TWI840241B - Quasi-resonant switching power supply and its frequency-jittering control circuit - Google Patents

Abstract

A quasi-resonant switching power supply and a frequency-jittering control circuit thereof are provided. The frequency-jittering control circuit is configured to: generate a quasi-resonant valley detection signal based on a resonant voltage characteristic signal that characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping frequency 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; A control signal is generated; based on a pulse width modulation signal used to control the on and off of a transistor in a quasi-resonant switching power supply, an insertion valley enable signal is generated; based on a quasi-resonant valley detection signal, an upper clamping frequency control signal, and an insertion valley enable signal, an on control signal is generated for controlling the transistor in the quasi-resonant switching power supply to change from an off state to an on state. The transistor in the quasi-resonant switching power supply changes from an off state to an on state at different times in different switching cycles when the insertion valley enable signal is in a valid state and an invalid state.

Description

Quasi-resonant switching power supply and its frequency jitter control circuit

The present invention relates to the field of circuits, and more specifically to a quasi-resonant switching power supply and a frequency-jittering control circuit thereof.

When the switching power supply operates in quasi-resonant mode, the drain voltage of the transistor can be reduced when it changes from the off state to the on state, the conduction loss of the transistor can be reduced, and the stress of the transistor can be reduced, thereby improving the system efficiency. However, in actual applications of switching power supplies, under some loads, when different numbers of resonant valleys of the resonant voltage on the auxiliary winding of the transformer are detected in continuous switching cycles, the control transistor may change from the off state to the on state (the operating mode of the switching power supply in this case is called quasi-resonant jitter valley conduction mode), but under other loads, when a fixed number of resonant valleys of the resonant voltage are detected in continuous switching cycles, the control transistor may change from the off state to the on state (the operating mode of the switching power supply in this case is called quasi-resonant single valley conduction mode). When the switching power supply operates in the quasi-resonant single valley conduction mode, the system operating frequency remains fixed, which causes the distribution of the single frequency working energy of the switching power supply to be too concentrated, and the generated high-order harmonic energy is relatively large, which will discharge a large amount of electromagnetic radiation through the printed circuit board or wires, causing certain electromagnetic radiation damage to the human body and causing serious electromagnetic interference to other electronic equipment.

According to the embodiment of the present invention, the frequency jitter control circuit for the quasi-resonant switching power supply is configured to: generate a quasi-resonant valley detection signal based on a resonant voltage characteristic signal representing the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping frequency 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 pulse width modulation signal for controlling the conduction and shutdown of the transistor in the quasi-resonant switching power supply based on a pulse width modulation signal for controlling the conduction and shutdown of the transistor in the quasi-resonant switching power supply; , generating an insertion valley enable signal; and based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the insertion valley enable signal, generating a conduction control signal for controlling the transistor in the quasi-resonant switching power supply to change from the off state to the on state, wherein the moment when the transistor in the quasi-resonant switching power supply changes from the off state to the on state in the switching cycle in which the insertion valley enable signal is in the effective state is different from the moment when the transistor changes from the off state to the on state in the switching cycle in which the insertion valley enable signal is in the ineffective state.

The frequency jitter control circuit for a quasi-resonant switching power supply according to an embodiment of the present invention is configured to: generate a quasi-resonant valley detection signal based on a resonant voltage characteristic signal that characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping frequency 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 enable signal based on the quasi-resonant valley detection signal ; and based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the insertion valley enable signal, generate a conduction control signal for controlling the transistor in the quasi-resonant switching power supply to change from the off state to the on state, wherein the moment when the transistor in the quasi-resonant switching power supply changes from the off state to the on state in the switching cycle when the insertion valley enable signal is in the effective state is different from the moment when the transistor changes from the off state to the on state in the switching cycle when the insertion valley enable signal is in the ineffective state.

