Switching converter and control circuit and control method thereof

Abstract

The invention discloses a switching converter and a control circuit and a control method thereof. The switching converter includes a pre-stage circuit that converts an AC input voltage into a first output voltage and a post-stage circuit that converts the first output voltage into a second output voltage. The control circuit includes: a voltage sampling circuit generating a voltage sampling signal, including a first sampling path coupled to receive a first voltage signal representative of an AC input voltage; the second sampling path is coupled to receive a second voltage signal, and a peak value of the second voltage signal represents the first output voltage; the first pin is coupled to the voltage sampling circuit to receive the voltage sampling signal; the discharge circuit receives the voltage sampling signal through a first pin and is used for carrying out discharge control on the safety capacitor; and the switch control circuit is used for receiving the voltage sampling signal through the first pin and generating a switch control signal to control a post-stage circuit. The switching converter can control the discharge of the safety capacitor, and ensures the normal operation of a post-stage circuit at the same time.

Description

Technical Field

[0001] Embodiments of the present invention relate to electronic circuits, and more particularly to switching converters and control circuits and methods thereof. Background Art

[0002] Figure 1 FIG. 1 shows a circuit diagram of an existing switching converter 100. Figure 1 As shown, the safety capacitor XCAP is coupled between the two input terminals of the switching converter 100. The rectifier bridge composed of diodes D1-D4 and capacitor C1 converts the AC input voltage Vac into a voltage VREC. The switching circuit 10 is coupled to the output terminal of the rectifier bridge and converts the voltage VREC into an output voltage Vout. The sampling circuit 20 composed of diodes D6-D7 and resistor R1 is coupled between the two input terminals of the switching converter 100 to detect the AC input voltage Vac and generate a sampling signal Vsam representing the AC input voltage Vac. The integrated circuit control device 30 receives the sampling signal Vsam through the pin HV, and controls the discharge of the safety capacitor XCAP and the operation of the switching circuit 10 according to the sampling signal Vsam.

[0003] In high-power applications, a switch circuit is usually added between the rectifier bridge and the switch circuit 10 to convert the voltage VREC into a higher voltage Vbus. The switch circuit 10 uses the voltage Vbus as an input voltage to generate an output voltage Vout to meet the load requirements. However, in this case, Figure 1 The sampling circuit 20 shown cannot detect the voltage Vbus, that is, the pin HV coupled to the output end of the sampling circuit 20 cannot detect the voltage Vbus, resulting in that some functions in the integrated circuit control device 30 cannot be implemented. For example, the integrated circuit control device 30 cannot generate a switch control signal according to the voltage Vbus to control the operation of the switch circuit 10. One solution is to add a Vbus sampling pin to the integrated circuit control device 30 and couple it to a Vbus sampling circuit to detect the voltage Vbus. However, this solution requires an additional pin, which will undoubtedly increase the cost and is not conducive to the further miniaturization of the integrated circuit control device 30. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention proposes a switching converter and a control circuit and a control method thereof, which can control the discharge of a safety capacitor and ensure the normal operation of a subsequent circuit.

[0005] According to an embodiment of the present invention, a control circuit for a switching converter is disclosed. The switching converter includes a front-stage circuit for converting an AC input voltage into a first output voltage and a rear-stage circuit for converting the first output voltage into a second output voltage. The control circuit includes: a voltage sampling circuit for generating a voltage sampling signal, including: a first sampling path having a first end and a second end, wherein the first end is coupled to receive a first voltage signal representing the AC input voltage; and a second sampling path having a first end and a second end, wherein the first end is coupled to receive a second voltage signal, and the second end is coupled together with the second end of the first sampling circuit to provide the voltage sampling signal, wherein the peak value of the second voltage signal represents the first output voltage; a first pin coupled to the second end of the first sampling path and the second end of the second sampling path; a discharge circuit for receiving the voltage sampling signal through the first pin, detecting whether a power supply is coupled to the switching converter based on the voltage sampling signal, and determining whether to discharge a safety capacitor coupled between the input ends of the switching converter based on the detection result; and a switch control circuit for receiving the voltage sampling signal through the first pin, and generating a switch control signal based on the voltage sampling signal to control the rear-stage circuit to generate the second output voltage.

[0006] According to another embodiment of the present invention, a switching converter is disclosed, which includes: a front-stage circuit, receiving an AC input voltage, and converting the AC input voltage into a first output voltage; a rear-stage circuit, receiving the first output voltage, and converting the first output voltage into a second output voltage; and the control circuit as described above.

[0007] According to another embodiment of the present invention, a control method for a switching converter is disclosed, wherein the switching converter includes a front-stage circuit that converts an AC input voltage into a first output voltage and a rear-stage circuit that converts the first output voltage into a second output voltage, and the control method includes: receiving a first voltage signal representing the AC input voltage; receiving a second voltage signal containing first output voltage information; generating a voltage sampling signal based on the first voltage signal or based on the second voltage signal; generating a switch control signal based on the voltage sampling signal to control the rear-stage circuit to generate the second output voltage; and detecting whether a power supply is coupled to the switching converter based on the voltage sampling signal, and determining whether to discharge the safety capacitor coupled between the input terminals of the switching converter based on the detection result.

