Zero-current switch active clamping forward converter and control method and equipment thereof

Abstract

The invention discloses a zero-current switch active clamping forward converter and a control method and equipment thereof, and relates to the technical field of converters, and the main points of the technical scheme are that a resonance current signal is sampled from the secondary side of a transformer T1, and a self-adaptive conduction time signal is generated in combination with a pulse signal; generating a complementary driving signal with a dead zone based on the self-adaptive conduction time signal so as to control the on and off of a primary side main power MOS tube Q1 and a reset MOS tube Q2 in the main power circuit; the pulse signal is used for triggering the operation of the zero-cross detection control unit, so that the self-adaptive conduction time signal dynamically adjusts the conduction time of the primary side main power MOS tube Q1, the zero-current switch active clamping forward converter can be ensured to realize zero-current turn-off in a full-load range, the turn-off loss of a power device in the converter in the full-load range can be reduced, and the power consumption of the converter in the full-load range can be reduced. Converter efficiency is improved, harmonic waves in the switching process are reduced, and EMI characteristics of the converter are optimized.

Description

Technical Field

[0001] This invention relates to the field of converter technology, and more specifically, to a zero-current switching active clamp forward converter and its control method and device. Background Technology

[0002] Zero-current switching (ZCS) active clamp forward converter topologies belong to the category of resonant converters. Their output and input gain functions depend on the converter's switching frequency; that is, the higher the required gain, the higher the switching frequency, and vice versa. This topology is suitable for control using PFM (Pulse Frequency Modulation) methods.

[0003] Existing zero-current switching active clamp forward converters generally include a main power circuit and a control module. The control module includes a loop compensation unit, a PFM control unit, a fixed pulse width (TON) (Timer On Delay) unit, and a dead-time setting unit. Its control strategy involves feeding the main power circuit output voltage back to the loop compensation unit for calculation. The calculated value is used to control the PFM control unit to generate a frequency pulse signal. This frequency pulse signal is then used by the fixed pulse width (TON) unit to generate a fixed-width frequency pulse signal, which is then used by the dead-time setting unit to generate a complementary drive signal with a dead time to drive the primary-side main power MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) Q1 and the reset MOSFET Q2 in the main power circuit, thereby controlling the converter's output. Depending on the load, the PFM control unit outputs frequency pulses of different frequencies corresponding to different loads, but the pulse width of the drive signal for Q1 remains constant across the entire load range; only the frequency of the drive signal changes.

[0004] However, when this topology is operating normally, the secondary leakage inductance Lr of the transformer T1 in the main power circuit will resonate with the secondary resonant capacitor Cr. The resonant current will exhibit a sinusoidal variation, and its resonant time will change according to the load. If a fixed-time PFM control method is used, zero-current turn-off can only be achieved at a single load point, not across the entire load range. Because the TON time is fixed, the resonant current fails to turn off the Q1 drive after reaching zero, resulting in a non-zero current through Q1 and D2 when the drive is turned off. This prevents the achievement of ZCS, increases line losses, and worsens the EMI (electromagnetic interference) characteristics of the line. Therefore, researching and designing a zero-current switching active clamp forward converter and its control method and equipment that can overcome the above defects is a problem that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a zero-current switching active clamp forward converter and its control method and device, which can ensure that the zero-current switching active clamp forward converter achieves zero-current turn-off across the entire load range, reduce the turn-off losses of power devices in the converter across the entire load range, improve converter efficiency, reduce harmonics during the switching process, and optimize the EMI characteristics of the converter.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: In a first aspect, a zero-current switching active clamp forward converter is provided, including a main power circuit and a control module, wherein the control module includes: The loop compensation unit is configured to receive the output voltage feedback signal of the main power circuit and perform compensation calculations. The PFM control unit is connected to the loop compensation unit and is configured to generate a pulse signal based on the compensation output. A zero-crossing detection control unit is connected to the PFM control unit and connected to the secondary side of transformer T1 in the main power circuit through a current sampling unit. It is configured to generate an adaptive on-time signal based on the resonant current signal sampled from the secondary side of transformer T1 and the pulse signal. The dead-time setting unit is connected to the zero-crossing detection control unit and is configured to generate a complementary drive signal with a dead time based on the adaptive conduction time signal to control the conduction and turn-off of the primary-side main power MOSFET Q1 and the reset MOSFET Q2 in the main power circuit. The pulse signal is used to trigger the operation of the zero-crossing detection control unit, so that the adaptive conduction time signal dynamically adjusts the conduction time of the primary-side main power MOSFET Q1, thereby achieving zero-current turn-off across the entire load range.

