Quasi-resonant switching power supply and its dithering control circuit

Abstract

Provided are a quasi-resonant switching power supply and a frequency jitter control circuit thereof. The frequency jitter control circuit is configured to generate a quasi-resonant valley bottom detection signal based on a resonant voltage representation signal representing a resonant voltage on an auxiliary winding of a transformer in the quasi-resonant switching power supply; generate an upper clamping frequency control signal for controlling a maximum operating frequency of the quasi-resonant switching power supply based on an output feedback control signal related to an output voltage of the quasi-resonant switching power supply; generate a valley bottom insertion enable signal based on a pulse width modulation signal for controlling turn-on and turn-off of a switching tube in the quasi-resonant switching power supply; and generate a turn-on control signal for controlling the switching tube in the quasi-resonant switching power supply to change from a turn-off state to a turn-on state based on the quasi-resonant valley bottom detection signal, the upper clamping frequency control signal, and the valley bottom insertion enable signal. The switching tube in the quasi-resonant switching power supply changes from the turn-off state to the turn-on state at different times in different switching periods of the valley bottom insertion enable signal in active and inactive states.

Description

Technical Field

[0001] This invention relates to the field of circuits, and more specifically to a quasi-resonant switching power supply and its frequency dithering control circuit. Background Technology

[0002] Operating a switching power supply in quasi-resonant mode can reduce the drain voltage of the switching transistor when it transitions from off to on, decrease conduction losses, and reduce stress on the transistor, thereby improving system efficiency. However, in practical applications, under certain loads, the switching transistor may be switched from off to on when different numbers of resonant valleys are detected on the auxiliary winding of the transformer during consecutive switching cycles (this operating mode is called quasi-resonant jitter valley conduction mode). Under other loads, the switching transistor may be switched from off to on when a fixed number of resonant valleys are detected during consecutive switching cycles (this operating mode is called quasi-resonant single valley conduction mode). When the switching power supply operates in quasi-resonant single valley conduction mode, the system operating frequency remains constant. This results in an overly concentrated distribution of energy at a single frequency, generating significant high-order harmonic energy. This energy can be concentrated and released through printed circuit boards or wires, causing electromagnetic radiation damage to humans and severe electromagnetic interference to other electronic devices. Summary of the Invention

[0003] According to an embodiment of the present invention, a frequency dithering control circuit for a quasi-resonant switching power supply is configured to: generate a quasi-resonant valley detection signal based on a resonant voltage characterization signal characterizing the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping control signal for controlling the maximum operating frequency of the quasi-resonant switching power supply based on an output feedback control signal related to the output voltage of the quasi-resonant switching power supply; generate a valley-entry enable signal based on a pulse width modulation signal for controlling the on and off states of the switching transistors in the quasi-resonant switching power supply; and generate a turn-on control signal for controlling the switching transistors in the quasi-resonant switching power supply to change from an off state to an on state based on the quasi-resonant valley detection signal, the upper clamping control signal, and the valley-entry enable signal, wherein the time when the switching transistors in the quasi-resonant switching power supply change from an off state to an on state during a switching cycle in which the valley-entry enable signal is active is different from the time when they change from an off state to an on state during a switching cycle in which the valley-entry enable signal is inactive.

[0004] According to an embodiment of the present invention, a frequency dithering control circuit for a quasi-resonant switching power supply is configured to: generate a quasi-resonant valley detection signal based on a resonant voltage characterization signal characterizing the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping control signal for controlling the maximum operating frequency of the quasi-resonant switching power supply based on an output feedback control signal related to the output voltage of the quasi-resonant switching power supply; generate a valley-entry enable signal based on the quasi-resonant valley detection signal; and generate a turn-on control signal for controlling the switching transistor in the quasi-resonant switching power supply to change from an off state to a turn-on state based on the quasi-resonant valley detection signal, the upper clamping control signal, and the valley-entry enable signal, wherein the time when the switching transistor in the quasi-resonant switching power supply changes from an off state to a turn-on state during a switching cycle in which the valley-entry enable signal is in an active state is different from the time when it changes from an off state to a turn-on state during a switching cycle in which the valley-entry enable signal is in an inactive state. Attached Figure Description

[0005] The invention can be better understood from the following description of specific embodiments of the invention in conjunction with the accompanying drawings, wherein:

[0006] Figure 1 The circuit schematic of a traditional quasi-resonant switching power supply is shown.

