PFC circuit and air conditioning equipment

Abstract

Embodiments of the present application disclose a PFC circuit and an air conditioner. The PFC overcurrent protection circuit in the PFC circuit includes a sampling circuit, a control circuit, and an enabling switch circuit. The control circuit and the enabling switch circuit: one end of a first resistor is connected to the sampling circuit, the other end of the first resistor is connected to the control end of a first switching tube, the other end of a second resistor is connected to the first end of the first switching tube, one end of the second resistor is connected to the output end of a first power supply, and the second end of the first switching tube is grounded; one end of a third resistor is connected to the control end of the second switching tube, the other end of the third resistor is connected to the first end of the first switching tube, one end of a fourth resistor is connected to the output end of the second power supply, the other end of the fourth resistor is connected to the first end of the second switching tube and one end of a fifth resistor, and the second end of the second switching tube is connected to the other end of the fifth resistor and grounded. This can provide effective overcurrent protection while meeting the requirements of simple circuits and low cost in practical applications.

Description

Technical Field

[0001] The present application relates to the field of circuit technology, and in particular to a PFC circuit and air-conditioning equipment. Background Art

[0002] A power factor correction (PFC) circuit primarily controls the input voltage and current to be in phase, thereby correcting the power utilization of the electrical device in which the PFC circuit is located, effectively achieving power factor correction for the device. Traditional PFC circuits lack the flexibility to adjust the output voltage, making them unsuitable for a variety of applications. Therefore, a microcontroller unit (MCU) or digital signal processor (DSP) is incorporated into the PFC circuit. The MCU or DSP outputs a pulse width modulation (PWM) signal, which is then transmitted via a driver chip to the field-effect transistors (MOSFETs) or insulated gate bipolar transistors (IGBTs) in the PFC circuit, thereby regulating the output voltage. However, MCUs are prone to malfunctions such as system crashes and program errors, which can cause erroneous PWM signals, resulting in overcurrent in the PFC circuit and damage to the device in which the PFC circuit is located.

[0003] In the prior art, the PFC circuit implements overcurrent protection of the PFC circuit through a comparator. Figure 1 The figure shows an example schematic diagram of a PFC circuit in the prior art. A sampling resistor Rs samples the current signal in the current loop of the Boost PFC circuit. This current signal is transmitted to an operational amplifier U01, causing the operational amplifier U01 to output a voltage signal corresponding to the current signal. A comparator U02 receives this voltage signal and, based on it, determines whether an overcurrent condition exists in the Boost PFC circuit. When an overcurrent condition occurs in the Boost PFC circuit, the comparator U02 outputs a shutdown enable signal to disable the driver chip U03, thereby providing overcurrent protection for the PFC circuit. However, the comparator circuit (including internal and peripheral circuits) is complex and costly, making the PFC circuit unable to meet the requirements of simple and low-cost circuits in practical applications. Summary of the Invention

[0004] The present invention provides a PFC circuit that can effectively provide overcurrent protection while meeting the requirements of a simple and low-cost PFC circuit in practical applications. The technical solution is as follows:

[0005] The PFC circuit includes a digitally controlled Boost PFC circuit and a PFC overcurrent protection circuit. The digitally controlled Boost PFC circuit includes a Boost PFC circuit, a driver chip, and a single-chip microcomputer. The PFC overcurrent protection circuit includes a sampling circuit, a control circuit, and an enable switch circuit. The Boost PFC circuit is respectively connected to the sampling circuit and the driver chip. The control circuit is respectively connected to the sampling circuit and the enable switch circuit. The driver chip is connected to the single-chip microcomputer. The control circuit includes a first power supply, a first resistor, a second resistor, and a first switch tube. The enable switch circuit includes a second power supply, a third resistor, a fourth resistor, a fifth resistor, and a second switch tube.

[0006] The first resistor is connected to the sampling circuit and the first switch tube respectively, the second resistor is connected to the first power supply, the first switch tube and the third resistor respectively, and one end of the first switch tube is grounded;

[0007] The third resistor is connected to the first switching tube and the second switching tube respectively, the fourth resistor is connected to the second power supply and the fifth resistor respectively, and one end of the second switching tube is connected to the fifth resistor and grounded;

[0008] In which, the sampling circuit converts the current signal collected from the Boost PFC circuit into a first voltage signal, and transmits the first voltage signal to the control circuit, so that the control circuit outputs a second voltage signal to the enable switch circuit, and the second voltage signal is used to control the enable switch circuit to output a switch signal, and the switch signal is used to control whether the driver chip is enabled.

[0009] The beneficial effects of the technical solutions provided by some embodiments of the present application include at least:

