CN116388552B - Switching circuit control method, control chip and switching circuit - Google Patents

Abstract

The embodiment of the invention provides a switching circuit control method, a control chip and a switching circuit. The switching circuit control method is used for controlling a switching circuit, the switching circuit at least comprises an inductor and a switching tube capable of controlling the inductor to perform excitation, and the switching circuit at least comprises an N-th working stage, an (N+1) -th working stage … … and an (N+M) -th working stage; in the N working stage, the switching tube is opened at the Nth valley bottom, in the (N+1) working stage, the switching tube is opened … … at the (N+1) th valley bottom, in the (N+M) working stage, the switching tube is opened at the (N+M) th valley bottom; when the first preset condition group is met, the switching circuit is sequentially switched to the (N+M) th working stage from the N-th working stage and the (N+1) th working stage … …; wherein N and M are positive integers; the first preset condition group characterizes that the reference current of the inductor gradually decreases. The control method can sequentially and adaptively control the switching tube to be turned on at the valley bottom, and has a more stable control effect.

Description

Switching circuit control method, control chip and switching circuit

Technical field

The present invention relates to the field of switch circuit control, and in particular, to a switch circuit control method, a control chip and a switch circuit.

Background technique

Figure 1 shows a single-phase BOOST PFC controller and its circuit operating with conventional CRM or DCM. Taking this circuit as an example, in the CRM/DCM multi-mode switching circuit, the dead time Tdcmoff in the DCM working mode is calculated. If the Tdcmoff time is between the bottom number 3 and the bottom number 4, then it is possible It will jump to the bottom 3 to turn on. If the bottom of the previous switching cycle is 5, then the bottom will jump from the bottom 5 of the previous switching cycle to the bottom 3. This will not only cause the input current distortion (average current) due to the selection of bottom 3 to turn on. Inaccurate), there will also be a problem that the input current is distorted due to oscillation due to the valley opening at different valley numbers, thus making the iTHD larger; Figure 2 illustrates this situation. In the CRM working mode, the switch tube is turned on at the first valley, but when switching to DCM, it may jump directly from the first valley to the third valley or more valleys, and sometimes it is not even switched on from the bottom. In this way It will cause the peak value of the inductor current to jump, for example, from I _dcm-pk2 to I _crm-pk3 . If the current peak value suddenly changes significantly, it will easily cause oscillation and cause input current distortion.

Contents of the invention

In view of this, embodiments of the present invention provide a switching circuit control method, a control chip and a switching circuit. This control method can select different valley numbers to open according to different working stages, thereby achieving stable switching between different working stages.

In order to solve the above technical problems, this application adopts the following technical solutions:

A switching circuit control method for controlling a switching circuit. The switching circuit at least includes an inductor and a switching tube capable of controlling the inductor for excitation. The switching circuit at least includes an Nth working stage, an (N+1) ) working stage...(N+M)th working stage; in the Nth working stage, the switching tube is turned on at the Nth valley, and in the (N+1)th working stage; the switching tube is turned on at the (N+th)th working stage; 1) The first valley is turned on... In the (N+M)th working stage, the switch tube is turned on at the (N+M)th valley; when the first preset condition group is met, the switch circuit is operated by the Nth stage, the (N+1)th working stage...switch to the (N+M)th working stage in turn; where N and M are both positive integers; the first preset condition group represents that the reference current of the inductor gradually decreases .

This control method controls the opening of the switching tube by increasing the number of valleys one by one based on whether the first preset condition group is met. Since the number of valleys opening in adjacent working stages changes only by one, the energy difference generated is very small, that is, the inductance The change of current is very small, thus ensuring the stability of switching.

A switching circuit control chip, suitable for controlling a switching circuit. The switching circuit at least includes an inductor and a switching tube capable of controlling the inductor for excitation. The switching circuit at least includes an Nth working stage, an (N+1) ) working stage...the (N+M) working stage; in the N working stage, the switch tube is turned on at the Nth valley; in the (N+1) working stage, the switching tube is turned on at the (N+ 1) The first valley is turned on... In the (N+M)th working stage, the switch tube is turned on at the (N+M)th valley; the switch circuit control chip at least includes an adaptive valley number generation unit and an adaptive lock. Valley control unit; the adaptive valley number generation unit is used to add 1 to N to obtain the opening valley number of the next working state when the first preset condition group is met, and update N with (N+1), Until the opening valley number (N+M) of the (N+M)th working stage is obtained, and the opening valley number of each working stage is sent to the adaptive locking valley control unit; the first preset condition group represents the reference of the inductor The current gradually decreases; the adaptive locking valley control unit is used to generate a corresponding control signal for controlling the opening of the switch tube according to the opening valley number calculated by the adaptive valley number generating unit; wherein, N and M are all positive integers.

The control chip can control the opening of the switch tube by increasing the number of valleys one by one according to whether the first preset condition group is met. Since the number of valley openings in adjacent working stages changes only by one, the energy difference generated is very small. That is, the change in the inductor current is very small, thus ensuring stable switching.

A switching circuit, including a switching unit, an output voltage sampling unit, an input voltage sampling unit, a current sampling unit, an inductor current zero-crossing sampling unit and the above-mentioned switching circuit control chip; the output voltage sampling unit and the switching unit output end Electrically connected to sample the output voltage sampling signal; the input voltage sampling unit is electrically connected to the input end of the switch unit to sample the input voltage sampling signal; the output voltage sampling unit and the input voltage sampling unit are also connected to the switch circuit control chip The reference current generating unit is electrically connected; the current sampling unit is electrically connected to the switch unit, and the inductor current sampling signal of the switch unit is sampled; the inductor current zero-crossing sampling unit is electrically connected to the switch unit, for Obtain the inductor current zero-crossing signal of the inductor of the switch unit; the current sampling unit is electrically connected to the Ton signal control unit of the switch circuit control chip; the inductor current zero-crossing sampling unit is electrically connected to the switch circuit control chip. The adaptive lock bottom control unit is electrically connected; the switch circuit control chip is at least used to control the operation of the switch unit according to the output voltage sampling signal, the input voltage sampling signal, the inductor current sampling signal and the inductor current zero-crossing signal.

Under the control of the above-mentioned switch circuit control chip, the switching circuit can realize the number of valleys to be increased one by one to turn on the switching tube. Since the number of valleys to turn on at the valleys in adjacent working stages changes only by one, the energy difference generated is very small, that is, The change in inductor current is very small, thus ensuring the stability of circuit control.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention and are not relevant to the present invention. For those of ordinary skill in the field, other drawings can be obtained based on these drawings without exerting creative efforts, but these drawings should fall within the protection scope of this application.

Figure 1 is a schematic diagram of a boost circuit in the prior art;

Figure 2 is a schematic waveform diagram of the boost circuit described in Figure 1;

Figure 3 is a flow chart of a control method provided by an embodiment of the present invention;

Figure 4 is a schematic waveform diagram according to the control method shown in Figure 3 according to the embodiment of the present invention;

Figure 5 is a schematic waveform diagram of the first first/second preset condition group provided by the embodiment of the present invention;

Figure 6 is another waveform schematic diagram of the first first/second preset condition group provided by the embodiment of the present invention;

Figure 7 is a schematic waveform diagram of the second first/second preset condition group provided by the embodiment of the present invention;

Figure 8 is a schematic waveform diagram of the third first/second preset condition group provided by the embodiment of the present invention;

Figure 9 is a schematic diagram of a waveform obtained using a timing method according to an embodiment of the present invention;

Figure 10 is a flow chart of switching tube opening control with a maximum off time provided by an embodiment of the present invention;

Figure 11 is a schematic flowchart of obtaining the maximum number of valleys provided by an embodiment of the present invention;

Figure 12 is a block diagram of a switch circuit control chip provided by an embodiment of the present invention;

Figure 13 is a block diagram of another switch circuit control chip provided by an embodiment of the present invention;

Figure 14 is a schematic diagram of a switching circuit provided by an embodiment of the present invention.

