A control circuit and chip for a switching power supply

Abstract

The present invention provides a control circuit and chip of a switching power supply, wherein the switching power supply includes a high voltage input terminal and a power supply voltage terminal, and the circuit includes: a controllable current source is connected to the high voltage input terminal and the power supply voltage terminal respectively; a first detection module is configured to obtain a first electrical signal representing the severity of the load; a second detection module is configured to obtain a second electrical signal representing the voltage of the power supply voltage terminal; a control module is connected to the controllable current source, the first detection module, and the second detection module respectively, and is configured to control the controllable current source to work to raise the voltage of the power supply voltage terminal through the high voltage input terminal when it is determined that the switching power supply is in a low load state and the power supply voltage terminal is in an undervoltage state according to the first electrical signal and the second electrical signal. The circuit can generate current to charge the power supply voltage terminal through the controllable current source, and can prevent the primary control chip from shutting down and restarting due to undervoltage when the switching power supply is in a low load state and the power supply voltage terminal is in an undervoltage state, causing high output ripple.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated circuits, and in particular relates to a control circuit and a chip of a switching power supply. Background Art

[0002] Switching power supplies are usually implemented with switching regulators. Existing switching power supplies usually control the on and off of a power switch tube through a switching signal to adjust the VCC voltage in the switching power supply. That is, when the switching power supply is in a light-load and undervoltage state, the MOS tube is controlled to be turned on to charge VCC. However, this method supplies power to VCC by turning on the GATE switch and the auxiliary winding of the transformer. On the one hand, the charging speed of VCC is affected by factors such as the output voltage. On the other hand, turning on the MOS tube under light load will cause the output voltage to be too high or unstable, and some energy will be wasted. Summary of the invention

[0003] In view of the defects in the prior art, the present invention provides a control circuit and chip of a switching power supply, which can directly charge VCC from the primary side, accelerate and stabilize the charging speed, and avoid uncontrollable charging time and high or unstable output voltage caused by transmitting energy to VCC from the secondary side.

[0004] In a first aspect, a control circuit of a switching power supply is provided, wherein the switching power supply comprises a high voltage input terminal and a power supply voltage terminal, and the control circuit comprises:

[0005] A controllable current source is connected to the high voltage input terminal and the power supply voltage terminal respectively;

[0006] A first detection module is configured to obtain a first electrical signal for characterizing the severity of the load;

[0007] A second detection module is configured to obtain a second electrical signal for representing the voltage at the power supply voltage terminal;

[0008] The control module is connected to the controllable current source, the first detection module, and the second detection module respectively. The control module is configured to control the controllable current source to raise the voltage of the power supply voltage terminal through the high-voltage input terminal when it is determined according to the first electrical signal and the second electrical signal that the switching power supply is in a low-load state and the power supply voltage terminal is in an under-voltage state.

[0009] In a second aspect, a control chip of a switching power supply is provided, wherein the control chip comprises the control circuit of the switching power supply of the first aspect.

[0010] It can be seen from the above technical solutions that the control circuit and chip of the switching power supply provided by the present invention avoid the situation where the output voltage is unstable due to restarting due to undervoltage of the power supply voltage terminal VCC when the switching power supply is in a low-load state and the power supply voltage terminal is in an undervoltage state. At the same time, a controllable current source is used to generate current to charge the power supply voltage terminal VCC, and the charging rate is easier to control, thereby achieving accelerated and stable charging speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for the specific embodiments or the description of the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn according to the actual scale.

[0012] Figure 1 It is a module block diagram of the control circuit of the switching power supply provided in the embodiment.

[0013] Figure 2 4 is a circuit diagram of a switching power supply provided in an embodiment.

[0014] Figure 3 It is a timing diagram of the control circuit provided in the embodiment.

[0015] Figure 4 It is a module block diagram of the control module provided in the embodiment.

[0016] Figure 5 A circuit diagram of a controllable current source provided in an embodiment.

[0017] Figure 6 Another circuit diagram of the controllable current source provided in the embodiment. DETAILED DESCRIPTION

[0018] The embodiments of the technical solution of the present invention will be described in detail below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and are therefore only used as examples, and the protection scope of the present invention cannot be limited thereto. It should be noted that, unless otherwise specified, the technical terms or scientific terms used in this application should be the common meanings understood by those skilled in the art to which the present invention belongs.