[0010] In one or more embodiments of the present application, the PFC circuit includes a digitally controlled Boost PFC circuit and a PFC overcurrent protection circuit. The digitally controlled Boost PFC circuit includes a Boost PFC circuit, a driver chip, and a single-chip microcomputer. The PFC overcurrent protection circuit includes a sampling circuit, a control circuit, and an enable switch circuit. The Boost PFC circuit is respectively connected to the sampling circuit and the driver chip, the control circuit is respectively connected to the sampling circuit and the enable switch circuit, the driver chip is connected to the single-chip microcomputer, the control circuit includes a first power supply, a first resistor, a second resistor, and a first switch tube, and the enable switch circuit includes a second power supply, a third resistor, a fourth resistor, a fifth resistor, and a second switch tube, wherein: the first resistor is respectively connected to the sampling circuit and the first switch tube, the second resistor is respectively connected to the first power supply, the first switch tube, and the third resistor, one end of the first switch tube is grounded, the third resistor is respectively connected to the first switch tube and the second switch tube, the fourth resistor is respectively connected to the second power supply and the fifth resistor, one end of the second switch tube is connected to the fifth resistor and grounded, wherein the sampling circuit will be connected from the Boost The current signal collected in the PFC circuit is converted into a first voltage signal, and the first voltage signal is transmitted to the control circuit, so that the control circuit outputs a second voltage signal to the enable switch circuit. The second voltage signal is used to control the enable switch circuit to output a switch signal, and the switch signal is used to control whether the driver chip is enabled. The structure of the PFC circuit can be formed by connecting a Boost PFC circuit, a driver chip, a single-chip microcomputer, a sampling circuit, a control circuit, and an enable switch circuit. The output switch signal can be controlled by the first switch tube in the control circuit and the second switch tube in the enable switch circuit to control whether the driver chip is enabled, which can provide effective overcurrent protection. At the same time, by using basic circuit components, the requirements of the PFC circuit for simple circuit and low cost in practical applications can be met. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0012] Figure 1 This is a topological circuit diagram of a PFC circuit in the prior art provided by an embodiment of the present application;

[0013] Figure 2 This is a topological circuit diagram of a PFC circuit provided in an embodiment of the present application;

[0014] Figure 3This is a topological circuit diagram of a digitally controlled Boost PFC circuit provided in an embodiment of the present application;

[0015] Figure 4 This is a topological circuit diagram of a sampling circuit provided in an embodiment of the present application;

[0016] Figure 5 is a topological circuit diagram of a control circuit provided in an embodiment of the present application;

[0017] Figure 6 is a topological circuit diagram of another control circuit provided in an embodiment of the present application;

[0018] Figure 7 is a topological circuit diagram of an enabling switch circuit provided in an embodiment of the present application;

[0019] Figure 8 is a topological circuit diagram of another enabling switch circuit provided in an embodiment of the present application;

[0020] Figure 9 This is a topological circuit diagram of another PFC circuit provided in an embodiment of the present application;

[0021] Figure 10 This is a topological circuit diagram of another PFC circuit provided in an embodiment of the present application;

[0022] Figure 11 This is a topological circuit diagram of another PFC circuit provided in an embodiment of the present application;

[0023] Figure 12 This is a topological circuit diagram of another PFC circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0025] In the description of this application, it should be understood that the terms "first", "second", etc. are used for descriptive purposes only and should not be understood to indicate or imply relative importance. In the description of this application, it should be noted that, unless otherwise expressly specified and limited, "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units inherent to these processes, methods, products or devices. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In addition, in the description of this application, unless otherwise specified, "multiple" refers to two or more. "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0026] The present application is described in detail below with reference to specific embodiments.

[0027] like Figure 2 As shown, Figure 2 This is a topological circuit diagram of a PFC circuit provided in an embodiment of the present application. The PFC circuit 1 includes: a digitally controlled Boost PFC circuit 11 and a PFC overcurrent protection circuit 12. The digitally controlled Boost PFC 11 circuit includes a Boost PFC circuit 111, a driver chip U1, and a single-chip microcomputer U2. The PFC overcurrent protection circuit 12 includes a sampling circuit 121, a control circuit 122, and an enable switch circuit 123. The Boost PFC circuit 111 is respectively connected to the sampling circuit 121 and the driver chip U1. The control circuit 122 is respectively connected to the sampling circuit 121 and the enable switch circuit 123. The driver chip U1 is connected to the single-chip microcomputer U2. The control circuit 122 includes a first power supply VCC1, a first resistor R1, a second resistor R2, and a first switch tube Q1. The enable switch circuit 123 includes a second power supply VCC2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a second switch tube Q2. Specifically:

[0028] One end of a first resistor R1 is connected to the sampling circuit 121, the other end of the first resistor R1 is connected to the control end of the first switch tube Q1, one end of a second resistor R2 is connected to the output end of the first power supply VCC1, the other end of the second resistor R2 is connected to the first end of the first switch tube Q1, and the second end of the first switch tube Q1 is grounded;

[0029] One end of a third resistor R3 is connected to the control end of the second switch tube Q2, the other end of the third resistor R3 is connected to the first end of the first switch tube Q1, one end of a fourth resistor R4 is connected to the output end of the second power supply VCC2, the other end of the fourth resistor R4 is respectively connected to the first end of the second switch tube Q2 and one end of a fifth resistor R5, a second end of the second switch tube Q2 is connected to the other end of the fifth resistor and is grounded;

[0030] Among them, the sampling circuit 121 converts the current signal collected from the Boost PFC circuit 111 into a first voltage signal, and transmits the first voltage signal to the control circuit 122, so that the control circuit 122 outputs a second voltage signal to the enable switch circuit 123, and the second voltage signal is used to control the enable switch circuit 123 to output a switch signal, and the switch signal is used to control whether the driver chip U1 is enabled.