[0008] According to an embodiment of the present invention, a voltage sampling circuit generates a voltage sampling signal based on a first voltage signal representing an AC input voltage and a second voltage signal containing first output voltage information. The control circuit can receive the voltage sampling signal through only one pin, and then perform discharge control of the safety capacitor according to the voltage sampling signal, and generate a switch control signal according to the voltage sampling signal to control the operation of the subsequent circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to better understand the present invention, the present invention will be described in detail according to the following drawings:

[0010] Figure 1 A circuit schematic diagram of an existing switching converter 100 is shown;

[0011] Figure 2 1 shows a circuit block diagram of a switching converter 200 according to an embodiment of the present invention;

[0012] Figure 3 FIG. 2 shows a circuit schematic diagram of a switching converter 200A according to another embodiment of the present invention;

[0013] Figures 4A to 4C It shows the working waveform diagram of the voltage sampling circuit 22A when the front-stage circuit 20A is in power operation according to an embodiment of the present invention;

[0014] Figures 5A-5B It shows a working waveform diagram of the voltage sampling circuit 22A when the front-stage circuit 20A is not in power operation according to another embodiment of the present invention;

[0015] Figure 6 FIG. 2 shows a circuit schematic diagram of a switching converter 200B according to another embodiment of the present invention;

[0016] Figure 7 The present invention shows an embodiment of Figure 3 The circuit schematic diagram of the detection circuit 231A shown;

[0017] Figure 8 shows a working waveform diagram of a detection circuit 231A according to an embodiment of the present invention;

[0018] Fig. 9 The present invention shows an embodiment of Figure 3 The circuit schematic diagram of the switch control circuit 24B shown;

[0019] Fig.10 A flow chart of a control method 1000 for a switching converter according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0020] The specific embodiments of the present invention will be described in detail below. It should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is obvious to those of ordinary skill in the art that these specific details do not have to be used to implement the present invention. In other examples, in order to avoid confusing the present invention, known circuits, materials or methods are not specifically described.

[0021] Throughout the specification, references to "one embodiment", "an embodiment", "an example" or "an example" mean that a particular feature, structure or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment", "in an embodiment", "an example" or "an example" that appear in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures or characteristics may be combined in one or more embodiments or examples in any appropriate combination and / or sub-combination. In addition, it should be understood by those of ordinary skill in the art that the diagrams provided herein are for illustrative purposes and that the diagrams are not necessarily drawn to scale. The same reference numerals indicate the same elements. It should be understood that when an "element" is said to be "connected to" or "coupled" to another element, it may be directly connected or coupled to another element or there may be an intermediate element. In contrast, when an element is said to be "directly connected to" or "directly coupled to" another element, there is no intermediate element. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0022] Throughout the specification, relative terms such as first and second, etc. may be used only to distinguish one entity or action from another entity or action, and do not necessarily or imply the existence of such an order between these entities or actions. Numerical sequences such as "first", "second", "third", etc. refer only to different individuals in a plurality and do not imply any order or sequence unless specifically defined in the claim language. The order of the text in any claim does not mean that the processing steps must be performed in such order or logical order unless specifically specified in the claim language. Without departing from the scope of the present invention, these processing steps can be interchanged in any order, as long as such interchange does not cause the claim language to contradict and does not appear logically absurd.

[0023] Figure 2 FIG. 2 shows a circuit block diagram of a switching converter 200 according to an embodiment of the present invention. Figure 2As shown, the switching converter 200 includes a safety capacitor XCAP, a front-stage circuit 20, a rear-stage circuit 21 and a control circuit. The switching converter 200 has two input terminals for coupling to a power supply. The safety capacitor XCAP is coupled between the input terminals of the switching converter 200. In one embodiment, the safety capacitor XCAP includes one or more capacitors. The front-stage circuit 20 is coupled between the input terminals of the switching converter 200 to receive an AC input voltage Vac. The front-stage circuit 20 includes a switch tube, and the AC input voltage Vac is converted into a first output voltage Vout1 by turning the switch tube on and off. The rear-stage circuit 21 is coupled to the output terminal of the front-stage circuit 20 to receive the first output voltage Vout1, and converts the first output voltage Vout1 into a second output voltage Vout2 to drive a load.

[0024] The control circuit includes a voltage sampling circuit 22, a discharge circuit 23 and a switch control circuit 24. The voltage sampling circuit 22 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives a first voltage signal V1 representing an AC input voltage Vac, and the second input terminal receives a second voltage signal V2 containing information of a first output voltage Vout1. Based on the first voltage signal V1 or the second voltage signal V2, the voltage sampling circuit 22 generates a voltage sampling signal Vsam at the output terminal. In one embodiment, the first voltage signal V1 represents a half-cycle signal of the AC input voltage Vac, and the peak value of the second voltage signal V2 represents the first output voltage Vout1. In one embodiment, the second voltage signal V2 is the voltage across the switch tube of the front-stage circuit 20.