[0007] Furthermore, the current sampling unit is configured as follows: The resonant current signal is proportionally amplified. The amplified signal is input to the ZCD port of the zero-crossing detection control unit for zero-crossing detection.

[0008] Furthermore, the zero-crossing detection control unit includes a comparator CP, an SR flip-flop K1, a minimum TON generator TON2, a maximum TON generator TON1, a NOT gate N0T, a first AND gate AND1, and a second AND gate AND2; wherein: The pulse signal is input to the minimum TON generator TON2 and the maximum TON generator TON1 to generate the minimum pulse width signal and the maximum pulse width signal; The comparator CP is configured to compare the resonant current signal with a reference value and output a zero-crossing detection signal; The output of the minimum TON generator TON2 is connected to the input of the NOT gate N0T and the S input of the SR flip-flop K1. The output of the NOT gate N0T and the output of the comparator CP are connected to the input of the first AND gate AND1; The output of the first AND gate AND1 is connected to the R input of the SR flip-flop K1; The output of the maximum TON generator TON1 and the Q output of the SR flip-flop K1 are connected to the input of the second AND gate AND2; The adaptive on-time signal is output from the output terminal of the second AND gate AND2.

[0009] Furthermore, the minimum pulse width set by the minimum TON generator TON2 is greater than the dead time of the dead time setting unit to ensure the normal turn-on of the primary-side main power MOSFET Q1.

[0010] Furthermore, the maximum pulse width set by the maximum TON generator TON1 is used to limit the output of the adaptive conduction time signal when the resonant current signal fails to cross zero abnormally, thereby achieving fault protection.

[0011] Furthermore, the main power circuit also includes a reset capacitor C1, a clamping diode D1, a transformer T1, a secondary leakage inductance Lr, a rectifier diode D2, a resonant capacitor Cr, a freewheeling diode D3, an output filter inductor Lf, an output capacitor Co, and an output load LODA; wherein: The source of the primary-side main power MOSFET Q1 is connected to the positive input terminal, and the drain is connected to the first terminal of the primary winding of the transformer T1, the first terminal of the reset capacitor C1, and the positive terminal of the clamping diode D1. The source of the reset MOS transistor Q2 is connected to the second terminal of the reset capacitor C1 and the negative terminal of the clamping diode D1, and the drain is connected to the negative input terminal and the second terminal of the primary winding of the transformer T1. The first end of the secondary winding of the transformer T1 is connected to the first end of the secondary leakage inductance Lr, and the second end of the secondary leakage inductance Lr is connected to the positive terminal of the rectifier diode D2. The negative terminal of the rectifier diode D2 is connected to the first terminal of the resonant capacitor Cr, the negative terminal of the freewheeling diode D3, and the first terminal of the output filter inductor Lf. The positive terminal of the freewheeling diode D3 is connected to the second terminal of the secondary winding of the transformer T1, the second terminal of the resonant capacitor Cr, the first terminal of the output capacitor Co, and the first terminal of the LODA. The second terminal of the output filter inductor Lf is connected to the second terminal of the output capacitor Co and the second terminal of the output load LODA; The secondary leakage inductance Lr and the resonant capacitor Cr form a resonant network, causing the resonant current to cross zero across the entire load range.

[0012] Secondly, a control method for a zero-current switching active clamp forward converter is provided, including the following steps: The loop compensation unit receives the output voltage feedback signal from the main power circuit and performs compensation calculations to generate a compensated output. Based on the compensation output, a pulse signal is generated by the PFM control unit; The zero-crossing detection control unit receives the pulse signal as a trigger and generates an adaptive on-time signal based on the resonant current signal sampled from the secondary side of transformer T1 in the main power circuit. Based on the adaptive on-time signal, a complementary drive signal with a dead time is generated by the dead time setting unit to control the on and off of the primary-side main power MOSFET Q1 and the reset MOSFET Q2 in the main power circuit, thereby achieving zero-current turn-off across the entire load range.