100: Quasi-resonant switching power supply

400,700: Frequency jitter control circuit for quasi-resonant switching power supply

DC: reference voltage

f1,f2,f3,f4,f5,f6,f7,f8: system operating frequency

FB_d: Output feedback control signal

PWM: Pulse Width Modulation

Q1: Transistor

Qr_max: upper clamping frequency control signal

Qr_on: Quasi-resonant valley detection signal

Qr_on`: Quasi-harmonic valley bottom guidance signal

Rdw: Downward bias resistance

Rup: Upward bias resistor

T1: Transformer

Tri_on: conduction control signal

Valley_insert_ENA, Valley_insert_ENA1: insert valley bottom enable signal

Vaux: Auxiliary winding induced voltage

Vaux`: resonant voltage characteristic voltage

Vin: Input voltage

Vout: output voltage

Vref: Threshold voltage

X1,X2,X3,X4,Y1,Y2,Y3,Y4,Y5: The number of resonance valleys in each switching cycle

The present invention can be better understood from the following description of the specific implementation of the present invention in conjunction with the drawings, wherein:

Figure 1 shows the circuit schematic of a traditional quasi-resonant switching power supply.

FIG2 shows the operating waveforms of multiple signals when the quasi-resonant switching power supply shown in FIG1 operates in a quasi-resonant single valley conduction mode.

Figure 3 shows the spectrum energy distribution diagram of the quasi-resonant switching power supply shown in Figure 1 when it operates in the quasi-resonant single valley conduction mode.

FIG4 shows a circuit schematic diagram of a frequency jitter control circuit for a quasi-resonant switching power supply according to an embodiment of the present invention.

FIG5 shows example waveforms of multiple signals when the frequency jitter control circuit shown in FIG4 uses a fixed multi-cycle counting method to implement a valley-insertion frequency jitter control scheme.

FIG6 shows example waveforms of multiple signals when the frequency jitter control circuit shown in FIG4 uses a pseudo-random multi-cycle counting method to implement a valley-insertion frequency jitter control scheme.

FIG7 shows a circuit schematic diagram of a frequency jitter control circuit for a quasi-resonant switching power supply according to another embodiment of the present invention.

FIG8 shows an example waveform diagram of multiple signals when the frequency jitter control circuit shown in FIG7 uses the adjacent fixed multi-cycle counting valley bottom number comparison method to implement the valley bottom frequency jitter control scheme.

FIG9 shows an example waveform diagram of multiple signals when the frequency jitter control circuit shown in FIG7 uses the adjacent pseudo-random multi-cycle counting valley bottom number comparison method to implement the valley bottom frequency jitter control scheme.

Figure 10 shows the spectrum distribution diagram when the valley-interpolation frequency jittering scheme is implemented by using a fixed multi-cycle counting method or an adjacent fixed multi-cycle counting valley number comparison method.

Figure 11 shows the spectrum distribution diagram when the valley-insertion frequency jittering scheme is implemented by using a pseudo-random multi-cycle counting method or a valley-number comparison method of adjacent pseudo-random multi-cycle counting.

The features and exemplary embodiments of various aspects of the present invention are described in detail below. In the detailed description below, many specific details are set forth in order to provide a comprehensive understanding of the present invention. However, it is obvious to a person skilled in the art that the present invention can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is in no way limited to any specific configuration and algorithm set forth below, but covers any modification, substitution and improvement of elements, components and algorithms without departing from the spirit of the present invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessary ambiguity of the present invention.

FIG1 shows a circuit schematic diagram of a conventional quasi-resonant switching power supply. In the quasi-resonant switching power supply 100 shown in FIG1 , when the 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 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. In addition, when the transistor Q1 is in the off state, the auxiliary winding induced voltage Vaux on the auxiliary winding of the transformer T1 can represent the resonant voltage on the primary winding of the transformer T1. The auxiliary winding induced voltage Vaux can generate a resonant voltage representative voltage Vaux` through the voltage division of the upper bias resistor Rup and the lower bias resistor Rdw. By comparing the resonant voltage representative voltage Vaux` with the threshold voltage Vref, a quasi-resonant valley bottom detection signal Qr_on can be obtained. Based on the quasi-resonant switching power supply 100 The output feedback control signal FB_d related to the output voltage Vout can generate an upper clamping frequency control signal Qr_max for controlling the maximum operating frequency of the quasi-resonant switching power supply 100; based on the upper clamping frequency control signal Qr_max and the quasi-resonant valley detection signal Qr_on, a conduction control signal Tri_on for controlling the transistor Q1 from the off state to the on state can be generated; based on the conduction control signal Tri_on, a pulse width modulation (PWM) signal for controlling the on and off of the transistor Q1 can be generated to realize the quasi-resonant valley conduction control of the transistor Q1.