[0019] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0020] It should also be understood that the terms used in this specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. As used in the specification of the present invention and the appended claims, unless the context clearly indicates otherwise, the singular forms "a", "an" and "the" are intended to include plural forms.

[0021] As used in this specification and the appended claims, the term "if" may be interpreted as "when" or "upon" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if [described condition or event] is detected" may be interpreted as meaning "upon determination" or "in response to determining" or "upon detection of [described condition or event]" or "in response to detecting [described condition or event]," depending on the context.

[0022] Example:

[0023] A control circuit 1 of a switching power supply, see Figure 1 The switching power supply includes a high voltage input terminal 2 and a power supply voltage terminal 3, and the control circuit 1 includes:

[0024] A controllable current source 14 is connected to the high voltage input terminal 2 and the power supply voltage terminal 3 respectively;

[0025] The first detection module 12 is configured to obtain a first electrical signal for representing the weight of the load;

[0026] The second detection module 13 is configured to obtain a second electrical signal for representing the voltage of the power supply voltage terminal 3;

[0027] The control module 11 is connected to the controllable current source 14, the first detection module 12, and the second detection module 13 respectively. The control module 11 is configured to control the controllable current source 14 to work so as to raise the voltage of the power supply voltage terminal 3 through the high-voltage input terminal 2 when it is determined according to the first electrical signal and the second electrical signal that the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an under-voltage state.

[0028] In this embodiment, the power supply voltage terminal 3 being in an undervoltage state can be regarded as a state in which the control circuit 1 cannot guarantee long-term stable operation at the rated working voltage. The switching power supply being in a low-load state can be regarded as a state in which the load connected to the switching power supply has a light power consumption or a state in which the switching power supply is not connected to a load. That is, the switching power supply being in a low-load state can be a light-load state or a no-load state.

[0029] In this embodiment, the control circuit 1 can be applied to Figure 2The flyback switching power supply described above may include a capacitor 21, a diode 22, an auxiliary winding 23, a resistor 24, a capacitor 25, a diode 26, a main winding 27, an external power switch tube 28, a resistor 29, a diode 30, a secondary coil 31 and a capacitor 32; wherein the first end of the resistor 24, the first end of the capacitor 25 and the same-name end of the main winding 27 are all connected to the power supply V IN , the second end of the resistor 24 and the second end of the capacitor 25 are connected to the first end of the diode 26, the second end of the diode 26 and the opposite end of the main winding 27 are connected to the first end of the external power switch tube 28, the second end of the external power switch tube 28 is connected to the ground of the primary side through the resistor 29, and the third end of the external power switch tube 28 is connected to the switch control end. The same end of the auxiliary winding 23 is connected to the ground of the primary side, the opposite end of the auxiliary winding 23 is connected to the first end of the diode 22, the second end of the diode 22 is connected to the ground of the secondary side through the capacitor 21, and the second end of the diode 22 can be used as the power supply voltage terminal 3. The opposite end of the secondary coil 31 is connected to the first end of the diode 30, the second end of the diode 30 is respectively connected to the first end of the capacitor 32, the output sampling module and the output terminal, and the same end of the secondary coil 31 and the second end of the capacitor 32 are connected to the ground of the secondary side. Among them, the power supply voltage terminal 3 is represented by VCC in the figure. The high-voltage input terminal 2 of the switching power supply is used to provide the input of the controllable current source 14, and the high-voltage input terminal 2 is represented by HV in the figure. The switching power supply may further include a feedback signal receiving pin FB, and the feedback signal receiving pin FB in the switching power supply may obtain a parameter for characterizing a load power usage condition between the output terminal and the reference ground terminal of the secondary side.

[0030] In this embodiment, the first detection module 12 can be connected to the pin FB in the switching power supply, and obtain a first electrical signal representing the severity of the load through the FB pin. The load severity includes heavy load state, normal working state, light load state, no-load state, etc.

