CN117394661B - Conduction time generation circuit and switching converter - Google Patents
Conduction time generation circuit and switching converter Download PDFInfo
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- CN117394661B CN117394661B CN202311676802.XA CN202311676802A CN117394661B CN 117394661 B CN117394661 B CN 117394661B CN 202311676802 A CN202311676802 A CN 202311676802A CN 117394661 B CN117394661 B CN 117394661B
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
- H02M3/1566—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators with means for compensating against rapid load changes, e.g. with auxiliary current source, with dual mode control or with inductance variation
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Abstract
The invention provides a conduction time generation circuit and a switching converter, wherein the conduction time generation circuit comprises: the slope module generates a slope signal according to the driving signal of the main power tube; the time adjustment module is used for generating a time adjustment signal for adjusting the on time based on the preset on time according to the change of the load; the time signal generation module generates a second time signal according to the ramp signal, the time adjustment signal and the output feedback signal, wherein the second time signal characterizes the adjusted conduction time of the switching converter, and the adjusted conduction time and the load are in positive correlation. The on-time generating circuit provided by the invention can adjust the constant on-time of the switching converter based on the change of the load, thereby realizing the constant frequency of the switching converter. Meanwhile, the on-time generating circuit provided by the invention also adjusts the on-time adaptively according to the change of the output voltage so as to realize the constant frequency of the switching converter.
Description
Technical Field
The invention belongs to the technical field of power electronics, and particularly relates to a conduction time generation circuit and a switching converter.
Background
The BUCK converter of COT (constant on time) architecture has the advantages of being fast in transient response, simple in structure, high in light load efficiency and the like, and becomes a research hot spot in the field of DC-DC switching power supplies. The on time Ton of the main power tube is constant in the COT control mode, and the duty ratio is changed by adjusting the off time Toff, so that stable control of output voltage is realized. However, since there is no fixed clock inside the BUCK converter, the COT control mode actually belongs to a variable frequency control mode. In practice, the on-resistance of the power tube shifts the frequency of the BUCK converter when the load changes.
In order to solve the problem, the prior art adopts a COT (chip on board) control BUCK converter modulated by a PLL (phase locked loop) to realize locking of a switching frequency, but in a double-loop system formed by the BUCK converter and the PLL, in order to simultaneously maintain stability of the BUCK system and the PLL system, the bandwidth of the PLL needs to be far lower than that of the BUCK, so that the frequency recovery speed of the BUCK system in transient response is reduced, and the area and the complexity of a chip are increased.
Therefore, there is a need in the art for a simple on-time generation circuit to replace the PLL system to solve the problem of frequency offset of the BUCK converter controlled by the COT.
Disclosure of Invention
In order to solve the technical problem that the frequency of a COT-controlled BUCK converter in the prior art is offset along with the change of a load, the invention provides a conduction time generation circuit and a switching converter, wherein the conduction time generation circuit is applied to the COT-controlled switching converter, and the switching converter comprises a main power tube and a freewheel tube, and comprises:
the slope module generates a slope signal according to the driving signal of the main power tube;
the time adjustment module is used for generating a time adjustment signal according to the change of the load, wherein the time adjustment signal is used for adjusting the conduction time of the switching converter on the basis of the preset conduction time, and the preset conduction time represents the conduction time of the switching converter when the load is equal to zero;
the time signal generation module is used for generating a second time signal according to the slope signal, the time adjustment signal and the output feedback signal, wherein the output feedback signal represents the output voltage of the switching converter, the second time signal represents the adjusted conduction time of the switching converter, and the adjusted conduction time and the load are in positive correlation.
Further, when the load is equal to zero, the time signal generating module generates a first time signal according to the ramp signal and the output feedback signal, wherein the first time signal represents the preset on-time.
Further, the time adjustment signal controls the change ratio of the on time to be in direct proportion to the load.
Further, the magnitude of the preset conduction time is in a direct proportion relation with the output voltage of the switching converter, and the time adjustment signal controls the change ratio of the conduction time to be in an inverse proportion relation with the output voltage of the switching converter.
Further, the change ratio of the on time controlled by the time adjustment signal satisfies the formula:wherein I represents the load size, R represents the resistance of the shunt tube, and V represents the output voltage.