FIG2 shows the operating waveforms of multiple signals when the quasi-resonant switching power supply shown in FIG1 works in a quasi-resonant single valley conduction mode, wherein N1=N2=N3=N4, and the system operating frequency in this case is fixed to f1. FIG3 shows the spectrum energy distribution diagram when the quasi-resonant switching power supply shown in FIG1 works in a quasi-resonant single valley conduction mode. It can be seen that since the system operating frequency of the quasi-resonant switching power supply 100 shown in FIG1 remains fixed, the peak energy of the single switching frequency and its higher-order harmonics is very high, and the system's external electromagnetic radiation energy is very high at this time.

In view of the above situation, a quasi-resonant switching power supply and its frequency jitter control circuit according to the embodiment of the present invention are proposed, which can solve the problem that the quasi-resonant switching power supply works in a quasi-resonant single valley conduction mode, the system operating frequency is fixed, and the external electromagnetic radiation is too large to meet the current switching power supply electromagnetic compatibility standard.

FIG4 shows a circuit schematic diagram of a frequency jitter control circuit for a quasi-resonant switching power supply according to an embodiment of the present invention. The frequency jitter control circuit 400 for a quasi-resonant switching power supply shown in FIG4 is configured to: generate a quasi-resonant valley detection signal Qr_on based on a resonant voltage characteristic signal Vaux` that characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping frequency control signal Qr_max for controlling the maximum operating frequency of the quasi-resonant switching power supply based on an output feedback control signal FB_d related to the output voltage of the quasi-resonant switching power supply; and generate a frequency jitter control signal Qr_max for controlling the maximum operating frequency of the quasi-resonant switching power supply based on the output feedback control signal FB_d related to the output voltage of the quasi-resonant switching power supply. A PWM signal for controlling the on and off of the transistor in the quasi-resonant switching power supply is used to generate a valley enable signal Valley_insert_ENA; and a conduction control signal Tri_on is generated based on the quasi-resonant valley detection signal Qr_on, the upper clamping frequency control signal Qr_max, and the valley enable signal Valley_insert_ENA to control the transistor in the quasi-resonant switching power supply from the off state to the on state. Here, the moment when the transistor in the quasi-resonant switching power supply changes from the off state to the on state in the switching cycle in which the insertion valley enable signal Valley_insert_ENA is in the valid state is different from the moment when the transistor changes from the off state to the on state in the switching cycle in which the insertion valley enable signal Valley_insert_ENA is in the invalid state.

In some embodiments, in a switching cycle in which the valley insertion enable signal Valley_insert_ENA is in an invalid state, when the upper clamping frequency control signal Qr_max is in a valid state 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 mth resonant valley, the conduction control signal Tri_on controls the transistor in the quasi-resonant switching power supply from the off state to the on state. In the switching cycle when the valley insertion enable signal Valley_insert_ENA is in the valid state, when the upper clamping frequency control signal Qr_max is in the valid state 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+nth resonant valley, the conduction control signal Tri_on controls the transistor in the quasi-resonant switching power supply from the off state to the on state, and m and n are both integers greater than or equal to 1.

In some embodiments, as shown in FIG. 4 , the resonant voltage characteristic signal Vaux is a resonant voltage characteristic voltage generated by the auxiliary winding induced voltage Vaux on the auxiliary winding of the transformer in the quasi-resonant switching power supply through the voltage division of the upper bias resistor Rup and the lower bias resistor Rdw, and the frequency jitter control circuit 400 for the quasi-resonant switching power supply is further configured to generate a quasi-resonant valley detection signal Qr_on by comparing the resonant voltage characteristic voltage Vaux` with the threshold voltage Vref.

