阅读说明：本技术 开关控制电路、开关控制方法和开关电源 (Switch control circuit, switch control method and switch power supply ) 是由 俞秀峰 夏飞鹏 于 2021-07-09 设计创作，主要内容包括：本发明提出了一种开关控制电路、开关控制方法和开关电源,开关控制电路用于控制开关电源中的开关管,开关控制电路包括控制芯片。控制芯片设有复用引脚,复用引脚用于分别耦接开关管的第一端和开关管的第二端；开关管的第二端耦接采样电阻。其中,在第一状态下,控制芯片通过复用引脚获取表征流过开关管的电流的电流采样信号。在第二状态下,控制芯片通过复用引脚获取表征开关管第一端的端电压的电压表征信号。控制芯片根据电流采样信号和电压表征信号控制开关管。本发明提出的一种开关控制电路、开关控制方法和开关电源,可省去开关电源中的辅助绕组,并采用引脚复用的形式简化了控制芯片的引脚排布,有效降低系统成本。(The invention provides a switch control circuit, a switch control method and a switch power supply. The control chip is provided with a multiplexing pin which is used for being respectively coupled with the first end of the switch tube and the second end of the switch tube; the second end of the switch tube is coupled with the sampling resistor. In the first state, the control chip obtains a current sampling signal representing the current flowing through the switching tube through the multiplexing pin. And in a second state, the control chip acquires a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin. And the control chip controls the switching tube according to the current sampling signal and the voltage representation signal. The switch control circuit, the switch control method and the switch power supply provided by the invention can save an auxiliary winding in the switch power supply, simplify the pin arrangement of a control chip by adopting a pin multiplexing mode, and effectively reduce the system cost.)

1. A switch control circuit is used for controlling a switch tube in a switch power supply and is characterized by comprising a control chip, wherein the control chip is provided with a multiplexing pin which is used for being respectively coupled with a first end of the switch tube and a second end of the switch tube; the second end of the switching tube is coupled with the sampling resistor; wherein the content of the first and second substances,

in a first state, the control chip acquires a current sampling signal representing current flowing through the switching tube through a multiplexing pin;

and in a second state, the control chip acquires a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin.

2. The switch control circuit of claim 1, wherein the multiplexing pin is coupled to a first terminal of a switch tube through a first resistor, and the multiplexing pin is coupled to a second terminal of the switch tube through a second resistor.

3. The switch control circuit of claim 1, wherein the control chip comprises:

the input end of the current control circuit is coupled with the multiplexing pin and used for controlling the switching state of the switching tube according to the current sampling signal;

the input end of the valley bottom conduction control circuit is coupled with the multiplexing pin and is used for controlling the conduction of the switch tube in a waveform valley bottom setting area of the voltage representation signal; and

and the input end of the driving signal generating circuit is respectively coupled with the current control circuit and the valley bottom conduction control circuit and is used for outputting a driving signal to control the switch tube.

4. The switch control circuit of claim 3, wherein the valley conduction control circuit comprises:

a first switch, a first end of which is coupled with the multiplexing pin;

a second switch, wherein a first terminal of the second switch is coupled to the second terminal of the first switch, and a second terminal of the second switch is coupled to ground; and

and the input end of the zero-crossing detection circuit is coupled with the second end of the first switch and used for controlling the switching tube to be conducted in a waveform valley bottom set area of the voltage representation signal according to the voltage representation signal.

5. The switch control circuit of claim 3, wherein the current control circuit comprises:

a first end of the third switch is coupled with the multiplexing pin; and

a first input terminal of the first comparing circuit is coupled to the second terminal of the third switch, and a second input terminal of the first comparing circuit is coupled to the first reference signal terminal for receiving the first reference signal.

6. The switch control circuit of claim 4, wherein the zero-crossing detection circuit further comprises:

a follower, the non-inverting input terminal of which is coupled to the second terminal of the first switch, and the inverting input terminal of which is coupled to the output terminal of the follower; and

and the non-inverting input end of the hysteresis comparator is coupled with the reference voltage source to receive the reference voltage, and the inverting input end of the hysteresis comparator is coupled with the output end of the follower.

7. The switch control circuit of claim 4, wherein the control chip further comprises:

and the input end of the input undervoltage protection circuit is coupled with the second end of the first switch and used for generating an input undervoltage protection signal according to the voltage representation signal.

