A control method and circuit for a switching power supply

Abstract

In order to solve the problem that the current switching power supply control method requires the use of an error amplifier for loop gain and phase compensation, which will cause increased chip power consumption and cost, and the compensation capacitor will also occupy chip area, the present invention provides a switching power supply control method and circuit. The control method includes comparing the feedback voltage Vfb with three sawtooth waves respectively to generate three corresponding comparison voltages, setting the charging current of the variable current source to be the same as the charging current of the fixed current source, and controlling the charging current of the variable current source based on the comparison result of the second comparison voltage and the third comparison voltage. The first comparison voltage and the charging current of the variable current source are used to jointly control the first timing unit and the second timing unit to generate a drive signal, and the output voltage of the switching power supply is controlled by the drive signal. The control circuit can implement the above control method through multiple modules.

Description

Technical Field

[0001] The invention relates to a control method and circuit for a switching power supply. Background Art

[0002] Existing switching power supply control methods are categorized as pulse width modulation (PWM) and pulse frequency modulation (PFM), depending on whether the frequency changes when the duty cycle is adjusted. PFM includes constant off-time (CFT), constant on-time (COT), and modulation methods where both the on-time and off-time vary. Furthermore, depending on the feedback signal, it can be further categorized as voltage-mode and current-mode. Regardless of which control method is used, an error amplifier (EA) is required for loop gain and phase compensation. The compensation capacitors in the error amplifier occupy chip area, and the EA increases chip power consumption, driving up costs. Summary of the Invention

[0003] In order to solve the technical problems that the current control methods of switching power supplies require the use of an error amplifier for loop gain and phase compensation, the error amplifier will cause increased chip power consumption and increase costs, and the compensation capacitor in the error amplifier will also occupy chip area, the present invention provides a control method and circuit for a switching power supply.

[0004] In order to achieve the above object, the present invention adopts the following technical solutions:

[0005] A method for controlling a switching power supply is characterized in that it comprises the following steps:

[0006] S1, compares the feedback voltage Vfb of the switching power supply with the first sawtooth wave, the second sawtooth wave and the third sawtooth wave respectively to generate a corresponding first comparison voltage, a second comparison voltage U1 and a third comparison voltage U2;

[0007] The amplitude of the first sawtooth wave is greater than 0 and less than V1, V1 is greater than 2 times the reference voltage Vref, and the first comparison voltage is a square wave voltage;

[0008] The amplitude of the second sawtooth wave is greater than 0 and less than Vref;

[0009] The amplitude of the third sawtooth wave is greater than Vref and less than 2 times Vref;

[0010] S2, setting the charging current of the variable current source to be the same as the charging current of the fixed current source; comparing the second comparison voltage U1 and the third comparison voltage U2, if U1>U2, then increasing the charging current of the variable current source until U1<U2, then stopping increasing the charging current of the variable current source; if U1<U2, then decreasing the charging current of the variable current source until U1>U2, then stopping decreasing the charging current of the variable current source; if U1=U2, then keeping the charging current of the variable current source unchanged;

[0011] Wherein, the fixed current source is a charging current source of a first timing unit with a fixed time period; the variable current source is a charging current source of a second timing unit with a variable time period;

[0012] S3, the first comparison voltage and the charging current of the variable current source are used to jointly control the first timing unit and the second timing unit to generate a driving signal, and the output voltage Vout of the switching power supply is controlled by the driving signal.

[0013] Furthermore, the variable current source and the fixed current source specifically control the start of the variable current source charging time and the start time of the fixed current source charging by the rising edge of the first comparison voltage.

[0014] Furthermore, the variable current source and the fixed current source specifically control the end time of charging of the variable current source by comparing the charging potential of the variable current source with the comparison level Vx, and control the end time of charging of the fixed current source by comparing the charging potential of the fixed current source with the comparison level Vx.