In some embodiments, as shown in FIG. 4 , the frequency jitter control circuit 400 for a 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.

In some embodiments, as shown in FIG. 4 , the frequency jitter control circuit 400 for the quasi-resonant switching power supply is further configured to: generate a quasi-resonant valley bottom conduction signal Qr_on` based on the quasi-resonant valley bottom detection signal Qr_on, the upper clamping frequency control signal Qr_max, and the insertion valley bottom enable signal Valley_insert_ENA; and generate a conduction control signal Tri_on based on the quasi-resonant valley bottom conduction signal Qr_on`, wherein the conduction control signal Tri_on is used to control the 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 valley bottoms in the current switching cycle.

FIG5 shows an example waveform diagram of multiple signals when the frequency jitter control circuit shown in FIG4 uses a fixed multi-cycle counting method to implement the valley insertion frequency jitter control scheme. As shown in FIG4 and FIG5, in some embodiments, whenever the count of the switching cycle of the PWM signal reaches N, the valley insertion enable signal Valley_insert_ENA is in a valid state in the N+1th switching cycle of the PWM signal, where N is a fixed integer greater than or equal to 1. In each switching cycle in which the valley insertion enable signal Valley_insert_ENA is in an invalid state, when the upper clamping frequency control signal Qr_max is in an effective state 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 mth resonant valley, the PWM signal changes from a low level to a high level, so that the transistor in the quasi-resonant switching power supply changes from an off state to an on state, where m is an integer greater than or equal to 1. In the switching cycle when the valley insertion enable signal Valley_insert_ENA is in the valid state, when the upper clamping frequency control signal Qr_max is in the valid state 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+1th resonant valley, the PWM signal changes from a low level to a high level, so that the transistor in the quasi-resonant switching power supply changes from the off state to the on state. By adopting a valley insertion frequency jitter control scheme with a fixed multi-cycle count, the system operating frequency of the quasi-resonant switching power supply changes periodically in the manner of f1->f2->f1->f2.

FIG6 shows an example waveform diagram of multiple signals when the frequency jitter control circuit shown in FIG4 adopts a pseudo-random multi-cycle counting method to implement a valley insertion frequency jitter control scheme. As shown in FIG4 and FIG6, in some embodiments, when the count of the switching cycle of the PWM signal reaches N1, the insertion valley enable signal Valley_insert_ENA is in a valid state in the N1+1th switching cycle of the PWM signal, and after the N1+1th switching cycle of the PWM signal ends, when the re-count of the switching cycle of the PWM signal reaches N2, the insertion valley enable signal Valley_insert_ENA is in a valid state in the N2+1th switching cycle of the PWM signal, and 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 in a multi-cycle counting valley insertion enable control unit. In each switching cycle in which the valley insertion enable signal Valley_insert_ENA is in an invalid state, when the upper clamping frequency control signal Qr_max is in an effective state 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 mth resonant valley, the PWM signal changes from a low level to a high level, so that the transistor in the quasi-resonant switching power supply changes from an off state to an on state, and m is an integer greater than or equal to 1. In the switching cycle when the valley insertion enable signal Valley_insert_ENA is in the valid state, when the upper clamping frequency control signal Qr_max is in the valid state 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+1th resonant valley, the PWM signal changes from a low level to a high level, so that the transistor in the quasi-resonant switching power supply changes from the off state to the on state. By adopting the pseudo-random multi-cycle counting valley insertion frequency jitter control scheme, the system operating frequency of the quasi-resonant switching power supply changes randomly without a fixed cycle in the manner of f3->f4->f3->f4.