[0031] It should be noted that the Boost PFC circuit 111 refers to the main circuit for power factor correction in the PFC circuit 1. The Boost PFC circuit 11, the single-chip microcomputer U2, and the driver chip U1 form a digitally controlled Boost PFC circuit 11. In the digitally controlled Boost PFC circuit 11, the PWM signal output by the single-chip microcomputer U2 is driven and transmitted to the third switch in the Boost PFC circuit 111 via the driver chip U1. This third switch can be PWM-modulated to adjust the output voltage of the Boost PFC circuit 111. Furthermore, to provide overcurrent protection for the Boost PFC circuit 111, a current signal in the current loop of the Boost PFC circuit 111 can be collected to determine whether an overcurrent condition exists in the Boost PFC circuit 111. In this embodiment of the present application, the sampling resistor Rs in the sampling circuit 121 is located in the Boost PFC circuit 111 to collect the current signal in the current loop of the Boost PFC circuit 111.

[0032] According to some embodiments, Figure 3 FIG. 1 shows a topological circuit diagram of a feasible digitally controlled Boost PFC circuit 11, wherein the Boost PFC circuit 111 includes a rectifier bridge BD, a boost inductor L, a third switch tube Q3, a first diode D1, and an energy storage capacitor C. The sampling circuit 121 includes a sampling resistor Rs, wherein:

[0033] The Boost PFC circuit 111 includes a first AC input terminal, a second AC input terminal, a DC positive output terminal, and a DC negative output terminal. The first input terminal of the rectifier bridge BD is the first AC input terminal, the second input terminal of the rectifier bridge BD is the second AC input terminal, the positive output terminal of the rectifier bridge BD is connected to one end of the boost inductor L, the other end of the boost inductor L is respectively connected to the positive electrode of the first diode D1 and the collector of the third switch tube Q3, the negative electrode of the first diode D1 is connected to the positive electrode of the energy storage capacitor C, the positive electrode of the energy storage capacitor C is the DC positive output terminal, the negative output terminal of the rectifier bridge BD is connected to one end of the sampling resistor Rs, the other end of the sampling resistor Rs is respectively connected to the emitter of the third switch tube Q3 and the negative electrode of the energy storage capacitor C and grounded, the negative electrode of the energy storage capacitor C is the DC negative output terminal, and the gate of the third switch tube Q3 is connected to the output terminal of the driver chip U1.

[0034] It should be noted that the first AC input terminal and the second AC input terminal of the Boost PFC circuit 111 are used to receive the AC voltage input to the PFC circuit 1 and convert the AC voltage into a DC voltage. This DC voltage passes through a boost chopper circuit (Boost Chopper, Boost boost circuit) composed of an energy storage capacitor C, a boost inductor L, a third switch Q3, and a first diode D1. This can ensure that the output voltage and current are in phase, thereby achieving power factor correction. It is easy to understand that this constant DC voltage is output through the DC positive output terminal and the DC negative output terminal. The PFC circuit 1 can output this DC voltage to loads such as an inverter circuit and a motor.

[0035] Optionally, in practical applications, in order to ensure the circuit environment and reduce electromagnetic interference, an RC circuit, a filter, and an electromagnetic interference (EMI) filtering circuit may be provided in the Boost PFC circuit 111 .

[0036] Optionally, the third switch tube Q3 may be a MOS tube or an IGBT, and is used in the PFC main circuit to receive a PWM signal, thereby adjusting the output voltage of the PFC main circuit.

[0037] It is easy to understand that the sampling resistor Rs is in the current loop of the Boost circuit, and the current on the sampling resistor Rs is also the current in the Boost circuit. Therefore, the current sampled on the sampling resistor Rs is the current in the Boost PFC circuit 111, that is, the current signal. The PFC overcurrent protection circuit 12 can determine whether an overcurrent condition occurs in the digitally controlled Boost PFC circuit 111 based on the current signal.

[0038] According to some embodiments, Figure 4 As shown, the sampling circuit 121 further includes a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, an operational amplifier U3, a feedback resistor, and a third power supply VCC3, wherein:

[0039] One end of the sampling resistor Rs is connected to one end of the seventh resistor R7, the other end of the sampling resistor Rs is connected to one end of the eighth resistor R8, the other end of the seventh resistor R7 is respectively connected to one end of the feedback resistor and the inverting input terminal of the operational amplifier U3, the other end of the eighth resistor R8 is connected to the non-inverting input terminal of the operational amplifier U3, the output end of the operational amplifier U3 is respectively connected to the other end of the feedback resistor and one end of the first resistor R1, the output end of the third power supply VCC3 is connected to one end of the tenth resistor R10, the other end of the tenth resistor R10 is respectively connected to one end of the ninth resistor R9 and one end of the eleventh resistor R11, the other end of the ninth resistor R9 is connected to the non-inverting input terminal of the operational amplifier U3, and the other end of the eleventh resistor R11 is grounded.

[0040] It should be noted that the feedback resistor is used to adjust the amplification gain of the operational amplifier U3. Figure 4 A complete description of the working principle of the sampling circuit 131 provided in the embodiment of the present application is given below:

[0041] Since there is a current signal on the sampling resistor Rs, there is a potential difference between one end and the other end of the sampling resistor Rs. The inverting input end of the operational amplifier U3 is connected to one end of the sampling resistor Rs via the seventh resistor R7, and the non-inverting input end of the operational amplifier U3 is connected to the other end of the sampling resistor Rs via the eighth resistor R8. Therefore, the inverting input end and the non-inverting input end of the operational amplifier U3 amplify the potential difference, thereby obtaining a first voltage signal.

