CN212627660U

CN212627660U - Control circuit and switch mode power supply circuit

Info

Publication number: CN212627660U
Application number: CN202020696400.1U
Authority: CN
Inventors: 俞秀峰; 张波; 叶俊
Original assignee: Hangzhou Biyi Microelectronics Co ltd
Current assignee: Hangzhou Biyi Microelectronics Co ltd
Priority date: 2020-04-29
Filing date: 2020-04-29
Publication date: 2021-02-26
Anticipated expiration: 2030-04-29

Abstract

The utility model provides a control circuit and switched mode power supply circuit. The control circuit includes: a comparison circuit, a first input terminal of which is coupled to the input terminal of the switch mode power supply circuit, and a second input terminal of which is coupled to the threshold signal; a control adjusting circuit, a first input end of which is coupled to the output end of the comparing circuit, and a second input end of which receives a feedback signal, and is used for adjusting the control function according to the comparing circuit; and an on/off control circuit that controls the power switch based on an output of the control adjustment circuit. The utility model provides a switched mode power supply circuit and control circuit can promote the electric current virtual value when input voltage is great, and the system frequency is reduced, reduces the electric current virtual value when input voltage is great, but self-adaptation optimization system efficiency.

Description

Control circuit and switch mode power supply circuit

Technical Field

The utility model relates to an electron field, concretely but not limited to relate to a control circuit and switched mode power supply circuit.

Background

The switch mode power supply circuit is used for converting an input voltage into an output voltage based on the on and off actions of the switch and supplying power to a load. In the control, the switch mode power supply circuit controls the switch based on a feedback signal at the output terminal. In a flyback switching mode power supply circuit, the control of the primary side switch is often realized by adjusting the frequency of the switch or adjusting the current peak value when the switch is turned off based on a feedback signal, so as to further control the output voltage.

On the other hand, in order to improve the power supply efficiency, it is necessary to reduce the loss of the system. Losses on the power switch include switching losses and conduction losses, wherein the switching losses are due to the delayed nature of the switch turning on or off, increasing with increasing switching frequency; the conduction loss is determined by the conduction resistance value of the switch and the current, and increases with the increase of the current. When the input voltage of the switch mode power supply circuit is higher, the effective current is lower, the influence of the switching loss on the system efficiency is larger, and when the input voltage is lower, the effective current is higher, and the influence of the conduction loss on the system efficiency is larger.

SUMMERY OF THE UTILITY MODEL

To the above-mentioned one or more problems or situations that propose, the utility model provides a control circuit and switch mode power supply circuit.

According to an aspect of the utility model, a control circuit for switched mode power supply circuit is proposed, switched mode power supply circuit includes power switch, and switched mode power supply circuit has input and output, control circuit includes: the comparison circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the comparison circuit is coupled with the input end of the switch mode power supply circuit, and the second input end of the comparison circuit is coupled with the threshold signal; the control adjusting circuit is provided with a first input end, a second input end and an output end, the first input end of the control adjusting circuit is coupled with the output end of the comparison circuit, and the second input end of the control adjusting circuit receives a feedback signal; and the input end of the on/off control circuit is coupled with the output end of the control adjusting circuit, and the output end of the on/off control circuit is coupled with the control end of the power switch.

In one embodiment, the control circuit includes: a peak current setting circuit for providing a peak current signal at an output terminal of the peak current setting circuit according to the feedback signal and the peak current control function; the valley bottom number setting circuit provides a valley bottom number signal at the output end of the valley bottom number setting circuit according to the feedback signal and the valley bottom number control function; the control adjusting circuit is positioned in the peak current setting circuit and/or the valley bottom number setting circuit and is used for adjusting the peak current control function and/or the valley bottom number control function according to the comparison result provided by the comparison circuit.

In one embodiment, the on/off control circuit includes: the current comparison circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the current comparison circuit is coupled with the current sampling resistor, and the second input end of the current comparison circuit is coupled with the output end of the peak current setting circuit; the valley bottom detection and counting circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the valley bottom detection and counting circuit is coupled with the power switch, and the second input end of the valley bottom detection and counting circuit is coupled with the output end of the valley bottom number setting circuit; and the trigger circuit is provided with a set input end, a reset input end and an output end, wherein the set input end of the trigger circuit is coupled with the output end of the valley bottom detection and counting circuit, the reset input end of the trigger circuit is coupled with the output end of the current comparison circuit, and the output end of the trigger circuit is coupled with the control end of the power switch.