FIG7 shows a circuit schematic diagram of a frequency jitter control circuit for a quasi-resonant switching power supply according to another embodiment of the present invention. The frequency jitter control circuit 700 for a quasi-resonant switching power supply shown in FIG7 is configured to: generate a quasi-resonant valley detection signal Qr_on based on a resonant voltage characteristic signal Vaux` that characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply; generate an upper clamping frequency control signal Qr_m for controlling the maximum operating frequency of the quasi-resonant switching power supply based on an output feedback control signal FB_d related to the output voltage of the quasi-resonant switching power supply ax; based on the quasi-resonant valley detection signal Qr_on, generate the insertion valley enable signal Valley_insert_ENA1; and based on the quasi-resonant valley detection signal Qr_on, the upper clamping frequency control signal Qr_max, and the insertion valley enable signal Valley_insert_ENA1, generate the conduction control signal Tri_on for controlling the transistor in the quasi-resonant switching power supply to change from the off state to the on state. Here, the moment when the transistor in the quasi-resonant switching power supply changes from the off state to the on state in the switching cycle in which the insertion valley enable signal Valley_insert_ENA1 is in the valid state is different from the moment when the transistor changes from the off state to the on state in the switching cycle in which the insertion valley enable signal Valley_insert_ENA1 is in the invalid state.

In some embodiments, in a switching cycle in which the valley insertion enable signal Valley_insert_ENA1 is in an invalid state, when the upper clamping frequency control signal Qr_max is in a valid state 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 mth resonant valley, the conduction control signal Tri_on controls the transistor in the quasi-resonant switching power supply from the off state to the on state. In the switching cycle when the valley insertion enable signal Valley_insert_ENA1 is in the valid state, when the upper clamping frequency control signal Qr_max is in the valid state 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+nth resonant valley, the conduction control signal Tri_on controls the transistor in the quasi-resonant switching power supply from the off state to the on state, and m and n are both integers greater than or equal to 1.

In some embodiments, as shown in FIG. 7 , the resonant voltage characteristic signal Vaux` is a resonant voltage characteristic voltage generated by the auxiliary winding induced voltage Vaux on the auxiliary winding of the transformer in the quasi-resonant switching power supply through the voltage division of the upper bias resistor Rup and the lower bias resistor Rdw, and the frequency jitter control circuit 700 for the quasi-resonant switching power supply is further configured to generate a quasi-resonant valley detection signal Qr_on by comparing the resonant voltage characteristic voltage Vaux` with the threshold voltage Vref.

In some embodiments, as shown in FIG. 7 , the frequency jitter 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 of the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply in each of a plurality of adjacent switching cycles indicated by the quasi-resonant valley detection signal Qr_on.

In some embodiments, as shown in FIG. 7 , the frequency jitter control circuit 700 for the quasi-resonant switching power supply is further configured to: generate a quasi-resonant valley bottom conduction signal Qr_on` based on the quasi-resonant valley bottom detection signal Qr_on, the upper clamping frequency control signal Qr_max, and the insertion valley bottom enable signal Valley_insert_ENA1; and generate a conduction control signal Tri_on based on the quasi-resonant valley bottom conduction signal Qr_on`, wherein the conduction control signal Tri_on is used to control the 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 valley bottoms in the current switching cycle.