[0015] The present invention also provides a switching power supply control circuit for implementing the above-mentioned switching power supply control method, which is special in that it includes a first voltage module, a second voltage module, a third voltage module, an analysis and control module, and a duty cycle adjustment module;

[0016] The first voltage module is used to compare the first sawtooth wave with the feedback voltage Vfb of the switching power supply, and generate a first comparison voltage according to the comparison result, wherein the first comparison voltage is a square wave voltage, the amplitude of the first sawtooth wave is greater than 0 and less than V1, and V1 is greater than 2 times the reference voltage Vref;

[0017] The second voltage module is used to compare the second sawtooth wave with the feedback voltage Vfb of the switching power supply and generate a second comparison voltage according to the comparison result; the amplitude of the second sawtooth wave is greater than 0 and less than Vref;

[0018] The third voltage module is used to compare the third sawtooth wave with the feedback voltage Vfb of the switching power supply and generate a third comparison voltage according to the comparison result; the amplitude of the third sawtooth wave is greater than Vref and less than 2 times Vref;

[0019] The analysis and control module is used to compare the second comparison voltage and the third comparison voltage, and control the working state of the duty cycle adjustment module according to the comparison result;

[0020] The duty cycle adjustment module includes a connected variable current source and a fixed current source, the fixed current source is a charging current source for a first timing unit with a fixed time period, and the variable current source is a charging current source for a second timing unit with a variable time period. The duty cycle adjustment module is used to control the charging current of the variable current source based on the comparison result of the second comparison voltage and the third comparison voltage in the analysis and control module, and jointly control the first timing unit and the second timing unit to generate a drive signal through the first comparison voltage and the charging current of the variable current source, and control the output voltage Vout of the switching power supply through the drive signal.

[0021] Furthermore, the first timing unit includes a D flip-flop Q2, a capacitor C4, a voltage comparator comp4, a switch S1, a switch S2 and a fixed current source;

[0022] Switch S1 and switch S2 are connected in series between a fixed current source and ground, and capacitor C4 is connected in parallel with switch S2. A voltage comparator comp4 has a non-inverting input connected to the connecting terminal of switches S1 and S2, an inverting input for inputting a comparison level Vx, and an output connected to a reset terminal of a D-type flip-flop Q2, thereby controlling the opening and closing of switch S2. A signal output of the D-type flip-flop Q2 is used to control the opening and closing of switch S1 and to output a drive signal for controlling the output voltage Vout of the switching power supply.

[0023] The second timing unit includes a D flip-flop Q1, a capacitor C3, a voltage comparator comp5, a switch S3, a switch S4, an AND gate circuit and a variable current source;

[0024] Switch S3 and switch S4 are connected in series between the variable current source and ground. Capacitor C3 is connected in parallel with switch S4. The non-inverting input of voltage comparator comp5 is connected to the connecting terminal of switches S3 and S4. The inverting input is used to input a preset comparison level. The output is connected to the reset terminal of D-type flip-flop Q1 and controls the opening and closing of switch S4. The clock control terminal of D-type flip-flop Q1 is connected to the output terminal of the first voltage module. The signal output terminal and the output terminal of the first voltage module are respectively connected to the two input terminals of an AND gate circuit. The output terminal of the AND gate circuit is used to control the opening and closing of switch S3.

[0025] The clock control terminal of the D flip-flop Q2 is connected to the signal output terminal of the D flip-flop Q1.

[0026] Furthermore, the first voltage module includes a first sawtooth wave generator and a voltage comparator comp1; the non-inverting input terminal of the voltage comparator comp1 is connected to the output terminal of the first sawtooth wave generator, the inverting input terminal is connected to the feedback voltage Vfb of the switching power supply, and the output terminal of the voltage comparator comp1 is connected to the clock control terminal of the D flip-flop Q1 in the second timing unit.

[0027] The second voltage module includes a second sawtooth wave generator, a voltage comparator comp2 and a first filtering unit. The non-inverting input terminal of the voltage comparator comp2 is connected to the output terminal of the second sawtooth wave generator, and the inverting input terminal is connected to the feedback voltage Vfb of the switching power supply. The input side of the first filtering unit is connected to the output terminal of the voltage comparator comp2, and the output side is connected to the analysis and control module.

[0028] The third voltage module includes a third sawtooth wave generator, a voltage comparator comp3 and a second filtering unit. The non-inverting input end of the voltage comparator comp3 is connected to the feedback voltage Vfb of the switching power supply, and the inverting input end is connected to the third sawtooth wave generator. The input side of the second filtering unit is connected to the output end of the voltage comparator comp3, and the output side is connected to the analysis and control module.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The control method of the switching power supply proposed in the present invention can control the charging current of the second timing unit according to the comparison result of the second comparison voltage and the third comparison voltage through simple comparison calculation, thereby completing the control. The control method has low cost and does not require the participation of a compensation capacitor, thereby avoiding the compensation capacitor occupying the chip area and reducing the chip power consumption.