In one embodiment, the control adjustment circuit selects one of a first peak current control function and a second peak current control function based on a comparison result of the comparison circuit, the first peak current control function sets a first peak current larger than a second peak current set by the second peak current control function in the same feedback signal interval, the first peak current control function is selected to control the switch mode power supply circuit when the input voltage is larger than a first threshold, and the second peak current control function is selected to control the switch mode power supply circuit when the input voltage is smaller than a second threshold, wherein the first threshold is larger than or equal to the second threshold.

In one embodiment, the control adjustment circuit selects one from a first valley number control function and a second valley number control function based on a comparison result of the comparison circuit, the first valley bottom number control function and the second valley bottom number control function are used for setting the power switch to be conducted at the Nth valley bottom of the oscillation signal according to the feedback signal, wherein N is a positive integer and is called valley bottom number, in the same feedback signal interval, the first valley bottom number set by the first valley bottom number control function is larger than the second valley bottom number set by the second valley bottom number control function, selecting the first valley digital control function to control the switch mode power supply circuit when the input voltage is greater than a first threshold, selecting the second valley number control function to control the switch mode power supply circuit when the input voltage is less than a second threshold, wherein the first threshold is greater than or equal to the second threshold.

According to another aspect of the present invention, a control circuit for a switched mode power supply circuit is presented, the switched mode power supply circuit comprising a power switch, the switched mode power supply circuit converting an input voltage at an input of the switched mode power supply circuit into an output voltage at an output of the switched mode power supply circuit based on a switching action of the power switch, the control circuit comprising: a comparison circuit for comparing an input voltage signal representative of the input voltage with at least one threshold; and the control adjusting circuit adjusts a peak current control function and/or a valley bottom number control function based on a comparison result of the comparison circuit, wherein the power switch is turned off when the current flowing through the power switch reaches a peak current, the power switch is turned on at the valley bottom position of an Nth oscillation signal of a voltage difference between two ends of the power switch, N is called a valley bottom number, the peak current is set by a feedback signal and the peak current control function, the valley bottom number is set by the feedback signal and the valley bottom number control function, and the feedback signal changes along with the change of the output voltage.

According to a further aspect of the present invention, a control circuit for a switched mode power supply circuit is presented, the switched mode power supply circuit comprising a power switch, the switched mode power supply circuit converting an input voltage at an input of the switched mode power supply circuit into an output voltage at an output of the switched mode power supply circuit based on a switching action of the power switch, the control circuit comprising: a comparison circuit for comparing an input voltage signal representative of the input voltage with at least one threshold; and a control adjustment circuit for adjusting control of the power switch according to a comparison result of the comparison circuit, wherein when the input voltage jumps from being greater than the threshold value to being less than the threshold value, a switching frequency of the power switch increases and a current flowing through the power switch decreases.

According to a further aspect of the present invention, a switched-mode power supply circuit is provided, comprising a control circuit and a power switch as described in any of the above embodiments.

The utility model provides a control circuit and switched mode supply circuit can promote the electric current virtual value when input voltage is great, reduces system frequency, reduces switching loss, improves system frequency when input voltage is lower, reduces the electric current virtual value, reduces the conduction loss, but self-adaptation optimization system efficiency.

Drawings

Fig. 1 shows a switched mode power supply circuit according to an embodiment of the invention;

fig. 2 shows a circuit schematic of a control circuit according to an embodiment of the invention;

fig. 3 shows a circuit schematic of a switched mode power supply circuit system according to an embodiment of the invention;

fig. 4 shows a control function waveform diagram of a control method according to an embodiment of the present invention;

fig. 5 shows a control function waveform diagram of a control method according to another embodiment of the present invention;

fig. 6 shows a schematic flow diagram of a method of controlling a switched mode power supply circuit according to an embodiment of the invention;

fig. 7 shows a schematic flow chart of a method of controlling a switched mode power supply circuit according to an embodiment of the invention.

Detailed Description

For further understanding of the present invention, preferred embodiments of the present invention will be described below with reference to examples, but it should be understood that these descriptions are only for the purpose of further illustrating the features and advantages of the present invention, and are not intended to limit the claims of the present invention.

The description in this section is for exemplary embodiments only, and the present invention is not limited to the scope of the embodiments described. Combinations of different embodiments, or technical features of different embodiments, or similar prior art means, or technical features of embodiments, may be substituted for each other within the scope of the present invention.

The term "coupled" or "connected" in this specification includes both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as a conductor, wherein the electrically conductive medium may contain parasitic inductance or parasitic capacitance, or through an intermediate circuit or component as described in the embodiments in the specification; indirect connections may also include connections through other active or passive devices that perform the same or similar function, such as connections through switches, signal amplification circuits, follower circuits, and so on. "plurality" or "plurality" means two or more. "A and/or B" means that A may be, B may be, or both A and B may be included.

