CN115995975A - Switching power supply control circuit and method and switching power supply - Google Patents
Switching power supply control circuit and method and switching power supply Download PDFInfo
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Abstract
The invention relates to the technical field of switching power supplies, and provides a switching power supply control circuit and method and a switching power supply, wherein the control circuit comprises: the frequency-reducing control module is used for controlling the switching power supply to enter an intermittent working mode when the compensation voltage of the switching power supply is lower than a preset frequency-reducing threshold voltage, wherein the intermittent working mode comprises a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero, and the frequency-reducing control module adjusts the time of the second time period according to the time of the first time period. The invention can ensure that the switching power supply maintains relatively stable loop gain in the high-frequency and low-frequency designs, and is beneficial to improving the stability of the system, thereby improving the output quality of the switching power supply.
Description
Technical Field
The invention relates to the technical field of switching power supplies, in particular to a switching power supply control circuit and method and a switching power supply.
Background
With the rapid development of power electronics technology, the demands for small size, high efficiency and high reliability of switching converters are gradually increasing. For high efficiency requirements, it is often not sufficient for a switching power supply to be operated in a state corresponding to different load conditions. For example, in the case of light load or OTP (Over Temperature Protection, over-temperature protection), in order to reduce switching loss of the switching power supply when the output current is reduced, the switching power supply may enter a DCM (discontinuous conduction) state.
In DCM, the switching power supply normally generates a compensation voltage Vcomp lower than a predetermined limiting threshold voltage V TH A fixed DCM time is inserted. As shown in fig. 1, the turn-on control signal Von characterizing the DCM time of the conventional switching power supply is a voltage obtained by comparing the compensation voltage Vcomp and the clipping threshold voltage V by the comparator 3 TH Is compared with the sawtooth signal. Wherein the compensation voltage Vcomp and the clipping threshold voltage V TH Obtained by means of a subtractor 1, the sawtooth signal is generated by means of a sawtooth generator 2.
As can be seen from fig. 1, the DCM time of the conventional switching power supply is only related to the compensation voltage Vcomp, and the smaller the compensation voltage Vcomp, the longer the DCM time. However, different switching frequencies can affect the loop gain of the system, in high-frequency design, the loop gain of the system is easy to be too large when the system enters a down-conversion mode, so that the system is unstable, or the switching loss of the system is easy to increase under the condition of too large peak value of the inductive current; in the low-frequency design, the loop gain of the system is easy to be too small when the system enters the frequency-reducing mode, so that the frequency-reducing effect on the system is not obvious, and the switching loss cannot be effectively reduced. In addition, in the constant current scheme of peak current control, the DCM time of the system is fixed, and the power frequency ripple of the output current of the system is increased, so that the output quality of the switching power supply is affected.
Accordingly, there is a need to provide an improved solution to overcome the above technical problems in the prior art.
Disclosure of Invention
In order to solve the technical problems, the invention provides a switching power supply control circuit, a switching power supply control method and a switching power supply, which can enable the switching power supply to keep relatively stable loop gain in high-frequency and low-frequency designs, are beneficial to improving the stability of a system, and can effectively inhibit power frequency ripple waves in a peak current control scheme, so that the output quality of the switching power supply can be improved.
According to a first aspect of the present invention, there is provided a switching power supply control circuit comprising: a down-conversion control module for controlling the switching power supply to enter an intermittent working mode when the compensation voltage of the switching power supply is lower than a preset down-conversion threshold voltage, wherein the intermittent working mode comprises a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero,
the frequency-reducing control module adjusts the time of the second time period according to the time of the first time period.
Optionally, the frequency-reducing control module controls the time of the second time period to be positively correlated with the time of the first time period.
Optionally, the time of the second period of time is controlled by the down-conversion control module to increase with the time of the first period of time.
Optionally, the frequency-reducing control module obtains a reference signal according to a difference value between the frequency-reducing threshold voltage and the compensation voltage and a first voltage, and compares the reference signal with a sawtooth wave signal to obtain a conduction trigger signal, wherein the first voltage is used for representing time when the inductance current of the switching power supply is greater than zero; and
the control circuit further comprises a turn-off control module and a driving module, wherein the turn-off control module is used for providing a turn-off trigger signal for controlling a main switching tube in the switching power supply to turn off, and the driving module is used for generating a driving control signal of the main switching tube according to the turn-off trigger signal and the turn-on trigger signal.
