Switching power supply circuit and primary side control circuit and method thereof

Abstract

The present application discloses a switching power supply circuit, a primary side control circuit and a method for the switching power supply circuit. The switching power supply circuit comprises: a primary side switching circuit, a secondary side switching circuit and a primary side control circuit, wherein the primary side control circuit controls the peak value of the primary side current according to the frequency at which the primary side switching circuit is turned on, wherein: when the frequency is greater than the frequency threshold, the peak value has a first form; when the frequency is less than the frequency threshold, the peak value has a second form. The switching power supply circuit of the present invention realizes peak current mode control on the primary side under the premise of mainly controlling the secondary side, thereby improving the conversion efficiency.

Description

Technical Field

[0001] The present invention relates to an electronic circuit, and more particularly to a switching power supply circuit and a primary side control circuit and method thereof. Background Art

[0002] With the rapid development of information technology, various electronic devices are increasingly used, such as mobile phones and portable computers. These devices can be powered by external adapter power supplies (or chargers). The adapter power supply is usually an AC to DC converter, that is, the mains power of the power grid, such as the domestic 50Hz / 220V AC power, is converted into a low-voltage DC power (such as 5V DC output) and electrically isolated. A typical circuit topology of this circuit is a flyback converter. In order to maintain the stability of the output voltage, the traditional adapter power supply needs to sample the secondary output voltage and feed the sampled voltage signal back to the primary side to control the primary power switch. Due to the input and output isolation, the feedback circuit needs to be electrically isolated to ensure electrical safety, which increases the size of the electronic equipment and is contrary to the current requirements of miniaturization.

[0003] In addition, in order to better achieve control on the output side, in some cases, it is necessary to place part of the control circuit on the secondary side. The secondary side control circuit determines the turn-on time of the primary side switch based on the output voltage, and transmits the indication signal of the turn-on of the primary side switch to the primary side (such as a drive transformer, isolation capacitor, etc.) through appropriate technical means; there may also be no isolator to further save costs.

[0004] In this application, it is usually impossible to achieve traditional peak current mode control, because the current of the primary switch is sampled on the primary side, and the control circuit on the secondary side cannot obtain the primary switch current information. At the same time, in order to optimize efficiency, the switching frequency and peak current of the primary switch usually need to be flexibly set. Therefore, under the premise that the turn-on signal of the primary switch is given by the secondary side, how to generate the corresponding primary switch turn-off current control signal on the primary side based on the turn-on control signal given by the secondary side to achieve peak current mode control, further achieve flexible regulation of current and frequency, and optimize efficiency, is still an unresolved problem in this field. Summary of the invention

[0005] Therefore, the purpose of the present invention is to solve the above technical problems in the prior art and to provide an improved switching power supply circuit and method.

[0006] According to an embodiment of the present invention, a switching power supply circuit is proposed, comprising: a primary power switch coupled to the primary side of an electrical isolation device, the primary power switch being periodically turned on and off to transfer an input voltage to a secondary side of the electrical isolation device; a secondary switch circuit coupled to the secondary side of the electrical isolation device, the secondary switch circuit being periodically turned on and off to provide a required output voltage; a primary control circuit generating a primary control signal to control the primary switch circuit, the primary control circuit controlling the peak value of the primary current according to the frequency at which the primary switch circuit is turned on, wherein: when the frequency is greater than a frequency threshold, the peak value has a first form; when the frequency is less than the frequency threshold, the peak value has a second form.

[0007] According to an embodiment of the present invention, a primary control circuit for a switching power supply circuit is also proposed, wherein the switching power supply circuit has a primary switching circuit coupled to the primary side and a secondary switching circuit coupled to the secondary side, wherein the primary control circuit includes: a peak setting circuit, which generates a reference peak value according to the frequency at which the primary switching circuit is turned on, wherein: when the frequency is greater than a frequency threshold, the reference peak value has a first form; when the frequency is less than the frequency threshold, the reference peak value has a second form; and a peak current comparison circuit, which compares a current sampling signal representing the primary current with a reference peak value, and generates a reset signal to control the disconnection of the primary switching circuit.

