A switching converter and a control method thereof

Abstract

The application discloses a switching converter and a control method thereof. On the basis of an asymmetric half-bridge flyback converter, negative current is configured according to the input voltage of the switching converter, the zero-crossing moment of the demagnetizing current of a transformer is detected, and a turn-off delay time is calculated, so that the falling edge of an auxiliary tube driving signal is controlled, and the turn-off moment of the auxiliary switch tube is controlled to be the moment after the zero-crossing moment of the demagnetizing current by the delay turn-off delay time, so that the magnetizing current of the transformer is controlled to be negative current from the turn-off moment of the auxiliary switch tube to the turn-on moment of the main switch tube, and the zero-voltage turn-on of the main switch tube is realized. Therefore, the application can reduce the difficulty of realizing the zero-voltage turn-on control of the main switch tube, and the application does not need to increase a high-voltage sampling resistor when realizing the zero-voltage turn-on of the main switch tube, so that large sampling loss is not caused. When the switching converter is used for ACDC application, the requirements of small size, low cost and low power consumption in small power application occasions can be met.

Description

Technical Field

[0001] This invention relates to the field of switching power supplies, specifically a switching converter and its control method. Background Technology

[0002] Switching converters, which began to be developed and applied in the 1960s, mostly used hard-switching technology. However, with the development of science and technology, various industries have placed higher demands on power supplies, and high efficiency, high power density, and miniaturization have become the main research topics in the power supply industry. Adopting soft-switching technology reduces switching losses, thus enabling the switching frequency of switching converters to reach the megahertz level, making high efficiency, high power density, and miniaturization of switching power supplies possible.

[0003] Asymmetric half-bridge flyback converters, due to their soft-switching characteristics, have become a research hotspot in high-efficiency switching power supply applications. Chinese patent application number 201911352361.1, entitled "Switching Power Supply Device," proposes the use of such... Figure 1 The asymmetrical half-bridge flyback converter and controller shown herein utilize a unidirectional clamping network 311 connected in parallel with the primary side of the transformer to control the negative peak value of the magnetizing inductor current. Depending on the load current, the converter is controlled to operate in either asymmetrical half-bridge flyback mode (AHBF Mode, unidirectional clamping network 311 is not active) or clamped asymmetrical half-bridge flyback mode (CAHBF Mode, unidirectional clamping network 311 is active). Under light no-load conditions, the converter operates in CAHBF mode, clamping the magnetizing current through the unidirectional clamping network 311, thus solving the problem of low no-load efficiency caused by excessively large negative magnetizing current in the original asymmetrical half-bridge flyback converter under light no-load conditions.

[0004] Because a large negative value of the converter's excitation current will cause a decrease in system efficiency, while a small negative value will prevent the main switch Q1 from achieving zero-voltage turn-on (ZVS), Chinese patent application number 202010966503.X, entitled "A Switching Power Supply Device and Mode Control Method," was published to further optimize system performance. Figure 2 The diagram illustrates a switching power supply device that discloses an adaptive method for achieving Zero-Switching (ZVS) when an asymmetric half-bridge flyback converter operates in CAHBF mode. This method involves using a switch detection unit (ZE) to detect the degree of soft switching achieved by the main switch Q1, controlling the drive pulse width of the auxiliary switch Q2, and thus controlling the negative value of the converter's magnetizing current. This ensures that the negative value of the magnetizing current before the main switch Q1 is turned on precisely achieves ZVS. While this control method can achieve ZVS, in ACDC applications, the use of a high-voltage sampling resistor in the switch detection unit (ZE) increases cost and introduces resistance sampling losses, making it difficult to meet the requirements of small size, low cost, and low power consumption in low-power applications. Summary of the Invention

[0005] One of the technical problems to be solved by the present invention is to provide a switching converter to solve the problem that existing switching power supply devices require a high-voltage sampling resistor in the switching detection unit ZE to detect the degree of soft switching of the main switching transistor Q1 when achieving zero-voltage turn-on of the main switching transistor Q1. This makes it difficult to meet the requirements of small size, low cost and low power consumption when the switching power supply device is used for AC / DC applications.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0007] A switching converter includes an asymmetric half-bridge flyback converter and a controller;

[0008] See Figure 3 The asymmetric half-bridge flyback converter includes a main switch, an auxiliary switch, a resonant capacitor, a transformer, a rectifier diode, an output capacitor, and a unidirectional clamping network composed of diodes and clamping switches.

[0009] Specifically: the drain of the main switching transistor is connected to the positive terminal of the voltage input terminal to connect to the input voltage Vin of the switching converter. The source of the main switching transistor, the drain of the auxiliary switching transistor, and the positive terminal of the resonant capacitor are connected together. The negative terminal of the resonant capacitor, the anode of the diode, and the same-name terminal of the primary winding of the transformer are connected together. The cathode of the diode is connected to the drain of the clamping switching transistor. The source of the auxiliary switching transistor, the source of the clamping switching transistor, and the opposite-name terminal of the primary winding of the transformer are connected together and then connected to the primary ground terminal. The opposite-name terminal of the secondary winding of the transformer is connected to the anode of the rectifier diode. The cathode of the rectifier diode is connected to the positive terminal of the output capacitor and then used to output the output voltage of the asymmetrical half-bridge flyback converter. The same-name terminal of the secondary winding of the transformer and the negative terminal of the output capacitor are connected to the secondary ground terminal.

[0010] The controller generates pulse width modulation signals for controlling the operation of the asymmetric half-bridge flyback converter, including: a main switch drive signal, an auxiliary switch drive signal, and a clamp switch drive signal, which are respectively input to the gate of the main switch, the gate of the auxiliary switch, and the gate of the clamp switch.

[0011] Its features are:

[0012] When the switching converter operates in clamped asymmetric half-bridge flyback mode (CAHBF mode):

[0013] The controller is equipped with a negative current I. nset = K*Vin+B, where Vin represents the input voltage of the switching converter, K and B are preset configuration parameters, and the negative current I... nsetThe negative current I increases with increasing input voltage Vin to ensure good zero-voltage turn-on (ZVS) of the main switch under different input voltages Vin. For the switching converter in specific system applications, configuration parameters K and B are fixed values. The negative increase indicates that the negative current I... nset It is negative, and the negative current I nset The absolute value of increases as the input voltage Vin increases.

[0014] Furthermore, the controller detects the operating parameters of the asymmetric half-bridge flyback converter to obtain the zero-crossing time of the transformer's demagnetizing current (e.g., Figure 5 At time t2', the turn-off delay time Td is calculated using the following formula, thereby controlling the falling edge of the auxiliary transistor drive signal (i.e., the turn-off time of the auxiliary switch) to be: the time after the zero-crossing time of the demagnetizing current has elapsed after the turn-off delay time Td (e.g., the time between the zero-crossing time of the demagnetizing current and the turn-off delay time Td). Figure 5 (t2'+Td=t3 time); so that: during the operation of the switching converter of the present invention, from the turn-off time of the auxiliary switch to the turn-on time of the main switch (e.g. Figure 5 The excitation current I of the transformer (from time t3 to t5) Lm Controlled to the negative current I nset This enables zero-voltage turn-on (ZVS) of the main switch.

[0015]

[0016] In the formula, T2 is the demagnetization time from the start time of demagnetization to the time when the demagnetizing current crosses zero (e.g., Figure 5 The time from t1 to t2' in the equation, where Ip is the peak value of the excitation current of the transformer (i.e., ...). Figure 5 Intermediate excitation current I Lm The demagnetization start time is the moment when the excitation current of the transformer reaches the peak value Ip.

[0017] Among them, see Figure 5 When the switching converter operates in clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode), the pulse width modulation signal generated by the controller simultaneously satisfies the following conditions: Condition 1: At the power-on moment of the switching converter, the main drive signal, auxiliary drive signal, and clamping transistor drive signal are at high, low, and low levels, respectively; Condition 2: The clamping transistor drive signal and the main drive signal are complementary signals, the rising edges of the auxiliary drive signal and the clamping transistor drive signal coincide, and the falling edge of the auxiliary drive signal precedes the falling edge of the clamping transistor drive signal; Condition 3: There is a dead time between the main drive signal and the clamping transistor drive signal. For example: Figure 5In the diagram, time t1 is the falling edge of the main drive signal, time t2 is the rising edge of the auxiliary drive signal and the clamping switch drive signal, time t3 is the falling edge of the auxiliary drive signal, time t4 is the falling edge of the clamping switch drive signal, and time t5 is the rising edge of the main drive signal. The falling edge time t3 of the auxiliary switch is between time t2 and time t4, and it is turned off until time t4. Time t1 to time t2 is the dead time from when the main switch is turned off to when the auxiliary switch and the clamping switch are turned on. Time t4 to time t5 is the dead time from when the clamping switch is turned off to when the main switch is turned on.

[0018] The controller can be any controller that satisfies the above description, that is, any controller capable of generating... Figure 5 The control device shown is for the waveforms of the three drive signals: the main drive signal, the auxiliary drive signal, and the clamping drive signal.

[0019] like Figures 4 to 6 As shown, when operating in clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode), the working principle of the switching converter of the present invention is as follows:

[0020] The switching converter of the present invention is in Figure 3 The asymmetric half-bridge flyback converter shown can be equivalent to... Figure 4 The equivalent circuit shown has the following equivalent relationships: The main switch Q1 is equivalent to an ideal switch, i.e., main switch S1 connected in parallel with diode D1 and resonant capacitor C1. The auxiliary switch Q2 is equivalent to an ideal switch, i.e., auxiliary switch S2 connected in parallel with diode D2 and resonant capacitor C2. The equivalent models of the main switch Q1 and auxiliary switch Q2 are connected in series between the positive terminal +Vin and the negative terminal -Vin of the voltage input. The midpoint SW of the series connection is connected to the positive terminal of the resonant capacitor. The transformer Tr is equivalent to an ideal transformer connected in series with the leakage inductance Lr, and connected in parallel with the magnetizing inductance Lm. The unidirectional clamping network composed of diode D3 and clamping switch Q3 is equivalent to one end of switch Sow connected to the negative terminal of the resonant capacitor and the positive terminal of the leakage inductance Lr, and the other end connected to the negative terminal -Vin of the voltage input with the negative terminal of the magnetizing inductance Lm. The anode of diode D is connected to the opposite terminal of the secondary winding of the transformer, and the cathode of diode D is connected to the positive terminal +Vo of the output capacitor Co. The output capacitor Co is connected to the load R. L In parallel connection, the negative terminal -Vo of the output capacitor Co is connected to the secondary winding of the transformer.

[0021] See Figures 3 to 5 In CAHBF mode, the switching converter of the present invention comprises five stages in each cycle: excitation stage, auxiliary switch zero-voltage turn-on stage, demagnetization stage, current clamping stage, and main switch zero-voltage turn-on stage. The working principle of each cycle is as follows:

[0022] Excitation Phase: From time t0 to time t1, the main control switch S1 is turned on, and the input voltage Vin charges the resonant capacitor Cr, leakage inductance Lr, and excitation inductance Lm, while the excitation current I... Lm and resonant inductor current I Lr Linear rise, that is, the input voltage Vin excites the transformer Tr. During this stage, the drive signals Vgs2 and Vgs3 are at low level, and the auxiliary switches S2 and Sow are turned off.