[0031] 2. The control circuit of the switching power supply proposed in the present invention does not require the use of an error amplifier for loop gain and phase compensation, and does not require a compensation network. By analyzing the joint action of the control module and the duty cycle adjustment module, the feedback voltage output by the switching power supply can be adjusted, thereby achieving the purpose of adjusting the output voltage of the switching power supply so that the output voltage of the switching power supply meets the design value requirements, effectively saving the chip area occupied by the compensation capacitor, while reducing the chip power consumption, thereby reducing the cost.

[0032] 3. In the second voltage module and the third voltage module of the present invention, corresponding comparison voltages can be generated through the processing results of the voltage comparator comp2 and the voltage comparator comp3 via the first filtering unit and the second filtering unit. By analyzing and comparing the comparison voltages generated by the second voltage module and the third voltage module through the control module, and adjusting the charging current of the second timing unit in the duty cycle adjustment module according to the comparison result, the purpose of adjusting the output voltage of the switching power supply can be achieved, with convenient control and simple logic. In addition, the control system of the present invention does not require the design of a high-bandwidth operational amplifier, and the system response speed is not limited by the operational amplifier bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic flowchart of the control method of the switching power supply of the present invention;

[0034] Figure 2 It is a schematic diagram of the control circuit of the switching power supply of the present invention;

[0035] Figure 3 It is a schematic diagram of the control circuit of the switching power supply corresponding to the embodiment of the present invention;

[0036] Figure 4 It is a schematic diagram of the duty cycle adjustment module;

[0037] Figure 5 It is a waveform diagram of the control circuit parameters of the switching power supply when Vref < Vfb < 2Vref;

[0038] Figure 6 It is a waveform diagram of the control circuit parameters of the switching power supply when 0 < Vfb < Vref;

[0039] Figure 7 It is a waveform diagram of the control circuit parameters of the switching power supply after the feedback voltage Vfb is adjusted in cooperation with the analysis control module and the duty cycle adjustment module;

[0040] Figure 8 It is a waveform diagram of the switching power supply parameters after the feedback voltage Vfb is adjusted in cooperation with the analysis control module and the duty cycle adjustment module.

[0041] Where: 1 - First voltage module, 2 - Second voltage module, 3 - Third voltage module, 4 - Analysis control module, 5 - Duty cycle adjustment module, 501 - First timing unit, 502 - Second timing unit, 6 - Boost topology, 7 - First sawtooth generator, 8 - Second sawtooth generator, 9 - Third sawtooth generator, 10 - AND gate circuit, 11 - Control circuit of the switching power supply. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0043] The present invention proposes a method and circuit for controlling a switching power supply without an error amplifier, so that the method and circuit can meet design requirements and are suitable for controlling the output voltages of different switching power supplies.

[0044] like Figure 1 As shown, the present invention proposes a control method for a switching power supply, the specific steps are:

[0045] S1, compares the feedback voltage Vfb of the switching power supply with the first sawtooth wave, the second sawtooth wave and the third sawtooth wave respectively to generate a corresponding first comparison voltage, a second comparison voltage U1 and a third comparison voltage U2;

[0046] The amplitude of the first sawtooth wave is greater than 0 and less than V1, V1 is greater than 2 times the reference voltage Vref, and the first comparison voltage is a square wave voltage;

[0047] The amplitude of the second sawtooth wave is greater than 0 and less than Vref;

[0048] The amplitude of the third sawtooth wave is greater than Vref and less than 2 times Vref;

[0049] S2, setting the charging current of the variable current source to be the same as the charging current of the fixed current source; comparing the second comparison voltage U1 and the third comparison voltage U2, if U1>U2, then increasing the charging current of the variable current source until U1<U2, then stopping increasing the charging current of the variable current source; if U1<U2, then decreasing the charging current of the variable current source until U1>U2, then stopping decreasing the charging current of the variable current source; if U1=U2, then keeping the charging current of the variable current source unchanged;

[0050] Wherein, the fixed current source is a charging current source of a first timing unit with a fixed time period; the variable current source is a charging current source of a second timing unit with a variable time period;

[0051] S3, the first comparison voltage and the charging current of the variable current source are used to jointly control the first timing unit and the second timing unit to generate a driving signal, and the output voltage Vout of the switching power supply is controlled by the driving signal.