[0013] Furthermore, the generation of the adaptive on-time signal includes: Based on the pulse signal, the minimum TON generator TON2 is triggered to generate the minimum pulse width signal and the maximum TON generator TON1 is triggered to generate the maximum pulse width signal. The S input terminal of the SR flip-flop K1 is set based on the minimum pulse width signal to enable the conduction of the primary-side main power MOSFET Q1. When the resonant current signal crosses zero, a zero-crossing detection signal is generated, and combined with the inverse value of the minimum pulse width signal, a turn-off signal is generated and sent to the R input terminal of the SR flip-flop K1. The adaptive on-time signal is generated by ANDing the output of the SR flip-flop K1 with the maximum pulse width signal to dynamically adjust the on-time of the primary-side main power MOSFET and achieve zero-current turn-off.

[0014] Furthermore, the minimum pulse width set by the minimum TON generator TON2 is greater than the dead time of the dead time setting unit to ensure the normal turn-on of the primary-side main power MOSFET Q1; And / or, the maximum pulse width set by the maximum TON generator TON1 is used to limit the output of the adaptive conduction time signal when the resonant current signal fails to cross zero abnormally, thereby achieving fault protection.

[0015] Thirdly, an electronic device is provided, comprising at least one zero-current switching active clamp forward converter as described in any one of the first aspects, the converter being used to provide a power output for the electronic device.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention samples the resonant current signal from the secondary side of transformer T1 and combines it with a pulse signal to generate an adaptive on-time signal. Then, based on the adaptive on-time signal, it generates a complementary drive signal with a dead zone to control the on and off of the primary-side main power MOSFET Q1 and the reset MOSFET Q2 in the main power circuit. The pulse signal is used to trigger the operation of the zero-crossing detection control unit, so that the adaptive on-time signal dynamically adjusts the on-time of the primary-side main power MOSFET Q1. This can ensure that the zero-current switching active clamp forward converter achieves zero-current turn-off across the entire load range, reduce the turn-off loss of power devices in the converter across the entire load range, improve the converter efficiency, reduce harmonics during the switching process, and optimize the EMI characteristics of the converter.

[0017] 2. This invention redesigns the zero-crossing detection control unit, setting the minimum TON (minimum pulse width) to be greater than the dead time to ensure the normal activation of Q1. In addition, a maximum TON generator TON1 is designed to limit the output of SR flip-flop K1, ensuring normal drive operation when the resonant current fails to cross zero due to abnormal conditions. Furthermore, a logic gate NOT gate NOT is designed to ensure that the S input and R input of SR flip-flop K1 are not high simultaneously. That is, when the minimum TON is high, it ensures that the value sent by the comparator CP to the R input of SR flip-flop K1 is not high, thus ensuring the normal operation of SR flip-flop K1. Attached Figure Description

[0018] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 This is a circuit diagram of the zero-current switching active clamp forward converter in Embodiment 1 of the present invention; Figure 2 This is a circuit diagram of the zero-crossing detection control unit in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the main waveforms of the zero-crossing detection control method in Embodiment 1 of the present invention; Figure 4 This is a circuit schematic diagram of a zero-current switching active clamp forward converter in the prior art; Figure 5 This is a schematic diagram of the main waveforms of the PFM control method in the existing technology; Figure 6 This is a flowchart of the overall control in Embodiment 1 of the present invention.

[0019] The attached diagram shows the markings and corresponding component names: 1. Main power circuit; 2. Loop compensation unit; 3. PFM control unit; 4. Zero-crossing detection control unit; 5. Dead zone setting unit. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0021] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly or indirectly attached to that other component. When a component is referred to as being "connected to" another component, it can be directly or indirectly connected to that other component.