[0023] Auxiliary switch zero-voltage turn-on stage: From time t1 to time t2, the main switch S1 is turned off, and the resonant capacitors C1 and C2, the leakage inductance Lr, and the magnetizing inductance Lm form a series resonance, and the resonant inductance current I... Lr Charging resonant capacitor C1 and discharging resonant capacitor C2 causes the voltage VC1 across resonant capacitor C1 to rise and the voltage VC2 across resonant capacitor C2 to fall. When resonant capacitor C2 is fully discharged, the voltage VC2 across resonant capacitor C2 drops to zero, diode D2 naturally conducts, and the resonant inductor current I... Lr At time t2, the current flows through diode D2, and the auxiliary switch S2 is turned on, achieving zero-voltage turn-on of the auxiliary switch S2. During this stage, the drive signal Vgs3 is still at a low level, and switch Sow is turned off.

[0024] Demagnetization Phase: From time t2 to time t3, auxiliary switch S2 is turned on, main switch S1 remains off, rectifier switch D is turned on, the current I2 in rectifier switch D increases, the voltage across magnetizing inductor Lm is clamped (negative at the top, positive at the bottom), and the magnetizing current I... Lm As the voltage decreases linearly, transformer Tr demagnetizes. At time t3, the excitation current I... Lm When the set value is reached, the negative current I nset At this time, the auxiliary switch S2 is turned off. During this stage, the drive signal Vgs3 is high, and the switch Sow is turned on. The turn-on time of the switch Sow can be any time between time t2 and time t3 (that is, the switch Sow can be turned on or off between time t2 and time t3). Since the switch Sow only allows current to flow from the anode to the cathode of D3, no current flows through the switch Sow during the demagnetization stage.

[0025] Current clamping phase: From time t3 to time t4, at time t3, auxiliary switch S2 is turned off, switch Sow continues to conduct, and resonant capacitors C1, C2, Cr and leakage inductance Lr form a series resonance, and the resonant inductor current I... Lr The voltage is negative and rapidly increases in the positive direction, discharging resonant capacitor C1 and charging resonant capacitor C2. This causes the voltage VC1 across resonant capacitor C1 to decrease and the voltage VC2 across resonant capacitor C2 to increase. When VC2 equals the voltage VCr across resonant capacitor Cr, the anode voltage of switch Sow becomes zero, and the excitation current I... Lmand resonant inductor current I Lr When the currents are equal, rectifier switch D is turned off, and excitation current I... Lm (This stage is called clamping current) naturally flows from the anode to the cathode through the switch Sow. The switch Sow keeps the clamping current basically unchanged. At time t4, the drive signal Vgs3 becomes low and the switch Sow is turned off.

[0026] Zero-voltage turn-on stage of the main switch: From time t4 to time t5, at time t4, switch Sow is turned off, and the main switch S1 and auxiliary switch S2 remain off. The clamping current held by switch Sow is released, and it continues to discharge the resonant capacitor C1 and charge the resonant capacitor C2. The voltage VC1 across the resonant capacitor C1 continues to decrease, and the voltage VC2 across the resonant capacitor C2 continues to rise until the voltage across the resonant capacitor C1 drops to zero. The clamping current begins to flow through diode D1. At time t5, the drive signal Vgs1 becomes high, and the main switch S1 is turned on, achieving zero-voltage turn-on of the main switch S1.

[0027] Therefore, this invention, based on an asymmetric half-bridge flyback converter, configures the negative current I according to the input voltage Vin of the switching converter. nset The system detects the zero-crossing moment of the transformer's demagnetizing current and calculates the turn-off delay time Td. Based on this, it controls the falling edge of the auxiliary switch drive signal, ensuring the auxiliary switch's turn-off moment is set after the zero-crossing moment of the demagnetizing current has elapsed past the turn-off delay time Td. This ensures that during the operation of the switching converter, from the turn-off moment of the auxiliary switch to the turn-on moment of the main switch, the transformer's excitation current I... Lm Controlled as a negative current I nset This invention achieves zero-voltage turn-on (ZVS) of the main switch. Therefore, this invention can reduce the difficulty of implementing ZVS control of the main switch. Furthermore, this invention does not require the addition of a high-voltage sampling resistor when achieving ZVS of the main switch, and will not generate significant sampling loss. When the switching converter is used in ACDC applications, it can meet the requirements of small size, low cost, and low power consumption in low-power applications.

[0028] Preferably: obtaining the zero-crossing time of the demagnetizing current (e.g.) Figure 5 The method for time t2' is as follows:

[0029] The operating parameters detected by the controller include: the excitation current of the transformer, the excitation voltage of the transformer, and the demagnetizing voltage;

[0030] Since the transformer is in an energized state when the main switch is turned on, and the energizing current gradually increases from negative, the controller records the peak value of the energizing current as the peak value Ip, the time it takes for the energizing current to rise from zero to the peak value Ip as the energizing time T1, and the energizing voltage of the transformer at time t within the energizing time T1 as Vp(t). The energizing volt-seconds Vp*T1 of the transformer within the energizing time T1 are then calculated according to Formula 2.

[0031]

[0032] In the formula, Vp(t) = Vin(t) - V Cr Vin(t) represents the voltage value of the input voltage Vin at time t within the excitation time T1. Cr (t) represents the voltage value at time t of the negative terminal of the resonant capacitor during the excitation time T1;

[0033] Since the transformer is in a demagnetizing state when the main switch is turned off, and the excitation current gradually decreases from its peak value Ip, the controller records the excitation current from the point when the peak value Ip begins to decrease as the demagnetizing current, and records the transformer from the start of demagnetization (e.g., the time when the excitation current begins to decrease) as the demagnetizing current. Figure 5 The demagnetizing voltage at time t' after starting at time t1 in the equation is denoted as Vn(t'), and is calculated continuously according to Formula 3 from the start time of demagnetization of the transformer (e.g., time t1). Figure 5 The number of demagnetizing volt-seconds Vn*ΔT after time t1 begins:

[0034]

[0035] In the formula, Vn(t')=V Cr (t'), V Cr (t') represents the moment when the negative terminal of the resonant capacitor begins demagnetization (e.g., t'). Figure 5 The voltage value at time t' after starting from time t2 in the equation;

[0036] Based on the principle that the transformer magnetizing inductance satisfies volt-second balance in each switching cycle, the controller determines whether the demagnetizing volt-seconds Vn*ΔT and the magnetizing volt-seconds Vp*T1 are equal, and determines the moment when the two are equal as the moment when the demagnetizing current crosses zero, that is, the moment when the demagnetizing current drops to zero (e.g., the moment when the demagnetizing current drops to zero). Figure 5 The time T2 from the start of demagnetization to the zero-crossing time of the demagnetizing current (e.g., time t2' in the equation) is calculated accordingly. Figure 5 (The time from time t1 to time t2' in the text).

[0037] Therefore, this invention calculates the excitation volt-seconds Vp*T1 of the transformer within the excitation time T1 according to Formula 2, and continuously calculates the demagnetization volt-seconds Vn*ΔT within the time ΔT after the start of demagnetization according to Formula 3, and continuously judges whether the two are equal, so as to quickly determine the zero-crossing time of the demagnetizing current. It has the advantages of high detection efficiency and real-time reliability of the zero-crossing time of the demagnetizing current.

[0038] The excitation voltage and demagnetization voltage of the transformer can be detected in various ways, including but not limited to the following:

[0039] Method 1: Sampling directly on the primary winding of the transformer or sampling after reducing the voltage amplitude through a voltage divider resistor;

[0040] Method 2: Sampling directly using the auxiliary winding of the transformer or sampling after reducing the voltage amplitude through a voltage divider resistor;

[0041] Method 3: Sampling directly on the amplitude-side winding of the transformer or sampling after reducing the voltage amplitude through a voltage divider resistor.

[0042] The calculation of the excitation volt-seconds, the demagnetization volt-seconds, and the turn-off delay Td can be achieved by various means, including but not limited to the following:

[0043] Firstly, an analog circuit scheme is adopted, in which the excitation voltage and demagnetization voltage are converted into two current signals by a voltage-controlled current source. These two current signals are then used to charge two capacitors of the same capacitance value, so as to calculate the excitation volt-seconds and demagnetization volt-seconds respectively.

[0044] Secondly, digital circuits, such as microcontrollers, are used to sample, store, and calculate the excitation voltage, demagnetization voltage, excitation time, and demagnetization time.

[0045] Preferably, the configuration method for configuration parameter K and configuration parameter B is as follows:

[0046] For the switching converter in a specific system application, experimental tests were conducted with different input voltages Vin to determine the negative current I corresponding to each input voltage Vin that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition. nset Based on the data obtained through measurement, according to I nset =K*Vin+B This calculation formula fits to obtain: the values ​​of configuration parameters K and B of the switching converter under the specific system application; wherein, the efficiency condition is that the working efficiency of the switching converter is above the preset efficiency threshold, and the zero-voltage turn-on condition is that the main switch can achieve zero-voltage turn-on (ZVS) during the operation of the switching converter.

[0047] Therefore, this invention conducts experimental tests on switching converters under specific system applications with different input voltages Vin, to measure the negative current I that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition for each input voltage Vin. nset By fitting the obtained data, the values ​​of configuration parameters K and B can be determined, thus avoiding negative current I. nset Too large an output will cause a decrease in the efficiency of the switching converter, while too small an output will prevent the main switching transistor from achieving zero-voltage turn-on (ZVS).

[0048] As a preferred embodiment of the present invention: the controller includes an output voltage isolation sampling unit, a pulse width control unit, a compensation parameter configuration unit, and a ZVS control unit;

[0049] The two input terminals of the output voltage isolation sampling unit are respectively connected to the two ends of the output capacitor. The output terminal of the output voltage isolation sampling unit is connected to the control input terminal of the pulse width control unit. The ground terminal GND of the pulse width control unit is grounded. The pulse width control unit isolates and samples the output voltage of the asymmetric half-bridge flyback converter through the output voltage isolation sampling unit to generate the main drive signal, auxiliary drive signal, and clamp drive signal. These signals are then output through the main drive signal output terminal GND of the pulse width control unit. Q1 Auxiliary tube drive signal output terminal G Q2 and clamping transistor drive signal output terminal G Q3 Output;

[0050] Furthermore, the compensation parameter configuration unit can adjust the configuration parameter K and configuration parameter B within a preset parameter adjustment range. The input terminal of the compensation parameter configuration unit is connected to the drain of the main switching transistor to detect the input voltage Vin of the switching converter. The output terminal of the compensation parameter configuration unit outputs the negative current I to the negative current parameter input terminal of the ZVS control unit. nset =K*Vin+B compensation parameter configuration signal;

[0051] The source of the auxiliary switching transistor, the source of the clamping switching transistor, and the opposite-named terminal of the primary winding of the transformer are connected and then connected to the primary ground terminal through a current sampling resistor. The current sampling input terminal of the ZVS control unit is connected to the source of the auxiliary switching transistor, and the voltage sampling input terminal of the ZVS control unit is connected to the same-named terminal of the primary winding of the transformer. The output terminal of the ZVS control unit outputs the zero-crossing time of the demagnetizing current and the turn-off delay time Td to the auxiliary switching transistor turn-off control input terminal of the pulse width control unit. Based on this, the pulse width control unit controls the falling edge of the auxiliary transistor drive signal to be the time after the zero-crossing time of the demagnetizing current is delayed by the turn-off delay time Td.