[0031] In some examples, the first electrical signal acquired by the first detection module 12 may be a voltage, current, power or other signal, and the type of the first electrical signal is not specifically limited here. Specifically, the first electrical signal may be a voltage used to characterize the load, and when the feedback mode of the switching power supply is a positive polarity connection method, the voltage is positively correlated with the load severity of the switching power supply, that is, the greater the voltage, the heavier the load of the switching power supply; when the feedback mode of the switching power supply is a negative polarity connection method, the voltage is negatively correlated with the load severity of the switching power supply, that is, the greater the voltage, the lighter the load of the switching power supply.

[0032] In this embodiment, the second detection module 13 can be connected to the power supply voltage terminal 3 in the switching power supply in a direct or indirect manner to obtain a second electrical signal for characterizing the voltage of the power supply voltage terminal 3, and the state of the voltage of the power supply voltage terminal 3 includes an overvoltage state, a normal working state, an undervoltage state, etc. Among them, the voltage of the power supply voltage terminal 3 can be compared with a preset voltage, and when the voltage of the power supply voltage terminal 3 is less than the preset voltage, it can be regarded that the power supply voltage terminal 3 is in an undervoltage state, and at this time, the preset voltage can be greater than the undervoltage lockout threshold UVLO_ON, and less than the undervoltage lockout turn-off threshold UVLO_OFF.

[0033] In this embodiment, the first load threshold voltage V FB_TH1 and the first threshold voltage V CC_TH1 The first load threshold voltage V FB_TH1 and the first threshold voltage V CC_TH1 It can be set by the user according to specific usage requirements. Whether the switching power supply is in a low-load state can be determined by the first electrical signal, and whether the switching power supply is in an undervoltage state can be determined by the second electrical signal. The working states of the switching power supply include the following:

[0034] ① When the first electrical signal is greater than the first load threshold voltage V FB_TH1 When , it indicates that the switching power supply is currently in normal working state.

[0035] ② When the first electrical signal is less than the first load threshold voltage V FB_TH1 , and the second electrical signal is greater than the first threshold voltage V CC_TH1 , it indicates that the switching power supply is currently in a light load or zero load state.

[0036] ③ When the first electrical signal is less than the first load threshold voltage V FB_TH1 , and the second electrical signal is less than the first threshold voltage V CC_TH1 , it indicates that the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an undervoltage state.

[0037] Among them, the first load threshold voltage V FB_TH1 It can be the highest voltage of the switching power supply under light load state. When the first electrical signal is less than the first load threshold voltage V FB_TH1 , the switching power supply is considered to be in a low-load state. The first threshold voltage V CC_TH1 It can be set to a voltage greater than the undervoltage lockout threshold UVLO_ON. When the second electrical signal is less than the first threshold voltage V CC_TH1 , it is considered that the power supply voltage terminal 3 is in an undervoltage state.

[0038] In this embodiment, when the controllable current source 14 is working, it can be regarded as that the circuit between the high voltage input terminal 2 and the power supply voltage terminal 3 is turned on, and the current of the path formed between the high voltage input terminal 2 and the power supply voltage terminal 3 is the current of the controllable current source 14 .

[0039] It should be noted that in the prior art, Figure 2 As shown, when the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an undervoltage state, the external power switch tube 28 is usually switched on and off for a few cycles by timing control. After the external power switch tube 28 is turned off, there is energy flowing from the opposite-name end of the secondary coil 31 into the load of the transformer secondary coil 31. Due to the effect of coil coupling, there is energy flowing from the opposite-name end of the auxiliary winding 23 through the diode 22 to the capacitor 21, charging VCC, thereby raising the voltage of the capacitor 21, and synchronously raising VCC. The synchronous main winding 27 will transfer electrical energy to the secondary coil 31. Since the switching power supply is in a low-load state at this time, the electrical energy transferred to the secondary coil 31 will cause the voltage of the secondary coil 31 to be too high. In the present embodiment, when the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an under-voltage state, the controllable current source 14 of the control circuit 1 outputs current to the power supply voltage terminal 3 to supplement power for the power supply voltage terminal 3 and raise the voltage of the power supply voltage terminal 3. This can prevent excessive energy from being output to the secondary coil 31, causing the output voltage to be too high. At the same time, it can avoid the situation where the output voltage is unstable due to the under-voltage of the power supply voltage terminal 3 when the switching power supply is low-loaded and the restart causes the output voltage to be unstable. At the same time, the controllable current source 14 generates current to charge the power supply voltage terminal 3, which can further accelerate and stabilize the charging speed and avoid energy transmission to the auxiliary coil to cause more energy loss.