FIG8 shows an example waveform diagram of multiple signals when the frequency jitter control circuit shown in FIG7 adopts the adjacent fixed multi-cycle counting valley bottom number comparison method to implement the valley insertion frequency jitter control scheme. As shown in FIG7 and FIG8, in some embodiments, whenever the number of resonant valley bottoms in each of the adjacent T switching cycles of the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply indicated by the quasi-resonant valley bottom detection signal Qr_on is equal, the valley insertion enable signal Valley_insert_ENA1 is in a valid state in the next switching cycle immediately after the T switching cycles, and T is a fixed integer greater than or equal to 1. That is, based on the quasi-resonant valley detection signal Qr_on, the number of resonance valleys of the resonance 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 resonance valleys of the resonance 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 (for example, X1 =X2 or X3=X4), then the valley enable signal Valley_insert_ENA1 is in a valid state in the next switching cycle immediately after the T switching cycles; otherwise (for example, X1≠X2 or X3≠X4), the valley enable signal Valley_insert_ENA1 is in an invalid state in the next switching cycle immediately after the T switching cycles. In each switching cycle when the valley insertion enable signal Valley_insert_ENA1 is in an invalid state, when the upper clamping frequency control signal Qr_max is in an effective state 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 mth resonant valley, the PWM signal changes from a low level to a high level, so that the transistor in the quasi-resonant switching power supply changes from an off state to an on state, where m is an integer greater than or equal to 1. In the switching cycle in which the valley insertion enable signal Valley_insert_ENA1 is in the valid state, when the upper clamping frequency control signal Qr_max is in the valid state 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+1th resonant valley, the PWM signal changes from a low level to a high level, so that the transistor in the quasi-resonant switching power supply changes from the off state to the on state. It should be noted here that after the current switching cycle in which the valley insertion enable signal Valley_insert_ENA1 is in the valid state ends and before the next switching cycle starts, the valley insertion enable signal Valley_insert_ENA1 needs to be reset to an invalid state. By adopting the interpolated valley frequency jitter control scheme of the adjacent fixed multi-cycle counting valley number comparison method, the system operating frequency of the quasi-resonant switching power supply changes periodically in the manner of f5->f6->f5->f6.

FIG9 shows an example waveform diagram of multiple signals when the frequency jitter control circuit shown in FIG7 adopts the adjacent pseudo-random multi-cycle counting valley number comparison method to implement the valley insertion frequency jitter control scheme. As shown in FIG7 and FIG9, in some embodiments, when the number of resonant valleys in each of the adjacent T1 switching cycles of the resonant voltage 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 not equal, the valley insertion enable signal Valley_insert_ENA1 is in an invalid state in the next switching cycle immediately after the T1 switching cycles, and is immediately after the T1 switching cycles. After the end of the next switching cycle, when the number of resonance valleys in each of the adjacent T2 switching cycles of the resonance voltage 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, the insertion valley enable signal Valley_insert_ENA1 is in a valid state in the next switching cycle immediately after 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. That is, the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply is compared with the number of resonant valleys Y1 and Y2 in each of the adjacent T1 switching cycles. If Y1=Y2, the valley insertion enable signal Valley_insert_ENA1 is in a valid state in the next switching cycle immediately after the T1 switching cycles, otherwise the valley insertion enable signal Valley_insert_ENA1 is in an invalid state in the next switching cycle immediately after the T1 switching cycles. Next, the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply is compared with the number of resonant valleys Y3, Y4, and Y5 in each of the adjacent T2 switching cycles. If Y3=Y4=Y5, the valley enable signal Valley_insert_ENA1 is in a valid state in the next switching cycle immediately after the T2 switching cycles, otherwise the valley enable signal Valley_insert_ENA1 is in an invalid state in the next switching cycle immediately after the T1 switching cycles. Through the above valley-interpolation frequency jitter control scheme using adjacent pseudo-random multi-cycle counting valley number comparison method, the system operating frequency of the switching power supply changes in the manner of f7->f8->f7->f8 without a fixed cycle (because T1 and T2 are random numbers).

By using the frequency jitter control circuit for the quasi-resonant switching power supply according to the embodiment of the present invention, the quasi-resonant switching power supply can be operated in the quasi-resonant jitter valley conduction mode under a certain fixed load, so that the system operating frequency of the quasi-resonant switching power supply changes regularly or randomly in a plurality of consecutive switching cycles. By using the above-mentioned valley jitter control scheme, the energy distribution of the quasi-resonant switching power supply can be not concentrated on a single frequency, but the energy of the quasi-resonant switching power supply can be dispersed and distributed on multiple baseband frequencies.

