The voltage V of the auxiliary winding Is zero at the moment when the secondary current Is becomes zero_AUXA specific value of (a); referring to FIG. 2, Knee-Voltage is Knee Voltage, and the Voltage V of the auxiliary winding is at this time_AUXIs specifically a value of

Wherein N is_AUXNumber of exciting inductance turns, V, for auxiliary winding_dIs the forward conduction voltage, N, of a freewheeling diode Do_SThe number of turns of the exciting inductance of the secondary winding of the transformer is set. Ip represents the current of the primary side.

The output voltage of the primary feedback flyback converter can be expressed as:

wherein, V_INFor bus voltage, T_ONFor the turn-on time, R, of the power transistor Q1 in one switching cycle_LIs a load resistance, T_SWIs the switching period, L, of the power tube Q1_PExcitation inductance as primary side, I_PKIs the peak current limit of the main side, i.e. the maximum achievable peak current. The regulation mechanism of the system isRegulating other variables, such as T, by negative feedback according to the regulated voltage VC in response to the magnitude of the output voltage_SWOr is T_ONMaintaining the output voltage V_OUTThe stability of (2). Due to the output voltage V_OUTRepresents R_LThus, the regulation voltage VC also reflects R_L(ii) a level of (d); the higher the regulated voltage VC, the heavier the system load.

When the PWM modulation mode is adopted, the system keeps the switching period T of the power tube Q1 as shown in formula (1)_SWRegulating T according to the regulated voltage VC without changing (i.e. keeping the switching frequency of the system constant)_ONIs made such that V is the proportion of the on-time to the period_OUTConstant; peak current limit in the process I_PKIs associated with T_ONThe linear variation is a fixed frequency control mode.

When a PFM modulation mode is adopted, the system keeps the peak current limit threshold voltage of the main side unchanged, and therefore I is enabled to be constant_PKThe change is not changed; and adjusting the switching period T of the power tube Q1 according to the regulated voltage VC_SWThereby making V_OUTConstant, it is a frequency conversion control mode. The invention combines the mixed modulation control mode of PWM and PFM, so that the load range and the light load efficiency of the system are greatly improved.

Referring to fig. 3, a hybrid modulation control method applied to a primary feedback flyback converter provided in this embodiment may include the following steps:

s31: and acquiring the regulation voltage output by the error amplifier in the primary side feedback flyback converter.

The non-inverting input end of the error amplifier is used for inputting a set voltage VREF, and the sampling holding current transmits the collected knee voltage reflecting the output voltage to the inverting input end of the error amplifier. The error amplifier outputs a regulated voltage VC. After the mixed modulation control circuit obtains the regulated voltage VC, subsequent analysis is carried out, the load level is determined, and then a corresponding modulation mode is executed.

S32: if the adjusting voltage is in the first voltage range or in the second voltage range, the modulation mode of PFM is adopted.

The first voltage range and the second voltage range are both predetermined. The first voltage range corresponds to heavy loads and the second voltage range corresponds to light loads. The transient response speed of the system is ensured by a modulation mode of PFM during heavy load; and when the load is light, the switching loss is reduced and the system efficiency is improved by a PFM modulation mode.

S33: if the regulating voltage is in the third voltage range, a PWM (pulse-width modulation) mode is adopted.

The maximum value in the third voltage range is less than the minimum value in the first voltage range. The minimum value in the third voltage range is greater than the maximum value in the second voltage range. The third voltage range is also preset and corresponds to the medium load; i.e., medium load is lighter than heavy load and heavier than light load. And the switching frequency of the system is fixed beyond the sound range (2 KHz-20 KHz) identified by human ears by a PWM (pulse-width modulation) mode during medium load, so that the noise problem is avoided.

S34: and if the regulated voltage is smaller than the preset voltage threshold, controlling the switching frequency of the system to be the preset lowest switching frequency, and setting the peak current limit threshold voltage of the main edge to be the preset lowest voltage.

When the regulated voltage is smaller than the preset voltage threshold, it indicates that the current load is an extremely light load, that is, the system is in a state of maximum work conduction, and in order to maintain necessary energy transmission, the switching frequency of the system and the peak current threshold voltage of the main side are both fixed at corresponding minimum values, wherein the minimum value at which the switching frequency of the system is fixed needs to be a compromise between better load response and lower switching loss.

