Output voltage high-precision sampling circuit and control system of active clamping flyback converter

Abstract

The invention discloses an output voltage high-precision sampling circuit and a control system of an active clamping flyback converter, the circuit comprises a sampling module and a high-precision voltage reduction module, the voltage sampling module respectively collects an auxiliary winding voltage Vaux and a primary side current ip of the active clamping flyback converter; a sampled signal is transmitted to a high-precision voltage reduction module; the input of the high-precision voltage reduction module is a primary side current ip and an auxiliary winding voltage Vaux, and a corrected output voltage Voc is output by carrying out voltage correction prediction on an auxiliary winding voltage slope abrupt change point and a primary side current first zero crossing point. According to the invention, high output voltage sampling precision can be realized, and accurate output voltage sampling and control can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of switching converters, and in particular to a high-precision output voltage sampling circuit and control system of an active clamp flyback converter. Background Art

[0002] With the rapid development of communications technology, the energy consumption of communications systems continues to increase. Constrained by limited equipment space, communications power systems must achieve higher power density, higher efficiency, and greater reliability. To meet these demands, the active clamp flyback converter (ACF) has become a key topology in the communications power supply field due to its advantages such as high operating frequency, high conversion efficiency, low voltage stress, and low EMI noise. By introducing a clamping circuit, the ACF enables soft switching operation, significantly reducing switching losses and electromagnetic interference, making it particularly suitable for high-frequency applications.

[0003] Traditional secondary-side feedback control methods typically rely on optocouplers to achieve closed-loop regulation of the output voltage. However, optocouplers exhibit nonlinear response, aging, and temperature drift, which can reduce the system's output accuracy and reliability. To address this, primary-side regulation (PSR) technology has been proposed. This technology predicts the output voltage by sampling the voltage of the transformer's auxiliary winding, eliminating the optocoupler, simplifying the circuit structure, and improving system reliability and integration.

[0004] However, under high-frequency operating conditions, the output voltage sampling accuracy of primary-side feedback technology is significantly affected by parasitic parameters (such as secondary-side leakage inductance and parasitic resistance). Furthermore, due to the presence of high-frequency oscillations and the nonlinear characteristics of the auxiliary winding voltage waveform, traditional sampling methods struggle to accurately capture output voltage information, resulting in large sampling errors. Therefore, how to effectively compensate for the influence of parasitic parameters and improve the sampling accuracy of primary-side feedback has become a key issue in the research of high-frequency active-clamp flyback converters. Summary of the Invention

[0005] In order to solve the problem of low sampling accuracy of primary-side feedback in a high-frequency active-clamp flyback converter, the present invention proposes a high-precision output voltage sampling circuit and control system for an active-clamp flyback converter. By sampling the auxiliary winding voltage and primary-side current, the voltage difference caused by the secondary-side leakage inductance is eliminated, thereby improving the sampling accuracy of the primary-side feedback.

[0006] The technical solution for achieving the purpose of the present invention is:

[0007] A high-precision sampling circuit for the output voltage of an active clamp flyback converter includes a sampling module and a high-precision voltage restoration module, wherein:

[0008] The voltage sampling module respectively collects the auxiliary winding voltage V aux and the primary current i p , the sampled signal is transmitted to the high-precision voltage restoration module;

[0009] The input of the high-precision voltage restoration module is the primary current i p and the auxiliary winding voltage V aux By predicting the voltage correction of the auxiliary winding voltage slope mutation point and the first zero-crossing point of the primary current, the corrected output voltage V is output. oc .

[0010] Furthermore, the high-precision voltage restoration module performs voltage correction prediction, specifically including:

[0011] When the circuit works in the intermittent conduction mode, after the main circuit is turned off, the output diode is first turned on at t1 and first turned off at t2. The secondary diode current i d Reach peak I speak The time is t peak , determine the slope ratio relationship between the rising and falling phases of the secondary diode current;

[0012] Based on the slope proportional relationship, the auxiliary winding sampling voltage difference at time t1 and time t2 is calculated;

[0013] Based on the voltage difference, determine the corrected output voltage V oc .

[0014] Furthermore, the slope ratio relationship between the secondary diode current rising phase and the falling phase is:

[0015]

[0016] Among them, k up is the secondary diode current i d Slope of the rising phase, k down is the slope of the descending phase.