[0052] Among them, see Figure 3 Vsw and Vaux represent the positive and negative voltages of the resonant capacitor, respectively. When the main switch is turned on, the negative voltage Vaux of the resonant capacitor is the excitation voltage of the transformer. When the auxiliary switch is turned on, the negative voltage Vaux of the resonant capacitor is the demagnetizing voltage of the transformer.

[0053] Therefore, this invention employs an output voltage isolation sampling unit, a pulse width control unit, a compensation parameter configuration unit, and a ZVS control unit to form the controller of an asymmetric half-bridge flyback converter. The compensation parameter configuration unit can adjust the configuration parameter K and configuration parameter B within preset parameter adjustment ranges. Thus, the switching converter of this invention can achieve negative current I under different system applications. nset Flexible configuration ensures that the main switch can achieve zero-voltage turn-on (ZVS) in different system applications.

[0054] Preferably, the controller further includes a mode determination unit;

[0055] The input terminal of the mode determination unit detects the load current of the switching converter, and determines that the switching converter is in a light load state when the load current is less than a preset load current threshold; otherwise, it determines that the switching converter is in a heavy load state.

[0056] The output of the mode determination unit is connected to the mode control terminal of the pulse width control unit. When the mode determination unit outputs a determination result indicating that the switching converter is in a light-load state to the pulse width control unit, the pulse width control unit controls the switching converter to operate in the clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode). When the mode determination unit outputs a determination result indicating that the switching converter is in a heavy-load state to the pulse width control unit, the pulse width control unit controls the switching converter to operate in the asymmetric half-bridge flyback mode (AHBF mode).

[0057] Therefore, the switching converter of the present invention can achieve system efficiency optimization over a wide load range.

[0058] The switching converter operates in AHBF mode, that is, the control method and working principle of the asymmetric half-bridge flyback converter operating in AHBF mode are disclosed in Chinese Patent Application No. 201911352361.1, "Switching Power Supply Device". It will not be described in detail here, but only the difference between AHBF mode and the CAHBF mode of this invention will be briefly explained as follows:

[0059] When the converter operates in AHBF mode, the clamping switch is always in the off state during one switching cycle. The main switch and the auxiliary switch work in a complementary manner. Each cycle includes four stages: excitation stage, auxiliary switch zero-voltage turn-on stage, demagnetization stage, and main switch zero-voltage turn-on stage.

[0060] The working principles of the excitation stage and the auxiliary switch zero-voltage turn-on stage are the same as those of the excitation stage and the auxiliary switch zero-voltage turn-on stage in the CAHBF mode described above, and will not be described again here. The working principles of the demagnetization stage and the main switch zero-voltage turn-on stage in the AHBF mode are as follows:

[0061] Demagnetization Stage: Auxiliary switch S2 remains on, main switch S1 is off, rectifier switch D is on, and the current I2 in rectifier switch D increases. The voltage across the magnetizing inductor Lm is clamped (negative at the top, positive at the bottom), and the magnetizing current ILM decreases linearly, demagnetizing the transformer. When the magnetizing current reaches the set value, auxiliary switch S2 is turned off. During this stage, drive signal Vgs3 is low, and switch Sow is off.

[0062] During the zero-voltage turn-on stage of the main switch: The main switch S1 and the auxiliary switch S2 remain off. The resonant capacitors C1, C2, Cr and the leakage inductance Lr form a series resonance. The resonant inductor current ILr is negative and rapidly increases in the positive direction, discharging the resonant capacitor C1 and charging the resonant capacitor C2. This causes the voltage VC1 across the resonant capacitor C1 to decrease and the voltage VC2 across the resonant capacitor C2 to increase. When VC2 increases to the same level as VCr, the magnetizing current ILm and the resonant inductor current ILr become equal. The rectifier switch D turns off, and the magnetizing current ILm and the resonant inductor current ILr are released, continuing to discharge the resonant capacitor C1 and charge the resonant capacitor C2. The voltage VC1 across the resonant capacitor C1 continues to decrease, and the voltage VC2 across the resonant capacitor C2 continues to increase. When the voltage across the resonant capacitor C1 drops to zero, the resonant inductor current ILr begins to flow through the diode D1. At this time, the main switch S1 is turned on, and the main switch S1 achieves zero-voltage turn-on.

[0063] The second technical problem to be solved by this invention is to provide a control method for a switching converter, so as to solve the problem that when the existing switching power supply device achieves zero-voltage turn-on of the main switching transistor Q1, a high-voltage sampling resistor is required in the switching detection unit ZE to detect the degree of soft switching of the main switching transistor Q1. This makes it difficult to meet the requirements of small size, low cost and low power consumption when the switching power supply device is used for AC / DC applications.

[0064] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0065] A control method for a switching converter, applicable to switching converters employing an asymmetric half-bridge flyback converter;

[0066] See Figure 3 The asymmetric half-bridge flyback converter includes a main switch, an auxiliary switch, a resonant capacitor, a transformer, a rectifier diode, an output capacitor, and a unidirectional clamping network composed of diodes and clamping switches.

[0067] Specifically: the drain of the main switching transistor is connected to the positive terminal of the voltage input terminal to connect to the input voltage Vin of the switching converter. The source of the main switching transistor, the drain of the auxiliary switching transistor, and the positive terminal of the resonant capacitor are connected together. The negative terminal of the resonant capacitor, the anode of the diode, and the same-name terminal of the primary winding of the transformer are connected together. The cathode of the diode is connected to the drain of the clamping switching transistor. The source of the auxiliary switching transistor, the source of the clamping switching transistor, and the opposite-name terminal of the primary winding of the transformer are connected together and then connected to the primary ground terminal. The opposite-name terminal of the secondary winding of the transformer is connected to the anode of the rectifier diode. The cathode of the rectifier diode is connected to the positive terminal of the output capacitor and then used to output the output voltage of the asymmetrical half-bridge flyback converter. The same-name terminal of the secondary winding of the transformer and the negative terminal of the output capacitor are connected to the secondary ground terminal.

[0068] The asymmetric half-bridge flyback converter is controlled by a pulse width modulation signal, which includes a main switch drive signal, an auxiliary switch drive signal, and a clamp switch drive signal, which are respectively input to the gate of the main switch, the gate of the auxiliary switch, and the gate of the clamp switch.

[0069] Its features are:

[0070] When the switching converter operates in clamped asymmetric half-bridge flyback mode (CAHBF mode for short), the control method includes:

[0071] Negative current configuration step: Detect the input voltage Vin of the switching converter, and configure the negative current I accordingly. nset =K*Vin+B, where K and B are preset configuration parameters, and the negative current I... nset The negative current I increases with increasing input voltage Vin to ensure good zero-voltage turn-on (ZVS) of the main switch under different input voltages Vin. For the switching converter in specific system applications, configuration parameters K and B are fixed values. The negative increase indicates that the negative current I... nset It is negative, and the negative current I nset The absolute value of increases as the input voltage Vin increases.

[0072] Demagnetizing current zero-crossing time detection step: Detect the operating parameters of the asymmetric half-bridge flyback converter to obtain the zero-crossing time of the transformer's demagnetizing current (e.g., Figure 5(at time t2' in the text);

[0073] The shutdown delay time calculation steps are as follows: The shutdown delay time Td is calculated using the following formula:

[0074]

[0075] In the formula, T2 is the demagnetization time from the start of demagnetization to the time when the demagnetizing current crosses zero (e.g., Figure 5 The time from t1 to t2' in the equation, where Ip is the peak value of the excitation current of the transformer (i.e., ...). Figure 5 Intermediate excitation current I Lm The demagnetization start time is the moment when the excitation current of the transformer reaches the peak value Ip.

[0076] Auxiliary switch turn-off control steps: The falling edge of the auxiliary switch drive signal (i.e., the turn-off time of the auxiliary switch) is controlled to be the time after the zero-crossing time of the demagnetizing current has elapsed for a delay of the turn-off delay time Td (e.g., the time after the turn-off delay time Td). Figure 5 (t2'+Td=t3 time); so that: during the operation of the switching converter of the present invention, from the turn-off time of the auxiliary switch to the turn-on time of the main switch (e.g. Figure 5 The excitation current I of the transformer (from time t3 to t5) Lm Controlled to the negative current I nset This enables zero-voltage turn-on (ZVS) of the main switch.

[0077] Among them, see Figure 5 When the switching converter operates in clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode), the pulse width modulation signal controlling the operation of the asymmetric half-bridge flyback converter simultaneously satisfies the following conditions: Condition 1: At the power-on moment of the switching converter, the master drive signal (Vgs1), the auxiliary drive signal (Vgs2), and the clamp drive signal (Vgs3) are high, low, and low, respectively; Condition 2: The clamp drive signal (Vgs3) and the master drive signal (Vgs1) are complementary signals, the rising edges of the auxiliary drive signal (Vgs2) and the clamp drive signal (Vgs3) coincide, and the falling edge of the auxiliary drive signal (Vgs2) precedes the falling edge of the clamp drive signal (Vgs3); Condition 3: There is a dead time between the master drive signal (Vgs1) and the clamp drive signal (Vgs3). For example: Figure 5In the diagram, time t1 is the falling edge of the main drive signal, time t2 is the rising edge of the auxiliary drive signal and the clamping switch drive signal, time t3 is the falling edge of the auxiliary drive signal, time t4 is the falling edge of the clamping switch drive signal, and time t5 is the rising edge of the main drive signal. The falling edge time t3 of the auxiliary switch is between time t2 and time t4, and it is turned off until time t4. Time t1 to time t2 is the dead time from when the main switch is turned off to when the auxiliary switch and the clamping switch are turned on. Time t4 to time t5 is the dead time from when the clamping switch is turned off to when the main switch is turned on.

[0078] The control method of the switching converter of the present invention is the same as the working principle of the switching converter described in Embodiment 1, and will not be repeated here.

[0079] Therefore, this invention, based on an asymmetric half-bridge flyback converter, configures the negative current I according to the input voltage Vin of the switching converter. nset The system detects the zero-crossing moment of the transformer's demagnetizing current and calculates the turn-off delay time Td. Based on this, it controls the falling edge of the auxiliary switch drive signal, ensuring the auxiliary switch's turn-off moment is set after the zero-crossing moment of the demagnetizing current has elapsed past the turn-off delay time Td. This ensures that during the operation of the switching converter, from the turn-off moment of the auxiliary switch to the turn-on moment of the main switch, the transformer's excitation current I... Lm Controlled as a negative current I nset This invention achieves zero-voltage turn-on (ZVS) of the main switch. Therefore, this invention can reduce the difficulty of implementing ZVS control of the main switch. Furthermore, this invention does not require the addition of a high-voltage sampling resistor when achieving ZVS of the main switch, and will not generate significant sampling loss. When the switching converter is used in ACDC applications, it can meet the requirements of small size, low cost, and low power consumption in low-power applications.