[0022] It should be understood that the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0024] Example 1: A zero-current switching active clamp forward converter, such as Figure 1As shown, the circuit includes a main power circuit 1 and a control module. The control module includes a loop compensation unit 2, a PFM control unit 3, a zero-crossing detection control unit 4, and a dead-time setting unit 5. The input terminal of the loop compensation unit 2 is connected to the output voltage terminal of the main power circuit 1. The output terminal of the loop compensation unit 2 is connected to the input terminal of the PFM control unit 3. The output terminal PFM_OUT of the PFM control unit 3 is connected to one input terminal PFM_CLK of the zero-crossing detection control unit 4. The other input terminal ZCD of the zero-crossing detection control unit 4 is connected to the resonant current sampling point in the main power circuit 1 through a current sampling unit. The output terminal of the zero-crossing detection control unit 4 is connected to the input terminal of the dead-time setting unit 5, and the output terminal of the dead-time setting unit 5 is connected to the control point of the main power circuit 1.

[0025] Specifically, loop compensation unit 2 is configured to receive the output voltage feedback signal FB from main power circuit 1 and perform compensation calculations to obtain the compensated output COMP; PFM control unit 3 is connected to loop compensation unit 2 and configured to generate a pulse signal based on the compensated output COMP; zero-crossing detection control unit 4 is connected to PFM control unit 3 and connected to the secondary side of transformer T1 in main power circuit 1 through a current sampling unit, configured to generate an adaptive conduction time signal based on the resonant current signal and pulse signal sampled from the secondary side of transformer T1; dead-time setting unit 5 is connected to the loop compensation unit 2. The zero-crossing detection control unit 4 is configured to generate complementary drive signals LGATE (low-side gate drive) and HGATE (high-side gate drive) with dead time based on the adaptive on-time signal PWM. HGATE controls the on and off of the primary-side main power MOSFET Q1 in the main power circuit 1, and LGATE controls the on and off of the reset MOSFET Q2 in the main power circuit 1. The pulse signal is used to trigger the operation of the zero-crossing detection control unit 4, so that the adaptive on-time signal dynamically adjusts the on-time of the primary-side main power MOSFET Q1 to achieve zero-current turn-off across the entire load range.

[0026] like Figure 1 As shown, the main power circuit 1 includes a primary-side main power MOSFET Q1, a reset capacitor C1, a clamping diode D1, a reset MOSFET Q2, a transformer T1, a secondary-side leakage inductance Lr, a rectifier diode D2, a resonant capacitor Cr, a freewheeling diode D3, an output filter inductor Lf, an output capacitor Co, and an output load LODA.

[0027] Specifically, the source of the primary power MOSFET Q1 is connected to the positive input terminal, and its drain is connected to the first terminal of the primary winding of transformer T1, the first terminal of reset capacitor C1, and the positive terminal of clamping diode D1; the source of the reset MOSFET Q2 is connected to the second terminal of reset capacitor C1 and the negative terminal of clamping diode D1, and its drain is connected to the negative input terminal and the second terminal of the primary winding of transformer T1; the first terminal of the secondary winding of transformer T1 is connected to the first terminal of the secondary leakage inductance Lr, and the second terminal of the secondary leakage inductance Lr is connected to the positive terminal of rectifier diode D2; the rectifier diode... The negative terminal of transistor D2 is connected to the first terminal of resonant capacitor Cr, the negative terminal of freewheeling diode D3, and the first terminal of output filter inductor Lf; the positive terminal of freewheeling diode D3 is connected to the second terminal of the secondary winding of transformer T1, the second terminal of resonant capacitor Cr, the first terminal of output capacitor Co, and the first terminal of LODA; the second terminal of output filter inductor Lf is connected to the second terminal of output capacitor Co and the second terminal of output load LODA; wherein, the secondary leakage inductance Lr and resonant capacitor Cr form a resonant network, so that the resonant current crosses zero in the full load range.

[0028] This invention sets a resonant current sampling point between the secondary leakage inductance Lr and the rectifier diode D2, and configures a current sampling unit at this point to sample the resonant current of the converter. The current sampling unit is configured to: proportionally amplify the resonant current signal; and input the amplified signal to the ZCD port of the zero-crossing detection control unit 4 for zero-crossing detection.

[0029] The zero-crossing detection control unit 4 in this invention can generate a TON signal with the same time width as the resonant current based on the sampled resonant current signal, which is used to control the primary-side main power MOSFET Q1. This achieves zero-current turn-off (ZCS).