[0007] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals when the quasi-resonant switching power supply operates in the quasi-resonant single valley conduction mode.

[0008] Figure 3 It shows Figure 1 The diagram shows the spectral energy distribution of a quasi-resonant switching power supply operating in a quasi-resonant single-valley conduction mode.

[0009] Figure 4 A circuit diagram of a frequency dithering control circuit for a quasi-resonant switching power supply according to an embodiment of the present invention is shown.

[0010] Figure 5 It shows Figure 4 The waveform diagram shown is an example of multiple signals when the frequency dithering control circuit uses a fixed multi-cycle counting method to implement the valley bottom frequency dithering control scheme.

[0011] Figure 6 It shows Figure 4 The waveform diagram shown is an example of multiple signals when the frequency dithering control circuit uses a pseudo-random multi-cycle counting method to implement the valley bottom frequency dithering control scheme.

[0012] Figure 7 A circuit diagram of a frequency dithering control circuit for a quasi-resonant switching power supply according to another embodiment of the present invention is shown.

[0013] Figure 8 It shows Figure 7 The waveform diagram shown is an example of multiple signals when the frequency dithering control circuit uses the adjacent fixed multi-cycle counting valley number comparison method to implement the valley dithering control scheme.

[0014] Figure 9 It shows Figure 7 The waveform diagram shown is an example of multiple signals when the frequency dithering control circuit uses the adjacent pseudo-random multi-cycle counting valley number comparison method to implement the valley dithering control scheme.

[0015] Figure 10 The spectrum distribution diagram is shown when the valley dithering scheme is implemented by using a fixed multi-cycle counting method or a method of comparing the valley numbers of adjacent fixed multi-cycle counting.

[0016] Figure 11 The spectrum distribution diagram is shown when the valley dithering scheme is implemented by using pseudo-random multi-cycle counting or the comparison of valley numbers of adjacent pseudo-random multi-cycle counting. Detailed Implementation

[0017] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. Numerous specific details are set forth in the following detailed description to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific configurations and algorithms presented below, but covers any modifications, substitutions, and improvements to elements, components, and algorithms without departing from the spirit of the invention. Well-known structures and techniques are not shown in the drawings and the following description in order to avoid unnecessarily obscuring the invention.

[0018] Figure 1 The circuit schematic of a traditional quasi-resonant switching power supply is shown. Figure 1In the quasi-resonant switching power supply 100 shown, when the switching transistor Q1 is in the on state, the input voltage Vin charges the primary winding of the transformer T1, and the primary winding of the transformer T1 stores energy; when the switching transistor Q1 is in the off state, the energy stored in the primary winding of the transformer T1 is transferred to the load through the secondary winding of the transformer T1. Furthermore, when the switch Q1 is in the off state, the auxiliary winding voltage Vaux on the auxiliary winding of the transformer T1 can characterize the resonant voltage on the primary winding of the transformer T1. The auxiliary winding voltage Vaux can generate the resonant voltage characterization voltage Vaux‵ through the voltage division of the upper bias resistor Rup and the lower bias resistor Rdw. By comparing the resonant voltage characterization voltage Vaux‵ with the threshold voltage Vref, the quasi-resonant valley detection signal Qr_on can be obtained. Based on the output feedback control signal FB_d related to the output voltage Vout of the quasi-resonant switching power supply 100, the upper clamp frequency control signal Qr_max can be generated to control the maximum operating frequency of the quasi-resonant switching power supply 100. Based on the upper clamp frequency control signal Qr_max and the quasi-resonant valley detection signal Qr_on, the conduction control signal Tri_on can be generated to control the switch Q1 from the off state to the conduction state. Based on the conduction control signal Tri_on, a pulse width modulation (PWM) signal can be generated to control the conduction and turn-off of the switch Q1, realizing the quasi-resonant valley conduction control of the switch Q1.

[0019] Figure 2 It shows Figure 1 The diagram shows the waveforms of multiple signals when the quasi-resonant switching power supply operates in the quasi-resonant single valley conduction mode, where N1 = N2 = N3 = N4, and the system operating frequency is fixed at f1 in this case. Figure 3 It shows Figure 1 The diagram shows the spectral energy distribution of a quasi-resonant switching power supply operating in a quasi-resonant single-valley conduction mode. It can be seen that, due to... Figure 1 The quasi-resonant switching power supply 100 shown maintains a fixed operating frequency, so the peak energy of the single switching frequency and its higher harmonics is very high, and the electromagnetic radiation energy of the system to the outside is very high at this time.