[0017] Furthermore, the auxiliary winding sampling voltage difference is:

[0018]

[0019] Among them, L sk is the secondary side leakage inductance, V aux1 、V aux2 They are the sampling voltages at time t1 and time t2 respectively.

[0020] Furthermore, the corrected output voltage V oc for:

[0021]

[0022] Among them, V f is the secondary side diode voltage drop.

[0023] A control system for an active clamp flyback converter includes the output voltage high-precision sampling circuit, an output control module, and a switch tube drive module. The input of the output control module is the corrected output voltage V oc and the target voltage V ref , adjust the duty cycle of the output tube according to the output voltage, and the output tube conduction time T on , Auxiliary tube conduction time T sr and dead time t dead The switch tube drive module input is the next cycle main conduction time T on , Auxiliary tube conduction time T sr and dead time t dead , output as the driving signal of the main switch tube M1 and the auxiliary switch tube M2 for the next cycle.

[0024] Furthermore, the output control module specifically includes: the current switching cycle starts at time t0, the current cycle ends at time t0+Ts, and the next switching cycle begins; in the current switching cycle, when the main switch tube is turned on at time t0, the current cycle ends at time t0+Ts, and the next switching cycle begins; on During this phase, the main circuit is turned on, i.e. the main control signal duty_main is set to 1. During the rest of the current switching cycle, the main circuit is turned off, i.e. the main control signal duty_main is set to 0. At t0+T on +t dead to t0+T on +t dead +T sr Stage, T s -t dead -T sr to T s -t dead During the current switching cycle, the auxiliary tube is turned on and its control signal duty_sr is set to 1. During the rest of the current switching cycle, the auxiliary tube is turned off and its control signal duty_sr is set to 0.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] In this invention, a high-precision voltage restoration module determines the first conduction and cutoff times of the secondary diode based on the auxiliary winding voltage slope mutation point. At this point, the diode conduction voltage drop remains constant. Output voltage acquisition at this time accurately reflects the true level of the converter's output voltage, enabling precise control of the output voltage across the full load range. Furthermore, the disclosed acquisition circuit is widely applicable and simple to implement, and its high-precision sampling concept can be extended to other high- and low-frequency switching converter control methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0028] Figure 1 This is a structural block diagram of the primary side feedback high-precision control system of the present invention.

[0029] Figure 2 It is a schematic diagram of the circuit topology of the active clamp flyback converter of the present invention.

[0030] Figure 3 Schematic diagram of the key waveforms of the active clamp flyback converter in DCM mode.

[0031] Figure 4 It is the output voltage change curve under different input voltages. DETAILED DESCRIPTION

[0032] References throughout this specification to "one embodiment" or "an embodiment" mean that the specific features, structures, or characteristics described in conjunction with that embodiment are included in at least one embodiment of the present invention. Therefore, the phrases "in one embodiment" or "in an embodiment" that appear throughout this specification do not necessarily all refer to the same embodiment. The verbs "comprise" and "have" are used herein as open limitations that neither exclude nor require the presence of unrecited features. Unless otherwise expressly stated, the features recited in the dependent claims may be freely combined with each other. The use of "one" or "an" (i.e., in the singular) to define an element throughout this document does not exclude the possibility of multiple such elements. Furthermore, the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Unless otherwise specified, the term "connected" is used to specify a direct electrical connection between circuit elements, while the term "coupled" is used to specify an electrical connection between circuit elements that may be direct or may be via one or more other elements. In contrast, when an element is said to be "directly connected to" or "directly coupled to" another element, there are no intervening elements. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. When referring to the voltage of a node or terminal, unless otherwise indicated, the voltage is considered to be the voltage between the node and a reference potential (usually ground). In addition, when referring to the potential of a node or terminal, unless otherwise indicated, the potential is considered to refer to the reference potential. The voltage and potential of a given node or a given terminal will be further designated with the same reference numerals. A signal that alternates between a first logic state (e.g., a logic low state) and a second logic state (e.g., a logic high state) is referred to as a "logic signal." The high and low states of different logic signals of the same electronic circuit may be different. In particular, the high and low states of a logic signal may correspond to a voltage or current that may not be completely constant in the high or low state.

[0033] Refer to the following Figures 1 to 3 The output voltage high-precision sampling circuit and method provided according to some embodiments of the present invention are described.