8. The switch control circuit of claim 4, wherein the control chip further comprises:

and the input end of the output overvoltage protection circuit is coupled with the second end of the first switch and used for generating an output overvoltage protection signal according to the voltage characterization signal.

9. The switch control circuit of claim 4, wherein the undervoltage input protection circuit comprises:

and the input end of the filter circuit is coupled with the second end of the first switch and used for filtering the voltage representation signal.

10. A switching power supply, characterized in that it comprises a switch control circuit according to any one of claims 1-9.

11. A switch control method is used for controlling a switch control circuit in a switch power supply, and is characterized in that the switch control circuit comprises a control chip, the control chip is provided with a multiplexing pin, and the multiplexing pin is used for being respectively coupled with a first end of a switch tube and a second end of the switch tube; the second end of the switching tube is coupled with the sampling resistor; the switch control method comprises the following steps:

under a first state, acquiring a current sampling signal representing current flowing through a switching tube through a multiplexing pin, and controlling the switching tube according to the current sampling signal; and

and in a second state, acquiring a voltage representation signal representing the terminal voltage of the first end of the switching tube through a multiplexing pin, and controlling the switching tube to be conducted in a waveform valley bottom set area of the voltage representation signal.

12. The switch control circuit of claim 11, wherein the switch control method further comprises:

and generating an input under-voltage protection signal according to the voltage characterization signal so as to protect the switch control circuit.

13. The switch control circuit of claim 11, wherein the switch control method further comprises:

and generating an output overvoltage protection signal according to the voltage characterization signal so as to protect the switch control circuit.

14. The switch control circuit of claim 11, wherein in the second state, the voltage representative signal is proportional to a terminal voltage at the first terminal of the switching tube.

Technical Field

The invention belongs to the technical field of power electronics, relates to a switching power supply control technology, and particularly relates to a switching control circuit, a switching control method and a switching power supply.

Background

The power factor PF is the ratio of the ac input active power to the input apparent power. The power factor PF can measure the effective utilization degree of electric power, and the lower the power factor PF is, the larger the reactive power of the electric equipment is, the lower the electric energy utilization rate is, the larger the harmonic component of the input current is, the waveform distortion of the input current is caused, the pollution is caused to a power grid, and the electric equipment is damaged in severe cases. Therefore, it is necessary to select a power factor correction circuit to increase the power factor PF of the switching power supply. In the switching power supply, in an intermittent mode (namely a DCM mode), the drain terminal voltage of a switching tube in the switching power supply is obtained by detecting a switching control circuit, and the switching control circuit controls the switching tube to be conducted at the bottom of the waveform valley of the drain terminal voltage, so that the switching loss of the switching power supply can be effectively reduced, and the system efficiency is improved.

In the prior art as shown in fig. 1, the boost switching power supply includes a control chip, and the control chip is provided with a zero-crossing detection pin ZCD and a current sampling pin CS. The zero-cross detection pin ZCD is coupled with the auxiliary winding through a resistor, and a feedback signal representing the voltage of the drain terminal of the switching tube can be obtained through the auxiliary winding, so that the switching tube Q can be controlled to be conducted at the bottom of the waveform valley of the voltage of the drain terminal. The current sampling pin CS is coupled to the switching tube Q and the sampling resistor Rcs, respectively, and the control chip can obtain a current sampling signal representing a current flowing through the switching tube Q through the current sampling pin CS, thereby controlling an output current of the switching power supply. In the technical scheme shown in fig. 1, zero-crossing detection is realized through the auxiliary winding, so that the circuit cost is high. In addition, in order to ensure that the switching power supply can stably work, a protection circuit, such as an input undervoltage protection circuit and an output overvoltage protection circuit, needs to be arranged in the control chip. Therefore, the control chip is required to detect and obtain the input voltage signal and the output voltage signal to realize the related protection operation, and the related signals cannot be directly obtained through the auxiliary winding.

In view of the above, there is a need to provide a new structure or control method for solving at least some of the above problems.

Disclosure of Invention

The invention provides a switch control circuit, a switch control method and a switch power supply aiming at one or more problems in the prior art.

The invention discloses a switch control circuit, which is used for controlling a switch tube in a switch power supply and comprises a control chip, wherein the control chip is provided with a multiplexing pin, and the multiplexing pin is used for being respectively coupled with a first end of the switch tube and a second end of the switch tube; the second end of the switching tube is coupled with the sampling resistor; wherein the content of the first and second substances,

in a first state, the control chip acquires a current sampling signal representing current flowing through the switching tube through a multiplexing pin;

and in a second state, the control chip acquires a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin.