[0040] Furthermore, in some embodiments, the control module 11 is further configured to determine, based on the second electrical signal, that the voltage at the power supply voltage terminal 3 is less than the first threshold voltage V CC_TH1 When the power supply voltage terminal 3 is judged to be in an undervoltage state, and when it is determined that the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an undervoltage state, the controllable current source 14 is controlled to be a first current, and the voltage of the power supply voltage terminal 3 is raised until the second threshold voltage V CC_TH2 .

[0041] In this embodiment, the first threshold voltage V CC_TH1It can be set to a voltage greater than the undervoltage lockout threshold UVLO_ON and less than the undervoltage lockout shutdown threshold UVLO_OFF, wherein the undervoltage lockout threshold UVLO_ON is the non-operating voltage of the switching power supply. When the input voltage of the switching power supply is lower than the undervoltage lockout threshold UVLO_ON, the switching power supply does not work; the undervoltage lockout shutdown threshold UVLO_OFF is the voltage at which the switching power supply turns off the undervoltage lockout function. Different switching power supplies have different undervoltage lockout thresholds UVLO_ON and undervoltage lockout shutdown thresholds UVLO_OFF. In this way, when the voltage at the power supply voltage terminal 3 is less than the first threshold voltage V CC_TH1 When the first threshold voltage V CC_TH1 A voltage greater than the undervoltage lockout threshold UVLO_ON indicates that the current switching power supply has entered an undervoltage state but has not yet reached the undervoltage lockout state.

[0042] In this embodiment, the second threshold voltage V CC_TH2 can be set to be greater than the first threshold voltage V CC_TH1 The control circuit 1 controls the controllable current source 14 to charge the capacitor C2, and increases the voltage of the power supply voltage terminal 3 until the power supply voltage terminal 3 is greater than the second threshold voltage V CC_TH2 , the power supply voltage at terminal 3 is greater than the second threshold voltage V CC_TH2 After that, the controllable current source 14 can be controlled to output zero. In this way, the control circuit 1 can ensure that the voltage of the power supply voltage terminal 3 is always greater than the undervoltage lockout threshold UVLO_ON, so that the voltage of the power supply voltage terminal 3 is always at the first threshold voltage V CC_TH1 With the second threshold voltage V CC_TH2 As a preferred embodiment, the second threshold voltage V CC_TH2 Can be synchronized to be less than or equal to the undervoltage lockout shutdown threshold UVLO_OFF.

[0043] In this embodiment, when it is determined that the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an undervoltage state, a path is formed between the high-voltage input terminal 2 and the power supply voltage terminal 3 by controlling the controllable current source 14, and the current of the path is a first current.

[0044] In this embodiment, the voltage of the power supply voltage terminal 3 can be always kept at the first threshold voltage V CC_TH1 With the second threshold voltage V CC_TH2 At the same time, the external power switch tube 28 is in the cut-off state, and is turned on when the switching power supply starts a new startup cycle to provide power to the power supply voltage terminal 3, thereby avoiding the startup cycle taking a long time and speeding up the startup speed.

[0045] Furthermore, in some embodiments, the control module 11 is further configured to control the controllable current source 14 to be a second current when the switching power supply is in the startup phase, and to raise the voltage of the power supply voltage terminal 3 to the undervoltage lockout threshold UVLO_OFF.

[0046] In this embodiment, if Figure 3 As shown, when the switching power supply is in the startup phase, the controllable current source 14 can also output current to the power supply voltage terminal 3 to raise the voltage of the power supply voltage terminal 3. LL and the second current I start The size of the first current I is determined according to the charging efficiency and charging time required by the user. LL and the second current I start The relative size relationship between them is not specifically limited. The control circuit 1 can ensure that the switching power supply starts quickly and stably.