[0034] See Figure 1 The present invention discloses a high-precision sampling control system for an active clamp flyback converter, which includes a main topology circuit and a closed-loop control system. The input of the sampling module is an analog value V representing the voltage of the voltage divider resistor on the auxiliary winding. aux , representing the analog value V of the voltage across the primary sampling resistor p The sampling module performs corresponding calculations based on the actual voltage divider resistor sampling value, the primary side sampling voltage value and the voltage sampling chip parameters to obtain a digital signal V representing the voltage of the voltage divider resistor on the auxiliary winding. auxd , a digital signal V representing the voltage across the primary sampling resistor pd, and input it into the high-precision voltage restoration module. In the high-precision voltage restoration module, the slope of the secondary-side diode current is predicted by the restoration algorithm, thereby obtaining the voltage on the secondary-side leakage inductance, outputting the corrected output voltage, and inputting it into the output control module to adjust the conduction time of the main tube. Finally, the drive isolation module generates the drive signals duty_main and duty_sr, which are output to the main topology of the active clamp flyback converter and input into the gates of the two switching tubes of the converter to drive them on and off to realize the switching circuit drive of the next cycle.

[0035] Figure 2 This is a schematic diagram of the main topology circuit of the active clamp flyback converter, including the main switch tube, auxiliary switch tube, clamping capacitor, transformer, and secondary diode. The transformer includes primary winding, secondary winding, and auxiliary winding. The positive terminal of the input DC voltage is connected to the primary leakage inductance L. k , input capacitance V in The positive and negative terminals correspond to the positive input terminal and the input ground respectively. The clamping circuit adopts an active clamping structure, with a clamping capacitor C c The auxiliary switch tube M2 replaces the traditional RCD circuit, the clamping capacitor C c One end is connected to the filtered DC voltage, and the other end is connected to the drain of the auxiliary switch tube M2. The drain of the main switch tube M1 is connected to the source of the auxiliary switch tube M2, and its source is connected to the input ground through the sampling resistor. p The same-name termination primary leakage inductance L k The right port of the auxiliary winding is connected to the drain of the main switch tube M1, and the opposite-name terminal is connected to the input ground, and the voltage at the same-name terminal is the auxiliary winding voltage V aux . Transformer secondary winding N s The same-name terminal is connected to the positive terminal of the output diode D1, the opposite-name terminal is connected to the output ground, and the negative terminal of the output diode is connected to the output capacitor C out The positive electrode of the output capacitor is connected to the output ground. The output voltage is V o , duty_main and duty_sa are the control signals of the main and auxiliary tubes respectively. The primary side feedback technology can be used to sample the primary auxiliary winding voltage V aux The output voltage is obtained. Compared with traditional secondary-side feedback technology that directly samples the output voltage, this eliminates the optocoupler and its associated circuitry, simplifies the converter circuit, improves converter reliability, increases converter lifespan, and reduces costs.

[0036] Continue to read Figure 1 The closed-loop control system includes a voltage sampling module, a high-precision voltage reduction module, an output control module, and a drive isolation module. The system is connected to a controlled active clamp flyback converter to form a closed loop. The present invention can sample the auxiliary winding voltage V aux and the primary current ip To calculate the voltage difference caused by the secondary side leakage inductance and make corrections to achieve high-precision voltage sampling.

[0037] The voltage sampling module collects the auxiliary winding voltage V aux and the primary current i p The sampling module performs corresponding calculations based on the actual sampling value and the ADC sampling chip parameters to obtain the primary current i p The digital signal V of the sampling resistor voltage pd and the digital signal V of the voltage divider resistor on the auxiliary winding auxd , and transmits the sampled signal to the high-precision voltage restoration module.

[0038] The input of the high-precision voltage restoration module is the voltage digital value V of the primary current sampling resistor pd and the digital value of the voltage divider resistor voltage on the auxiliary winding V auxd By predicting the auxiliary winding voltage slope mutation point and the primary current first zero crossing point, the corrected output voltage V is output. oc .