Detailed ways

In order to better understand the technical solution of the present invention, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

It should be clear that the described embodiments are only some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

The terminology used in the embodiments of the present invention is only for the purpose of describing specific embodiments and is not intended to limit the present invention. As used in this embodiment and the appended claims, the singular forms "a," "the" and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. Electrical connections include direct electrical connections and indirect electrical connections.

It should be understood that the term "and/or" used in this article is only an association relationship describing related objects, indicating that there can be three relationships, for example, A and/or B, which can mean: A alone exists, and A and A exist simultaneously. B, there are three situations of B alone. In addition, the character "/" in this article generally indicates that the related objects are an "or" relationship.

Switching circuit topology includes boost (boost) circuit and its derived totem pole bridgeless BOOST PFC (power factor correction) circuit, buck (step-down) circuit, flyback (flyback conversion) circuit, etc. The switching circuit at least includes a switching tube and an inductor. A common single-phase boost circuit is shown in Figure 1. The power conversion function or power factor correction function is achieved by controlling the switching tube Q. According to the control form of the inductor current, the switching circuit has three working modes: CCM working mode (Continuous Conduction Mode: inductor current continuous mode), DCM working mode (DiscontinuousConduction Mode: inductor current discontinuous mode) and CRM working mode (Critical Conduction mode) : critical conduction mode). This application mainly improves the control method of switching from the DCM working mode or the CRM working mode to the DCM working mode to achieve more optimized control.

Specifically, embodiments of the present application provide a switching circuit control method for controlling a switching circuit. The switching circuit at least includes an inductor and a switching tube capable of controlling the inductor for excitation. The switching circuit at least includes (M +1) work stage: Nth work stage, (N+1)th work stage... (N+M)th work stage. The opening valleys of the switching tubes in each working stage are different, but they increase or decrease by one in turn: in the Nth working stage, the switching tubes are opened at the Nth valley; in the (N+1)th working stage, the switching tubes are turned on Turn on at the (N+1)th valley... In the (N+M)th working stage, the switch tube turns on at the (N+M)th valley. Among them, N and M are both positive integers. The switching conditions of adjacent working stages are determined by the first preset condition group. As shown in Figure 3, the control method includes steps S11: Determine whether the relevant parameters of the switching circuit satisfy the first preset condition group; S12: If satisfied, then Switch work phases. That is, when the first preset condition group is satisfied, the switching circuit gradually switches from the Nth working stage, the (N+1)th working stage... to the (N+M)th working stage in sequence. When the second preset condition group is satisfied, the switch circuit switches from the (N+M)th working stage to the Nth working stage in sequence, that is, the switch circuit switches from the (N+M)th working stage to the (N+M)th working stage in sequence. N+M-1) Work stage...The (N+1)th work stage switches to the Nth work stage. The number of work stages is determined by the size of M. The first preset condition group represents that the reference current of the inductor gradually decreases, and the second preset condition group represents that the reference current of the inductor gradually increases.

This control method can make the switch from CRM to DCM work, or when DCM is working, the dead time Tdcmoff changes according to certain rules to realize that the number of valleys is increased one by one to activate or the number of valleys is reduced one by one to activate. Due to the adjacent work There is only one change in the number of valley openings at the bottom of the stage, so the energy difference generated is very small, that is, the change in the inductor current is very small, thus ensuring the stability of switching. Among them, in the CRM working mode, the switch tube is turned on at the first bottom. In addition, in this control method, since the bottom of each turn-on is known in advance, the average value of the inductor current can be calculated more accurately. This not only achieves high efficiency, but also has small input current distortion and very small iTHD.

The above control method shows the inductor current waveform _IL , the Vds waveform of the switch tube, the switch tube turn-off signal Vrst timing diagram, the Vds bottom Vsetzcd timing diagram and the switch tube drive signal Vgate in the DCM operating mode and when the DCM switches to the CRM operating mode. The timing diagram is shown in Figure 4. Specifically, the third working stage in the DCM working mode (the third valley activation) and the second working stage (the second valley activation) switch to the first working phase in the CRM working mode. (The first valley opens). Vds refers to the voltage between the drain (D pole) and source (S pole) of the switch tube. The change in Vds during the dead time is caused by the resonance between the parasitic capacitance/inductance of the switch tube and other devices. As shown in Figure 4, in DCM working mode and when DCM switches to CRM, it is activated at different valleys according to certain specifications and the number of valleys increases or decreases one by one, that is, the valley activation is locked. When the valley is locked, the time of Tdcmoff (n) can be obtained regularly, so that the reference current peak value I _dcm-PK (n) of the corresponding working stage in the DCM working mode can be adjusted according to formula (1), or the switching tube can be turned on. Time Tdcmon (n) indirectly adjusts I _dcm-PK (n) so that the average value of the inductor current in each working stage is equal to I _in-ac . I _in-ac is an AC current signal with the same frequency and phase as the input voltage.

I _dcm-PK (n) = 2*I _ref-ac (n) * (T _dcmzcd (n) + T _dcmoff (n))/T _dcmzcd (n)...Formula (1);

Among them, I _ref-ac (n) is the reference average value of the inductor current in the n-th working stage, which is proportional to I _in-ac ; T _dcmzcd (n) is the sum of the inductor excitation and demagnetization times in the n-th working stage; The T _dcmoff (n) is the dead time after demagnetization of the inductor in the nth working stage; the nth working stage is turned on at the nth valley, and the dead time is (n-1) resonance cycles ; When the inductor current reaches the peak reference current I _dcm-PK (n), the switch tube is controlled to turn off; where n is a positive integer and N≤n≤(N+M).

In addition, the information of the previous switching cycle can also be used to adjust the reference current peak value I _dcm-PK (n), that is, the reference current peak value I _dcm-PK (n) of the corresponding working stage in the DCM operating mode is adjusted through formula (2);

I _dcm-PK (n)=2*I _ref-ac (n)*(T _dcmzcd (n-1)+T _dcmoff (n-1))/T _dcmzcd (n-1)...Formula (2);

Among them, I _ref-ac (n) is the reference average value of the inductor current in the nth working stage, which is proportional to I _in-ac ; T _dcmzcd (n-1) is the inductor excitation sum in the (n-1)th working stage. The sum of the demagnetization times; the T _dcmoff (n-1) is the dead time after the inductor is demagnetized in the (n-1)th working stage; the nth working stage is turned on at the nth valley, and the The dead time is (n-1) resonance periods; when the inductor current reaches the peak reference current I _dcm-PK (n), the switch is controlled to turn off; where n is a positive integer and N≤ (n-1)≤(N+M).