[0020] In view of the above, a quasi-resonant switching power supply and its frequency dithering control circuit according to an embodiment of the present invention are proposed. This can solve the problem that the quasi-resonant switching power supply operates in a quasi-resonant single valley conduction mode, the system operating frequency remains unchanged, and the external electromagnetic radiation is too large to meet the current electromagnetic compatibility standards for switching power supplies.

[0021] Figure 4 A circuit diagram of a frequency dithering control circuit for a quasi-resonant switching power supply according to an embodiment of the present invention is shown. Figure 4The frequency dithering control circuit 400 for the quasi-resonant switching power supply shown is configured to: generate a quasi-resonant valley detection signal Qr_on based on a resonant voltage characterization signal Vaux‵, which characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping control signal Qr_max, which controls the maximum operating frequency of the quasi-resonant switching power supply, based on an output feedback control signal FB_d, which is related to the output voltage of the quasi-resonant switching power supply; generate a valley insertion enable signal Valley_insert_ENA, which controls the switching transistors in the quasi-resonant switching power supply to turn on; and generate a turn-on control signal Tri_on, which controls the switching transistors in the quasi-resonant switching power supply to change from the off state to the on state, based on the quasi-resonant valley detection signal Qr_on, the upper clamping control signal Qr_max, and the valley insertion enable signal Valley_insert_ENA. Here, the moment when the switching transistor in the quasi-resonant switching power supply changes from the off state to the on state during the switching cycle when the valley enable signal Valley_insert_ENA is in an active state is different from the moment when it changes from the off state to the on state during the switching cycle when the valley enable signal Valley_insert_ENA is in an inactive state.

[0022] In some embodiments, during a switching cycle in which the valley-insert_ENA enable signal is inactive, when the upper-clamp frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply reaches the m-th resonant valley, the turn-on control signal Tri_on controls the switch in the quasi-resonant switching power supply to change from the off state to the on state. During a switching cycle in which the valley-insert_ENA enable signal is active, when the upper-clamp frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply reaches the (m+n)-th resonant valley, the turn-on control signal Tri_on controls the switch in the quasi-resonant switching power supply to change from the off state to the on state, where m and n are integers greater than or equal to 1.

[0023] In some embodiments, such as Figure 4 As shown, the resonant voltage characterization signal Vaux‵ is the resonant voltage characterization voltage generated by the voltage division of the auxiliary winding voltage Vaux on the auxiliary winding of the transformer in the quasi-resonant switching power supply through the upper bias resistor Rup and the lower bias resistor Rdw. The frequency dithering control circuit 400 for the quasi-resonant switching power supply is further configured to generate the quasi-resonant valley detection signal Qr_on by comparing the resonant voltage characterization voltage Vaux‵ with the threshold voltage Vref.

[0024] In some embodiments, such as Figure 4 As shown, the frequency dithering control circuit 400 for the quasi-resonant switching power supply is further configured to generate a valley insertion enable signal Valley_insert_ENA by counting the switching cycles of the PWM signal.

[0025] In some embodiments, such as Figure 4 As shown, the frequency dithering control circuit 400 for the quasi-resonant switching power supply is further configured to: generate a quasi-resonant valley turn-on signal Qr_on‵ based on the quasi-resonant valley detection signal Qr_on, the upper clamping frequency control signal Qr_max, and the valley insertion enable signal Valley_insert_ENA; and generate a turn-on control signal Tri_on based on the quasi-resonant valley turn-on signal Qr_on‵, wherein the turn-on control signal Tri_on is used to control the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state when the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply reaches a predetermined number of resonant valleys in the current switching cycle.