As an embodiment of the present invention, the multiplexing pin is coupled to the first end of the switch tube through a first resistor, and the multiplexing pin is coupled to the second end of the switch tube through a second resistor.

As an embodiment of the present invention, the control chip includes:

the input end of the current control circuit is coupled with the multiplexing pin and used for controlling the switching state of the switching tube according to the current sampling signal;

the input end of the valley bottom conduction control circuit is coupled with the multiplexing pin and is used for controlling the conduction of the switch tube in a waveform valley bottom setting area of the voltage representation signal; and

and the input end of the driving signal generating circuit is respectively coupled with the current control circuit and the valley bottom conduction control circuit and is used for outputting a driving signal to control the switch tube.

As an embodiment of the present invention, the valley bottom conduction control circuit includes:

a first switch, a first end of which is coupled with the multiplexing pin;

a second switch, wherein a first terminal of the second switch is coupled to the second terminal of the first switch, and a second terminal of the second switch is coupled to ground; and

and the input end of the zero-crossing detection circuit is coupled with the second end of the first switch and used for controlling the switching tube to be conducted in a waveform valley bottom set area of the voltage representation signal according to the voltage representation signal.

As an embodiment of the present invention, the current control circuit includes:

a first end of the third switch is coupled with the multiplexing pin; and

a first input terminal of the first comparing circuit is coupled to the second terminal of the third switch, and a second input terminal of the first comparing circuit is coupled to the first reference signal terminal for receiving the first reference signal.

As an embodiment of the present invention, the zero-cross detection circuit further includes:

a follower, the non-inverting input terminal of which is coupled to the second terminal of the first switch, and the inverting input terminal of which is coupled to the output terminal of the follower; and

and the non-inverting input end of the hysteresis comparator is coupled with the reference voltage source to receive the reference voltage, and the inverting input end of the hysteresis comparator is coupled with the output end of the follower.

As an embodiment of the present invention, the control chip further includes: and the input end of the input undervoltage protection circuit is coupled with the second end of the first switch and used for generating an input undervoltage protection signal according to the voltage representation signal.

As an embodiment of the present invention, the control chip further includes: and the input end of the output overvoltage protection circuit is coupled with the second end of the first switch and used for generating an output overvoltage protection signal according to the voltage characterization signal.

As an embodiment of the present invention, the undervoltage protection circuit includes: and the input end of the filter circuit is coupled with the second end of the first switch and used for filtering the voltage representation signal.

Another embodiment of the invention discloses a switching power supply, which comprises the switching control circuit as described in any one of the above.

The invention discloses a switch control method, which is used for controlling a switch control circuit in a switch power supply, wherein the switch control circuit comprises a control chip, the control chip is provided with a multiplexing pin, and the multiplexing pin is used for being respectively coupled with a first end of a switch tube and a second end of the switch tube; the second end of the switching tube is coupled with the sampling resistor; the switch control method comprises the following steps:

under a first state, acquiring a current sampling signal representing current flowing through a switching tube through a multiplexing pin, and controlling the switching tube according to the current sampling signal; and

and in a second state, acquiring a voltage representation signal representing the terminal voltage of the first end of the switching tube through a multiplexing pin, and controlling the switching tube to be conducted in a waveform valley bottom set area of the voltage representation signal.

As an embodiment of the present invention, the switch control method further includes: and generating an input under-voltage protection signal according to the voltage characterization signal so as to protect the switch control circuit.

As an embodiment of the present invention, the switch control method further includes: and generating an output overvoltage protection signal according to the voltage characterization signal so as to protect the switch control circuit.

As an embodiment of the present invention, in the second state, the voltage characterization signal is in a proportional relationship with a terminal voltage of the first terminal of the switching tube.

The invention provides a switch control circuit, a switch control method and a switch power supply. The control chip is provided with a multiplexing pin which is used for being respectively coupled with the first end of the switch tube and the second end of the switch tube; the second end of the switch tube is coupled with the sampling resistor. In the first state, the control chip obtains a current sampling signal representing the current flowing through the switching tube through the multiplexing pin. And in a second state, the control chip acquires a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin. And the control chip controls the switching tube according to the current sampling signal and the voltage representation signal. The switch control circuit, the switch control method and the switch power supply provided by the invention can omit an auxiliary winding in the switch power supply, and adopt a pin multiplexing form, thereby simplifying the pin arrangement of a control chip and reducing the system cost.

