mode. When mode_F = 0, it is the DCM mode. When Vo is greater than Vomax, it outputs mode_F = 0. The mode switching module starts the DCM mode. When Vo is less than Vomin, When output mode_F = 1, the mode switching module starts CCM mode. When Vo is between Vomin and Vref, mode_F keeps the current mode unchanged.

As shown in FIG. 1c, the mode switching module receives the output signal mode_F of the voltage detection module and a signal Vsense that reflects the magnitude of the output voltage. The Vsense signal and the zero-level signal GND are compared by a comparator COMP to generate a signal ZCMP that reacts when the inductor current drops to zero. This signal and mode_F pass through the NOR gate NOR1 to obtain the DCM_ON signal. When mode_F = 0, DCM_ON = ZCMP_B ); When mode_F = 1, ZCMP is blocked and DCM_ON = 0. The internal clock signal Fclk passes through the inverter INV to obtain FclkB, and this signal and mode_F pass through the AND gate AND to output the CCM_ON signal. When mode_F = 1, CCM_ON = FclkB; when mode_F = 0, FclkB is blocked, and CCM_ON = 0. CCM_ON and DCM_ON pass the NOR gate NOR2 to obtain the signal mode_ctl which finally controls the power tube to be turned off. The mode_ctl signal is passed to the PWM module. In both modes (CCM and DCM), the shutdown signal of the power tube is determined by the output signal V _{PI of the} PID module. In short, when Mode_F = 1, Mode_ctl is determined by the internal clock Fclk. At this time, the system works in CCM mode. The system on is determined by the internal clock and the system off is determined by the output of the PID. When Mode_F = 0, Mode_ctl is determined by the comparison result between Vsense and zero level, where Vsense is the voltage reflecting the inductor current, which can be equal to IL * Rsense, IL is the inductor current, Rsense is the sampling resistor, and the comparator COMP is a zero-current comparison When the inductor current drops to zero, the system can be turned on in the next cycle, that is, the system is turned on by the current zero-crossing comparator, and turned off by the PID output signal.

When Vo <Vomin, the logic unit output mode_F = 1, and the constant-frequency CCM mode is switched in the logic unit output mode. In this mode, the power tube turn-on is determined by the rising edge of the internal clock, and the power tube turn-off is output by the PID module. It is determined that the high input power of the system causes Vo to rapidly rise to the reference voltage Vref, and maintains the mode operation until Vo is greater than the upper limit voltage Vomax. When Vo is lower than the lower limit voltage Vomin, the logic unit output mode_F = 1, and the constant-frequency CCM mode in the logic unit output mode switching. In this mode, the power transistor turn-on is determined by the rising edge of the internal clock, and the power transistor turn-off is performed by the PID. The output signal of the module determines that the high input power of the system causes Vo to quickly rise to the reference voltage Vref, and maintains this mode of operation until Vo is greater than the upper limit voltage Vomax, and the system switches to DCM mode.

When Vo ＞ Vomax, the logic unit output mode_F = 0, and the logic unit output mode is switched in the DCM mode. In this mode, the power tube needs to be turned on after the inductor current becomes zero. In Vds (the drain-source voltage of the main power tube), The next valley is turned on; the power tube is turned off by the output signal of the PID module. In this mode, the system's input low power causes Vo to quickly drop to the reference voltage Vref, and keeps the mode working until Vo is less than the lower limit voltage Vomin, and the system switches to CCM mode. When Vo is larger than the upper limit voltage Vomax, the logic unit output mode is switched in DCM mode. In this mode, the power tube needs to be turned on after the inductor current becomes zero, and then turned on at the next valley of Vds; the power tube is turned off by PID The module output signal V _{PI is} determined. By inputting small power, the output is quickly reduced to the reference voltage Vref, and the mode is maintained until Vo is smaller than the lower limit voltage Vomin.