[0025] exist Figure 2 In the illustrated embodiment, the voltage sampling circuit 22 includes a first sampling path 22-1 and a second sampling path 22-2. The first sampling path 22-1 has a first end and a second end, wherein the first end is coupled to the input end of the switching converter 200 to receive the first voltage signal V1. The second sampling path 22-2 has a first end and a second end, wherein the first end is coupled to the pre-stage circuit 20 to receive the second voltage signal V2. The second end of the first sampling path 22-1 and the second end of the second sampling path 22-2 are coupled together to provide a voltage sampling signal Vsam.

[0026] In one embodiment, according to the difference between the difference between the second voltage signal V2 and the first voltage signal V1 and a threshold voltage Vth, the voltage sampling circuit 22 generates the voltage sampling signal Vsam based on the second voltage signal V2 or based on the first voltage signal V1. In a further embodiment, when the difference between the second voltage signal V2 and the first voltage signal V1 is greater than the threshold voltage Vth, the second sampling path 22-2 is turned on, and the voltage sampling circuit 22 generates the voltage sampling signal Vsam based on the second voltage signal V2; when the difference between the second voltage signal V2 and the first voltage signal V1 is less than the threshold voltage Vth, the first sampling path 22-1 is turned on, and the voltage sampling circuit 22 generates the voltage sampling signal Vsam based on the first voltage signal V1.

[0027] exist Figure 2 In the embodiment shown, the discharge circuit 23 and the switch control circuit 24 are integrated into the integrated circuit control device IC1. The integrated circuit control device IC1 has a plurality of pins. The plurality of pins include a pin HV coupled to the output end of the voltage sampling circuit 22 to receive the voltage sampling signal Vsam and a pin DRV providing the switch control signal CTRL. In one embodiment, the voltage sampling circuit 22 and the integrated circuit control device IC1 are packaged in the same module.

[0028] The discharge circuit 23 receives the voltage sampling signal Vsam through the pin HV, and detects whether the power source is coupled to the switching converter 200 according to the voltage sampling signal Vsam. When it is detected that the power source is not coupled to the switching converter 200, the discharge circuit 23 controls the safety capacitor XCAP to discharge.

[0029] In one embodiment, when the power supply is coupled to the switching converter 200, the voltage sampling signal Vsam is a pulsating voltage. When the power supply is not coupled to the switching converter 200, the voltage sampling signal Vsam is substantially unchanged. The discharge circuit 23 can determine whether the power supply is coupled to the switching converter 200 by detecting whether the voltage sampling signal Vsam is a pulsating voltage or substantially unchanged, and then decide whether to discharge the safety capacitor XCAP.

[0030] The switch control circuit 24 receives the voltage sampling signal Vsam through the pin HV, and generates a switch control signal CTRL according to the voltage sampling signal Vsam to control the operation of the subsequent circuit 21 .

[0031] In one embodiment, the switch control circuit 24 samples and holds the peak value of the power sampling signal Vsam, and generates a switch control signal CTRL based on the sample and hold result to control the subsequent circuit 21 .

[0032] Figure 3FIG. 2 shows a circuit schematic diagram of a switching converter 200A according to another embodiment of the present invention. The switching converter 200A includes a safety capacitor XCAP, a front-stage circuit 20A, a rear-stage circuit 21A and a control circuit. Figure 3 As shown, the safety capacitor XCAP is coupled between the first node T1 and the second node T2. The front-stage circuit 20A includes a rectifier bridge and a BOOST circuit, wherein the rectifier bridge includes diodes D1-D4, and the BOOST circuit includes an inductor L1, a switch tube M1, a diode D5 and a capacitor C1, and the connection relationship thereof is as shown in FIG. Figure 3 As shown. The front stage circuit 20A is coupled to the first node T1 and the second node T2 to receive the AC input voltage Vac, and convert the AC input voltage Vac into a first output voltage Vout1. In one embodiment, the front stage circuit 20A also includes a capacitor C2 coupled between the output end of the rectifier bridge and the reference ground GND1, which is used to prevent the parasitic capacitance of the rectifier bridge and the inductor L1 from oscillating. The rear stage circuit 21A adopts a Flyback topology structure, including a transformer Tr, a switch tube M2, a diode D6 and a capacitor C3, and the connection relationship thereof is as shown. Figure 3 The rear stage circuit 21A is coupled to the front stage circuit 20A to receive the first output voltage Vout1 and convert the first output voltage Vout1 into a second output voltage Vout2.

[0033] The control circuit includes a voltage sampling circuit 22A, a discharge circuit 23A and a switch control circuit 24A. Figure 3 In the illustrated embodiment, the discharge circuit 23A and the switch control circuit 24A are integrated into the integrated circuit control device IC1A, wherein the integrated circuit control device IC1A has a pin HV.

[0034] The voltage sampling circuit 22A includes a first sampling path 22-1A and a second sampling path 22-2A, wherein the first sampling path 22-1A has a first end coupled to the first node T1 and a second end coupled to the pin HV, and is configured to detect the AC input voltage Vac. The second sampling path 22-2A has a first end coupled to the switch tube M1 and a second end coupled to the pin HV, and is configured to detect the first output voltage Vout1.