Specifically, in one embodiment, referring to Figures 5 and 6, in a power frequency cycle, the switching circuit has multiple modes (DCM/CRM/CCM), and the switching between modes is determined by the reference instantaneous value of the inductor current and The preset mode switching threshold is determined; Figure 5 has DCM, CRM and CCM working modes; while Figure 6 has CRM and DCM working modes. This application does not limit the control of the CCM working mode and the switching conditions of each mode. In this embodiment, multiple working stages occur in the same power frequency cycle. Within one power frequency cycle, there are (M+1) preset reference values: RefN, Ref(N+1)...Ref( N+M). The first preset condition group includes the reference instantaneous value I _{ref_ac_trans} of the inductor current sequentially decreasing from the (N)th preset reference value RefN to the (N+M)th preset reference value Ref(N+M); the Nth working stage, The (N+1) working stage...(N+M) working stage is located in the same power frequency cycle.

The second preset condition group includes the instantaneous reference value I _{ref_ac_trans} of the inductor current increasing from the (N+M) preset reference value Ref(N+M) to the Nth preset reference value RefN; N+1) working stage...The (N+M) working stage is located in the same power frequency cycle.

In the embodiments shown in Figures 5 and 6, within a power frequency voltage or current cycle, the valley opening changes as the real-time value of the reference signal changes according to the number of valleys within a certain range. Taking N=1, M=4 as an example, Ref5<Ref4<Ref3<Ref2<Ref1, when I _{ref_ac_trans} <Ref5, the switch circuit works in the fifth working stage, and the switch tube is turned on at the bottom of the fifth valley; when Ref5<I _{ref_ac_trans} < Ref4, the switching circuit works in the fourth working stage, and the switching tube is turned on at the fourth valley; when Ref4<I _{ref_ac_trans} <Ref3, the switching circuit works in the third working stage, and the switching tube is turned on at the third valley; when Ref3<I _{ref_ac_trans} < Ref2, the switching circuit works in the second working stage, and the switching tube is turned on at the second valley; when Ref2<I _{ref_ac_trans} <Ref1, the switching circuit works in the first working stage, and the switching tube is turned on at the first valley, which is also the CRM working mode. Among them, Ref1 can also be used as the mode switching threshold for switching between CCM and CRM working modes, and Rer2 can be used as the mode switching threshold for switching between CRM and DCM working modes.

In another embodiment, as shown in Figure 7, this application provides a switching circuit control method, that is, the number of valley openings changes according to the reference current peak value of the inductor, but within a power frequency cycle, the number of valley openings is The trough number is kept inconvenient. This way of working is suitable for CRM or DCM working situations. In Figure 7, taking N=1 as an example, the situation of opening from valley 1 to valley (1+M) is illustrated. In this embodiment, there are (M+1) preset peak values: RefpkN, Refpk(N+1)...Refpk(N+M). The first preset condition group includes the reference current peak value of the inductor current decreasing from the (N)th preset peak value to the (N+M)th preset peak value in sequence; the Nth working stage, the (N+1)th working stage... ...The (N+M) working stage is located in different power frequency cycles.

The second preset condition group includes the reference current peak value of the inductor current increasing from the (N+M)th preset peak value to the Nth preset peak value in sequence; the Nth working stage, the (N+1)th working stage... ...and the (N+M) working stage are located in different power frequency cycles.

In another embodiment, in order to obtain the switching conditions of different working stages, the first preset condition group can be obtained using the following steps:

step1: Determine the reference signal that determines the change in the valley number. This reference signal is used to characterize the peak value or instantaneous value of the reference signal I _{ref_valley} of the input average current, or is used to characterize the combination of the instantaneous value and peak value of the reference signal I _{ref_valley} .

step2: Configure the switching step adjustment factor A, step. A is a constant, and step is set according to efficiency, which is used to optimize efficiency debugging. Different step values have different depth advancement speeds of DCM. The final step value is determined based on the on-state loss and switching loss.

step3: Use the following formula to calculate the valley switching threshold.

I _{ref_valley} (n~ n+1)=I _{ref_set} / (A+n×step);

Among them: I _{ac_valley} (n~n+1) refers to the current reference threshold switching from the nth valley to the (n+1)th valley.

Assume that CCM is defined as 0 troughs and CRM is 1 trough. I _{ref_set} can be defined as the mode switching threshold for switching the CCM working mode to the CRM working mode or the mode switching threshold for switching the CRM working mode to the DCM working mode.

The system can automatically configure the switching threshold between CCM/CRM/DCM based on the above formula. And it will automatically lock the bottom according to the input average current and configured parameters. After locking the valley, use a specific calculation formula to calculate the current loop reference in DCM operating mode to ensure that the input current always follows the input voltage.

In Figure 8, the switching threshold A between CCM/CRM working modes is configured as 1. The switching thresholds of different step values under parameter A=1 are 0.33, 0.45, 0.59, 0.75, 0.96, 1.22, 1.56, 2. According to A, step and I _{ref_set} construct the switching curve in Figure 8. It can be seen that the step value can be set to multiple levels. In actual work, it is assumed that the default level step=2 is used. If the CRM working mode frequency is too high and exceeds a certain limit value, the step can be automatically switched to the next level to avoid CRM The operating frequency is too high. The changing trend of the drawings is favorable for switching circuits. For example, the BOOST PFC converter operates in the first to third valleys when the power is large, and operates at a lower valley number when the power is lighter, which is beneficial to improving efficiency.

In this embodiment, the first preset condition group is that the reference value representing the inductor current decreases to I _{ref_valley} (n~n+1); where, I _{ref_valley} (n~ n+1)=I _{ref_set} / (A+ n×Step). The second preset condition group is that the reference value of the inductor current increases to I _{ref_valley} (n~n-1)=I _{ref_set} /[A+(n-1)×Step], which I _{ac_valley} (n~n-1) refers to is the current reference threshold for switching from the nth valley to the (n-1)th valley.

Of course, in addition to the above-mentioned first/second preset condition group, other preset condition groups can also be set to meet the working stage switching requirements. The calculation formula of I _{ref_valley} (n~n+1)/I _{ref_valley} (n~n-1) is not limited to the above examples. It can be a direct proportional function, an inverse proportional function, a quadratic equation, etc., and the step adjustment factor is not limited to 2. Can be any number.

Furthermore, in the above embodiment, the valley bottom can be detected by the inductor current zero-crossing detection circuit, such as by the ZCD winding of the inductor. However, during the off time of DCM operation, the oscillation amplitude of Vds will gradually decrease over time, and the inductor current will also gradually decrease, causing the zero-crossing detection circuit to be unable to detect the Vsetzcd signal. As shown in Figure 9, at the bottom of 5 Vsetzcd can be detected, but cannot be detected from valley 6 to valley 8. In this case, the technology of the present invention provides a method of adaptively accurately simulating the detected valley, so that the valley can be increased and opened according to the target set valley. This method of adaptive and precise simulation to detect the bottom of the valley will time the time between two adjacent Vsetzcd signals, such as Tr1 and Tr2, etc., Tr1, Tr2... are the real resonance periods, and use the first duration Trto to record the latest The duration between two valleys retains a certain incremental time Td, that is, Trto=Tr+Td. Trto is equivalent to the resonance period, which is also the resonance duration of two adjacent valleys. When each Vsetzcd signal comes, timer cnt_TO is used to time Trto. If the Vsetzcd signal is not waited for at a certain time and cnt_TO=Trto is found, it is considered that the valley bottom has been found. The time of this valley uses the time of Trto as the equivalent length of two adjacent valleys. If the bottom number at this time reaches the target value, a signal Vset is generated that triggers the opening of the switch. If it does not, the bottom number is increased by one, and the timing is repeated until the bottom number reaches the target value. For example, in Figure 9, taking the eighth opening valley number as an example, the Vsetzcd signal can be detected at valley 5, but no Vsetzcd signal is detected between valley 6 and valley 8, then Trto=Tr4+Td. When the cnt_TO timing reaches Trto, it is considered that the bottom has been detected, and the number of bottoms is increased by 1. This repeated timing, when the number of bottoms reaches the target bottom of 8, generates a signal Vset that triggers the opening of the switch.

