A power conversion circuit and a control method thereof

Abstract

The embodiment of the present application provides a power conversion circuit and a control method thereof. In the embodiment of the present application, the power conversion circuit determines the polarity of an alternating voltage through a PFC circuit controller, determines a signal for controlling the turn-off of a secondary switch according to the inductor current, determines a signal for controlling the re-conduction of the secondary switch and a signal for controlling the turn-off of a primary switch according to the series midpoint voltage of a switch S1 and a switch S2, and performs PWM control on the switch S1 and the switch S2. The power conversion circuit can control the turn-off of the secondary switch according to the inductor current, control the re-conduction of the secondary switch and the turn-off of the primary switch according to the series midpoint voltage of the switch S1 and the switch S2, and realize ZVS of the switch in the PFC circuit. In addition, the embodiment of the present application further provides a power supply comprising the power conversion circuit.

Description

Technical Field

[0001] This application relates to the field of circuit technology, and in particular to a power conversion circuit and its control method. Background Technology

[0002] With the development of modern technology, power supplies are used in various fields. For example, adapters for personal computers (PCs) and charging power supplies for mobile phones, tablets, and other devices are essential power devices in people's daily lives. These power supplies generally need to convert alternating current (AC) to direct current (DC) to power DC-consuming devices. Therefore, the DC-to-AC (AC-DC) circuit in the power supply is crucial. Among them, the totem-pole power factor correction (PFC) circuit can achieve rectification and PFC functions in a single stage, requiring fewer conducting components, making it a high-efficiency AC-DC circuit.

[0003] Figure 1 This is a schematic diagram of a totem-pole PFC circuit in the prior art. The totem-pole PFC circuit consists of an AC input, a PFC inductor L, switches S1, S2, S3, and S4, an output filter capacitor COUT, and a load Load. To improve the efficiency of the totem-pole PFC, switches S1 and S2 need to implement zero-voltage switching (ZVS) control.

[0004] However, there is currently no good ZVS scheme to enable ZVS control for switches S1 and S2. Summary of the Invention

[0005] This application provides a power conversion circuit and its control method, which can achieve ZVS of the switching transistor in the PFC circuit.

[0006] In a first aspect, embodiments of this application provide a power conversion circuit, including: a power factor correction (PFC) circuit module and a PFC circuit controller; the PFC circuit module includes a switch S1, a switch S2, a switch S3, a switch S4, an inductor L, an AC input terminal, and a load; the inductor L and the AC input terminal are connected in series between the midpoint of the series connection of switch S1 and switch S2 and the midpoint of the series connection of switch S3 and switch S4; the two ends of the series connection of switch S1 and switch S2, and the two ends of the series connection of switch S3 and switch S4 are connected in parallel with the load; the PFC circuit controller is used to perform PWM control on switch S1 and switch S2 based on the collected load voltage, inductor L current, AC voltage of the AC input terminal, and midpoint voltage of the series connection of switch S1 and switch S2.

[0007] In the first aspect, the PFC circuit controller can perform PWM control on the switches S1 and S2 based on the collected load voltage, inductor L current, AC input voltage and series midpoint voltage of switches S1 and S2, thereby achieving ZVS conduction of switches S1 and S2.

[0008] In conjunction with the first aspect, in one implementation of this application, the PFC circuit controller includes: a voltage sampling unit for acquiring the voltage of the load; a current sampling unit for acquiring the current of inductor L; an AC signal processing unit for acquiring the AC voltage at the AC input terminal, and outputting an AC voltage polarity identifier and an AC sampling voltage based on the AC voltage, wherein the AC sampling voltage is obtained by sampling the AC voltage; a turn-off control unit for outputting an inductor L current polarity identifier, a comparison result of the inductor L current with a first threshold, and a comparison result of the load voltage and the AC sampling voltage based on the inductor L current, the load voltage, and the AC sampling voltage; a turn-on control unit for outputting a first turn-on indication signal and a second turn-on indication signal based on the series midpoint voltage of switches S1 and S2 and the AC voltage polarity identifier; and a pulse width modulation (PWM) control unit for performing PWM control on switches S1 and S2 based on the first turn-on indication signal, the second turn-on indication signal, the AC voltage polarity identifier, the inductor L current polarity identifier, the comparison result of the inductor L current with the first threshold, and the comparison result of the load voltage and the AC sampling voltage.

[0009] In this implementation, the circuit determines the polarity of the AC voltage through an AC signal processing unit, determines the signal to turn off the auxiliary switch based on the inductor current through a shutdown control unit, and determines the signals to turn the auxiliary switch back on and the main switch off through an on control unit based on the series midpoint voltage of switches S1 and S2. A pulse width modulation (PWM) control unit performs PWM control on switches S1 and S2. This circuit can control the auxiliary switch to turn off using the inductor current, and control the auxiliary switch to turn back on and the main switch to turn off using the series midpoint voltage of switches S1 and S2, thus achieving ZVS (Zero-Voltage Switching) for the switches in the PFC circuit.

[0010] In conjunction with the first aspect, in one implementation of this application embodiment, the turn-on control unit is used to: detect the rate of change of the series midpoint voltage of switching transistors S1 and S2; select a first turn-on comparison value from a first comparison value and a second comparison value based on the polarity identifier of the AC voltage; select a second turn-on comparison value from a third comparison value and a fourth comparison value based on the polarity identifier of the AC voltage; compare the rate of change with the first turn-on comparison value to obtain a first turn-on indication signal; and compare the rate of change with the second turn-on comparison value to obtain a second turn-on indication signal. In this implementation, the turn-on control unit can determine the time period of the series midpoint voltage increase and decrease based on the rate of change of the series midpoint voltage, thereby determining the time period when the series midpoint voltage reaches its highest value and the time period when it reaches its lowest value, that is, determining the moment when the series midpoint voltage just reaches its highest value and the moment when it just reaches its lowest value, and then represent them through the first turn-on indication signal and the second turn-on indication signal.

[0011] In conjunction with the first aspect, in one implementation of this application, the activation control unit includes a detection circuit, a two-to-one switch MUX1, a two-to-one switch MUX2, a comparator CMP2, a comparator CMP3, and a NOT gate INV1; the detection circuit includes a detection capacitor and a detection resistor connected in series, the first end of the detection capacitor is connected to the midpoint of the series connection between switching transistors S1 and S2, the second end of the detection capacitor is connected to the first end of the detection resistor, and the second end of the detection resistor is grounded; the midpoint of the series connection between the detection capacitor and the detection resistor is connected to the first input terminal of comparator CMP2 and the first input terminal of comparator CMP3. The input terminals of the two-to-one switch MUX1 are connected to the interface corresponding to the polarity indicator of the AC voltage. The two input terminals receive the first and second voltage inputs respectively, and the output terminal is connected to the second input terminal of comparator CMP2. The control terminal of the two-to-one switch MUX2 is connected to the interface corresponding to the polarity indicator of the AC voltage. The two input terminals receive the third and fourth voltage inputs respectively, and the output terminal is connected to the second input terminal of comparator CMP3. The output terminal of comparator CMP2 outputs a first turn-on indication signal; the output terminal of comparator CMP3 outputs a second turn-on indication signal through NOT gate INV1. In this implementation, the turn-on control unit specifically detects the change in the series midpoint voltage of switches S1 and S2 through a series detection capacitor and detection resistor, accurately determining when the series midpoint voltage of switches S1 and S2 rises to the load voltage or falls to 0. This implementation makes the solution provided in this application embodiment more comprehensive.

[0012] In conjunction with the first aspect, in one implementation of this application embodiment, the shutdown control unit is configured to: compare the current of inductor L with a preset inductor current zero-crossing threshold to obtain the current polarity identifier of inductor L; calculate a first threshold based on the AC sampling voltage; compare the current of inductor L with the first threshold to obtain a comparison result of the current of inductor L and the first threshold; and calculate a comparison result of the load voltage and the AC sampling voltage based on the load voltage and the AC sampling voltage. This implementation makes the solution provided by the embodiments of this application more comprehensive.

[0013] In conjunction with the first aspect, in one implementation of this application, the shutdown control unit includes a threshold calculation subunit, a voltage comparison subunit, a comparator CMP4, and a comparator CMP5. The first input terminal of comparator CMP4 receives the current of inductor L, the second input terminal receives a preset inductor current zero-crossing threshold, and the output terminal outputs the current polarity indicator of inductor L. The first input terminal of comparator CMP5 receives the current of inductor L, and the output terminal outputs the comparison result between the current of inductor L and the first threshold. The threshold calculation subunit is used to calculate the first threshold based on the AC sampling voltage and output the first threshold to the second input terminal of comparator CMP5. The voltage comparison subunit is used to obtain and output the comparison result between the load voltage and the AC sampling voltage based on the load voltage and the AC sampling voltage. This implementation makes the solution provided by this application embodiment more comprehensive.