[0035] exist Figure 3 In the illustrated embodiment, the first sampling path 22-1A includes a first unidirectional device D7. The input end of the first unidirectional device D7 is coupled to the first node T1, and the output end of the first unidirectional device D7 is coupled to the pin HV. In one embodiment, the first sampling path 22-1A further includes a resistor R1 coupled between the output end of the first unidirectional device D7 and the pin HV.

[0036] The second sampling path 22-2A includes a second unidirectional device D8 and a varistor VDR connected in series. The input end of the second unidirectional device D8 is coupled to the common connection point of the inductor L1 and the switch tube M1. The first end of the varistor VDR is coupled to the output end of the second unidirectional device D8, and the second end of the varistor VDR is coupled to the pin HV. In one embodiment, the first unidirectional device D7 and the second unidirectional device D8 both include diodes.

[0037] When the difference between the second voltage signal V2 and the first voltage signal V1 is greater than the threshold voltage Vth, the second sampling path 22-2A is turned on, for example, the varistor VDR and the second unidirectional device D8 are both turned on, and the voltage sampling circuit 22A generates a voltage sampling signal Vsam based on the second voltage signal V2. When the difference between the second voltage signal V2 and the first voltage signal V1 is less than the threshold voltage Vth, the varistor VDR is open, the first sampling path 22-1A is turned on, for example, the first unidirectional device D7 is turned on, and the voltage sampling circuit 22A generates a voltage sampling signal Vsam based on the first voltage signal V1.

[0038] In one embodiment, the power supply is coupled to the switching converter 200A, and the front stage circuit 20A performs power operation. At this time, the change frequency of the first voltage signal V1 is equal to the frequency f1 of the AC input voltage Vac, the change frequency of the second voltage signal V2 is equal to the switching frequency fs of the front stage circuit 20A, that is, the switching frequency of the switch tube M1, and the change frequency of the voltage sampling signal Vsam is also equal to the switching frequency fs. At this time, the waveforms of each signal are as follows: Figures 4A to 4C shown. Figure 4A Schematic waveform diagram of the AC input voltage Vac, the first voltage signal V1, the second voltage signal V2 and the voltage sampling signal Vsam. Figure 4B and 4C It is the experimental waveform diagram of the AC input voltage Vac and the voltage sampling signal Vsam, where Figure 4C Yes Figure 4B The waveform diagram is a magnified view of area 41 in FIG.

[0039] In another embodiment, the power supply is coupled to the switching converter 200A, and the front stage circuit 20A is not in power operation. At this time, the change frequency of the first voltage signal V1 is equal to the frequency f1 of the AC input voltage Vac, the second voltage signal V2 is substantially unchanged, and the change frequency of the voltage sampling signal Vsam is equal to the frequency f1 of the AC input voltage Vac. At this time, the waveforms of the various signals are as follows: Figures 5A-5B shown. Figure 5A Schematic waveform diagram of the AC input voltage Vac, the first voltage signal V1, the second voltage signal V2 and the voltage sampling signal Vsam. Figure 5B It is the experimental waveform diagram of the AC input voltage Vac and the voltage sampling signal Vsam.

[0040] In yet another embodiment, the power source is not coupled to the switching converter 200A. In this case, the first voltage signal V1 and the second voltage signal V2 are substantially unchanged, and the voltage sampling signal Vsam is also substantially unchanged.

[0041] According to the embodiment of the present invention, regardless of whether the front-stage circuit 20A is in power operation, the discharge circuit 23A can receive the voltage sampling signal Vsam through the pin HV, and detect whether the power supply is coupled to the switching converter 200A according to the voltage sampling signal Vsam, thereby performing discharge control of the safety capacitor XCAP. At the same time, the peak value of the voltage sampling signal Vsam represents the first output voltage Vout1, so the switch control circuit 24A can receive the voltage sampling signal Vsam through the same pin HV to obtain information about the first output voltage Vout1, and generate a voltage control signal CTRL to control the rear-stage circuit 21A. In other words, according to the embodiment of the present invention, there is no need to add an additional pin to detect the first output voltage Vout1, thereby reducing the cost and the size of the integrated circuit control device IC1A.

[0042] continue Figure 3 In the description, Figure 3 In the illustrated embodiment, the integrated circuit control device IC1A further includes a pin VCC, a pin DRV, and a pin CS. A power supply capacitor C4 is coupled to the pin VCC to generate a power supply voltage Vcc to power the circuits within the integrated circuit control device IC1A. The pin DRV provides a switch control signal CTRL to control the subsequent circuit 21A. The pin CS is coupled to the subsequent circuit 21A to receive a current detection signal Vcs representing the current flowing through the subsequent circuit 21A. Figure 3 In the illustrated embodiment, the integrated circuit control device IC1A further includes a resistor R2 coupled between the pin HV and the reference ground GND1 .

[0043] The discharge circuit 23A includes a detection circuit 231 and a current source IS. The detection circuit 231 receives a voltage sampling signal Vsam through a pin HV, detects whether the power supply is coupled to the switching converter 200A based on the voltage sampling signal Vsam, and generates an identification signal FLAG. When the identification signal FLAG indicates that the power supply is not coupled to the switching converter 200A, the discharge circuit 23A turns on the current source IS to provide the energy in the safety capacitor XCAP to the power supply capacitor C4 through the current source IS.