System switching frequency f_SWAnd the peak current limiting threshold voltage V of the main side_PEAKThe variation with the regulated voltage VC is shown in fig. 4. When the regulated voltage VC is in the first voltage range (i.e., [ V3, V4 ]]Interval), the peak current limit threshold voltage V of the main side is set_PEAKIs a preset maximum voltage V_PEAKmaxAnd the larger the regulation voltage VC is, the higher the switching frequency f of the control system is_SWThe larger; when the regulated voltage VC is the maximum value V4 in the first voltage range, the switching frequency f of the system is controlled_SWAt a predetermined maximum switching frequency f_SWMAX(ii) a When the regulated voltage VC is the minimum value V3 in the first voltage range, the switching frequency f of the system is controlled_SWTo a predetermined intermediate switching frequency f_SWPWM. Intermediate switching frequency f_SWPWMLess than the highest switching frequency f_SWMAX。

When the regulated voltage VC is in a third voltage range (i.e. (V2, V3)) to control the switching frequency f of the system_SWTo a predetermined intermediate switching frequency f_SWPWMAnd the larger the regulation voltage VC is, the peak current limit threshold voltage V of the main edge is set_PEAKThe larger. When the regulated voltage VC is in a second voltage range, the peak current of the main side limits the threshold voltage V_PEAKHas a value interval of (V)_PEAKmin，V_PEAKmax)，V_PEAKmaxAt a predetermined maximum voltage, V_PEAKminIs a preset minimum voltage. Intermediate switching frequency f_SWPWMGreater than the lowest switching frequency f_SWMIN。V_PEAKInfluences the turn-on time, V, of the power tube Q1_PEAKThe larger the pulse width, the longer the power transistor Q1 is turned on in one cycle, and the output voltage is kept stable by adjusting the pulse width.

When the regulated voltage VC is in the second voltage range (i.e., [ V1, V2 ]]Interval), the peak current limit threshold voltage V of the main side is set_PEAKIs a preset minimum voltage V_PEAKminAnd the larger the regulation voltage VC is, the higher the switching frequency f of the control system is_SWThe larger. When the regulated voltage VC is the maximum value V2 in the third voltage range, the switching frequency f of the system is controlled_SWTo a predetermined intermediate switching frequency f_SWPWM(ii) a When the regulated voltage VC is the minimum value V1 in the third voltage range, the switching frequency f of the system is controlled_SWAt a predetermined minimum switching frequency f_SWMIN. The preset voltage threshold is the minimum value V1 of the third voltage range.

The peak current limit threshold voltage V of the main edge corresponding to different regulated voltages VC can be obtained through the following formula_PEAK：

Wherein, V_PEAKmin、V_PEAKmaxV2, V3, V4 and k are parameters previously designed according to the system. When different systems apply the strategy of the invention, the technicians in the field can adjust the relevant parameters according to the actual requirements. V_PEAKmaxAnd V_PEAKminThe maximum current and the minimum current which can flow through the main side are respectively determined. Normally, V4 is determined by the highest value of the tuning voltage VC, V1, V2, V3 may be set to 0.25V4, 0.5V4, 0.75V4, respectively, or the proportions may be adjusted appropriately so that the intervals [ V1, V2 ]]、[V2,V3]、[V3,V4]The light load, the medium load and the heavy load can be represented correctly respectively.

And f_SWMAXIs the highest switching frequency of the system, determined by the application; f. of_SWMINThe lowest switching frequency of the system represents the limit that the system can process; f. of_SWPWMIt is usually set well above the noise range, for example from 25-30 KHz.

The regulation voltage VC is generated by an error amplifier and its main function is to characterize the deviation between the actual output voltage and the set value. Because the inverting input terminal of the error amplifier inputs a AND output voltage V_OUTProportional voltage, the final purpose of the entire control loop is to clamp the non-inverting and inverting inputs of the error amplifier to the same voltage by negative feedback, i.e.:

wherein R is₁Is a first divider resistor, R₂Is a second divider resistor.

Under the modulation mode of the hybrid modulation control method provided by the invention, the load range of the system is greatly widened and can be expressed as:

wherein, I_{OUT_MAX}Is the maximum value of the output current, I_{OUT_MIN}For minimum value of output current, outputThe current also represents the load R_LThe size of (d); i is_{P_peakmax}Is the maximum value of the peak current of the main side and is I_{P_peakmin}Is the minimum value of the peak current of the main side, the peak current of the main side and V_PEAKIs in direct proportion.

For a single PWM modulation scheme or a single PFM modulation scheme, the obtained load ranges are respectively determined by

And

determining; the mixed modulation control mode provided by the invention can obtain the product of the two modes, and the product is properly set

And

the ratio of (2) can greatly widen the load range of the system. In addition, the PFM control mode is adopted under the condition of light load, the switching frequency can be reduced, so that the switching loss is well reduced, the light load efficiency of the system is improved, and the system has higher output efficiency in the whole load range.