[0052] Furthermore, the starting time of charging for both the variable current source and the fixed current source can be controlled by the rising edge of the first comparison voltage. The ending time of charging can be controlled by comparing the charging potential of the variable current source with the comparison level Vx, while the ending time of charging for the fixed current source can be controlled by comparing the charging potential of the fixed current source with the comparison level Vx.

[0053] like Figure 2 As shown, the present invention also provides a switching power supply control circuit capable of implementing the above-mentioned switching power supply control method, comprising a first voltage module 1, a second voltage module 2, a third voltage module 3, an analysis and control module 4, and a duty cycle adjustment module 5. The first voltage module 1 is configured to compare a first sawtooth wave with a feedback voltage Vfb of the switching power supply and generate a first comparison voltage based on the comparison result. The first comparison voltage is a square wave voltage, and the amplitude of the first sawtooth wave is greater than 0 and less than V1, and V1 is greater than twice the reference voltage Vref. The second voltage module 2 is configured to compare a second sawtooth wave with the feedback voltage Vfb of the switching power supply and generate a second comparison voltage based on the comparison result. The amplitude of the second sawtooth wave is greater than 0 and less than Vref. The third voltage module 3 is configured to compare a third sawtooth wave with the feedback voltage Vfb of the switching power supply and generate a third comparison voltage based on the comparison result. The amplitude of the third sawtooth wave is greater than Vref and less than twice Vref.

[0054] The analysis and control module 4 is configured to compare the second comparison voltage and the third comparison voltage, and control the working state of the duty cycle adjustment module 5 according to the comparison result.

[0055] The duty cycle adjustment module 5 includes a variable current source and a fixed current source connected to each other. The fixed current source is a charging current source of the first timing unit 501 with a fixed time period, and the variable current source is a charging current source of the second timing unit 502 with a variable time period. The duty cycle adjustment module 5 is used to control the charging current of the variable current source according to the comparison result of the second comparison voltage and the third comparison voltage in the analysis control module 4, and jointly control the first timing unit 501 and the second timing unit 502 to generate a drive signal through the first comparison voltage and the charging current of the variable current source, and control the output voltage Vout of the switching power supply through the drive signal.

[0056] Similarly, the switching power supply control circuit provided by the present invention can be applied to a variety of switching power supplies. Below, a boost switching power supply is used as an example to specifically illustrate the control method and circuit of the present invention:

[0057] like Figure 3As shown, a boost switching power supply includes a boost topology structure 6 and a control circuit 11 of the switching power supply. The boost topology structure 6 is an existing structure. After the feedback voltage Vfb is regulated by the control circuit 11 of the switching power supply, a drive signal Ndriver is sent to the NMOS transistor M2, and a drive signal Pdriver is sent to the PMOS transistor M1 through the buffer, thereby controlling the output voltage Vout of the boost switching power supply.

[0058] Corresponding to Figure 2 As shown, the control circuit 11 of the switching power supply includes a first voltage module 1 , a second voltage module 2 , a third voltage module 3 , an analysis and control module 4 and a duty cycle adjustment module 5 .

[0059] The first voltage module 1 includes a first sawtooth wave generator 7 and a voltage comparator comp1. The non-inverting input of the voltage comparator comp1 is connected to the output of the first sawtooth wave generator 7, and the inverting input is connected to the feedback voltage Vfb of the boost topology 6. The first sawtooth wave generator 7 can generate a sawtooth wave with an amplitude of 0-V1, where V1 is a set value greater than twice the reference voltage Vref. After comparing the feedback voltage Vfb of the boost topology 6 with the sawtooth wave sawtooth1 generated by the first sawtooth wave generator 7, a first comparison voltage is generated. This first comparison voltage is a square wave fb_comp with a certain duty cycle. However, this first comparison voltage cannot adjust the output voltage Vout of the boost switching power supply to the designed value. The analysis control module 4 and the duty cycle adjustment module 5 must work together to achieve the designed output voltage Vout.