The error calculation module calculates the current voltage error. The input of the error calculation module is the output Vo of the sampling module. The difference between the calculated reference voltage Vref and the sampling voltage Vo is the current sampling error, which is recorded as e1 and output to the PID module. PID The module performs compensation operation according to the input error e1 signal, performs PID operation through the proportional parameter Kp, the integral parameter K _i , and the differential parameter K _d , and the compensation result V _{PI is} input to the PWM module for determining the peak current value of the next cycle.

The PWM module includes a PWM unit and a driving unit. The input of the PWM unit is the mode switching result mode_ctl output by the mode switching module and the compensation result V _PI output by the PID module. After calculating the switching cycle Ts and peak current Ipeak information during control, the driving unit is used. Output the duty cycle waveform, realize the loop control on the gate of the switching power supply power tube, the switching result mode_ctl controls the switching tube on, the V _PI signal determines the switching tube off, and the drive unit should choose a circuit with a small delay time as much as possible. Then, the output voltage of the switching power supply is sampled again, and the above process is repeated to control the switching on and off of the power tube of the switching power supply to make the system more stable and obtain higher output accuracy.

Referring to Figure 2, when the load is large, for a switching power supply with intermittent output current, due to the existence of the zero point in the right half plane, when the circuit works in CCM mode, the change in its input current is in phase with the change in the energy received by the output. Hysteresis, even with the PID compensation scheme, still has a large ripple. Therefore, when the sampling voltage Vo is larger than Vomax, the system works in DCM mode by mode switching, so that the transmitted energy is reduced and Vo can be reduced as soon as possible. When the sampling voltage Vo is lower than Vomin, the system works in the CCM mode through mode switching, so that the transmission energy increases rapidly, and Vo is adjusted to a preset range. It can also be seen from the figure that the sampling voltage Vo exceeds Vomax and Vomin. This is because the energy obtained by the intermittent switching power supply structure is separated from the stored energy on the inductor current, so the output energy is obtained from the There is a certain hysteresis in the change of inductor current, which eventually brings the output voltage beyond the set range. Therefore, the setting range of the output voltage is smaller than the allowable adjustment range, leaving a certain margin.

FIG. 3 is an example of a flyback circuit. The method and system used in the present invention can also be applied to other types of switching power supply circuit structures. Here, a single-tube quasi-resonant circuit with primary side feedback is taken as an example. The single tube quasi-resonant converter has an input of 90 to 265V, an output of 20V, a maximum current of 4A, an inductance of 1.6mH, a transformer turn ratio of 104/24, and a constant voltage output. An example and the corresponding test waveform are given below to increase the working method of optimizing the output accuracy performance in this example.

The flyback converter obtains the sampling voltage Vo by sampling the output voltage. The precision control module is used to compare the sampling voltage Vo with the set Vomax and Vomin. When Vo is greater than Vomax, the output mode_F = 0, and the mode switching module starts the DCM mode. When Vo is less than Vomin, the mode_F = 1 is output, and the mode switching module starts the CCM mode. When Vo is between Vomin and Vref, mode_F remains the current mode. When Vsense is 0, ZCMP = 1, which indicates that the inductor current energy is completely released. This point is the current zero current point. This Vo compares with the zero-level signal to generate a valley-on signal. In DCM mode, the switch-on time is determined again. In the CCM mode, the ZCMP signal is shielded by mode_F = 1, and the conduction of the switch is determined by the internal clock. At the same time, the error detection module detects the error e1, sends it to the PID module, and obtains the appropriate V _PI through the PID algorithm. This value determines the peak current value of the next cycle. Finally, the compensation result V _PI is given by the PID module and the mode switching module. After the control signal mode_ctrl is calculated to obtain the switching cycle and peak current information during control, the drive unit outputs a duty cycle waveform to implement loop control on the gate of the switching power supply power tube; then the output voltage of the switching power supply is sampled again, and Repeat the above process to cycle control the switching on and off of the power tube of the switching power supply to make the system more stable, so as to obtain higher output accuracy. The corresponding simulation waveform is shown in Figure 4.