[0080] Preferably, the step of detecting the zero-crossing time of the demagnetizing current includes:

[0081] Operating parameter detection steps: Detect the operating parameters of the asymmetric half-bridge flyback converter, including: the excitation current of the transformer, the excitation voltage of the transformer, and the demagnetizing voltage;

[0082] Steps for calculating excitation volt-seconds: Since the transformer is in an energized state when the main switch is turned on, the excitation current gradually increases from negative to large. Therefore, the peak value of the excitation current is denoted as the peak excitation current Ip, the time for the excitation current to rise from zero to the peak excitation current Ip is denoted as the excitation time T1, and the excitation voltage of the transformer at time t within the excitation time T1 is denoted as Vp(t). The excitation volt-seconds Vp*T1 of the transformer within the excitation time T1 are calculated according to Formula 2:

[0083]

[0084] In the formula, Vp(t) = Vin(t) - V Cr Vin(t) represents the voltage value of the input voltage Vin at time t within the excitation time T1. Cr (t) represents the voltage value at time t of the negative terminal of the resonant capacitor during the excitation time T1;

[0085] Demagnetizing volt-seconds calculation steps: Since the transformer is in a demagnetizing state when the main switch is turned off, the excitation current gradually decreases from its peak value Ip. Therefore, the excitation current from the point when it begins to decrease from its peak value Ip is recorded as the demagnetizing current. The transformer is then demagnetized from the start of demagnetization (e.g., the demagnetizing current from the beginning of demagnetization). Figure 5 The demagnetizing voltage at time t' after starting at time t1 in the equation is denoted as Vn(t'), and is calculated continuously according to Formula 3 from the start time of demagnetization of the transformer (e.g., time t1). Figure 5 The number of demagnetizing volt-seconds Vn*ΔT after time t1 begins:

[0086]

[0087] In the formula, Vn(t')=V Cr (t'), V Cr (t') represents the moment when the negative terminal of the resonant capacitor begins demagnetization (e.g., t'). Figure 5 The voltage value at time t' after starting from time t2 in the equation;

[0088] Determining the zero-crossing moment of the demagnetizing current: Based on the principle that the transformer's magnetizing inductance satisfies volt-second balance in each switching cycle, determine whether the demagnetizing volt-seconds Vn*ΔT and the magnetizing volt-seconds Vp*T1 are equal. The moment when these two are equal is determined as the zero-crossing moment of the demagnetizing current, that is, the moment when the demagnetizing current drops to zero (e.g., the moment when the demagnetizing current drops to zero). Figure 5 The time T2 from the start of demagnetization to the zero-crossing time of the demagnetizing current (e.g., time t2' in the equation) is calculated accordingly. Figure 5 (The time from time t1 to time t2' in the text).

[0089] Therefore, this invention calculates the excitation volt-seconds Vp*T1 of the transformer within the excitation time T1 according to Formula 2, and continuously calculates the demagnetization volt-seconds Vn*ΔT within the time ΔT after the start of demagnetization according to Formula 3, and continuously judges whether the two are equal, so as to quickly determine the zero-crossing time of the demagnetizing current. It has the advantages of high detection efficiency and real-time reliability of the zero-crossing time of the demagnetizing current.

[0090] Preferably, the configuration method for configuration parameter K and configuration parameter B is as follows:

[0091] For the switching converter in a specific system application, experimental tests were conducted with different input voltages Vin to determine the negative current I corresponding to each input voltage Vin that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition. nset Based on the data obtained through measurement, according to I nset =K*Vin+B This calculation formula fits to obtain: the values ​​of configuration parameters K and B of the switching converter under the specific system application; wherein, the efficiency condition is that the working efficiency of the switching converter is above the preset efficiency threshold, and the zero-voltage turn-on condition is that the main switch can achieve zero-voltage turn-on (ZVS) during the operation of the switching converter.

[0092] Therefore, this invention conducts experimental tests on switching converters under specific system applications with different input voltages Vin, to measure the negative current I that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition for each input voltage Vin. nset By fitting the obtained data, the values ​​of configuration parameters K and B can be determined, thus avoiding negative current I. nset Too large an output will cause a decrease in the efficiency of the switching converter, while too small an output will prevent the main switching transistor from achieving zero-voltage turn-on (ZVS).

[0093] Compared with the prior art, the present invention has the following beneficial effects:

[0094] First, based on the use of an asymmetric half-bridge flyback converter, this invention configures the negative current I according to the input voltage Vin of the switching converter. nset The system detects the zero-crossing moment of the transformer's demagnetizing current and calculates the turn-off delay time Td. Based on this, it controls the falling edge of the auxiliary switch drive signal, ensuring the auxiliary switch's turn-off moment is set after the zero-crossing moment of the demagnetizing current has elapsed past the turn-off delay time Td. This ensures that during the operation of the switching converter, from the turn-off moment of the auxiliary switch to the turn-on moment of the main switch, the transformer's excitation current I... Lm Controlled as a negative current I nset This invention achieves zero-voltage turn-on (ZVS) of the main switch. Therefore, this invention can reduce the difficulty of implementing ZVS control of the main switch. Furthermore, this invention does not require the addition of a high-voltage sampling resistor when achieving ZVS of the main switch, and will not generate significant sampling loss. When the switching converter is used in ACDC applications, it can meet the requirements of small size, low cost, and low power consumption in low-power applications.

[0095] Secondly, this invention calculates the excitation volt-seconds Vp*T1 of the transformer within the excitation time T1 according to Formula 2, and continuously calculates the demagnetization volt-seconds Vn*ΔT within the time ΔT after the start of demagnetization according to Formula 3, and continuously judges whether the two are equal, so as to quickly determine the zero-crossing time of the demagnetizing current. It has the advantages of high detection efficiency and real-time reliability of the zero-crossing time of the demagnetizing current.

[0096] Third, this invention conducts experimental tests on switching converters under specific system applications with different input voltages Vin, to measure the negative current I that can simultaneously meet the efficiency condition and the zero-voltage turn-on condition for each input voltage Vin. nset By fitting the obtained data, the values ​​of configuration parameters K and B can be determined, thus avoiding negative current I. nset Too large an output will cause a decrease in the efficiency of the switching converter, while too small an output will prevent the main switching transistor from achieving zero-voltage turn-on (ZVS).

[0097] Fourth, the present invention employs an output voltage isolation sampling unit, a pulse width control unit, a compensation parameter configuration unit, and a ZVS control unit to form the controller of the asymmetric half-bridge flyback converter. The compensation parameter configuration unit can adjust the configuration parameter K and the configuration parameter B within a preset parameter adjustment range. Therefore, the switching converter of the present invention can realize the negative current I under different system applications. nset Flexible configuration ensures that the main switch can achieve zero-voltage turn-on (ZVS) in different system applications. Attached Figure Description

[0098] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments:

[0099] Figure 1 The circuit diagram of the clamped asymmetric half-bridge flyback converter disclosed in Chinese Patent Application No. 201911352361.1;

[0100] Figure 2 The circuit diagram of the switching power supply device disclosed in Chinese Patent Application No. 202010966503.X;

[0101] Figure 3 This is a circuit diagram of one embodiment of the switching converter of the present invention;

[0102] Figure 4 This is the equivalent circuit schematic of the asymmetric half-bridge flyback converter in this invention;

[0103] Figure 5 This is a typical operating waveform diagram of the switching converter of the present invention when it is operating in CAHBF mode;

[0104] Figure 6 This is a schematic diagram of the negative current control waveform when the switching converter of the present invention is operating in CAHBF mode. Detailed Implementation

[0105] The present invention will now be described in detail with reference to the embodiments and accompanying drawings to help those skilled in the art better understand the inventive concept of the present invention. However, the scope of protection of the claims of the present invention is not limited to the following embodiments. For those skilled in the art, all other embodiments obtained without creative effort without departing from the inventive concept of the present invention are within the scope of protection of the present invention.

[0106] Example 1

[0107] like Figure 3 and Figure 5 As shown, the present invention discloses a switching converter, including an asymmetric half-bridge flyback converter and a controller;

[0108] See Figure 3 The asymmetric half-bridge flyback converter includes a main switch Q1, an auxiliary switch Q2, a resonant capacitor Cr, a transformer Tr, a rectifier diode D, an output capacitor Co, and a unidirectional clamping network composed of a diode D3 and a clamping switch Q3.

[0109] Specifically: The drain of the main switch Q1 is connected to the positive terminal of the voltage input terminal to connect to the input voltage Vin of the switching converter. The source of the main switch Q1, the drain of the auxiliary switch Q2, and the positive terminal of the resonant capacitor Cr are connected. The negative terminal of the resonant capacitor Cr, the anode of the diode D3, and the same-name terminal of the primary winding of the transformer Tr are connected. The cathode of the diode D3 is connected to the drain of the clamping switch Q3. The source of the auxiliary switch Q2, the source of the clamping switch Q3, and the opposite-name terminal of the primary winding of the transformer Tr are connected and then connected to the primary ground terminal. The opposite-name terminal of the secondary winding of the transformer Tr is connected to the anode of the rectifier diode D. The cathode of the rectifier diode D is connected to the positive terminal of the output capacitor Co and then used to output the output voltage Vout of the asymmetric half-bridge flyback converter. The same-name terminal of the secondary winding of the transformer Tr and the negative terminal of the output capacitor Co are connected to the secondary ground terminal.

[0110] The controller generates pulse width modulation signals for controlling the operation of the asymmetric half-bridge flyback converter, including: main switch drive signal Vgs1, auxiliary switch drive signal Vgs2 and clamp switch drive signal Vgs3, which are respectively input to the gate of the main switch Q1, the gate of the auxiliary switch Q2 and the gate of the clamp switch Q3.

[0111] When the switching converter operates in clamped asymmetric half-bridge flyback mode (CAHBF mode):

[0112] The controller is equipped with a negative current I.nset = K*Vin+B, where Vin represents the input voltage of the switching converter, K and B are preset configuration parameters, and the negative current I... nset The negative current I increases with increasing input voltage Vin to ensure good zero-voltage turn-on (ZVS) of the main switch Q1 under different input voltages Vin. For the switching converter in specific system applications, configuration parameters K and B are fixed values. The negative increase indicates that the negative current I... nset It is negative, and the negative current I nset The absolute value of increases as the input voltage Vin increases.

[0113] Furthermore, the controller detects the operating parameters of the asymmetric half-bridge flyback converter to obtain the zero-crossing time of the demagnetizing current of the transformer Tr (e.g., Figure 5 At time t2', the turn-off delay time Td is calculated according to the following formula, thereby controlling the falling edge of the auxiliary tube drive signal Vgs2 (i.e., the turn-off time of the auxiliary switch Q2) to be: the time after the zero-crossing time of the demagnetizing current has elapsed after the turn-off delay time Td (e.g., the time after the zero-crossing time of the demagnetizing current). Figure 5 (t2'+Td=t3 time); so that: during the operation of the switching converter of the present invention, from the turn-off time of the auxiliary switch Q2 to the turn-on time of the main switch Q1 (e.g. Figure 5 The excitation current I of the transformer Tr (from time t3 to t5) Lm Controlled to the negative current I nset This enables zero-voltage turn-on (ZVS) of the main switch Q1;

[0114]

[0115] In the formula, T2 is the demagnetization time from the start of demagnetization to the time when the demagnetizing current crosses zero (e.g., Figure 5 The time from t1 to t2' in the equation (where Ip is the peak value of the excitation current of the transformer Tr, i.e.) Figure 5 Intermediate excitation current I Lm The demagnetization start time is the moment when the excitation current of the transformer Tr reaches the peak value Ip.