[0014] In conjunction with the first aspect, in one implementation of this application embodiment, the threshold calculation subunit is specifically used to calculate a first threshold from the AC sampling voltage and the load voltage, and outputs the first threshold to the second input terminal of the comparator CMP5. This implementation makes the solution provided by the embodiments of this application more comprehensive.

[0015] In conjunction with the first aspect, in one implementation of the embodiments of this application, the AC signal processing unit is used to: acquire the AC voltage at both ends of the AC input terminal; sample the AC voltage to obtain an AC sampling voltage; and compare the AC sampling voltage with a zero-crossing threshold of the AC sampling voltage to obtain the polarity identifier of the AC voltage. This implementation makes the solution provided by the embodiments of this application more comprehensive.

[0016] In conjunction with the first aspect, in one implementation of this application embodiment, the AC signal processing unit includes an AC voltage sampling subunit and a comparator CMP1; the AC voltage sampling subunit is connected to both ends of the AC input terminal and is used to obtain and output an AC sampling voltage based on the AC voltage at the AC input terminal; the first input terminal of the comparator CMP1 receives the AC sampling voltage, the second input terminal receives the zero-crossing threshold of the AC sampling voltage, and the output terminal outputs the polarity indicator of the AC voltage. This implementation makes the solution provided by the embodiments of this application more comprehensive.

[0017] In conjunction with the first aspect, in one implementation of this application, the current sampling unit includes a sampling resistor, a voltage sensor, and a calculation subunit; the sampling resistor is connected in series in the line between the load and the AC input terminal; the voltage sensor is connected across the two ends of the sampling resistor to detect the voltage across the sampling resistor; the calculation subunit is connected to the voltage sensor to calculate the current of the inductor L based on the voltage across the sampling resistor and the resistance value of the sampling resistor. This implementation makes the solution provided by the embodiments of this application more comprehensive.

[0018] In conjunction with the first aspect, in one implementation of the embodiments of this application, the current sampling unit is specifically a current transformer; the current transformer is connected to one end of the inductor L and is used to detect the current in the inductor L. This implementation makes the solution provided by the embodiments of this application more comprehensive.

[0019] In conjunction with the first aspect, in one implementation of this application embodiment, when the AC input terminal outputs a positive voltage, and the switching transistor S2 is the main switch and the switching transistor S1 is the auxiliary switch, the PWM control unit is used to: when Ts is greater than Ts_min and tcm_flag is a first preset value, determine the time when the auxiliary switch is turned off based on the current polarity identifier icom0 of the inductor L, and determine the time when the main switch is turned on based on the second turn-on indication signal, wherein Ts is the time since the last main switch was turned on, Ts_min is the set minimum period limit, and tcm_flag is the comparison result identifier of the load voltage and the AC sampling voltage; when Ts is greater than Ts_min and tcm_flag is a second preset value, determine the time when the main switch is turned on based on the comparison result ico of the current of the inductor L and the first threshold. m1 determines the time when the auxiliary switch is turned off, and the time when the main switch is turned on is determined according to the second turn-on indication signal. When Ts is less than Ts_min and tcm_flag is the first preset value, the time when the auxiliary switch is turned off is determined according to the current polarity identifier icom0 of the inductor L. This continues until Ts is greater than Ts_min, at which point the main switch is turned on according to the second turn-on indication signal. When Ts is less than Ts_min and tcm_flag is the second preset value, the time when the auxiliary switch is turned off for the first time is determined according to the current polarity identifier icom0 of the inductor L. This continues until Ts is greater than Ts_min, at which point the auxiliary switch is turned on again according to the first turn-on indication signal, the time when the auxiliary switch is turned off again according to icom1, and the time when the main switch is turned on according to the second turn-on indication signal. This implementation method makes the solution provided in the embodiments of this application more comprehensive.

[0020] In a second aspect, embodiments of this application provide a power conversion circuit control method for controlling a circuit as described in the first aspect. The circuit control method includes: acquiring the voltage across the load terminals, the current through the inductor L, and the AC voltage at the AC input terminal; determining the polarity of the AC voltage and the AC sampling voltage based on the AC voltage, wherein the AC sampling voltage is obtained by sampling the AC voltage; determining the current polarity identifier of the inductor L, the comparison result of the current of the inductor L with a first threshold, and the comparison result of the voltage of the load and the AC sampling voltage based on the current of the inductor L, the voltage of the load, and the AC sampling voltage; determining a first turn-on indication signal and a second turn-on indication signal based on the series midpoint voltage of the switches S1 and S2 in the circuit and the polarity identifier of the AC voltage; and performing pulse width modulation (PWM) control on the switches S1 and S2 based on the first turn-on indication signal, the second turn-on indication signal, the polarity identifier of the AC voltage, the current polarity identifier of the inductor L, the comparison result of the current of the inductor L with the first threshold, and the comparison result of the voltage of the load and the AC sampling voltage.

[0021] In conjunction with the second aspect, in one implementation of this application embodiment, determining the first turn-on indication signal and the second turn-on indication signal based on the polarity identifier of the series midpoint voltage of switching transistors S1 and S2 in the circuit and the AC voltage includes: detecting the rate of change of the series midpoint voltage of switching transistors S1 and S2 in the circuit; selecting a first turn-on comparison value from a first comparison value and a second comparison value based on the polarity identifier of the AC voltage; selecting a second turn-on comparison value from a third comparison value and a fourth comparison value based on the polarity identifier of the AC voltage; comparing the rate of change with the first turn-on comparison value to obtain the first turn-on indication signal; and comparing the rate of change with the second turn-on comparison value to obtain the second turn-on indication signal. This implementation makes the solution provided by the embodiments of this application more comprehensive.

[0022] In conjunction with the second aspect, in one implementation of this application embodiment, when the AC input terminal outputs a positive voltage, and the switching transistor S2 is the main switch and the switching transistor S1 is the auxiliary switch, the method includes: when Ts is greater than Ts_min and tcm_flag is a first preset value, determining the time when the auxiliary switch is turned off based on the current polarity indicator icom0 of the inductor L, and determining the time when the main switch is turned on based on a second turn-on indication signal, wherein Ts is the time since the last main switch was turned on, Ts_min is a set minimum period limit, and tcm_flag is an indicator of the comparison result between the load voltage and the AC sampling voltage; when Ts is greater than Ts_min and tcm_flag is a second preset value, determining the time when the main switch is turned on based on the current of the inductor L and a first threshold value... The comparison result icom1 determines the time when the auxiliary switch is turned off, and the second turn-on indication signal determines the time when the main switch is turned on. When Ts is less than Ts_min and tcm_flag is a first preset value, icom0 determines the time when the auxiliary switch is turned off, until Ts is greater than Ts_min, then the second turn-on indication signal determines the time when the main switch is turned on. When Ts is less than Ts_min and tcm_flag is a second preset value, icom0 determines the time when the auxiliary switch is turned off for the first time, until Ts is greater than Ts_min, then the first turn-on indication signal determines the time when the auxiliary switch is turned on again, icom1 determines the time when the auxiliary switch is turned off again, and the second turn-on indication signal determines the time when the main switch is turned on. This implementation method makes the solution provided in this application embodiment more comprehensive.

[0023] Thirdly, embodiments of this application provide a power supply, including: the power conversion circuit as described in the first aspect. Attached Figure Description

[0024] Figure 1 The schematic diagram of the totem pole PFC circuit provided in the embodiments of this application; Figure 2a This is one of the schematic diagrams illustrating the working principle of a totem pole PFC circuit. Figure 2b This is the second schematic diagram of the working principle of the totem pole PFC circuit; Figure 2c This is the third schematic diagram illustrating the working principle of the totem pole PFC circuit. Figure 2d This is the fourth schematic diagram illustrating the working principle of the totem pole PFC circuit. Figure 3 The waveform diagram of PFC circuit operation under CRM mode provided in the embodiments of this application; Figure 4 The waveform diagram of PFC circuit operation in DCM mode provided in the embodiments of this application; Figure 5 A schematic diagram of the circuit provided in the embodiments of this application; Figure 6 This is a schematic diagram of one type of current sampling unit 506 according to an embodiment of this application; Figure 7 This is a schematic diagram of another current sampling unit 506 according to an embodiment of this application; Figure 8a A schematic diagram of the AC signal processing unit 507 provided in an embodiment of this application; Figure 8b for Figure 8a The circuit waveform diagram corresponding to the AC signal processing unit 507 shown; Figure 9a A schematic diagram of the shutdown control unit 508 provided in an embodiment of this application; Figure 9b This is a schematic diagram of the inductor and parasitic capacitance resonant circuit in an embodiment of this application; Figure 10a This is one of the inductor current comparison waveforms in the embodiments of this application; Figure 10b This is the second waveform diagram of inductor current comparison in the embodiments of this application; Figure 11a This is one of the graphs showing the threshold versus input voltage in the embodiments of this application; Figure 11b This is the second graph showing the threshold versus input voltage in the embodiments of this application; Figure 12 The output-input-output waveform diagram of the voltage comparator subunit provided in the embodiments of this application; Figure 13 A schematic diagram of an activation control unit 509 provided in an embodiment of this application; Figure 14a This is one of the input / output waveform diagrams of the activation control unit 509 provided in the embodiments of this application; Figure 14b This is the second input / output waveform diagram of the activation control unit 509 provided in the embodiments of this application; Figure 15 A schematic diagram of the first judgment logic executed by the PWM control unit 510 provided in the embodiments of this application; Figure 16a This is a waveform diagram of the first mode in the embodiments of this application; Figure 16b This is a waveform diagram of the second mode in the embodiments of this application; Figure 16c This is a waveform diagram of the third mode in the embodiments of this application; Figure 16d This is a waveform diagram of the fourth mode in the embodiments of this application; Figure 17This is a schematic diagram of another totem pole PFC circuit provided in an embodiment of this application. Detailed Implementation