Optionally, the magnitude of the reference signal is inversely related to the compensation voltage and positively related to the first voltage.
Optionally, the magnitude of the first voltage is inversely related to the switching frequency of the switching power supply.
Optionally, the down-conversion control module includes:
the first voltage generating unit is used for charging a capacitor by using a current source and outputting the first voltage at two ends of the capacitor when the inductance current of the switching power supply is larger than zero;
a reference signal generating unit for receiving the first voltage, the down-conversion threshold voltage and the compensation voltage and outputting the reference signal;
a sawtooth wave generator for providing the sawtooth wave signal when the zero-crossing detection signal is detected;
and the positive phase input end of the comparator receives the sawtooth wave signal, the negative phase input end of the comparator receives the reference signal, and the output end of the comparator outputs the conduction trigger signal.
Optionally, the reference signal is a product of a difference between the down-conversion threshold voltage and the compensation voltage and the first voltage.
Optionally, the first voltage generating unit includes:
a current source;
the first switch, the current input end is connected with said current source, the current output end is connected with first end of the said electric capacity, the control end receives the first control signal;
the second end of the capacitor is connected with the reference ground;
and the RS trigger is characterized in that a setting end receives a driving control signal of the main switching tube, a resetting end receives a zero-crossing detection signal, and an output end outputs the first control signal, wherein the first voltage generating unit outputs the first voltage at a first end of the capacitor.
Optionally, the first voltage generating unit further includes:
a second switch connected between the first end of the capacitor and a reference ground, the second switch being controlled by the output signal of the comparator for providing a charge bleed path for the capacitor during each switching cycle.
Optionally, the reference signal generating unit includes:
the subtracter comprises a first input end for receiving the down-conversion threshold voltage, a second input end for receiving the compensation voltage and an output end for outputting a difference signal between the down-conversion threshold voltage and the compensation voltage;
the input end of the amplitude limiting circuit is connected with the output end of the subtracter and is used for carrying out amplitude limiting clamping processing on the difference signal according to a preset amplitude limiting threshold value;
and the first input end of the multiplier is connected with the output end of the amplitude limiting circuit to receive the difference signal after amplitude limiting clamping, the second input end of the multiplier receives the first voltage, and the output end of the multiplier outputs the reference signal.
Optionally, the driving module controls the main switching tube to be turned on when detecting the rising edge of the turn-on trigger signal, and controls the main switching tube to be turned off when detecting the rising edge of the turn-off trigger signal.
Optionally, the driving module is an RS flip-flop.
According to a second aspect of the present invention, there is provided a switching power supply comprising: a power conversion circuit; and a switching power supply control circuit as described above.
According to a third aspect of the present invention, there is provided a control method of a switching power supply, comprising: when the compensation voltage of the switching power supply is lower than a preset frequency-reducing threshold voltage, controlling the switching power supply to enter an intermittent working mode, wherein the intermittent working mode comprises a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero;
and acquiring the time of the first time period, and adjusting the time of the second time period according to the time of the first time period.
Optionally, the adjusted time of the second time period is positively correlated with the time of the first time period.
Optionally, acquiring the time of the first period of time includes: and charging a capacitor by using a current source during a period when the inductance current of the switching power supply is greater than zero, so as to obtain a first voltage which characterizes the time of the first time period at two ends of the capacitor.
Optionally, adjusting the time of the second time period according to the time of the first time period includes:
obtaining a reference signal according to the difference value between the frequency-reducing threshold voltage and the compensation voltage of the switching power supply and the first voltage;
and comparing the reference signal with the sawtooth wave signal to obtain a conduction trigger signal for controlling the conduction of the main switching tube in the switching power supply, wherein the time period from the zero crossing time of the switching power supply to the rising edge time of the conduction trigger signal is the second time period.
Optionally, the magnitude of the reference signal is inversely related to the compensation voltage and positively related to the first voltage.
Optionally, the magnitude of the first voltage is inversely related to the switching frequency of the switching power supply.
Optionally, the method further comprises: a charge bleed path is provided for the capacitor in each switching cycle.
Optionally, the reference signal is a product of a difference between the down-conversion threshold voltage and the compensation voltage and the first voltage.