Fig. 1 shows a switched-mode power supply circuit 100 according to an embodiment of the present invention, the switched-mode power supply circuit 100 comprising a control circuit 10 and a power switch Q, the switched-mode power supply circuit 100 transforming an input voltage Vin at an input of the switched-mode power supply circuit 100 into an output voltage Vo at an output of the switched-mode power supply circuit 100 based on a switching action of the power switch Q. The control circuit 10 includes a comparison circuit 11 and a control adjustment circuit 12. The comparison circuit 11 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the comparison circuit 11 is coupled to the input terminal of the switch mode power supply circuit 100 for receiving the input voltage Vin, and the second input terminal of the comparison circuit 11 is coupled to the threshold signal. The comparison circuit 11 may also have a third input and a fourth input receiving further threshold signals. The comparison circuit 11 is used for comparing the input voltage Vin with at least one threshold. The control adjustment circuit 12 has a first input terminal, a second input terminal and an output terminal, the first input terminal of the control adjustment circuit 12 is coupled to the output terminal of the comparison circuit 11, and the second input terminal of the control adjustment circuit 12 receives the feedback signal Vfb. The control adjusting circuit 12 adjusts a control function for controlling the power switch Q based on the comparison result of the comparing circuit 11, for example, selecting one of at least two control functions f1 and f2 based on the comparison result, wherein the control function is used for setting the on and/or off condition of the power switch Q according to the output feedback signal Vfb. The feedback signal Vfb varies following the variation of the output voltage Vo.

In one embodiment, the comparison circuit 11 compares the input voltage or other signals that can represent the value of the input voltage with a threshold signal Vth, and selects the first control function f1 to control the on condition or the off condition of the power switch Q when the input voltage signal Vin is greater than the threshold signal Vth; when the input voltage signal Vin is smaller than the threshold signal Vth, the second control function f2 is selected to control the on condition or the off condition of the power switch Q. In another embodiment, the comparison circuit 11 compares the input voltage Vin with two threshold signals Vth1 and Vth2, respectively, where Vth1> Vth2, and selects the first control function f1 to control the on condition or the off condition of the power switch Q when the input voltage Vin is greater than Vth 1; when the input voltage Vin is less than Vth2, selecting a second control function f2 to control the on condition or the off condition of the power switch Q; when the input voltage Vin is less than Vth1 and greater than Vth2, a third control function is selected to control the on condition or the off condition of the power switch Q, or the original control function is kept unchanged. The comparison circuit 11 may also compare the input voltage Vin with more threshold values, and adjust a control function for controlling the on-condition or the off-condition of the power switch Q based on the comparison result.

In one embodiment, the control function comprises a peak current control function, and the control adjustment circuit 12 adjusts the peak current control function based on the comparison result of the comparison circuit 11, wherein the power switch Q is turned off when the current flowing through the power switch reaches a peak current, which is set by the feedback signal Vfb and the peak current control function. In another embodiment, the control function comprises a bottom number control function, and the control adjusting circuit 12 adjusts the bottom number control function based on the comparison result of the comparing circuit 11, wherein the power switch Q is turned on at the nth bottom position of the oscillating signal of the voltage difference between two ends of the power switch, N is a positive integer, N is called the bottom number, and the bottom number is set by the feedback signal Vfb and the bottom number control function. In yet another embodiment, the control adjustment circuit 12 simultaneously adjusts the peak current control function and the valley number control function based on the comparison result of the comparison circuit 11.

The control circuit 10 further comprises an on/off control circuit 13, which is indicated by a blank frame in fig. 1. An input terminal of the on/off control circuit 13 is coupled to an output terminal of the control adjusting circuit 12, and an output terminal of the on/off control circuit 13 is coupled to a control terminal of the power switch Q.