[0116] Among them, see Figure 5When the switching converter operates in clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode), the pulse width modulation signal generated by the controller simultaneously satisfies the following conditions: Condition 1: At the power-on moment of the switching converter, the main drive signal (Vgs1), auxiliary drive signal (Vgs2), and clamp drive signal (Vgs3) are high, low, and low, respectively; Condition 2: The clamp drive signal (Vgs3) and the main drive signal (Vgs1) are complementary signals, the rising edges of the auxiliary drive signal (Vgs2) and the clamp drive signal (Vgs3) coincide, and the falling edge of the auxiliary drive signal (Vgs2) precedes the falling edge of the clamp drive signal (Vgs3); Condition 3: There is a dead time between the main drive signal (Vgs1) and the clamp drive signal (Vgs3). For example: Figure 5 In the diagram, time t1 is the falling edge of the main drive signal, time t2 is the rising edge of the auxiliary drive signal and the clamping switch drive signal, time t3 is the falling edge of the auxiliary drive signal, time t4 is the falling edge of the clamping switch drive signal, and time t5 is the rising edge of the main drive signal. The falling edge time t3 of the auxiliary switch is between time t2 and time t4, and it is turned off until time t4. Time t1 to time t2 is the dead time from when the main switch is turned off to when the auxiliary switch and the clamping switch are turned on. Time t4 to time t5 is the dead time from when the clamping switch is turned off to when the main switch is turned on.

[0117] The controller can be any controller that satisfies the above description, that is, any controller capable of generating... Figure 5 The control device shown is for the waveforms of the three drive signals: the main drive signal Vgs1, the auxiliary drive signal Vgs2, and the clamping drive signal Vgs3.

[0118] like Figures 4 to 6 As shown, when operating in clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode), the working principle of the switching converter of the present invention is as follows:

[0119] The switching converter of the present invention is in Figure 3 The asymmetric half-bridge flyback converter shown can be equivalent to... Figure 4The equivalent circuit shown has the following equivalent relationships: The main switch Q1 is equivalent to an ideal switch, i.e., main switch S1 connected in parallel with diode D1 and resonant capacitor C1. The auxiliary switch Q2 is equivalent to an ideal switch, i.e., auxiliary switch S2 connected in parallel with diode D2 and resonant capacitor C2. The equivalent models of the main switch Q1 and auxiliary switch Q2 are connected in series between the positive terminal +Vin and the negative terminal -Vin of the voltage input. The midpoint SW of the series connection is connected to the positive terminal of the resonant capacitor Cr. The transformer Tr is equivalent to an ideal transformer T connected in series with the leakage inductance Lr, and connected in parallel with the magnetizing inductance Lm. The unidirectional clamping network composed of diode D3 and clamping switch Q3 is equivalent to one end of switch Sow connected to the negative terminal of resonant capacitor Cr and the positive terminal of leakage inductance Lr, and the other end connected to the negative terminal of magnetizing inductance Lm and the negative terminal -Vin of the voltage input. The anode of diode D is connected to the opposite-name terminal of the secondary winding of transformer T, and the cathode of diode D is connected to the positive terminal +Vo of output capacitor Co. Output capacitor Co is connected to the load R. L In parallel connection, the negative terminal -Vo of the output capacitor Co is connected to the secondary winding of the transformer T.

[0120] See Figures 3 to 5 In CAHBF mode, the switching converter of the present invention comprises five stages in each cycle: excitation stage, auxiliary switch zero-voltage turn-on stage, demagnetization stage, current clamping stage, and main switch zero-voltage turn-on stage. The working principle of each cycle is as follows:

[0121] Excitation Phase: From time t0 to time t1, the main control switch S1 is turned on, and the input voltage Vin charges the resonant capacitor Cr, leakage inductance Lr, and excitation inductance Lm, while the excitation current I... Lm and resonant inductor current I Lr Linear rise, that is, the input voltage Vin excites the transformer Tr. During this stage, the drive signals Vgs2 and Vgs3 are at low level, and the auxiliary switches S2 and Sow are turned off.

[0122] Auxiliary switch zero-voltage turn-on stage: From time t1 to time t2, the main switch S1 is turned off, and the resonant capacitors C1 and C2, the leakage inductance Lr, and the magnetizing inductance Lm form a series resonance, and the resonant inductance current I... Lr Charging resonant capacitor C1 and discharging resonant capacitor C2 causes the voltage VC1 across resonant capacitor C1 to rise and the voltage VC2 across resonant capacitor C2 to fall. When resonant capacitor C2 is fully discharged, the voltage VC2 across resonant capacitor C2 drops to zero, diode D2 naturally conducts, and the resonant inductor current I... Lr At time t2, the current flows through diode D2, and the auxiliary switch S2 is turned on, achieving zero-voltage turn-on of the auxiliary switch S2. During this stage, the drive signal Vgs3 is still at a low level, and switch Sow is turned off.

[0123] Demagnetization Phase: From time t2 to time t3, auxiliary switch S2 is turned on, main switch S1 remains off, rectifier switch D is turned on, current I2 in rectifier switch D increases, voltage across magnetizing inductor Lm is clamped (negative at the top, positive at the bottom), and magnetizing current I... Lm As the voltage decreases linearly, transformer Tr demagnetizes. At time t3, the excitation current I... Lm When the set value is reached, the negative current I nset At this time, the auxiliary switch S2 is turned off. During this stage, the drive signal Vgs3 is high, and the switch Sow is turned on. The turn-on time of the switch Sow can be any time between time t2 and time t3 (that is, the switch Sow can be turned on or off between time t2 and time t3). Since the switch Sow only allows current to flow from the anode to the cathode of D3, no current flows through the switch Sow during the demagnetization stage.

[0124] Current clamping phase: From time t3 to time t4, at time t3, auxiliary switch S2 is turned off, switch Sow continues to conduct, and resonant capacitors C1, C2, Cr and leakage inductance Lr form a series resonance, and the resonant inductor current I... Lr The voltage is negative and rapidly increases in the positive direction, discharging resonant capacitor C1 and charging resonant capacitor C2. This causes the voltage VC1 across resonant capacitor C1 to decrease and the voltage VC2 across resonant capacitor C2 to increase. When VC2 equals the voltage VCr across resonant capacitor Cr, the anode voltage of switch Sow becomes zero, and the excitation current I... Lm and resonant inductor current I Lr When the currents are equal, rectifier switch D is turned off, and excitation current I... Lm (This stage is called clamping current) naturally flows from the anode to the cathode through the switch Sow. The switch Sow keeps the clamping current basically unchanged. At time t4, the drive signal Vgs3 becomes low and the switch Sow is turned off.

[0125] Zero-voltage turn-on stage of the main switch: From time t4 to time t5, at time t4, switch Sow is turned off, and the main switch S1 and auxiliary switch S2 remain off. The clamping current held by switch Sow is released, and it continues to discharge the resonant capacitor C1 and charge the resonant capacitor C2. The voltage VC1 across the resonant capacitor C1 continues to decrease, and the voltage VC2 across the resonant capacitor C2 continues to rise until the voltage across the resonant capacitor C1 drops to zero. The clamping current begins to flow through diode D1. At time t5, the drive signal Vgs1 becomes high, and the main switch S1 is turned on, achieving zero-voltage turn-on of the main switch S1.

[0126] Therefore, this invention, based on an asymmetric half-bridge flyback converter, configures the negative current I according to the input voltage Vin of the switching converter. nsetThe demagnetizing current of transformer Tr is detected at its zero-crossing moment, and the turn-off delay time Td is calculated. This is used to control the falling edge of the auxiliary transistor drive signal Vgs2, ensuring that the turn-off moment of auxiliary switch Q2 is set after the zero-crossing moment of the demagnetizing current has elapsed past the turn-off delay time Td. This ensures that during the operation of the switching converter, from the turn-off moment of auxiliary switch Q2 to the turn-on moment of main switch Q1, the excitation current I of transformer Tr... Lm Controlled as a negative current I nset This invention achieves zero-voltage turn-on (ZVS) of the main switch Q1. Therefore, this invention reduces the difficulty of implementing zero-voltage turn-on (ZVS) control of the main switch Q1. Furthermore, this invention does not require the addition of a high-voltage sampling resistor when implementing zero-voltage turn-on (ZVS) of the main switch Q1, and will not generate significant sampling losses. When the switching converter is used in ACDC applications, it can meet the requirements of small size, low cost, and low power consumption in low-power applications.

[0127] The above is the basic implementation method of this embodiment one, and further optimizations, improvements and limitations can be made based on this basic implementation method:

[0128] Preferably: obtaining the zero-crossing time of the demagnetizing current (e.g.) Figure 5 The method for time t2' is as follows:

[0129] The operating parameters detected by the controller include: the excitation current I of the transformer Tr. Lm The excitation voltage and demagnetizing voltage of the transformer Tr;

[0130] Since the transformer Tr is in an energized state when the main switch Q1 is turned on, the energizing current I... Lm The excitation current I gradually increases from negative to large; therefore, the controller will... Lm The peak value is denoted as the excitation current peak value Ip, and the excitation current I... Lm The time from zero to the peak excitation current Ip is denoted as the excitation time T1, and the excitation voltage of the transformer Tr at time t within the excitation time T1 is denoted as Vp(t). The excitation volt-seconds Vp*T1 of the transformer Tr within the excitation time T1 are calculated according to Formula 2:

[0131]

[0132] In the formula, Vp(t) = Vin(t) - V Cr Vin(t) represents the voltage value of the input voltage Vin at time t within the excitation time T1. Cr (t) represents the voltage value of the negative terminal of the resonant capacitor Cr at time t within the excitation time T1;

[0133] Since the transformer Tr is in a demagnetizing state when the main switch Q1 is turned off, the excitation current I... Lm As the peak excitation current Ip gradually decreases, the controller will control the excitation current I from the point where the peak excitation current Ip begins to decrease. Lm Let be denoted as the demagnetizing current, and let Tr be the current from the start of demagnetization of the transformer (e.g., at the beginning of demagnetization). Figure 5 The demagnetizing voltage at time t' after starting at time t1 in the equation is denoted as Vn(t'). The transformer Tr is continuously calculated according to Formula 3 from the start time of demagnetization (e.g., time t1 in the equation). Figure 5 The number of demagnetizing volt-seconds Vn*ΔT after time t2 begins:

[0134]

[0135] In the formula, Vn(t')=V Cr (t'), V Cr (t') represents the moment when the negative terminal of the resonant capacitor Cr starts demagnetizing (e.g., t'). Figure 5 The voltage value at time t' after starting from time t1;

[0136] Based on the principle that the transformer magnetizing inductance satisfies volt-second balance in each switching cycle, the controller determines whether the demagnetizing volt-seconds Vn*ΔT and the magnetizing volt-seconds Vp*T1 are equal, and determines the moment when the two are equal as the moment when the demagnetizing current crosses zero, that is, the moment when the demagnetizing current drops to zero (e.g., the moment when the demagnetizing current drops to zero). Figure 5 The time T2 from the start of demagnetization to the zero-crossing time of the demagnetizing current (e.g., time t2' in the equation) is calculated accordingly. Figure 5 (The time from time t1 to time t2' in the text).