The beneficial effects of the invention at least comprise:
according to the embodiment of the invention, when the compensation voltage of the switching power supply is lower than the preset frequency-reducing threshold voltage, the switching power supply is controlled to enter an intermittent working mode comprising a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero, and the time of the second time period when the inductance current is greater than zero is adjusted by utilizing the time of the first time period, wherein in the process, the dynamic adjustment of the time of the second time period along with the switching frequency of the switching power supply in the intermittent working mode is realized on the basis of the corresponding relation between the time of the first time period and the switching frequency of the switching power supply, so that the switching power supply can maintain relatively stable loop gain in high-frequency and low-frequency designs, the stability of a switching power supply system is improved, and in a peak current control scheme, the power frequency ripple can be effectively restrained, and the output quality of the switching power supply is improved.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.
Drawings
Fig. 1 is a schematic circuit diagram showing a conventional switching power supply generating a turn-on control signal in DCM mode;
fig. 2 shows a schematic structural diagram of a switching power supply according to an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating a configuration of the down conversion control module of FIG. 2;
fig. 4 shows a timing waveform diagram of a part of signals in a switching power supply according to an embodiment of the invention;
fig. 5 shows a schematic structural diagram of a down-conversion control method of a switching power supply according to an embodiment of the present invention.
Detailed Description
In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Preferred embodiments of the present invention are shown in the drawings. The invention may, however, be embodied in different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
As shown in fig. 2, the switching power supply disclosed in the embodiment of the invention includes: a power conversion circuit 10 and a control circuit 20.
The power conversion circuit 10 may be, for example, a Flyback topology (Flyback), and includes an absorption network 11 connected across a primary winding Np of a transformer TR, a main switching tube Q1 and a sampling resistor Rs connected in series between one end of the primary winding Np and a reference ground, the other end of the primary winding Np receiving an input voltage Vin, a rectifying tube D1 connected between one end of a secondary winding Ns of the transformer TR and an output terminal, and an output capacitor Co at the output terminal. The main switching transistor Q1 is, for example, an NMOS transistor. The main switching transistor Q1 is driven by a driving control signal Vgs to perform power conversion of the input voltage Vin, forming an output voltage Vout. It will be appreciated that in other examples of the present invention, the power conversion circuit 10 may be any other type of power conversion circuit, such as any type of layout design including Boost (Boost), buck (Buck), buck-Boost (Buck-Boost), cuk, sepic, and Zeta, which is not limited by the present invention.
The control circuit 20 is configured to provide a drive control signal Vgs to the power conversion circuit 10. In this embodiment, the control circuit 20 includes: a down-conversion control module 21, a shut-down control module 22 and a drive module 23.
The down-conversion control module 21 is used for compensating voltage of the switching power supplyVcomp is lower than a preset down-conversion threshold voltage V TH The switching power supply is controlled to enter an intermittent operation mode (DCM) to realize frequency reduction. The intermittent operation mode of the open source voltage comprises a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero in each switching period. In this embodiment, the down-conversion control module 21 is further configured to adjust the time of the second period according to the time of the first period in each switching cycle.
In each switching period of the switching power supply, the first time period corresponds to a time period from the rising edge arrival time of the on trigger signal Von of the main switching tube Q1 in the switching power supply to the zero crossing time of the switching power supply; the second period corresponds to a period between the zero crossing time of the switching power supply and the arrival time of the next rising edge of the on trigger signal Von of the main switching tube Q1.
Specifically, the time of the second period is positively correlated with the time of the first period by the down conversion control module 21. That is, the down control module 21 controls the time of the second period to increase (or decrease) with the increase (or decrease) of the time of the first period.
By analogy to a first time period of the switching power supply in the intermittent working mode by a critical conduction mode (BCM), the corresponding relation exists between the time of the first time period of the switching power supply in the intermittent working mode and the switching frequency of the switching power supply, and based on the corresponding relation, when the time of the second time period is adjusted according to the time of the first time period, the dynamic adjustment of the time of the second time period along with the switching frequency of the switching power supply in the intermittent working mode can be realized, so that the switching power supply can maintain relatively stable loop gain in high-frequency and low-frequency designs, and the stability of a switching power supply system is improved. Meanwhile, in the peak current control scheme, the power frequency ripple wave can be effectively restrained, so that the output quality of the switching power supply is improved.