Drawings

The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:

fig. 1 is a schematic diagram of a prior art boost switching power supply;

fig. 2 is a schematic diagram of a circuit structure of a boost switching power supply according to an embodiment of the invention;

FIG. 3 is a schematic diagram of a circuit structure of a control chip according to an embodiment of the invention;

FIG. 4 is a schematic diagram of a circuit structure of a control chip according to another embodiment of the invention;

FIG. 5 is a schematic diagram of a circuit structure of a control chip according to another embodiment of the present invention;

fig. 6 is a schematic circuit diagram of a flyback switching power supply according to an embodiment of the present invention.

Detailed Description

For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.

The description in this section is for several exemplary embodiments only, and the present invention is not limited only to the scope of the embodiments described. Combinations of different embodiments, and substitutions of features from different embodiments, or similar prior art means may be substituted for or substituted for features of the embodiments shown and described.

The term "coupled" or "connected" in this specification includes both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as a conductor, wherein the electrically conductive medium may contain parasitic inductance or parasitic capacitance, or through an intermediate circuit or component as described in the embodiments in the specification; indirect connections may also include connections through other active or passive devices that perform the same or similar function, such as connections through switches, signal amplification circuits, follower circuits, and so on. "plurality" or "plurality" means two or more.

The embodiment of the invention discloses a switch control circuit, which is used for controlling the switch state of a switch tube in a switch power supply, wherein the switch state of the switch tube comprises a conducting state and a switching-off state. The invention is suitable for a step-down switching power supply, a step-up and step-down switching power supply, a flyback switching power supply and the like. The switch control circuit controls the switch state of the switch tube so as to control the output of the switch power supply. The switch control circuit comprises a control chip, the control chip is provided with multiplexing pins, the multiplexing pins can be respectively coupled with the first end of the switch tube and the second end of the switch tube, and the second end of the switch tube is coupled with the sampling resistor. In the first state, the switching tube is in a conducting state, and the control chip acquires a current sampling signal representing current flowing through the switching tube through the multiplexing pin; and in the second state, the switching tube is in a turn-off state, and the control chip acquires a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin. The current sampling signal can be obtained through the multiplexing pin, so that the output current of the switching power supply is controlled according to the current sampling signal. In addition, a voltage representation signal can be obtained through the multiplexing pin, so that the switching tube is controlled to be in a conducting state in a waveform valley bottom setting area of the voltage representation signal according to the voltage representation signal. The invention can omit the auxiliary winding in the switch power supply and adopts the pin multiplexing mode, thereby simplifying the pin arrangement of the control chip and reducing the system cost.

In the embodiment of the present invention, the current sampling signal may be a current signal or a voltage signal. In an embodiment of the invention, the current sampling signal is a sampling voltage at the first end of the sampling resistor, and the current sampling signal may represent a current flowing through the switching tube. In another embodiment, the current sampling signal is proportional to the sampled voltage at the first terminal of the sampling resistor. In an embodiment of the invention, the voltage characterization signal is a terminal voltage of the first terminal of the switching tube. In another embodiment, the voltage characterization signal is proportional to the terminal voltage at the first terminal of the switching tube.

In an embodiment of the invention, the control chip includes a switch tube, and the control chip is provided with a drain terminal pin. The output end of a driving signal generating circuit in the switch control circuit is coupled with the drain terminal pin, and the drain electrode of the switch tube is coupled with the drain terminal pin. In another embodiment of the present invention, the control chip does not include the switch Q1, the control chip has a control pin, the output terminal of the driving signal generating circuit in the switch control circuit is coupled to the control pin, and the control terminal of the switch is coupled to the control pin. In an embodiment of the present invention, the switch tube may be one of a metal oxide semiconductor field effect transistor (MOSFET for short), a junction field effect transistor (JFET for short), an insulated gate bipolar transistor (IGBT for short), and the like.

In an embodiment of the invention, the multiplexing pin is coupled to the first end of the switch tube through a first resistor, that is, the multiplexing pin is coupled to the second end of the first resistor, and the first end of the first resistor is coupled to the first end of the switch tube. In addition, the multiplexing pin is coupled to the second end of the switch tube through the second resistor, that is, the multiplexing pin is coupled to the first end of the second resistor, and the second end of the second resistor is coupled to the second end of the switch tube.