[0026] Figure 5 It shows Figure 4 The waveform diagram shown illustrates multiple signals when the frequency dithering control circuit employs a fixed multi-cycle counting method to implement the valley-level dithering control scheme. (Example waveform diagram follows.) Figure 4 and Figure 5 As shown, in some embodiments, whenever the count of the switching cycles of the PWM signal reaches N, the valley insertion enable signal Valley_insert_ENA is active in the (N+1)th switching cycle of the PWM signal, where N is a fixed integer greater than or equal to 1. In each switching cycle where the valley insertion enable signal Valley_insert_ENA is inactive, when the upper clamping frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply has reached the m-th resonant valley, the PWM signal changes from low to high, causing the switching transistor in the quasi-resonant switching power supply to change from off to on, where m is an integer greater than or equal to 1. During the switching cycle when the valley insertion enable signal Valley_insert_ENA is active, when the upper clamp frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply reaches the (m+1)th resonant valley, the PWM signal changes from low to high, causing the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state. By adopting a valley insertion frequency dithering control scheme with fixed multi-cycle counting, the system operating frequency of the quasi-resonant switching power supply changes periodically in the manner of f1->f2->f1->f2.

[0027] Figure 6 It shows Figure 4 The waveform diagram shown illustrates multiple signals when the frequency dithering control circuit employs a pseudo-random multi-cycle counting method to implement the valley-entry frequency dithering control scheme. (Example waveform diagram follows.) Figure 4 and Figure 6 As shown, in some embodiments, when the count of the switching cycles of the PWM signal reaches N1, the valley insertion enable signal Valley_insert_ENA is active in the (N1+1)th switching cycle of the PWM signal. Furthermore, after the (N1+1)th switching cycle of the PWM signal ends, when the count of the switching cycles of the PWM signal re-reaches N2, the valley insertion enable signal Valley_insert_ENA is active in the (N2+1)th switching cycle of the PWM signal. N1 and N2 are both integers greater than or equal to 1, and N1 ≠ N2. Here, N1 and N2 can be random numbers generated by a pseudo-random timing generator within the multi-cycle counting valley insertion enable control unit. In each switching cycle when the valley insertion enable signal Valley_insert_ENA is inactive, when the upper clamp frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply reaches the m-th resonant valley, the PWM signal changes from low to high, causing the switching transistor in the quasi-resonant switching power supply to change from off to on, where m is an integer greater than or equal to 1. In a switching cycle when the valley insertion enable signal Valley_insert_ENA is active, when the upper clamp frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply reaches the (m+1)-th resonant valley, the PWM signal changes from low to high, causing the switching transistor in the quasi-resonant switching power supply to change from off to on. By adopting a pseudo-random multi-cycle counting valley dithering control scheme, the system operating frequency of the quasi-resonant switching power supply changes randomly without a fixed period in the manner of f3->f4->f3->f4.

[0028] Figure 7 A circuit diagram of a frequency dithering control circuit for a quasi-resonant switching power supply according to another embodiment of the present invention is shown. Figure 7The frequency dithering control circuit 700 for the quasi-resonant switching power supply shown is configured to: generate a quasi-resonant valley detection signal Qr_on based on a resonant voltage characterization signal Vaux‵, which characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping control signal Qr_max, which controls the maximum operating frequency of the quasi-resonant switching power supply, based on an output feedback control signal FB_d, which is related to the output voltage of the quasi-resonant switching power supply; generate a valley insertion enable signal Valley_insert_ENA1, based on the quasi-resonant valley detection signal Qr_on; and generate a turn-on control signal Tri_on, which controls the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state, based on the quasi-resonant valley detection signal Qr_on, the upper clamping control signal Qr_max, and the valley insertion enable signal Valley_insert_ENA1. Here, the moment when the switching transistor in the quasi-resonant switching power supply changes from the off state to the on state during the switching cycle when the valley enable signal Valley_insert_ENA1 is in an active state is different from the moment when it changes from the off state to the on state during the switching cycle when the valley enable signal Valley_insert_ENA1 is in an inactive state.

[0029] In some embodiments, during a switching cycle in which the valley-insert_ENA1 enable signal is inactive, when the upper clamping frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply has reached the m-th resonant valley, the turn-on control signal Tri_on controls the switch in the quasi-resonant switching power supply to change from the off state to the on state. During a switching cycle in which the valley-insert_ENA1 enable signal is active, when the upper clamping frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply has reached the (m+n)-th resonant valley, the turn-on control signal Tri_on controls the switch in the quasi-resonant switching power supply to change from the off state to the on state, where m and n are integers greater than or equal to 1.

[0030] In some embodiments, such as Figure 7 As shown, the resonant voltage characterization signal Vaux‵ is the resonant voltage characterization voltage generated by the voltage division of the auxiliary winding voltage Vaux on the auxiliary winding of the transformer in the quasi-resonant switching power supply through the upper bias resistor Rup and the lower bias resistor Rdw. The frequency dithering control circuit 700 for the quasi-resonant switching power supply is further configured to generate the quasi-resonant valley detection signal Qr_on by comparing the resonant voltage characterization voltage Vaux‵ with the threshold voltage Vref.