In this embodiment, whenever the zero-crossing detection circuit detects a zero-crossing signal, the timer cnt_T0 is used for timing. If the zero-crossing detection circuit detects a zero-crossing signal during the timing period, it is considered that the bottom has been found and the timing is cleared. ; If the zero-crossing signal is not detected and the timing reaches the first duration Trto, the moment is also determined to be the bottom moment; and then the valley number is calculated based on the zero-crossing signal and the first duration Trto until the valley number reaches the determination of the switching tube The opening trough number. Generally, the first few valleys can be detected using the zero-crossing detection circuit. As the resonance capability decreases, the valleys of the subsequent resonance cycles need to be measured by the timer cnt_T0.

Furthermore, in the above embodiment, if the switching circuit operates in the DCM operating mode, the opening valley of each working stage can be calculated according to the above switching circuit control method (also a valley adaptive control algorithm). However, the time corresponding to the turn-on valley number should not exceed the maximum turn-off time T _offmax of the switch tube. Therefore, when the bottom that determines the switch tube to be turned on has not been reached but the maximum off time is reached, the switch tube is controlled to be turned on. The maximum value of the valley number n is limited by the maximum off-time T _offmax of DCM operation and the period Tr between valleys. If the maximum off-time is limited to less than or equal to 40us, the period Tr is determined by the hardware design, so the maximum valley number is also It's limited. In this embodiment, if the maximum number of valleys set according to the first preset condition group has not been reached, and the maximum off-time of DCM operation has reached T _offmax , then the maximum number of valleys does not need to reach the set maximum value. The Vset signal can be generated, triggering Vgate to be positive, and controlling the switching tube to turn on. Figure 10 shows a schematic flow chart for implementing this embodiment.

In switching circuits, the switching frequency often needs to limit the minimum operating frequency. An operating frequency that is too low will cause noise that can be recognized by the human ear, and the current ripple caused by a switching frequency that is too low is difficult to filter out. Moreover, when working with different input voltages and working at the lowest frequency, the valley numbers are also different. Existing technology often limits a fixed maximum number of valleys. However, under low pressure, it is often limited by the lowest frequency before the maximum number of valleys is triggered. Under high pressure, it is easy to cause the number of valleys to exceed the maximum valley limit, resulting in unreliable control. , cannot be compatible with high and low voltages, and its application is greatly limited. In the control method provided by this application, the value of the valley number n can be adaptively changed, and the valley number n can be adaptively changed according to the peak value and/or instantaneous value of the reference signal (current). The larger the reference signal value, the smaller the value of the valley number n.

In addition, considering the noise problem, the switching circuit is generally set with a minimum frequency limit, such as 25kHz. When the switching cycle reaches the preset value, it will be forced to turn on. At this time, the valley number no longer proceeds as expected. According to I _dcm- in formula (1) The input current I _in-ac (n) under _PK (n) operation will violate expectations, that is, I _in-ac will be distorted. Therefore, the maximum valley number needs to be limited. When the parasitic capacitance of the switch tube is larger or the PFC inductance is larger, the corresponding maximum valley number should be smaller to avoid distortion of I _in-ac due to the lowest frequency limit.

As mentioned above, considering that different systems need to set different maximum valley numbers to achieve optimal operation, this application also proposes an adaptive maximum valley number selection strategy. As shown in Figure 11, the initial value of the preset valley configuration is the maximum number of valleys N _{valley_max} ; switching frequency detection is performed in every (or every N, that is, multiple) power frequency half-waves. For lower switching frequencies ( The number of switches close to the lowest limit frequency 25kHz (for example, lower than 35kHz) is counted and recorded as N _{fsw_low} . If N _{fsw_low} is greater than the preset value N _{fsw_th_H} , the maximum number of valleys N _{valley_max} in the next power frequency cycle is automatically reduced by 1. , and when N _{fsw_low} is less than another preset value N _{fsw_th_L} , the maximum number of valleys N _{valley_max} in the next power frequency cycle is automatically increased by 1.

Under this strategy, regardless of different input voltages or different loads, N _{valley_max} will be automatically adjusted to a more optimized value, so that it is not distorted by the lowest frequency of 25kHz, and the lowest switching value in the power frequency half-wave is achieved. The frequency is adjusted to a lower value; thus manual debugging and configuration time can be reduced, and both efficiency and THD optimization can be achieved within the full working range. That is to say, when the switching circuit is working, the maximum valley number calculated according to the first/second preset condition group is less than or equal to the maximum valley number N _{valley_max} determined by the maximum valley number determination module, and the maximum opening valley number is the (N+ M) The number of valleys in the working stage (N+M) is less than or equal to N _{valley_max} .

The switching circuit control method provided by the above embodiments has at least one or more of the following advantages:

1. While maintaining the high efficiency characteristics of multi-mode operation, it is ensured that under CRM/DCM operation, the valley opening changes according to the prescribed rules, ensuring that the average value of the inductor current does not oscillate and distort due to the jump of the inductor current.

2. The valley adjustment curve can be configured adaptively to prevent the CRM mode working frequency from being too high.

3. Supplementary strategies can avoid operating below the minimum operating frequency, causing noise that can be recognized by the human ear, and causing large current ripples.

4. Supplementary strategies can avoid non-bottom turn-on, causing switching losses and EMI interference.

5. The supplementary strategy can automatically identify the required maximum number of valleys and lock the valley before the lowest frequency, which not only facilitates engineer design, but also achieves both efficiency optimization and THD optimization within the full working range.

In order to implement the switch circuit control method provided in the above embodiments, embodiments of the present application provide a switch circuit control chip IC, which is suitable for controlling the switch circuit. The switch circuit at least includes an inductor and a switch tube capable of controlling the inductor for excitation. The switching circuit at least includes the Nth working stage, the (N+1)th working stage...the (N+M)th working stage; in the Nth working stage, the switch tube is turned on at the Nth valley...in the (Nth) +M) working stage, the switch tube is turned on at the (N+M)th valley. As shown in Figure 12, the switch circuit control chip IC at least includes an adaptive valley number generation unit 11 and an adaptive lock valley control unit 12;

The adaptive valley number generating unit 11 is used to add 1 to N to obtain the opening valley number of the next working state when the first preset condition group is met, and update N with (N+1) until the (Nth +M) the opening valley number (N+M) of the working stage, and send the opening valley number of each working stage to the adaptive locking valley control unit;

The adaptive lock bottom control unit 12 is used to generate a corresponding control signal for controlling the opening of the switch tube according to the opening valley number calculated by the adaptive valley number generation unit; wherein, N and M are both positive integers.