In an embodiment of the present invention, as shown in fig. 2, the Boost-type switching power supply (i.e., Boost switching power supply) includes a first inductor Lm, a switching tube Q1, a first diode D1, and a second capacitor C2. The first terminal of the first inductor Lm is coupled to the input voltage, the first terminal of the switch Q1 is coupled to the second terminal of the first inductor Lm, the second terminal of the switch Q1 is coupled to the first terminal of the sampling resistor Rcs, and the second terminal of the sampling resistor Rcs is coupled to ground. An anode terminal of the first diode D1 is coupled to the second terminal of the first inductor Lm, a first terminal of the second capacitor C2 is coupled to a cathode terminal of the first diode D1, and a second terminal of the second capacitor C2 is coupled to ground. The switch control circuit in the switching power supply is used for controlling the switching state of the switching tube Q1. The switch control circuit comprises a control chip, and the control chip is provided with a control terminal pin GATE and a multiplexing pin SENSE. The control terminal pin GATE is coupled to the control terminal of the switch Q1, the multiplexing pin SENSE is coupled to the second terminal of the first resistor R1 and the first terminal of the second resistor R2, respectively, the first terminal of the first resistor R1 is coupled to the first terminal of the switch Q1, and the second terminal of the second resistor R2 is coupled to the second terminal of the switch Q1 and the first terminal of the sampling resistor Rcs, respectively. In this embodiment, the first terminal of the switching transistor Q1 is a drain, and the second terminal of the switching transistor is a source. In another embodiment, the control chip further has a power supply pin VDD, a system ground pin GND, a compensation pin COM, a feedback pin FB, and a high voltage input pin HV. The power supply pin VDD is coupled to a first terminal of the third capacitor C3, a second terminal of the third capacitor C3 is coupled to ground, and the system ground pin GND is coupled to ground. The compensation pin COM is coupled to the first end of the fifth resistor R5 and the first end of the fifth capacitor C5, respectively, the second end of the fifth resistor R5 is coupled to the first end of the fourth capacitor C4, the second end of the fourth capacitor C4 is coupled to ground, and the second end of the fifth capacitor C5 is coupled to ground. The feedback pin FB is coupled to the second terminal of the third resistor R3 and the first terminal of the fourth resistor R4, respectively, the first terminal of the third resistor R3 is coupled to the first terminal of the second capacitor C2, and the second terminal of the fourth resistor R4 is coupled to ground.

In an embodiment of the present invention, as shown in fig. 3, the control chip 10 includes a current control circuit 11, a valley conduction control circuit 12, and a driving signal generating circuit 13. An input terminal of the current control circuit 11 is coupled to the multiplexing pin SENSE, and an output terminal of the current control circuit 11 is coupled to a first input terminal of the driving signal generating circuit 13. An input terminal of the valley conduction control circuit 12 is coupled to the multiplexing pin SENSE, and an output terminal of the valley conduction control circuit 12 is coupled to a second input terminal of the driving signal generating circuit 13. The current control circuit 11 includes a third switch S3 and a current detection circuit 110, a first terminal of the third switch S3 is coupled to the multiplexing pin SENSE, an input terminal of the current detection circuit 110 is coupled to a second terminal of the third switch S3, a control terminal of the third switch S3 receives a driving signal (i.e., the PWM signal in fig. 3) output by the driving signal generation circuit, and the control chip 10 controls a switching state of the third switch S3 according to the driving signal. The output terminal of the current detection circuit 110 is coupled to the first input terminal of the driving signal generation circuit 13, and the current detection circuit 110 generates a first control signal to the driving signal generation circuit 13 according to the current sampling signal to control the output current of the switching power supply. The valley conduction control circuit 12 includes a first switch S1, a second switch S2, and a zero-cross detection circuit 120. The first terminal of the first switch S1 is coupled to the multiplexing pin SENSE, the first terminal of the second switch S2 is coupled to the second terminal of the first switch S1, and the second terminal of the second switch S2 is coupled to ground. The driving signal terminal is coupled to the input terminal of the not gate, and the output terminal of the not gate is coupled to the control terminal of the first switch S1; the driving signal terminal is further coupled to the control terminal of the second switch S2, and the driving signal terminal is used for providing a driving signal (i.e. the PWM signal in fig. 3). The input terminal of the zero-crossing detection circuit 120 is coupled to the second terminal of the first switch S1, the output terminal of the zero-crossing detection circuit 120 is coupled to the second input terminal of the driving signal generation circuit 13, and the zero-crossing detection circuit 120 generates the second control signal to the driving signal generation circuit 13 according to the voltage representation signal. The driving signal generating circuit 13 generates a driving signal according to the first control signal and the second control signal to control the switching state of the switching tube Q1.