[0137] Therefore, this invention calculates the excitation volt-seconds Vp*T1 of transformer Tr within the excitation time T1 according to Formula 2, and continuously calculates the demagnetization volt-seconds Vn*ΔT of transformer Tr within the time ΔT after the start of demagnetization according to Formula 3, and continuously judges whether the two are equal, so as to quickly determine the zero-crossing time of the demagnetizing current. It has the advantages of high detection efficiency and real-time reliability of the zero-crossing time of the demagnetizing current.

[0138] The excitation voltage and demagnetization voltage of the transformer Tr can be detected in various ways, including but not limited to the following:

[0139] Method 1: Sampling directly on the primary winding of transformer Tr or sampling after reducing the voltage amplitude through a voltage divider resistor;

[0140] Method 2: Direct sampling using the auxiliary winding of transformer Tr or sampling after reducing the voltage amplitude through a voltage divider resistor;

[0141] Method 3: Sampling is performed directly on the amplitude-side winding of transformer Tr or after the voltage amplitude is reduced by a voltage divider resistor.

[0142] The calculation of the excitation volt-seconds, the demagnetization volt-seconds, and the turn-off delay Td can be achieved by various means, including but not limited to the following:

[0143] Firstly, an analog circuit scheme is adopted, in which the excitation voltage and demagnetization voltage are converted into two current signals by a voltage-controlled current source. These two current signals are then used to charge two capacitors of the same capacitance value, so as to calculate the excitation volt-seconds and demagnetization volt-seconds respectively.

[0144] Secondly, digital circuits, such as microcontrollers, are used to sample, store, and calculate the excitation voltage, demagnetization voltage, excitation time, and demagnetization time.

[0145] Preferably, the configuration method for configuration parameter K and configuration parameter B is as follows:

[0146] For the switching converter in a specific system application, experimental tests were conducted with different input voltages Vin to determine the negative current I corresponding to each input voltage Vin that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition. nset Based on the data obtained through measurement, according to I nset =K*Vin+B This calculation formula fits to obtain: the values ​​of configuration parameters K and B of the switching converter under the specific system application; wherein, the efficiency condition is that the working efficiency of the switching converter is above the preset efficiency threshold, and the zero-voltage turn-on condition is that the main switch Q1 can achieve zero-voltage turn-on (ZVS) during the operation of the switching converter.

[0147] Therefore, this invention conducts experimental tests on switching converters under specific system applications with different input voltages Vin, to measure the negative current I that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition for each input voltage Vin. nset By fitting the obtained data, the values ​​of configuration parameters K and B can be determined, thus avoiding negative current I. nset Too large an output will cause a decrease in the efficiency of the switching converter, while too small an output will prevent the main switch Q1 from achieving zero voltage turn-on (ZVS).

[0148] Example 2

[0149] Based on the above embodiment one, this embodiment two also adopts the following preferred implementation method:

[0150] The controller includes an output voltage isolation sampling unit, a pulse width control unit, a compensation parameter configuration unit, and a ZVS control unit;

[0151] The two input terminals V1 and V2 of the output voltage isolation sampling unit are respectively connected to the two ends of the output capacitor Co. The output terminal V3 of the output voltage isolation sampling unit is connected to the control input terminal FB of the pulse width control unit. The ground terminal GND of the pulse width control unit is grounded. The pulse width control unit isolates and samples the output voltage Vout of the asymmetric half-bridge flyback converter through the output voltage isolation sampling unit to generate the main drive signal Vgs1, the auxiliary drive signal Vgs2, and the clamping drive signal Vgs3. These signals are then output through the main drive signal output terminal G of the pulse width control unit. Q1 Auxiliary tube drive signal output terminal G Q2 and clamping transistor drive signal output terminal G Q3 Output;

[0152] Furthermore, the compensation parameter configuration unit can adjust the configuration parameter K and configuration parameter B within a preset parameter adjustment range. The input terminal V4 of the compensation parameter configuration unit is connected to the drain of the main switching transistor Q1 to detect the input voltage Vin of the switching converter. The output terminal V5 of the compensation parameter configuration unit outputs the negative current I to the negative current parameter input terminal V6 of the ZVS control unit. nset =K*Vin+B compensation parameter configuration signal;

[0153] The source of the auxiliary switch Q2, the source of the clamping switch Q3, and the opposite-named terminal of the primary winding of the transformer Tr are connected and then connected to the primary ground terminal through the current sampling resistor R. The current sampling input terminal V7 of the ZVS control unit is connected to the source of the auxiliary switch Q2, and the voltage sampling input terminal V8 of the ZVS control unit is connected to the same-named terminal of the primary winding of the transformer Tr. The output terminal V9 of the ZVS control unit outputs the demagnetizing current zero-crossing time and the turn-off delay time Td to the auxiliary switch turn-off control input terminal V10 of the pulse width control unit. Based on this, the pulse width control unit controls the falling edge of the auxiliary tube drive signal Vgs2 to be such that the demagnetizing current zero-crossing time is after the turn-off delay time Td.

[0154] Among them, see Figure 3 Vsw and Vaux represent the positive and negative voltages of the resonant capacitor Cr, respectively. When the main switch Q1 is turned on, the negative voltage Vaux of the resonant capacitor Cr is the excitation voltage of the transformer Tr. When the auxiliary switch Q2 is turned on, the negative voltage Vaux of the resonant capacitor Cr is the demagnetizing voltage of the transformer Tr.

[0155] Therefore, this invention employs an output voltage isolation sampling unit, a pulse width control unit, a compensation parameter configuration unit, and a ZVS control unit to form the controller of an asymmetric half-bridge flyback converter. The compensation parameter configuration unit can adjust the configuration parameter K and configuration parameter B within preset parameter adjustment ranges. Thus, the switching converter of this invention can achieve negative current I under different system applications. nset Flexible configuration ensures that the main switch Q1 can achieve zero-voltage turn-on (ZVS) well in different system applications.

[0156] The above is the basic implementation method of this embodiment two, and further optimizations, improvements and limitations can be made based on this basic implementation method:

[0157] Preferably, the controller further includes a mode determination unit;

[0158] The input terminal V11 of the mode determination unit detects the load current of the switching converter, and determines that the switching converter is in a light load state when the load current is less than a preset load current threshold; otherwise, it determines that the switching converter is in a heavy load state.

[0159] The output terminal V12 of the mode determination unit is connected to the mode control terminal V13 of the pulse width control unit. When the mode determination unit outputs a determination result to the pulse width control unit that the switching converter is in a light load state, the pulse width control unit controls the switching converter to operate in the clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode); when the mode determination unit outputs a determination result to the pulse width control unit that the switching converter is in a heavy load state, the pulse width control unit controls the switching converter to operate in the asymmetric half-bridge flyback mode (abbreviated as: AHBF mode).

[0160] Therefore, the switching converter of the present invention can achieve system efficiency optimization over a wide load range.

[0161] The switching converter operates in AHBF mode, that is, the control method and working principle of the asymmetric half-bridge flyback converter operating in AHBF mode are disclosed in Chinese Patent Application No. 201911352361.1, "Switching Power Supply Device". It will not be described in detail here, but only the difference between AHBF mode and the CAHBF mode of this invention will be briefly explained as follows:

[0162] When the converter operates in AHBF mode, the clamping switch is always in the off state during one switching cycle. The main switch and the auxiliary switch work in a complementary manner. Each cycle includes four stages: excitation stage, auxiliary switch zero-voltage turn-on stage, demagnetization stage, and main switch zero-voltage turn-on stage.

[0163] The working principles of the excitation stage and the auxiliary switch zero-voltage turn-on stage are the same as those of the excitation stage and the auxiliary switch zero-voltage turn-on stage in the CAHBF mode described above, and will not be described again here. The working principles of the demagnetization stage and the main switch zero-voltage turn-on stage in the AHBF mode are as follows:

[0164] Demagnetization Stage: Auxiliary switch S2 remains on, main switch S1 is off, rectifier switch D is on, and the current I2 in rectifier switch D increases. The voltage across the magnetizing inductor Lm is clamped (negative at the top, positive at the bottom), and the magnetizing current ILm decreases linearly, demagnetizing the transformer. When the magnetizing current reaches the set value, auxiliary switch S2 is turned off. During this stage, drive signal Vgs3 is low, and switch Sow is off.

[0165] During the zero-voltage turn-on stage of the main switch: The main switch S1 and the auxiliary switch S2 remain off. The resonant capacitors C1, C2, Cr and the leakage inductance Lr form a series resonance. The resonant inductor current ILr is negative and rapidly increases in the positive direction, discharging the resonant capacitor C1 and charging the resonant capacitor C2. This causes the voltage VC1 across the resonant capacitor C1 to decrease and the voltage VC2 across the resonant capacitor C2 to increase. When VC2 increases to the same level as VCr, the magnetizing current ILm and the resonant inductor current ILr become equal. The rectifier switch D turns off, and the magnetizing current ILm and the resonant inductor current ILr are released, continuing to discharge the resonant capacitor C1 and charge the resonant capacitor C2. The voltage VC1 across the resonant capacitor C1 continues to decrease, and the voltage VC2 across the resonant capacitor C2 continues to increase. When the voltage across the resonant capacitor C1 drops to zero, the resonant inductor current ILr begins to flow through the diode D1. At this time, the main switch S1 is turned on, and the main switch S1 achieves zero-voltage turn-on.

[0166] Example 3

[0167] The present invention also discloses a control method for a switching converter, applicable to switching converters employing an asymmetric half-bridge flyback converter;

[0168] See Figure 3 The asymmetric half-bridge flyback converter includes a main switch Q1, an auxiliary switch Q2, a resonant capacitor Cr, a transformer Tr, a rectifier diode D, an output capacitor Co, and a unidirectional clamping network composed of a diode D3 and a clamping switch Q3.

[0169] Specifically: The drain of the main switch Q1 is connected to the positive terminal of the voltage input terminal to connect to the input voltage Vin of the switching converter. The source of the main switch Q1, the drain of the auxiliary switch Q2, and the positive terminal of the resonant capacitor Cr are connected. The negative terminal of the resonant capacitor Cr, the anode of the diode D3, and the same-name terminal of the primary winding of the transformer Tr are connected. The cathode of the diode D3 is connected to the drain of the clamping switch Q3. The source of the auxiliary switch Q2, the source of the clamping switch Q3, and the opposite-name terminal of the primary winding of the transformer Tr are connected and then connected to the primary ground terminal. The opposite-name terminal of the secondary winding of the transformer Tr is connected to the anode of the rectifier diode D. The cathode of the rectifier diode D is connected to the positive terminal of the output capacitor Co and then used to output the output voltage Vout of the asymmetric half-bridge flyback converter. The same-name terminal of the secondary winding of the transformer Tr and the negative terminal of the output capacitor Co are connected to the secondary ground terminal.