[0047] The timing diagram of the control circuit 1 is shown in Figure 3 Phase a is the start-up phase of the switching power supply. In phase a, the controllable current source 14 outputs the second current I start The power supply voltage terminal 3 is charged until the voltage of the power supply voltage terminal 3 reaches the undervoltage lockout threshold UVLO_OFF. At this time, the switching power supply is successfully started and enters the normal working state. Stage b is the normal working state of the switching power supply. Stage c is when the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an undervoltage state, the controllable current source 14 outputs the first current I LL The power supply voltage terminal 3 is charged until the voltage of the power supply voltage terminal 3 reaches the second threshold voltage V CC_TH2 Phase d is a low-load state. Phase c and phase d are repeated.

[0048] Further, in some embodiments, see Figure 2 The switching power supply may further include a switch control terminal Gate connected to the external power switch tube 28, and the control module 11 is further configured to determine that the switching power supply is in a low-load state according to the first electrical signal, and determine that the voltage of the power supply voltage terminal 3 is greater than the second threshold voltage V according to the second electrical signal. CC_TH1 When the control switch control terminal outputs a pulse modulation signal to the external power switch tube 28.

[0049] In this embodiment, it should be noted that the "external power switch tube 28" described in this embodiment is "external" relative to the control circuit 1, and is not "external" to the carrier where the control circuit 1 is located, and does not limit the specific position of the "external power switch tube 28".

[0050] In this embodiment, the control module 11 not only uses the controllable current source 14 to raise the voltage of the power supply voltage terminal 3, but also can raise the voltage of the power supply voltage terminal 3 through the external switch tube 2. That is, when the switching power supply is in a low-load state and the voltage of the power supply voltage terminal 3 is greater than the first threshold voltage V CC_TH1 When the switch control terminal outputs a pulse modulation signal to the external power switch tube 28, controls the on and off of the external power switch tube 28, thereby achieving the effect of raising the voltage of the power supply voltage terminal 3. The control circuit 1 charges the capacitor 21 through the auxiliary winding 23, and can also achieve that when the switching power supply is in a low-load state, and the voltage of the power supply voltage terminal 3 is greater than the first threshold voltage V CC_TH1 When the power supply voltage is increased, the voltage at the power supply voltage terminal 3 is increased.

[0051] Further, in some embodiments, see Figure 4 The control module 11 includes a hysteresis comparison unit 111 and a logic circuit 112; the hysteresis comparison unit 111 is configured to obtain a comparison result including whether the switching power supply is in a low-load state according to the first electrical signal; the logic circuit 112 is configured to control the working state of the controllable current source 14 according to the comparison result.

[0052] In this embodiment, the hysteresis comparison unit 111 may include a hysteresis comparator. When the control module 11 passes the first load threshold voltage V FB_TH1 When determining whether the switching power supply is in a low-load state, one input terminal of the comparator receives a first electrical signal, and the other input terminal of the comparator receives a first load threshold voltage V FB_TH1 Thus, the comparison result of the hysteresis comparison unit 111 includes a voltage VFB corresponding to the first electrical signal, which is used to indicate that the feedback voltage VFB is less than the first load threshold voltage V FB_TH1 When the feedback voltage VFB corresponding to the first electrical signal is less than the first load threshold voltage V FB_TH1 When the load voltage is below the first load threshold voltage V, the hysteresis comparison unit 111 outputs a signal for indicating that the switch power supply is in a low load state. The hysteresis comparison unit 111 can prevent the load voltage from exceeding the first load threshold voltage V FB_TH1 The phenomenon of frequent changes in comparison results caused by jittering back and forth near the reference point is more conducive to determining the working state of the switching power supply.

[0053] In this embodiment, the control module 11 may further include a voltage determination module 113, which is configured to determine the voltage of the power supply voltage terminal 3, that is, to achieve the following comparison results: ① The power supply voltage terminal 3 is equal to the first threshold voltage V CC_TH1 ② The comparison result of the power supply voltage terminal 3 and the second threshold voltage V CC_TH2③ The comparison result of the power supply voltage terminal 3 and the undervoltage lockout threshold UVLO_OFF; ④ The comparison result of the power supply voltage terminal 3 and the undervoltage lockout threshold UVLO_ON. Thus, the first terminal of the voltage determination module 113 receives the voltage of the power supply voltage terminal 3, the second terminal receives the undervoltage lockout threshold UVLO_OFF, and the third terminal receives the first threshold voltage V CC_TH1 , the fourth terminal receives the second threshold voltage V CC_TH2 , the fifth terminal receives the undervoltage lockout threshold UVLO_ON.