[0025] The technical solutions in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0026] Figure 1 This is a schematic diagram of a totem pole PFC circuit provided in an embodiment of this application. The totem pole power factor correction (PFC) circuit can achieve rectification and PFC functions in a single stage, requires few conducting components, and is a high-efficiency AC-DC circuit. Figure 1 The totem pole PFC circuit shown consists of an AC input, a PFC inductor L, four switches S1~S4, and an output filter capacitor C. OUT The load consists of S1 and S2, which can be field-effect transistors or transistors made of silicon semiconductor materials (Si) or third-generation wide bandgap semiconductor materials such as silicon carbide (SiC) or gallium nitride (GaN), including but not limited to metal-oxide-semiconductor field-effect transistors (MOSFETs), high electron mobility field-effect transistors (HEMTs), or insulated gate bipolar transistors (IGBTs); S3 and S4 can be MOSFETs, HEMTs, IGBTs, or diodes made of materials such as Si, SiC, or GaN. Figure 2a This is one of the schematic diagrams illustrating the working principle of a totem pole PFC circuit. Figure 2b This is the second schematic diagram of the working principle of the totem pole PFC circuit. Figure 2c This is the third schematic diagram illustrating the working principle of the totem pole PFC circuit. Figure 2d This is the fourth schematic diagram illustrating the working principle of a totem pole PFC circuit. When the input VAC is positive, the working principle is as follows: Figure 2a and Figure 2b As shown, S4 is on, S2 acts as the main switch to charge the inductor, and S1 acts as the secondary switch to discharge the inductor. When the input VAC is negative, the working principle is as follows: Figure 2c and Figure 2dAs shown, S3 is on, S1 is on as the main switch to charge the inductor, and S2 is on as the secondary switch to discharge the inductor. In low-power applications, totem-pole PFC circuits typically operate in critical conduction mode (CRM) or discontinuous current mode (DCM), with the peak current automatically following the input voltage waveform to achieve PFC functionality (generally, totem-pole PFC circuits use CRM / DCM mode in low-power applications. As power increases, the peak current increases, leading to excessive current stress; therefore, continuous conduction mode (CCM) is required for higher power applications). Taking VAC as the positive time as an example, the operating waveform is as follows... Figure 3 and Figure 4 As shown ( Figure 3 This is a waveform diagram of the PFC circuit operating in CRM mode provided in an embodiment of this application. Figure 4 (This is a waveform diagram of the PFC circuit in DCM mode provided in the embodiment of this application). In CRM mode, the auxiliary switch turns off when the inductor current reaches 0 (at time t2), and then after a short dead time ( Figure 3 The main switch is turned on after time t2 to time t3; in DCM mode, the auxiliary switch is turned off after a relatively long resonant time ( Figure 4 (From time t2 to time t3), then turn on the main switch. DCM mode is a working mode entered after setting a maximum frequency limit to prevent CRM mode from operating at too high a frequency.

[0027] To improve the efficiency of totem-pole PFC, S1 and S2 need to implement zero-voltage switching (ZVS) control. (The last part, "V," appears to be incomplete and requires further context.) AC Taking the time-based CRM mode as an example, such as Figure 3 At time t0, after the main switch (S2) is turned off, the inductor current will charge the parasitic capacitance of S2, while the parasitic capacitance of S1 discharges. After the voltage at point SW1 rises to Vout (ignoring the on-state voltage drop of S1), the auxiliary switch (S1) is turned on, and S1 achieves ZVS. Since the inductor current is usually relatively large during this process, ZVS of the auxiliary switch is relatively easy to achieve. At time t2, the inductor current is 0, turning off the auxiliary switch (S1). Then, the inductor L resonates with the parasitic capacitances of S1 and S2. When Vout... AC When the voltage is greater than 0.5Vout, the resonant energy is insufficient to make the voltage at SW1 resonate to 0. The main switch (S2) can only be turned on at the voltage valley at time t3. The same logic applies to DCM mode. Therefore, in CRM / DCM mode, the main switch of the totem pole PFC cannot achieve full-range ZVS.

[0028] To address the aforementioned technical problems, this application provides a circuit in which the main switch can achieve ZVS, thus solving the technical problem that the main switch of the totem pole PFC cannot achieve full-range ZVS. Figure 5 This is a schematic diagram of a circuit provided in an embodiment of this application. The circuit includes a power factor correction (PFC) circuit module 501 and a PFC circuit controller 502.

[0029] The PFC circuit module 501 includes switching transistors S1, S2, S3, and S4, an inductor L, a capacitor Co, an AC input terminal 503, and a load 504. The inductor L and the AC input terminal 503 are connected in series between the midpoint SW1 of the series connection of switching transistors S1 and S2 and the midpoint SW2 of the series connection of switching transistors S3 and S4. The two ends of the series connection of switching transistors S1 and S2, the two ends of the series connection of switching transistors S3 and S4, and the load 504 are connected in parallel. The capacitor Co is also connected in parallel with the load 504.

[0030] The PFC circuit controller 502 includes: Voltage sampling unit 505 is used to acquire the voltage vo_sns of load 504; The current sampling unit 506 is used to obtain the current cs_sns of the inductor L; AC signal processing unit 507 is used to acquire the AC voltage V at AC input terminal 503. AC According to AC voltage V AC The output AC voltage polarity identifier PAC and the AC sampling voltage vac_sns, the AC sampling voltage vac_sns being based on the AC voltage V AC Obtained by sampling; The shutdown control unit 508 is used to output the current polarity flag icom0 of inductor L, the comparison result icom1 of the current of inductor L with the first threshold, and the comparison result tcm_flag of the voltage of load 504 and the AC sampling voltage based on the current cs_sns of inductor L, the voltage vo_sns of load 504 and AC sampling voltage vac_sns. The turn-on control unit 509 is used to output a first turn-on indication signal dt_ctrl1 and a second turn-on indication signal dt_ctrl2 based on the voltage at the midpoint SW1 of the series connection of the switching transistors S1 and S2 and the polarity of the AC voltage. The pulse width modulation (PWM) control unit 510 is used to perform PWM control on the switching transistors S1 and S2 based on the first turn-on indication signal dt_ctrl1, the second turn-on indication signal dt_ctrl2, the polarity identifier PAC of the AC voltage, the current polarity identifier icom0 of the inductor L, the comparison result icom1 of the current of the inductor L and the first threshold, and the comparison result tcm_flag of the voltage of the load 504 and the AC sampling voltage.

[0031] The following is a detailed description of each unit of the PFC circuit controller 502: I. Voltage sampling unit 505; In this embodiment, the voltage sampling unit 505 can specifically be a voltage sensor, a voltage sampling circuit, etc. The voltage sampling unit 505 can be connected to both ends of the load 504, thereby obtaining the sampled voltage vo_sns by sampling the output voltage Vout across the load 504. In some cases, such as... Figure 5 As shown, if one end of the load 504 is grounded, the voltage sampling unit 505 can also be connected only to the non-grounded end of the load 504.