[0042] Furthermore, the third power source VCC3 generates a reference voltage Vref via the tenth resistor R10 and the eleventh resistor R11. The reference voltage Vref is further divided by the eighth resistor R8 and the ninth resistor R9 and input into the non-inverting input terminal of the operational amplifier U3. This allows the reference voltage Vref to be amplified by the operational amplifier U3 and output as an initial current sampling operating voltage. This initial current sampling operating voltage can serve as a reference signal for PFC current sampling and can also ensure that the PFC overcurrent protection circuit is in a normal state and that overcurrent protection is not being performed on the digitally controlled Boost PFC circuit.

[0043] Furthermore, based on the operational characteristics of operational amplifier U3, when the current signal is less than the current threshold, the output voltage of operational amplifier U3 (i.e., the first voltage signal) is a normal-state voltage corresponding to reference voltage Vref. It is understood that the normal-state voltage is any voltage value within the voltage range from reference voltage Vref to the on-state voltage (Vth_ON) of first switch Q1. When the current signal is greater than the current threshold, the output voltage of operational amplifier U3 (i.e., the first voltage signal) decreases. The current threshold refers to the maximum current allowed or protected in the Boost PFC circuit. When the current signal is greater than the current threshold, the Boost PFC circuit experiences an overcurrent problem. In this case, operational amplifier U3 reduces the output first voltage signal based on the normal-state voltage. When the current signal is less than the current threshold, the Boost PFC circuit does not experience an overcurrent problem. In this case, the first voltage signal output by operational amplifier U3 is the normal-state voltage.

[0044] According to some embodiments, the control circuit 122 receives a first voltage signal and outputs a second voltage signal under the control of the first voltage signal. Figure 5 As shown, a topological circuit diagram of a feasible control circuit is shown, in which the output end of the first power supply VCC1 is connected to one end of the second resistor R2, the other end of the second resistor R2 is respectively connected to the drain of the first switch tube Q1 and the other end of the third resistor R3, one end of the first resistor R1 is connected to the output end of the operational amplifier U3, the other end of the first resistor R1 is connected to the gate of the first switch tube Q1, and the source of the first switch tube Q1 is grounded.

[0045] Schematically, taking the first switch tube Q1 as an NPN transistor as an example, Figure 6 As shown, a topological circuit diagram of a feasible control circuit is shown, in which the output end of the first power supply VCC1 is connected to one end of the second resistor R2, the other end of the second resistor R2 is respectively connected to the collector of the first switch tube Q1 and the other end of the third resistor R3, one end of the first resistor R1 is connected to the output end of the operational amplifier U3, the other end of the first resistor R1 is connected to the base of the first switch tube Q1, and the emitter of the first switch tube Q1 is grounded.

[0046] It should be noted that the first switch transistor Q1 can be an NPN transistor or an NMOS transistor. Among them, the NMOS transistor has a faster response speed. Therefore, in the embodiment of the present application, the NMOS transistor is used as the first switch transistor Q1 to respond more quickly to overcurrent phenomena in the PFC circuit.

[0047] It is easy to understand that the first voltage signal is divided by the first resistor R1 and then transmitted to the gate of the first switch Q1. Therefore, the first voltage signal can control the gate voltage (Vth_Q1) of the first switch Q1. When the first voltage signal gradually decreases from the normal state voltage, Vth_Q1 decreases accordingly. When Vth_Q1 is less than the voltage (Vth_ON) that can turn on the first switch Q1, that is, Vth_Q1 < Vth_ON, the first switch Q1 is turned off, so that the output voltage of the first power supply VCC1 is output to the enable switch circuit 123 through the second resistor R2. In other words, the second voltage signal output by the control circuit 122 is the output voltage of the first power supply VCC1. When the first voltage signal is the reference voltage Vref, Vth_Q1 meets the conduction requirement of the first switch Q1. The first switch Q1 operates in the saturation region and is turned on. The output voltage of the first power supply VCC1 can be transmitted through the second resistor R2 and the first switch Q1, and finally transmitted to the ground terminal. The second voltage signal output by the control circuit 122 is close to zero.

[0048] According to some embodiments, the enable switch circuit 123 receives a second voltage signal and outputs a switch signal under the control of the second voltage signal. Specifically, the switch signal includes a shutdown enable signal and an enable signal. When the enable switch circuit 123 outputs the shutdown enable signal, the driver chip U1 is controlled to be disabled, so that the driver chip U1 cannot drive the PWM signal sent by the microcontroller U2, thereby providing overcurrent protection for the Boos PFC circuit. When the enable switch circuit 123 outputs the enable signal, the driver chip U1 is controlled to be enabled, so that the driver chip U1 can drive the PWM signal sent by the microcontroller U2, thereby allowing the Boos PFC circuit to operate normally.

[0049] Optionally, when the second switch tube Q2 is an NPN transistor, the shutdown enable signal is a low level signal and the enable signal is a high level signal; when the second switch tube Q2 is a PNP transistor, the shutdown enable signal is a high level signal and the enable signal is a low level signal.

[0050] According to some embodiments, when the second switch tube Q2 is an NPN transistor, as shown in FIG. Figure 7 As shown in the topological circuit diagram of a feasible enabling switch circuit, the output end of the second power supply VCC2 is connected to one end of the fourth resistor R4, the other end of the fourth resistor R4 is respectively connected to the collector of the second switch tube Q2 and one end of the fifth resistor R5, one end of the third resistor R3 is connected to the base of the second switch tube Q2, and the emitter of the second switch tube Q2 is connected to the other end of the fifth resistor R5 and grounded.