[0044] The discharge circuit 23A further includes a first comparison circuit 232, a switch S1 and a third unidirectional device D9. The first comparison circuit 232 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives a power supply voltage Vcc, the second input terminal receives a first threshold voltage Vth1, the first comparison circuit 232 compares the power supply voltage Vcc with the first threshold voltage Vth1, and generates a first comparison signal CA1 at the output terminal. The switch S1 has a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to a current source IS, the second terminal is coupled to a reference ground GND1, and the control terminal receives the first comparison signal CA1. When the power supply voltage Vcc is greater than the first threshold voltage Vth1, the switch S1 is turned on, thereby discharging the safety capacitor XCAP to the ground. The input terminal of the third unidirectional device D9 is coupled to the current source, and the output terminal is coupled to the power supply capacitor C4, for preventing the power supply capacitor C4 from being discharged through the switch S1. In one embodiment, the first comparison circuit 232 includes a comparator CMP1, and the third unidirectional device D9 includes a diode.

[0045] The switch control circuit 24A receives the voltage sampling signal Vsam through the pin HV, and generates a switch control signal CTRL based on the voltage sampling signal Vsam and the current detection signal Vcs to control the subsequent circuit 21A. Figure 3 In the illustrated embodiment, a resistor Rcs is coupled to the switch tube M2 for providing a current detection signal Vcs, wherein the current detection signal Vcs represents the current flowing through the switch tube M2.

[0046] Figure 6 FIG. 2 shows a circuit schematic diagram of a switching converter 200B according to yet another embodiment of the present invention. Figure 6 The switching converter 200B shown is Figure 3 The switching converter 200A shown is similar except that Figure 6 The first sampling path 22-1B of the voltage sampling circuit 22B shown in the figure also includes a third terminal coupled to the second node T2 and a fourth unidirectional device D10, and the first sampling path 221B is configured to detect the AC input voltage Vac. The input terminal of the fourth unidirectional device D10 is coupled to the second node T2, and the output terminal of the fourth unidirectional device D10 is coupled to the pin HV. In one embodiment, the fourth unidirectional device D10 includes a diode.

[0047] Although the front-stage circuit in the above embodiment is described by taking the BOOST circuit as an example and the rear-stage circuit is described by taking the Flyback topology as an example, those skilled in the art will understand that these embodiments are only for illustration and are not used to limit the present invention, and other suitable circuit structures also meet the spirit and protection scope of the present invention. The voltage sampling circuit may also adopt other suitable circuit structures as long as the corresponding functions can be achieved. In addition, the switch tubes M1 and M2 of the switching converter may be any controllable semiconductor switching devices, such as BJT, JFET, MOSFET, IGBT or GaNFET, etc.

[0048] Figure 7 2 is a circuit diagram of a detection circuit 231A according to an embodiment of the present invention. The detection circuit 231A includes a second comparison circuit 233, a one-shot circuit 234, a timing circuit 235, a third comparison circuit 236, an OR gate circuit 237 and a logic circuit 238.

[0049] The second comparison circuit 233 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the voltage sampling signal Vsam, the second input terminal receives the second threshold voltage Vth2, the second comparison circuit 233 compares the voltage sampling signal Vsam with the second threshold voltage Vth2, and generates a second comparison signal CA2 at the output terminal. In one embodiment, the second comparison circuit 232 includes a comparator CMP2.

[0050] The one-shot circuit 234 has an input terminal and an output terminal, wherein the input terminal receives the second comparison signal CA2, and based on the second comparison signal CA2, the one-shot circuit 234 generates a trigger signal Trig. In one embodiment, when the voltage sampling signal Vsam changes from being lower than the second threshold voltage Vth2 to being higher than the second threshold voltage Vth2, the one-shot circuit 234 is triggered and generates a short pulse as the trigger signal Trig.

[0051] The timing circuit 235 has an input terminal and an output terminal, wherein the input terminal receives a trigger signal Trig. The timing circuit 235 generates a timeout signal OT at the output terminal based on the trigger signal Trig and a time threshold Tth. In one embodiment, when the timing time of the timing circuit 235 reaches the time threshold Tth, the timeout signal OT changes from a low level to a high level. When the trigger signal Trig comes, the timing circuit 235 is reset.

[0052] The third comparison circuit 236 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the voltage sampling signal Vsam, the second input terminal receives the third threshold voltage Vth3, the third comparison circuit 236 compares the voltage sampling signal Vsam with the third threshold voltage Vth3, and generates a third comparison signal CA3 at the output terminal. In one embodiment, the third comparison circuit 236 includes a comparator CMP3.

[0053] The OR gate circuit 237 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the trigger signal Trig, the second input terminal receives the third comparison signal CA3, and the OR gate circuit 237 performs a logic OR operation on the trigger signal Trig and the third comparison signal CA3 to generate an OR signal OR1 at the output terminal.

[0054] The logic circuit 238 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the timeout signal OT, the second input terminal receives the OR signal OR1, and based on the OR signal OR1 and the timeout signal OT, the output terminal of the logic circuit 238 provides the identification signal FLAG. In one embodiment, the logic circuit 238 includes an RS flip-flop FF1.