In some embodiments of the present invention, the down-conversion control module 21 is based on the down-conversion threshold voltage V TH And the difference of the compensation voltage Vcomp (i.e. V TH -Vcomp) and a first voltage V A Obtaining reference informationNumber V B And for reference signal V B And comparing the signal with the sawtooth wave signal to obtain a conduction trigger signal Von. Wherein the first voltage V A The time for representing the inductor current of the switching power supply is greater than zero, namely the first time period. That is, embodiments of the present invention pass the first voltage V characterizing the time of the first period of time A The rising edge arrival time of the on trigger signal Von of the main switching tube Q1 is adjusted, so that dynamic adjustment of the time of the second time period along with the switching frequency of the switching power supply is equivalently realized.
The off control module 22 is configured to provide an off trigger signal Voff for controlling the main switching tube Q1 of the switching power supply to be turned off. Alternatively, the off control module 22 may be implemented in various manners, such as peak current control (i.e., obtaining the compensation signal Vcomp according to the feedback signal of the output voltage Vo by using an error amplifying circuit and a compensation network, obtaining a current peak according to the compensation signal Vcomp, and outputting the off trigger signal Voff when the sampled inductor current of the switching power supply reaches the current peak), or constant on time Control (COT), i.e., starting to time when the driving control signal Vgs of the main switching transistor Q1 changes from low level to high level, and outputting the off trigger signal Voff when the time value reaches a preset time threshold value, etc. The specific structure of the shutdown control module 22 may be referred to in the art and will not be described in detail herein.
The driving module 23 is configured to generate a driving control signal Vgs of the main switching tube Q1 according to the off trigger signal Voff and the on trigger signal Von. The driving module 23 may be implemented, for example, by an RS flip-flop, that is, the set terminal of the RS flip-flop receives the on trigger signal Von, the reset terminal of the RS flip-flop receives the off trigger signal Voff, and the output terminal of the RS flip-flop outputs the driving control signal Vgs to the main switching tube Q1. The RS flip-flop may output a high level when a rising edge of the on trigger signal Von arrives, and output a low level when a rising edge of the off trigger signal Voff arrives, thereby implementing on/off control of the main switching tube Q1. Optionally, a driving unit may be further disposed between the output terminal of the RS flip-flop and the control terminal of the main switching tube Q1, so as to give a suitable voltage value to the high/low level output by the RS flip-flop, thereby better implementing driving control of the main switching tube Q1.
Referring to fig. 3, in the present embodiment, the down-conversion control module 21 further includes: a first voltage generating unit 211, a reference signal generating unit 212, a sawtooth wave generator 213, and a comparator 214.
The first voltage generating unit 211 is configured to charge the capacitor with a current source and output a first voltage V across the capacitor during a period when the inductor current of the switching power supply is greater than zero A . Illustratively, the first voltage generating unit 211 includes: a current source I1, a first switch K1, a capacitor C1 and an RS flip-flop 2111. One end of the current source I1 is connected to the power source VCC, the current input end of the first switch K1 is connected to the other end of the current source I1, the current output end of the first switch K1 is connected to the first end of the capacitor C1, and the second end of the capacitor C1 is connected to the reference ground. The set terminal of the RS flip-flop 2111 receives the driving control signal Vgs of the main switching transistor Q1, the reset terminal of the RS flip-flop 2111 receives the zero-crossing detection signal ZCD, and the output terminal of the RS flip-flop 2111 is connected to the control terminal of the first switch K1 to output the first control signal to the control terminal of the first switch K1.
The first switch K1 is turned on when the rising edge of the drive control signal Vgs comes, and turned off when the zero-crossing detection signal ZCD is detected, which corresponds to the first switch K1 being turned on only during a period in which the inductor current of the switching power supply is greater than zero in each switching cycle. In a critical conduction mode (BCM), the on time of the first switch K1 corresponds to the period duration of the current switching period, that is, the period in which the inductor current is greater than zero. Therefore, in case the capacitance of the capacitor C1 and/or the output current of the current source I1 are/is selected to be proper (i.e. the capacitor C1 is not charged to a saturated state during the conduction period of the first switch K1), the first voltage V A Can be used to characterize the operating time of the switching power supply in critical conduction mode (BCM), i.e. equivalently the time of the first period of time of the switching power supply in discontinuous operation mode (DCM), as well as the current switching frequency of the switching power supply. It will be appreciated that due to the first voltage V A The operating time of the switching power supply in critical conduction mode (BCM) is characterized, so it is known from t=1/f that when the switching power supply is operating in high frequency stateFirst voltage V A Smaller; when the switching power supply is operated in a low frequency state, the first voltage V A Larger.