[0008] According to an embodiment of the present invention, a method for a switching power supply circuit is also proposed, wherein the switching power supply circuit comprises: an electrical isolation device having a primary side and a secondary side, a primary switching circuit coupled to the primary side of the electrical isolation device, and a secondary switching circuit coupled to the secondary side of the electrical isolation device, wherein the method comprises: receiving an input voltage at the primary side, and generating an output voltage at the secondary side by controlling the on and off of the primary switching circuit and the secondary switching circuit; receiving an indication signal transmitted from the secondary side indicating that the primary switching circuit is on, and controlling the primary switching circuit to be on; and controlling the peak value of the primary current according to the frequency at which the primary switching circuit is turned on, wherein when the frequency is greater than a frequency threshold, the peak value has a first form; and when the frequency is less than the frequency threshold, the peak value has a second form.

[0009] According to the switching power supply circuit and primary side control circuit and method of various aspects of the present invention, peak current mode control is implemented on the primary side under the premise of mainly controlling the secondary side, thereby improving conversion efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 A schematic diagram of the circuit structure of a switching power supply circuit 100 according to an embodiment of the present invention is shown;

[0011] Figure 2 The primary current peak value I according to the embodiment of the present invention is shown. PSchematic diagram of the relationship with the conduction frequency f of the primary switching circuit;

[0012] Figure 3 A schematic diagram of the circuit structure of a secondary switch circuit Q2 according to an embodiment of the present invention is shown;

[0013] Figure 4 is a schematic diagram of a circuit structure of a switching power supply circuit 400 according to an embodiment of the present invention;

[0014] Figure 5 is a schematic diagram of a circuit structure of a switching power supply circuit 500 according to an embodiment of the present invention;

[0015] Figure 6 is a circuit structure diagram of a frequency determination circuit 111 according to an embodiment of the present invention;

[0016] Figure 7 The circuit structure diagram of the peak selection circuit 112 according to the embodiment of the present invention is schematically shown;

[0017] Figure 8 Schematically shows a circuit structure diagram of a peak selection circuit 112 according to another embodiment of the present invention;

[0018] Fig. 9 Schematically shows an embodiment of the present invention Figure 7 and Figure 8 A schematic diagram of the circuit structure of the first frequency / peak generator 31;

[0019] Fig.10 Schematically shows an embodiment of the present invention Figure 7 and Figure 8 A schematic diagram of the circuit structure of the second frequency / peak generator 32;

[0020] Fig.11 A method flow chart 1100 for a switching power supply circuit according to an embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0021] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not have to be used to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, materials or methods are not specifically described.

[0022] Throughout the specification, reference to "one embodiment", "embodiment", "one example" or "example" means that a particular feature, structure or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment", "in an embodiment", "one example" or "example" that appear in various places throughout the specification do not necessarily refer to the same embodiment or example. In addition, specific features, structures or characteristics can be combined in one or more embodiments or examples in any appropriate combination and / or sub-combination. In addition, it should be understood by those of ordinary skill in the art that the drawings provided herein are for illustrative purposes, and the drawings are not necessarily drawn to scale. It should be understood that when an element is said to be "coupled to" or "connected to" another element, it can be directly coupled or coupled to another element or there can be an intermediate element. On the contrary, when an element is said to be "directly coupled to" or "directly connected to" another element, there is no intermediate element. The same reference numerals indicate the same element. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0023] Figure 1 FIG. 1 is a schematic diagram showing a circuit structure of a switching power supply circuit 100 according to an embodiment of the present invention. Figure 1 In the illustrated embodiment, the switching power supply circuit 100 includes: a primary switch circuit Q1, coupled to the primary side T1 of the electrical isolation device T, the primary switch circuit Q1 is periodically turned on and off to transfer the input voltage Vin to the secondary side T2 of the electrical isolation device T; a secondary switch circuit Q2, coupled to the secondary side T2 of the electrical isolation device T, the secondary switch circuit Q2 is periodically turned on and off to provide the required output voltage Vo; a primary control circuit U1, generating a primary control signal G Q1 Control the primary switch circuit Q1, the primary control circuit U1 controls the peak value I of the primary current according to the frequency f at which the primary switch circuit Q1 is turned on P , where: When the frequency f is greater than the frequency threshold f1, the peak value I P It has a first form; when the frequency f is less than the frequency threshold f1, the peak value I P Has a second form.