[0051] Specifically, the second switch tube Q2 can receive the second voltage signal through the third resistor R3. Therefore, the second voltage signal can control the base current (Ib_Q2) of the second switch tube Q2. When the second voltage signal is close to the output voltage of the first power supply VCC1, Ib_Q2 increases accordingly. When Ib_Q2 is greater than the current (Ib_ON) that can turn on the second switch tube Q2, that is, Ib_Q2>Ib_ON, the second switch tube Q2 is turned into the on state, so that the output voltage of the second power supply VCC2 is transmitted through the fourth resistor R4 and the second switch tube Q2, and finally transmitted to the ground terminal, then the voltage of the shutdown enable signal output by the enable switch circuit 123 to the driver chip U1 is zero (low level signal), and the shutdown The closed enable signal is a low-level signal, which can disable the driver chip U1 and thus cannot drive the PWM signal output by the microcontroller U2; when the second voltage signal is close to zero, Ib_Q2 cannot meet the conduction requirement of the second switch tube Q2, and the second switch tube Q2 is in the cut-off state, so that the output voltage of the second power supply VCC2 is transmitted to the driver chip U1 via the fourth resistor R4 (high-level signal), and the enable signal is a high-level signal, which can enable the driver chip U1 and thus drive the PWM signal output by the microcontroller U2.

[0052] According to some embodiments, when the second switch tube Q2 is a PNP transistor, as shown in FIG. Figure 8 As shown in the topological circuit diagram of a feasible enabling switch circuit, the output end of the second power supply VCC2 is connected to one end of the fourth resistor R4, the other end of the fourth resistor R4 is respectively connected to the emitter of the second switch tube Q2 and one end of the fifth resistor R5, one end of the third resistor R3 is connected to the base of the second switch tube Q2, and the collector of the second switch tube Q2 is connected to the other end of the fifth resistor R5 and grounded.

[0053] Specifically, the second switch tube Q2 can receive the second voltage signal through the third resistor R3. Therefore, the second voltage signal can control the base current (Ib_Q2) of the second switch tube Q2. When the second voltage signal approaches the output voltage of the first power supply VCC1, Ib_Q2 increases accordingly, and the second switch tube Q2 changes to the cut-off state, so that the output voltage of the second power supply VCC2 is transmitted to the driver chip U1 via the fourth resistor R4 (high-level signal). The shutdown enable signal is a high-level signal, which can disable the driver chip U1 and thus cannot drive the PWM signal output by the microcontroller U2. When the second voltage signal is close to zero, Ib_Q2 meets the conduction requirement of the second switch tube Q2, and the second switch tube Q2 is in the on state, so that the output voltage of the second power supply VCC2 is transmitted via the fourth resistor R4 and the second switch tube Q2, and finally transmitted to the ground terminal. Then, the voltage of the shutdown enable signal output by the enable switch circuit 123 to the driver chip U1 is zero (low-level signal), and the enable signal is a low-level signal, which can enable the driver chip U1 and thus drive the PWM signal output by the microcontroller U2.

[0054] In summary, taking the second switch tube as an NPN transistor as an example, a feasible topology circuit diagram of the PFC circuit is as follows: Figure 9 As shown below, combined Figure 9 A complete description of the working principle of a PFC circuit provided in an embodiment of the present application is given below:

[0055] When an overcurrent problem occurs in the PFC main circuit, the current in the PFC main circuit's current loop exceeds the normal value, causing the current signal across sampling resistor Rs in sampling circuit 121 to exceed the current threshold. The first voltage signal output by operational amplifier U3 then begins to decrease from reference voltage Vref. At this point, the first voltage signal controls the gate voltage of first switch Q1 to decrease. When the gate voltage of first switch Q1 fails to meet the on-state requirement for first switch Q1, first switch Q1 is cut off. A second voltage signal, output from first power supply VCC1 via second resistor R2, is transmitted via a third resistor to second switch Q2. The second voltage signal approaches the first power supply VCC1. The second voltage signal controls the base current of second switch Q2, ensuring that the base current meets the on-state requirement for second switch Q2, turning on second switch Q2. At this time, the output voltage of the second power supply VCC2 is transmitted to the ground via the fourth resistor R4 and the second switch tube Q2, so that the switching signal output to the driver chip U1 is a low-level signal. The low-level signal is a shutdown enable signal, so that the driver chip U1 is not enabled. The PWM signal output by the microcontroller U2 cannot be driven by the driver chip U1 and transmitted to the third switch tube Q3, thereby preventing the erroneous PWM signal from causing an overcurrent problem in the PFC circuit and avoiding damage to the device where the PFC circuit is located.

[0056] When the PFC main circuit operates normally, the current in its current loop is normal, causing the current signal sampled by sampling resistor RS to be less than the current threshold. The first voltage signal output by operational amplifier U3 is a normal voltage. At this point, the first voltage signal is transmitted via first resistor R1 to the gate of first switch Q1, turning on first switch Q1. Because first switch Q2 is on, the voltage output by first power supply VCC1 via second resistor R2 is transmitted to ground via second resistor R2 and first switch Q1, causing the second voltage signal output to enable switch circuit 123 to approach zero. The second voltage signal is transmitted via third resistor R3 to the base of second switch Q2, causing the base current of second switch Q2 to fail to meet the on-state requirement, turning off second switch Q2. At this point, the output voltage of second power supply VCC2 is transmitted via fourth resistor R4 to driver chip U1 as a high-level signal, which serves as an enable signal, enabling driver chip U1. The PWM signal output by the single chip microcomputer U2 is driven by the driver chip U1 and transmitted to the third switch tube Q3, so that the PFC main circuit can work normally and flexibly adjust the output voltage.