In a preferred embodiment of the present invention, the first voltage generating unit 211 further includes a second switch K2. The second switch K2 is connected between the first end of the capacitor C1 and the ground, and the second switch K2 is controlled by the on trigger signal Von outputted by the comparator 214, i.e. is turned on during the high level of the on trigger signal Von to provide a charge discharging path for the capacitor C1 in each switching cycle, thereby enabling the first voltage V A In the switching period, the zero state is set, and the next time the voltage rises from zero, so that the first voltage V output by the first voltage generating unit 211 is favorably improved A Accuracy of (3).
Alternatively, the first switch K1 and the second switch K2 are, for example, NMOS transistors.
The reference signal generating unit 212 is used for receiving the first voltage V A Down-conversion threshold voltage V TH And a compensation voltage Vcomp outputting a reference signal V B . In the present embodiment, the reference signal V B Is inversely related to the compensation voltage Vcomp and is related to the first voltage V A Positive correlation. And a first voltage V A The magnitude of (2) is inversely related to the switching frequency of the switching power supply. Specifically, reference signal V B For the purpose of down-converting threshold voltage V TH And the difference of the compensation voltage Vcomp is compared with the first voltage V A Product of (V), i.e. V B ＝(V TH -Vcomp)*V A 。
Illustratively, the reference signal generating unit 212 includes: subtractor 2121, limiter circuit 2122, and multiplier 2123. Wherein a first input terminal of subtractor 2121 receives a down-conversion threshold voltage V TH A second input terminal of the subtractor 2121 receives the compensation voltage Vcomp, and an output terminal of the subtractor 2121 outputs a down-conversion threshold voltage V TH And a difference signal V of the compensation voltage Vcomp TH Vcomp. An input terminal of the clipping circuit 2122 is connected to an output terminal of the subtractor 2121 for clipping the difference signal V according to a preset clipping threshold TH Vcomp performs a clamp clip process. A first input of multiplier 2123 is coupled to an output of clip circuit 2122 for receiving a clip clampThe second input of the multiplier 2123 receives the first voltage V A The output of multiplier 2123 outputs reference signal V B . Wherein the clipping circuit 2122 clamps the minimum value of the output value of the subtractor 2121 to zero power, avoiding the difference signal V TH The negative pressure generated by Vcomp is convenient for subsequent circuit processing.
The sawtooth generator 213 is configured to provide a sawtooth signal when the zero crossing detection signal ZCD is detected. Illustratively, one implementation of the sawtooth generator 213 is: when the zero-crossing detection signal ZCD is switched to the high level, the output voltage of the sawtooth wave generator 213 starts to rise; when the output voltage of the sawtooth wave generator 213 rises to a preset voltage threshold or a preset period of time elapses, the sawtooth wave generator 213 is lowered to a start value, thereby generating a sawtooth wave signal.
The positive phase input end of the comparator 214 is connected with the sawtooth wave generator 213 to receive the sawtooth wave signal, the negative phase input end of the comparator 214 is connected with the reference signal generating unit 212 to receive the reference signal, and the output end of the comparator 214 is connected with the driving module 23 to output the on trigger signal Von to the driving module 23. Specifically, when the output voltage of the sawtooth wave generator 213 reaches the reference voltage V B At this time, the on trigger signal Von outputted from the comparator 214 starts to switch from the low level to the high level.
Referring to fig. 4, the following describes the operation of the switching power supply according to the embodiment of the present invention:
at a compensation voltage Vcomp greater than the down-conversion threshold voltage V TH When the difference signal output by the subtractor 2121 is smaller than 0, the clipping circuit 2122 limits the difference signal to a preset voltage value (e.g., 0V) according to a preset lower clipping threshold (e.g., 0V), and the on trigger signal Von output by the comparator 214 is switched from low level to high level when the output voltage of the sawtooth wave generator 213 just begins to rise (i.e., when the zero crossing detection signal ZCD is detected to be valid), so as to trigger the main switching tube Q1 to be turned on. That is, at this time, the ZCD time inserted by the switching power supply at the zero crossing point of the current is substantially zero, and the switching power supply still operates according to the original switching frequency at this time, which corresponds to not performing the down-conversion process.