Further, the time signal generating module is configured to superimpose the time adjustment signal and the ramp signal to obtain a superimposed signal, an average slope of the superimposed signal is smaller than a slope of the ramp signal, and the time signal generating module is configured to generate the second time signal according to the superimposed signal and the output feedback signal.
Further, the ramp module obtains a first current signal according to the input voltage of the switching converter, and integrates the first current signal to obtain a first voltage signal when the driving signal in an effective state drives the main power tube to be conducted, wherein the first voltage signal represents the ramp signal.
Further, the time adjustment module comprises a conversion unit, a first adjustment unit and a second adjustment unit, wherein,
the conversion unit obtains a second current signal according to the change of the load;
the first regulating unit controls the first current signal to be changed into a difference current signal of the first current signal and the second current signal;
the second adjusting unit controls the change time length of the first current signal to be a preset time length, the integral value of the difference current signal in the preset time length is the time adjusting signal, and the preset time length is smaller than the preset conduction time.
Preferably, the ramp module includes a first current source unit and a first capacitor, the first current source unit generates the first current signal, and the first current signal flows to the first capacitor when the driving signal in an active state drives the main power tube to be turned on.
Preferably, the switching unit comprises a fourth switching tube, the first regulating unit comprises a fifth switching tube and a sixth switching tube constituting a second current mirror, the second regulating unit comprises a seventh switching tube, wherein,
the grid electrode of the fourth switching tube receives control voltage representing the load size, the drain electrode of the fourth switching tube is connected with the reference end of the second current mirror, the seventh switching tube is connected between the output end of the second current mirror and the first current source unit, and the size ratio of the fifth switching tube to the sixth switching tube is N: and 1, the conduction time of the seventh switching tube is the preset duration.
Preferably, the gate of the shunt tube receives an input voltage of the switching converter, the second adjusting unit further includes an inverter chain formed by connecting a plurality of inverters in series, an input end of the inverter chain receives a driving signal in an effective state, an output end of the inverter chain is connected with the gate of the seventh switching tube, and the preset duration and the input voltage are in a negative correlation.
Preferably, the time signal generating module includes:
the comparison unit is used for comparing the superposition signal and the output feedback signal to generate a second turn-off trigger signal, and the second turn-off trigger signal represents the turn-off time of the main power tube;
and the logic unit is used for generating the second time signal after performing logic processing on the second turn-off trigger signal.
A switching converter comprising the on-time generating circuit described above.
A control method of on time is applied to a COT controlled switching converter, and comprises the following steps:
acquiring a preset conduction time, wherein the preset conduction time represents the conduction time of the switching converter when the load of the switching converter is zero;
acquiring a time adjustment signal according to a load change signal, wherein the load change signal represents the change amount of the load of the switching converter;
and adjusting the conduction time of the switching converter on the basis of the preset conduction time according to the time adjustment signal, wherein the adjusted conduction time and the load are in positive correlation, and the preset conduction time represents the conduction time of the switching converter when the load is equal to zero.
Further, the time adjustment signal controls the change ratio of the on time to be in direct proportion to the load;
further, the magnitude of the preset conduction time is in a direct proportion relation with the output voltage of the switching converter, and the change ratio of the control conduction time is in an inverse proportion relation with the output voltage of the switching converter.
Further, the change ratio of the on time controlled by the time adjustment signal satisfies the formula:wherein I represents the load size, R represents the resistance of the shunt tube, and V represents the output voltage.
The on-time generating circuit provided by the invention can adjust the constant on-time of the switching converter based on the change of the load, thereby realizing the constant frequency of the switching converter. Meanwhile, the on-time generating circuit also adjusts the on-time adaptively according to the change of the output voltage so as to realize the constant frequency of the switching converter. In addition, the on-time generating circuit sets the judging reference of the load change as zero, so that the structure and control logic of the on-time generating circuit are simplified, and the applicability of the on-time generating circuit is improved.
Drawings
FIG. 1 is a block diagram showing a conduction time generation circuit according to the present invention;
FIG. 2 is a block diagram showing a further refinement of the on-time generating circuit according to the present invention;
FIG. 3 is a schematic diagram showing a specific circuit structure of the on-time generating circuit according to the present invention;
fig. 4 is a comparison chart of on-time generated by the on-time generating circuit according to the present invention under the condition that the load is zero and the load varies.