In an embodiment of the invention, when the driving signal is at a first level (e.g., a high level), the switch Q1 is controlled to be turned on, and at this time, the third switch S3 is turned on, the current control circuit 11 obtains the current sampling signal, and the current control circuit 11 generates the first control signal according to the current sampling signal and the first reference signal. When the driving signal is at the second level (e.g., low level), the switching tube Q1 is controlled to be turned off, the first switch S1 is turned on, the second switch S2 is turned off, and the valley-bottom conduction control circuit 12 obtains the voltage characterization signal. As can be seen from fig. 2, the terminal voltage of the first end of the switching tube Q1 is a voltage Vdrain, and when the switching power supply is in the discontinuous mode, the voltage Vdrain may generate an oscillation signal, and the switching tube Q1 is controlled to be turned on at the valley bottom position of the voltage Vdrain, so that the loss of the switching tube Q1 may be effectively reduced, and the efficiency of the switching power supply may be improved. Setting the resistance value of the sampling resistor Rcs to be much smaller than that of the second resistor R2, and when the driving signal is at the second level, setting Vsense to Vdrain R2/(R1+ R2); the Vsense is a voltage characterization signal obtained from the multiplexing pin, Vdrain is a terminal voltage of the first end of the switching tube Q1, R1 is a resistance value of the first resistor, and R2 is a resistance value of the second resistor, so that the voltage Vsense is proportional to the voltage Vdrain. In an embodiment of the present invention, 5 × Rcs < R2, Rcs is a resistance value of the sampling resistor, and R2 is a resistance value of the second resistor. The valley bottom conduction control circuit 12 generates a second control signal according to the voltage representation signal to control the conduction of the switching tube in the waveform valley bottom setting area of the voltage representation signal. In a specific embodiment, the zero-crossing detection circuit 120 obtains the zero-crossing detection signal according to the voltage representation signal so as to obtain the valley bottom position of the voltage representation signal, and controls the conduction of the switching tube in the waveform valley bottom setting region of the voltage representation signal. The waveform bottom setting region of the voltage representation signal may be a waveform bottom position of the voltage representation signal, or may be a setting region near the waveform bottom position of the voltage representation signal.

In an embodiment of the present invention, as shown in fig. 4, the control chip 20 includes a current control circuit 21 and a valley conduction control circuit 22. An input terminal of the current control circuit 21 is coupled to the multiplexing pin SENSE, and an output terminal of the current control circuit 21 outputs the first control signal OCP. The current control circuit 21 includes a third switch S3 and a first comparison circuit 210, a first terminal of the third switch S3 is coupled to the multiplexing pin SENSE, a first input terminal of the first comparison circuit 210 is coupled to a second terminal of the third switch S3, a second input terminal of the first comparison circuit 210 is coupled to a first reference signal terminal to receive a first reference signal Vref, and the first comparison circuit 210 is configured to compare the current sampling signal and the first reference signal Vref, so as to output the first control signal OCP. An input terminal of the valley bottom conduction control circuit 22 is coupled to the multiplexing pin SENSE, and an output terminal of the valley bottom conduction control circuit 22 outputs a second control signal. The valley-bottom conduction control circuit 22 includes a first switch S1, a second switch S2, and a zero-crossing detection circuit. The zero-crossing detection circuit includes a follower 220 and a hysteresis comparator 221, wherein a non-inverting input terminal of the follower 220 is coupled to the second terminal of the first switch S1, and an inverting input terminal of the follower 220 is coupled to an output terminal of the follower 220. The non-inverting input terminal of the hysteresis comparator 221 is coupled to the reference voltage source to receive the reference voltage, and the inverting input terminal of the hysteresis comparator 221 is coupled to the output terminal of the follower 220. After the voltage characterization signal is processed by the follower 220 and the hysteresis comparator 221, zero-crossing detection is performed to obtain the wave form valley bottom position of the voltage characterization signal, so that the valley bottom conduction control circuit performs valley bottom conduction control on the switching tube Q1.