The technical effects of the switch circuit control chip refer to the technical effects of the above-mentioned switch circuit control method, which will not be described in detail here and later. The two can be quoted and learned from each other.

In one embodiment, the control chip also includes a shaping adjustment unit 13, which is used to calculate the peak reference current I _dcm-PK (n) of the inductor according to the following formula (1),

_Idcm-PK (n)=2* _Iref-ac (n)*( _Tdcmzcd (n)+ _Tdcmoff (n))/ _Tdcmzcd (n);

Among them, I _ref-ac (n) is the reference average value of the inductor current in the n-th working stage; T _dcmzcd (n) is the sum of the excitation and demagnetization time of the inductor in the n-th working stage; the T _dcmoff (n ) is the dead time after demagnetization of the inductor in the nth working stage; the nth working stage is turned on at the nth valley, and the dead time is (n-1) resonance cycles; when the inductor When the current reaches the peak reference current I _dcm-PK (n), the switch tube is controlled to turn off; where n is a positive integer and N≤n≤(N+M).

In addition, the shaping adjustment unit can also use the information of the previous switching cycle to adjust the reference current peak value Idcm-PK(n), that is, adjust the reference current peak value Idcm-PK(n) of the corresponding working stage in the DCM operating mode through formula (2) ;

I _dcm-PK (n)=2*I _ref-ac (n)*(T _dcmzcd (n-1)+T _dcmoff (n-1))/T _dcmzcd (n-1)...Formula (2);

Among them, I _ref-ac (n) is the reference average value of the inductor current in the n-th working stage; T _dcmzcd (n) is the sum of the excitation and demagnetization time of the inductor in the n-th working stage; the T _dcmoff (n) is the dead time after demagnetization of the inductor in the nth working stage; the nth working stage is turned on at the nth valley, and the dead time is (n-1) resonance cycles; when the inductor current When the peak reference current I _dcm-PK (n) is reached, the switching tube is controlled to turn off; where n is a positive integer and N≤(n-1)≤(N+M).

In one embodiment, the adaptive valley number generation unit includes an inductor current input port and a comparison module;

The adaptive valley number generation unit is preset with the Nth preset reference value, the (N+1)th preset reference value... the (N+M)th preset reference value; the inductor current input port is used to receive the reference of the inductor current Instantaneous value; the comparison module is used to compare the reference instantaneous value with each of the preset reference values; when the reference instantaneous value is sequentially reduced from the Nth preset reference value to the (N+M)th preset Reference value, the adaptive valley number generating unit sequentially sends the opening valley number N, (N+1)...(N+M) to the adaptive locking valley control unit; when the reference instantaneous value (N +M) The preset reference value is sequentially increased to the Nth preset reference value, and the adaptive valley number generating unit sequentially sends the opening valley number (N+M)...(N+1), N to the adaptive Bottom locking control unit; the Nth working stage, the (N+1)th working stage... and the (N+M)th working stage are located in the same power frequency cycle;

In another embodiment, the adaptive valley number generating unit is preset with the Nth preset peak value, the (N+1)th preset peak value... the (N+M)th preset peak value; the inductor current input port is used for After receiving the reference current peak value of the inductor; the comparison module is used to compare the reference current peak value with each of the preset peak values; when the reference current peak value decreases from the Nth preset peak value to the (Nth) +M) preset peak value, the adaptive valley number generation unit sequentially sends the opening valley number N, (N+1)...(N+M) to the adaptive locking valley control unit; when the reference current The peak value increases sequentially from the (N+M) preset peak value to the Nth preset peak value, and the adaptive valley number generating unit sequentially sends the opening valley number (N+M), ..., (N+1), N to the adaptive locking bottom control unit; the Nth working stage, the (N+1)th working stage... the (N+M)th working stage are located in different power frequency cycles.

Referring to Figure 13, in one embodiment, the adaptive valley number generating unit 11 is preset with switching step adjustment factors A and step. The adaptive valley number generating unit 11 is also preset with a reference signal threshold I _{ref_set} , and I _{ref_set} is a switch. The mode switching threshold for the circuit to switch from the CCM working mode to the CRM working mode or the mode switching threshold for the switching circuit to switch from the CRM working mode to the DCM working mode; the adaptive valley number generation unit 11 includes an inductor current input port, a calculation module and a judgment module ;

The inductor current input port is used to receive a reference value characterizing the inductor current, such as the reference instantaneous value I _{ref_ac_trans} of the inductor current and/or the reference peak value I _{ref_ac_pk} of the inductor current.

The calculation module is used to calculate the current reference threshold I _{ref_valley} (n~ n+1) for switching from the nth valley to the (n+1)th valley, I _{ref_valley} (n~ n+1)=I _{ref_set} / (A+ n×step);

The judgment module is used to judge whether the reference value of the inductor current drops to the I _{ref_valley} (n~ n+1); if so, add 1 to n to obtain the opening valley number of the (n+1)th working stage. Further, n is updated using n+1 until switching from the Nth working stage to the (N+M)th working stage.

In addition, the judgment module can also be used to judge whether the reference value of the inductor current increases to I _{ref_valley} (n~n-1); if so, subtract 1 from n to obtain the turn-on valley number of the (n-1)th working stage. Further, (n-1) is used to update n until switching from the (N+M)th working stage to the Nth working stage.

Further, as shown in Figure 13, the switch circuit control chip IC includes a zero-crossing detection port; the adaptive lock valley control unit 12 is electrically connected to the zero-crossing detection port, and receives the zero-crossing signal Vzcd of the inductor current through the zero-crossing detection port. In order to achieve control, the adaptive lock bottom control unit 12 is electrically connected to the zero-crossing detection port, so as to find the time when the turn-on control signal of the switching tube needs to be generated based on the bottom number sent from the adaptive bottom number generation unit 11 .

In one embodiment, the adaptive valley number generation unit 11 includes a timing module and a counting module;

The timing module is used to time the time between the zero-crossing signals of two adjacent inductor currents to obtain the resonance time Tr; add the increment time Td on the basis of the resonance time Tr to obtain the first time length Trto; wherein, the process A zero signal represents the bottom;

Whenever the zero-crossing detection port receives a zero-crossing signal, the timer cnt_T0 is used for timing. If the zero-crossing detection port receives a zero-crossing signal during the timing, the timing is cleared; if no zero-crossing signal is detected and the timing duration is When the first duration Trto is reached, the moment is determined to be the valley moment, and the first duration Trto is equivalent to two adjacent fixed resonance durations; subsequently, the valley number is obtained by timing the first duration Trto.

A counting module, configured to calculate the bottom number based on at least the zero-crossing signal and the first duration Trto until the bottom number reaches the bottom number that determines the turning on of the switch tube.

Further, in one embodiment, the adaptive valley number generation unit 11 can also be configured to include a maximum valley number determination module; the maximum valley number determination module presets the valley configuration initial value to be the maximum valley number N _{valley_max} ; the maximum valley number determination module is At:

Detect the switching frequency of the switching circuit in one or more power frequency half-waves;

If the number of times the switching frequency is less than the preset limit frequency (such as 35kHz) is greater than the preset value N _{fsw_th_H} , then set the maximum number of valleys in the next power frequency cycle to (N _{valley_max} -1), and use (N _{valley_max} -1) Update N _{valley_max} ; if the number of times the switching frequency is less than the preset limit frequency (such as 35kHz) is less than the preset value N _{fsw_th_L} , then set the maximum number of valleys in the next power frequency cycle to (N _{valley_max} +1), and use (N _{valley_max} +1) to update N _{valley_max} ; (N+M) is less than or equal to N _{valley_max} . That is to say, when the switching circuit is operating, the maximum valley number calculated according to the first/second preset condition group is less than or equal to the maximum valley number N _{valley_max} determined by the maximum valley number determination module.