[0030] like Figure 2 As shown, the zero-crossing detection control unit 4 designed in this invention includes a comparator CP, an SR flip-flop K1, a minimum TON generator TON2, a maximum TON generator TON1, a logic gate NOT gate N0T, a first AND gate AND1, and a second AND gate AND2.

[0031] Specifically, the PFM_CLK port is connected to the inputs of the maximum TON generator TON1 and the minimum TON generator TON2. The pulse signal is input to the minimum TON generator TON2 and the maximum TON generator TON1 to generate the minimum pulse width signal and the maximum pulse width signal. The reference value Ref is connected to the positive input of the comparator CP. The comparator CP is configured to compare the resonant current signal with the reference value and output a zero-crossing detection signal. The output of the minimum TON generator TON2 is connected to the input of the NOT gate N0T and the S input of the SR flip-flop K1. The output of the NOT gate N0T and the output of the comparator CP are connected to the input of the first AND gate AND1. The output of the first AND gate AND1 is connected to the R input of the SR flip-flop K1. The output of the maximum TON generator TON1 and the Q output of the SR flip-flop K1 are connected to the input of the second AND gate AND2. The output of the second AND gate AND2 outputs the adaptive on-time signal PWM.

[0032] The pulse signal output from PFM control unit 3 is sent to zero-crossing detection control unit 4 to generate a maximum pulse width signal and a minimum pulse width signal. The minimum pulse width signal is sent to the S terminal of SR flip-flop K1 to turn on the primary-side main power MOSFET Q1. The resonant current signal sampled from the secondary side is sent to zero-crossing detection control unit 4 and compared with the reference value Ref. When the resonant sampling current is less than the reference value Ref, the comparator CP outputs high. The comparator CP output is ANDed with the inverse value of the minimum pulse width signal, and the resulting signal is sent to the R terminal of SR flip-flop K1 to turn off the primary-side main power MOSFET Q1. The maximum pulse width signal is ANDed with the output of SR flip-flop K1 to limit the maximum width of the SR flip-flop K1 output.

[0033] Specifically, based on the operating characteristics of the zero-current switching active clamp forward converter, the primary current is the sum of the secondary resonant current referred to the primary side and the transformer primary excitation current. This means that even when the resonant current crosses zero, there is still excitation current flowing in the primary side. This current has a very small value but does not cross zero, and it changes with the load, making it difficult to set the threshold of the comparator CP. To optimize the zero-crossing comparison threshold setting, based on the operating characteristics of the zero-current switching active clamp forward converter, since the secondary leakage inductance Lr and resonant capacitor Cr are always in a resonant state, the secondary resonant current can achieve zero-crossing across the entire load range. Therefore, the current signal input to the zero-crossing detection and control unit 4 needs to be obtained from the resonant inductor Lr.

[0034] In some optional examples, the minimum pulse width set by the minimum TON generator TON2 is greater than the dead time of the dead time setting unit 5 to ensure the normal turn-on of the primary-side main power MOSFET Q1.

[0035] In some optional examples, the maximum pulse width set by the maximum TON generator TON1 is used to limit the output of the adaptive on-time signal when the resonant current signal fails to cross zero abnormally, thereby achieving fault protection.