[0024] In one embodiment of the present invention, the peak value I P The first form includes: Peak I P Fixed to the first value I P1 Or peak I P As the conduction frequency f of the primary switch circuit Q1 decreases (such as the peak value I P As the frequency f decreases, it decreases with a first slope, and when the frequency f drops to the frequency threshold f1, the peak value I P Having a first value IP1 Peak I P The second form includes: Peak I P It is positively correlated with the frequency f. The larger the frequency f, the higher the peak value I P The higher the peak value, the P As the frequency f decreases, it decreases with the second slope and has a valley limit, that is, when the peak value I P As the frequency f decreases to a second value I P2 When the frequency f decreases, it no longer decreases and is limited to the second value I P2 .

[0025] Peak I P The relationship with frequency f can be as follows Figure 2 As shown, the peak value I P Down to the second value I P2 The corresponding frequency f is not fixed.

[0026] In one embodiment of the present invention, the electrical isolation device T comprises a transformer, and the transformer comprises a primary winding and a secondary winding. In one embodiment, the electrical isolation device comprises a piezoelectric transformer.

[0027] In one embodiment of the present invention, the primary switch circuit Q1 includes a power metal oxide semiconductor field effect transistor MOSFET, and the power MOSFET has a body diode and a parasitic capacitor. In other embodiments, the primary switch circuit Q1 may also include other switch devices, such as BJT, IGBT, etc.

[0028] In one embodiment of the present invention, the secondary switch circuit Q2 includes: a power switch device (such as a power MOSFET), the power switch device having a body diode, such as Figure 3 As shown in the left figure (a); or the secondary side switch circuit Q2 includes two (or more) switch devices connected in parallel, such as Figure 3 As shown in the middle figure (b); or the secondary side switch circuit Q2 may also include a diode and a switch device connected in parallel, such as Figure 3 As shown in the right figure (c). In one embodiment, the secondary switch circuit Q2 is turned on, which means that all or part of the switch devices of the secondary switch circuit Q2 are turned on (such as only the diode or the body diode is turned on), and current flows through them; for example, after the primary switch circuit Q1 is turned off, when the secondary switch circuit Q2 performs the freewheeling action, part or all of the switch devices of the secondary switch circuit Q2 are turned on, and a current with a first current direction flows through them. The secondary switch circuit Q2 is turned off, which means that all the switch devices of the secondary switch circuit Q2 are turned off, and no current flows through them.

[0029] In one embodiment of the present invention, when the primary switch circuit Q1 is disconnected or when current is detected flowing through the secondary switch circuit Q2, the secondary switch circuit Q2 performs freewheeling until the freewheeling ends (i.e., the current flowing through it is zero or close to zero); before the primary switch circuit Q1 is turned on in the next switching cycle, the secondary transmits a signal indicating that the primary switch is turned on to the primary control circuit U1, and the primary control circuit U1 detects the indication signal and generates a set signal Set to turn on the primary switch circuit Q1. As for what indication method the secondary side uses to guide the primary side to turn on, it is not the technical content to be discussed in the present invention, and for the sake of simplicity, it will not be discussed in detail here.

[0030] Figure 4 FIG. 4 is a schematic diagram of a circuit structure of a switching power supply circuit 400 according to an embodiment of the present invention. Figure 4 The embodiment shown is a schematic diagram of the circuit structure of the primary side control circuit U1 according to an embodiment of the present invention. Figure 4 In the embodiment shown, the primary control circuit U1 includes: a peak setting circuit 11, which generates a reference peak value I according to a set signal Set for controlling the primary switch circuit Q1 to be turned on. RP , where: When the frequency f of the set signal Set is greater than the frequency threshold f1, the reference peak value I RP It has a first form; when the frequency f is less than the frequency threshold f1, the reference peak value I RP Having a second form; a peak current comparison circuit 12, comparing the current sampling signal I representing the primary current (such as flowing through the primary switching circuit Q1) CS With reference peak I RP , generating a reset signal Res to control the disconnection of the primary switch circuit Q1.