At a compensation voltage Vcomp smaller than the down-conversion threshold voltage V TH When the difference signal output by the subtractor 2121 is greater than 0, the on trigger signal Von output by the comparator 214 is switched from low level to high level only when the output voltage of the sawtooth generator 213 rises to the voltage value corresponding to the difference signal, thereby triggering the main switching tube Q1 to be turned on. That is, at this time, the ZCD time inserted by the switching power supply at the zero crossing point of the current is greater than zero, and the period duration of the switching power supply at this time is longer, which is equivalent to performing the down-conversion process.
Further, during the down-conversion process, it is assumed that the switching power supply operates in a high frequency state, and the inductance current i of the switching power supply L2 When the zero crossing time of (1) is t0, the sawtooth wave generator 213 starts to output the sawtooth wave signal at the time t0 and reaches the reference voltage V at the time t1 B2 That is, the on trigger signal Von2 of the main switching tube Q1 starts to switch from low level to high level at time t1, thereby triggering the main switching tube Q1 to be turned on at time t 1. In the process, the switching power supply inserts ZCD time T at time T0 ZCD2 The time of the second period is shown in fig. 4, that is, the time period between t0 and t 1.
In the down-conversion process, it is assumed that the switching power supply operates in a low frequency state and the inductance current i of the switching power supply L1 When the zero crossing time of (1) is t0, the sawtooth wave generator 213 starts to output a sawtooth wave signal at time t0, and reaches the reference voltage V at time t2 (time t2 is later than time t 1) B1 That is, the on trigger signal Von1 of the main switching tube Q1 starts to switch from low level to high level at time t2, thereby triggering the main switching tube Q1 to be turned on at time t 2. In the process, the switching power supply inserts ZCD time T at time T0 ZCD1 The time of the second period is shown in fig. 4, that is, the time period between t0 and t 2.
It can be seen that the down-conversion control module 21 in the embodiment of the invention can obtain different times of the first time period according to different switching frequencies of the switching power supply at a certain time of the compensation voltage Vcomp, thereby obtaining different reference voltages V B . And based on the different reference voltages V B The arrival time of the rising edge of the on trigger signal Von output by the comparator 214 is changed, namely the reference signal V B The dynamic adjustment can be realized along with the change of the switching frequency of the switching power supply, the dynamic adjustment of the conduction moment of the main switching tube Q1 along with the switching frequency is realized, and the method specifically comprises the following steps: the higher the switching frequency of the switching power supply (the smaller the time corresponding to the first period), the obtained reference voltage V B The smaller the arrival time of the rising edge of the on trigger signal Von is, the earlier. In the embodiment of the invention, the earlier the rising time of the on trigger signal Von comes, which is equivalent to the DCM time T of the switching power supply in DCM mode DCM The smaller (i.e., the time of the second period of time). That is, under the condition that the sawtooth wave signal and the compensation signal are unchanged, the invention can correspondingly obtain different DCM time under different switching frequencies, and realize the dynamic adjustment of the DCM time (namely the time for keeping the inductance current in a zero current state) of the switching power supply under the intermittent working mode, thereby ensuring that the switching power supply can keep relatively stable loop gain in high-frequency and low-frequency designs, being beneficial to improving the stability of a switching power supply system, and effectively inhibiting the power frequency ripple in a peak current control scheme, and further improving the output quality of the switching power supply.
Further, the invention also discloses a control method of the switching power supply, which can be applied to the switching power supply shown in fig. 1 to 4, and as shown in fig. 5, the method comprises the following steps:
in step S1, when the compensation voltage of the switching power supply is lower than a preset down-conversion threshold voltage, the switching power supply is controlled to enter an intermittent operation mode, wherein the intermittent operation mode comprises a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero.