[0057] It should be noted that when the second switching tube is a PNP transistor, the working principle of the PFC circuit is similar to the working principle of the PFC circuit when the second switching tube is an NPN transistor. For details, please refer to the working principle of the PFC circuit when the second switching tube is an NPN transistor, which will not be repeated here.

[0058] In the embodiment of the present application, a PFC circuit structure can be formed by connecting a Boost PFC circuit, a driver chip, a single-chip microcomputer, a sampling circuit, a control circuit, and an enable switch circuit. The output switch signal can be controlled by a first switch tube in the control circuit and a second switch tube in the enable switch circuit to control whether the driver chip is enabled, thereby performing effective overcurrent protection. At the same time, by using basic circuit elements, the requirements of a simple circuit and low cost for the PFC circuit in practical applications can be met.

[0059] like Figure 10 As shown, Figure 10This is a topological circuit diagram of a PFC circuit provided in an embodiment of the present application. The PFC circuit 1 includes a digitally controlled Boost PFC circuit 11 and a PFC overcurrent protection circuit 12. The digitally controlled Boost PFC 11 includes a Boost PFC circuit 111, a driver chip U1, and a single-chip microcomputer U2. The PFC overcurrent protection circuit 12 includes a sampling circuit 121, a control circuit 122, and an enabling switch circuit 123. Specifically, the Boost PFC circuit 111, the driver chip U1, and the enabling switch circuit 123 are the same as those in the above embodiment. For details, please refer to the above embodiment and will not be repeated here.

[0060] In an embodiment of the present application, the sampling circuit 121 can simultaneously transmit the first voltage signal to the microcontroller U2, and the control circuit 122 can simultaneously output the second voltage signal to the microcontroller U2. The sampling circuit 121 is connected to the microcontroller U2 and further includes a fourteenth resistor R14, wherein one end of the fourteenth resistor R14 is connected to the output end of the operational amplifier U3, and the other end of the fourteenth resistor R14 is connected to the second input end of the microcontroller U2. The control circuit 122 is connected to the microcontroller U2 and further includes a sixth resistor R6, wherein one end of the sixth resistor R6 is connected to the other end of the first resistor R2, and the other end of the sixth resistor R6 is connected to the first input end of the microcontroller U2.

[0061] It should be noted that, upon receiving the first voltage signal and / or the second voltage signal, the microcontroller U2 can determine whether an overcurrent condition exists in the Boost PFC circuit 111 based on the first voltage signal and / or the second voltage signal. When an overcurrent condition is determined to exist in the Boost PFC circuit 111, software overcurrent protection is implemented on the Boost PFC circuit 111. Software overcurrent protection refers to the implementation of overcurrent protection on the PFC circuit by software-based technical means, such as modifying a program in the microcontroller U2 and adjusting an output PWM signal, upon detecting an overcurrent condition in the Boost PFC circuit 11.

[0062] According to some embodiments, Figure 11 As shown, the control circuit 122 also includes a twelfth resistor R12 and a second diode D2, and the enabling switch circuit 123 includes a thirteenth resistor R13, wherein: one end of the twelfth resistor R12 is respectively connected to the other end of the first resistor R1, the anode of the second diode D2 is respectively connected to the other end of the second resistor R2 and the gate of the first transistor Q1, the cathode of the second diode D2 is respectively connected to the other end of the third resistor R3, and one end of the thirteenth resistor R13 is respectively connected to one end of the third resistor R3 and the base of the second transistor Q2.

[0063] It should be noted that a second diode D2 is provided in the control circuit 122 to prevent noise generated by the power device during switching from interfering with the output second voltage signal. Furthermore, when the PFC circuit recovers from an overcurrent condition, the time it takes for the output signal of the second switch Q2 to switch from a shutdown enable signal to an enable signal can be delayed, allowing the driver chip U1 to remain in a disabled state, thereby extending the duration of overcurrent protection. Furthermore, a twelfth resistor R12 is provided in the control circuit 122 to prevent damage to the first switch Q1 (NMOS transistor) due to external electromagnetic fields or electrostatic induction, while ensuring that the first switch Q1 (NMOS transistor) can be effectively turned on or off.

[0064] It is easy to understand that when the current in the current loop of the PFC circuit reaches the current threshold, the second voltage signal (the second voltage signal corresponding to the shutdown enable signal, i.e., a high-level signal) generated at the drain of the first switch Q1 after the first voltage signal is divided by the first resistor and the twelfth resistor is very short. This results in the second switch Q2 outputting the shutdown enable signal for a very short time, which makes it impossible to control the driver chip U1 to remain in the disabled state. As a result, the third switch Q3 cannot be fully closed in a timely manner, and thus overcurrent cannot be quickly prevented and overcurrent protection cannot be implemented in a timely manner. Specifically, when the first switch Q1 transitions from the off state to the on state, due to the reverse blocking effect of the second diode D2, the base voltage of the second switch Q2 can only be discharged through the thirteenth resistor, causing the operating state of the second switch Q2 to change.