[0036] Because the signal output from PFM control unit 3 to zero-crossing detection control unit 4 is a high-frequency, variable-frequency narrow pulse signal (around 80ns), if this signal is directly sent to the S terminal of SR flip-flop K1 in zero-crossing detection control unit 4 without passing through the minimum TON generator TON2, the output pulse width of SR flip-flop K1 will be very narrow. After deducting the dead time (around 100ns) from the output from the zero-crossing detection unit to the dead-time setting unit 5, the drive sent to the primary-side main power MOSFET Q1 will disappear, preventing Q1 from turning on. To avoid this problem, the minimum TON (minimum pulse width) needs to be set greater than the dead time to ensure the normal turning on of the primary-side main power MOSFET Q1. The maximum TON generator TON1 is set to limit the output of SR flip-flop K1, ensuring normal drive when the resonant current fails to cross zero due to abnormal conditions. The NOT gate (N0T) is used to ensure that the S and R inputs of the SR flip-flop K1 are not both high simultaneously. Specifically, when the minimum TON is high, it ensures that the value sent by the comparator CP to the R input of the SR flip-flop K1 is not high, thus guaranteeing the normal operation of the SR flip-flop K1. In the SR flip-flop K1, S is the set input, R is the reset input, and Q is the output. The main waveforms of the zero-crossing detection control are as follows: Figure 3 As shown, ag corresponds to the primary-side main power MOSFET Q1 drive, reset MOSFET Q2 drive, Cr voltage, resonant current, PFM output pulse, minimum TON output, and comparator CP output, respectively. The input pulse signal generates the minimum pulse width and maximum pulse width through the minimum TON generator TON2 and the maximum TON generator TON1. The minimum TON is sent to the S input terminal of SR flip-flop K1. According to the truth table of SR flip-flop K1 (Q=1 when S=1, R=0), it is ANDed with the maximum TON (maximum pulse width), and then passed through the dead-time setting unit 5 to generate complementary drive. After subtracting the dead time, it controls the primary-side main power MOSFET Q1 to turn on and the reset MOSFET Q2 to turn off. When the primary-side main power MOSFET Q1 is turned on, the secondary-side leakage inductance Lr and resonant capacitor Cr begin to resonate. When the resonant current returns from its maximum value to 0, the comparator CP output changes from low to high. At this time, the minimum TON output value is low. After ANDing with the inverse value of the minimum TON, it is sent to the R terminal of the SR flip-flop K1. According to the truth table of the SR flip-flop K1 (Q=0 when S=0, R=1), the SR flip-flop K1 output is low. After ANDing with the maximum TON, it passes through the dead-time setting unit 5 to generate complementary drive. After subtracting the dead time, it controls the primary-side main power MOSFET Q1 to turn off and resets the MOSFET Q2 to turn on.

[0037] The circuit diagram of a zero-current switching active clamp forward converter in the prior art is as follows: Figure 4 As shown, the main power circuit 1 has the same structure as the main power circuit 1 described in this embodiment, and the main waveforms of the PFM control mode are as follows. Figure 5 As shown, AF corresponds to the driving of the primary-side main power MOSFET Q1, the driving of the reset MOSFET Q2, the Cr voltage, the resonant current, the PFM output pulse, and the TON output, respectively. The PFM control unit 3 outputs frequency pulses of different frequencies corresponding to different loads, but the pulse width of the driving signal of the primary-side main power MOSFET Q1 remains constant across the entire load range; only the frequency of its driving signal changes. This invention can achieve zero-crossing detection control that follows the resonant current change, ensuring that the primary-side main power MOSFETs Q1 and D2 achieve zero-current turn-off across the entire load range.

[0038] Example 2: A control method for a zero-current switching active clamp forward converter, such as... Figure 6 As shown, it includes the following steps: S1: The loop compensation unit 2 receives the output voltage feedback signal of the main power circuit 1 and performs compensation calculations to generate a compensated output; S2: Based on the compensation output, a pulse signal is generated by the PFM control unit 3; S3: The zero-crossing detection control unit 4 receives a pulse signal as a trigger and generates an adaptive on-time signal based on the resonant current signal sampled from the secondary side of transformer T1 in the main power circuit 1. S4: Based on the adaptive on-time signal, a complementary drive signal with a dead time is generated by the dead-time setting unit 5 to control the on and off of the primary-side main power MOSFET Q1 and the reset MOSFET Q2 in the main power circuit 1, so as to achieve zero-current turn-off across the entire load range.

[0039] It should be noted that the zero-current switching active clamp forward converter described in this embodiment can be any of the forward converters described in Embodiment 1, or other forward converters with added or modified components while maintaining functionality.

[0040] In some optional examples, the generation of the adaptive on-time signal includes: triggering a minimum TON generator TON2 to generate a minimum pulse width signal and a maximum TON generator TON1 to generate a maximum pulse width signal based on a pulse signal; setting the S input of SR flip-flop K1 based on the minimum pulse width signal to enable the primary-side main power MOSFET Q1 to turn on; generating a zero-crossing detection signal when the resonant current signal crosses zero, and combining it with the inverse value of the minimum pulse width signal to generate a turn-off signal to the R input of SR flip-flop K1; and generating an adaptive on-time signal by ANDing the output of SR flip-flop K1 with the maximum pulse width signal to dynamically adjust the on-time of the primary-side main power MOSFET and achieve zero-current turn-off.