In each switching period of the switching power supply, the first time period corresponds to a time period from the rising edge arrival time of the conduction trigger signal of the main switching tube in the switching power supply to the zero crossing time of the switching power supply; the second time period corresponds to a time period from the zero crossing time of the switching power supply to the next rising edge arrival time of the on trigger signal of the main switching tube.
Specifically, the down control module controls the time of the second period to be positively correlated with the time of the first period. That is, the down control module controls the time of the second period to increase (or decrease) with the increase (or decrease) of the time of the first period.
In step S2, the time of the first period is acquired, and the time of the second period is adjusted according to the time of the first period.
In this embodiment, the method for obtaining the time of the first time period includes: during periods when the inductor current of the switching power supply is greater than zero, the capacitor is charged by the current source to obtain a first voltage across the capacitor that characterizes the time of the first period. In a preferred embodiment of the present invention, further comprising: and providing a charge release path for the capacitor according to the conduction trigger signal in each switching period, so that the first voltage has a zeroing state in the switching period, and the next time the first voltage rises from zero, thereby improving the accuracy of the acquired first voltage.
In this embodiment, the magnitude of the reference signal is inversely related to the compensation voltage, and is inversely related to the first voltage, and the magnitude of the first voltage is inversely related to the switching frequency of the switching power supply. Specifically, the reference signal is a product of a difference between the down-conversion threshold voltage and the compensation voltage and the first voltage.
Further, the method for adjusting the time of the second time period according to the time of the first time period comprises the following steps: obtaining a reference signal according to the difference value between the frequency-reducing threshold voltage and the compensation voltage of the switching power supply and the first voltage; and comparing the reference signal with the sawtooth wave signal to obtain a conduction trigger signal for controlling the conduction of the main switching tube in the switching power supply. The time period from the zero crossing time of the switching power supply to the rising edge time of the on trigger signal is the second time period.
Specifically, the reference signal may be input to the negative phase input terminal of the comparator, and the sawtooth wave signal may be input to the positive phase input terminal of the comparator, so that when the sawtooth wave signal is greater than the reference signal, a high-level conduction trigger signal is output, and conversely, a low-level conduction trigger signal is output.
In this embodiment, the obtained first time periods are different in time under different switching frequencies, and the obtained first voltages are different in magnitude, so that the obtained reference signals are different under different switching frequencies, and different DCM times can be correspondingly obtained under different switching frequencies, so that dynamic adjustment of DCM times (i.e. the time when the inductor current keeps a zero current state) of the switching power supply under an intermittent working mode is realized, and therefore, the switching power supply can keep relatively stable loop gain in high-frequency and low-frequency designs, which is beneficial to improving the stability of a switching power supply system, and in a peak current control scheme, the power frequency ripple can be effectively restrained, so that the output quality of the switching power supply is improved.
In this embodiment, the specific implementation of each step in the down-conversion control method of the switching power supply can be referred to the foregoing embodiments of the switching power supply, and will not be described herein again.
Finally, it should be noted that: it is apparent that the above examples are only illustrative of the present invention and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.
Claims (17)
1. A switching power supply control circuit, comprising:
a down-conversion control module for controlling the switching power supply to enter an intermittent working mode when the compensation voltage of the switching power supply is lower than a preset down-conversion threshold voltage, wherein the intermittent working mode comprises a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero,
the frequency-reducing control module adjusts the time of the second time period according to the time of the first time period.
2. The switching power supply control circuit of claim 1 wherein the down-conversion control module controls the time of the second period to positively correlate with the time of the first period.
3. The switching power supply control circuit of claim 2 wherein the down conversion control module controls the time of the second period to increase as the time of the first period increases.
4. A switching power supply control circuit according to any one of claims 1 to 3, wherein,
the frequency-reducing control module obtains a reference signal according to the difference value between the frequency-reducing threshold voltage and the compensation voltage and a first voltage, and obtains a conduction trigger signal after comparing the reference signal with a sawtooth wave signal, wherein the first voltage is used for representing the time when the inductance current of the switching power supply is larger than zero;
the control circuit further comprises a turn-off control module and a driving module, wherein the turn-off control module is used for providing a turn-off trigger signal for controlling a main switching tube in the switching power supply to turn off, and the driving module is used for generating a driving control signal of the main switching tube according to the turn-off trigger signal and the turn-on trigger signal.