Further, in one embodiment, the switch tube of the switching circuit is set with a maximum off-time; when the valley that determines the switch tube to turn on has not been reached, but the maximum off-time has been reached, the adaptive lock bottom control The unit generates a control signal to control the opening of the switch tube.

Figure 13 shows a control chip of a switching circuit, which includes an adaptive valley control function. The switching circuit control chip includes an adaptive valley number generation unit 11, an adaptive valley number control unit 12, a shaping condition unit 13, and a reference current. Generation unit 14, mode control unit 15, Ton signal control unit 16 and CCM-Toff control unit 17; wherein, the control method of the reference current generation unit 14, mode control unit 15, Ton signal control unit 16 and CCM-Toff control unit 17 Reference can be made to existing technology.

The reference current sampling unit 14 is used to generate an inductor current reference value based on the input voltage sampling value Vin and the output voltage sampling value Vo of the switching circuit; the inductor current reference value includes the inductor current reference average value I _ref-ac and the inductor current reference instantaneous value ( I _{ref_ac_trans} ) and/or the reference current peak value of the inductor current (I _{ref_ac_pk} );

The mode control unit 15 is used to determine the operating mode of the switching circuit based on the inductor current reference value generated by the reference current sampling unit 14;

The Ton signal control unit 16 is configured to determine the working mode, the inductor reference current in each working mode (such as the inductor reference current I _ref-DCM in the DCM working mode generated by the shaping adjustment unit and the CRM generated by the reference current sampling unit 14 The peak reference current I _ref—CCM /I _ref—CRM ) and the inductor current sampling signal Vcs in the /CCM operating mode generate a control signal that controls the switch tube to turn off. The inductor current sampling signal can be obtained directly by sampling the inductor current, or it can be obtained by sampling the switching tube circuit.

The CCM-Toff control unit 17 is used to generate a control signal to control the switch tube to turn off according to the working mode (CCM working mode), the input voltage sampling value, the output voltage sampling value and the switching period Ts.

The adaptive valley number generation unit 11 is used to generate a turn-on valley number; the adaptive locking valley control unit 12 is used to generate a switching tube turn-off in the CRM and/or DCM operating mode based on at least the valley number and the zero-crossing signal of the inductor current. control signal. That is to say, the shaping adjustment unit 13, the adaptive valley number generation unit 11 and the adaptive locking valley control unit 12 are used to perform switching tube turn-off control in CRM and DCM operating modes. In Figure 13, the adaptive valley number generation unit realizes the valley number control law of Figure 8; the shaping adjustment unit 13 realizes that the I _ref-DCM signal changes with the change of the valley number. The adaptive valley number generation unit 11 and the adaptive valley locking control unit 12 implement the control strategies of Figures 4 to 11 and the signal control of Toff.

In this application, the instantaneous value (I _{ref_ac_trans} ) of the reference current (I _{ref_ac} ) that characterizes the input average current can also be used to control the CCM/CRM/DCM combined operation within a power frequency cycle. The three working modes can be freely switched according to the instantaneous value of the input average current (I _{ref_ac_trans} ); the peak value (I _{ref_ac_pk} ) can also be used to control only one working mode including CCM, CRM and DCM in a power frequency cycle. Or the three working modes of CCM/CRM/DCM include the combination of CCM, CRM/DCM and DCM within one power frequency cycle.

The switch circuit control chip has at least one or more of the following advantages:

1. While maintaining the high efficiency characteristics of multi-mode operation, it is ensured that under CRM/DCM operation, the valley opening changes according to the prescribed rules, ensuring that the average value of the inductor current does not oscillate and distort due to the jump of the inductor current.

2. The valley adjustment curve can be configured adaptively to prevent the CRM mode working frequency from being too high.

3. Supplementary strategies can avoid operating below the minimum operating frequency, causing noise that can be recognized by the human ear, and causing large current ripples.

4. Supplementary strategies can avoid non-bottom turn-on, causing switching losses and EMI interference.

5. The supplementary strategy can automatically identify the required maximum number of valleys and lock the valley before the lowest frequency, which not only facilitates engineer design, but also achieves both efficiency optimization and THD optimization within the full working range.

Based on the above switching circuit control method and control chip, embodiments of the present application also provide a switching circuit. As shown in FIG. 1 and FIG. 14 , the switching circuit includes a switching unit 20, an output voltage sampling unit 22, and an input voltage sampling unit. 21. Current sampling unit 23, inductor current zero-crossing sampling unit 24 and the above-mentioned switching circuit control chip IC; the switching unit can be a Flyback converter, a BOOST converter (as shown in Figure 1) or a single-phase totem pole bridgeless BOOST PFC converter (as shown in Figure 14); the switching circuit control chip IC is used to control each switching tube in the switching unit 20, so that the switching circuit has better performance.

The output voltage sampling unit 22 is electrically connected to the output terminal of the switch unit 20, and samples the output voltage sampling signal Vo; the input voltage sampling unit 21 is electrically connected to the input terminal of the switch unit 20, and samples the input voltage sampling signal Vin; the output voltage sampling unit 22 and the input voltage The sampling unit 21 is also electrically connected to the reference current generating unit 14 of the switch circuit control chip IC; the current sampling unit 23 is electrically connected to the switch unit 23, and samples the inductor current of the switch unit 20 to obtain the inductor current sampling signal Vcs; the inductor current crosses zero. The sampling unit 24 is electrically connected to the switching unit 20 and is used to obtain the inductor current zero-crossing signal Vzcd of the switching unit 20, which is used to represent the resonance valley; the current sampling unit 23 is electrically connected to the Ton signal control unit 16 of the switching circuit control chip IC. ; The inductor current zero-crossing sampling unit 24 is electrically connected to the adaptive locking bottom control unit 12 of the switching circuit control chip IC; the switching circuit control chip IC is at least used to measure the output voltage sampling signal Vo, the input voltage sampling signal Vin, and the inductor current sampling signal Vcs and the inductor current zero-crossing signal Vzcd control the operation of the switching unit. The specific control method is described with reference to the aforementioned switch circuit control method and switch circuit control chip embodiments, and will not be described again in this application.

The switching circuit control method and switching circuit control chip proposed in the embodiment of this application are not only suitable for traditional single-phase BOOST PFC converters, BUCK converters, Flyback converters, but also can be used for single-phase totem pole bridgeless BOOST PFC converters. As shown in Figure 14, the single-phase totem pole bridgeless BOOST PFC converter has slightly different requirements for the control chip than the traditional BOOST PFC converter (shown in Figure 1). Due to the different reference grounds, Vin, Vo and Vcs In addition to the different signal sampling methods, in addition to Vgda, the output of the control chip also needs to generate a Vdgb. A dead time needs to be inserted between Vgdb and Vgda to ensure work safety. In the positive and negative half cycles of the power frequency cycle, Vgda and Vgdb need to interact with each other. Change the master-slave relationship.