Detailed Description
Based on the problem that the switching frequency of the COT controlled switching converter in the prior art shifts along with the load change, the present invention proposes a turn-on time generating circuit to solve the above problem, specifically, as shown in fig. 1, the turn-on time generating circuit includes a ramp module, a time adjustment module, and a time signal generating module, wherein:
when a main power tube in the switching converter is conducted, the slope module generates a slope signal;
when the load of the switching converter is not equal to zero (namely, when the load changes), the time adjustment module generates a time adjustment signal according to the change of the load of the switching converter, wherein the time adjustment signal is used for adjusting the conduction time of the switching converter on the basis of the preset conduction time, and the conduction time of the switching converter is the preset conduction time when the load is equal to zero;
when the load of the switching converter is zero, the time generation signal generation module outputs a first time signal according to the ramp signal and the output feedback signal, wherein the first time signal represents that the on time of the switching converter is a preset on time when the load is zero, and the output feedback signal represents the output of the switching converter;
when the load of the switching converter is not equal to zero (namely, when the load is changed), the time signal generating module generates a second time signal according to the ramp signal, the time adjusting signal and the output feedback signal, the second time signal represents the conduction time of the switching converter after adjustment on the basis of the preset conduction time, and when other parameters of the switching converter are unchanged, only the load is changed, the adjusted conduction time and the load are in positive correlation. That is, if the load increases, the on-time of the switching converter increases based on the preset on-time; if the load decreases, the on-time of the switching converter decreases based on the preset on-time.
Therefore, the on-time generating circuit provided by the invention can adjust the constant on-time of the switching converter based on the change of the load, thereby realizing the constant frequency of the switching converter. Meanwhile, the on-time generating circuit sets the judging reference of the load change as zero, so that the structure and control logic of the on-time generating circuit are simplified, and the applicability of the on-time generating circuit is improved.
Further, when the output of the switching converter is stable, the time adjustment signal controls the change ratio of the on time to be in a direct proportion to the load size in the process of adjusting the on time of the switching converter based on the preset on time. Meanwhile, because the preset on time is in direct proportion to the output voltage of the switching converter, when the switching converterWhen the output changes, the reference of the time adjustment signal for adjusting the on-time (i.e. the magnitude of the preset on-time) will change, so that the time adjustment signal also controls the change ratio of the on-time to be inversely proportional to the magnitude of the load when the load of the switching converter is stable and the output changes. Specifically, the change ratio K of the on-time satisfies:the specific analysis results are as follows:
in actual conditions, the main power tube and the freewheel tube have on-resistances, the on-resistance of the main power tube is Rds1, the on-resistance of the freewheel tube is Rds2, and IL is the inductance current average value representing the load size, so that the actual switching periodThe method meets the following conditions:wherein->Much smaller than Vin, so. Therefore, if the on time of the switching converter is controlled under the control of COT +.>Constant, as the load increases when the output voltage stabilizes, the switching period of the switching converter decreases and the switching frequency increases. And it is known that in order to control the switching frequency of the switching converter to be constant, it is necessary to adjust the on-time to change in positive correlation with the load change when the output voltage is stable.
In the invention, the zero load is set as the basis for judging whether the load changes or not. When the load is zero as the judging reference, the on-time generating circuit does not need to judge whether the load is changed below the reference or is changed above the reference, so that the control logic of the on-time generating circuit is simplified, and the circuit junction of the corresponding on-time generating circuit is simplifiedThe structure is also simplified. Meanwhile, when the load is zero as a judgment reference, the current load of the switching converter is the load variation, and the on-time generating circuit does not need to make a difference between the current load and the reference load to obtain the load variation. Specifically, when the load is zero and the output is stable at Vout, the on-time of the switching converter under the control of COT is a preset on-time TS, which is a reference for adjusting the on-time, and the switching period at that timeThe method meets the following conditions: />. In order to achieve a stable switching frequency during load changes, it is necessary to ensure that the control +.>ThenWherein->For the change ratio K of the on-time, +.>For the amount of change in on-time, it is clear that IL characterizes both the current load magnitude and the load change. Therefore, the time adjustment signal always controls the change ratio K of the on-time to be equal toIn this way a constant switching frequency can be achieved>. Similarly, when the load is stable and the output of the switching converter changes, the magnitude of the preset on-time TS changes due to the proportional relationship between the preset on-time TS and the output voltage, and the time adjustment signal adjusts the reference of the on-time (i.e.Preset on-time) has been changed, the time adjustment signal controls the change ratio of the on-time to be inversely proportional to the output voltage, so as to achieve constant frequency of the switching converter, and the change ratio K of the on-time is still equal to +.>。
Specifically, the ramp module generates a first current signal with a first current value according to the input voltage of the switching converter, and integrates the first current signal to obtain a first voltage signal when the driving signal in an effective state drives the main power tube to be conducted, wherein the first voltage signal represents the ramp signal;
the time adjustment module comprises a conversion unit, a first adjustment unit and a second adjustment unit, wherein the conversion unit acquires a second current signal with a second current value according to the change of a load, the first adjustment unit controls the first current signal to be changed into a difference current signal of the first current signal and the second current signal, the second adjustment unit controls the change duration of the first current signal to be a preset duration, the integral value of the difference current signal in the preset duration is a time adjustment signal, and the preset duration is smaller than the preset conduction time.