Figure 10 shows the spectrum distribution diagram when the valley-insertion frequency-jittering scheme is implemented by using a fixed multi-cycle counting method or an adjacent fixed multi-cycle counting valley-bottom number comparison method. Figure 11 shows the spectrum distribution diagram when the valley-insertion frequency-jittering scheme is implemented by using a pseudo-random multi-cycle counting method or an adjacent pseudo-random multi-cycle counting valley-bottom number comparison method. It can be seen that through the above valley-insertion frequency-jittering control scheme, the energy of the quasi-resonant switching power supply can be distributed on multiple basebands and have more high-frequency harmonic components, so that the energy radiated by the quasi-resonant switching power supply to the outside is greatly reduced, and finally the electromagnetic compatibility requirements of the switching power supply are met.

It should be noted that the frequency jitter control circuit for quasi-resonant switching power supply according to the embodiment of the present invention can be applied to switching power supplies using topological structures such as buck, boost, buck-boost, flyback, forward, and asymmetric half-bridge.

The present invention may be implemented in other specific forms without departing from its spirit and essential features. For example, the algorithm described in a specific embodiment may be modified, and the system architecture does not deviate from the basic spirit of the present invention. Therefore, the present embodiments are considered to be exemplary rather than restrictive in all aspects, the scope of the present invention is defined by the attached claims rather than the above description, and all changes that fall within the meaning and scope of equivalents of the claims are therefore included in the scope of the present invention.

400: Frequency jitter control circuit for quasi-resonant switching power supply

DC: reference voltage

FB_d: Output feedback control signal

PWM: Pulse Width Modulation

Qr_max: upper clamping frequency control signal

Qr_on: Quasi-resonant valley detection signal

Qr_on`: Quasi-harmonic valley bottom guidance signal

Rdw: Downward bias resistance

Rup: Upward bias resistor

Tri_on: conduction control signal

Valley_insert_ENA: insert valley bottom enable signal

Vaux: Auxiliary winding induced voltage

Vaux`: resonant voltage characteristic voltage

Vref: Threshold voltage

Claims (15)

A frequency jitter control circuit for a quasi-resonant switching power supply is configured as: Based on the resonant voltage characterization signal that characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply, a quasi-resonant valley bottom 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 frequency control signal for controlling the maximum operating frequency of the quasi-resonant switching power supply is generated; Based on the pulse width modulation signal used to control the on and off of the transistor in the quasi-resonant switching power supply, a valley bottom enable signal is generated; and Based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the insertion valley enable signal, a conduction control signal is generated for controlling the transistor in the quasi-resonant switching power supply to change from an off state to an on state, wherein The moment when the transistor in the quasi-resonant switching power supply changes from the off state to the on state in the switching cycle when the insertion valley enable signal is in the valid state is different from the moment when the transistor changes from the off state to the on state in the switching cycle when the insertion valley enable signal is in the invalid state. The frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 1 is further configured as: The valley insertion enable signal is generated by counting the switching cycles of the pulse width modulation signal. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 2, wherein whenever the count of the switching cycle of the pulse width modulation signal reaches N, the insertion valley enable signal is in a valid state in the N+1th switching cycle of the pulse width modulation signal, and N is a fixed integer greater than or equal to 1. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 2, wherein when the count of the switching cycle of the pulse width modulation signal reaches N1, the insertion valley enable signal is in a valid state in the N1+1th switching cycle of the pulse width modulation signal, and After the N1+1th switching cycle of the pulse width modulation signal ends, when the recount of the switching cycle of the pulse width modulation signal reaches N2, the valley insertion enable signal is in a valid state in the N2+1th switching cycle of the pulse width modulation signal, and N1 and N2 are both integers greater than or equal to 1 and N1≠N2. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 4, wherein N1 and N2 are random numbers generated by a pseudo-random timing generator. The frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 1 is further configured as: Based on the quasi-resonant valley bottom detection signal, the upper clamping frequency control signal, and the valley bottom insertion enable signal, a quasi-resonant valley bottom conduction signal is generated; and Based on the quasi-resonant valley conduction signal, the conduction control signal is generated, wherein the conduction control signal is used to control the transistor in the quasi-resonant switching power supply to change from an off state to an 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. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 1, wherein, in a switching cycle in which the insertion valley enable signal is in an invalid state, when the upper clamping frequency control signal is in an effective state and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer reaches the mth resonant valley, the conduction control signal controls the transistor in the quasi-resonant switching power supply to change from an off state to an on state, and In the switching cycle in which the insertion valley enable signal is in an effective state, when the upper clamping frequency control signal is in an effective state and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer reaches the m+nth resonant valley, the conduction control signal controls the transistor in the quasi-resonant switching power supply from the off state to the on state, and m and n are both integers greater than or equal to 1. A frequency jitter control circuit for a quasi-resonant switching power supply is configured as: Based on the resonant voltage characterization signal that characterizes the resonant voltage on the auxiliary winding of the transformer in the quasi-resonant switching power supply, a quasi-resonant valley bottom 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 frequency control signal for controlling the maximum operating frequency of the quasi-resonant switching power supply is generated; Based on the quasi-resonant valley detection signal, generate a valley insertion enable signal; and Based on the quasi-resonant valley detection signal, the upper clamping frequency control signal, and the insertion valley enable signal, a conduction control signal is generated for controlling the transistor in the quasi-resonant switching power supply to change from an off state to an on state, wherein The moment when the transistor in the quasi-resonant switching power supply changes from the off state to the on state in the switching cycle when the insertion valley enable signal is in the valid state is different from the moment when the transistor changes from the off state to the on state in the switching cycle when the insertion valley enable signal is in the invalid state. The frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 8 is further configured as: The insertion valley enable signal is generated by counting and comparing the number of resonance valleys of the resonance voltage on the auxiliary winding of the transformer in each of a plurality of adjacent switching cycles indicated by the quasi-resonance valley detection signal. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 9, wherein whenever the number of resonant valleys of the resonant voltage on the auxiliary winding of the transformer indicated by the quasi-resonant valley detection signal in each of the T adjacent switching cycles is equal, the valley insertion enable signal is in a valid state in the next switching cycle immediately after the T switching cycles, and T is a fixed integer greater than or equal to 1. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 9, wherein when the number of resonant valleys of the resonant voltage on the auxiliary winding of the transformer indicated by the quasi-resonant valley detection signal in each of the adjacent T1 switching cycles is equal, the insertion valley enable signal is in a valid state in the next switching cycle immediately after the T1 switching cycles, and After the next switching cycle immediately following the T1 switching cycles ends, when the number of resonance valleys of the resonance voltage on the auxiliary winding of the transformer indicated by the quasi-resonance valley detection signal in each of the adjacent T2 switching cycles is equal, in the next switching cycle immediately following the T2 switching cycles, the insertion valley enable signal is in a valid state, T1 and T2 are both integers greater than or equal to 1 and T1≠T2. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 11, wherein T1 and T2 are random numbers generated by a pseudo-random timing generator. The frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 8 is further configured as: Based on the quasi-resonant valley bottom detection signal, the upper clamping frequency control signal, and the valley bottom insertion enable signal, a quasi-resonant valley bottom conduction signal is generated; and Based on the quasi-resonant valley conduction signal, the conduction control signal is generated, wherein the conduction control signal is used to control the transistor in the quasi-resonant switching power supply to change from an off state to an 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. A frequency jitter control circuit for a quasi-resonant switching power supply as described in claim 8, wherein, in a switching cycle in which the insertion valley enable signal is in an invalid state, when the upper clamping frequency control signal is in an effective state and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer reaches the mth resonant valley, the conduction control signal controls the transistor in the quasi-resonant switching power supply to change from an off state to an on state, and In the switching cycle in which the insertion valley enable signal is in an effective state, when the upper clamping frequency control signal is in an effective state and the quasi-resonant valley detection signal indicates that the resonant voltage on the auxiliary winding of the transformer reaches the m+nth resonant valley, the conduction control signal controls the transistor in the quasi-resonant switching power supply from the off state to the on state, and m and n are both integers greater than or equal to 1. A quasi-resonant switching power supply, comprising a frequency-jittering control circuit for a quasi-resonant switching power supply as described in any one of claims 1 to 14.

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