Fig. 2 shows a circuit schematic diagram of a control circuit 200 according to an embodiment of the present invention. The control circuit 200 includes a comparison circuit 21, a signal setting circuit 22, an on/off control circuit 23, and a drive circuit 24. The signal setting circuit 22 includes a peak current setting circuit 221 and a valley number setting circuit 222 for providing a peak current signal Vpk according to the feedback signal Vfb and a peak current control function, and providing a valley number signal N according to the feedback signal Vfb and a valley number control function, respectively. The control adjustment circuit is located in the peak current setting circuit 221 and/or the valley number setting circuit 222, and is configured to adjust the peak current control function and/or the valley number control function according to the comparison result provided by the comparison circuit 21. An input terminal of the on/off control circuit 23 is coupled to an output terminal of the control adjusting circuit, an output terminal of the on/off control circuit 23 is coupled to a control terminal of the power switch Q, and the on/off control circuit 23 controls the power switch to be turned on and off at least based on an output of the control adjusting circuit. The on/off control circuit 23 includes a current comparison circuit 231, a bottom detection and count circuit 232, and a flip-flop circuit 233. The current comparison circuit 231 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the current comparison circuit 231 is coupled to the current sampling resistor Rcs, the second input terminal of the current comparison circuit 231 is coupled to the output terminal of the peak current setting circuit 221, and the current comparison circuit 231 is configured to compare a current sampling signal Vcs with a peak current signal Vpk, wherein the current sampling signal Vcs represents a current value flowing through the power switch Q, and the peak current signal Vpk is set and provided by the peak current setting circuit 221 according to a peak current control function and the feedback signal Vfb. When the current sampling signal Vcs is greater than the peak current signal Vpk, the flip-flop circuit 233 is set, and the on/off control circuit 23 outputs a signal of a first state for turning off the power switch Q. The valley bottom detecting and counting circuit 232 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal of the valley bottom detecting and counting circuit 232 is coupled to the power switch Q, the second input terminal of the valley bottom detecting and counting circuit 232 is coupled to the output terminal of the valley bottom number setting circuit 222, the valley bottom detecting and counting circuit 232 is used for detecting the valley bottom position of the voltage difference Vds between the two ends of the power switch Q when entering the oscillation period and counting, when the valley bottom counting reaches the preset valley bottom number, the trigger circuit 233 is reset, and the on/off control circuit 23 outputs a signal of the second state for turning on the power switch Q. The preset valley number is set and provided by the valley number setting circuit 222 according to the valley number control function and the feedback signal Vfb. The trigger circuit 233 has a set input S, a reset input R, and an output, wherein the set input S of the trigger circuit 233 is coupled to the output of the valley detection and counting circuit 232, the reset input R of the trigger circuit 233 is coupled to the output of the current comparing circuit 231, and the output of the trigger circuit 233 is coupled to the control terminal of the power switch Q. The control circuit 200 may further include other protection circuits and logic circuits that perform logic operations on the output signal of the on/off control circuit 23 and the protection signal. The drive circuit amplifies the switching control signal output from the on/off control circuit 23 or the logic circuit to provide a drive voltage suitable for driving the power switch Q.

Fig. 3 shows a circuit schematic of a switched mode power supply circuit system according to an embodiment of the invention. The switch mode power supply circuit 300 is a flyback voltage converter circuit, and includes a primary circuit and a secondary circuit isolated by a transformer T, wherein the primary circuit includes a power switch Q and is coupled to a rectifier circuit for receiving an input voltage Vin, and the secondary circuit provides an output voltage Vo. And a feedback signal Vfb of the output voltage Vo is transmitted from the secondary side circuit to the primary side circuit through an optocoupler, and the feedback signal Vfb changes along with the change of the output voltage Vo. The feedback signal Vfb falls when the output voltage Vo rises, and rises when the output voltage Vo falls.

In one embodiment, the control adjustment circuit 12 selects one of at least two peak current control functions based on the comparison result of the comparison circuit 11, wherein the peak current control function is used for setting the peak current flowing through the power switch Q when the power switch Q is turned off according to the feedback signal Vfb.

Fig. 4 shows a control function waveform diagram of a control method according to an embodiment of the present invention. The upper graph is the peak

current control functions

41 and 42 and the lower graph is the valley level control function 43. The abscissa of the above graph is the feedback signal Vfb and the ordinate is the peak current Ipk. Where the dashed line 41 represents the first peak current control function and the solid line 42 represents the second peak current control function. The control adjustment circuit 12 shown in fig. 1 selects one from the first peak current control function 41 and the second peak current control function 42 for controlling the off condition of the power switch Q based on the comparison result of the comparison circuit 11. In one embodiment, the first peak current control function 41 is selected to control the switching mode power supply circuit 100 when the input voltage Vin is greater than a first threshold Vth1, and the second peak current control function 42 is selected to control the switching mode power supply circuit 100 when the input voltage Vin is less than a second threshold Vth2, wherein the first threshold Vth1 is greater than or equal to the second threshold Vth 2.

In a preferred embodiment, when the input voltage Vin is greater than the threshold Vth, the first peak current control function 41 is selected, with the current gain k1 being greater, and when the input voltage Vin is less than the threshold Vth, the second peak current control function 42 is selected, with the current gain k2 being lower. The current gain characterizes the ratio of the current signal Ipk to the feedback signal Vfb, i.e. the slope of the peak current control function curve.