[0060] The second voltage module 2 includes a second sawtooth wave generator 8, a voltage comparator comp2, and a first filtering unit. The non-inverting input of the voltage comparator comp2 is connected to the output of the second sawtooth wave generator 8, and the inverting input is connected to the feedback voltage Vfb of the boost topology 6. In one embodiment of the present invention, the first filtering unit includes a resistor R3 and a capacitor C1. One end of the resistor R3 is connected to the output of the voltage comparator comp2, and the other end is connected in parallel with the capacitor C1 and then connected to the analysis and control module 4. The third voltage module 3 includes a third sawtooth wave generator 9, a voltage comparator comp3, and a second filtering unit. The second filtering unit includes a resistor R4 and a capacitor C2. The non-inverting input of the voltage comparator comp3 is connected to the feedback voltage Vfb of the boost topology 6, and the inverting input is connected to the third sawtooth wave generator 9. One end of the resistor R4 is connected to the output of the voltage comparator comp3, and the other end is connected in parallel with the capacitor C2 and then connected to the analysis and control module 4.

[0061] Among them, the first filtering unit and the second filtering unit can be of the same composition or different compositions. In addition, the first filtering unit and the second filtering unit can also be composed of other units with filtering functions, which does not affect the protection scope of this application.

[0062] In the above embodiment of the present invention, when adjusting the charging current I2 of the second timing unit 502, whether increasing the charging current I2 or decreasing the charging current I2, the adjustment is performed in a step-by-step manner. In other embodiments of the present invention, other adjustment methods can also be used, as long as the adjustment can be performed and the adjustment effect is achieved.

[0063] like Figure 4 FIG. 5 is a schematic diagram of a duty cycle adjustment module 5, comprising a first timing unit 501 and a second timing unit 502. The first timing unit 501 comprises a D flip-flop Q2, a capacitor C4, a voltage comparator comp4, a switch S1, a switch S2, and a fixed current source. Switches S1 and S2 are connected in series between the fixed current source and ground. Capacitor C4 is connected in parallel with switch S2. The non-inverting input of the voltage comparator comp4 is connected to the terminal where switches S1 and S2 are connected. The inverting input is used to input a preset comparison level Vx. The output is connected to the reset terminal of the D flip-flop Q2 and controls the opening and closing of the switch S2. The signal output of the D flip-flop Q2 is used to control the opening and closing of the switch S1 and to output a drive signal for controlling the boost topology 6. The second timing unit 502 includes a D flip-flop Q1, a capacitor C3, a voltage comparator comp5, a switch S3, a switch S4, an AND gate circuit 10, and a variable current source. The variable current source is used to provide a charging current I2. Switches S3 and S4 are connected in series between the variable current source and ground. Capacitor C3 is connected in parallel with switch S4. The non-inverting input of the voltage comparator comp5 is connected to the connecting terminal of switches S3 and S4. The inverting input is used to input a preset comparison level. The output is connected to the reset terminal of the D flip-flop Q1 and controls the opening and closing of switch S4. The negative terminal of capacitor C3 is grounded. The clock control terminal of the D flip-flop Q1 is connected to the output terminal of the voltage comparator comp1. The signal output terminal and the output terminal of the voltage comparator comp1 are respectively connected to the two input terminals of the AND gate circuit 10. The output terminal of the AND gate circuit 10 is used to control the opening and closing of switch S3. The clock control terminal of the D flip-flop Q2 is connected to the signal output terminal of the D flip-flop Q1.

[0064] Based on the control circuit of the switching power supply in the above embodiment, the control method of the switching power supply of the present invention is adopted, and the specific steps are as follows:

[0065] (1) After the boost switching power supply system is powered on and the soft start is completed, it is determined whether the system is stable after about 500μS. After the system is stable, the subsequent control method is continued.

[0066] (2) generating a first comparison voltage through the first voltage module 1, and inputting the first comparison voltage into the second timing unit 502;

[0067] Figure 4 In the example, square wave fb_comp enters D flip-flop Q1. Vdd is a high level within the control circuit. The rising edge of square wave fb_comp sets the output of D flip-flop Q1's signal output terminal Q high. The square wave fb_comp is ANDed with the output of Q1's signal output terminal Q to control switch S3 to close, charging capacitor C3. When the potential of capacitor C3 exceeds the comparison level Vx, the output T_off of voltage comparator comp5 goes high, clearing D flip-flop Q1 and closing switch S4 to discharge capacitor C3. The comparison level Vx is manually set. Simultaneously, the rising edge of square wave fb_comp passes through D flip-flops Q1 and Q2, setting the output of D flip-flop Q2's signal output terminal Q high. This in turn closes switch S1, charging capacitor C4. When the potential of capacitor C4 exceeds the comparison level Vx, the output Ton_off of voltage comparator comp4 goes high, clearing D flip-flop Q2 and closing switch S2 to discharge capacitor C4. The first and second timing units 501 and 502 begin operating simultaneously, but do not end simultaneously.