While, for purposes of simplicity of explanation, the foregoing method embodiments have been described as a series of acts or combination of acts, it will be appreciated by those skilled in the art that the present invention is not limited by the illustrated ordering of acts, as some steps may occur in other orders or concurrently with other steps in accordance with the invention.

The following are embodiments of circuits of the invention that may be used to implement embodiments of methods of the invention. For details not disclosed in the circuit embodiments of the present invention, reference is made to the method embodiments of the present invention.

Referring to fig. 5, the hybrid modulation control circuit applied to the primary-side feedback flyback converter provided in this embodiment includes: anacquisition unit 51, aPFM unit 52, aPWM unit 53 and an extremely lightload control unit 54.

The obtainingunit 51 is configured to obtain a regulated voltage output by an error amplifier in the primary feedback flyback converter.

ThePFM unit 52 is configured to adopt a modulation scheme of PFM if the regulated voltage is within the first voltage range or within the second voltage range.

And thePWM unit 53 is configured to adopt a PWM modulation method if the regulated voltage is within the third voltage range. The maximum value in the third voltage range is smaller than the minimum value in the first voltage range; the minimum value in the third voltage range is greater than the maximum value in the second voltage range.

And an extreme lightload control unit 54, configured to control the system switching frequency to be a preset minimum switching frequency if the regulated voltage is smaller than a preset voltage threshold, and set a peak current limit threshold voltage of the main edge to be a preset minimum voltage.

In some embodiments, thePFM unit 52 includes: heavy load control unit and light load control unit. And the heavy load control unit is used for setting the peak current limit threshold voltage of the main edge as the preset highest voltage when the regulating voltage is in the first voltage range, and controlling the switching frequency of the system to be larger if the regulating voltage is larger. When the regulated voltage is the maximum value in the first voltage range, controlling the switching frequency of the system to be the preset highest switching frequency; when the regulated voltage is the minimum value in the first voltage range, controlling the switching frequency of the system to be a preset intermediate switching frequency; the intermediate switching frequency is less than the highest switching frequency.

The PWM unit is specifically used for: when the regulated voltage is in the third voltage range, the switching frequency of the control system is a preset intermediate switching frequency, the intermediate switching frequency is greater than the lowest switching frequency, the larger the regulated voltage is, the larger the peak current limit threshold voltage of the main edge is set to be, and when the regulated voltage is in the second voltage range, the value interval of the peak current limit threshold voltage of the main edge is (the preset lowest voltage, the preset highest voltage).

The hybrid modulation control circuit comprises a unit for controlling the switching frequency of the system, and referring to fig. 6, the unit generates a clock signal CV _ CLK with a certain pulse width according to the regulated voltage VC, so as to determine the switching period of the power tube Q1 on the main side; the unit includes: a narrow pulse circuit, a counter, an RS latch, a first not gate INV1, a second not gate INV2, an OR gate OR, a variable current generating circuit, an electronic switch MS, a capacitor C, and a comparator COMP;

the input end of the narrow pulse circuit is used for receiving a GATE control signal GATE _ CTR (namely an input signal of a Driver) of the power tube Q1 on the main side; and the output end of the narrow pulse circuit is respectively connected with the reset end of the counter and the reset end of the RS latch. When the rising edge of the GATE control signal GATE _ CTR comes, the narrow pulse circuit is triggered to generate and output a high-level narrow pulse.

The output end of the RS latch is connected to the input end of the first not gate INV 1. An output end of the first not gate INV1 serves as an output end of the clock signal CV _ CLK, and is used for outputting the clock signal CV _ CLK. The output end of the first not gate INV is also connected with the input end of a second notgate INV 2; the output end of the second not gate INV2 is connected to one input end of the OR gate OR; the other input terminal of OR gate OR is connected to the output terminal of comparator COMP. The output end of the OR gate OR is connected with the control end of the electronic switch MS; the current input end of the electronic switch MS is connected with the non-inverting input end of the comparator COMP, and the current output end of the electronic switch MS is grounded. When the signal of the control end of the electronic switch MS is high level, the electronic switch is conducted; and when the signal of the control end of the electronic switch MS is low level, the electronic switch is switched off.

An inverting input end of the comparator COMP is used for inputting a reference voltage; the output end of the comparator COMP is also connected to the input end of the counter. The output end of the counter is connected with the set end of the RS latch; the counter is used for counting the narrow pulses output by the comparator COMP and inverting the output from a low level to a high level when the counting result is N.