[0031] In one embodiment of the present invention, the reference peak value I RP The first form includes: reference peak I RP Fixed to the first reference value I RP1 Or refer to the peak value I RP As the frequency f decreases, it decreases (such as the reference peak I RP As the frequency f decreases, it decreases with a first slope, and when the frequency f drops to the frequency threshold f1, the reference peak value I RP With a first reference value I RP1 . Reference peak I RP The second form includes: reference peak I RP It is positively correlated with the frequency f. The larger the frequency f, the higher the reference peak value I RP The higher the reference peak value I RP As the frequency f decreases, it decreases with the second slope and has a valley limit, that is, when the reference peak value I RP As the frequency f decreases to the second reference value IRP2 When the reference peak value I RP It no longer decreases with the decrease of frequency f and is limited to the second reference value I RP2 The reference peak value I RP The first reference value I RP1 Corresponding to the first value I P1 , reference peak I RP The second reference value I RP2 Corresponding to the second value I P2 , such as the first reference value I RP1 With the first value I P1 Proportional to the second reference value I RP2 With the second value I P2 Directly proportional.

[0032] In one embodiment of the present invention, the primary control circuit U1 further includes: a primary logic circuit (such as an RS trigger) 13, which is set based on the set signal Set to turn on the primary switch circuit Q1, and based on the current sampling signal I CS With reference peak I RP The comparison result is reset to turn off the primary switch circuit Q1.

[0033] Figure 5 FIG. 5 is a schematic diagram of a circuit structure of a switching power supply circuit 500 according to an embodiment of the present invention. Figure 5 The embodiment shown is a schematic diagram of the circuit structure of a peak value setting circuit 11 according to an embodiment of the present invention. Figure 5 In the illustrated embodiment, the peak setting circuit 11 includes: a frequency determination circuit 111, which determines the conduction frequency of the primary switch circuit Q1 (e.g., determines the frequency according to the set signal Set); a peak selection circuit 112, which selects a corresponding reference peak value I according to the conduction frequency of the primary switch circuit Q1. RP :When the conduction frequency of the primary switch circuit Q1 is greater than the frequency threshold f1, the reference peak value I RP Having a first form (fixed to a first reference value I RP1 or decreases with the first slope as the frequency f decreases); when the conduction frequency of the primary switch circuit Q1 is less than the frequency threshold f1, the reference peak value I RP The second form (as the frequency f decreases, it decreases with the second slope until it drops to the second reference value I RP2 ).

[0034] Figure 6 The circuit structure diagram of the frequency determination circuit 111 according to an embodiment of the present invention is schematically shown. Figure 6In the illustrated embodiment, the frequency determination circuit 111 includes: a monostable circuit 21, in response to a set signal Set, generating a high level duration of a predetermined time T ON1 The logic unit 22, in response to the set signal Set (such as in response to the rising edge of the set signal Set), transmits the intermediate signal M1 to its first output terminal Q to provide a high-frequency signal f H The intermediate signal M1 is inverted and transmitted to its second output terminal / Q to provide a low frequency signal f L ; The scheduled duration is T ON1 is the time period corresponding to the frequency threshold f1, that is, T ON1 =1 / f1.

[0035] In one embodiment of the present invention, the logic unit 22 is a D flip-flop.

[0036] When the frequency of the setting signal Set is greater than the frequency threshold f1, the interval between two adjacent rising edges of the setting signal Set is shorter than the predetermined time length T1. At this time, the intermediate signal M1 remains at a high level. Accordingly, the signal at the first output terminal Q of the logic unit 22 (i.e., the high frequency signal f H ) also remains at a high level, and the signal at the second output terminal / Q (i.e., the low-frequency signal f L ) is low level. On the contrary, when the frequency of the setting signal Set is less than the frequency threshold f1, the interval between two adjacent rising edges of the setting signal Set is longer than the predetermined time length T1. At this time, the intermediate signal M1 has already jumped to a low level before the next rising edge of the setting signal Set. Accordingly, the signal at the first output terminal Q of the logic unit 22 (i.e., the high frequency signal f H ) is also at a low level, and the signal at the second output terminal / Q (i.e., the low-frequency signal f L ) is high level.