In another embodiment of the present invention, as shown in fig. 5, the control chip 30 includes a current control circuit (not shown), a valley-bottom conduction control circuit and an under-voltage input protection circuit. The valley-bottom conduction control circuit includes a first switch S1, a second switch S2, a follower 320, and a hysteresis comparator 321. The input terminal of the brown-out protection circuit is coupled to the output terminal of the follower 320, and the brown-out protection circuit includes a filter circuit and a second comparator circuit (not shown in the figure). The filter circuit comprises a sixth resistor R6 and a sixth capacitor C6, wherein a first end of the sixth resistor R6 is coupled to the output end of the follower 320, a first end of the sixth capacitor C6 is coupled to a second end of the sixth resistor R6, a second end of the sixth capacitor C6 is coupled to ground, and the filter circuit outputs a filter signal. The first input end of the second comparing circuit is coupled to the first end of the sixth capacitor C6, the second input end of the second comparing circuit is coupled to the second reference signal end to receive the second reference signal, the second comparing circuit outputs a third control signal according to the filtering signal and the second reference signal, and when the filtering signal is lower than the second reference signal, the control chip triggers the input under-voltage protection mechanism. As can be seen from fig. 2 and fig. 5, the terminal voltage of the first end of the first inductor Lm is a voltage Vin, the terminal voltage of the first end of the switching tube Q1 is a voltage Vdrain, and the terminal voltage of the second end of the first inductor Lm is also a voltage Vdrain. Namely, the voltages at the two ends of the first inductor Lm are the voltage Vin and the voltage Vdrain, respectively, and it can be known from the principle of the inductor volt-second balance that the average voltage of the voltage Vdrain is equal to the voltage Vin. The terminal voltage at the multiplexing pin SENSE is a voltage Vsense, and the voltage Vsense is in a proportional relation with the voltage Vdrain, so that the detection representation of the voltage Vin can be realized by a filtering signal obtained by filtering the voltage Vsense, and the input under-voltage protection control can be performed by the filtering signal.

In another embodiment of the invention, the control chip comprises a current control circuit, a valley bottom conduction control circuit and an output overvoltage protection circuit. The valley bottom conduction control circuit comprises a first switch, a second switch, a follower and a hysteresis comparator. The input end of the output overvoltage protection circuit is coupled with the output end of the follower, and the output overvoltage protection circuit comprises a third comparison circuit. The first input end of the third comparison circuit is coupled with the output end of the follower, the second input end of the third comparison circuit is coupled with the third reference signal end to receive a third reference signal, the third comparison circuit outputs a fourth control signal according to the output signal of the follower and the third reference signal, and when the output signal of the follower is larger than the third reference signal, the control chip triggers and outputs an overvoltage protection mechanism. When the driving signal of the switching tube Q1 is at a first level (e.g., high level), the switching tube Q1 is turned off, the first diode D1 is freewheeling, the voltage at the first end of the switching tube is the voltage Vdrain, which can represent the output voltage Vo, and the voltage Vsense is proportional to the voltage Vdrain, so that the output voltage Vo can be represented by a voltage representation signal (i.e., the voltage Vsense), which can be used to output the over-voltage protection control.

In an embodiment of the present invention, as shown in fig. 6, the switching power supply is a flyback switching power supply, and the flyback switching power supply includes a primary side circuit, a secondary side circuit, and a transformer winding. The transformer winding comprises a primary winding and a secondary winding, the primary circuit comprises a switch control circuit, the switch control circuit is used for controlling the on-off state of a switch tube in the primary circuit, and the output control of the flyback switching power supply is realized by controlling the on-off state of the switch tube through the switch control circuit. The switch control circuit comprises a control chip, the control chip is provided with multiplexing pins, the multiplexing pins can be respectively coupled with the first end of the switch tube and the second end of the switch tube, and the second end of the switch tube is coupled with the sampling resistor. In the first state, the switching tube is in a conducting state, and the control chip acquires a current sampling signal representing current flowing through the switching tube through the multiplexing pin; and in the second state, the switching tube is in a turn-off state, and the control chip acquires a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin. The current sampling signal can be obtained through the multiplexing pin, so that the output current of the flyback switching power supply is controlled according to the current sampling signal. In addition, a voltage representation signal can be obtained through the multiplexing pin, so that the switching tube is controlled to be in a conducting state in a waveform valley bottom setting area of the voltage representation signal according to the voltage representation signal. An embodiment of the invention discloses a switching power supply, which comprises the switching control circuit.