[0031] In some embodiments, such as Figure 7 As shown, the frequency dithering control circuit 700 for the quasi-resonant switching power supply is further configured to generate a valley insertion enable signal Valley_insert_ENA1 by counting and comparing the number of resonant valleys in each switching cycle of the auxiliary winding of the transformer in the quasi-resonant switching power supply, as indicated by the quasi-resonant valley detection signal Qr_on.

[0032] In some embodiments, such as Figure 7 As shown, the frequency dithering control circuit 700 for the quasi-resonant switching power supply is further configured to: generate a quasi-resonant valley turn-on signal Qr_on‵ based on the quasi-resonant valley detection signal Qr_on, the upper clamping frequency control signal Qr_max, and the valley insertion enable signal Valley_insert_ENA1; and generate a turn-on control signal Tri_on based on the quasi-resonant valley turn-on signal Qr_on‵, wherein the turn-on control signal Tri_on is used to control the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state when the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply reaches a predetermined number of resonant valleys in the current switching cycle.

[0033] Figure 8 It shows Figure 7 The waveform diagram shown illustrates multiple signals in a valley-interpolation frequency dithering control scheme achieved by comparing the number of valleys in adjacent fixed multi-cycle counting. Figure 7 and Figure 8As shown, in some embodiments, whenever the number of resonant valleys on the auxiliary winding of the transformer in the quasi-resonant switching power supply, as indicated by the quasi-resonant valley detection signal Qr_on, is equal in each of the T adjacent switching cycles, the valley insertion enable signal Valley_insert_ENA1 is active in the next switching cycle immediately following those T switching cycles, where T is a fixed integer greater than or equal to 1. In other words, based on the quasi-resonant valley detection signal Qr_on, the number of resonant valleys of the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply in each of the T adjacent switching cycles is counted and compared. If the number of resonant valleys of the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply in each of the T adjacent switching cycles is equal (e.g., X1 = X2 or X3 = X4), then the valley insertion enable signal Valley_insert_ENA1 is in a valid state in the next switching cycle immediately following the T switching cycles; otherwise (e.g., X1 ≠ X2 or X3 ≠ X4), the valley insertion enable signal Valley_insert_ENA1 is in an invalid state in the next switching cycle immediately following the T switching cycles. In each switching cycle when the valley-insert_ENA1 enable signal is inactive, when the clamping frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply has reached the m-th resonant valley, the PWM signal changes from low to high, causing the switching transistor in the quasi-resonant switching power supply to change from off to on, where m is an integer greater than or equal to 1. In a switching cycle when the valley-insert_ENA1 enable signal is active, when the clamping frequency control signal Qr_max is active and the quasi-resonant valley detection signal Qr_on indicates that the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply has reached the (m+1)-th resonant valley, the PWM signal changes from low to high, causing the switching transistor in the quasi-resonant switching power supply to change from off to on. It is important to note that after the current switching cycle in which the valley insertion enable signal Valley_insert_ENA1 is in an active state ends and before the start of the next switching cycle, the valley insertion enable signal Valley_insert_ENA1 needs to be reset to an inactive state. By employing a valley insertion frequency dithering control scheme that compares the number of valleys counted over adjacent fixed multi-cycle periods, the system operating frequency of the quasi-resonant switching power supply changes periodically in the pattern f5->f6->f5->f6.