[0037] That is, when the frequency of the set signal Set is greater than the frequency threshold f1, the high frequency signal f H is a high level, low frequency signal f L is low level; and when the frequency of the set signal Set is less than the frequency threshold f1, the low frequency signal f L is a high level, high frequency signal f H The peak selection circuit 112 then selects the corresponding reference peak value according to the states of the signals output by the frequency determination circuit 111.

[0038] Figure 7 The circuit structure diagram of the peak selection circuit 112 according to an embodiment of the present invention is schematically shown. Figure 7 In the embodiment shown, the peak selection circuit 112 includes: a first selection switch S1, which receives the high frequency signal f HControl on and off, when the high frequency signal f H When the first selection switch S1 is turned on, the reference peak value I RP is coupled to the first reference value I RP1 Or coupled to the output of the first frequency / peak generator 31, wherein the first frequency / peak generator 31 generates a first reference signal I linearly changing with a first slope as the frequency f changes according to the frequency f of the set signal Set. RPS1 The second selection switch S2 is affected by the low frequency signal f L Control on and off, when the low frequency signal f L When the second selection switch S2 is turned on, the reference peak value I RP is coupled to the second frequency / peak generator 32, and the second frequency / peak generator 32 generates a second reference signal I linearly changing with a second slope according to the frequency f of the set signal Set. RPS2 , wherein the second frequency / peak generator 32 has a valley limit, that is, when the second reference signal I RPS2 As the frequency decreases, it decreases to the second reference value I RP2 When the second reference signal I RPS2 It no longer decreases with the decrease of frequency f and is limited to the second reference value I RP2 .

[0039] In one embodiment of the present invention, the second frequency-peak generator 32 also has a peak limit. RPS2 As the frequency f increases, it increases to the first reference value I RP1 When the second reference signal I RPS2 It no longer increases with the increase of frequency f and is limited to the first reference value I RP1 .

[0040] From the Figure 6 and Figure 7 As can be seen from the discussion, due to the high frequency signal f H and low frequency signal f L The states of each other are opposite, so the first selection switch S1 and the second selection switch S2 are complementary. Therefore, a high frequency signal f H and low frequency signal f L One of them controls the first selection switch S1 and the second selection switch S2 as follows Figure 8 The circuit structure diagram of the peak selection circuit 112 is shown in FIG. Figure 8 In the embodiment shown, the first selection switch S1 and the second selection switch S2 are both powered by the high frequency signal f HThe first selection switch S1 is turned on at a high level, and the second selection switch S2 is turned on at a low level. Those skilled in the art should be aware that there are a variety of logic circuits in the prior art that can implement the above functions, so that the reference peak value I RP When the frequency f of the set signal Set is greater than the frequency threshold f1, it is coupled to the first reference value I RP1 Or the output of the first frequency / peak generator 31, and is coupled to the output of the second frequency / peak generator 32 when the frequency f of the set signal Set is less than the frequency threshold f1. For the sake of simplicity, it will not be described in detail here.

[0041] In addition, those skilled in the art should realize that the frequency determination circuit 111 and the peak selection circuit 112 may also adopt other circuit structures, such as using a digital technology method, using a high-frequency pulse to count the primary switching frequency, using digital count value comparison to achieve frequency determination to select the corresponding reference peak, and so on.

[0042] Fig. 9 Schematically shows an embodiment of the present invention Figure 7 and Figure 8 FIG. 1 is a schematic diagram of the circuit structure of the first frequency / peak generator 31. Fig. 9 In the illustrated embodiment, the first frequency / peak generator 31 comprises: a first monostable unit 311, which generates a pulse signal P in response to a set signal Set. S ; Low-pass filter unit 312, the pulse signal P S Perform low-pass filtering to obtain the first reference signal I RPS1 .

[0043] Assume that the pulse signal P S The high level duration is set to T ON2 , the pulse amplitude is V S , then the first reference signal I RPS1 The relationship between the frequency f of the set signal Set is:

[0044] I RPS1 =V S *T ON2 *f

[0045] Therefore, the first reference signal I RPS1 It is proportional to the frequency f of the set signal Set.