The time signal generating module is used for superposing the time adjustment signal and the slope signal to obtain a superposed signal, wherein the average slope of the superposed signal is smaller than that of the slope signal, and the time signal generating module is used for comparing the superposed signal with the output feedback signal and generating a second time signal when the superposed signal reaches the output feedback signal. Specifically, the time signal generating module comprises a comparing unit and a logic unit, one input end of the comparing unit is connected with the output end of the slope module and the output end of the time adjusting signal, the other input end of the comparing unit receives the output voltage of the switching converter, and when the superposition signal reaches the output voltage, the comparing unit determines the turn-off time of the main power tube and generates a second turn-off trigger signal to represent the turn-off time; the logic unit carries out logic processing on the second turn-off trigger signal to obtain a second time signal, wherein the second time signal represents the turn-on time of the main power tube after adjustment. When the load is zero and the ramp signal reaches the output voltage, the comparison unit determines the turn-off time of the main power tube and generates a first turn-off trigger signal to represent the turn-off time, and the logic unit carries out logic processing on the second turn-off trigger signal to obtain a first time signal, wherein the first time signal represents the preset turn-on time TS.
According to the structure, when the load is zero and the output is stable, the first voltage signal steadily rises at the first rate when the main power tube is turned on, and the main power tube is controlled to be turned off until the first voltage signal reaches the output voltage of the switching converter, so that the on-time generating circuit controls the on-time of the main power tube to be the preset on-time TS. When the load changes, the first regulating unit and the second regulating unit prolong the time period that the first voltage signal reaches the output voltage by reducing the average rising speed of the first voltage signal, so that the on-time of the main power tube is prolonged on the basis of the preset on-time TS. In the adjusting process, the time adjusting signal output by the time adjusting module precisely controls the change ratio of the on time of the main power tube to be always equal to. Therefore, no matter how the load changes when the output is stable, the conduction time generation circuit controls the ratio of the variation of the conduction time of the main power tube after adjustment relative to the preset conduction time TS and the preset conduction time TS to always satisfy +.>Thereby achieving a constant switching frequency. Meanwhile, the on-time generating circuit can adaptively adjust the on-time according to the change of the output voltage so as to control the inverse relation between the change ratio of the on-time and the output voltage, thereby realizing constant frequency.
Preferably, in the first embodiment, as shown in fig. 2, specific:
the ramp module comprises a first current source unit and a first capacitor, wherein the first current source generates a first current signal with a first current value according to input voltage, the first current signal flows into the first capacitor when the driving signal in an effective state drives the main power tube to be conducted, the first capacitor is charged by current with the first current value, and the voltage of the first capacitor represents the ramp signal.
The time adjustment module comprises a conversion unit, a first adjustment unit and a second adjustment unit, wherein the conversion unit converts the load size into a second current signal with a second current value, the first adjustment unit extracts current from the charging current of the first capacitor, the extracted current size is equal to the second current value, the second adjustment unit controls the duration of the first adjustment unit for extracting the current to be a preset duration, the preset duration is smaller than a preset conduction time, and the electric charge quantity represented by the product of the difference value of the first current value and the second current value and the preset duration represents the time adjustment signal. The control of the preset duration being smaller than the preset conduction time is to enable the conduction time generation circuit to adaptively adjust the conduction time according to the change of the output voltage, so that the change ratio of the conduction time is controlled to be in inverse proportion to the output voltage, and therefore the frequency is constant.