As can be seen from fig. 4, the current gain of the first peak current control function 41 is larger than the current gain of the second peak current control function 42. The first peak current Ipk1 set by the first peak current control function 41 is larger than the second peak current Ipk2 set by said second peak current control function FI2 during the same interval of the feedback signal Vfb or under the same feedback signal Vfb.

The lower waveform of fig. 4 is the valley number control function 43, and in this embodiment, the valley number control function 43 is not affected by the input voltage. In another embodiment, the switching off of the power switch is controlled by selecting one of the at least two peak current control functions based on the input voltage, while the switching on of the power switch is controlled by selecting one of the at least two valley number control functions based on the input voltage.

Through the control, when the input voltage Vin is higher, the peak current Ipk curve is raised, the Vfb value is lower under the same power, the corresponding valley bottom number N is larger, the switching frequency is reduced, namely, the dominant switching loss at the moment is reduced, and therefore the system efficiency at the time of high input voltage is optimized. When the input voltage Vin is lower, the peak current Ipk curve is reduced, the feedback signal Vfb is higher under the same power, the corresponding valley number N is less, the frequency is improved, the effective value of the current is reduced, and the system efficiency in low-voltage input is optimized.

According to the system energy relation, under the conditions of given input and output and system parameters, the valley bottom number N and the peak current Ipk are in one-to-one correspondence, and meanwhile, the effective value of the current is increased along with the increase of the peak current Ipk. The relationship between the bottom number N of valleys and the primary side peak current Ipk will be described based on the flyback voltage conversion circuit. The primary output power Po of the flyback voltage conversion circuit is:

wherein Lm is a primary winding inductance of the transformer T, Ipk is a peak current when the primary power switch Q is turned off, and Fs is a switching frequency of the power switch Q.

The primary side peak current Ipk is a function based on the feedback signal Vfb:

where vcs (vfb) is the peak current voltage detection signal and Rcs is the current sampling resistor. The switching period Ts is:

wherein Ton is the time that the primary power switch Q switched on, Toff is the rectification time of the secondary circuit, Tdem is the time between the end of the secondary rectification and the conduction of the primary power switch, Nps is the turn ratio of the transformer winding, the valley number N is the function based on the feedback signal Vfb, Tring is the oscillation period of the oscillation signal, wherein:

substituting the formulas (2), (3) and (4) into the formula (1) to obtain the output power as follows:

when the parameters such as Lm, Rcs, Nps, Tring, etc. are fixed values, the output power Po is affected by the input voltage Vin, the output voltage Vo, the valley number n (vfb) and the peak current signal vcs (vfb). When the input voltage Vin, the output voltage Vo and the output power Po are fixed, the valley number N (Vfb) and the primary side peak current Vcs (Vfb)/Rcs are in a one-to-one correspondence relationship, and when the primary side peak current Vcs (Vfb)/Rcs rises, the valley number N (Vfb) rises correspondingly; when the number of valleys N decreases, the higher the frequency, the lower the effective value of the current.

Therefore, in combination with the waveform of fig. 4, when the input voltage is large, the current gain increases, the primary peak current and the valley number increase relatively at the same time, and the switching frequency Fs decreases relatively, which is beneficial to reducing the switching loss. When the input voltage is lower, the current gain is reduced, the primary side peak current and the valley number are relatively reduced simultaneously, and the conduction loss is favorably reduced.

Continuing with the description of fig. 4, in a preferred embodiment, a first peak current control function 41 is selected when the input voltage Vin is greater than the threshold Vth, and a second peak current control function 42 is selected when the input voltage Vin is less than the threshold Vth. In this way, when the input voltage Vin jumps from being greater than the preset threshold Vth to being smaller than the preset threshold Vth, the control function jumps from the first peak current control function 41 to the second peak current control function 42, so that the effective current flowing through the power switch Q decreases and the switching frequency of the power switch increases, at which time the conduction loss of the system decreases. Because the conduction loss is dominant when the input voltage is lower, the system loss when the input voltage is lower is reduced, and the system efficiency is improved. On the contrary, when the input voltage Vin jumps from being less than the preset threshold Vth to being greater than the preset threshold Vth, the effective current flowing through the power switch Q increases and the switching frequency of the power switch decreases, at this time, the switching loss of the system decreases. Because the switching loss is dominant when the input voltage is higher, the system loss is reduced when the input voltage is higher, and the system efficiency is improved.