[0046] Fig.10 Schematically shows an embodiment of the present invention Figure 7 and Figure 8 FIG. 4 is a schematic diagram of the circuit structure of the second frequency / peak generator 32. Fig.10 The second frequency / peak generator 32 is shown with Fig. 9 The first frequency / peak generator 31 is similar to the one shown, and includes a monostable unit (321) and a low-pass filter unit (322). Fig. 9 The first frequency / peak generator 31 shown is different in that Fig.10 In the embodiment shown, the second frequency / peak generator 32 further includes: a clamping unit 323 for clamping the second reference signal I RPS2 Perform peak clamping and valley clamping.

[0047] In one embodiment of the present invention, at the frequency threshold f1, the first form of the peak has a first value, and the second form has a second value. At this time, an offset can be added to the first form or the second form at the frequency threshold f1 for processing. How to perform the offset processing is a technique well known to those skilled in the art, and for the sake of simplicity, it will not be discussed in detail here.

[0048] Fig.11 A method flow chart 1100 for a switching power supply circuit according to an embodiment of the present invention is schematically shown. The switching power supply circuit comprises: an electrical isolation device having a primary side and a secondary side, a primary side switching circuit coupled to the primary side of the electrical isolation device, and a secondary side switching circuit coupled to the secondary side of the electrical isolation device, and the method comprises:

[0049] Step 1101, receiving an input voltage at the primary side, and generating an output voltage at the secondary side by controlling the on and off of the primary side switch circuit and the secondary side switch circuit.

[0050] Step 1102, receiving an indication signal transmitted from the secondary side to instruct the primary side switch circuit to be turned on, and controlling the primary side switch circuit to be turned on.

[0051] Step 1103, controlling the peak value of the primary current according to the frequency at which the primary switching circuit is turned on, wherein when the frequency is greater than a frequency threshold, the peak value has a first form; and when the frequency is less than the frequency threshold, the peak value has a second form.

[0052] Step 1104: when the primary current reaches a peak value, the primary switch circuit is controlled to be disconnected.

[0053] In one embodiment of the present invention, the first form of the peak value includes: the peak value is fixed to a first value or the peak value decreases with a first slope as the primary switch circuit is turned on at a lower frequency, and when the frequency drops to a frequency threshold, the peak value has a first value. The second form of the peak value includes: the peak value decreases with a second slope as the primary switch circuit is turned on at a lower frequency, and has a valley limit (when the peak value decreases to a second value as the frequency decreases, it no longer continues to decrease as the frequency decreases, but is limited to the second value).

[0054] The aforementioned switching power supply circuit and method according to multiple embodiments of the present invention control the conduction of the primary switching circuit through the indication signal given by the secondary circuit, and generate a peak current signal for controlling the disconnection of the primary switching circuit based on the frequency information of the primary switching circuit, thereby realizing peak current mode control on the primary side. At the same time, at different switching frequencies, the peak current information can be flexibly set, realizing multi-mode control and improving conversion efficiency.

[0055] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the present invention can be embodied in a variety of forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A switching power supply circuit, comprising: A primary power switch coupled to the primary side of the electrical isolation device, wherein the primary power switch is periodically turned on and off to transfer the input voltage to the secondary side of the electrical isolation device; A secondary side switch circuit is coupled to the secondary side of the electrical isolation device, wherein the secondary side switch circuit is periodically turned on and off to provide a desired output voltage; A primary control circuit generates a primary control signal to control the primary switch circuit, wherein the primary control circuit controls the peak value of the primary current according to the frequency at which the primary switch circuit is turned on, wherein: when the frequency is greater than a frequency threshold, the peak value has a first form; when the frequency is less than the frequency threshold, the peak value has a second form; The first form of the peak value includes: the peak value is fixed to a first value or the peak value decreases as the conduction frequency of the primary switch circuit decreases; the second form of the peak value includes: the peak value is positively correlated with the frequency.