More specifically, as shown in fig. 3, the first current source unit includes a first current source I1, a first switching tube M1, a second switching tube M2, and a third switching tube M3, the conversion unit includes a fourth switching tube M4, a resistor R1, the first adjustment unit includes a fifth switching tube M5 and a sixth switching tube M6, the second adjustment unit includes a seventh switching tube M7 and an inverter chain U1, the inverter chain U1 is composed of a plurality of inverters connected in series, the comparison unit includes a comparator CMP1, and the logic unit includes an RS flip-flop. The grid electrode of the fourth switching tube M4 receives a control voltage VC (representing the load size), the source electrode of the fourth switching tube M4 is connected with a resistor R1 and then grounded, the drain electrode of the fourth switching tube M4 is connected with the reference end of the first current mirror, the source electrode of the seventh switching tube M7 is connected with the output end of the first current mirror, the drain electrode of the seventh switching tube M7 is connected with the input end of the first current source I1, the grid electrode of the seventh switching tube M7 is connected with the output end of the inverter chain U1, and the output end of the inverter chain U1 receives a driving signal Drive in an effective state; wherein the fifth switching tube M5 and the sixth switching tube M6 form a second current mirror, and the size ratio of the fifth switching tube M5 to the sixth switching tube M6 is 1:1, one end of the common gate common drain of the fifth switching tube M5 is a reference end of the second current mirror, and the drain electrode of the sixth switching tube M6 is an output end of the second current mirror. The input end of the first current source I1 is connected with the reference end of the first current mirror, the output end of the first current source I1 is grounded, the output end of the first current mirror is connected with the drain electrode of the first switching tube M1, the source electrode of the first switching tube M1 is grounded, the first switching tube M1 is controlled to be turned off when a driving signal Drive in an effective state drives the main power tube to be turned on, and the first capacitor C1 is connected with the first switching tube M1 in parallel; the second switching tube M2 and the third switching tube M3 form a first current mirror, the size ratio of the second switching tube M2 to the third switching tube M3 is N1, one end of the common-drain common-gate of the second switching tube M2 is a reference end of the first current mirror, and the drain electrode of the third switching tube M3 is an output end of the first current mirror. The inverting input terminal of the comparator CMP1 receives the output voltage Vout, the non-inverting input terminal of the comparator CMP1 is connected with the positive electrode of the first capacitor C1, and the output terminal of the comparator CMP1 is connected with the reset terminal of the RS trigger.
In summary, the fourth switch M4 converts the control voltage VC into a second current signal having a second current value proportional to the load size, which can be expressed as. When the driving signal Drive in the active state drives the main power tube to be on, the first switching tube M1 is off, the first current source I1 generates a first current signal with a first current value to charge the first capacitor C1, the first current value is related to the input voltage and has the magnitude of Vin/R, and R and the capacitor C1 are determined according to the expected frequency of the switching converter. After receiving the driving signal Drive in the effective state, the inverter chain U1 controls the duration of continuous conduction of the seventh switching tube M1 to be a preset duration T1 (T1 is less than a preset conduction time TS), so that the charging current of the first capacitor C1 is reduced to Vin/R-kIL/N in the T1 time, and thus the duration of charging the first capacitor C1 to Vout is prolonged, when the voltage Vramp of the first capacitor C1 is equal to Vout, the comparator CMP1 outputs a flip-flop, the output signal after the flip-flop is a second turn-off trigger signal, the RS trigger determines the turn-off time of the main power tube according to the second turn-off trigger signal, thereby outputting a complete driving signal Drive in the effective state (i.e., a second time signal), and the complete driving signal Drive in the effective state characterizes the regulated switching converterOn time. Specifically, as shown in fig. 4, the dotted line part is the working waveform diagram of the on-time generating circuit when the load is zero, and the solid line part is the working waveform diagram of the on-time generating circuit when the load is changed, and the comparison shows that the on-time generating circuit provided by the invention can adjust the on-time of the switching converter and accurately control when the load is changed>To control the switching frequency constant.