[0055] In one embodiment, Figure 7 The detection circuit 231A compares the voltage sampling signal Vsam with a plurality of threshold voltages and provides a plurality of comparison results to the one-shot circuit 234. The one-shot circuit 234 generates a short pulse to reset the timing circuit 235 and the reset logic circuit 238 according to the plurality of comparison results.

[0056] Figure 8 According to an embodiment of the present invention Figure 7 The working waveform diagram of the detection circuit 231A is shown below. Figure 8 To illustrate the working principle of the detection circuit 231A. Figure 8 As shown, before time t1, the power supply is coupled to the switching converter 200, and the voltage sampling signal Vsam is a changing value. The voltage sampling signal Vsam changes from lower than the second threshold voltage Vth2 to higher than the second threshold voltage Vth2 before the timing time of the timing circuit 235 reaches the time threshold Tth, and the second comparison signal CA2 changes from a low level to a high level. The one-shot circuit 234 generates a short pulse under the triggering of the rising edge of the second comparison signal CA2 to reset the timing circuit 235 and the reset logic circuit 238. Before time t1, the timeout signal OT and the identification signal FLAG both maintain a low level.

[0057] At time t1, the switching converter 200 is disconnected from the power supply. Due to the presence of the safety capacitor XCAP, the AC input voltage Vac remains unchanged, and the voltage sampling signal Vsam also remains unchanged. At time t2, the timing time of the timing circuit 235 reaches the time threshold Tth, the timeout signal OT changes from a low level to a high level, the logic circuit 238 is set, and the identification signal FLAG changes from a low level to a high level, indicating that the power supply is not coupled to the switching converter 200. Thereafter, the capacitor XCAP is discharged, the AC input voltage Vac gradually decreases, and the voltage sampling signal Vsam also gradually decreases.

[0058] At time t3, the AC input voltage Vac decreases to the safety threshold voltage, the voltage sampling signal Vsam decreases to the third threshold voltage Vth3, the third comparison signal CA3 changes from low level to high level, the logic circuit 238 is reset, and the identification signal FLAG changes from high level to low level.

[0059] In one embodiment, during the time period t2-t3, if the power source is recoupled to the switching converter 200, when the voltage sampling signal Vsam changes from lower than the second threshold voltage Vth2 to higher than the second threshold voltage Vth2, the second comparison signal CA2 changes from a low level to a high level, the one-shot circuit 234 is triggered, the logic circuit 238 is reset, and the identification signal FLAG changes from a high level to a low level, indicating that the power source is coupled to the switching converter 200. At the same time, the timing circuit 235 is reset, and the timeout signal OT also changes from a high level to a low level.

[0060] In one embodiment, at time t2, the identification signal FLAG indicates that the power supply is not coupled to the switching converter 200, and the safety capacitor XCAP is discharged for a first time period. After the first time period, the safety capacitor XCAP stops discharging, and the detection circuit 231 detects whether the power supply is recoupled to the switching converter 200. If the power supply is not coupled to the switching converter 200, the safety capacitor XCAP is discharged for the first time period again. Thereafter, the discharge is stopped again, and it is detected whether the power supply is recoupled to the switching converter 200. The above steps are repeated until the AC input voltage Vac is reduced to the safety threshold voltage.

[0061] Fig. 9 According to an embodiment of the present invention Figure 2 The switch control circuit 24B includes a sampling and holding circuit 241 , a compensation circuit 242 , a fourth comparison circuit 243 , a modulation signal generation circuit 244 , an error amplifier circuit 245 , a fifth comparison circuit 246 and a logic circuit 247 .

[0062] The sample-and-hold circuit 241 receives the voltage sampling signal Vsam, and samples and holds the peak value of the voltage sampling signal Vsam to generate a sample-and-hold signal Vpk, wherein the sample-and-hold signal Vpk represents the first output voltage Vout1 .

[0063] The compensation circuit 242 receives the sample-and-hold signal Vpk and generates a compensation signal based on the sample-and-hold signal Vpk. Fig. 9 In the illustrated embodiment, the compensation circuit 242 includes a current source IS1 that provides a current proportional to the sample-and-hold signal Vpk. The current flows through a resistor Rcs1 coupled to the pin CS to generate a compensation signal.

[0064] The fourth comparison circuit 243 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the superimposed signal Vad of the current detection signal Vcs and the compensation signal, and the second input terminal receives the fourth threshold voltage Vth4. The fourth comparison circuit 243 compares the superimposed signal Vad with the fourth threshold voltage Vth4, and generates a fourth comparison signal CA4 at the output terminal to control the turn-off of the switch tube M2. In one embodiment, the fourth comparison circuit 243 includes a comparator CMP4.

[0065] The modulation signal generating circuit 244 generates a modulation signal VM, and the modulation signal VM may be a sawtooth wave signal, a triangle wave signal, or other suitable signals.

[0066] The error amplifier circuit 245 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives a feedback voltage signal VFB representing the second output signal Vout2, and the second input terminal receives a reference voltage signal VREF. Based on the difference between the reference voltage signal VREF and the feedback voltage signal VFB, the error amplifier circuit 245 generates an error amplified signal VCOMP at the output terminal.