[0065] It should be noted that by adjusting the resistance of the thirteenth resistor R13, the time it takes for the second switch Q2 to change its operating state can be adjusted, thereby adjusting the duration of the overcurrent protection. Furthermore, when the driver chip is enabled, the second diode D2 can block interference with the first voltage signal caused by noise and other interference from the operation of the third switch Q3.

[0066] Optionally, in practical applications, in order to protect the components in the circuit and avoid electromagnetic interference, the PFC circuit 1 also includes components such as an RC circuit and a filter capacitor, such as Figure 12As shown, a filter capacitor is added to the Boost PFC circuit 111, wherein one end of the filter capacitor is respectively connected to the positive output end of the rectifier bridge BD and one end of the boost inductor L, and the other end of the filter capacitor is respectively connected to the negative output end of the rectifier bridge BD and one end of the sampling resistor Rs; a capacitor is added to the operational amplifier U3 in the sampling current 121, wherein the capacitor and the feedback resistor are connected in parallel to form an RC circuit; a capacitor is added to the first switch tube Q1 in the control circuit 122, wherein one end of the capacitor is respectively connected to one end of the first resistor R1 and the gate of the first switch tube Q1, and the other end of the capacitor is connected to the first switch tube Q 1 is connected to the source of the first switching transistor Q2 and is grounded, and the capacitor can form an RC circuit with the first resistor R1; a filter capacitor is added at the sixth resistor R6 in the sampling circuit 121, wherein one end of the filter capacitor is respectively connected to the other end of the sixth resistor and the first input terminal of the single-chip microcomputer, and the other end of the filter capacitor is grounded; and a filter capacitor is added to the first transistor Q2 in 123, wherein one end of the filter capacitor is respectively connected to one end of the third resistor R3 and the base of the second switching transistor Q2, and the other end of the filter capacitor is connected to the emitter of the second switching transistor Q2 and is grounded, and the filter capacitor can form an RC circuit with the third resistor R3.

[0067] It is easy to understand that the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6, the ninth resistor R9, the tenth resistor R10, the eleventh resistor R11 and the fourteenth resistor R14 play the role of voltage division and current limiting in the PFC circuit, which can adjust the voltage and current in the circuit, thereby avoiding burning of components due to excessive current and protecting the components in the circuit.

[0068] It should be noted that when the PFC circuit is laid out on a printed circuit board (PCB), the control circuit 122 is placed close to the sampling circuit 121 and the weak-signal portion of the microcontroller U2, while the enabling switch circuit 123 is located close to the third switch tube Q3 and the strong-signal portion of the driver chip U1. This can improve the anti-interference performance of the PFC circuit and the area utilization of the PCB.

[0069] In an embodiment of the present application, a Boost PFC circuit structure is constructed by connecting a driver chip, a single-chip microcontroller, a sampling circuit, a control circuit, and an enable switch circuit. A first switch in the control circuit and a second switch in the enable switch circuit control output switching signals to control whether the driver chip is enabled, thereby providing effective overcurrent protection. By using basic circuit components, the PFC circuit meets the requirements of simple and low-cost circuits in practical applications. Furthermore, adding a second diode between the first and second switches adjusts the time it takes for the second switch to change its operating state, thereby adjusting the duration of overcurrent protection. When the driver chip is enabled, it blocks interference from the operating noise and other interference from the third switch on the first voltage signal. Furthermore, sending the first and / or second voltage signals to the single-chip microcontroller enables the microcontroller to implement software overcurrent protection for the PFC circuit. Furthermore, adding voltage dividers, current limiters, and filters to the PFC circuit prevents electromagnetic interference, thereby ensuring a good circuit environment.

[0070] An embodiment of the present application further provides an air-conditioning device, which includes the above-mentioned PFC circuit. The output switching signal can be controlled by a first switching tube in the control circuit and a second switching tube in the enable switching circuit to control whether the driver chip is enabled, thereby providing effective overcurrent protection. At the same time, by using basic circuit elements, the requirements of a simple and low-cost PFC circuit in practical applications can be met.

[0071] The serial numbers of the above embodiments of the present application are for description only and do not represent the advantages or disadvantages of the embodiments.