What is disclosed above is only the preferred embodiment of the present application, and cannot be used to limit the scope of rights of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this specification still belong to this application. Scope covered by the application.

Claims (11)

1. A switching circuit control method for controlling a switching circuit. The switching circuit at least includes an inductor and a switching tube capable of controlling the inductor for excitation. It is characterized in that the switching circuit at least includes an Nth working stage. , (N+1)th working stage...(N+M)th working stage; in the Nth working stage, the switch tube is turned on at the Nth valley; in the (N+1)th working stage , the switch tube is turned on at the (N+1)th valley... In the (N+M)th working stage, the switch tube is turned on at the (N+M)th valley; when the first preset is satisfied Condition group, the switch circuit switches from the Nth working stage, the (N+1)th working stage... to the (N+M)th working stage; where N and M are both positive Integer; the first preset condition group represents that the reference current of the inductor gradually decreases; The peak reference current I _dcm-PK (n) of the inductor is calculated according to formula (1) or (2): I _dcm-PK (n) = 2*I _ref-ac (n) * (T _dcmzcd (n) + T _dcmoff (n)) / T _dcmzcd (n)...Formula (1); where, I _ref-ac ( n) is the reference average value of the inductor current in the nth working stage; T _dcmzcd (n) is the sum of the excitation and demagnetization times of the inductor in the nth working stage; the T _dcmoff (n) is all the times in the nth working stage The dead time after the inductor is demagnetized; in the nth working stage, the switch is turned on at the nth valley, and the dead time is (n-1) resonance periods; when the inductor current reaches the When the peak reference current I _dcm-PK (n) is reached, the switch tube is controlled to turn off; where n is a positive integer and N≤n≤(N+M); I _dcm-PK (n)=2*I _ref-ac (n)*(T _dcmzcd (n-1)+T _dcmoff (n-1))/T _dcmzcd (n-1)...Formula (2); where , I _ref-ac (n) is the reference average value of the inductor current in the n-th working stage; T _dcmzcd (n) is the sum of the excitation and demagnetization times of the inductor in the n-th working stage; the T _dcmoff (n) is The dead time after demagnetization of the inductor in the nth working stage; in the nth working stage, the switch tube is turned on at the nth valley bottom, and the dead time is (n-1) resonance periods; when the When the inductor current reaches the peak reference current I _dcm-PK (n), the switch is controlled to turn off; where n is a positive integer and N≤(n-1)≤(N+M); The first preset condition group is that the reference value characterizing the inductor current decreases to I _{ref_valley} (n~ n+1); Among them, I _{ref_valley} (n~ n+1)=I _{ref_set} / (A+n×step), Among them, I _{ac_valley} (n~n+1) refers to the current reference threshold for switching from the nth valley to the (n+1)th valley; A and step are the switching step adjustment factors, and step is determined based on efficiency A set of values, A is a constant; I _{ref_set} is the mode switching threshold for the switching circuit to switch from the CCM working mode to the CRM working mode or the mode switching threshold for the switching circuit to switch from the CRM working mode to the DCM working mode. 2. The switching circuit control method according to claim 1, wherein the valley bottom is obtained by detecting a zero-crossing signal by a zero-crossing detection circuit; If the zero-crossing detection circuit cannot detect a zero-crossing signal as the resonant amplitude of the voltage between the drain and source of the switch tube decreases, the valley bottom is obtained through the following steps: Timing the time between two adjacent valleys detected by the zero-crossing detection circuit to obtain the resonance time; Add an increment time to the resonance time to obtain a first duration; Whenever the zero-crossing detection circuit detects a zero-crossing signal, the timer cnt_T0 is used for timing. If the zero-crossing detection circuit detects a zero-crossing signal during the timing period, the timing is cleared; if no zero-crossing signal is detected but When the timing duration reaches the first duration, the moment is determined to be the valley moment, and the first duration is equivalent to the resonance duration of two adjacent valleys; The valley number is calculated at least based on the zero-crossing signal and the first duration until the valley number reaches the valley number that determines the opening of the switch tube. 3. The switching circuit control method according to claim 1, characterized in that the switching circuit operates in the DCM operating mode; when the bottom that determines the opening of the switching tube has not been reached, but the maximum off time is reached, the control circuit is controlled. The switch tube is turned on. 4. The switching circuit control method according to claim 1, further comprising the steps of: The initial value of the default valley configuration is the maximum number of valleys N _{valley_max} ; Detect the switching frequency of the switching circuit in one or more power frequency half-waves; If the number of times the switching frequency is less than the preset limit frequency is greater than the preset value N _{fsw_th_H} , then set the maximum number of valleys in the next power frequency cycle to (N _{valley_max} -1), and use (N _{valley_max} -1) Update N _{valley_max} ; If the number of times the switching frequency is less than the preset limit frequency is less than the preset value N _{fsw_th_L} , then set the maximum number of valleys in the next power frequency cycle to (N _{valley_max} +1), and use (N _{valley_max} +1) Update N _{valley_max} ; (N+M) is less than or equal to N _{valley_max} . 5. The switching circuit control method according to claim 1, characterized in that when the second preset condition group is met, the switching circuit switches from the (N+M)th working stage... to the Nth working stage in sequence. ;The second preset condition group represents that the reference current of the inductor gradually increases; The second preset condition group includes the instantaneous reference value of the inductor current increasing from the (N+M)th preset reference value... to the Nth preset reference value in turn; the Nth working stage, the (N+1)th ) Working stage...The (N+M) working stage is located in the same power frequency cycle; or, The second preset condition group includes the reference current peak value of the inductor current increasing from the (N+M)th preset peak value...to the Nth preset peak value in sequence; the Nth working stage, the (N+1)th ) working stage...The (N+M) working stage is located in different power frequency cycles; or, The second preset condition group includes the reference value of the inductor current increasing to I _{ref_valley} (n~n-1)=I _{ref_set} /[A+(n-1)×Step], I _{ac_valley} (n~n-1 ) refers to the current reference threshold for switching from the nth valley to the (n-1)th valley; among them, I _{ac_valley} (n~n-1) refers to the switching from the nth valley to the (n-1) ) is the current reference threshold of the valley; A and step are switching step adjustment factors, step is a set of values determined according to efficiency, and A is a constant; I _{ref_set} is the mode in which the switch circuit switches from the CCM operating mode to the CRM operating mode The switching threshold may be a mode switching threshold for the switch circuit to switch from the CRM working mode to the DCM working mode. 6. A switching circuit control chip, suitable for controlling a switching circuit. The switching circuit at least includes an inductor and a switching tube capable of controlling the excitation of the inductor. It is characterized in that the switching circuit at least includes an Nth working stage. , (N+1)th working stage...