In one embodiment, the switch mode power supply circuit 100 shown in fig. 1 includes a flyback voltage converter circuit, and as shown in fig. 3, a primary side switch Q of the flyback voltage converter circuit employs quasi-resonance control, and the control circuit 10 controls the primary side power switch Q to be turned on at an nth valley position of an oscillation period of a voltage difference between two ends of the switch Q, where the larger the number N of valleys, the lower the switching frequency. In one embodiment, the control adjustment circuit 12 selects one of at least two valley count control functions for controlling the power switch Q based on the comparison result of said comparison circuit 11. And the valley bottom number control function is used for setting the valley bottom number N when the power switch Q is conducted according to the feedback signal Vfb. In one embodiment, the control adjustment circuit 12 selects one from the first valley number control function and the second valley number control function based on the comparison result of the comparison circuit 11.

Fig. 5 shows a control function waveform diagram of a control method according to another embodiment of the present invention. The bottom graph is the valley

number control functions

51 and 52 and the top graph is the peak current control function 53. The abscissa of the lower graph is the feedback signal Vfb, and the ordinate is the number N of valleys. Where the dashed line 51 represents a first valley level control function and the solid line 52 represents a second valley level control function. Referring to fig. 1, the control adjustment circuit 12 selects one from the first bottom-of-valley-number control function 51 and the second bottom-of-valley-number control function 52 for controlling the conduction condition of the power switch Q based on the comparison result of the comparison circuit 11. In one embodiment, the first valley level control function 51 is selected to control the switching mode power supply circuit 100 when the input voltage Vin is greater than a first threshold Vth1, and the second valley level control function 52 is selected to control the switching mode power supply circuit 100 when the input voltage Vin is less than a second threshold Vth2, wherein the first threshold Vth1 is greater than or equal to the second threshold Vth 2. In a preferred embodiment, the first valley level control function 51 is selected to control the switched mode power supply circuit 100 when the input voltage Vin is greater than the threshold Vth, and the second valley level control function 52 is selected to control the switched mode power supply circuit 100 when the input voltage Vin is less than the threshold Vth. As can be seen from the figure, the first valley number control function 51 sets a first valley number larger than a second valley number set by the second valley number control function 52 in the same interval of the feedback signal Vfb or the same feedback signal Vfb. Thus, when the input voltage Vin is high, the valley number is increased, so that the switching frequency is reduced, and the switching loss is reduced. When the input voltage Vin is low, the valley bottom number is reduced, and the peak current Ipk is also reduced correspondingly according to the relation between the valley bottom number and the peak current, so that the conduction loss at the moment is also reduced.

In a preferred embodiment, when the input voltage Vin jumps from being greater than the preset threshold Vth to being less than the preset threshold, the valley number control function also jumps from the first valley number control function 51 to the second valley number control function 52, the valley number N decreases, the switching frequency Fs of the power switch Q increases, and the current flowing through the power switch decreases. Therefore, when the input voltage is larger, the switching frequency is lower and the effective current is higher, so that the switching loss is reduced; when the input voltage is lower, the switching frequency is increased and the effective current is reduced, so that the conduction loss is reduced, and the switching loss is dominant when the input voltage is higher and the conduction loss is dominant when the input voltage is lower, so that the loss of the system is reduced, and the efficiency of the system is improved.

The upper waveform of fig. 5 is the peak current control function 53, and in this embodiment, the peak current control function 53 is not affected by the input voltage. In another embodiment, the switching on of the power switch is controlled by selecting one of the at least two valley number control functions based on the input voltage, while the switching off of the power switch is controlled by selecting one of the at least two peak current control functions based on the input voltage.

Fig. 6 shows a flow diagram of a method 600 for controlling a switched-mode power supply circuit according to an embodiment of the invention. The method 600 comprises detecting an input voltage Vin of the switched mode power supply circuit in step 601. The input voltage can be detected by detecting the bus voltage behind the rectifying circuit, voltage signals of other parts which can reflect the input voltage in partial time periods, and other signals which can reflect the input voltage in other forms, such as PWM signals.

The method 600 further includes comparing the input voltage Vin to at least one threshold at step 602. In one embodiment, comparing the input voltage Vin to at least one threshold value comprises comparing the input voltage to one threshold value. In another embodiment, comparing the input voltage Vin to at least one threshold value includes comparing the input voltage Vin to two or more threshold values, respectively.