[0072] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the scope of rights of the present application. Therefore, equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A power factor correction (PFC) circuit, comprising a digitally controlled Boost PFC circuit and a PFC overcurrent protection circuit, wherein the digitally controlled Boost PFC circuit comprises a Boost PFC circuit, a driver chip, and a single-chip microcomputer, wherein: The PFC overcurrent protection circuit includes a sampling circuit, a control circuit, and an enable switch circuit. The Boost PFC circuit is connected to the sampling circuit and the driver chip, respectively. The control circuit is connected to the sampling circuit and the enable switch circuit, respectively. The driver chip is connected to a single-chip microcomputer. The control circuit includes a first power supply, a first resistor, a second resistor, and a first switch tube. The enable switch circuit includes a second power supply, a third resistor, a fourth resistor, a fifth resistor, and a second switch tube. One end of the first resistor is connected to the sampling circuit, the other end of the first resistor is connected to the control end of the first switch tube, one end of the second resistor is connected to the output end of the first power supply, the other end of the second resistor is connected to the first end of the first switch tube, and the second end of the first switch tube is grounded; One end of the third resistor is connected to the control end of the second switching transistor, the other end of the third resistor is connected to the first end of the first switching transistor, one end of the fourth resistor is connected to the output end of the second power supply, the other end of the fourth resistor is respectively connected to the first end of the second switching transistor and one end of the fifth resistor, and the second end of the second switching transistor is connected to the other end of the fifth resistor and is grounded; The sampling circuit converts the current signal collected from the Boost PFC circuit into a first voltage signal, and transmits the first voltage signal to the control circuit, so that the control circuit outputs a second voltage signal to the enable switch circuit. The second voltage signal is used to control the enable switch circuit to output a switch signal, and the switch signal is used to control whether the driver chip is enabled. The control circuit is connected to the single chip microcomputer, and the control circuit further includes a sixth resistor, wherein: One end of the sixth resistor is connected to one end of the first resistor, and the other end of the sixth resistor is connected to the first input end of the single chip microcomputer; The control circuit further includes a twelfth resistor and a second diode, and the enabling switch circuit includes a thirteenth resistor, wherein: One end of the twelfth resistor is connected to the other end of the first resistor and the control end of the first switch tube respectively, the anode of the second diode is connected to the other end of the second resistor and the first end of the first switch tube respectively, and the cathode of the second diode is connected to the other end of the third resistor; One end of the thirteenth resistor is connected to one end of the third resistor and the control end of the second switch tube respectively.

2. The PFC circuit according to claim 1, wherein: The switch signal includes a shutdown enable signal, and the shutdown enable signal is used to control the driver chip to be disabled, wherein: When the second switch tube is an NPN transistor, the shutdown enable signal is a low level signal; When the second switch tube is a PNP transistor, the shutdown enable signal is a high level signal.

3. The PFC circuit according to claim 2, wherein: The second switch tube is an NPN transistor, wherein: The output end of the second power supply is connected to one end of the fourth resistor, the other end of the fourth resistor is respectively connected to the collector of the second switching tube and one end of the fifth resistor, one end of the third resistor is connected to the base of the second switching tube, and the emitter of the second switching tube is connected to the other end of the fifth resistor and grounded.

4. The PFC circuit according to claim 2, wherein: The second switch tube is a PNP transistor, wherein: The output end of the second power supply is connected to one end of the fourth resistor, the other end of the fourth resistor is respectively connected to the emitter of the second switching tube and one end of the fifth resistor, one end of the third resistor is connected to the base of the second switching tube, and the collector of the second switching tube is connected to the other end of the fifth resistor and grounded.

5. The PFC circuit according to claim 3 or 4, characterized in that: The first switch tube is an NMOS tube, wherein: The output end of the first power supply is connected to one end of the second resistor, the other end of the second resistor is connected to the drain of the first switching tube, one end of the first resistor is connected to the sampling circuit, the other end of the first resistor is connected to the gate of the first switching tube, and the source of the first switching tube is grounded.

6. The PFC circuit according to claim 5, characterized in that: The Boost PFC circuit includes a rectifier bridge, a boost inductor, a third switch tube, a first diode, and an energy storage capacitor. The sampling circuit includes a sampling resistor, wherein: The Boost PFC circuit includes a first AC input terminal, a second AC input terminal, a DC positive output terminal, and a DC negative output terminal. The first input terminal of the rectifier bridge is the first AC input terminal, and the second input terminal of the rectifier bridge is the second AC input terminal. The positive output end of the rectifier bridge is connected to one end of the boost inductor, the other end of the boost inductor is respectively connected to the positive electrode of the first diode and the collector of the third switching tube, the negative electrode of the first diode is connected to the positive electrode of the energy storage capacitor, and the positive electrode of the energy storage capacitor is the DC positive output end; The negative output terminal of the rectifier bridge is connected to one end of the sampling resistor, and the other end of the sampling resistor is respectively connected to the emitter of the third switching tube and the negative electrode of the energy storage capacitor and grounded, and the negative electrode of the energy storage capacitor is the negative output terminal of the DC power; The gate of the third switch tube is connected to the output end of the driver chip.

7. The PFC circuit according to claim 6, wherein: The sampling circuit further includes a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, an eleventh resistor, a feedback resistor, an operational amplifier, and a third power supply, wherein: The other end of the sampling resistor is connected to one end of the seventh resistor, one end of the sampling resistor is connected to one end of the eighth resistor, the other end of the seventh resistor is respectively connected to one end of the feedback resistor and the inverting input terminal of the operational amplifier, the other end of the eighth resistor is connected to the non-inverting input terminal of the operational amplifier, and the output terminal of the operational amplifier is respectively connected to the other end of the feedback resistor and one end of the first resistor; The output end of the third power supply is connected to one end of the tenth resistor, the other end of the tenth resistor is respectively connected to one end of the ninth resistor and one end of the eleventh resistor, the other end of the ninth resistor is connected to the non-inverting input end of the operational amplifier, and the other end of the eleventh resistor is grounded.

8. The PFC circuit according to claim 7, wherein: The sampling circuit is connected to the single chip microcomputer, and the sampling circuit further includes a fourteenth resistor, wherein: One end of the fourteenth resistor is connected to the other end of the second resistor, and the other end of the fourteenth resistor is connected to the second input end of the single chip microcomputer.

9. An air conditioning device, characterized in that: The PFC circuit comprises the PFC circuit according to any one of claims 1 to 8.

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