[0034] Figure 9 It shows Figure 7The waveform diagram shown illustrates multiple signals when the frequency dithering control circuit employs an adjacent pseudo-random multi-cycle counting valley number comparison method to implement the valley dithering control scheme. (See example waveform diagram.) Figure 7 and Figure 9 As shown, in some embodiments, when the number of resonant valleys on the auxiliary winding of the transformer in the quasi-resonant switching power supply, indicated by the quasi-resonant valley detection signal Qr_on, is unequal in each of the adjacent T1 switching cycles, the valley insertion enable signal Valley_insert_ENA1 is in an invalid state in the next switching cycle immediately following the T1 switching cycles. Conversely, after the next switching cycle immediately following the T1 switching cycles, when the number of resonant valleys on the auxiliary winding of the transformer in the quasi-resonant switching power supply, indicated by the quasi-resonant valley detection signal Qr_on, is equal in each of the adjacent T2 switching cycles, the valley insertion enable signal Valley_insert_ENA1 is in an active state in the next switching cycle immediately following the T2 switching cycles. T1 and T2 are both integers greater than or equal to 1, and T1 ≠ T2. Here, T1 and T2 can be random numbers generated by a pseudo-random timing generator. In other words, the number of resonant valleys Y1 and Y2 of the resonant voltage on the auxiliary winding of the transformer in the aligning resonant switching power supply in each of the adjacent T1 switching cycles are compared. If Y1 = Y2, the valley insertion enable signal Valley_insert_ENA1 is active in the next switching cycle immediately following the T1 switching cycle; otherwise, it is inactive. Next, the number of resonant valleys Y3, Y4, and Y5 of the resonant voltage on the auxiliary winding of the transformer in the aligning resonant switching power supply in each of the adjacent T2 switching cycles are compared. If Y3 = Y4 = Y5, the valley insertion enable signal Valley_insert_ENA1 is active in the next switching cycle immediately following the T2 switching cycle; otherwise, it is inactive. By employing the valley dithering frequency control scheme described above, which uses adjacent pseudo-random multi-cycle counting valley number comparison, the system operating frequency of the switching power supply changes without a fixed period in the manner of f7->f8->f7->f8 (because T1 and T2 are random numbers).

[0035] By using the frequency dithering control circuit for a quasi-resonant switching power supply according to an embodiment of the present invention, the quasi-resonant switching power supply can operate in a quasi-resonant dithering valley conduction mode under a fixed load, thereby causing the system operating frequency of the quasi-resonant switching power supply to change regularly or randomly over multiple consecutive switching cycles. Through the above-described valley dithering control scheme, the energy distribution of the quasi-resonant switching power supply is not concentrated on a single frequency, but rather dispersed across multiple fundamental frequencies.

[0036] Figure 10 The spectrum distribution diagram is shown when the valley dithering scheme is implemented by using a fixed multi-cycle counting method or a method of comparing the valley numbers of adjacent fixed multi-cycle counting. Figure 11 The spectral distribution diagram is shown when the valley dithering scheme is implemented using either a pseudo-random multi-cycle counting method or an adjacent pseudo-random multi-cycle counting valley number comparison method. It can be seen that through the above valley dithering control scheme, the energy of the quasi-resonant switching power supply can be distributed across multiple fundamental frequencies and possess more high-frequency harmonic components. This significantly reduces the energy radiated by the quasi-resonant switching power supply, ultimately meeting the electromagnetic compatibility requirements of the switching power supply.

[0037] It should be noted that the frequency dithering control circuit for quasi-resonant switching power supplies according to embodiments of the present invention can be applied to switching power supplies with topologies such as buck, boost, buck-boost, flyback, forward, and asymmetric half-bridge.

[0038] This invention can be implemented in other specific forms without departing from its spirit and essential characteristics. For example, the algorithm described in a particular embodiment can be modified without departing from the basic spirit of the invention. Therefore, the present embodiments are to be regarded as exemplary rather than limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and all changes falling within the meaning and scope of the claims and their equivalents are thus included within the scope of the invention.

Claims

1. A frequency dithering control circuit for a quasi-resonant switching power supply, configured as follows: Based on the resonant voltage characterization signal, which characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply, a quasi-resonant valley detection signal is generated. Based on the output feedback control signal related to the output voltage of the quasi-resonant switching power supply, an upper clamping control signal is generated to control the maximum operating frequency of the quasi-resonant switching power supply. A valley-filling enable signal is generated by counting the switching cycles of the pulse width modulation signal used to control the on and off states of the switching transistors in the quasi-resonant switching power supply. as well as Based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the valley insertion enable signal, a turn-on control signal is generated to control the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state, wherein... The timing at which the switching transistor in the quasi-resonant switching power supply changes from the off state to the on state during the switching cycle when the valley enable signal is active is different from the timing at which it changes from the off state to the on state during the switching cycle when the valley enable signal is inactive.

2. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 1, wherein, Whenever the count of the switching cycles of the pulse width modulation signal reaches N, the valley bottom enable signal is in an active state in the (N+1)th switching cycle of the pulse width modulation signal, where N is a fixed integer greater than or equal to 1.

3. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 1, wherein, When the count of the switching cycles of the pulse width modulation signal reaches N1, the valley enable signal is active in the (N1+1)th switching cycle of the pulse width modulation signal, and After the (N1+1)th switching cycle of the pulse width modulation signal ends, when the count of the switching cycles of the pulse width modulation signal reaches N2, the valley bottom enable signal is in an active state during the (N2+1)th switching cycle of the pulse width modulation signal, where N1 and N2 are both integers greater than or equal to 1 and N1≠N2.

4. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 3, wherein, N1 and N2 are random numbers generated by a pseudo-random timer generator.

5. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 1, further configured as follows: Based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the valley insertion enable signal, a quasi-resonant valley conduction signal is generated; and Based on the quasi-resonant valley bottom conduction signal, the conduction control signal is generated, wherein... The conduction control signal is used to control the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state when the resonant voltage on the auxiliary winding of the transformer reaches a predetermined number of resonant valleys in the current switching cycle.

6. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 1, wherein, During a switching cycle in which the valley enable signal is inactive, when the upper clamp frequency control signal is active and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer has reached the m-th resonant valley, the conduction control signal controls the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state. During the switching cycle in which the valley enable signal is active, when the upper clamp frequency control signal is active and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer has reached the (m+n)th resonant valley, the conduction control signal controls the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state, where m and n are both integers greater than or equal to 1.

7. A frequency dithering control circuit for a quasi-resonant switching power supply, configured as follows: Based on the resonant voltage characterization signal, which characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply, a quasi-resonant valley detection signal is generated. Based on the output feedback control signal related to the output voltage of the quasi-resonant switching power supply, an upper clamping control signal is generated to control the maximum operating frequency of the quasi-resonant switching power supply. A valley insertion enable signal is generated by counting and comparing the number of resonant valleys on the auxiliary winding of the transformer, as indicated by the quasi-resonant valley detection signal, in each of several adjacent switching cycles. as well as Based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the valley insertion enable signal, a turn-on control signal is generated to control the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state, wherein... The timing at which the switching transistor in the quasi-resonant switching power supply changes from the off state to the on state during the switching cycle when the valley enable signal is active is different from the timing at which it changes from the off state to the on state during the switching cycle when the valley enable signal is inactive.

8. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 7, wherein, Whenever the number of resonant valleys on the auxiliary winding of the transformer, as indicated by the quasi-resonant valley detection signal, is equal in each of the T adjacent switching cycles, the valley enable signal is active in the next switching cycle immediately following the T switching cycles, where T is a fixed integer greater than or equal to 1.

9. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 7, wherein, When the number of resonant valleys on the auxiliary winding of the transformer, as indicated by the quasi-resonant valley detection signal, is equal in each of the adjacent T1 switching cycles, the valley insertion enable signal is active in the next switching cycle immediately following the T1 switching cycles. After the next switching cycle immediately following the T1 switching cycles, when the number of resonant valleys on the auxiliary winding of the transformer, as indicated by the quasi-resonant valley detection signal, is equal in each of the adjacent T2 switching cycles, the valley insertion enable signal is active in the next switching cycle immediately following the T2 switching cycles, where T1 and T2 are both integers greater than or equal to 1 and T1 ≠ T2.

10. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 9, wherein, T1 and T2 are random numbers generated by a pseudo-random timer generator.

11. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 7, further configured as follows: Based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the valley insertion enable signal, a quasi-resonant valley conduction signal is generated; and Based on the quasi-resonant valley bottom conduction signal, the conduction control signal is generated, wherein... The conduction control signal is used to control the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state when the resonant voltage on the auxiliary winding of the transformer reaches a predetermined number of resonant valleys in the current switching cycle.

12. The frequency dithering control circuit for a quasi-resonant switching power supply according to claim 7, wherein, During a switching cycle in which the valley enable signal is inactive, when the upper clamp frequency control signal is active and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer has reached the m-th resonant valley, the conduction control signal controls the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state. During the switching cycle in which the valley enable signal is active, when the upper clamp frequency control signal is active and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer has reached the (m+n)th resonant valley, the conduction control signal controls the switching transistor in the quasi-resonant switching power supply to change from the off state to the on state, where m and n are both integers greater than or equal to 1.

13. A quasi-resonant switching power supply, comprising the frequency dithering control circuit for a quasi-resonant switching power supply as described in any one of claims 1 to 12.

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