[0054] In this embodiment, the logic circuit 112 is used to determine whether to control the working state of the controllable current source 14 according to the above comparison result. For example, when the received hysteresis comparison unit 111 outputs a feedback voltage VFB corresponding to the first electrical signal that is less than the first load threshold voltage V FB_TH1 As a result, the voltage determination module 113 outputs a power supply voltage terminal 3 that is less than the first threshold voltage V CC_TH1 When the result is , it means that the switching power supply is in a low-load state, and the power supply voltage terminal 3 is in an undervoltage state, the controllable current source 14 is controlled to work; when the received voltage determination module 113 outputs that the power supply voltage terminal 3 is greater than or equal to the second threshold voltage V CC_TH2 When the received voltage judgment module 113 outputs the result that the power supply voltage terminal 3 is greater than the undervoltage lockout threshold UVLO_OFF, it indicates that the switch power supply startup phase has been completed, and the controllable current source 14 is controlled to stop working. The control circuit 1 implements logic control through the hysteresis comparison unit 111 and the logic circuit 112, which reduces the development difficulty and cost.

[0055] Further, in some embodiments, see Figure 5 , the controllable current source 14 may include a constant current source 31, a first diode 32 and a first switch tube 33;

[0056] Among them, the high-voltage input terminal 2 is connected to the first end of the constant current source 31 and the first end of the first switch tube 33 respectively; the control module 11 is connected to the second end of the constant current source 31, the second end of the first switch tube 33, and the second end of the first diode 32 respectively; the power supply voltage terminal 3 is connected to the third end of the first switch tube 33 and the first end of the first diode 32 respectively.

[0057] In this embodiment, the second end of the first switch tube 33 is a gate. When the first end of the first switch tube 33 can be a drain, the third end of the first switch tube 33 can be a source; when the first end of the first switch tube 33 can be a source, the third end of the first switch tube 33 can be a drain. The first switch tube 33 can be a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET). Therefore, the gate level of the first switch tube 33 can be controlled to control whether the first switch tube 33 is turned on. Among them, the first diode 32 can include a Zener diode and a voltage regulator. The second end of the first diode 32 is a cathode, and the first end of the first diode 32 is an anode. In this way, Figure 3 In the phase a and phase c of the embodiment, when the first switch tube 33 is turned on, the current flows in the direction of: high voltage input terminal 2 → first switch tube 33 → power supply voltage terminal 3. At this time, the second current I start With the first current I LL The constant current source 31 and the first diode 32 form a clamping circuit to provide Vgate for the gate of the first switch tube 33. Figure 3 In the phase b and the phase d, the first switch tube 33 is turned off, and the high voltage input terminal 2 stops charging the power supply voltage terminal 3.

[0058] In this embodiment, by using a controllable current source 14 including a constant current source 31, a first diode 32 and a first switch tube 33, the control module 11 can control the controllable current source 14 to work so that the second current I start With the first current I LL The voltage of the power supply voltage terminal 3 is raised through the high-voltage input terminal 2 when the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an undervoltage state.

[0059] Further, in some embodiments, see Figure 6 , the controllable current source 14 may include a second switch tube 41, one or more third switch tubes 42 and a second diode 43;

[0060] Among them, the high-voltage input terminal 2 is connected to the first end of the second switch tube 41 and the first end of the third switch tube 42 respectively, the control module 11 is connected to the third end of the second switch tube 41 and the second end of the third switch tube 42 respectively, the second end of the second switch tube 41 is connected to the reference voltage terminal, the third end of the third switch tube 42 is connected to the first end of the second diode 43, and the second end of the second diode 43 is connected to the power supply voltage terminal 3.

[0061] In this embodiment, the reference voltage terminal may be a reference ground terminal. The second switch tube 41 may be a junction field-effect transistor (JFET), in which case the first terminal of the second switch tube 41 may be a drain, the second terminal of the second switch tube 41 may be a gate, and the third terminal of the second switch tube 41 may be a source. The third switch tube 42 may be a MOSFET, the second terminal of the third switch tube 42 may be a gate, when the first terminal is a drain, the third terminal is a source; when the first terminal is a source, the third terminal is a drain. In addition, the substrate terminal of the third switch tube 43 may be connected to the voltage reference terminal Vref.