[0032] II. Current sampling unit 506; In this embodiment, the current sampling unit 506 for obtaining the current cs_sns of the inductor L can be implemented in various ways. This embodiment provides two such methods as follows: Figure 6 This is a schematic diagram of one type of current sampling unit 506 according to an embodiment of this application. Figure 6 As shown, the current sampling unit 506 includes a sampling resistor Rcs, a voltage sensor, and a calculation subunit; the sampling resistor Rcs is connected in series in the line between the load 504 and the AC input terminal 503; the voltage sensor is connected across the two ends of the sampling resistor Rcs. Figure 6 Since one end of the sampling resistor Rcs is grounded, only the non-grounded end of Rcs needs to be connected (this is used to detect the voltage across Rcs). The calculation subunit is connected to a voltage sensor and is used to calculate the current cs_sns of the inductor L based on the voltage across Rcs and the resistance of Rcs. Specifically, the current through Rcs is obtained by dividing the voltage across Rcs by the resistance of Rcs. Figure 6 As shown in the circuit, the current flowing through the sampling resistor Rcs can reflect the current flowing through the inductor L.

[0033] Figure 7 This is a schematic diagram of another current sampling unit 506 according to an embodiment of this application. Figure 7As shown, the current sampling unit 506 is specifically a current transformer (CT); the current transformer is connected to one end of the inductor L and is used to detect the current cs_sns of the inductor L.

[0034] It is understood that in practical applications, there are various ways to obtain the current cs_sns of inductor L, and this application embodiment does not limit this.

[0035] III. AC signal processing unit 507; In this embodiment, the AC signal processing unit 507 is used to acquire the AC voltage V at the AC input terminal 503. AC According to AC voltage V AC The output AC voltage polarity identifier PAC and the AC sampling voltage vac_sns, the AC sampling voltage vac_sns being based on the AC voltage V AC The sampled signal is obtained. The AC signal processing unit 507 can be implemented in various ways. One such implementation is provided in this embodiment as follows: Figure 8a This is a schematic diagram of an AC signal processing unit 507 provided in an embodiment of this application. The AC signal processing unit 507 includes an AC voltage sampling subunit 5071 and a comparator CMP1; the AC voltage sampling subunit is connected to both ends of the AC input terminal 503 (wherein, the ACL terminal is used to connect to the AC live wire, and the ACN terminal is used to connect to the AC neutral wire), and is used to process the AC voltage V at the AC input terminal 503. AC The AC sampling voltage vac_sns is obtained and output; the first input of comparator CMP1 receives the AC sampling voltage vac_sns, and the second input receives the zero-crossing threshold V of the AC sampling voltage. AC_TH The polarity indicator PAC of the output AC voltage is displayed at the output terminal.

[0036] Figure 8b for Figure 8a The circuit waveform diagram corresponding to the AC signal processing unit 507 is shown. It can be seen that the AC voltage V at the AC input terminal 503... AC The AC sampling voltage vac_sns is obtained after sampling by the AC voltage sampling subunit. Furthermore, comparator CMP1 is used to compare the AC sampling voltage vac_sns with the zero-crossing threshold V. AC_TH Comparison: If the AC sampling voltage vac_sns is greater than the zero-crossing threshold V AC_TH (That is, the voltage at the ACL terminal is greater than the voltage at the ACN terminal, and the voltage at the AC input terminal 503 is positive) then the output is 1 (PAC=1). If the AC sampling voltage vac_sns is less than the zero-crossing threshold V AC_TH(That is, if the voltage at the ACL terminal is less than the voltage at the ACN terminal, and the voltage at the AC input terminal 503 is negative, then the output is 0 (PAC=0).

[0037] IV. Shutdown control unit 508; In this embodiment, the shutdown control unit 508 is used to output the current polarity identifier icom0 of inductor L and the current of inductor L and the first threshold voltage V based on the current cs_sns of inductor L, the voltage vo_sns of load 504 and AC sampling voltage vac_sns. CS_TH1 The comparison results are icom1 and tcm_flag, which are the voltage of load 504 and the AC sampling voltage. The shutdown control unit 508 can be implemented in various ways; one such implementation is provided in this embodiment as follows: Figure 9a This is a schematic diagram of a shutdown control unit 508 provided in an embodiment of this application. The shutdown control unit 508 includes a threshold calculation subunit 5081, a voltage comparison subunit 5082, a comparator CMP4, and a comparator CMP5. The first input terminal of the comparator CMP4 receives the current cs_sns of the inductor L, and the second input terminal receives a preset inductor current zero-crossing threshold V. CS_TH0 The output terminal outputs the polarity identifier of the current in inductor L, icom0; the first input terminal of comparator CMP5 receives the current cs_sns of inductor L, and the output terminal outputs the current cs_sns of inductor L and the first threshold V. CS_TH1 The comparison result is icom1; the threshold calculation subunit 5081 is used to calculate the first threshold V based on the AC sampling voltage. CS_TH1 and output the first threshold V CS_TH1 The voltage comparison subunit 5082 is used to obtain and output the comparison result of the voltage vo_sns of the load 504 and the AC sampling voltage vac_sns based on the voltage vo_sns of the load 504 and the AC sampling voltage vac_sns.

[0038] Figure 9a The signal output by the shutdown control unit 508 shown can be used to control the shutdown time of the auxiliary switch. After the auxiliary switch is turned off, the inductor L resonates with the parasitic capacitances of the switching transistors S1 and S2, as shown below. Figure 9b As shown ( Figure 9b (This is a schematic diagram of the resonant circuit for inductance and parasitic capacitance in an embodiment of this application). To ensure that the voltage at SW1 can rise to Vout or fall to 0 after the secondary switch is turned off, thus achieving ZVS for the main switch, the inductor current must satisfy the following formula at the turn-off moment: ; Among them, C DS =C DS1 +CDS2 C DS1 Including the parasitic capacitance of the switching transistor S1 and the external capacitance, C DS2 This includes the parasitic capacitance of the switching transistor S2 and the external capacitor. The AC input terminal 503 and the load 504 can be referred to the previous description.

[0039] According to the above conditional formula, in |V AC ≤0.5V OUT When the above equation is always satisfied, that is, when the auxiliary switch is turned off when the inductor current is 0, the voltage at SW1 can resonate and rise to Vout or fall to 0. When |V AC |>0.5V OUT When the auxiliary switch is turned off, the above equation must be satisfied. V CS_THO The zero-crossing threshold for inductor current is defined as cs_sns when it is below V. CS_THO When icom0 is set to zero, which is the moment when the inductor current crosses zero, the waveform is as follows: Figure 10a As shown. V CS_TH1 To satisfy the threshold of the inductor current (i.e. the first threshold) in the above formula. When cs_sns is lower than V CS_TH1 When icom1 is set to zero, it is the moment when the inductor current satisfies the above condition formula, and the waveform is as follows. Figure 10b As shown.

[0040] The above situation is that the current sampling unit 506 adopts, as shown in the example Figure 6 The diagram illustrates the case where the inductor current cs_sns is obtained by sampling the inductor current. In other cases, the current sampling unit 506 uses a different method... Figure 7 The inductor current cs_sns is obtained by sampling the inductor current in the manner shown. The waveform of the inductor current cs_sns will then be altered, as shown below. Figure 10b As shown. Although the waveform of the inductor current cs_sns has changed, the above conditional formula still applies, demonstrating that the shutdown control unit 508 provided in this application embodiment has wide applicability.

[0041] The formula for calculating the first threshold mentioned above is: ; In other embodiments, the formula for calculating the first threshold can be simplified as follows: take vo_sns = vac_sns, Substituting into this formula yields the simplified calculation formula for the first threshold: ; When the input voltage (RMS value) is different, VCS_TH1 is calculated by taking the peak voltage point, and the threshold voltage V at the peak point under different input voltages can be plotted. CS_TH1 The curves for different input voltages are as follows: Figure 11a As shown. Figure 11a This is one of the graphs showing the threshold versus input voltage in this embodiment. Line 1101 represents the curve corresponding to the calculation formula of the first threshold, and line 1102 represents the curve corresponding to the simplified calculation formula of the first threshold. It can be seen that the approximate threshold curves all satisfy the conditional formula for inductor current. Therefore, in some cases, the threshold calculation subunit in the shutdown control unit 508 does not need to sample the output voltage to calculate the first threshold. The threshold calculation subunit obtains the first threshold by performing logical calculations based on the AC sampled voltage and relevant parameters built into the threshold calculation subunit, using the simplified calculation formula of the first threshold. This scheme is simpler to calculate and easier to implement.

[0042] In other embodiments, the simplified calculation formula for the first threshold can also be transformed into: V AC >V TH0 ; V AC ≤V TH0 ; ; In this modified formula, the threshold calculation subunit can obtain a more suitable threshold setting by adjusting the parameters k2 and a, while meeting the requirements of the inductor current condition formula. It does not require sampling the output voltage, and the calculation is simple and easy to implement. Figure 11b This is the second graph showing the threshold versus input voltage in an embodiment of this application. Line 1101 represents the curve corresponding to the calculation formula of the first threshold, and line 1103 represents the curve corresponding to the modified formula. It can be seen that line 1103 is quite similar to line 1101, and both satisfy the inductor current condition formula.