FIG. 4 is a simulation output waveform of the flyback circuit of FIG. 3 under different loads according to the present invention. Vo, Vcr, Ip refer to the output voltage respectively (the sampling circuit samples and holds the output voltage, the sampling voltage Vo reflects the output voltage, and the sampling voltage Vo is equal to the output voltage without considering the sampling delay, so Vo is the output voltage. Same below), resonance voltage and primary current. It is set here that once Vo is greater than 20V, the system works in DCM or even frequency modulation state. When the output voltage is lower than 20V, the system works in CCM mode, so that the output voltage rises as quickly as possible, and keep this mode until Vo is higher than 20V. Ideally, CCM It is evenly distributed with DCM, and its output voltage ripple is the smallest. Otherwise, it is completely adjusted by the system without any control. If the CCM and DCM work unevenly, the output ripple will be very large.

Figure 5 is a test waveform using a high-precision low-ripple control algorithm with an output voltage of 12V and a corresponding load of 1.2A. As shown in the figure, the system works in the switching state between CCM and DCM, and its output voltage ripple is within 100mV.

Figure 6 is the output voltage ripple under steady state when the patent algorithm is not used in the dynamic adjustment patent, the average value is 17.3V, and the output ripple reaches 2V.

Figure 7 shows the output voltage ripple waveform under steady state when the patented algorithm is used. The output ripple peak-to-peak value is 500mV. Through comparison, it can be seen that the effect is obvious and the ripple is reduced to the previous 1/4.

The above content is a further detailed description of the present invention in combination with specific preferred embodiments. It cannot be considered that the specific implementation of the present invention is limited to these descriptions. The invention described herein can have many variations. Such changes cannot artificially deviate from the present invention. Spirit and scope. Therefore, all changes obvious to those skilled in the art should be included in the scope of the claims.

Claims

A control method for improving the output accuracy of a switching power supply is characterized in that it is based on a control system consisting of a sampling module, an accuracy control module, an error calculation module, a PID module, and a PWM module. The control system is connected to a controlled switching power supply to form a control system. A closed loop

The sampling module includes a sampling circuit and a sampling calculation module. The sampling circuit obtains output voltage information through the output voltage division of the switching power supply. The sampling calculation module calculates the sampling voltage Vo corresponding to the output voltage information according to the output voltage information and outputs it to the error calculation module. And precision control module;

The accuracy control module includes a voltage monitoring module and a mode switching module. The voltage monitoring module receives the sampling voltage Vo output by the sampling module and is respectively set with the set sampling voltage Vo upper limit Vomax and the sampling voltage Vo lower limit Vomin according to the size of the sampling voltage Vo. The voltage relationship determines whether to use the mode switch and choose whether to use the CCM mode or the DCM mode. The voltage monitoring module includes two comparators and a logic unit, one of which is used to compare the setting of the sampling voltage Vo and the sampling voltage Vo. The value is between the limit value Vomax and the other comparator is used to compare the size between the sampling voltage Vo and the set lower limit value Vomin of the sampling voltage Vo. The outputs of the two comparators are respectively connected to the logic unit. The comparison result of the comparator outputs the mode selection result mode_F to the mode switching module. When Vo <Vomin, the logic unit outputs mode_F = 1, which is the CCM mode. When Vo> Vomax, the logic unit outputs mode_F = 0, which is the DCM mode. When Vo Between Vomin and Vref, the mode selection result mode_F keeps the currently selected mode unchanged; the mode switching module is connected The mode selection result output by the voltage detection module, mode_F, and the output voltage information Vsense obtained by the output voltage division are compared with the output voltage information Vsense and the zero-level signal GND to generate a signal ZCMP that reacts when the inductor current drops to zero. The signal ZCMP determines The signal that the power tube is turned on in DCM mode, and the internal clock Fclk is the signal that determines the power tube on in CCM mode. The power-off signal of the power tube in DCM mode and CCM mode is determined by the output signal V PI of the PID module; ZCMP The signal and the internal clock Fclk pass a two-to-one logic combination gate circuit, and generate a mode switching result control signal mode_ctl to the PWM module according to different values of the mode selection result mode_F;