2. The switching power supply circuit according to claim 1, wherein: The first form of the peak value includes: the peak value is fixed to a first value or the peak value decreases with a first slope as the frequency decreases.

3. The switching power supply circuit according to claim 1, wherein: The second form of the peak value includes: the peak value decreases with a second slope as the frequency decreases, and has a valley value definition.

4. The switching power supply circuit according to claim 1, wherein the primary side control circuit comprises: The peak setting circuit generates a reference peak value according to a setting signal for controlling the conduction of the primary switch circuit, wherein: when the frequency of the setting signal is greater than a frequency threshold, the reference peak value has a first form; when the frequency is less than the frequency threshold, the reference peak value has a second form; The peak current comparison circuit compares the current sampling signal representing the primary current with the reference peak value and generates a reset signal to control the disconnection of the primary switch circuit.

5. The switching power supply circuit as claimed in claim 4, wherein the peak setting circuit comprises: A frequency determination circuit determines the conduction frequency of the primary switch circuit; The peak selection circuit selects a corresponding reference peak value according to the conduction frequency of the primary switch circuit: when the conduction frequency of the primary switch circuit is greater than the frequency threshold, the reference peak value has a first form; When the conduction frequency of the primary switch circuit is less than the frequency threshold, the reference peak value is in the second form.

6. A primary side control circuit for a switching power supply circuit, the switching power supply circuit having a primary side switch circuit coupled to a primary side and a secondary side switch circuit coupled to a secondary side, the primary side control circuit comprising: The peak setting circuit generates a reference peak value according to the frequency at which the primary switch circuit is turned on, wherein: when the frequency is greater than a frequency threshold, the reference peak value has a first form; when the frequency is less than the frequency threshold, the reference peak value has a second form; the first form of the reference peak value includes: the reference peak value is fixed to a first reference value or the reference peak value decreases as the frequency decreases; the second form of the reference peak value includes: the reference peak value is positively correlated with the frequency; The peak current comparison circuit compares the current sampling signal representing the primary current with the reference peak value and generates a reset signal to control the disconnection of the primary switch circuit.

7. The primary side control circuit according to claim 6, wherein the peak setting circuit comprises: A frequency determination circuit determines the conduction frequency of the primary switch circuit; The peak selection circuit selects a corresponding reference peak value according to the conduction frequency of the primary switch circuit: when the frequency at which the primary switch circuit is turned on is greater than a frequency threshold, the reference peak value has a first form; When the frequency at which the primary switch circuit is turned on is less than the frequency threshold, the reference peak value is in the second form.

8. The primary side control circuit according to claim 6, wherein: The first form of the reference peak value includes: the peak value is fixed to a first value or the peak value decreases with a first slope as the frequency decreases; The second form of the reference peak value includes: the peak value decreases with a second slope as the frequency decreases, and has a valley value definition.

9. A method for a switching power supply circuit, the switching power supply circuit comprising: An electrical isolation device having a primary side and a secondary side, a primary side switch circuit coupled to the primary side of the electrical isolation device, and a secondary side switch circuit coupled to the secondary side of the electrical isolation device, the method comprising: An input voltage is received at the primary side, and an output voltage is generated at the secondary side by controlling the on and off of the primary side switch circuit and the secondary side switch circuit; receiving an indication signal transmitted from the secondary side indicating that the primary side switch circuit is turned on, and controlling the primary side switch circuit to be turned on; According to the frequency at which the primary switching circuit is turned on, the peak value of the primary current is controlled, wherein when the frequency is greater than a frequency threshold, the peak value has a first form; when the frequency is less than the frequency threshold, the peak value has a second form; the first form of the peak value includes: the peak value is fixed to a first value or the peak value decreases as the conduction frequency of the primary switching circuit decreases; the second form of the peak value includes: the peak value is positively correlated with the frequency.

10. The method of claim 9, wherein: The first form of the peak value includes: the peak value is fixed to a first value or the peak value decreases with a first slope as the conduction frequency of the primary switch circuit decreases, and when the frequency decreases to a frequency threshold, the peak value has the first value; The second form of the peak value includes: the peak value decreases with a second slope as the conduction frequency of the primary switch circuit decreases, and has a valley value definition.

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