[0041] In some optional examples, the minimum pulse width set by the minimum TON generator TON2 is greater than the dead time of the dead time setting unit 5 to ensure the normal turn-on of the primary-side main power MOSFET Q1.

[0042] In some optional examples, the maximum pulse width set by the maximum TON generator TON1 is used to limit the output of the adaptive on-time signal when the resonant current signal fails to cross zero abnormally, thereby achieving fault protection.

[0043] Example 3: An electronic device including at least one zero-current switching active clamp forward converter as in any one of Examples 1, the converter being used to provide power output for the electronic device.

[0044] Working principle: This invention samples the resonant current signal from the secondary side of transformer T1 and combines it with a pulse signal to generate an adaptive on-time signal. Then, based on the adaptive on-time signal, it generates a complementary drive signal with a dead time to control the on and off of the primary-side main power MOSFET Q1 and the reset MOSFET Q2 in the main power circuit 1. The pulse signal is used to trigger the operation of the zero-crossing detection control unit 4, so that the adaptive on-time signal dynamically adjusts the on-time of the primary-side main power MOSFET Q1. This can ensure that the zero-current switching active clamp forward converter achieves zero-current turn-off (ZCS) across the entire load range, which can reduce the turn-off loss of power devices in the converter across the entire load range, improve the converter efficiency, reduce harmonics during the switching process, and optimize the EMI characteristics of the converter.

[0045] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A zero-current switching active clamp forward converter, comprising a main power circuit (1) and a control module, characterized in that, The control module includes: The loop compensation unit (2) is configured to receive the output voltage feedback signal of the main power circuit (1) and perform compensation calculations; The PFM control unit (3) is connected to the loop compensation unit (2) and is configured to generate a pulse signal based on the compensation output; The zero-crossing detection control unit (4) is connected to the PFM control unit (3) and connected to the secondary side of the transformer T1 in the main power circuit (1) through the current sampling unit. It is configured to generate an adaptive on-time signal based on the resonant current signal sampled from the secondary side of the transformer T1 and the pulse signal. The dead zone setting unit (5) is connected to the zero-crossing detection control unit (4) and is configured to generate a complementary drive signal with a dead zone based on the adaptive conduction time signal to control the conduction and turn-off of the primary-side main power MOSFET Q1 and the reset MOSFET Q2 in the main power circuit (1). The pulse signal is used to trigger the operation of the zero-crossing detection control unit (4), so that the adaptive conduction time signal dynamically adjusts the conduction time of the primary-side main power MOS transistor Q1, thereby achieving zero-current turn-off across the entire load range.

2. The zero-current switching active clamp forward converter according to claim 1, characterized in that, The current sampling unit is configured as follows: The resonant current signal is proportionally amplified. The amplified signal is input to the ZCD port of the zero-crossing detection control unit (4) for zero-crossing detection.

3. A zero-current switching active clamp forward converter according to claim 1, characterized in that, The zero-crossing detection control unit (4) includes a comparator CP, an SR flip-flop K1, a minimum TON generator TON2, a maximum TON generator TON1, a NOT gate N0T, a first AND gate AND1, and a second AND gate AND2; wherein: The pulse signal is input to the minimum TON generator TON2 and the maximum TON generator TON1 to generate the minimum pulse width signal and the maximum pulse width signal; The comparator CP is configured to compare the resonant current signal with a reference value and output a zero-crossing detection signal; The output of the minimum TON generator TON2 is connected to the input of the NOT gate N0T and the S input of the SR flip-flop K1. The output of the NOT gate N0T and the output of the comparator CP are connected to the input of the first AND gate AND1; The output of the first AND gate AND1 is connected to the R input of the SR flip-flop K1; The output of the maximum TON generator TON1 and the Q output of the SR flip-flop K1 are connected to the input of the second AND gate AND2; The adaptive on-time signal is output from the output terminal of the second AND gate AND2.

4. A zero-current switching active clamp forward converter according to claim 3, characterized in that, The minimum pulse width set by the minimum TON generator TON2 is greater than the dead time of the dead time setting unit (5) to ensure the normal turn-on of the primary-side main power MOSFET Q1.