[0043] The voltage comparator subunit is described in detail below.

[0044] From the above conditional formula, it can be seen that in |V AC ≤0.5V OUT When using icom0 to detect the zero-crossing moment of the inductor current, at |V AC |>0.5V OUT At that time, icom1 is used to detect the moment when the inductor current satisfies the above condition formula. In this embodiment, the voltage comparison subunit can be used to determine and distinguish |V AC ≤0.5V OUT and |V AC |>0.5V OUT There are two scenarios. Specifically, half of the voltage vo_sns of load 504 is compared with the AC sampling voltage vac_sns. Let half of the voltage vo_sns of load 504 be V.O_th Then when |vac_sns|≤V O_th When, i.e., |V AC ≤0.5V OUT tcm_flag is set to 0 (in some embodiments, this is the first preset value); otherwise, tcm_flag is set to 1 (in some embodiments, this is the second preset value). The corresponding waveform is shown below. Figure 12 As shown ( Figure 12 (This is a diagram showing the input and output waveforms of the voltage comparator subunit provided in an embodiment of this application).

[0045] V. Activate control unit 509; In this embodiment, the turn-on control unit 509 outputs a first turn-on indication signal dt_ctrl1 and a second turn-on indication signal dt_ctrl2 based on the voltage at the midpoint SW1 of the series connection of switching transistors S1 and S2 and the polarity identifier PAC of the AC voltage. The first turn-on indication signal dt_ctrl1 is generally used to determine the moment when the auxiliary switch turns on again, and the second turn-on indication signal dt_ctrl2 is used to determine the moment when the main switch turns on. Specifically, the turn-on control unit 509 detects the rate of change dV / dt of the bridge arm midpoint voltage, and then enables the PWM control unit 510 to control the turn-on of the main switch according to the rate of change dV / dt, thus achieving ZVS of the main switch. In some cases, the PWM control unit 510 can also control the re-turn-on of the auxiliary switch according to the rate of change dV / dt. To further ensure accurate judgment, the turn-on control unit 509 can appropriately process the rate of change dV / dt of the bridge arm midpoint voltage to output the first turn-on indication signal dt_ctrl1 and the second turn-on indication signal dt_ctrl2. One processing method provided in this application embodiment is as follows: The turn-on control unit 509 detects the rate of change of the series midpoint voltage of switching transistors S1 and S2 through a detection circuit; it selects a first turn-on comparison value from a first comparison value and a second comparison value based on the polarity of the AC voltage using a two-to-one switch MUX1; it selects a second turn-on comparison value from a third comparison value and a fourth comparison value based on the polarity of the AC voltage using a two-to-one switch MUX2; it compares the rate of change with the first turn-on comparison value using comparator CMP2 to obtain a first turn-on indication signal dt_ctrl1; and it compares the rate of change with the second turn-on comparison value using comparator CMP3 to obtain a second turn-on indication signal dt_ctrl2. The following... Figure 13 To describe the above situation: Figure 13This is a schematic diagram of an activation control unit 509 provided in an embodiment of this application. The activation control unit 509 includes a detection circuit, a two-to-one switch MUX1, a two-to-one switch MUX2, a comparator CMP2, a comparator CMP3, and a NOT gate INV1. The detection circuit includes a detection capacitor Cd and a detection resistor Rd connected in series. The first end of the detection capacitor Cd is connected to the midpoint of the series connection between switching transistors S1 and S2, and the second end of the detection capacitor Cd is connected to the first end of the detection resistor Rd, which is grounded. The midpoint of the series connection between the detection capacitor Cd and the detection resistor Rd is connected to the first input terminal of comparator CMP2 and the first input terminal of comparator CMP3, such that the voltage V at the midpoint of the series connection between the detection capacitor Cd and the detection resistor Rd is... DT It can be input to the first input terminal of comparator CMP2 and the first input terminal of comparator CMP3.

[0046] Understandably, during the dead time between the switching transitions of S1 and S2, the voltage at SW1 will either increase (from S2 on to S1 on) or decrease (from S1 on to S2 on). This voltage change at SW1 will generate a current id across capacitor Cd, the magnitude of which is: ; The current id flowing through resistor Rd generates a voltage V at the midpoint of the series connection between sensing capacitor Cd and sensing resistor Rd. DT V DT Size is ; As can be seen from the above formula, V DT The rate of change of the voltage at the midpoint SW1 of the series connection between switching transistors S1 and S2 is positively correlated, therefore it can be used as... V DT This represents the rate of voltage change at the midpoint SW1 of the series circuit. V DT By comparing with other set voltage values, the first activation indication signal and the second activation indication signal can be obtained, as follows: The control terminal of the 2-to-1 switch MUX1 is connected to the interface corresponding to the AC voltage polarity indicator PAC, and the two input terminals receive the first voltage V respectively. HM_THS Second voltage V LM_THS The input and output terminals are connected to the second input terminal of comparator CMP2. When the polarity indicator PAC of the AC voltage is 0, the two-to-one switch MUX1 outputs the first voltage V. HM_THS The voltage is fed to the second input terminal of comparator CMP2; when the polarity indicator PAC of the AC voltage is 1, the two-to-one switch MUX1 outputs the second voltage V. LM_THS To the second input terminal of comparator CMP2.

[0047] The control terminal of the 2-to-1 switch MUX2 is connected to the interface corresponding to the AC voltage polarity indicator PAC, and the two input terminals receive a third voltage V respectively. HM_THM and the fourth voltage V LM_THM The input and output terminals are connected to the second input terminal of comparator CMP3. When the polarity indicator PAC of the AC voltage is 0, the 2-to-1 switch MUX2 outputs the third voltage V. HM_THM The voltage is fed to the second input terminal of comparator CMP3; when the polarity indicator PAC of the AC voltage is 1, the 2-to-1 switch MUX2 outputs the fourth voltage V. LM_THM To the second input terminal of comparator CMP3.

[0048] The first input terminal of comparator CMP2 is connected to the midpoint of the series connection between the sensing capacitor Cd and the sensing resistor Rd. The second input terminal of comparator CMP2 is connected to the output terminal of the 2-to-1 multiplexer MUX1. The output terminal of comparator CMP2 outputs the first on-indication signal dt_ctrl1. Specifically, comparator CMP2 is used to convert the voltage V at the midpoint of the series connection between the sensing capacitor Cd and the sensing resistor Rd into a signal. DT The output voltage V of the two-to-one switch MUX1 THS Compare them. If the series midpoint voltage V... DT Greater than voltage V THS If the comparator CMP2 output signal (first on-indicator signal dt_ctrl1) is set to 1; if the series midpoint voltage V DT Less than voltage V THS If the signal at the output of comparator CMP2 (the first on-indicator signal dt_ctrl1) is set to 0, then the signal at the output of comparator CMP2 is set to 0.

[0049] The first input terminal of comparator CMP3 is connected to the midpoint of the series connection between the sensing capacitor Cd and the sensing resistor Rd. The second input terminal of comparator CMP3 is connected to the output terminal of the 2-to-1 multiplexer MUX2. The output terminal of comparator CMP3 outputs a second on-state indication signal dt_ctrl2 through NOT gate INV1. Specifically, comparator CMP3 is used to convert the voltage V at the midpoint of the series connection between the sensing capacitor Cd and the sensing resistor Rd into a signal. DT The output voltage V of the 2-to-1 switch MUX2 THM Compare them. If the series midpoint voltage V... DT Greater than voltage V THM Then the output signal of comparator CMP3 is set to 1 (the output signal of comparator CMP3 becomes the second turn-on indicator signal dt_ctrl2 after passing through NOT gate INV1, and the second turn-on indicator signal dt_ctrl2 is set to 0); if the series midpoint voltage V DT Less than voltage V THMThen the output signal of comparator CMP3 is set to 0 (the output signal of comparator CMP3 becomes the second on-state indicator signal dt_ctrl2 after passing through the NOT gate INV1, and the second on-state indicator signal dt_ctrl2 is set to 1).

[0050] In the embodiments of this application, the voltages input to the second input terminals of comparators CMP2 and CMP3 are different in two cases: when the polarity indicator PAC of the AC voltage is 1 or 0. The following will explain these two cases in detail.

[0051] When PAC=1, the input / output waveforms of the control unit 509 are as follows: Figure 14a As shown ( Figure 14a (This is one of the input / output waveform diagrams of the turn-on control unit 509 provided in the embodiments of this application). When PAC=1, the two-way switch MUX1 and the two-way switch MUX2 select channel 1 value, therefore the output voltage V of the two-way switch MUX1 is... THS =V LM_THS The output voltage V of the two-to-one switch MUX2 THM =V LM_THM At this time, the input and output voltage waveforms are as follows: Figure 14a As shown, for comparator CMP2, when V DT Voltage greater than threshold V THS The first activation indicator signal dt_ctrl is set to 1 (V DT Voltage less than threshold V THS Then the first on-indicator signal dt_ctrl is 0); for comparator CMP3, when V DT Voltage less than threshold V THM The second activation indicator signal dt_ctr2 is set to 1 (V DT Voltage greater than threshold V THM Then the second activation indicator signal dt_ctr2 is 0).