In the present embodiment, the on-time generation circuit is analyzed to determine the change ratio of the on-time =If the load stabilizes the proportion of the preset time period T1 to the adjusted on-time Ton is inversely proportional to the output voltage, that is, the change ratio of the on-time controlled by the time adjustment module is inversely proportional to the output voltage, so that the on-time generating circuit also adaptively adjusts the on-time according to the change of the output voltage to control the change ratio of the on-time to inversely proportional to the output voltage, thereby realizing the constant frequency.
Further, in this embodiment, when the continuous current tube is driven by the input voltage, the on-resistance Rds2 of the continuous current tube and the input voltage form a negative correlation, and the delay time (i.e. the preset duration T1) of the inverter chain U1 also forms a negative correlation with the input voltage. Therefore, the input voltage after the offset of the two does not affect the working process of the conduction time generation circuit, and the input voltage is utilized to drive the follow-up tube without additionally arranging power supply drive, thereby simplifying the structure and saving the cost. In addition, because the on-resistance Rds2 of the continuous current pipe and the delay of the inverter chain are positively correlated with the temperature, the temperature after the two are counteracted does not influence the working process of the on-time generating circuit.
In addition, in other embodiments, considering the specific composition structure of the comparator, if the input voltage of the comparator is large, the comparator may not work, so that the output voltage may be scaled down to a certain extent to represent the output feedback signal, and the current magnitude of the corresponding first current source is also scaled down equally.
As is clear from the above, the on-time generating circuit in this embodiment has a simple structure and simple control logic, and on this basis, the on-time of the switching converter under the COTs control and the load size change in positive correlation, thereby realizing the constant switching frequency. Meanwhile, the on-time generating circuit also adaptively adjusts the on-time according to the change of the output voltage so as to control the change ratio of the on-time to be in inverse relation with the output voltage.
The invention also proposes a switching converter under COT control comprising the above proposed on-time generating circuit to adjust the constant on-time of the switching converter based on the variation of the load, thereby achieving a constant frequency of the switching converter.
The invention also provides a control method of the on time, which is used for controlling the on time of the switching converter under the control of COT, and comprises the following steps:
acquiring a preset conduction time, wherein the preset conduction time represents the conduction time of the switching converter when the load of the switching converter is zero;
acquiring a time adjustment signal according to a load change signal, wherein the load change signal represents the change amount of the load of the switching converter;
and adjusting the conduction time of the switching converter on the basis of the preset conduction time according to the time adjustment signal, wherein the adjusted conduction time and the load are in positive correlation, and the load corresponding to the preset conduction time is zero.
Further, when the output voltage of the switching converter is constant, the time adjustment signal controls the ratio of on-time to be in direct proportion to the load size, specifically, the ratio of on-time to be K satisfies:。
further, the preset conduction time is in direct proportion to the output voltage, when the load is stable and the output is performedWhen the voltage changes, the time adjustment signal controls the change ratio of the on time to be in inverse proportion to the output voltage, and specifically, the change ratio K of the on time satisfies the following conditions:。
therefore, the control method of the on-time provided by the invention can adjust the constant on-time of the switching converter based on the change of the load when the output voltage is stable, so that the on-time change ratio is in a direct proportion relation with the load size, and the frequency of the switching converter is constant. Meanwhile, when the load is stable, the on time of the switching converter can be adjusted based on the change of the output voltage, and the change ratio of the on time is controlled to be in inverse proportion to the output voltage, so that the frequency of the switching converter is constant.
Claims (13)
1. An on-time generation circuit for use in a COT-controlled switching converter comprising a main power tube and a freewheel tube, comprising:
the slope module generates a slope signal according to the driving signal of the main power tube;
the time adjustment module is used for generating a time adjustment signal according to the change of the load, wherein the time adjustment signal is used for adjusting the conduction time of the switching converter on the basis of the preset conduction time, and the preset conduction time represents the conduction time of the switching converter when the load is equal to zero;
the time signal generation module is used for generating a second time signal according to the slope signal, the time adjustment signal and the output feedback signal, wherein the output feedback signal represents the output voltage of the switching converter, the second time signal represents the adjusted conduction time of the switching converter, and the adjusted conduction time and the load are in positive correlation.
2. The on-time generation circuit of claim 1, wherein the time signal generation module generates a first time signal from the ramp signal and the output feedback signal when the load is equal to zero, the first time signal being indicative of the preset on-time.
3. The on-time generation circuit of claim 1, wherein the time adjustment signal controls a ratio of on-time variation in direct proportion to a load size.