The method 600 comprises adjusting a control function based on the comparison result in step 603, for example selecting a first control function 1 when the input voltage Vin fulfils a first condition and selecting a second control function 2 when the input voltage Vin fulfils a second condition, wherein the control functions are adapted to set the on and/or off condition of the power switch Q of the switched-mode power supply circuit in dependence on a feedback signal Vfb that varies as the output voltage Vo of the switched-mode power supply circuit varies. In one embodiment, step 603 includes selecting one of at least two peak current control functions for setting a peak current Ipk through the power switch Q when the power switch Q is off based on the feedback signal Vfb. Specifically, the at least two peak current control functions may include a first peak current control function and a second peak current control function, wherein in the same feedback signal interval, a first peak current Ipk1 set by the first peak current control function is greater than a second peak current Ipk2 set by the second peak current control function, the first peak current control function is selected to control the switching mode power supply circuit when the input voltage Vin is greater than a first threshold Vth1, and the second peak current control function is selected to control the switching mode power supply circuit when the input voltage Vin is less than a second threshold Vth2, wherein the first threshold Vth1 is greater than or equal to the second threshold Vth 2. Therefore, when the input voltage Vin is higher, the peak current is higher, the switching frequency is lower, the switching loss is reduced, and when the input voltage is lower, the peak current is lower, the conduction loss is reduced, so that the system loss is lower under different input voltages, and the system efficiency is optimized and improved. In another embodiment, step 603 includes selecting one of at least two valley count control functions for setting the power switch Q to conduct at an nth valley of the oscillating signal of the voltage across the power switch Q based on the feedback signal Vfb, where N is a positive integer and is referred to as the valley count. Specifically, the at least two valley number control functions may include a first valley number control function and a second valley number control function, in the same feedback signal interval, a first valley number N1 set by the first valley number control function is greater than a second valley number N2 set by the second valley number control function, the first valley number control function is selected to control the switching mode power supply circuit when the input voltage Vin is greater than a first threshold Vth1, and the second valley number control function is selected to control the switching mode power supply circuit when the input voltage Vin is less than a second threshold Vth2, wherein the first threshold Vth1 is greater than or equal to the second threshold Vth 2. Like this, when input voltage is higher, the valley bottom number is higher, and switching frequency is lower, is favorable to reducing the switching loss this moment, and when input voltage is lower, the valley bottom number is lower, and the effective current is lower, is favorable to reducing the conduction loss this moment, therefore the efficiency of system obtains optimizing and improvement.

Fig. 7 shows a flow diagram of a method 700 for controlling a switched-mode power supply circuit according to an embodiment of the invention, wherein step 701 corresponds to step 601 of method 600. The method 700 includes comparing the input voltage Vin to a threshold Vth at step 702. When the input voltage Vin is greater than the threshold Vth, the control function 1 is selected for controlling the on and/or off condition of the power switch Q in step 703. When the input voltage Vin is less than the threshold Vth, control function 2 is selected at step 704 for controlling the on and/or off condition of the power switch Q. In one embodiment,

control functions

1 and 2 are peak current control functions that increase current gain when the input voltage Vin is greater than a threshold Vth and decrease current gain when the input voltage Vin is less than the threshold Vth. In another embodiment, control function 1 and control function 2 are valley number control functions. In yet another embodiment, control function 1 and control function 2 comprise both a peak current control function and a valley number control function, respectively. In the above three embodiments, when the input voltage jumps from greater than the threshold Vth to less than the threshold Vth, the switching frequency Fsw of the power switch Q rises and the current flowing through the power switch Q decreases. By means of the control, the switching loss is low when the input voltage Vin is high, the conduction loss is low when the input voltage Vin is low, and the efficiency of the system is optimized.

Those skilled in the art should understand that the logic controls of "high" and "low", "set" and "reset", "and" or "," in-phase "and" reverse "in the above logic controls can be interchanged or changed, and the subsequent logic controls can be adjusted to achieve the same functions or purposes as those of the above embodiments.

The description and applications of the present invention are illustrative and are not intended to limit the scope of the invention to the embodiments described above. The descriptions related to the effects or advantages in the specification may not be reflected in practical experimental examples due to uncertainty of specific condition parameters or influence of other factors, and the descriptions related to the effects or advantages are not used for limiting the scope of the invention. Variations and modifications of the embodiments disclosed herein are possible, and alternative and equivalent various components of the embodiments will be apparent to those skilled in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other components, materials, and parts, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the present invention.

Claims

1. A control circuit usable with a switch mode power supply circuit including a power switch, the switch mode power supply circuit having an input and an output, the control circuit comprising:

the comparison circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the comparison circuit is coupled with the input end of the switch mode power supply circuit, and the second input end of the comparison circuit is coupled with the threshold signal;

the control adjusting circuit is provided with a first input end, a second input end and an output end, the first input end of the control adjusting circuit is coupled with the output end of the comparison circuit, and the second input end of the control adjusting circuit receives a feedback signal; and

and the input end of the on/off control circuit is coupled with the output end of the control adjusting circuit, and the output end of the on/off control circuit is coupled with the control end of the power switch.