The error calculation module receives the sampling voltage Vo output from the sampling module, and subtracts the difference between the sampling voltage Vo with the reference voltage Vref to obtain the current sampling voltage error e1 and outputs it to the PID module. The PID module uses the proportional parameter Kp and the integration parameter according to the sampling voltage error e1. K i , the differential parameter K d is subjected to PID calculation, and the compensation result V PI is obtained and output to the PWM module for determining the peak current value of the next cycle;

The PWM module includes a PWM unit and a driving unit. The input of the PWM unit is the mode switching result control signal mode_ctl output by the mode switching module and the compensation result V PI output by the PID module. The switching cycle Ts and the peak current Ipeak are calculated and output through the driving unit. The duty cycle waveform realizes loop control on the gate of the power tube of the switching power supply. The mode switching result mode_ctl determines the power tube on, and the compensation result V PI determines the power tube off.

The above process is repeated, and the output voltage of the switching power supply is sampled again, and the turning on and off of the power tube of the switching power supply is cyclically controlled to make the system more stable, thereby obtaining higher output accuracy.
The control method for improving the output accuracy of a switching power supply according to claim 1, characterized in that when the sampling voltage Vo is smaller than the lower limit voltage Vomin, the voltage detection module output signal mode_F controls the mode switching module to make it into a constant frequency CCM mode In this mode, the turn-on of the power tube is determined by the rising edge of the internal clock, and the turn-off of the power tube is determined by the output signal V PI of the PID module. The system input high power causes the sampling voltage Vo to quickly rise to the reference voltage Vref, and maintains the The mode works, until the sampling voltage Vo is greater than the upper limit voltage Vomax, the system will switch to DCM mode;

When the sampling voltage Vo is larger than the upper limit voltage Vomax, the voltage detection module output signal mode_F controls the mode switching module to make it into DCM mode. In this mode, the power tube needs to be turned on after the inductor current becomes zero. The next valley of the source voltage Vds is turned on, and the power tube is turned off is determined by the output signal V PI of the PID module. In this mode, the small input power of the system causes the sampling voltage Vo to quickly fall to the reference voltage Vref, and keeps the mode working until The sampling voltage Vo is lower than the lower limit voltage Vomin, and the system will switch to CCM mode.
The control method for improving the output accuracy of a switching power supply according to claim 1, wherein the two comparators in the voltage monitoring module are COMP1 and COMP3, the positive end of the comparator COMP1 is connected to Vomax, and the negative end is connected to Vo, The positive terminal of the comparator COMP3 is connected to Vo and the negative terminal is connected to Vomin. The output signal SMAX of the comparator COMP1 and the output signal SMIN of the comparator COMP3 are connected to the logic unit, and the logic unit outputs the mode selection result mode_F.
The control method for improving the output accuracy of a switching power supply according to claim 1, wherein the mode switching module comprises a comparator COMP, an inverter INV, an AND gate AND and two NOR gates NOR1 and NOR2, a comparator The positive input terminal of COMP is connected to the zero-level signal GND, the negative input terminal of comparator COMP is connected to the output voltage information Vsense obtained by dividing the voltage, and the output of comparator COMP is connected to one input terminal of NOR gate NOR1, or the other of NOR gate NOR1. One input terminal is connected to the mode selection result mode_F and one input terminal of the AND gate AND the other input terminal of the AND gate is connected to the output of the inverter INV, the input of the inverter INV is connected to the internal clock Fclk, and the output of the AND gate is connected One input terminal of the NOR gate NOR2, the other input terminal of the NOR gate NOR2 is connected to the output of the NOR gate NOR1, or the NOR gate NOR2 output mode switching result control signal mode_ctl.