The output end of the variable current generating circuit is respectively connected with the current input end of the electronic switch MS and one end of the capacitor C; the other end of the capacitor C is grounded. The input end of the variable current generating circuit receives the regulation voltage VC; the variable circuit generating circuit regulates the output current value I according to the regulated voltage VC_EATo control the system switching frequency. The variable current generating circuit obtains a current value I according to the regulated voltage VC_EACan be represented by the following formula:

wherein, I_CO、V1、V2、V3、V4、k₁、k₂All are preset parameters, and different system applications can automatically adjust related parameters by using the strategy of the invention.

The working principle of the unit shown in fig. 6 is described in detail below: when the rising edge of the GATE control signal GATE _ CTR comes, the narrow pulse circuit is triggered to generate and output a high-level narrow pulse, the count of the counter is cleared, the output of the RS latch is enabled to be at a low level, and then CV _ CLK is set to be at a high level. After CV _ CLK is set to high, electronic switch MS is turned off and current I controlled by regulated voltage VC_EAThe capacitor C is charged, and when the voltage of the capacitor C is higher than the reference voltage Vref, the output of the comparator COMP is inverted to a high level. When the comparator COMP outputs high level, the electronic switch MS is turned on, and the voltage on the capacitor C is pulled down to zero immediately, and I_EAThe capacitor C will be recharged. During repeated charging and discharging of the capacitor C, the output of the comparator COMP appears as a narrow pulse. The counter will count the narrow pulses output by the comparator COMP, and when the N narrow pulses are counted, the output of the counter will be inverted from low level to high level, so that the RS latch outputs high level, pulling the CV _ CLK low, and ending one timing period of the unit.

From the description of fig. 6, the system switching frequency can be expressed as:

wherein f is_swTo the system switching frequency, C₁The size of the capacitance C. For the primary side feedback flyback converter, the value range of the system switching frequency is [ f [ ]_SWMIN，f_SWMAX]The switching frequency range of the system can be controlled by changing the counting period N of the counter and the size C of the capacitor C₁And the reference voltage Vref of the comparator is set, so that the use of off-chip capacitor is avoided, and the cost of the system is greatly saved.

For the circuit embodiments, since they substantially correspond to the method embodiments, reference may be made to the partial description of the method embodiments for relevant points. The above described circuit embodiments are merely illustrative, wherein the units illustrated as separate components may or may not be physically separate. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The embodiments in the present description are mainly described as different from other embodiments, the same and similar parts in the embodiments may be referred to each other, and the features described in the embodiments in the present description may be replaced with each other or combined with each other.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A hybrid modulation control circuit applied to a primary feedback flyback converter is characterized by comprising:

the extreme light load control unit is used for controlling the switching frequency of the system to be a preset lowest switching frequency and setting the peak current limit threshold voltage of the main edge to be a preset lowest voltage if the regulating voltage is smaller than a preset voltage threshold;

the unit for controlling the switching frequency of the system comprises: the circuit comprises a narrow pulse circuit, a counter, an RS latch, a first NOT gate, a second NOT gate, an OR gate, a variable current generating circuit, an electronic switch, a capacitor and a comparator;

the output end of the counter is connected with the set end of the RS latch, the counter is used for counting the narrow pulses output by the comparator and outputting the narrow pulses which are turned from low level to high level when the counting result is N, and the N is a positive integer which is more than or equal to 1;

2. The circuit of claim 1, wherein the PFM unit comprises:

3. The circuit of claim 1, wherein the PFM unit comprises:

4. The circuit according to claim 1, wherein the PWM unit is specifically configured to:

and the intermediate load control unit is used for controlling the switching frequency of the system to be a preset intermediate switching frequency when the regulating and controlling voltage is within a third voltage range, the intermediate switching frequency is greater than the lowest switching frequency, the larger the regulating and controlling voltage is, the larger the threshold voltage of the peak current limit of the main edge is set to be, and the value interval of the threshold voltage of the peak current limit of the main edge is (the preset lowest voltage, the preset highest voltage) when the regulating and controlling voltage is within the third voltage range.

5. A hybrid modulation control method applied to a primary feedback flyback converter, characterized in that, applied to the hybrid modulation control circuit of claim 1, it comprises:

6. The method of claim 5, wherein the modulation scheme of the PFM when the regulated voltage is within the first voltage range comprises:

7. The method of claim 5, wherein the modulation scheme of the PFM when the regulated voltage is within the second voltage range comprises:

8. The method of claim 5, wherein the PWM modulation when the regulated voltage is within a third voltage range comprises: