Switching power supply, switching power supply control circuit and control method

Abstract

The present application discloses a switching power supply, a control circuit and a control method for the switching power supply. The control circuit includes: a quasi-resonant control unit, which generates a detection signal according to the terminal voltage between the first end and the second end of the power switch tube included in the switching power supply; a modulation unit, which provides a switching signal to the control end of the power switch tube according to the detection signal, and detects the state of the detection signal. When the switching power supply is in a discontinuous conduction mode, the modulation unit adjusts the effective pulse width of the switching signal to increase or decrease the on time and off time of the power switch tube in each switching cycle, so that the duration of the switching cycle changes cycle by cycle. When the detection signal indicates that the terminal voltage resonates to the trough, the modulation unit outputs an effective switching signal to turn on the power switch tube, thereby realizing quasi-resonant control. The switching power supply, the control circuit and the control method of the switching power supply provided in the present application can simultaneously realize the quasi-resonant control technology and the frequency jitter control technology.

Description

Technical Field

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

[0002] The switching power supply is a commonly used circuit in the field of integrated circuits. Among them, the flyback switching power supply occupies a very important position in the low-power switching power supply due to its advantages such as simple structure, small size and multi-channel output.

[0003] The working principle of the traditional flyback switching power supply is: using the switching signal to control the conduction and shutdown of the power switch tube, the primary inductance in the transformer stores energy when the power switch tube is turned on, and the secondary inductance in the transformer is coupled with the primary inductance and discharges to the output capacitor when the power switch tube is turned off to maintain the output voltage provided by both ends of the output capacitor.

[0004] A flyback switching power supply usually has two operating modes: continuous conduction mode (CCM) and discontinuous conduction mode (DCM). The difference between the two is that in the continuous conduction mode, the switching signal will control the power switch tube to turn on again when the secondary inductance in the transformer has not completely discharged; while in the discontinuous conduction mode, the switching signal will control the power switch tube to turn on only after the secondary inductance discharge is completed.

[0005] Among them, in the discontinuous conduction mode, when the secondary inductor has been discharged and the power switch tube is not turned on, due to the combined effect of the primary inductor, the drain-source parasitic capacitance of the power switch tube, and the current sampling resistor and other circuit components, the drain-source voltage of the power switch tube will have a sinusoidal oscillation phenomenon. Therefore, the flyback switching power supply working in the discontinuous conduction mode widely adopts the quasi-resonant (QR) technology, which can turn on the power switch tube again to start the next switching cycle when the drain-source voltage of the power switch tube drops to the trough, thereby reducing the switching loss of the power switch tube and improving the efficiency of the flyback switching power supply.

[0006] Frequency jitter control technology is another technology used in switching power supplies. This technology mainly generates a series of sidebands around the main frequency band of the switching power supply's operating frequency by continuously changing the switching power supply's operating cycle, so that the noise energy of electromagnetic interference (EMI) can be dispersed in a wider frequency band, thereby reducing the impact of electromagnetic interference on the switching power supply.

[0007] However, in the control circuit of the existing switching power supply, if the quasi-resonant control technology is adopted, the noise interference of the switching power supply can no longer be reduced by the frequency jitter control technology. The specific reason is: the existing flyback switching power supply changes the switching cycle of the switching power supply by changing the frequency of the switching signal, thereby realizing the frequency jitter control technology, but the effective pulse width of the switching signal in each switching cycle is constant, so the discharge time of the secondary inductor in each switching cycle is constant, and the sinusoidal resonance parameters of the drain-source voltage of the power switch tube are the same; if the quasi-resonant control technology is adopted at the same time on this basis, the power switch tube will turn on again when the drain-source voltage resonates to the trough to start the next switching cycle, and because the sinusoidal resonance parameters of the drain-source voltage have not changed, the trough of the drain-source voltage appears at the same time in each switching cycle, that is, the length of the switching cycle does not change. Therefore, in the flyback switching power supply of the prior art, the quasi-resonant control technology is not compatible with the existing frequency jitter control technology. Summary of the invention

[0008] In view of the above problems, the purpose of the present invention is to provide a switching power supply, a control circuit and a control method for a switching power supply, by adjusting the effective time of the switching signal, so that the charging time of the primary inductance and the discharge time of the secondary inductance in the transformer are increased or decreased at the same time, thereby making the length of the switching cycle change from cycle to cycle, and being able to apply quasi-resonant control technology in a discontinuous conduction mode, so that each power switch tube can be turned on at the trough of the terminal voltage.

[0009] According to a first aspect of the present invention, a control circuit of a switching power supply is provided, comprising: a quasi-resonant control unit, for generating a detection signal according to a terminal voltage between a first end and a second end of a power switch tube included in the switching power supply; and a modulation unit, for providing the switching signal to the control end of the power switch tube according to the detection signal, and detecting the state of the detection signal; when the switching power supply is in a discontinuous conduction mode, the modulation unit adjusts the effective pulse width of the switching signal to increase or decrease the on time and off time of the power switch tube in each switching cycle, so that the duration of the switching cycle changes cycle by cycle, thereby realizing frequency jitter control of the switching signal; when the detection signal indicates that the terminal voltage resonates to a trough, the modulation unit outputs the effective switching signal to turn on the power switch tube, thereby realizing quasi-resonant control.

[0010] Optionally, the switching power supply also includes: a transformer, including a primary inductor and a secondary inductor coupled to each other, the power switch tube is connected in series with the primary inductor to control a first current flowing through the primary inductor, and the control end of the power switch tube receives the switching signal; and an output unit, connected to the secondary inductor to provide the output voltage according to a second current flowing through the secondary inductor.

[0011] Optionally, the modulation unit includes: an oscillation circuit, which generates a clock signal according to the detection signal and sets a window time, wherein the clock signal provides a valid pulse within the window time and when the detection signal indicates that the terminal voltage resonates to a trough; a pre-shutdown circuit, which is used to generate a pre-shutdown signal according to the first current and the output voltage; a logic circuit, which counts the valid pulses of the clock signal to obtain a count value, and generates a delay control signal in the form of a digital signal according to the count value, wherein the delay control signal indicates a delay duration; a delay circuit, which is used to generate a shutdown signal, wherein when the switching power supply is in a discontinuous conduction mode, the delay circuit delays the pre-shutdown signal according to the delay control signal to obtain the shutdown signal; and a latch circuit, which is used to generate the switching signal, wherein the set end of the latch circuit receives the clock signal, and the reset end of the latch circuit receives the shutdown signal.

[0012] Optionally, the value represented by the delay control signal is proportional to the delay duration.

[0013] Optionally, the delay control signal has a delay period, each delay period corresponds to a plurality of switching periods, and within each switching period, the delay circuit provides delay according to the delay control signal, and within each delay period, the delay duration represented by the delay control signal first increases and then decreases.

[0014] Optionally, the pre-shutdown circuit includes: a reference voltage module, used to generate a reference voltage based on the output voltage; a comparator, used to generate the pre-shutdown signal based on a comparison result between the reference voltage and a first sampling voltage, wherein the first sampling voltage represents the first current, and the pre-shutdown signal is valid when and only when the first sampling voltage is greater than or equal to the reference voltage.

[0015] Optionally, the delay circuit includes: a current generating module, used to provide a charging current; a variable capacitor, the capacitance of which is controlled by the delay control signal, the first end of the variable capacitor is grounded, and the second end is connected to the control module to provide a charging voltage; a control module, connected to the current generating module, when the pre-shutdown signal is valid, the control module provides the charging current to the second end of the variable capacitor; and a processing module, connected to the control module, for generating the shutdown signal according to the charging voltage.

[0016] Optionally, the current generating module provides the variable charging current or provides the constant charging current according to the input voltage.

[0017] Optionally, the current generating module includes a reference current source and / or a voltage-controlled current source, the output end of the current generating module provides the charging current, the reference current source provides a reference current component of the charging current at the output end of the current generating module, and the voltage-controlled current source provides a voltage-controlled current component of the charging current at the output end of the current generating module according to the input voltage.

[0018] Optionally, the transformer also includes an auxiliary coil coupled with the primary inductor and the secondary inductor, and the quasi-resonant control unit includes: a sampling circuit, wherein a first end of the auxiliary coil is connected to a first end of the sampling circuit, and a second end of the auxiliary coil and a second end of the sampling circuit are grounded, the sampling circuit includes a first resistor and a second resistor connected in series between the first end and the second end of the sampling circuit, a connection point between the first resistor and the second resistor provides a second sampling voltage, and the second sampling voltage represents the terminal voltage; and a judgment circuit, which judges whether the terminal voltage resonates to a trough according to the second sampling voltage, and provides the detection signal according to the judgment result.

[0019] Optionally, the modulation unit also includes a mode judgment circuit, which judges the working mode of the switching power supply according to the detection signal. When the detection signal indicates that the switching power supply is in a continuous conduction mode, the mode judgment circuit controls the delay circuit to directly output the pre-shutdown signal as the shutdown signal, and the mode judgment circuit controls the logic circuit to output a logic control signal to the oscillation circuit. The oscillation circuit adjusts the frequency of the clock signal according to the logic control signal to make the switching period continuously change.

[0020] Optionally, the logic circuit generates the logic control signal or the delay control signal using the same circuit structure.

[0021] According to a second aspect of the present invention, a control method for a switching power supply is provided, comprising: generating a detection signal according to a terminal voltage between a first end and a second end of a power switch tube included in the switching power supply; providing the switching signal to a control end of the power switch tube according to the detection signal; detecting a state of the detection signal, and when the switching power supply is in a discontinuous conduction mode, adjusting an effective pulse width of the switching signal to increase or decrease a conduction time and a turn-off time of the power switch tube in each switching cycle, so that the duration of the switching cycle changes cycle by cycle, and when the detection signal indicates that the terminal voltage resonates to a trough, the switching signal is effective to turn on the power switch tube.

[0022] Optionally, the switching power supply also includes: a transformer, including a primary inductor and a secondary inductor coupled to each other, the power switch tube is connected in series with the primary inductor to control a first current flowing through the primary inductor, and the control end of the power switch tube receives the switching signal; and an output unit, connected to the secondary inductor to provide the output voltage according to a second current flowing through the secondary inductor.

[0023] Optionally, the control method further includes: setting a window time, wherein within the window time: the state of the detection signal is detected, and when the detection signal indicates that the terminal voltage resonates to a trough, the switching signal is effective to turn on the power switch tube.

[0024] Optionally, the step of generating the detection signal according to the terminal voltage between the first end and the second end of the power switch tube includes: providing an auxiliary coil coupled to the primary inductor and the secondary inductor; obtaining a second sampling voltage according to the current flowing through the auxiliary coil; judging whether the terminal voltage resonates to a trough according to the second sampling voltage; and providing the detection signal according to the judgment result.

[0025] Optionally, the step of adjusting the effective pulse width of the switching signal includes: generating a pre-shutdown signal according to the first current and the output voltage; generating a clock signal according to the detection signal, wherein within a window time, when the detection signal indicates that the terminal voltage resonates to a trough, the clock signal provides an effective pulse; counting the effective pulses of the clock signal to obtain a count value, and generating a delay control signal in the form of a digital signal according to the count value, wherein the delay control signal indicates a delay time; when the switching power supply is in a discontinuous conduction mode, delaying the pre-shutdown signal according to the delay control signal to obtain a shutdown signal; and setting the switching signal according to the effective pulse of the clock signal to make the switching signal valid, and resetting the switching signal when the shutdown signal is valid to make the switching signal invalid.

[0026] Optionally, the value represented by the delay control signal is proportional to the delay duration.

[0027] Optionally, the delay control signal has a delay period, each delay period corresponds to a plurality of switching periods, within each switching period, the delay circuit delays according to the delay control signal, and within each delay period, the delay duration represented by the delay control signal first increases and then decreases.

[0028] Optionally, the step of generating a pre-shutdown signal based on the first current and the output voltage includes: generating a reference voltage based on the output voltage; generating a first sampling voltage based on the first current; and generating the pre-shutdown signal based on a comparison result of the reference voltage and the first sampling voltage, and the pre-shutdown signal is valid so that the power switch tube is subsequently turned off when and only when the first sampling voltage is greater than or equal to the reference voltage.

[0029] Optionally, the step of delaying the pre-shutdown signal according to the delay control signal to obtain a shutdown signal includes: providing a charging current; providing a variable capacitor whose capacitance is controlled by the delay control signal, and the variable capacitor generates a charging voltage according to the charging current; when the pre-shutdown signal is valid, providing the charging current to the second end of the variable capacitor; and generating the shutdown signal according to the charging voltage.

[0030] Optionally, the step of providing the charging current includes: providing a constant charging current or providing a variable charging current according to the input voltage.

[0031] Optionally, the step of providing the switching signal according to the detection signal includes: judging the working mode of the switching power supply according to the detection signal, and when the detection signal indicates that the switching power supply is in a continuous conduction mode, stopping delaying the pre-shutdown signal to directly output the pre-shutdown signal as the shutdown signal, and adjusting the frequency or effective pulse width of the clock signal according to the delay control signal, so that the length of the switching cycle of the switching signal changes continuously.

[0032] According to a third aspect of the present invention, a switching power supply is further provided, comprising: a power switch tube, a control end of which is controlled by a switching signal; a transformer, comprising a primary inductor and a secondary inductor coupled to each other, the power switch tube being connected in series with the primary inductor to control a first current flowing through the primary inductor, the control end of the power switch tube receiving the switching signal; and an output unit connected to the secondary inductor to provide the output voltage according to a second current flowing through the secondary inductor; a control circuit for providing the switching signal, comprising: a quasi-resonant control unit for controlling the output voltage according to the terminal current between the first end and the second end of the power switch tube; voltage to generate a detection signal; a modulation unit, providing the switching signal according to the detection signal, and detecting the state of the detection signal. When the switching power supply is in a discontinuous conduction mode, the modulation unit adjusts the effective pulse width of the switching signal to increase or decrease the on-time and off-time of the power switch tube in each switching cycle, so that the duration of the switching cycle changes cycle by cycle, thereby realizing frequency jitter control of the switching signal. When the detection signal indicates that the terminal voltage resonates to a trough, the modulation unit outputs the effective switching signal to turn on the power switch tube, thereby realizing quasi-resonance control.

[0033] Optionally, the modulation unit includes: an oscillation circuit, which generates a clock signal according to the detection signal and sets a window time, wherein the clock signal provides a valid pulse within the window time and when the detection signal indicates that the terminal voltage resonates to a trough; a pre-shutdown circuit, which is used to generate a pre-shutdown signal according to the first current and the output voltage; a logic circuit, which counts the valid pulses of the clock signal to obtain a count value, and generates a delay control signal in the form of a digital signal according to the count value, wherein the delay control signal indicates a delay duration; a delay circuit, which is used to generate a shutdown signal, wherein when the switching power supply is in a discontinuous conduction mode, the delay circuit delays the pre-shutdown signal according to the delay control signal to obtain the shutdown signal; and a latch circuit, which is used to generate the switching signal, wherein the set end of the latch circuit receives the clock signal, and the reset end of the latch circuit receives the shutdown signal.

[0034] Optionally, the delay control signal has a delay period, each delay period corresponds to a plurality of switching periods, and within each switching period, the delay circuit provides delay according to the delay control signal, and within each delay period, the delay duration represented by the delay control signal first increases and then decreases.

[0035] Optionally, the delay circuit includes: a current generating module, used to provide a charging current; a variable capacitor, the capacitance of which is controlled by the delay control signal, the first end of the variable capacitor is grounded, and the second end is connected to the control module to provide a charging voltage; a control module, connected to the current generating module, when the pre-shutdown signal is valid, the control module provides the charging current to the second end of the variable capacitor; and a processing module, connected to the control module, for generating the shutdown signal according to the charging voltage.

[0036] Optionally, the current generating module provides the variable charging current or provides the constant charging current according to the input voltage.

[0037] Optionally, the modulation unit also includes a mode judgment circuit, which judges the working mode of the switching power supply according to the detection signal. When the detection signal indicates that the switching power supply is in a continuous conduction mode, the mode judgment circuit controls the delay circuit to directly output the pre-shutdown signal as the shutdown signal, and the mode judgment circuit controls the logic circuit to output a logic control signal to the oscillation circuit. The oscillation circuit adjusts the frequency of the clock signal according to the logic control signal to make the switching period continuously change.

[0038] The switching power supply, the control circuit and the control method of the switching power supply provided in each embodiment of the present invention can be compatible with the frequency jitter control technology and the quasi-resonance control technology in the discontinuous conduction mode, that is, in the discontinuous conduction mode, the power switch tube can be turned on at the trough of the terminal voltage, and the switching period can be changed from cycle to cycle at the same time, thereby effectively reducing the switching loss while reducing the noise interference and improving the efficiency of the controller.

[0039] In some preferred embodiments, the switching power supply, the control circuit and the control method of the switching power supply can also determine the current operating mode based on the detection signal: when in the continuous conduction mode, the control circuit directly implements the frequency jitter control technology by adjusting the frequency of the clock signal; when in the discontinuous conduction mode, the control circuit adjusts the effective pulse width of the switching signal to increase or decrease the on time and off time of the power switch tube in each switching cycle, thereby realizing quasi-resonant control technology while realizing frequency jitter control technology.

[0040] In some embodiments of the present invention, the switching power supply, the control circuit and the control method of the switching power supply can also be applied to various application scenarios that provide different input voltages. They are more flexible and can be adaptively adjusted under different input voltages so that the switching signal has the same jitter amplitude under different input voltages. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings.

[0042] Figure 1 A circuit diagram of a conventional switching power supply control circuit is shown.

[0043] Figure 2 A schematic diagram showing waveforms of a switching signal Vdr provided by a control circuit using a quasi-resonant control technique in a discontinuous conduction mode in the prior art and a terminal voltage VDS of a power switch tube M0 is shown.

[0044] Figure 3 The figure shows a waveform diagram of a switch signal Vdr provided by a control circuit using a frequency jitter control technology in a continuous conduction mode in the prior art and a terminal voltage VDS of the power switch tube M0.

[0045] Figure 4 The figure shows a waveform diagram of a switch signal Vdr provided by a control circuit using a frequency jitter control technology in a discontinuous conduction mode in the prior art and a terminal voltage VDS of the power switch tube M0.

[0046] Figure 5 The waveform diagram of the switching signal Vdr and the terminal voltage VDS of the power switch tube M0 provided by the control circuit which simultaneously adopts the frequency jitter control technology and the quasi-resonance control technology in the discontinuous conduction mode in the prior art is shown.

[0047] Figure 6 A schematic structural diagram of a switching power supply according to a first embodiment of the present invention is shown.

[0048] Figure 7 Show Figure 6 A schematic block diagram of the pre-shutdown circuit in the control circuit shown.

[0049] Figure 8 Show Figure 6 A schematic circuit diagram of a specific embodiment of a delay circuit in a control circuit is shown.

[0050] Fig. 9 A schematic diagram showing waveforms of a switch signal sw provided by the control circuit of the first embodiment of the present invention and a terminal voltage VDS of the power switch tube M1 in a discontinuous conduction mode is shown.

[0051] Fig.10 A schematic diagram of a switching power supply according to a second embodiment of the present invention is shown.

[0052] Fig.11a and Fig.11b Shown separately Fig.10 Schematic circuit diagrams of two specific embodiments of the medium delay circuit.

[0053] Fig.12 A schematic structural diagram of a switching power supply according to a third embodiment of the present invention is shown.

[0054] Fig.13 A schematic flow chart showing a method for controlling a switching power supply according to a fourth embodiment of the present invention is shown.

[0055] Fig.14 Show Fig.13 FIG. 2 is a schematic diagram of specific steps of step S330 in the control method of the third embodiment of the present invention. DETAILED DESCRIPTION

[0056] Various embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. In each of the accompanying drawings, the same elements are represented by the same or similar reference numerals. For the sake of clarity, the various parts in the accompanying drawings are not drawn to scale.

[0057] Figure 1 A circuit diagram showing a control circuit of a conventional switching power supply is shown.

[0058] like Figure 1 As shown, the conventional switching power supply includes a current sampling resistor Rcs, a transformer U1, a power switch tube M0, a diode D0, an input capacitor Cin, and an output capacitor Cout. The transformer includes a mutually coupled primary inductor Lp and a secondary inductor Ls, and the same-name end of the primary inductor Lp is in opposite phase to the same-name end of the secondary inductor Ls. Specifically, as Figure 1 As shown, the series circuit of the current sampling resistor Rcs, the primary inductor Lp and the power switch tube M0 is connected in parallel with the input capacitor Cin, the input voltage Vin is provided to the two ends of the input capacitor Cin, and the control end of the power switch tube M0 receives the switching signal Vdr; the secondary inductor Ls is connected in series between the anode of the diode D0 and the ground, the same-name end of the secondary inductor Ls is grounded, and the two ends of the output capacitor Cout are respectively connected to the cathode of the diode D0 and the ground and provide the output voltage Vout.

[0059] like Figure 1As shown, the conventional control circuit includes an oscillation circuit 1310 , a feedback circuit 1320 , a logic circuit 1330 , a peak current detection circuit 1340 , a latch circuit 1350 , a pulse width comparator Uc and a driving circuit 1360 . Among them, the oscillation circuit 1310 generates a clock signal clk0, and the clock frequency of the clock signal clk0 determines the operating frequency of the control circuit; the logic circuit 1330 receives the clock signal clk0, and generates a logic control signal ctl0 according to the clock signal clk0, and the oscillation circuit 1310 adjusts the frequency of the clock signal clk0 according to the logic control signal ctl0; the feedback circuit 1320 obtains a limiting voltage Vpmax corresponding to the peak current according to the output voltage Vout of the switching power supply; the peak current detection circuit 1340 samples the current I0 flowing through the power switch tube M0 to obtain a sampling voltage Vprl representing the peak value of the sampling current; the pulse width comparator Uc compares the sampling voltage Vprl representing the peak current with the peak limiting voltage Vpmax to generate a shutdown signal Soff0; the latch circuit 1350 and the drive circuit 1360 generate a switching signal Vdr according to the shutdown signal Soff0 and the clock signal clk0.

[0060] In such Figure 1 In the conventional switching power supply shown in the figure: when the power switch tube M0 is turned on under the control of the switching signal Vdr, a charging current is formed in the primary inductor Lp to store energy; when the power switch tube M0 is turned off under the control of the switching signal Vdr, the secondary inductor Ls begins to discharge to continue to provide electrical energy, so that the output voltage Vout remains basically unchanged. In the continuous conduction mode, the switch signal Vdr will control the power switch tube M0 to turn on again when the secondary inductor Ls is not completely discharged; in the discontinuous conduction mode, the switch signal Vdr will control the power switch tube M0 to turn on only after the secondary inductor Ls is discharged. Among them, in the discontinuous conduction mode, when the secondary inductor Ls has finished discharging and the power switch tube M0 has not yet turned on, due to the combined effect of the primary inductor Ls, the parasitic capacitance Cp of the power switch tube M0 (formed between the first end and the second end of the power switch tube M0) and the current sampling resistor Rcs, the terminal voltage VDS of the power switch tube M0 (that is, the voltage between the first end and the second end of the power switch tube M0, for example, the drain-source voltage of the power switch tube M0) will exhibit a sinusoidal oscillation phenomenon, and the oscillation frequency of the terminal voltage VDS is related to the primary inductor Lp and the parasitic capacitance Cp, and the attenuation factor is related to the current sampling resistor Rcs.

[0061] Due to the occurrence of this sinusoidal oscillation phenomenon, the flyback switching power supply working in the discontinuous conduction mode widely adopts the quasi-resonant (QR) technology. The quasi-resonant control technology mainly controls the power switch tube to conduct again when its terminal voltage VDS resonates to the minimum value (trough) in the discontinuous conduction mode to start the next switching cycle, thereby effectively reducing the switching loss of the power switch tube M0, thereby improving the efficiency of the flyback switching power supply.

[0062] Figure 2 The waveform diagram of the switching signal Vdr and the terminal voltage VDS of the power switch tube M0 provided by the control circuit using the quasi-resonant control technology in the discontinuous conduction mode in the prior art is shown. Among them, each switching cycle T includes a stage ton and a stage toff. The power switch tube M0 is turned on in the stage ton to store electric energy in the secondary inductor Ls, and the power switch tube M0 is turned off in the stage toff to discharge the secondary inductor Ls to the output capacitor Cout. At the beginning of the stage toff, the terminal voltage VDS of the power switch tube M0 is basically constant until the discharge of the secondary inductor Ls ends ( Figure 3 At the moment t1 shown in the figure), the terminal voltage VDS of the power switch tube M0 begins to oscillate sinusoidally; by detecting the terminal voltage VDS of the power switch tube M0 within the window time t_win, it can be found that when the terminal voltage VDS resonates to the valley ( Figure 2 At time t2 shown in the figure, the power switch tube M0 is turned on again, thus entering the next stage ton.

[0063] At present, in order to reduce the impact of noise on switching power supplies, the control circuits of some switching power supplies usually adopt frequency jitter control technology, that is, the operating frequency of the switching power supply (that is, the frequency of the switching signal Vdr) is set to be variable, so that a series of sidebands can be generated around the main frequency band of the operating frequency of the switching power supply, so that the noise energy of electromagnetic interference (EMI) can be distributed over a wider frequency band, reducing the impact of electromagnetic interference on the switching power supply.

[0064] Figure 3 A schematic diagram showing waveforms of a switch signal Vdr provided by a control circuit using a frequency jitter control technology in a continuous conduction mode in the prior art and a terminal voltage VDS of a power switch tube M0; Figure 4 The figure shows a waveform diagram of a switch signal Vdr provided by a control circuit using a frequency jitter control technology in a discontinuous conduction mode in the prior art and a terminal voltage VDS of the power switch tube M0.

[0065] like Figure 3 and Figure 4As shown, the switching period T of the switching signal Vdr is adjusted cycle by cycle. For example, assuming that the first switching period T=T1, each switching period T increases by Δt cycle by cycle under the effect of the frequency jitter control technology until the nth switching period T reaches the maximum value T1+n·Δt (n is a non-zero natural number), and then each switching period T decreases by Δt cycle by cycle until the switching period T reaches the minimum value T1, and then each switching period increases by Δt cycle by cycle, and so on and so forth, so that the switching period T changes continuously to realize the frequency jitter control technology.

[0066] However, if the existing control circuit of the switching power supply adopts the quasi-resonance control technology, it is no longer possible to reduce the noise interference of the switching power supply through the frequency jitter control technology. Figure 1 The traditional switching power supply and its control circuit shown are used to explain the specific reasons.

[0067] based on Figure 1 The conventional switching power supply and its control circuit shown in FIG. Figure 5 The waveform diagram of the switching signal Vdr and the terminal voltage VDS of the power switch tube M0 provided by the control circuit which simultaneously adopts the frequency jitter control technology and the quasi-resonance control technology in the discontinuous conduction mode in the prior art is shown.

[0068] from Figure 5 It can be seen that due to the adoption of quasi-resonant control technology, when the terminal voltage VDS of the power switch tube M0 resonates to the trough within the above-mentioned window time t_win, the next stage ton will be turned on. Since the stage ton of each switching cycle is basically unchanged, the conduction time of the power switch tube M0 is also basically constant. Therefore, in each switching cycle, the time for the terminal voltage VDS of the power switch tube M0 to resonate from a constant value to a trough within the window time is also basically constant. Once the terminal voltage VDS of the power switch tube M0 reaches the trough within the window time, the next switching cycle will be turned on. Therefore, each switching cycle also remains constant, that is, frequency jitter control cannot be achieved.

[0069] To solve the above problems, the present invention provides a new control circuit for a switching power supply, which can control the switching power supply to achieve frequency jitter while implementing a quasi-resonant control technique. The present invention can be presented in various forms, some examples of which will be described below.

[0070] Figure 6 A schematic structural diagram of a switching power supply according to a first embodiment of the present invention is shown.

[0071] like Figure 6 As shown, the switching power supply of the first embodiment of the present invention includes a transformer U1 , an input unit 2100 , an output unit 2200 , and a control circuit, wherein the control circuit includes a modulation unit 2300 and a quasi-resonance control unit 2400 .

[0072] The transformer U1 includes a primary inductor Lp located on the primary side and a secondary inductor Ls located on the secondary side, and the primary inductor Lp and the secondary inductor Ls are coupled to achieve mutual inductance. The turns ratio between the primary inductor Lp and the secondary inductor Ls is, for example, N:1, where N is a natural number greater than or equal to 1.

[0073] The input unit 2100 forms a loop with the primary inductor Lp to provide a first current I1 flowing through the primary inductor according to the input voltage Vin and the switch signal sw.

[0074] As a specific embodiment, Figure 6 As shown, the input unit 2100 includes a rectifier bridge 2110, a power switch tube M1, a current sampling resistor Rcs and an input capacitor Cin, wherein: the rectifier bridge 2110 is used to convert an input voltage in the form of an AC signal into an input voltage Vin in the form of a DC signal; the power switch tube M1 is connected in series with the primary inductor Lp in the transformer U1 to control a first current I1 flowing through the primary inductor Lp, and the control end of the power switch tube M1 receives a switch signal sw, so that the power switch tube M1 is turned on when the switch signal sw is valid and turned off when the switch signal sw is invalid. Shutdown, that is, the on-time ton and off-time toff of the power switch tube M1 in each switching cycle are controlled by the switch signal sw; the current sampling resistor Rcs is connected in series between the first end of the power switch tube M1 and the ground, and the first current I1 is sampled to obtain the first sampling voltage Vs1 representing the first current I1. The second end of the power switch tube M1 is connected to the opposite end of the primary inductor Lp, and the same end of the primary inductor Lp is connected to the ground with an input capacitor Cin, and the DC input voltage Vin is applied to both ends of the input capacitor Cin. It should be noted that Figure 6 Only one embodiment of the input unit of the switching power supply is shown. Those skilled in the art can modify it according to actual needs. Figure 6 The input unit shown is replaced with an input unit of another structure.

[0075] The output unit 2200 forms a loop with the secondary inductor Ls to provide an output voltage Vout according to the second current I2 flowing through the secondary inductor Ls.

[0076] As a specific embodiment, Figure 6As shown, the output unit 2200 includes a diode D1 and an output capacitor Cout, wherein the anode of the diode D1 is connected to the opposite-name end of the secondary inductor Ls, and the cathode is connected to the first end of the output capacitor Cout, and the second end of the output capacitor Cout is connected to the same-name end of the secondary inductor Ls and grounded. Due to the mutual inductance between the primary inductor Lp and the secondary inductor Ls, the secondary inductor Ls can generate a second current I2 according to the first current I1 in the primary inductor Lp, thereby forming an output voltage Vout at both ends of the output capacitor Cout.

[0077] In the control circuit of the first embodiment of the present invention: the modulation unit 2300 is connected to the control end of the power switch tube M1 to provide a switching signal sw, and adjusts the effective time of the switching signal sw (for example, the duration of the high level in this embodiment), so that the on time ton of the power switch tube M1 in each switching cycle is increased or decreased, and the off time toff of the power switch tube M1 in each switching cycle is also increased or decreased accordingly, so that the switching cycle of the switching power supply can be changed cycle by cycle, that is, frequency jitter control is realized, so that the noise energy of the electromagnetic interference is dispersed over a wider frequency band, reducing the influence of noise interference; the quasi-resonance control unit 2400 is used to judge whether the terminal voltage VDS of the power switch tube M1 (that is, the voltage between the first end and the second end of the power switch tube M1, for example, the drain-source voltage of the power switch tube M1) resonates to a valley within the window time, and generates a detection signal Sj according to the judgment result, so that the modulation unit 2300 can change the switching signal sw to an effective state when the terminal voltage VDS resonates to a valley (within the window time) to turn on the power switch tube M1, thereby realizing the quasi-resonance control technology in the discontinuous conduction mode.

[0078] As a specific embodiment of the quasi-resonance control unit 2400, Figure 6 As shown, the quasi-resonance control unit 2400 includes a judgment circuit 2410 and a sampling circuit 2420, and the transformer U1 also includes an auxiliary coil La coupled with the primary inductance Lp and the secondary inductance Ls. The sampling circuit 2420 is implemented by, for example, resistors R1 and R2 connected in series with the auxiliary coil La. Specifically, the same-name end of the auxiliary coil La is grounded, the opposite-name end of the auxiliary coil La is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the resistor R2. The common node between the resistors R1 and R2 provides a second sampling voltage Vs2, and the second sampling voltage can represent the terminal voltage VDS of the power switch tube M1; the judgment circuit 2410 is connected to the sampling circuit 2420 to receive the second sampling voltage Vs2, and the judgment circuit 2410 is used to judge whether the terminal voltage VDS resonates to the valley according to the second sampling voltage Vs2. When the terminal voltage VDS resonates to the valley within the window time, the quasi-resonance control unit 2400 provides a valid detection signal Sj, otherwise the quasi-resonance control unit 2400 provides an invalid detection signal Sj.

[0079] As a specific embodiment of the modulation unit 2300, Figure 6 As shown, the modulation unit 2300 includes an oscillation circuit 2310 , a pre-shutdown circuit 2320 , a logic circuit 2330 , a delay circuit 2340 and a latch circuit 2350 .

[0080] like Figure 6 As shown, the oscillator circuit 2310 is used to generate a clock signal clk according to the detection signal Sj and to set the window time t_win. During the window time, when the detection signal Sj characterizes the terminal voltage VDS to resonate to the valley, the clock signal clk provides a valid pulse to set the latch circuit 2350.

[0081] The pre-shutdown circuit 2320 is used to generate a pre-shutdown signal Soff_pre according to the first current I1 flowing through the primary inductor Lp and the output voltage Vout. Specifically, Figure 7 Show Figure 6 Schematic block diagram of the pre-shutdown circuit 2320 in the control circuit shown in FIG. Figure 7 As shown, the pre-shutdown circuit 2320 includes a reference voltage module 2321 and a comparator 2322 (for example, a pulse width comparator). The reference voltage module 2321 is used to generate a reference voltage Vref according to the output voltage Vout to limit the peak current of the first current I1; one of the input terminals of the comparator 2322 is connected to the non-grounded terminal of the current sampling resistor Rcs to obtain a first sampling voltage Vs1, and the first sampling voltage Vs1 represents the first current I1. The comparator 2322 generates a pre-shutdown signal Soff_pre according to the comparison result between the reference voltage Vref and the first sampling voltage Vs1. The pre-shutdown signal Soff_pre is valid when and only when the first sampling voltage Vs1 is greater than or equal to the reference voltage Vref.

[0082] like Figure 6As shown, the logic circuit 2330 is used to count the effective pulses of the clock signal clk to obtain a count value, and generate a delay control signal ctl_dly in the form of a digital signal according to the count value. As a specific embodiment, in the logic circuit, the delay control signal ctl_dly represents the count value, when the count value increases to a preset value, the logic circuit starts to subtract the effective pulses of the clock signal, and when the count value decreases to an initial value, the logic circuit starts to add the effective pulses of the clock signal. As an alternative embodiment, the logic circuit adds the effective pulses of the clock signal to obtain the count value, and resets the count value to the initial value when the count value increases to a preset value, during the period when the count value increases from the initial value to the intermediate value between the preset value and the initial value, the value represented by the delay control signal ctl_dly increases with the increase of the count value, and during the period when the count value increases from the intermediate value to the preset value, the value represented by the delay control signal ctl_dly decreases with the increase of the count value.

[0083] like Figure 6 As shown, the delay circuit 2340 is used to delay the pre-shutdown signal Soff_pre according to the delay control signal ctl_dly to obtain the shutoff signal Soff, wherein the delay control signal ctl_dly is used to represent the delay duration. Preferably, the value represented by the delay control signal ctl_dly is proportional to the delay duration. Figure 8 Show Figure 6 As a specific embodiment, the delay circuit in the control circuit is a schematic circuit diagram of a specific embodiment. Figure 8As shown, the delay circuit 2340 uses the current to charge and discharge the capacitor to achieve delay control. The delay circuit 2340 includes a current generating module A1, a variable capacitor Cx, a control module 2341 and a processing module 2342. Among them, the current generating module A1 is used to provide a charging current Ic (the charging speed of the variable capacitor Cx can be controlled by controlling the size of the charging current Ic), the capacitance of the variable capacitor Cx is controlled by the delay control signal ctl_dly, the first end of the variable capacitor Cx is grounded, and the second end is connected to the control module 2341; the control module 2341 is connected between the second end of the variable capacitor and the current generating module A1, and is used to control the charging and clearing of the variable capacitor Cx. For example, when and only when the pre-shutdown signal Soff_pre is valid, the control module 2341 provides the charging current Ic to the second end of the variable capacitor Cx; the processing module 2342 is connected to the control module 2341, and is used to complete the comparison and logic control according to the charging voltage, thereby generating the shutdown signal Soff. Specifically, when the capacitance of the variable capacitor Cx is at the maximum value Cx_max, the delay time length provided by the delay circuit 2340 for the on-time ton has the maximum value Where Vth is the capacitor comparison voltage threshold, from which we can deduce the maximum delay time of the entire switching cycle Wherein tdm refers to the time from when the power switch tube M1 starts to be turned off to when the secondary inductor Ls finishes discharging, that is, the time during which the terminal voltage VDS of the power switch tube M1 maintains a constant high level in this switching cycle.

[0084] As a specific embodiment, the current generating module A1 is implemented by a reference current source, and the reference current source provides a constant charging current Ic.

[0085] like Figure 6 As shown, the latch circuit 2350 is used to generate a switch signal sw. The set terminal of the latch circuit receives the clock signal clk, and the reset terminal of the latch circuit receives the off signal Soff.

[0086] exist Figure 6During the operation of the control circuit of the switching power supply of the first embodiment shown in the figure: after the power switch tube M1 is turned off, the quasi-resonant control unit 2400 uses the auxiliary coil La to detect the resonance of the terminal voltage VDS of the power switch tube M1, thereby detecting whether the terminal voltage VDS resonates to the bottom within the window time. When the terminal voltage VDS resonates to the trough, the quasi-resonant control unit 2400 provides a valid detection signal Sj; the modulation unit 2300 provides a switching signal sw to the control end of the power switch tube M1 according to the detection signal Sj. Within the window time, when the detection signal Sj changes from invalid to valid, the switching signal sw provided by the modulation unit 2300 causes the power switch tube M1 to enter the conducting state from the off state to end the current switching cycle and start the next switching cycle, thereby performing quasi-resonant control on the switching power supply.Specifically, during the operation of the modulation unit 2300: the oscillation circuit 2310 sets a window time for the detection signal, so that the quasi-resonance control unit 2400 can detect whether the terminal voltage VDS resonates to the trough within the window time. At the same time, the oscillation circuit 2310 provides a clock signal clk to the logic circuit 2330, and the logic circuit 2300 counts the valid pulses of the clock signal clk to obtain a count value, and generates a delay control signal ctl_dly (for example, 00...01, 00...10, 00...11, etc.) in the form of a digital signal according to the count value; the pre-closed The pre-shutdown circuit 2320 is connected to the non-grounded end of the current sampling resistor Rcs (used to sample the first current I1 flowing through the primary inductor Lp to generate the first sampling voltage Vs1) to obtain the first sampling voltage Vs1, the reference voltage module 2321 in the pre-shutdown circuit 2320 is used to generate a reference voltage Vref according to the output voltage Vout, and the comparator 2322 in the pre-shutdown circuit 2320 is used to generate a pre-shutdown signal Soff_pre according to the comparison result between the reference voltage Vref and the first sampling voltage Vs1, if and only if the first sampling voltage Vs1 When V is greater than or equal to the reference voltage Vref, the pre-shutdown signal Soff_pre is effective to limit the peak current of the first current I1; the delay circuit 2340 is used to delay the pre-shutdown signal Soff_pre according to the delay control signal ctl_dly to obtain the shutdown signal Soff, that is, the original on-time ton of the power switch tube is delayed by a certain delay time (the delay time is controlled by the delay control signal ctl_dly, for example, when the delay control signal ctl_dly is 00…00, the delay time is, for example, 0, and when the delay control signal ctl When _dly is 00…01, the delay time is, for example, Δt; when the delay control signal ctl_dly is 00…10, the delay time is, for example, 2Δt; and so on, until the delay control signal ctl_dly is 11…11, the delay time reaches a maximum value nΔt); the set end of the latch circuit 2350 receives the clock signal clk, and the reset end receives the shutdown signal Soff, thereby generating a switching signal sw provided to the control end of the power switch tube M1, so that the control circuit further realizes the frequency jitter control technology on the basis of realizing the quasi-resonant control technology.

[0087] Fig. 9 A schematic diagram showing waveforms of a switch signal sw provided by the control circuit of the first embodiment of the present invention and a terminal voltage VDS of the power switch tube M1 in a discontinuous conduction mode is shown. Fig. 9Only a part of the switching cycle T[1] to T[2n+1] experienced by the switching power supply during operation is intercepted as an illustration (n is a non-zero natural number), and the switching cycle T[1] to T[2n+1] is used as a cycle period of the switching cycle change as a preferred embodiment for description. However, the embodiments of the present invention are not limited to this, and the switching cycle may change according to other rules, or may not have a specific cycle period. Those skilled in the art may set the change of the switching cycle according to actual needs to implement the frequency jitter control technology.

[0088] like Fig. 9 As shown, the switching signal sw used to control the power switch tube M1 turns on the power switch tube M1 at the beginning of each switching cycle. After the conduction time ton, the switching signal sw changes from valid to invalid to turn off the power switch tube M1. After the power switch tube M1 is turned off, due to the quasi-resonant control technology implemented by the quasi-resonant control unit 2400, when the terminal voltage VDS of the power switch tube M1 resonates to the trough within the window time t_win, the switching signal sw changes from invalid to valid to turn on the power switch tube M1 again, thereby reducing the switching loss and enabling the next switching cycle to start.

[0089] Specifically, in the switching cycle T[1], the effective time of the switching signal sw corresponds to the on-time ton[1]=ton0 of the power switch tube M1 in the current switching cycle, and the ineffective time of the switching signal sw corresponds to the off-time toff[1] of the power switch tube M1 in the current switching cycle. During the on-time ton[1] of the power switch tube M1, the terminal voltage VDS of the power switch tube M1 is approximately 0. During the off time toff[1] of the power switch tube M1: the terminal voltage VDS of the power switch tube M1 remains basically constant during the initial period tdm[1] until the terminal voltage VDS of the power switch tube M1 begins to oscillate sinusoidally when the secondary inductor Ls finishes discharging; during the window time t_win, when the terminal voltage VDS resonates to a trough, the power switch tube M1 is turned on again, the terminal voltage VDS drops to 0, the switching cycle T[1] ends, and the next switching cycle T[2] starts. It can be seen that the off time toff[1] of the power switch tube M1 in this cycle = tdm[1] + the time from the end of the discharge of the secondary inductor Ls in this switching cycle to the time when the terminal voltage VDS resonates to a trough in the window time, where the time tdm[1] = tdm0.

[0090] In the switching cycle T[2], the effective time of the switching signal sw corresponds to the on-time ton[2]=ton0+Δt of the power switch tube M1 in this switching cycle, and the ineffective time of the switching signal sw corresponds to the off-time toff[2]=tdm[2]+the time from the end of the discharge of the secondary inductor Ls in this switching cycle to the time when the terminal voltage VDS resonates to the valley within the window time. Among them, due to the extension of the on-time of the power switch tube M1, the time tdm[2] required for the secondary inductor Ls to discharge completely is also extended. This causes the time for the terminal voltage VDS to resonate to the valley to be postponed, that is, the inactive time of the switch signal sw in this switching cycle is prolonged, the turn-off time of the power switch tube M1 is prolonged, and the total duration of the switching cycle T[2] is prolonged.

[0091] By analogy, from switching cycle T[2] to switching cycle T[n+1], the on-time of the power switch tube M1 in each switching cycle increases by Δt compared with the on-time of the power switch tube M1 in the previous adjacent switching cycle (for example, the on-time of the power switch tube M1 in switching cycle T[n+1] is ton[n+1]=ton0+n·Δt), so that the time from the start of the power switch tube M1 turning off to the end of the discharge of the secondary coil Ls in each switching cycle increases by Δt compared with the corresponding time in the previous adjacent switching cycle. For example, the off time of the power switch tube M1 in the switching cycle T[n+1] The conduction time ton[n+1] of the power switch tube M1 in the switching cycle T[n+1] is ton[1]+n·Δt. Therefore, the lengths of the switching cycles T[1] to T[n+1] are increased from switching cycle to switching cycle.

[0092] As a preferred embodiment, in a cycle, from switching cycle T[n+2] to T[2n+1], the on-time of the power switch tube M1 in each switching cycle is reduced by Δt compared with the on-time of the power switch tube M1 in the adjacent previous switching cycle (for example, the on-time of the power switch tube M1 in the switching cycle T[2n+1] is ton[2n+1]=ton0), so that the time from the start of the power switch tube M1 being turned off to the end of the discharge of the secondary coil Ls in each switching cycle is reduced by Δt compared with the corresponding time in the adjacent previous switching cycle. Therefore, the length of the switching period T[n+2] to the switching period T[2n+1] can be reduced switching period by switching period. The embodiments of the present invention are not limited thereto, and those skilled in the art can set the changing rule of the switching period according to actual needs. For example, multiple switching periods within a cycle can be continuously increased or continuously decreased cycle by cycle, and reset to the initial switching period length at the beginning of each cycle. The switching period can also have other changing rules instead of changing according to a specific cycle.

[0093] As described above, the control circuit of the switching power supply provided in the first embodiment of the present invention can continuously change the duration of the switching cycle based on the application of the quasi-resonant control technology, thereby realizing the frequency jitter control technology, thereby reducing the switching loss while also weakening the impact of noise.

[0094] Fig.10 A schematic diagram showing a switching power supply according to a second embodiment of the present invention. Fig.11a and Fig.11b Shown separately Fig.10 Schematic circuit diagrams of two specific embodiments of the medium delay circuit.

[0095] The control circuit of the second embodiment of the present invention is basically the same as the control circuit of the first embodiment, and the similarities are not repeated here. The difference is that the control circuit further includes a line voltage detection unit, which generates a line voltage Va=k·Vin (where k is a non-zero constant) according to the input voltage Vin, and the delay circuit adjusts the delay control signal ctl_dly according to the line voltage Va. The line voltage detection unit generates the line voltage Va according to the second sampled voltage Vs2 sampled from the input voltage Vin, for example, and therefore the line voltage Va can represent the input voltage Vin.

[0096] As a specific embodiment, Fig.11a As shown, the current generating module A1 is implemented by a voltage-controlled current source, which is controlled by the line voltage Va, so that the charging current Ic changes with the change of the line voltage Va, and thus the charging current Ic can change with the change of the input voltage Vin.

[0097] As an alternative specific embodiment, Fig.11bAs shown, the current generating module A1 is implemented by a reference current source and a voltage-controlled current source. The output terminals of the reference current source A11 and the voltage-controlled current source A12 serve together as the output terminals of the current generating module A1 to provide a charging current Ic, wherein the charging current Ic includes a reference current component I_bias provided by the reference current source A11 and a voltage-controlled current component I_vccs provided by the voltage-controlled current source A12, wherein the voltage-controlled current source A12 is controlled by the line voltage Va, so that the charging current Ic=I_vccs+I_bias changes with the change of the line voltage Va, thereby the charging current Ic can change with the change of the input voltage Vin. Specifically, the voltage-controlled current component provided by the voltage-controlled current source A12 in It is known from the above analysis that when the capacitance of the variable capacitor Cx is at the maximum value Cx_max, the delay time length provided by the delay circuit 2340 for the on-time ton has the maximum value. From this, it can be deduced that the maximum delay duration of the entire switching cycle is At this time there is Where Ns represents the number of turns on the secondary side, Np represents the number of turns on the primary side, and Vout represents the output voltage. It can be seen that when When the terminal voltage VDS of the power switch tube M1 changes, the maximum delay time of the switching cycle remains unchanged, thereby ensuring that the frequency jitter amplitude of the switching signal remains consistent when the terminal voltage VDS / input voltage Vin changes.

[0098] The control circuit of the second embodiment of the present invention can be applied to various application scenarios that provide different input voltages, has greater flexibility, and can be adaptively adjusted under different input voltages so that the switching signal has the same jitter amplitude under different input voltages.

[0099] Fig.12 A schematic structural diagram of a switching power supply according to a third embodiment of the present invention is shown.

[0100] like Fig.12 As shown, the control circuit of the third embodiment of the present invention is basically the same as the control circuit of the first embodiment of the present invention, and the similarities are not repeated here. The difference is that the modulation unit 2300 includes not only an oscillation circuit 2310, a pre-shutdown circuit 2320, a logic circuit 2330, a delay circuit 2340 and a latch circuit 2350, but also a mode judgment circuit 2360. The mode judgment circuit 2360 provides an enable signal en to the delay circuit 2340, and the oscillation circuit 2310 provides a window time for detection to the mode judgment circuit 2360.

[0101] The control circuit of the third embodiment of the present invention can operate in a continuous conduction mode or a discontinuous conduction mode. The mode judgment circuit 2360 receives a detection signal Sj provided by a judgment circuit 2410 in the quasi-resonant control unit 2400, and judges the working mode of the switching power supply according to the detection signal Sj.

[0102] When the detection signal Sj indicates that the switching power supply is in the continuous conduction mode: the mode judgment circuit 2360 provides an invalid enable signal en to the delay circuit 2340, so that the delay circuit 2340 directly outputs the pre-shutdown signal Soff_pre provided by the pre-shutdown circuit 2320 as the shutdown signal Soff without delay; at the same time, the mode judgment circuit 2360 provides the first state mode control signal mod to the logic circuit 2330, so that the logic circuit 2330 provides the logic control signal ctl_log to the oscillation circuit 2310; the oscillation circuit 2310 adjusts the clock frequency of the clock signal clk under the control of the logic control signal ctl_log, so that the clock frequency of the clock signal clk changes continuously to realize the frequency jitter control technology.

[0103] When the detection signal Sj indicates that the control circuit of the switching power supply is in a discontinuous conduction mode: the mode judgment circuit 2360 provides a valid enable signal en to the delay circuit 2340, and provides a second-state mode control signal mod to the logic circuit 2330, so that the delay circuit 2340 delays the pre-shutdown signal Soff_pre according to the delay control signal ctl_dly provided by the logic circuit 2330 to obtain the shutdown signal Soff. The specific working process is the same as that of the first embodiment, which is to increase or decrease the conduction time of the power switch tube M1 in each switching cycle by adjusting the effective pulse width of the switching signal sw, thereby realizing the quasi-resonant control technology and the frequency jitter control technology at the same time, which will not be repeated here.

[0104] The control circuit of the third embodiment of the present invention can determine the current working mode according to the detection signal. When in the continuous conduction mode, the control circuit directly implements the frequency jitter control technology by adjusting the frequency of the clock signal. When in the discontinuous conduction mode, the control circuit adjusts the effective pulse width of the switching signal to increase or decrease the conduction time of the power switch tube in each switching cycle, thereby simultaneously realizing the quasi-resonant control technology and the frequency jitter control technology.

[0105] Fig.13 The flowchart of the control method of the switching power supply according to the fourth embodiment of the present invention is shown, which includes steps S310 to S340.

[0106] In step S310, a detection signal is generated according to a terminal voltage between a first terminal and a second terminal of the power switch tube. Preferably, the step of generating a detection signal according to the terminal voltage between the first terminal and the second terminal of the power switch tube includes: providing an auxiliary coil coupled with a primary inductor and a secondary inductor; obtaining a second sampling voltage according to a current flowing through the auxiliary coil; judging whether the terminal voltage resonates to a valley according to the second sampling voltage; and providing a detection signal according to the judgment result.

[0107] In step S320, a switch signal is provided according to the detection signal.

[0108] In step S330, when the switching power supply is in the discontinuous conduction mode, the effective pulse width of the switching signal is adjusted to increase or decrease the conduction time of the power switch tube in each switching cycle, so that the switching cycle changes continuously.

[0109] In a preferred embodiment, step S320 further includes: judging the working mode of the switching power supply according to the detection signal, and when the detection signal indicates that the switching power supply is in a continuous conduction mode, stopping delaying the pre-shutdown signal to directly output the pre-shutdown signal as the shutdown signal, and adjusting the frequency of the clock signal according to the logic control signal so that the switching period of the switching signal changes continuously.

[0110] In step S340 , within the window time, when the detection signal indicates that the terminal voltage resonates to a valley, the switch signal is enabled to turn on the power switch tube.

[0111] As a specific embodiment, Fig.14 Show Fig.13 The specific step diagram of step S330 in the control method of the fourth embodiment of the present invention is shown, including steps S331 to S335.

[0112] In step S331, a clock signal is generated according to the detection signal. When the detection signal represents that the terminal voltage resonates to a valley within the window time, the clock signal provides a valid pulse.

[0113] In step S332, a pre-shutdown signal is generated according to the first current and the output voltage. Preferably, step S332 specifically includes: generating a reference voltage according to the output voltage; generating a first sampling voltage according to the first current; and generating a pre-shutdown signal according to a comparison result of the reference voltage and the first sampling voltage, and the pre-shutdown signal is valid when and only when the first sampling voltage is greater than or equal to the reference voltage.

[0114] In step S333, the effective pulses of the clock signal are counted to obtain a count value, and a delay control signal in the form of a digital signal is generated according to the count value, and the delay control signal represents the delay duration. Preferably, the value represented by the delay control signal is proportional to the delay duration. Further preferably, the delay control signal has a delay period, each delay period corresponds to a plurality of switching periods, and within each delay period, the delay duration represented by the delay control signal first increases and then decreases.

[0115] In step S334, a shutdown signal is generated, and when the switching power supply is in a discontinuous conduction mode, the pre-shutdown signal is delayed according to the delay control signal to obtain the shutdown signal. Preferably, the step of delaying the pre-shutdown signal according to the delay control signal to obtain the shutdown signal specifically includes: providing a variable capacitor whose charging current and capacitance are controlled by the delay control signal, and providing the charging current to the variable capacitor when and only when the pre-shutdown signal is valid; and generating the shutdown signal according to the charging voltage. Further preferably, the step of providing the charging current includes: providing a variable charging current according to the input voltage or providing a constant charging current.

[0116] In step S335 , the switch signal is set according to the valid pulse of the clock signal to make the switch signal valid, and the switch signal is reset when the shutdown signal is valid to make the switch signal invalid.

[0117] The switching power supply, the control circuit and the control method of the switching power supply provided by each embodiment of the present invention can be compatible with the frequency jitter control technology and the quasi-resonance control technology in the discontinuous conduction mode, that is, in the discontinuous conduction mode, the switch tube can be turned on at the trough of the terminal voltage, and the switching cycle can be continuously changed at the same time, thereby effectively reducing the switching loss while reducing noise interference, and improving the efficiency of the controller. In some preferred embodiments, the switching power supply, the control circuit and the control method of the switching power supply can also determine the current working mode according to the detection signal. When in the continuous conduction mode, the control circuit directly implements the frequency jitter control technology by adjusting the frequency of the clock signal. When in the discontinuous conduction mode, the control circuit increases or decreases the conduction time of the power switch tube in each switching cycle by adjusting the effective pulse width of the switching signal, thereby realizing the quasi-resonance control technology and the frequency jitter control technology at the same time.

[0118] In some embodiments of the present invention, the switching power supply, the control circuit and the control method of the switching power supply can also be applicable to various application scenarios with different input voltages, are more flexible, and can be adaptively adjusted under different input voltages so that the switching signal has the same jitter amplitude under different input voltages.

[0119] According to the embodiments of the present invention as described above, these embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and changes can be made based on the above description. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can make good use of the present invention and the modified use based on the present invention. The scope of protection of the present invention shall be based on the scope defined by the claims of the present invention.

Claims

1. A control circuit for a switching power supply, wherein: The control circuit comprises: A quasi-resonance control unit, configured to generate a detection signal according to a terminal voltage between a first terminal and a second terminal of a power switch tube included in the switching power supply; and a modulation unit, providing a switch signal to the control end of the power switch tube according to the detection signal, and detecting the state of the detection signal, When the switching power supply is in the discontinuous conduction mode, the modulation unit adjusts the effective pulse width of the switching signal to increase or decrease the on-time and off-time of the power switch tube in each switching cycle, so that the switching cycle changes cycle by cycle, thereby realizing frequency jitter control of the switching signal. When the detection signal indicates that the terminal voltage resonates to a valley, the modulation unit outputs the effective switching signal to turn on the power switch tube, thereby achieving quasi-resonant control.

2. The control circuit according to claim 1, wherein: The switching power supply further comprises: A transformer, comprising a primary inductor and a secondary inductor coupled to each other, wherein the power switch tube is connected in series with the primary inductor to control a first current flowing through the primary inductor, and a control end of the power switch tube receives the switch signal; and An output unit is connected to the secondary inductor to provide an output voltage according to a second current flowing through the secondary inductor.

3. The control circuit according to claim 2, wherein: The modulation unit comprises: an oscillator circuit, generating a clock signal according to the detection signal, and setting a window time, wherein during the window time and when the detection signal indicates that the terminal voltage resonates to a trough, the clock signal provides a valid pulse; a pre-shutdown circuit, configured to generate a pre-shutdown signal according to the first current and the output voltage; A logic circuit, which counts the effective pulses of the clock signal to obtain a count value, and generates a delay control signal in the form of a digital signal according to the count value, wherein the delay control signal represents the delay duration; a delay circuit, used for generating a shutdown signal, wherein when the switching power supply is in a discontinuous conduction mode, the delay circuit delays the pre-shutdown signal according to the delay control signal to obtain the shutdown signal; and A latch circuit is used to generate the switch signal, a set end of the latch circuit receives the clock signal, and a reset end of the latch circuit receives the shutdown signal.

4. The control circuit according to claim 3, wherein: The value represented by the delay control signal is proportional to the delay duration.

5. The control circuit according to claim 3, wherein: The delay control signal has a delay period, each of the delay periods corresponds to a plurality of the switching periods, In each of the switching cycles, the delay circuit provides delay according to the delay control signal. In each of the delay cycles, the delay duration represented by the delay control signal first increases and then decreases.

6. The control circuit according to claim 3, wherein: The pre-shutdown circuit comprises: A reference voltage module, used for generating a reference voltage according to the output voltage; A comparator generates the pre-shutdown signal according to a comparison result between the reference voltage and a first sampling voltage, wherein the first sampling voltage represents the first current, and the pre-shutdown signal is valid when and only when the first sampling voltage is greater than or equal to the reference voltage.

7. The control circuit according to claim 3, wherein: The delay circuit comprises: A current generating module, used for providing a charging current; A variable capacitor, the capacitance of which is controlled by the delay control signal, a first end of which is grounded, and a second end of which is connected to a control module to provide a charging voltage; a control module connected to the current generating module, and when the pre-shutdown signal is valid, the control module provides the charging current to the second end of the variable capacitor; and A processing module is connected to the control module and is used to generate the shutdown signal according to the charging voltage.

8. The control circuit according to claim 7, wherein: The current generating module provides the variable charging current or the constant charging current according to an input voltage.

9. The control circuit according to claim 8, wherein: The current generating module includes a reference current source and / or a voltage-controlled current source, and the output end of the current generating module provides the charging current. The reference current source provides a reference current component of the charging current at the output end of the current generating module, The voltage-controlled current source provides a voltage-controlled current component of the charging current at an output end of the current generating module according to the input voltage.