[0067] The fifth comparison circuit 246 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the modulation signal VM, the second input terminal receives the error amplification signal VCOMP, the fifth comparison circuit 246 compares the modulation signal VM with the error amplification signal VCOMP, and generates a pulse frequency modulation signal PFM at the output terminal to control the conduction of the switch tube M2. In one embodiment, the fifth comparison circuit 246 includes a comparator CMP5.

[0068] The logic circuit 247 has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the fourth comparison signal CA4, and the second input terminal receives the pulse frequency modulation signal PFM. Based on the fourth comparison signal CA4 and the pulse frequency modulation signal PFM, the logic circuit 247 generates a switch control signal CTRL to control the switch tube M2. In one embodiment, the logic circuit 247 includes an RS flip-flop FF2.

[0069] Those skilled in the art will understand that Fig. 9 The switch control circuit 24B shown is for illustration only and is not intended to limit the present invention. Other suitable switch control circuits can also meet the spirit and protection scope of the present invention.

[0070] Fig.10 1 is a flow chart of a control method 1000 for a switching converter according to an embodiment of the present invention. The switching converter includes a front-stage circuit for converting an AC input voltage Vac into a first output voltage Vout1 and a rear-stage circuit for converting the first output voltage Vout1 into a second output voltage Vout2. The switching converter 200 also includes a pin HV. The control method 1000 includes steps S101 to S106.

[0071] In step S101 , a first voltage signal V1 representing an AC input voltage Vac is received.

[0072] In step S102 , a second voltage signal V2 including information of the first output voltage Vout1 is received.

[0073] In step S103, a voltage sampling signal Vsam is generated based on the first voltage signal V1 or the second voltage signal V2. In one embodiment, according to the magnitude relationship between the first voltage signal V1 and the second voltage signal V2, the voltage sampling signal Vsam is generated based on the first voltage signal V1 or the second voltage signal V2. In a further embodiment, it is determined whether the difference between the second voltage signal V2 and the first voltage signal V1 is greater than the threshold voltage Vth. If so, the voltage sampling signal Vsam is generated based on the second voltage signal V2; if not, the voltage sampling signal Vsam is generated based on the first voltage signal V1.

[0074] In step S104 , the voltage sampling signal Vsam is received through the pin HV, and a switch control signal CTRL is generated based on the voltage sampling signal Vsam to control the subsequent circuit to generate the second output voltage Vout2 .

[0075] In step S105, a voltage sampling signal Vsam is received through the pin HV, and based on the voltage sampling signal Vsam, it is detected whether the power supply is coupled to the switching converter, and based on the detection result, it is determined whether to discharge the safety capacitor XCAP coupled between the input terminals of the switching converter. In one embodiment, when it is detected that the power supply is not coupled to the switching converter, the safety capacitor XCAP is discharged through a current source.

[0076] Note that in the flowcharts described above, the functions marked in the boxes can also be different from Fig.10For example, two blocks shown in succession may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the specific functionality involved.

[0077] Although the present invention has been described with reference to several typical embodiments, it should be understood that the terms used are illustrative and exemplary, rather than restrictive. Since the present invention can be embodied in a variety of forms without departing from the spirit or essence of the invention, it should be understood that the above embodiments are not limited to any of the foregoing details, but should be interpreted broadly within the spirit and scope defined by the appended claims, so all changes and modifications falling within the scope of the claims or their equivalents should be covered by the appended claims.

Claims

1. A control circuit for a switching converter, the switching converter comprising a front-stage circuit for converting an AC input voltage into a first output voltage and a rear-stage circuit for converting the first output voltage into a second output voltage, the control circuit comprising: The voltage sampling circuit generates a voltage sampling signal, including: A first sampling path having a first terminal and a second terminal, wherein the first terminal is coupled to receive a first voltage signal representing an AC input voltage; and A second sampling path having a first end and a second end, wherein the first end is coupled to receive a second voltage signal, and the second end is coupled to the second end of the first sampling circuit to provide the voltage sampling signal, wherein a peak value of the second voltage signal represents the first output voltage; A first pin coupled to a second end of the first sampling path and a second end of the second sampling path; a discharge circuit, receiving a voltage sampling signal through a first pin, detecting whether a power source is coupled to a switching converter based on the voltage sampling signal, and determining whether to discharge a safety capacitor coupled between input terminals of the switching converter based on the detection result; and The switch control circuit receives the voltage sampling signal through the first pin, and generates a switch control signal based on the voltage sampling signal to control the subsequent circuit to generate the second output voltage.

2. The control circuit according to claim 1, wherein: According to the magnitude relationship between the difference between the second voltage signal and the first voltage signal and a threshold voltage, the voltage sampling circuit selects to generate the voltage sampling signal based on the first voltage signal or based on the second voltage signal.

3. The control circuit as claimed in claim 2, wherein: When the difference between the second voltage signal and the first voltage signal is less than the threshold voltage, the first sampling path is turned on, and the voltage sampling circuit generates a voltage sampling signal based on the first voltage signal; as well as When the difference between the second voltage signal and the first voltage signal is greater than the threshold voltage, the second sampling path is turned on, and the voltage sampling circuit generates a voltage sampling signal based on the second voltage signal.