The embodiment of the invention also discloses a switch control method, which is used for controlling the switch control circuit in the switch power supply. The switch control circuit comprises a control chip, the control chip is provided with a multiplexing pin, and the multiplexing pin is used for being respectively coupled with a first end of the switch tube and a second end of the switch tube; the second end of the switch tube is coupled with the sampling resistor. The switch control method comprises the following steps:

under a first state, acquiring a current sampling signal representing current flowing through the switching tube through the multiplexing pin, and controlling the switching tube according to the current sampling signal; and

and in a second state, acquiring a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin, and controlling the switching tube to be conducted in a waveform valley bottom setting area of the voltage representation signal.

In an embodiment of the present invention, when the driving signal of the switching tube is at a first level (e.g., a high level), the driving signal is at a first state, the control chip obtains a current sampling signal through the multiplexing pin, the current sampling signal can represent a current flowing through the switching tube, a current control circuit in the control chip generates a first control signal according to the current sampling signal, and a driving signal generating circuit generates the driving signal according to the first control signal to control the switching state of the switching tube. The driving signal of the switching tube is in a second state when being in a second level (for example, a low level), the control chip acquires a voltage representation signal through the multiplexing pin, the voltage representation signal can represent the terminal voltage of the first end of the switching tube, the valley bottom conduction control circuit in the control chip generates a second control signal according to the voltage representation signal, and the driving signal generation circuit generates a driving signal according to the second control signal so as to control the switching state of the switching tube.

In an embodiment of the present invention, the switch control method further includes: and generating an input undervoltage protection signal according to the voltage characterization signal to protect the switch control circuit. In a specific embodiment, the input under-voltage protection circuit generates an input under-voltage protection signal according to the voltage characterization signal and the second reference signal to ensure that the switch control circuit works normally.

In an embodiment of the present invention, the switch control method further includes: and generating an output overvoltage protection signal according to the voltage characterization signal to protect the switch control circuit. In a specific embodiment, the output overvoltage protection circuit generates an output overvoltage protection signal according to the voltage characterization signal and the third reference signal to ensure that the switch control circuit works normally.

In an embodiment of the invention, in the second state, the voltage characterization signal is in a proportional relationship with the terminal voltage of the first terminal of the switching tube. The control chip controls the conduction of the switch tube in a wave form valley bottom setting area of the voltage representation signal.

The invention provides a switch control circuit, a switch control method and a switch power supply. The control chip is provided with a multiplexing pin which is used for being respectively coupled with the first end of the switch tube and the second end of the switch tube; the second end of the switch tube is coupled with the sampling resistor. In the first state, the control chip obtains a current sampling signal representing the current flowing through the switching tube through the multiplexing pin. And in a second state, the control chip acquires a voltage representation signal representing the terminal voltage of the first end of the switching tube through the multiplexing pin. The switch control circuit, the switch control method and the switch power supply provided by the invention can omit an auxiliary winding in the switch power supply, and adopt a pin multiplexing form, thereby simplifying the pin arrangement of a control chip and reducing the system cost. In addition, the control chip of the invention can realize at least two control functions of valley bottom conduction control, input undervoltage protection control and output overvoltage protection control on the same pin.

Those skilled in the art should understand that the logic controls such as "high" and "low", "set" and "reset", "and gate" and "or gate", "non-inverting input" and "inverting input" in the logic controls referred to in the specification or the drawings may be exchanged or changed, and the subsequent logic controls may be adjusted to achieve the same functions or purposes as the above-mentioned embodiments.

The description and applications of the invention herein are illustrative and are not intended to limit the scope of the invention to the embodiments described above. The descriptions related to the effects or advantages in the specification may not be reflected in practical experimental examples due to uncertainty of specific condition parameters or influence of other factors, and the descriptions related to the effects or advantages are not used for limiting the scope of the invention. Variations and modifications of the embodiments disclosed herein are possible, and alternative and equivalent various components of the embodiments will be apparent to those skilled in the art. It will be clear to those skilled in the art that the present invention may be embodied in other forms, structures, arrangements, proportions, and with other components, materials, and parts, without departing from the spirit or essential characteristics thereof. Other variations and modifications of the embodiments disclosed herein may be made without departing from the scope and spirit of the invention.