[0052] When PAC=0, the input / output waveforms of the control unit 509 are as follows: Figure 14b As shown ( Figure 14b (This is the second input / output waveform diagram of the turn-on control unit 509 provided in the embodiments of this application). When PAC=0, the two-way switch MUX1 and the two-way switch MUX2 select channel 0, that is, the output voltage V of the two-way switch MUX1 is... THS =V HM_THS The output voltage V of the two-to-one switch MUX2 THM =V HM_THM The signal waveform is as follows Figure 14b As shown. For comparator CMP2, when V DT Voltage greater than threshold V THSThe first activation indicator signal dt_ctrl is set to 1 (V DT Voltage less than threshold V THS Then the first on-indicator signal dt_ctrl is 0); for comparator CMP3, when V DT Voltage less than threshold V THM The second activation indicator signal dt_ctr2 is set to 1 (V DT Voltage greater than threshold V THM Then the second activation indicator signal dt_ctr2 is 0).

[0053] In this embodiment, the moment when the voltage of SW1 drops to 0 or rises to Vout can be obtained through the first turn-on indication signal dt_ctrl1 and the second turn-on indication signal dt_ctrl2. For example, Figure 14a When PAC=1, at time t0, dt_ctrl2 changes from 1 to 0, and the voltage at point SW1 decreases to 0. At time t1, dt_ctrl1 changes from 1 to 0, and the voltage at point SW increases to Vout. For example, ... Figure 14b When PAC=0, at time t0, dt_ctrl1 changes from 0 to 1, and the voltage at point SW1 decreases to 0. At time t1, dt_ctrl2 changes from 0 to 1, and the voltage at point SW1 increases to Vout. Therefore, the switching on can be controlled by the first on-indication signal dt_ctrl1 and the second on-indication signal dt_ctrl2, achieving ZVS. For example, when the voltage at point SW1 increases to Vout, S1 is turned on, and the voltage across S1 is 0 at the time of on-in. When the voltage at point SW1 decreases to 0, S2 is turned on, and the voltage across S2 is 0 at the time of on-in, thus achieving ZVS for the switch.

[0054] VI. PWM control unit 510; In this embodiment, the PWM control unit 510 performs PWM control on switching transistors S1 and S2 based on a first turn-on indication signal dt_ctrl1, a second turn-on indication signal dt_ctrl2, an AC voltage polarity indicator PAC, an inductor L current polarity indicator icom0, a comparison result icom1 of the inductor L current and a first threshold, and a comparison result tcm_flag of the load 504 voltage and the AC sampling voltage. Specifically, the first turn-on indication signal dt_ctrl1 and the second turn-on indication signal dt_ctrl2 can be input to the PWM control unit 510 by the turn-on control unit 509; the AC voltage polarity indicator PAC can be input to the PWM control unit 510 by the AC signal processing unit 507; and the inductor L current polarity indicator icom0, the comparison result icom1 of the inductor L current and the first threshold, and the comparison result tcm_flag of the load 504 voltage and the AC sampling voltage can be input to the PWM control unit 510 by the turn-off control unit 508.

[0055] Specifically, the PWM control unit 510 can be internally set with a minimum period limit Ts_min, which limits the maximum switching frequency of the switch. When Ts is less than Ts_min and the frequency is limited, the PFC enters DCM mode. When Ts is greater than Ts_min and the frequency is not limited, the PFC operates in CRM mode, and Ts is the time from when the main switch is turned on to when the timer starts.

[0056] In this embodiment, the PWM control unit 510 performs two judgment logics based on the polarity identifier PAC of the input AC voltage. When PAC=1 (V AC When PAC = 0 (V...), the PWM control unit 510 executes the first judgment logic. AC When the value is less than 0, the PWM control unit 510 executes the second judgment logic. The following is a detailed description of the first judgment logic: When PAC=1 (V) AC When the value is greater than 0, the main switch is S2 and the auxiliary switch is S1. The first judgment logic is as follows: Figure 15 As shown ( Figure 15 (A schematic diagram of the first judgment logic executed by the PWM control unit 510 provided in the embodiments of this application) specifically includes the following four modes: First mode: When Ts is greater than Ts_min and tcm_flag is a first preset value (in this embodiment, the first preset value can be 0), the PWM control unit 510 determines the time when the auxiliary switch is turned off based on the current polarity identifier icom0 of the inductor L, and determines the time when the main switch is turned on based on the second turn-on indication signal dt_ctrl2. Here, Ts is the time since the last main switch was turned on, and the PWM control unit 510 can calculate Ts using its built-in timer. Ts_min is a set minimum period limit, and the PWM control unit 510 can record the set Ts_min using its internal register.

[0057] Figure 16a This is a waveform diagram of the first mode in the embodiments of this application. Figure 16a As shown, at time t0, the main switch (S2) is turned on, and the PWM control unit 510 starts timing Ts using a timer. After time t1, Ts > Ts_min. At time t2, the inductor current crosses zero, and the PWM control unit 510 detects that icom0 becomes 0, and Ts > Ts_min, tcm_flag = 0. Figure 15 As can be seen from the flowchart, the PWM control unit 510 can control the auxiliary switch (S1) to turn off at time t2, the PFC circuit module 501 works in CRM mode, and then enters the judgment of flag2.

[0058] It is understood that in this embodiment, the determination of flag2 can be made by the PWM control unit 510 according to the second turn-on indication signal dt_ctrl2. When dt_ctrl2 changes from 1 to 0, flag2=yes. At this time, the voltage of SW1 resonates to 0. Since PAC=1, S2 is the main switch. At this time, the drain-source voltage of the main switch is 0. At time t4, the main switch is controlled to turn on, realizing ZVS (when V AC When the value is negative, i.e., PAC=0, S1 is the main switch. When dt_ctrl2 changes from 0 to 1, the voltage of SW1 resonates to Vout, and flag2=yes. At this time, the drain-source voltage of the main switch is 0, which controls the main switch to conduct, thus realizing ZVS.

[0059] The second mode: When Ts is greater than Ts_min and tcm_flag is the second preset value (in this embodiment, the second preset value can be 1), the PWM control unit 510 determines the time when the auxiliary switch is turned off based on the comparison result icom1 between the current of the inductor L and the first threshold, and determines the time when the main switch is turned on based on the second turn-on indication signal dt_ctrl2.

[0060] Figure 16b This is a waveform diagram of the second mode in the embodiments of this application. For example... Figure 16bAs shown in the figure, at time t0, the main switch (S2) is turned on, and the PWM control unit 510 starts timing Ts by a timer. After time t1, Ts>Ts_min. At time t2, the inductor current crosses zero, the PWM control unit 510 recognizes that icom0 becomes 0 and tcm_flag=1, according to Figure 15 of the flow chart, the PWM control unit 510 proceeds to the judgment of icom1. At time t3, the PWM control unit 510 recognizes that icom1 becomes 0, then the PWM control unit 510 controls the auxiliary switch (S1) to turn off, the PFC operates in CRM mode and proceeds to the judgment of flag2.

[0061] At time t4, the PWM control unit 510 recognizes that dt_ctrl2 changes from 1 to 0 and flag2=yes, which indicates that the voltage of SW1 resonates to 0 at this time. Therefore, at time t4, the PWM control unit 510 can control the main switch to turn on, realizing ZVS.

[0062] The third mode: When Ts is less than Ts_min and tcm_flag is a first preset value (i.e., 0), the PWM control unit 510 determines the turn-off time of the auxiliary switch according to icom0, until after Ts is greater than Ts_min, determines the turn-on time of the main switch according to the second turn-on indication signal dt_ctrl2.

[0063] Figure 16c is a working waveform diagram of the third mode in the embodiments of the present application. As shown in Figure 16c , at time t0, the main switch (S2) is turned on, and the PWM control unit 510 starts timing Ts by a timer. At time t1, Ts<Ts_min, the inductor current crosses zero, the PWM control unit 510 recognizes that icom0 becomes 0 and Ts<Ts_min, according to Figure 15 of the flow chart, the PWM control unit 510 can control the auxiliary switch (S1) to turn off, and the PFC operates in DCM mode. Then the PFC circuit module 501 enters a resonance state of the inductor L and a parasitic capacitance, until at time t4, Ts>Ts_min and tcm_flag=0, according to Figure 15 of the flow chart shown, the PWM control unit 510 proceeds to the judgment of flag2.