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

a peak current setting circuit for providing a peak current signal at an output terminal of the peak current setting circuit according to the feedback signal and the peak current control function;

the valley bottom number setting circuit provides a valley bottom number signal at the output end of the valley bottom number setting circuit according to the feedback signal and the valley bottom number control function;

the control adjusting circuit is positioned in the peak current setting circuit and/or the valley bottom number setting circuit and is used for adjusting the peak current control function and/or the valley bottom number control function according to the comparison result provided by the comparison circuit.

3. The control circuit of claim 2, wherein the on/off control circuit comprises:

the current comparison circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the current comparison circuit is coupled with the current sampling resistor, and the second input end of the current comparison circuit is coupled with the output end of the peak current setting circuit;

the valley bottom detection and counting circuit is provided with a first input end, a second input end and an output end, wherein the first input end of the valley bottom detection and counting circuit is coupled with the power switch, and the second input end of the valley bottom detection and counting circuit is coupled with the output end of the valley bottom number setting circuit; and

the trigger circuit is provided with a set input end, a reset input end and an output end, wherein the set input end of the trigger circuit is coupled with the output end of the valley bottom detection and counting circuit, the reset input end of the trigger circuit is coupled with the output end of the current comparison circuit, and the output end of the trigger circuit is coupled with the control end of the power switch.

4. The control circuit of claim 1 wherein the control adjustment circuit selects one from a first peak current control function and a second peak current control function based on a comparison result of the comparison circuit, in the same feedback signal interval, the first peak current set by the first peak current control function is larger than the second peak current set by the second peak current control function, selecting the first peak current control function to control the switched mode power supply circuit when an input voltage at an input of the switched mode power supply circuit is greater than a first threshold value, selecting the second peak current control function to control the switched mode power supply circuit when the input voltage at the input of the switched mode power supply circuit is less than a second threshold, wherein the first threshold is greater than or equal to the second threshold.

5. The control circuit of claim 1, wherein the control adjustment circuit selects one of a first and a second bottom number control function based on the comparison result of the comparison circuit, the first and second bottom number control functions being configured to set the power switch to conduct at an Nth bottom of the oscillating signal according to a feedback signal, where N is a positive integer and is referred to as a bottom number, the first bottom number control function setting a first bottom number greater than a second bottom number set by the second bottom number control function in a same feedback signal interval, the first bottom number control function being selected to control the switch mode power supply circuit when the input voltage at the input of the switch mode power supply circuit is greater than a first threshold value, the first bottom number control function being selected to control the switch mode power supply circuit when the input voltage at the input of the switch mode power supply circuit is less than a second threshold value, selecting the second valley digital control function to control the switch mode power supply circuit, wherein the first threshold is greater than or equal to the second threshold.

6. A control circuit usable with a switch-mode power supply circuit including a power switch, the switch-mode power supply circuit converting an input voltage at an input of the switch-mode power supply circuit to an output voltage at an output of the switch-mode power supply circuit based on a switching action of the power switch, the control circuit comprising:

a comparison circuit for comparing an input voltage signal representative of the input voltage with at least one threshold;

and the control adjusting circuit adjusts a peak current control function and/or a valley bottom number control function based on a comparison result of the comparison circuit, wherein the power switch is turned off when the current flowing through the power switch reaches a peak current, the power switch is turned on at the valley bottom position of an Nth oscillation signal of a voltage difference between two ends of the power switch, N is called a valley bottom number, the peak current is set by a feedback signal and the peak current control function, the valley bottom number is set by the feedback signal and the valley bottom number control function, and the feedback signal changes along with the change of the output voltage.

7. A control circuit usable with a switch-mode power supply circuit including a power switch, the switch-mode power supply circuit converting an input voltage at an input of the switch-mode power supply circuit to an output voltage at an output of the switch-mode power supply circuit based on a switching action of the power switch, the control circuit comprising:

a comparison circuit for comparing an input voltage signal representative of the input voltage with at least one threshold; and

and the control adjusting circuit is used for adjusting the control of the power switch according to the comparison result of the comparison circuit, wherein when the input voltage jumps from being larger than the threshold value to being smaller than the threshold value, the switching frequency of the power switch rises and the current flowing through the power switch decreases.

8. A switched mode power supply circuit comprising a control circuit as claimed in any one of claims 1 to 7 and a power switch.