5. The switching power supply control circuit of claim 4 wherein the magnitude of the reference signal is inversely related to the compensation voltage and positively related to the first voltage.
6. The switching power supply control circuit of claim 5 wherein the magnitude of the first voltage is inversely related to the switching frequency of the switching power supply.
7. The switching power supply control circuit of claim 4 wherein the down-conversion control module comprises:
the first voltage generating unit is used for charging a capacitor by using a current source and outputting the first voltage at two ends of the capacitor when the inductance current of the switching power supply is larger than zero;
a reference signal generating unit for receiving the first voltage, the down-conversion threshold voltage and the compensation voltage and outputting the reference signal;
a sawtooth wave generator for providing the sawtooth wave signal when the zero-crossing detection signal is detected;
and the positive phase input end of the comparator receives the sawtooth wave signal, the negative phase input end of the comparator receives the reference signal, and the output end of the comparator outputs the conduction trigger signal.
8. The switching power supply control circuit of claim 4 wherein the reference signal is a product of a difference between the down-conversion threshold voltage and the compensation voltage and the first voltage.
9. The switching power supply control circuit according to claim 7, wherein the first voltage generating unit includes:
the RS trigger is characterized in that a setting end receives a driving control signal of the main switching tube, a resetting end receives a zero-crossing detection signal, and an output end outputs the first control signal;
a first capacitor having a first end connected to a current source via a first switch and a second end connected to ground
A first switch, the current input end is connected with a current source, the current output end is connected with a first end of a capacitor, the control end receives the first control signal,
wherein a first end of the capacitor outputs the first voltage.
10. The switching power supply control circuit according to claim 9, wherein the first voltage generating unit further comprises:
a second switch connected between the first end of the capacitor and a reference ground, the second switch being controlled by the output signal of the comparator for providing a charge bleed path for the capacitor during each switching cycle.
11. The switching power supply control circuit according to claim 7, wherein the reference signal generating unit includes:
the subtracter comprises a first input end for receiving the down-conversion threshold voltage, a second input end for receiving the compensation voltage and an output end for outputting a difference signal between the down-conversion threshold voltage and the compensation voltage;
the input end of the amplitude limiting circuit is connected with the output end of the subtracter and is used for carrying out amplitude limiting clamping processing on the difference signal according to a preset amplitude limiting threshold value;
and the first input end of the multiplier is connected with the output end of the amplitude limiting circuit to receive the difference signal after amplitude limiting clamping, the second input end of the multiplier receives the first voltage, and the output end of the multiplier outputs the reference signal.
12. A switching power supply, comprising:
a power conversion circuit;
a switching power supply control circuit according to any one of claims 1 to 11.
13. A control method of a switching power supply, comprising:
when the compensation voltage of the switching power supply is lower than a preset frequency-reducing threshold voltage, controlling the switching power supply to enter an intermittent working mode, wherein the intermittent working mode comprises a first time period when the inductance current is greater than zero and a second time period when the inductance current is equal to zero;
and acquiring the time of the first time period, and adjusting the time of the second time period according to the time of the first time period.
14. The control method according to claim 13, wherein the adjusted time of the second period of time is positively correlated with the time of the first period of time.
15. The control method of claim 13, wherein obtaining the time of the first time period comprises: and charging a capacitor by using a current source during a period when the inductance current of the switching power supply is greater than zero, so as to obtain a first voltage which characterizes the time of the first time period at two ends of the capacitor.
16. The control method of claim 15, wherein adjusting the time of the second time period according to the time of the first time period comprises:
obtaining a reference signal according to the difference value between the frequency-reducing threshold voltage and the compensation voltage of the switching power supply and the first voltage;
and comparing the reference signal with the sawtooth wave signal to obtain a conduction trigger signal for controlling the conduction of the main switching tube in the switching power supply, wherein the time period from the zero crossing time of the switching power supply to the rising edge time of the conduction trigger signal is the second time period.
17. The control method of claim 16, wherein the reference signal is a product of a difference between the down threshold voltage and the compensation voltage and the first voltage.
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| CN202211252566.4A CN115995975A (en) | 2022-10-13 | 2022-10-13 | Switching power supply control circuit and method and switching power supply |
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| CN202211252566.4A CN115995975A (en) | 2022-10-13 | 2022-10-13 | Switching power supply control circuit and method and switching power supply |
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