[0062] When the number of the third switch tube 42 is 1, when the third switch tube 42 is turned on, the current flows as follows: high voltage input terminal 2 → third switch tube 42 → power supply voltage terminal 3. At this time, the third terminal of the second switch tube 41 provides a driving voltage for the second terminal of the third switch tube 42. At this time, the second current I start With the first current I LL equal.

[0063] When the number of the third switch tubes 42 is greater than or equal to 2, it is possible to select to control some or all of the third switch tubes 42 to be turned on, for example, to control two of the third switch tubes 42 to be turned on, at which time the current flows as follows: high voltage input terminal 2 → two third switch tubes 42 → power supply voltage terminal 3, at which time the third end of the second switch tube 41 provides a driving voltage for the second end of the two third switch tubes 42; for example, to control one of the third switch tubes 42 to be turned on, at which time the current flows as follows: high voltage input terminal 2 → one third switch tube 42 → power supply voltage terminal 3, at which time the third end of the second switch tube 41 provides a driving voltage for the second end of one third switch tube 42. It should be noted that the more the number of the third switch tubes 42 that are turned on, the greater the current flowing from the high voltage input terminal 2 to the power supply voltage terminal 3, and the faster the rate of raising the voltage of the power supply voltage terminal 3.

[0064] Therefore, in Figure 3 In the stage a, the second current I can be determined by controlling whether the third switch tube 42 is turned on and the number of the third switch tubes 42 that are turned on. start size; Figure 3 In the stage c, the first current I can be determined by controlling whether the third switch tube 42 is turned on and the number of the third switch tubes 42 that are turned on. LL Therefore, the second current I start can be less than or equal to or greater than the first current I LL .exist Figure 3 In the phase b and the phase d, the third switch tube 42 can be controlled to be turned off, so that the high voltage input terminal 2 and the power supply voltage terminal 3 are disconnected.

[0065] In this embodiment, by using a controllable current source 14 including a second switch tube 41, one or more third switch tubes 42 and a second diode 43, the control module 11 can control the controllable current source 14 to work, and determine the third switch tube 42 to be turned on based on actual needs, thereby controlling the second current I start , the first current I LL For the corresponding current size, etc., it meets the requirement of raising the voltage of the power supply voltage terminal 3 through the high voltage input terminal 2 when the switching power supply is in a low-load state and the power supply voltage terminal 3 is in an undervoltage state.

[0066] Further, in some embodiments, the low-load state is a light-load state or a no-load state.

[0067] In this embodiment, the light-load state is a state when the load of the switching power supply is relatively light, and the no-load state is a state when the switching power supply is not connected to a load.

[0068] Further, in some embodiments, the switch may include but is not limited to a forward switching power supply, a flyback switching power supply, and a resonant switching power supply.

[0069] In this embodiment, when the switching power supply feedback mode is a negative polarity connection method, VFB (feedback signal) is inversely proportional to the load severity. When the switching power supply feedback mode is a positive polarity connection method, the size of VFB is directly proportional to the load severity. The logic control provided in the above embodiment is the logic control of the flyback switching power supply. When the switching power supply feedback mode is a negative polarity connection method, for example, the logic control is as follows:

[0070] ① When the feedback voltage VFB corresponding to the first electrical signal is less than the second load threshold voltage V FB_TH2 When , the load is working normally, indicating that the switching power supply is currently in normal working state;

[0071] ② When the feedback voltage VFB corresponding to the first electrical signal is greater than the second load threshold voltage V FB_TH2 , and the second electrical signal is greater than the first threshold voltage V CC_TH1 , it indicates that the switching power supply is currently in a light load or zero load state.