[0064] At time t5, the PWM control unit 510 recognizes that dt_ctrl2 changes from 1 to 0 and flag2=yes, which indicates that the voltage of SW1 resonates to 0 at this time. Therefore, at time t5, the PWM control unit 510 can control the main switch to turn on, realizing ZVS.

[0065] The fourth mode: When Ts is less than Ts_min and tcm_flag is a second preset value (i.e., 1), the PWM control unit 510 determines the first turn-off moment of the secondary switch according to the current polarity identifier icom0 of the inductor L. After Ts is greater than Ts_min, the PWM control unit 510 determines the turn-on moment of the secondary switch again according to the first turn-on indication signal dt_ctrl1, determines the turn-off moment of the secondary switch again according to icom1, and determines the turn-on moment of the main switch according to the second turn-on indication signal dt_ctrl2.

[0066] Figure 16d it is an operating waveform diagram of the fourth mode in the embodiments of the present application. As shown in Figure 16d , at time t0, the main switch (S2) is turned on, and the PWM control unit 510 starts timing Ts by a timer. At time t1, Ts<Ts_min, the inductor current crosses zero, icom0=0, according to Figure 15 the flowchart, the PWM control unit 510 can control the secondary switch (S2) to turn off at time t1, and the PFC operates in DCM mode.

[0067] Then the PFC circuit module 501 enters the resonance state of the inductor L and the parasitic capacitance until time t4, Ts>Ts_min. Since tcm_flag=1, the PWM control unit 510 enters the judgment of flag1. The judgment of flag1 is controlled by dt_ctrl1. When dt_ctrl1 changes from 1 to 0, flag1=yes, at this time the voltage of SW1 resonates to Vout (when VAC is negative, that is, when PAC=0, when dt_ctrl1 changes from 0 to 1, the voltage of SW1 resonates to 0, and flag1=yes).

[0068] Therefore, at time t6, flag1=1, indicating that the voltage of SW1 has resonated to Vout. According to Figure 15 the flowchart, the PWM control unit 510 can control the secondary switch to turn on again, and realize ZVS when the secondary switch is turned on.

[0069] Until time t7, the PWM control unit 510 recognizes that icom1 becomes 0, so it controls the secondary switch (S1) to turn off. Moreover, the PWM control unit 510 enters the judgment of flag2.

[0070] At time t8, the PWM control unit 510 recognizes that dt_ctrl2 changes from 1 to 0, and flag2=yes, indicating that the voltage of SW1 has resonated to 0, then the PWM control unit 510 can control the main switch to turn on to realize ZVS.

[0071] In practical applications, when the PWM control unit 510 executes the first judgment logic, the specific execution mode is determined based on the set minimum period limit Ts_min, the time Ts since the last main switch was turned on, the comparison result tcm_flag of the voltage of the load 504 and the AC sampling voltage, and the specific circuit conditions. This application embodiment does not limit the above situations.

[0072] The analysis of the above four modes shows that, regardless of the mode, the embodiments of this application can achieve ZVS for the main switch and the auxiliary switch, that is, to achieve zero-voltage turn-on of the main switch in the full range of CRM mode and DCM mode.

[0073] At PAC=0 (V AC When the value is less than 0, the main switch is S1 and the auxiliary switch is S2. At this time, the PWM control unit 510 can execute the second judgment logic. The second judgment logic is... Figure 15 The first type of judgment logic shown follows the same process, only the methods for determining flag1 and flag2 differ, i.e., when V AC When the value is negative, i.e., when PAC=0, flag2=yes when dt_ctrl2 changes from 0 to 1, and flag1=yes when dt_ctrl1 changes from 0 to 1.

[0074] In this embodiment, the PWM control unit 510 may include one or more processors, a memory, and a communication bus. The memory may be a short-term storage memory or a persistent storage memory, storing program code. The communication bus is connected to multiple communication interfaces, which are respectively connected to the AC signal processing unit 507, the shutdown control unit 508, and the turn-on control unit 509. These interfaces are used to receive a first turn-on indication signal dt_ctrl1, a second turn-on indication signal dt_ctrl2, the polarity identifier PAC of the AC voltage, the current polarity identifier icom0 of the inductor L, the comparison result icom1 of the current of the inductor L with a first threshold, and the comparison result tcm_flag of the voltage of the load 504 and the AC sampling voltage. The processor communicates with the memory via the communication bus and executes the program code in the memory to implement the logical judgments of the PWM control unit 510.

[0075] In other embodiments, the PWM control unit 510 may be a programmable integrated circuit, an application-specific integrated circuit (ASIC), or a chip, etc., and this application embodiment does not limit this.

[0076] In other embodiments, such as Figure 5 In the totem pole PFC circuit shown, switches S3 and S4 can be replaced with MOSFETs, etc. Figure 17 As shown ( Figure 17 (This is a schematic diagram of another totem-pole PFC circuit provided in an embodiment of this application). The PWM control unit adds two output terminals, which are respectively connected to the control terminals of switch S3 and switch S4 to control the on and off of switches S3 and S4. Specifically, the PWM control unit can perform synchronous rectification on switches S3 and S4, that is, control the on and off times of switches S3 and S4 to be the same as described above. Figure 5 The switches S3 and S4 in the totem pole PFC circuit shown are the same. This is understandable. Figure 17 The totem pole PFC circuit shown is... Figure 15 The totem pole PFC circuit shown can be the same in all cases except for the differences mentioned above. Therefore, the embodiments of this application are similar. Figure 17 The other parts of the totem pole PFC circuit shown will not be described in detail.

[0077] This application embodiment also provides a power supply, which includes the above-described components. Figure 5 The circuits in the corresponding embodiments are shown. It is understood that the embodiments of this application can be used for power supplies requiring power factor correction ranging from tens of watts to several kilowatts.

Claims

1. A power conversion circuit, characterized in that, include: Power factor correction (PFC) circuit module and PFC circuit controller; The PFC circuit module includes switching transistors S1, S2, S3, and S4, an inductor L, a capacitor Co, an AC input terminal, and a load. The inductor L and the AC input terminal are connected in series between the midpoint of the series connection of the switching transistors S1 and S2 and the midpoint of the series connection of the switching transistors S3 and S4. The series terminals of the switching transistors S1 and S2, and the series terminals of the switching transistors S3 and S4 are connected in parallel with the load. The capacitor Co is connected in parallel with the load; The PFC circuit controller is used to perform PWM control on the switch S1 and the switch S2 based on the collected voltage of the load, the current of the inductor L, the AC voltage of the AC input terminal, and the series midpoint voltage of the switch S1 and the switch S2. The PFC circuit controller includes: A voltage sampling unit is used to acquire the voltage of the load; A current sampling unit is used to acquire the current of the inductor L; An AC signal processing unit is used to acquire the AC voltage at the AC input terminal, and output the polarity identifier of the AC voltage and an AC sampling voltage based on the AC voltage, wherein the AC sampling voltage is obtained by sampling the AC voltage. The shutdown control unit is configured to output, based on the current of the inductor L, the voltage of the load, and the AC sampling voltage, a polarity identifier of the current of the inductor L, a comparison result of the current of the inductor L with a first threshold, and a comparison result of the voltage of the load and the AC sampling voltage; The power-on control unit is used to output a first power-on indication signal and a second power-on indication signal based on the series midpoint voltage of the switch S1 and the switch S2 and the polarity of the AC voltage. A pulse width modulation (PWM) control unit is used to perform PWM control on the switching transistors S1 and S2 based on the first turn-on indication signal, the second turn-on indication signal, the polarity indicator of the AC voltage, the current polarity indicator of the inductor L, the comparison result of the current of the inductor L with a first threshold, and the comparison result of the load voltage and the AC sampling voltage.

2. The circuit according to claim 1, characterized in that, The activation control unit is used for: The rate of change of the series midpoint voltage of the switching transistors S1 and S2 is detected. A first turn-on comparison value is obtained by selecting one of a first comparison value and a second comparison value based on the polarity identifier of the AC voltage; and a second turn-on comparison value is obtained by selecting one of a third comparison value and a fourth comparison value based on the polarity identifier of the AC voltage. The first activation indication signal is obtained by comparing the rate of change with the first activation comparison value. The rate of change is compared with the second activation comparison value to obtain the second activation indication signal.