4. The control circuit of claim 1 , wherein the first sampling path comprises: The first unidirectional device has an input terminal and an output terminal, wherein the input terminal receives the first voltage signal, and the output terminal is coupled to the first pin.

5. The control circuit of claim 1 , wherein the second sampling path comprises: A second unidirectional device having an input terminal and an output terminal, wherein the input terminal receives the second voltage signal; as well as The varistor has a first end and a second end, wherein the first end is coupled to the output end of the second unidirectional device, and the second end is coupled to the first pin.

6. The control circuit of claim 1, wherein the discharge circuit comprises: A detection circuit detects whether the power supply is coupled to the switching converter based on the voltage sampling signal and generates an identification signal; as well as A current source is coupled between the safety capacitor and a power supply capacitor; in When the identification signal indicates that the power source is not coupled to the switching converter, the energy in the safety capacitor is provided to the power supply capacitor through the current source.

7. The control circuit as claimed in claim 6, wherein the discharge circuit further comprises: A first switch having a first terminal, a second terminal and a control terminal, wherein the first terminal is coupled to the current source and the second terminal is grounded; A first comparison circuit has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives the voltage across the power supply capacitor, the second input terminal receives the first threshold voltage, the first comparison circuit compares the voltage across the power supply capacitor with the first threshold voltage, generates a first comparison signal at the output terminal and provides it to the control terminal of the first switch; as well as a third unidirectional device having an input terminal and an output terminal, wherein the input terminal is coupled to the current source and the output terminal is coupled to the power supply capacitor; in When the voltage across the power supply capacitor is greater than a first threshold voltage, the first switch is turned on to release the energy in the safety capacitor to the ground.

8. The control circuit of claim 6, wherein the detection circuit comprises: A second comparison circuit has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives a voltage sampling signal, the second input terminal receives a second threshold voltage, the second comparison circuit compares the voltage sampling signal with the second threshold voltage, and generates a second comparison signal at the output terminal; A one-shot circuit has an input terminal and an output terminal, wherein the input terminal receives a second comparison signal, and based on the second comparison signal, the one-shot circuit generates a trigger signal at the output terminal; A timing circuit having an input terminal and an output terminal, wherein the input terminal receives a trigger signal, and based on the trigger signal and a time threshold, the timing circuit generates a timeout signal at its output terminal; A third comparison circuit has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives a voltage sampling signal, the second input terminal receives a third threshold voltage, the third comparison circuit compares the voltage sampling signal with the third threshold voltage, and generates a third comparison signal at the output terminal; An OR gate circuit has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives a trigger signal, the second input terminal receives a third comparison signal, and based on the trigger signal and the second comparison signal, the OR gate circuit generates an OR signal at the output terminal; as well as The logic circuit has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives an OR signal, the second input terminal receives a timeout signal, and based on the OR signal and the timeout signal, the logic circuit generates an identification signal at the output terminal.

9. The control circuit of claim 1, wherein the switch control circuit comprises: A sampling and holding circuit has an input end and an output end, wherein the input end receives a voltage sampling signal, the sampling and holding circuit samples and holds the peak value of the voltage sampling signal, and generates a sampling and holding signal at the output end; A compensation circuit generates a compensation signal based on the sample-and-hold signal; as well as The fourth comparison circuit has a first input terminal, a second input terminal and an output terminal, wherein the first input terminal receives a superimposed signal of a current detection signal representing a current flowing through a subsequent circuit and the compensation signal, and the second input terminal receives a fourth threshold voltage. The fourth comparison circuit compares the superimposed signal with the fourth threshold voltage and generates a fourth comparison signal at the output terminal to control the shutdown of the switch tube of the subsequent circuit.

10. A switching converter, comprising: The front stage circuit receives an AC input voltage and converts the AC input voltage into a first output voltage; a subsequent circuit, receiving the first output voltage and converting the first output voltage into a second output voltage; and A control circuit as claimed in any one of claims 1 to 9.

11. A control method for a switching converter, wherein the switching converter comprises a front-stage circuit for converting an AC input voltage into a first output voltage and a rear-stage circuit for converting the first output voltage into a second output voltage, the control method comprising: receiving a first voltage signal representing an AC input voltage; receiving a second voltage signal including first output voltage information; generating a voltage sampling signal based on the first voltage signal or based on the second voltage signal; Receiving a voltage sampling signal through the first pin, and generating a switch control signal based on the voltage sampling signal to control the subsequent circuit to generate the second output voltage; as well as A voltage sampling signal is received through the first pin, whether the power source is coupled to the switch converter is detected based on the voltage sampling signal, and whether the safety capacitor coupled between the input terminals of the switch converter is discharged is determined based on the detection result.

12. The control method according to claim 11, wherein When the difference between the second voltage signal and the first voltage signal is less than the threshold voltage, generating a voltage sampling signal based on the first voltage signal; and When the difference between the second voltage signal and the first voltage signal is greater than the threshold voltage, a voltage sampling signal is generated based on the second voltage signal.

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