10. The control circuit according to claim 2, wherein: The transformer further includes an auxiliary coil coupled to the primary inductor and the secondary inductor, The quasi-resonant control unit comprises: a sampling circuit, wherein the first end of the auxiliary coil is connected to the first end of the sampling circuit, the second end of the auxiliary coil and the second end of the sampling circuit are grounded, the sampling circuit comprises a first resistor and a second resistor connected in series between the first end and the second end of the sampling circuit, a connection point between the first resistor and the second resistor provides a second sampling voltage, and the second sampling voltage represents the terminal voltage; and A judgment circuit is used to judge whether the terminal voltage resonates to a valley according to the second sampling voltage, and provide the detection signal according to the judgment result.

11. The control circuit according to claim 3, wherein: The modulation unit further includes a mode determination circuit, which determines the working mode of the switching power supply according to the detection signal. When the detection signal indicates that the switching power supply is in the continuous conduction mode, the mode judgment circuit controls the delay circuit to directly output the pre-shutdown signal as the shutdown signal, and the mode judgment circuit controls the logic circuit to output a logic control signal to the oscillation circuit, and the oscillation circuit adjusts the frequency of the clock signal according to the logic control signal to make the switching period continuously change.

12. The control circuit according to claim 11, wherein: The logic circuit generates the logic control signal or the delay control signal using the same circuit structure.

13. A method for controlling a switching power supply, characterized in that: in, The control method comprises: Generate a detection signal according to a terminal voltage between a first terminal and a second terminal of a power switch tube included in the switching power supply; Providing a switch signal to the control end of the power switch tube according to the detection signal; detecting a state of the detection signal, When the switching power supply is in the discontinuous conduction mode, the effective pulse width of the switching signal is adjusted to increase or decrease the on-time and off-time of the power switch tube in each switching cycle, so that the switching cycle changes cycle by cycle. When the detection signal indicates that the terminal voltage resonates to a valley, the switch signal is effective to turn on the power switch tube.

14. The control method according to claim 13, wherein: The switching power supply further comprises: A transformer, comprising a primary inductor and a secondary inductor coupled to each other, wherein the power switch tube is connected in series with the primary inductor to control a first current flowing through the primary inductor, and a control end of the power switch tube receives the switch signal; and An output unit is connected to the secondary inductor to provide an output voltage according to a second current flowing through the secondary inductor.

15. The control method according to claim 14, characterized in that: Also includes: Set the window time, Wherein, within the window time: the state of the detection signal is detected, and when the detection signal indicates that the terminal voltage resonates to a valley, the switch signal is effective to turn on the power switch tube.

16. The control method according to claim 14, wherein: The step of generating the detection signal according to the terminal voltage between the first end and the second end of the power switch tube comprises: providing an auxiliary coil coupled to the primary inductor and the secondary inductor; Obtaining a second sampling voltage according to the current flowing through the auxiliary coil; Determining whether the terminal voltage resonates to a valley according to the second sampling voltage; and The detection signal is provided according to the determination result.

17. The control method according to claim 15, wherein: The step of adjusting the effective pulse width of the switching signal comprises: generating a pre-shutdown signal according to the first current and the output voltage; Generate a clock signal according to the detection signal, wherein within a window time, when the detection signal indicates that the terminal voltage resonates to a valley, the clock signal provides a valid pulse; Counting the effective pulses of the clock signal to obtain a count value, and generating a delay control signal in the form of a digital signal according to the count value, wherein the delay control signal represents the delay duration; When the switching power supply is in a discontinuous conduction mode, delaying the pre-shutdown signal according to the delay control signal to obtain a shutdown signal; and The switch signal is set according to a valid pulse of the clock signal to make the switch signal valid, and the switch signal is reset when the shutdown signal is valid to make the switch signal invalid.

18. The control method according to claim 17, wherein: The value represented by the delay control signal is proportional to the delay duration.

19. The control method according to claim 17, wherein: The delay control signal has a delay period, each of the delay periods corresponds to a plurality of the switching periods, In each of the switching cycles, a delay circuit is used to delay according to the delay control signal. In each of the delay cycles, the delay duration represented by the delay control signal first increases and then decreases.

20. The control method according to claim 17, wherein: The step of generating a pre-shutdown signal according to the first current and the output voltage comprises: generating a reference voltage according to the output voltage; generating a first sampling voltage according to the first current; and The pre-shutdown signal is generated according to a comparison result between the reference voltage and the first sampling voltage. When and only when the first sampling voltage is greater than or equal to the reference voltage, the pre-shutdown signal is effective so that the power switch tube is subsequently turned off.

21. The control method according to claim 17, wherein: The step of delaying the pre-shutdown signal according to the delay control signal to obtain a shutdown signal comprises: Provide charging current; Providing a variable capacitor whose capacitance is controlled by the delay control signal, wherein the variable capacitor generates a charging voltage according to the charging current; When the pre-shutdown signal is valid, providing the charging current to the second end of the variable capacitor; and The shutdown signal is generated according to the charging voltage.

22. The control method according to claim 21, wherein: The step of providing the charging current comprises: The charging current is provided to be constant or to be provided to be variable according to an input voltage.

23. The control method according to claim 17, wherein: The step of providing the switch signal according to the detection signal comprises: Determine the working mode of the switching power supply according to the detection signal, When the detection signal indicates that the switching power supply is in continuous conduction mode, the delay of the pre-shutdown signal is stopped to directly output the pre-shutdown signal as the shutdown signal, and the frequency of the clock signal is adjusted according to the delay control signal, so that the length of the switching cycle of the switching signal changes continuously.

24. A switching power supply, wherein: include: Power switch tube, the control end is controlled by the switch signal; A transformer, comprising a primary inductor and a secondary inductor coupled to each other, wherein the power switch tube is connected in series with the primary inductor to control a first current flowing through the primary inductor, and a control end of the power switch tube receives the switch signal; an output unit connected to the secondary inductor to provide an output voltage according to a second current flowing through the secondary inductor; as well as a control circuit for generating the switch signal, Wherein, the control circuit comprises: A quasi-resonance control unit, configured to generate a detection signal according to a terminal voltage between the first end and the second end of the power switch tube; and a modulation unit, providing the switch signal according to the detection signal, and detecting the state of the detection signal, When the switching power supply is in the discontinuous conduction mode, the modulation unit adjusts the effective pulse width of the switching signal to increase or decrease the on-time and off-time of the power switch tube in each switching cycle, so that the switching cycle changes cycle by cycle, thereby realizing frequency jitter control of the switching signal. When the detection signal indicates that the terminal voltage resonates to a valley, the modulation unit outputs the effective switching signal to turn on the power switch tube, thereby achieving quasi-resonant control.

25. The switching power supply according to claim 24, wherein: The modulation unit comprises: an oscillator circuit, generating a clock signal according to the detection signal, and setting a window time, wherein during the window time and when the detection signal indicates that the terminal voltage resonates to a trough, the clock signal provides a valid pulse; a pre-shutdown circuit, configured to generate a pre-shutdown signal according to the first current and the output voltage; A logic circuit, which counts the effective pulses of the clock signal to obtain a count value, and generates a delay control signal in the form of a digital signal according to the count value, wherein the delay control signal represents the delay duration; a delay circuit, used for generating a shutdown signal, wherein when the switching power supply is in a discontinuous conduction mode, the delay circuit delays the pre-shutdown signal according to the delay control signal to obtain the shutdown signal; and A latch circuit is used to generate the switch signal, a set end of the latch circuit receives the clock signal, and a reset end of the latch circuit receives the shutdown signal.

26. The switching power supply according to claim 25, wherein: The delay control signal has a delay period, each of the delay periods corresponds to a plurality of the switching periods, In each of the switching cycles, the delay circuit provides delay according to the delay control signal. In each of the delay cycles, the delay duration represented by the delay control signal first increases and then decreases.

27. The switching power supply according to claim 25, wherein: The delay circuit comprises: A current generating module, used for providing a charging current; A variable capacitor, the capacitance of which is controlled by the delay control signal, a first end of which is grounded, and a second end of which is connected to a control module to provide a charging voltage; a control module connected to the current generating module, and when the pre-shutdown signal is valid, the control module provides the charging current to the second end of the variable capacitor; and A processing module is connected to the control module and is used to generate the shutdown signal according to the charging voltage.

28. The switching power supply according to claim 27, wherein: The current generating module provides the variable charging current or the constant charging current according to an input voltage.

29. The switching power supply according to claim 25, wherein: The modulation unit further includes a mode determination circuit, which determines the working mode of the switching power supply according to the detection signal. When the detection signal indicates that the switching power supply is in the continuous conduction mode, the mode judgment circuit controls the delay circuit to directly output the pre-shutdown signal as the shutdown signal, and the mode judgment circuit controls the logic circuit to output a logic control signal to the oscillation circuit, and the oscillation circuit adjusts the frequency of the clock signal according to the logic control signal to make the switching period continuously change.

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