3. The circuit according to claim 1, characterized in that, The activation control unit includes a detection circuit, a two-to-one switch MUX1, a two-to-one switch MUX2, a comparator CMP2, a comparator CMP3, and a NOT gate INV1; The detection circuit includes a detection capacitor and a detection resistor connected in series. The first end of the detection capacitor is connected to the midpoint of the series connection between the switching transistor S1 and the switching transistor S2. The second end of the detection capacitor is connected to the first end of the detection resistor. The second end of the detection resistor is grounded. The midpoint of the series connection between the detection capacitor and the detection resistor is connected to the first input terminal of the comparator CMP2 and the first input terminal of the comparator CMP3; The control terminal of the two-to-one switch MUX1 is connected to the interface corresponding to the polarity mark of the AC voltage. The two input terminals receive the first voltage and the second voltage input respectively, and the output terminal is connected to the second input terminal of the comparator CMP2. The control terminal of the two-to-one switch MUX2 is connected to the interface corresponding to the polarity mark of the AC voltage. The two input terminals receive the input of the third voltage and the fourth voltage respectively, and the output terminal is connected to the second input terminal of the comparator CMP3. The first activation indication signal is output from the output terminal of the comparator CMP2; The output of the comparator CMP3 outputs the second enable indication signal through the NOT gate INV1.

4. The circuit according to claim 1, characterized in that, The shutdown control unit is used for: The current polarity of the inductor L is obtained by comparing the current of the inductor L with a preset inductor current zero-crossing threshold. The first threshold is calculated based on the AC sampling voltage; The current of the inductor L is compared with the first threshold to obtain the comparison result of the current of the inductor L and the first threshold. The comparison result of the load voltage and the AC sampling voltage is calculated based on the load voltage and the AC sampling voltage.

5. The circuit according to claim 1, characterized in that, The shutdown control unit includes a threshold calculation subunit, a voltage comparison subunit, a comparator CMP4, and a comparator CMP5; The comparator CMP4 receives the current of the inductor L at its first input terminal, receives a preset inductor current zero-crossing threshold at its second input terminal, and outputs the current polarity indicator of the inductor L at its output terminal. The first input terminal of the comparator CMP5 receives the current of the inductor L, and the output terminal outputs the comparison result of the current of the inductor L and the first threshold. The threshold calculation subunit is used to calculate the first threshold based on the AC sampling voltage and output the first threshold to the second input terminal of the comparator CMP5; The voltage comparison subunit is used to obtain and output the comparison result of the load voltage and the AC sampling voltage based on the load voltage and the AC sampling voltage.

6. The circuit according to claim 5, characterized in that, The threshold calculation subunit is specifically used to calculate the first threshold from the AC sampling voltage and the load voltage, and output the first threshold to the second input terminal of the comparator CMP5.

7. The circuit according to any one of claims 1 to 6, characterized in that, The AC signal processing unit is used for: Collect the AC voltage at both ends of the AC input terminal; The AC sampling voltage is obtained by sampling the AC voltage. The polarity of the AC voltage is obtained by comparing the AC sampling voltage with the zero-crossing threshold of the AC sampling voltage.

8. The circuit according to any one of claims 1 to 6, characterized in that, The AC signal processing unit includes an AC voltage sampling subunit and a comparator CMP1; The AC voltage sampling subunit is connected to both ends of the AC input terminal and is used to obtain and output the AC sampling voltage based on the AC voltage of the AC input terminal. The comparator CMP1 receives the AC sampling voltage at its first input terminal, the zero-crossing threshold of the AC sampling voltage at its second input terminal, and outputs the polarity indicator of the AC voltage at its output terminal.

9. The circuit according to any one of claims 1 to 6, characterized in that, The current sampling unit includes a sampling resistor, a voltage sensor, and a calculation subunit; The sampling resistor is connected in series in the line between the load and the AC input terminal; The voltage sensor is connected to both ends of the sampling resistor and is used to detect the voltage across the sampling resistor; The calculation subunit is connected to the voltage sensor and is used to calculate the current of the inductor L based on the voltage across the sampling resistor and the resistance value of the sampling resistor.

10. The circuit according to any one of claims 1 to 6, characterized in that, The current sampling unit is specifically a current transformer; The current transformer is connected to one end of the inductor L and is used to detect the current in the inductor L.

11. The circuit according to any one of claims 1 to 6, characterized in that, When the AC input terminal outputs a positive voltage, and the switching transistor S2 is the main switch and the switching transistor S1 is the auxiliary switch, the PWM control unit is used for: When Ts is greater than Ts_min and tcm_flag is the first preset value, the time when the auxiliary switch is turned off is determined according to the current polarity identifier icom0 of the inductor L, and the time when the main switch is turned on is determined according to the second turn-on indication signal. Here, Ts is the time since the last time the main switch was turned on, Ts_min is the set minimum period limit, and tcm_flag is the comparison result identifier of the load voltage and the AC sampling voltage. When Ts is greater than Ts_min and tcm_flag is the second preset value, the time when the auxiliary switch is turned off is determined according to the comparison result icom1 between the current of the inductor L and the first threshold, and the time when the main switch is turned on is determined according to the second turn-on indication signal. When Ts is less than Ts_min and tcm_flag is the first preset value, the time when the auxiliary switch is turned off is determined according to the current polarity identifier icom0 of the inductor L. The time when the main switch is turned on is determined according to the second turn-on indication signal after Ts is greater than Ts_min. When Ts is less than Ts_min and tcm_flag is the second preset value, the moment when the auxiliary switch is first turned off is determined according to the current polarity identifier icom0 of the inductor L. After Ts is greater than Ts_min, the moment when the auxiliary switch is turned on again is determined according to the first turn-on indication signal, the moment when the auxiliary switch is turned off again is determined according to icom1, and the moment when the main switch is turned on is determined according to the second turn-on indication signal.

12. A power conversion circuit control method for controlling the circuit as described in any one of claims 1 to 11, characterized in that, The circuit control method includes: Obtain the voltage across the load terminals, the current through the inductor L, and the AC voltage at the AC input terminal in the circuit; The polarity of the AC voltage and the AC sampling voltage are determined based on the AC voltage, and the AC sampling voltage is obtained by sampling based on the AC voltage; The polarity identifier of the current of the inductor L, the comparison result of the current of the inductor L with a first threshold, and the comparison result of the voltage of the load and the AC sampling voltage are determined based on the current of the inductor L, the voltage of the load, and the AC sampling voltage. The first turn-on indication signal and the second turn-on indication signal are determined based on the series midpoint voltage of the switching transistors S1 and S2 in the circuit and the polarity of the AC voltage. Based on the first turn-on indication signal, the second turn-on indication signal, the polarity indicator of the AC voltage, the polarity indicator of the current of the inductor L, the comparison result of the current of the inductor L with the first threshold, and the comparison result of the load voltage and the AC sampling voltage, pulse width modulation (PWM) control is performed on the switching transistors S1 and S2.

13. The method according to claim 12, characterized in that, The step of determining the first turn-on indication signal and the second turn-on indication signal based on the series midpoint voltage of the switching transistors S1 and S2 in the circuit and the polarity of the AC voltage includes: The rate of change of the series midpoint voltage of switching transistors S1 and S2 in the circuit is detected. A first turn-on comparison value is obtained by selecting one of a first comparison value and a second comparison value based on the polarity identifier of the AC voltage; and a second turn-on comparison value is obtained by selecting one of a third comparison value and a fourth comparison value based on the polarity identifier of the AC voltage. The first activation indication signal is obtained by comparing the rate of change with the first activation comparison value. The rate of change is compared with the second activation comparison value to obtain the second activation indication signal.

14. The method according to claim 12, characterized in that, When the AC input terminal outputs a positive voltage, and the switching transistor S2 is the main switch and the switching transistor S1 is the auxiliary switch, the method includes: When Ts is greater than Ts_min and tcm_flag is the first preset value, the time when the auxiliary switch is turned off is determined according to the current polarity identifier icom0 of the inductor L, and the time when the main switch is turned on is determined according to the second turn-on indication signal. Here, Ts is the time since the last time the main switch was turned on, Ts_min is the set minimum period limit, and tcm_flag is the comparison result identifier of the load voltage and the AC sampling voltage. When Ts is greater than Ts_min and tcm_flag is the second preset value, the time when the auxiliary switch is turned off is determined according to the comparison result icom1 between the current of the inductor L and the first threshold, and the time when the main switch is turned on is determined according to the second turn-on indication signal. When Ts is less than Ts_min and tcm_flag is the first preset value, the time when the auxiliary switch is turned off is determined according to icom0. Until Ts is greater than Ts_min, the time when the main switch is turned on is determined according to the second turn-on indication signal. When Ts is less than Ts_min and tcm_flag is the second preset value, the time when the auxiliary switch is turned off for the first time is determined according to icom0. After Ts is greater than Ts_min, the time when the auxiliary switch is turned on again is determined according to the first turn-on indication signal, the time when the auxiliary switch is turned off again is determined according to icom1, and the time when the main switch is turned on is determined according to the second turn-on indication signal.

15. A power supply, characterized in that, include: The power conversion circuit as described in any one of claims 1 to 11.

Images