(N+M)th working stage; in the Nth working stage, the switch tube is turned on at the Nth valley; in the (N+1)th working stage , the switch tube is turned on at the (N+1)th valley... In the (N+M)th working stage, the switch tube is turned on at the (N+M)th valley; the switch circuit control chip At least including an adaptive valley number generation unit and an adaptive locking valley control unit; The adaptive valley number generating unit is used to add 1 to N to obtain the opening valley number of the next working state when the first preset condition group is met, and update N with (N+1) until the (th) is obtained. N+M) the number of turn-on valleys in the working stage (N+M), and send the number of turn-on valleys in each working stage to the adaptive locking valley control unit; the first preset condition group represents the gradual decrease of the reference current of the inductor ; The adaptive lock valley bottom control unit is used to generate a corresponding control signal for controlling the opening of the switch tube according to the opening valley number calculated by the adaptive valley number generation unit; wherein, N and M are both positive integers; The switching circuit control chip also includes a shaping adjustment unit, which is used to calculate the peak reference current I _dcm-PK (n) of the inductor according to the following formula (1) or (2), I _dcm-PK (n) = 2*I _ref-ac (n) * (T _dcmzcd (n) + T _dcmoff (n)) / T _dcmzcd (n)...Formula (1); where, I _ref-ac ( n) is the reference average value of the inductor current in the nth working stage; T _dcmzcd (n) is the sum of the inductor excitation and demagnetization times in the nth working stage; the T _dcmoff (n) is the nth working stage The dead time after the inductor is demagnetized; in the nth working stage, the switch is turned on at the nth valley, and the dead time is (n-1) resonance cycles; when the inductor current When the peak reference current I _dcm-PK (n) is reached, the switch tube is controlled to turn off; where n is a positive integer and N≤n≤(N+M); I _dcm-PK (n)=2*I _ref-ac (n)*(T _dcmzcd (n-1)+T _dcmoff (n-1))/T _dcmzcd (n-1)...Formula (2); where , I _ref-ac (n) is the reference average value of the inductor current in the n-th working stage; T _dcmzcd (n) is the sum of the excitation and demagnetization times of the inductor in the n-th working stage; the T _dcmoff (n) is The dead time after demagnetization of the inductor in the nth working stage; in the nth working stage, the switch tube is turned on at the nth valley, and the dead time is (n-1) resonance cycles; When the inductor current reaches the peak reference current I _dcm-PK (n), the switch is controlled to turn off; where n is a positive integer and N≤(n-1)≤(N+M); The adaptive valley number generation unit is preset with switching step adjustment factors A and step. The adaptive valley number generation unit is also preset with a reference signal threshold I _{ref_set} . I _{ref_set} is when the switch circuit is switched from the CCM operating mode. The mode switching threshold to the CRM working mode or the mode switching threshold for the switch circuit to switch from the CRM working mode to the DCM working mode; the adaptive valley number generating unit includes an inductor current input port, a calculation module and a judgment module; The inductor current input port is used to receive a reference value characterizing the inductor current; _{The calculation module is used to calculate the current reference threshold I ref_valley (n~ n+1) for switching from the nth valley to the (n+1)th valley, I ref_valley (} n~ n+1)=I _{ref_set} / ( A+n×step); The judgment module is used to judge whether the reference value of the inductor current drops to the I _{ref_valley} (n~ n+1); if so, add 1 to n to obtain the opening valley number of the (n+1)th working stage; The judgment module is also used to judge whether the reference value of the inductor current increases to I _{ref_valley} (n~ n-1); if so, subtract 1 from n to obtain the opening valley number of the (n-1)th working stage. 7. The switching circuit control chip according to claim 6, characterized in that the switching circuit control chip includes a zero-crossing detection port; the adaptive lock bottom control unit is electrically connected to the zero-crossing detection port, and passes through the zero-crossing detection port. The zero-crossing detection port receives the zero-crossing signal of the inductor current; The adaptive bottom locking control unit includes a timing module and a counting module; The timing module is used to time the time between the zero-crossing signals of two adjacent inductor currents to obtain the resonance time; add an increment time on the basis of the resonance time to obtain the first duration; wherein, the A zero signal represents the bottom; Whenever the zero-crossing detection port receives a zero-crossing signal, the timer cnt_T0 is used for timing. If the zero-crossing detection port receives a zero-crossing signal during the timing period, the timing is cleared; if no zero-crossing signal is received but When the timing duration reaches the first duration, the moment is determined to be the valley moment, and the first duration is equivalent to the resonance duration of two adjacent valleys; The counting module is configured to calculate the bottom number based on at least the zero-crossing signal and the first duration until the bottom number reaches the bottom number that determines the turning on of the switch tube. 8. The switching circuit control chip according to claim 6, wherein the adaptive valley number generation unit further includes a maximum valley number determination module; the maximum valley number determination module presets the valley configuration initial value to be the maximum valley number. Number N _{valley_max} ; the maximum valley number determination module is used for: Detect the switching frequency of the switching circuit in one or more power frequency half-waves; If the number of times the switching frequency is less than the preset limit frequency is greater than the preset value N _{fsw_th_H} , then set the maximum number of valleys in the next power frequency cycle to (N _{valley_max} -1), and use (N _{valley_max} -1) Update N _{valley_max} ; If the number of times the switching frequency is less than the preset limit frequency is less than the preset value N _{fsw_th_L} , then set the maximum number of valleys in the next power frequency cycle to (N _{valley_max} +1), and use (N _{valley_max} +1) Update N _{valley_max} ; (N+M) is less than or equal to N _{valley_max} . 9. The switching circuit control chip according to claim 6, wherein the switching circuit has a maximum off time of the switching tube; When the off time arrives, the adaptive lock bottom control unit generates a control signal to control the switching tube to turn on. 10. The switching circuit control chip according to claim 6, further comprising a reference current generation unit, a mode control unit, a Ton signal control unit and a CCM-Toff control unit; The reference current sampling unit is used to generate an inductor current reference value based on the input voltage sampling value and the output voltage sampling value of the switching circuit; The mode control unit is used to determine the operating mode of the switching circuit according to the inductor current reference value; The Ton signal control unit is used to generate a control signal that controls the switch tube to turn off according to the working mode, the inductor reference current in each working mode, and the inductor current sampling signal; The CCM-Toff control unit is used to generate a control signal to control the switch tube to turn off according to the working mode, the input voltage sampling value, the output voltage sampling value and the switching period; The adaptive valley number generation unit is used to generate a turn-on valley number; the adaptive locking valley control unit is used to generate a switching tube in the CRM and/or DCM operating mode based on at least the valley number and the zero-crossing signal of the inductor current. shutdown control signal. 11. A switching circuit, characterized in that it includes a switching unit, an output voltage sampling unit, an input voltage sampling unit, a current sampling unit, an inductor current zero-crossing sampling unit and a switching circuit as claimed in any one of claims 6 to 10 Control chip; the output voltage sampling unit is electrically connected to the output terminal of the switch unit, and samples the output voltage sampling signal; the input voltage sampling unit is electrically connected to the input terminal of the switch unit, and samples the input voltage sampling signal; the output The voltage sampling unit and the input voltage sampling unit are also electrically connected to the reference current generating unit of the switching circuit control chip; the current sampling unit is electrically connected to the switching unit and samples the inductor current sampling signal of the switching unit; The inductor current zero-crossing sampling unit is electrically connected to the switch unit, and is used to obtain the inductor current zero-crossing signal of the inductor of the switch unit; the current sampling unit is electrically connected to the Ton signal control unit of the switch circuit control chip; The inductor current zero-crossing sampling unit is electrically connected to the adaptive locking bottom control unit of the switch circuit control chip; the switch circuit control chip is at least used to sample the output voltage sampling signal, the input voltage sampling signal, and the inductor current. The signal and the inductor current zero-crossing signal control the operation of the switching unit.