[0068] (3) The second sawtooth wave sawtooth2 generated by the second sawtooth wave generator 8 has an amplitude ranging from 0 to the reference voltage Vref, and the third sawtooth wave sawtooth3 generated by the third sawtooth wave generator 9 has an amplitude ranging from the reference voltage Vref to twice the reference voltage Vref. The feedback voltage Vfb is input to the control circuit 11 of the switching power supply.

[0069] A second comparison voltage U1 is generated by the second voltage module 2. If the feedback voltage of the boost topology 6 is within the range of 0 to the reference voltage Vref, then U1>0; otherwise, U1=0.

[0070] A third comparison voltage U2 is generated by the third voltage module 3. If the boost topology feedback voltage is within the range of the reference voltage Vref to twice the reference voltage 2Vref, then U2>0; otherwise, U2=0.

[0071] (4) The charging current I1 of the first timing unit 501 and the charging current I2 of the second timing unit 502 are initially the same. During control, the charging current I2 of the second timing unit 502 is controlled by the analysis control module 4 based on the comparison result of the second comparison voltage U1 and the third comparison voltage U2. The details are as follows:

[0072] The amplitude of the second sawtooth wave sawtooth2 generated by the second sawtooth wave generator 8 ranges from 0 to the reference voltage Vref, and the amplitude of the third sawtooth wave sawtooth3 generated by the third sawtooth wave generator 9 ranges from the reference voltage Vref to twice the reference voltage Vref. The feedback voltage Vfb is input to the control circuit 11 of the switching power supply.

[0073] As Figure 6 shown, when 0V < Vfb < Vref, the feedback voltage Vfb intersects with sawtooth2, and the first comparison signal A output by the voltage comparator comp2 will generate a certain duty cycle. After being filtered by the first filtering unit, a second comparison voltage U1 is generated. At this time, the second comparison signal B output by the voltage comparator comp3 is at a low level L, and the third comparison voltage U2 generated after being filtered by the second filtering unit is 0V. At this time, U1 > U2, indicating that the output voltage Vout is less than the designed value, and the duty cycle should be increased, that is, it is necessary to reduce the time period T of the second timing unit 502. According to T = UC / I, through analysis by the control module 4, it is determined that the charging current I2 of the second timing unit 502 in the duty cycle adjustment module 5 needs to be increased. Through analysis by the control module 4, the charging current I2 is increased by a mA. For example, a = 0.1 mA. At this time, U1 and U2 change. After a certain time, such as 200 us, it is determined again. If U1 > U2, then continue to adjust I2 to increase it by a mA until U1 < U2, and then stop adjusting the charging current I2 to keep the charging current I2 unchanged, and the system works normally.

[0074] As Figure 5 shown, when Vref < Vfb < 2Vref, the feedback voltage Vfb intersects with sawtooth3, and the second comparison signal B will generate a certain duty cycle. After being filtered, the third comparison voltage U2 is generated. At this time, the first comparison signal A is at a low level L, and U1 is 0V. At this time, U1 < U2, indicating that the output voltage Vout is greater than the designed value, and the duty cycle should be reduced, that is, it is necessary to increase the time period T of the second timing unit 502. According to T = UC / I, through analysis by the control module 4, it is determined that the charging current I2 of the second timing unit 502 in the duty cycle adjustment module 5 should be reduced. Through analysis by the control module 4, it is reduced by b mA. For example, b = 0.1 mA. At this time, U1 and U2 change. After a certain time, such as 200 us, it is determined again. If U1 < U2, then continue to adjust and reduce by b mA until U1 > U2, and then stop adjusting the charging current I2, and the system works normally. The signal output terminal of the D flip - flop Q2 in the first timing unit 501 outputs a driving signal Ndriver.

[0075] If U1 = U2, then through analysis by the control module 4, the charging current I2 of the second timing unit 502 is controlled to remain unchanged.

[0076] When the system is powered on, the Figure 5 or Figure 6 In the case shown, the analysis control module 4 and the duty cycle adjustment module 5 can cooperate to adjust the feedback voltage Vfb to Figure 7 As shown in the waveform, at this time, the first comparison signal A and the second comparison signal B both have a certain duty cycle, U1>0, U2>0, so that the output voltage Vout reaches the designed value.