[0170] The asymmetric half-bridge flyback converter is controlled by a pulse width modulation signal, which includes a main switch drive signal Vgs1, an auxiliary switch drive signal Vgs2, and a clamping switch drive signal Vgs3, which are respectively input to the gate of the main switch Q1, the gate of the auxiliary switch Q2, and the gate of the clamping switch Q3.

[0171] When the switching converter operates in clamped asymmetric half-bridge flyback mode (CAHBF mode for short), the control method includes:

[0172] Negative current configuration step: Detect the input voltage Vin of the switching converter, and configure the negative current I accordingly. nset =K*Vin+B, where K and B are preset configuration parameters, and the negative current I... nset The negative current I increases with increasing input voltage Vin to ensure good zero-voltage turn-on (ZVS) of the main switch Q1 under different input voltages Vin. For the switching converter in specific system applications, configuration parameters K and B are fixed values. The negative increase indicates that the negative current I... nset It is negative, and the negative current I nset The absolute value of increases as the input voltage Vin increases.

[0173] Demagnetizing current zero-crossing detection step: Detect the operating parameters of the asymmetric half-bridge flyback converter to obtain the zero-crossing time of the demagnetizing current of the transformer Tr (e.g., Figure 5 (at time t2' in the text);

[0174] The shutdown delay time calculation steps are as follows: The shutdown delay time Td is calculated using the following formula:

[0175]

[0176] In the formula, T2 is the demagnetization time from the start of demagnetization to the time when the demagnetizing current crosses zero (e.g., Figure 5 The time from t1 to t2' in the equation (where Ip is the peak value of the excitation current of the transformer Tr, i.e.) Figure 5 Intermediate excitation current I Lm The demagnetization start time is the moment when the excitation current of the transformer Tr reaches the peak value of the excitation current Ip.

[0177] Auxiliary switch turn-off control steps: The falling edge of the auxiliary switch drive signal Vgs2 (i.e., the turn-off time of the auxiliary switch Q2) is controlled to be the time after the zero-crossing time of the demagnetizing current has elapsed for a delay of the turn-off delay time Td (e.g., the time after the turn-off delay time Td). Figure 5 (t2'+Td=t3 time); so that: during the operation of the switching converter of the present invention, from the turn-off time of the auxiliary switch Q2 to the turn-on time of the main switch W1 (e.g. Figure 5 The excitation current I of the transformer Tr (from time t3 to t5) Lm Controlled to the negative current I nset This enables zero-voltage turn-on (ZVS) of the main switch Q1.

[0178] Among them, see Figure 5 When the switching converter operates in clamped asymmetric half-bridge flyback mode (i.e., CAHBF mode), the pulse width modulation signal controlling the operation of the asymmetric half-bridge flyback converter simultaneously satisfies the following conditions: Condition 1: At the power-on moment of the switching converter, the master drive signal (Vgs1), the auxiliary drive signal (Vgs2), and the clamp drive signal (Vgs3) are high, low, and low, respectively; Condition 2: The clamp drive signal (Vgs3) and the master drive signal (Vgs1) are complementary signals, the rising edges of the auxiliary drive signal (Vgs2) and the clamp drive signal (Vgs3) coincide, and the falling edge of the auxiliary drive signal (Vgs2) precedes the falling edge of the clamp drive signal (Vgs3); Condition 3: There is a dead time between the master drive signal (Vgs1) and the clamp drive signal (Vgs3). For example: Figure 5 In the diagram, time t1 is the falling edge of the main drive signal, time t2 is the rising edge of the auxiliary drive signal and the clamping switch drive signal, time t3 is the falling edge of the auxiliary drive signal, time t4 is the falling edge of the clamping switch drive signal, and time t5 is the rising edge of the main drive signal. The falling edge time t3 of the auxiliary switch is between time t2 and time t4, and it is turned off until time t4. Time t1 to time t2 is the dead time from when the main switch is turned off to when the auxiliary switch and the clamping switch are turned on. Time t4 to time t5 is the dead time from when the clamping switch is turned off to when the main switch is turned on.

[0179] The control method of the switching converter of the present invention is the same as the working principle of the switching converter described in Embodiment 1, and will not be repeated here.

[0180] Therefore, this invention, based on an asymmetric half-bridge flyback converter, configures the negative current I according to the input voltage Vin of the switching converter. nset The demagnetizing current of transformer Tr is detected at its zero-crossing moment, and the turn-off delay time Td is calculated. This is used to control the falling edge of the auxiliary transistor drive signal Vgs2, ensuring that the turn-off moment of auxiliary switch Q2 is set after the zero-crossing moment of the demagnetizing current has elapsed past the turn-off delay time Td. This ensures that during the operation of the switching converter, from the turn-off moment of auxiliary switch Q2 to the turn-on moment of main switch Q1, the excitation current I of transformer Tr... Lm Controlled as a negative current I nset This invention achieves zero-voltage turn-on (ZVS) of the main switch Q1. Therefore, this invention reduces the difficulty of implementing zero-voltage turn-on (ZVS) control of the main switch Q1. Furthermore, this invention does not require the addition of a high-voltage sampling resistor when implementing zero-voltage turn-on (ZVS) of the main switch Q1, and will not generate significant sampling losses. When the switching converter is used in ACDC applications, it can meet the requirements of small size, low cost, and low power consumption in low-power applications.

[0181] The above is the basic implementation method of this embodiment three, and further optimizations, improvements and limitations can be made based on this basic implementation method:

[0182] Preferably, the step of detecting the zero-crossing time of the demagnetizing current includes:

[0183] Operating parameter detection steps: Detect the operating parameters of the asymmetric half-bridge flyback converter, including: the magnetizing current I of the transformer Tr. Lm The excitation voltage and demagnetizing voltage of the transformer Tr;

[0184] Steps for calculating excitation volt-seconds: When the main switch Q1 is turned on, the transformer Tr is in an excitation state, and the excitation current I... Lm The excitation current I gradually increases from negative to large, therefore... Lm The peak value is denoted as the excitation current peak value Ip, and the excitation current I... Lm The time from zero to the peak excitation current Ip is denoted as the excitation time T1, and the excitation voltage of the transformer Tr at time t within the excitation time T1 is denoted as Vp(t). The excitation volt-seconds Vp*T1 of the transformer Tr within the excitation time T1 are calculated according to Formula 2:

[0185]

[0186] In the formula, Vp(t) = Vin(t) - V Cr Vin(t) represents the voltage value of the input voltage Vin at time t within the excitation time T1. Cr (t) represents the voltage value of the negative terminal of the resonant capacitor Cr at time t within the excitation time T1;

[0187] Demagnetizing volt-seconds calculation steps: Since the transformer Tr is in a demagnetizing state when the main switch Q1 is turned off, the excitation current I Lm As the peak excitation current Ip gradually decreases, the excitation current I will decrease from the peak excitation current Ip onwards. Lm Let be denoted as the demagnetizing current, and let Tr be the current from the start of demagnetization of the transformer (e.g., at the beginning of demagnetization). Figure 5 The demagnetizing voltage at time t' after starting at time t1 in the equation is denoted as Vn(t'). The transformer Tr is continuously calculated according to Formula 3 from the start time of demagnetization (e.g., time t1 in the equation). Figure 5 The number of demagnetizing volt-seconds Vn*ΔT after time t1 begins:

[0188]

[0189] In the formula, Vn(t')=V Cr (t'), V cr (t') represents the moment when the negative terminal of the resonant capacitor Cr starts demagnetizing (e.g., t'). Figure 5 The voltage value at time t' after starting from time t2 in the equation;

[0190] Determining the zero-crossing moment of the demagnetizing current: Based on the principle that the transformer's magnetizing inductance satisfies volt-second balance in each switching cycle, determine whether the demagnetizing volt-seconds Vn*ΔT and the magnetizing volt-seconds Vp*T1 are equal. The moment when these two are equal is determined as the zero-crossing moment of the demagnetizing current, that is, the moment when the demagnetizing current drops to zero (e.g., the moment when the demagnetizing current drops to zero). Figure 5 The time T2 from the start of demagnetization to the zero-crossing time of the demagnetizing current (e.g., time t2' in the equation) is calculated accordingly. Figure 5 (The time from time t1 to time t2' in the text).

[0191] Therefore, this invention calculates the excitation volt-seconds Vp*T1 of transformer Tr within the excitation time T1 according to Formula 2, and continuously calculates the demagnetization volt-seconds Vn*ΔT of transformer Tr within the time ΔT after the start of demagnetization according to Formula 3, and continuously judges whether the two are equal, so as to quickly determine the zero-crossing time of the demagnetizing current. It has the advantages of high detection efficiency and real-time reliability of the zero-crossing time of the demagnetizing current.

[0192] Preferably, the configuration method for configuration parameter K and configuration parameter B is as follows:

[0193] For the switching converter in a specific system application, experimental tests were conducted with different input voltages Vin to determine the negative current I corresponding to each input voltage Vin that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition. nset Based on the data obtained through measurement, according to I nset =K*Vin+B This calculation formula fits to obtain: the values ​​of configuration parameters K and B of the switching converter under the specific system application; wherein, the efficiency condition is that the working efficiency of the switching converter is above the preset efficiency threshold, and the zero-voltage turn-on condition is that the main switch Q1 can achieve zero-voltage turn-on (ZVS) during the operation of the switching converter.

[0194] Therefore, this invention conducts experimental tests on switching converters under specific system applications with different input voltages Vin, to measure the negative current I that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition for each input voltage Vin. nset By fitting the obtained data, the values ​​of configuration parameters K and B can be determined, thus avoiding negative current I. nset Too large an output will cause a decrease in the efficiency of the switching converter, while too small an output will prevent the main switch Q1 from achieving zero voltage turn-on (ZVS).

[0195] This invention is not limited to the specific embodiments described above. Based on the above content and in accordance with common technical knowledge and conventional methods in the field, without departing from the basic technical concept of this invention, this invention can also make other equivalent modifications, substitutions or alterations, all of which fall within the protection scope of this invention.