[0072] ③ When the feedback voltage VFB corresponding to the first electrical signal is greater than the first load threshold voltage V FB_TH1 , and the second electrical signal is less than the first threshold voltage V CC_TH1 , indicating that the switching power supply is currently in a no-load and power supply undervoltage state, the controllable current source 14 inside the chip is controlled to charge the capacitor 21, and the voltage of the power supply voltage terminal 3 is increased until the second electrical signal is greater than the second threshold voltage V CC_TH2 , when VCC is greater than the second threshold voltage V CC_TH2Then the controllable current source 14 is controlled to be zero. In this way, the control circuit can control the voltage of the power supply voltage terminal 3 to always be greater than the under-voltage lockout threshold UVLO_ON.

[0073] A control chip of a switching power supply, the control chip comprising the control circuit 1 of the switching power supply.

[0074] The chip provided in the embodiment of the present invention is briefly described. For matters not mentioned in the embodiment part, reference may be made to the corresponding contents in the aforementioned embodiment.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be included in the scope of the claims and specification of the present invention.

Claims

1. A control circuit of a switching power supply, characterized in that: The switching power supply includes a high voltage input terminal and a power supply voltage terminal, and the control circuit includes: A controllable current source, connected to the high voltage input terminal and the power supply voltage terminal respectively; A first detection module is configured to obtain a first electrical signal for characterizing the severity of the load; A second detection module is configured to obtain a second electrical signal for characterizing the voltage at the power supply voltage terminal; A control module is connected to the controllable current source, the first detection module, and the second detection module respectively. The control module is configured to control the controllable current source to work so as to raise the voltage of the power supply voltage terminal through the high-voltage input terminal when it is determined according to the first electrical signal and the second electrical signal that the switching power supply is in a low-load state and the power supply voltage terminal is in an undervoltage state; the switching power supply includes a forward switching power supply, a flyback switching power supply, and a resonant switching power supply.

2. The control circuit of the switching power supply according to claim 1, characterized in that: The control module is also configured to, when it is determined according to the second electrical signal that the voltage at the power supply voltage end is less than a first threshold voltage, judge that the power supply voltage end is in an undervoltage state, and when it is determined that the switching power supply is in a low-load state and the power supply voltage end is in an undervoltage state, control the controllable current source to a first current, and raise the voltage at the power supply voltage end to a second threshold voltage.

3. The control circuit of the switching power supply according to claim 2, characterized in that: The control module is further configured to control the controllable current source to a second current when the switching power supply is in a startup phase, and to raise the voltage of the power supply voltage terminal to an undervoltage lockout shutdown threshold.

4. The control circuit of the switching power supply according to claim 1, characterized in that: The switching power supply also includes a switching control terminal connected to an external switching tube. The control module is also configured to control the switching control terminal to output a pulse modulation signal to the external switching tube when it is determined that the switching power supply is in a low-load state according to the first electrical signal and when it is determined that the voltage at the power supply voltage terminal is greater than a second threshold voltage according to the second electrical signal.

5. The control circuit of the switching power supply according to claim 1, characterized in that: The control module includes a hysteresis comparison unit and a logic circuit; the hysteresis comparison unit is configured to obtain a comparison result including whether the switching power supply is in a low-load state according to the first electrical signal; and the logic circuit is configured to control the working state of the controllable current source according to the comparison result.

6. The control circuit of the switching power supply according to claim 1, characterized in that: The controllable current source includes a constant current source, a first diode and a first switch tube; Among them, the high-voltage input end is connected to the first end of the constant current source and the first end of the first switch tube respectively; the control module is connected to the second end of the constant current source, the second end of the first switch tube, and the second end of the first diode respectively; the power supply voltage end is connected to the third section of the first switch tube and the first end of the first diode respectively.

7. The control circuit of the switching power supply according to claim 1, characterized in that: The controllable current source includes a second switch tube, one or more third switch tubes and a second diode; Among them, the high-voltage input end is connected to the first end of the second switch tube and the first end of the third switch tube respectively, the control module is connected to the third end of the second switch tube and the second end of the third switch tube respectively, the second end of the second switch tube is connected to the reference voltage end, the third end of the third switch tube is connected to the first end of the second diode, and the second end of the second diode is connected to the power supply voltage end.

8. The control circuit of the switching power supply according to any one of claims 1 to 7, characterized in that: The low-load state is a light-load state or a no-load state.

9. A control chip for a switching power supply, characterized in that: The control chip comprises the control circuit of the switching power supply according to any one of claims 1 to 8.

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