[0077] In addition, the charging current I1 of the first timing unit 501 , the capacitance of the capacitor C4 , and the comparison level Vx are all set according to the formula T=UC / I.

[0078] like Figure 8 As shown, by simulating the circuit of the switching power supply system in the embodiment of the present invention, the output voltage Vout waveform, the feedback voltage Vfb waveform, the second comparison voltage U1 waveform, the third comparison voltage U2 waveform, and the inductor IL current waveform are obtained. The boost switching power supply system is adjusted by the control circuit 11 of the switching power supply. It can be seen that the second comparison voltage U1 and the third comparison voltage U2 are very close, indicating that the output voltage accuracy is within the design range. At the same time, when SW (the voltage signal at the right end of the inductor IL) is low, it indicates that the Nmos tube M2 is turned on, the Pmos tube M1 is turned off, the inductor IL current increases, and the output voltage Vout and the feedback voltage Vfb decrease. When SW is high, it indicates that the Nmos tube M2 is turned off, the Pmos tube M1 is turned on, the inductor IL current decreases, and the output voltage Vout and the feedback voltage Vfb increase. Obviously, the control circuit of the switching power supply proposed in the present invention does not require the use of an error amplifier for loop gain and phase compensation, and does not require a compensation network. By analyzing the joint action of the control module and the duty cycle adjustment module, the feedback voltage output by the switching power supply can be adjusted, thereby achieving the purpose of adjusting the output voltage of the switching power supply, so that the output voltage of the switching power supply meets the design value requirements, effectively saving the area of the chip occupied by the compensation capacitor, while reducing the chip power consumption, thereby reducing the cost.

[0079] In the above embodiment, the control circuit of the switching power supply is used in a boost switching power supply as an example for explanation. The control circuit of the switching power supply of the present invention can also be used in other types of switching power supplies to control the switching power supply to ensure that its output voltage meets the design requirements.

[0080] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for controlling a switching power supply, characterized in that: The following steps are involved: S1, compares the feedback voltage Vfb of the switching power supply with the first sawtooth wave, the second sawtooth wave and the third sawtooth wave respectively to generate a corresponding first comparison voltage, a second comparison voltage U1 and a third comparison voltage U2; The amplitude of the first sawtooth wave is greater than 0 and less than V1, V1 is greater than 2 times the reference voltage Vref, and the first comparison voltage is a square wave voltage; The amplitude of the second sawtooth wave is greater than 0 and less than Vref; The amplitude of the third sawtooth wave is greater than Vref and less than 2 times Vref; S2, setting the charging current of the variable current source to be the same as the charging current of the fixed current source; comparing the second comparison voltage U1 and the third comparison voltage U2, if U1>U2, then increasing the charging current of the variable current source until U1<U2, then stopping increasing the charging current of the variable current source; if U1<U2, then decreasing the charging current of the variable current source until U1>U2, then stopping decreasing the charging current of the variable current source; if U1=U2, then keeping the charging current of the variable current source unchanged; Wherein, the fixed current source is a charging current source of a first timing unit (501) with a fixed time period; and the variable current source is a charging current source of a second timing unit (502) with a variable time period; S3, the first comparison voltage and the charging current of the variable current source are used to jointly control the first timing unit (501) and the second timing unit (502) to generate a driving signal, and the output voltage Vout of the switching power supply is controlled by the driving signal.

2. A method for controlling a switching power supply according to claim 1, characterized in that: Specifically, the variable current source and the fixed current source control the start of the variable current source charging time and the start time of the fixed current source charging by the rising edge of the first comparison voltage.

3. The method for controlling a switching power supply according to claim 1, wherein: Specifically, the variable current source and the fixed current source control the end time of charging of the variable current source by comparing the charging potential of the variable current source with the comparison level Vx; and control the end time of charging of the fixed current source by comparing the charging potential of the fixed current source with the comparison level Vx.