5. A zero-current switching active clamp forward converter according to claim 3, characterized in that, The maximum pulse width set by the maximum TON generator TON1 is used to limit the output of the adaptive conduction time signal when the resonant current signal fails to cross zero abnormally, thereby achieving fault protection.

6. A zero-current switching active clamp forward converter according to claim 1, characterized in that, The main power circuit (1) also includes a reset capacitor C1, a clamping diode D1, a transformer T1, a secondary leakage inductance Lr, a rectifier diode D2, a resonant capacitor Cr, a freewheeling diode D3, an output filter inductor Lf, an output capacitor Co, and an output load LODA; wherein: The source of the primary-side main power MOSFET Q1 is connected to the positive input terminal, and the drain is connected to the first terminal of the primary winding of the transformer T1, the first terminal of the reset capacitor C1, and the positive terminal of the clamping diode D1. The source of the reset MOS transistor Q2 is connected to the second terminal of the reset capacitor C1 and the negative terminal of the clamping diode D1, and the drain is connected to the negative input terminal and the second terminal of the primary winding of the transformer T1. The first end of the secondary winding of the transformer T1 is connected to the first end of the secondary leakage inductance Lr, and the second end of the secondary leakage inductance Lr is connected to the positive terminal of the rectifier diode D2. The negative terminal of the rectifier diode D2 is connected to the first terminal of the resonant capacitor Cr, the negative terminal of the freewheeling diode D3, and the first terminal of the output filter inductor Lf. The positive terminal of the freewheeling diode D3 is connected to the second terminal of the secondary winding of the transformer T1, the second terminal of the resonant capacitor Cr, the first terminal of the output capacitor Co, and the first terminal of the LODA. The second terminal of the output filter inductor Lf is connected to the second terminal of the output capacitor Co and the second terminal of the output load LODA; The secondary leakage inductance Lr and the resonant capacitor Cr form a resonant network, causing the resonant current to cross zero across the entire load range.

7. A control method for a zero-current switching active clamp forward converter, characterized in that, Includes the following steps: The loop compensation unit (2) receives the output voltage feedback signal of the main power circuit (1) and performs compensation calculations to generate a compensation output; Based on the compensation output, a pulse signal is generated by the PFM control unit (3); The zero-crossing detection control unit (4) receives the pulse signal as a trigger and generates an adaptive on-time signal based on the resonant current signal sampled from the secondary side of transformer T1 in the main power circuit (1). Based on the adaptive on-time signal, a complementary drive signal with a dead time is generated by the dead time setting unit (5) to control the on and off of the primary power MOSFET Q1 and the reset MOSFET Q2 in the main power circuit (1), thereby achieving zero-current turn-off across the entire load range.

8. The control method for a zero-current switching active clamp forward converter according to claim 7, characterized in that, The generation of the adaptive on-time signal includes: Based on the pulse signal, the minimum TON generator TON2 is triggered to generate the minimum pulse width signal and the maximum TON generator TON1 is triggered to generate the maximum pulse width signal. The S input terminal of the SR flip-flop K1 is set based on the minimum pulse width signal to enable the conduction of the primary-side main power MOSFET Q1. When the resonant current signal crosses zero, a zero-crossing detection signal is generated, and combined with the inverse value of the minimum pulse width signal, a turn-off signal is generated and sent to the R input terminal of the SR flip-flop K1. The adaptive on-time signal is generated by ANDing the output of the SR flip-flop K1 with the maximum pulse width signal to dynamically adjust the on-time of the primary-side main power MOSFET and achieve zero-current turn-off.

9. The control method for a zero-current switching active clamp forward converter according to claim 8, characterized in that, The minimum pulse width set by the minimum TON generator TON2 is greater than the dead time of the dead time setting unit (5) to ensure the normal turn-on of the primary-side main power MOS transistor Q1; And / or, the maximum pulse width set by the maximum TON generator TON1 is used to limit the output of the adaptive conduction time signal when the resonant current signal fails to cross zero abnormally, thereby achieving fault protection.

10. An electronic device, characterized in that, Includes at least one zero-current switching active clamp forward converter as described in any one of claims 1-6, the converter being used to provide power output for the electronic device.

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