Claims

1. A switching converter, comprising an asymmetric half-bridge flyback converter and a controller; The asymmetric half-bridge flyback converter includes a main switch (Q1), an auxiliary switch (Q2), a resonant capacitor (Cr), a transformer (Tr), a rectifier diode (D), an output capacitor (Co), and a unidirectional clamping network composed of a diode (D3) and a clamping switch (Q3). The controller generates a pulse width modulation signal for controlling the operation of the asymmetric half-bridge flyback converter, including: The main switch drive signal (Vgs1), the auxiliary switch drive signal (Vgs2), and the clamp switch drive signal (Vgs3) are respectively input to the gate of the main switch (Q1), the gate of the auxiliary switch (Q2), and the gate of the clamp switch (Q3); Its features are: When the switching converter operates in clamped asymmetric half-bridge flyback mode: The controller is equipped with a negative current I. nset =K*Vin+B, where Vin represents the input voltage of the switching converter, K and B are preset configuration parameters, and the negative current I... nset It increases negatively as the input voltage Vin increases; Furthermore, the controller detects the operating parameters of the asymmetric half-bridge flyback converter to obtain the zero-crossing time of the demagnetizing current of the transformer (Tr), and calculates the turn-off delay time Td according to the following formula, thereby controlling the falling edge of the auxiliary tube drive signal (Vgs2) to be the time after the zero-crossing time of the demagnetizing current has been delayed by the turn-off delay time Td. [Formula 1]; In the formula, T2 is the demagnetization time from the start of demagnetization to the zero-crossing time of the demagnetizing current, Ip is the peak value of the excitation current of the transformer (Tr), and the start of demagnetization is the moment when the excitation current of the transformer (Tr) reaches the peak value Ip.

2. The switching converter according to claim 1, characterized in that: When the switching converter operates in clamped asymmetric half-bridge flyback mode, the pulse width modulation signal generated by the controller simultaneously satisfies the following conditions: Condition 1: At the power-on moment of the switching converter, the main drive signal (Vgs1), auxiliary drive signal (Vgs2), and clamp drive signal (Vgs3) are at high, low, and low levels, respectively; Condition 2: The clamp drive signal (Vgs3) and the main drive signal (Vgs1) are complementary signals, the rising edges of the auxiliary drive signal (Vgs2) and the clamp drive signal (Vgs3) coincide, and the falling edge of the auxiliary drive signal (Vgs2) precedes the falling edge of the clamp drive signal (Vgs3); Condition 3: There is a dead time between the main drive signal (Vgs1) and the clamp drive signal (Vgs3).

3. The switching converter according to claim 1, characterized in that: The method for obtaining the zero-crossing moment of the demagnetizing current is as follows: The operating parameters detected by the controller include: the excitation current (I) of the transformer (Tr). Lm The excitation voltage and demagnetizing voltage of the transformer (Tr); The controller will control the excitation current (I) Lm The peak value of the excitation current (Ip) is denoted as the peak value of the excitation current. Lm The time it takes for the excitation current to rise from zero to the peak value Ip is denoted as the excitation time T1, and the excitation voltage of the transformer (Tr) at time t within the excitation time T1 is denoted as Vp(t). The excitation volt-seconds of the transformer (Tr) within the excitation time T1 are calculated according to Formula 2. : [Formula 2]; The controller will control the excitation current (Ip) as it decreases from the peak excitation current Ip. Lm Let Vn(t) be the demagnetizing current, and let Vn(t) be the demagnetizing voltage of the transformer (Tr) at time t' after the start of demagnetization. Then, continuously calculate the demagnetizing volt-seconds (V / T) of the transformer (Tr) within the time interval ΔT after the start of demagnetization using Formula 3. : [Formula 3]; The controller determines the demagnetization volt-seconds. With excitation volt-seconds Whether they are equal, the moment when they are equal is determined as the zero-crossing moment of the demagnetizing current, and the time T2 from the start of demagnetization to the zero-crossing moment of the demagnetizing current is calculated accordingly.

4. The switching converter according to claim 1, characterized in that: The configuration method for configuration parameter K and configuration parameter B is as follows: For the switching converter, experimental tests were conducted with different input voltages Vin to determine the negative current I corresponding to each input voltage Vin that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition. nset Based on the data obtained through measurement, according to I nset =K*Vin+B This calculation formula fits to obtain the values ​​of the configuration parameters K and B of the switching converter; wherein, the efficiency condition is that the working efficiency of the switching converter is above the preset efficiency threshold, and the zero-voltage turn-on condition is that the main switch (Q1) can achieve zero-voltage turn-on during the operation of the switching converter.

5. The switching converter according to any one of claims 1 to 4, characterized in that: The controller includes an output voltage isolation sampling unit, a pulse width control unit, a compensation parameter configuration unit, and a ZVS control unit; The two input terminals of the output voltage isolation sampling unit are respectively connected to the two ends of the output capacitor (Co), and the output terminal of the output voltage isolation sampling unit is connected to the control input terminal of the pulse width control unit. The pulse width control unit performs isolation sampling on the output voltage of the asymmetric half-bridge flyback converter through the output voltage isolation sampling unit to generate the main drive signal (Vgs1), auxiliary drive signal (Vgs2), and clamp drive signal (Vgs3). Furthermore, the compensation parameter configuration unit can adjust the configuration parameter K and configuration parameter B within a preset parameter adjustment range. The input terminal of the compensation parameter configuration unit is connected to the drain of the main switching transistor (Q1) to detect the input voltage of the switching converter. The output terminal of the compensation parameter configuration unit outputs the negative current I to the negative current parameter input terminal of the ZVS control unit. nset =K*Vin+B is the compensation parameter configuration signal; The source of the auxiliary switch (Q2), the source of the clamping switch (Q3), and the opposite-named terminal of the primary winding of the transformer (Tr) are connected together and then connected to the primary ground terminal through a current sampling resistor (R). The current sampling input terminal of the ZVS control unit is connected to the source of the auxiliary switch (Q2), and the voltage sampling input terminal of the ZVS control unit is connected to the same-named terminal of the primary winding of the transformer (Tr). The output terminal of the ZVS control unit outputs the zero-crossing time of the demagnetizing current and the turn-off delay time Td to the auxiliary switch turn-off control input terminal of the pulse width control unit. Based on this, the pulse width control unit controls the falling edge of the auxiliary tube drive signal (Vgs2) to be such that the zero-crossing time of the demagnetizing current is after the turn-off delay time Td.

6. The switching converter according to claim 5, characterized in that: The controller further includes a mode determination unit; The input terminal of the mode determination unit detects the load current of the switching converter, and determines that the switching converter is in a light load state when the load current is less than a preset load current threshold. The output of the mode determination unit is connected to the mode control terminal of the pulse width control unit. When the mode determination unit outputs a determination result that the switching converter is in a light load state to the pulse width control unit, the pulse width control unit controls the switching converter to work in the clamped asymmetric half-bridge flyback mode.

7. A control method for a switching converter, applicable to switching converters employing an asymmetric half-bridge flyback converter; The asymmetric half-bridge flyback converter includes a main switch (Q1), an auxiliary switch (Q2), a resonant capacitor (Cr), a transformer (Tr), a rectifier diode (D), an output capacitor (Co), and a unidirectional clamping network composed of a diode (D3) and a clamping switch (Q3). The asymmetric half-bridge flyback converter operates under the control of a pulse width modulation (PWM) signal, which includes: The main switch drive signal (Vgs1), the auxiliary switch drive signal (Vgs2), and the clamp switch drive signal (Vgs3) are respectively input to the gate of the main switch (Q1), the gate of the auxiliary switch (Q2), and the gate of the clamp switch (Q3); Its features are: When the switching converter operates in clamped asymmetric half-bridge flyback mode, the control method includes: Negative current configuration step: Detect the input voltage Vin of the switching converter, and configure the negative current I accordingly. nset =K*Vin+B, where K and B are preset configuration parameters, and the negative current I... nset It increases negatively as the input voltage Vin increases; Demagnetizing current zero-crossing moment detection step: Detect the operating parameters of the asymmetric half-bridge flyback converter to obtain the demagnetizing current zero-crossing moment of the transformer (Tr); The shutdown delay time calculation steps are as follows: The shutdown delay time Td is calculated using the following formula: [Formula 1]; In the formula, T2 is the demagnetization time from the start of demagnetization to the time when the demagnetizing current crosses zero, Ip is the peak value of the excitation current of the transformer (Tr), and the start of demagnetization is the time when the excitation current of the transformer (Tr) reaches the peak value Ip. Auxiliary switch turn-off control steps: The falling edge of the auxiliary switch drive signal (Vgs2) is controlled to be the time after the zero crossing of the demagnetizing current has elapsed past the turn-off delay time Td.

8. The control method for the switching converter according to claim 7, characterized in that: When the switching converter operates in clamped asymmetric half-bridge flyback mode, the pulse width modulation signal controlling the operation of the asymmetric half-bridge flyback converter simultaneously satisfies the following conditions: Condition 1: At the power-on moment of the switching converter, the master drive signal (Vgs1), the auxiliary drive signal (Vgs2), and the clamp drive signal (Vgs3) are at high, low, and low levels, respectively; Condition 2: The clamp drive signal (Vgs3) and the master drive signal (Vgs1) are complementary signals, the rising edges of the auxiliary drive signal (Vgs2) and the clamp drive signal (Vgs3) coincide, and the falling edge of the auxiliary drive signal (Vgs2) precedes the falling edge of the clamp drive signal (Vgs3); Condition 3: There is a dead time between the master drive signal (Vgs1) and the clamp drive signal (Vgs3).

9. The control method for the switching converter according to claim 7 or 8, characterized in that: The step of detecting the zero-crossing time of the demagnetizing current includes: Operating parameter detection steps: Detect the operating parameters of the asymmetric half-bridge flyback converter, including: the excitation current (I) of the transformer (Tr). Lm The excitation voltage and demagnetizing voltage of the transformer (Tr); Excitation volt-second calculation steps: The excitation current (I...) Lm The peak value of the excitation current (Ip) is denoted as the peak value of the excitation current. Lm The time it takes for the excitation current to rise from zero to the peak value Ip is denoted as the excitation time T1, and the excitation voltage of the transformer (Tr) at time t within the excitation time T1 is denoted as Vp(t). The excitation volt-seconds of the transformer (Tr) within the excitation time T1 are calculated according to Formula 2. : [Formula 2]; Demagnetizing volt-seconds calculation steps: Start from the peak excitation current Ip when the excitation current (I) begins to decrease. Lm Let Vn(t) be the demagnetizing current, and let Vn(t) be the demagnetizing voltage of the transformer (Tr) at time t' after the start of demagnetization. Then, continuously calculate the demagnetizing volt-seconds (V / T) of the transformer (Tr) within the time interval ΔT after the start of demagnetization using Formula 3. : [Formula 3]; Steps for determining the zero-crossing time of the demagnetizing current: Determine the demagnetizing volt-seconds. With excitation volt-seconds Whether they are equal, the moment when they are equal is determined as the zero-crossing moment of the demagnetizing current, and the time T2 from the start of demagnetization to the zero-crossing moment of the demagnetizing current is calculated accordingly.

10. The control method for the switching converter according to claim 7 or 8, characterized in that: The configuration method for configuration parameter K and configuration parameter B is as follows: For the switching converter, experimental tests were conducted with different input voltages Vin to determine the negative current I corresponding to each input voltage Vin that simultaneously satisfies the efficiency condition and the zero-voltage turn-on condition. nset Based on the data obtained through measurement, according to I nset =K*Vin+B This calculation formula fits to obtain the values ​​of the configuration parameters K and B of the switching converter; wherein, the efficiency condition is that the working efficiency of the switching converter is above the preset efficiency threshold, and the zero-voltage turn-on condition is that the main switch (Q1) can achieve zero-voltage turn-on during the operation of the switching converter.

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