4. A control circuit for a switching power supply, for implementing the control method for a switching power supply according to any one of claims 1 to 3, characterized in that: It comprises a first voltage module (1), a second voltage module (2), a third voltage module (3), an analysis and control module (4) and a duty cycle adjustment module (5); The first voltage module (1) is used to compare the first sawtooth wave with the feedback voltage Vfb of the switching power supply, and generate a first comparison voltage according to the comparison result, wherein the first comparison voltage is a square wave voltage, the amplitude of the first sawtooth wave is greater than 0 and less than V1, and V1 is greater than 2 times the reference voltage Vref; The second voltage module (2) is used for comparing the second sawtooth wave with the feedback voltage Vfb of the switching power supply and generating a second comparison voltage according to the comparison result; the amplitude of the second sawtooth wave is greater than 0 and less than Vref; The third voltage module (3) is used to compare the third sawtooth wave with the feedback voltage Vfb of the switching power supply, and generate a third comparison voltage according to the comparison result; the amplitude of the third sawtooth wave is greater than Vref and less than 2 times Vref; The analysis and control module (4) is used to compare the second comparison voltage and the third comparison voltage, and control the working state of the duty cycle adjustment module (5) according to the comparison result; The duty cycle adjustment module (5) comprises a variable current source and a fixed current source connected to each other, the fixed current source being a charging current source of a first timing unit (501) having a fixed time period, and the variable current source being a charging current source of a second timing unit (502) having a variable time period, the duty cycle adjustment module (5) being used to control the charging current of the variable current source according to the comparison result of the second comparison voltage and the third comparison voltage in the analysis control module (4), and to jointly control the first timing unit (501) and the second timing unit (502) to generate a driving signal through the first comparison voltage and the charging current of the variable current source, and to control the output voltage Vout of the switching power supply through the driving signal.

5. A switching power supply control circuit as claimed in claim 4, characterized in that: The first timing unit (501) includes a D flip-flop Q2, a capacitor C4, a voltage comparator comp4, a switch S1, a switch S2 and a fixed current source; Switch S1 and switch S2 are connected in series between a fixed current source and ground, and capacitor C4 is connected in parallel with switch S2. A voltage comparator comp4 has a non-inverting input connected to the connecting terminal of switches S1 and S2, an inverting input for inputting a comparison level Vx, and an output connected to a reset terminal of a D-type flip-flop Q2, thereby controlling the opening and closing of switch S2. A signal output of the D-type flip-flop Q2 is used to control the opening and closing of switch S1 and to output a drive signal for controlling the output voltage Vout of the switching power supply. The second timing unit (502) includes a D flip-flop Q1, a capacitor C3, a voltage comparator comp5, a switch S3, a switch S4, an AND gate circuit (10) and a variable current source; The switch S3 and the switch S4 are connected in series between the variable current source and the ground, the capacitor C3 is connected in parallel with the switch S4, the non-inverting input terminal of the voltage comparator comp5 is connected to the end where the switch S3 and the switch S4 are connected, the inverting input terminal is used to input a preset comparison level, the output terminal is connected to the reset terminal of the D flip-flop Q1, and the switch S4 is controlled to be opened and closed at the same time; the clock control terminal of the D flip-flop Q1 is connected to the output terminal of the first voltage module (1), the signal output terminal and the output terminal of the first voltage module (1) are respectively connected to the two input terminals of the AND gate circuit (10), and the output terminal of the AND gate circuit (10) is used to control the switch S3 to be opened and closed; The clock control terminal of the D flip-flop Q2 is connected to the signal output terminal of the D flip-flop Q1.

6. A switching power supply control circuit according to claim 4 or 5, characterized in that: The first voltage module (1) comprises a first sawtooth wave generator (7) and a voltage comparator comp1; the non-inverting input terminal of the voltage comparator comp1 is connected to the output terminal of the first sawtooth wave generator (7), the inverting input terminal is connected to the feedback voltage Vfb of the switching power supply, and the output terminal of the voltage comparator comp1 is connected to the clock control terminal of the D flip-flop Q1 in the second timing unit (502); The second voltage module (2) comprises a second sawtooth wave generator (8), a voltage comparator comp2 and a first filtering unit, wherein the non-inverting input end of the voltage comparator comp2 is connected to the output end of the second sawtooth wave generator (8), the inverting input end is connected to the feedback voltage Vfb of the switching power supply, the input side of the first filtering unit is connected to the output end of the voltage comparator comp2, and the output side is connected to the analysis and control module (4); The third voltage module (3) comprises a third sawtooth wave generator (9), a voltage comparator comp3 and a second filtering unit, wherein the non-inverting input end of the voltage comparator comp3 is connected to the feedback voltage Vfb of the switching power supply, the inverting input end is connected to the third sawtooth wave generator (9), the input side of the second filtering unit is connected to the output end of the voltage comparator comp3, and the output side is connected to the analysis and control module (4).

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