4. The on-time generation circuit of claim 1, wherein the magnitude of the predetermined on-time is proportional to the output voltage of the switching converter, and the time adjustment signal controls the ratio of the on-time to vary in inverse proportion to the output voltage of the switching converter.
5. The on-time generation circuit of claim 1, wherein the time adjustment signal controls a ratio of changes in on-time to satisfy the formula:wherein I represents the load size, R represents the resistance of the shunt tube, and V represents the output voltage.
6. The on-time generation circuit of claim 1, wherein the time signal generation module superimposes the time adjustment signal and the ramp signal to obtain a superimposed signal, an average slope of the superimposed signal being smaller than a slope of the ramp signal, the time signal generation module generating the second time signal based on the superimposed signal and the output feedback signal.
7. The on-time generation circuit of claim 1, wherein the ramp module obtains a first current signal from an input voltage of the switching converter and integrates the first current signal to obtain a first voltage signal representative of the ramp signal when an active state drive signal drives the main power transistor on.
8. The on-time generation circuit of claim 7, wherein the time adjustment module comprises a conversion unit, a first adjustment unit, and a second adjustment unit, wherein,
the conversion unit obtains a second current signal according to the change of the load;
the first regulating unit controls the first current signal to be changed into a difference current signal of the first current signal and the second current signal;
the second adjusting unit controls the change time length of the first current signal to be a preset time length, the integral value of the difference current signal in the preset time length is the time adjusting signal, and the preset time length is smaller than the preset conduction time.
9. The on-time generation circuit of claim 8, wherein the ramp module includes a first current source unit and a first capacitor, the first current source unit generating the first current signal, the first current signal flowing to the first capacitor when an active state drive signal drives the main power transistor on.
10. The on-time generating circuit of claim 9, wherein the converting unit comprises a fourth switching tube, the first adjusting unit comprises a fifth switching tube and a sixth switching tube constituting a second current mirror, the second adjusting unit comprises a seventh switching tube, wherein,
the grid electrode of the fourth switching tube receives control voltage representing the load size, the drain electrode of the fourth switching tube is connected with the reference end of the second current mirror, the seventh switching tube is connected between the output end of the second current mirror and the first current source unit, and the size ratio of the fifth switching tube to the sixth switching tube is N: and 1, the conduction time of the seventh switching tube is the preset duration.
11. The on-time generation circuit of claim 10, wherein the gate of the shunt tube receives an input voltage of the switching converter, the second adjusting unit further comprises an inverter chain formed by a plurality of inverters connected in series, an input end of the inverter chain receives a driving signal in an active state, an output end of the inverter chain is connected with the gate of the seventh switching tube, and the preset duration is in negative correlation with the input voltage.
12. The on-time generation circuit of claim 6, wherein the time signal generation module comprises:
the comparison unit is used for comparing the superposition signal and the output feedback signal to generate a second turn-off trigger signal, and the second turn-off trigger signal represents the turn-off time of the main power tube;
and the logic unit is used for generating the second time signal after performing logic processing on the second turn-off trigger signal.
13. A switching converter comprising an on-time generating circuit according to any one of claims 1-12.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN108880237A (en) * | 2018-07-12 | 2018-11-23 | 矽力杰半导体技术(杭州)有限公司 | The switch time generation circuit and switch time control method of switch converters |
| CN110892629A (en) * | 2019-08-29 | 2020-03-17 | 杭州士兰微电子股份有限公司 | Switching converter, control method and control circuit thereof |
| WO2022007460A1 (en) * | 2020-07-08 | 2022-01-13 | 无锡力芯微电子股份有限公司 | Step-down direct current-direct current converter |
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| CN104022648B (en) * | 2014-04-23 | 2017-01-11 | 成都芯源系统有限公司 | Switch converter and control circuit and control method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN108880237A (en) * | 2018-07-12 | 2018-11-23 | 矽力杰半导体技术(杭州)有限公司 | The switch time generation circuit and switch time control method of switch converters |
| CN110892629A (en) * | 2019-08-29 | 2020-03-17 | 杭州士兰微电子股份有限公司 | Switching converter, control method and control circuit thereof |
| WO2022007460A1 (en) * | 2020-07-08 | 2022-01-13 | 无锡力芯微电子股份有限公司 | Step-down direct current-direct current converter |
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