[0039] The voltage sampling module generates a sampling signal by dividing the system clock by two. The ADC accurately captures the voltage of the voltage divider resistor on the auxiliary winding on the rising edge of the clock and samples the voltage of the primary current sampling resistor on the falling edge. aux Enter the register and pass through the subtractor with the V at the previous sampling moment aux [n-1] performs differential operation and inputs the result into the register, and the result is recorded as ΔV aux [n] First, we need to determine the rising and falling slopes of the secondary diode current. For the sampling point at time t1, if the ΔV aux [n+1] is much smaller than the ΔV of the previous cycle aux [n], we can determine the arrival of sampling time t1 and record the voltage V of the corresponding voltage divider resistor on the auxiliary winding aux1 For the sampling point at time t2, if the ΔV of this cycle aux [n+1] is much larger than the ΔV of the previous cycle aux [n], we can determine the arrival of sampling time t2 and record the voltage V of the corresponding voltage divider resistor on the auxiliary winding aux2 . V aux The corresponding expressions are shown in formula (8) and formula (9):

[0040]

[0041] Since the clamping capacitor in the present invention is very large, the secondary diode current rising and falling phases can be close to linear. Assume that the secondary diode current rising slope is k up , the descending slope is k down Since the secondary diode current at t1 and t2 is 0, the result of subtracting the two equations is shown in equation (10):

[0042]

[0043] The time when the secondary current reaches its peak is t peak , which is equivalent to the first zero-crossing moment of the primary current after the main circuit is turned off. According to the voltage V on the primary current sampling resistor sampled at the falling edge of the ADC clock p Determine the first zero crossing of the primary current. At this time, V p [n] is positive, this period V p [n+1] is negative, and the zero-crossing time is recorded as t peak . If Figure 3 The relationship between the rising and falling slopes of the secondary diode current can be derived:

[0044]

[0045] Substituting into formula (10) we can get:

[0046]

[0047] Therefore, the corrected output voltage V oc It can be expressed as:

[0048]

[0049] Due to the secondary diode voltage drop V f So, as long as V aux1 、V aux2 By calculating the values ​​of t1, t2 and tpeak, the output voltage can be predicted with high precision. In the high-precision voltage restoration module, the sampling error introduced by the parasitic resistance and capacitance is corrected by predicting the secondary diode current and its slope, thereby achieving high-precision output voltage prediction.

[0050] The output control module changes the duty cycle of the main tube according to the corrected output voltage, and then generates the main tube control signal duty_main and the auxiliary tube control signal duty_sr in the isolation drive control module. Specifically, the current switching cycle starts at time t0, ends at time t0+Ts, and the next switching cycle begins; in the current switching cycle, when the main switch tube is turned on at time t0, the auxiliary tube control signal duty_sr is generated from t0 to t0+Ts. onDuring this phase, the main circuit is turned on, i.e. the main circuit control signal duty_main is set to 1. During the rest of the current switching cycle, the main circuit is turned off, i.e. the main circuit control signal duty_main is set to 0. At t0+T on +t dead to t0+T on +t dead +T sr Stage, T s -t dead -T sr To T s -t dead During the current switching cycle, the auxiliary tube is turned on and its control signal duty_sr is set to 1. During the rest of the current switching cycle, the auxiliary tube is turned off and its control signal duty_sr is set to 0.

[0051] The input of the switch tube driving module is the next cycle main conduction time T on , Auxiliary tube conduction time T sr and dead time t dead , the output is the driving signal of the main switch tube M1 and the auxiliary switch tube M2 for the next cycle to complete the closed loop.

[0052] Figure 3 This diagram shows the key waveforms of an active-clamp flyback converter operating in DCM mode. There is a significant difference in the voltage across the auxiliary winding at times t1 and t2. The difference in the auxiliary winding voltage at these two times corresponds to the voltage across the secondary leakage inductance. Furthermore, the peak secondary current at the corresponding moment is equivalent to the first zero crossing of the primary current.

[0053] Figure 4 This is the output voltage curve when the input voltage varies from 24V to 96V, with the target output voltage set at 24V. It can be observed that the output voltage accuracy can be controlled within 1.8% when the input voltage varies from 24V to 96V, indicating that the present invention can achieve precise control of the output voltage over the full load range.

[0054] The above description is a further detailed description of the present invention in conjunction with specific preferred embodiments. The specific implementation of the present invention is not limited to these descriptions. The present invention described herein is subject to many variations (duty cycle, switching frequency, secondary leakage inductance, voltage divider resistor ratio), and such variations cannot deviate from the spirit and scope of the present invention. Therefore, all modifications obvious to those skilled in the art are included within the scope of the present claims.

Claims

1. A high-precision sampling circuit for the output voltage of an active clamp flyback converter, characterized in that: It includes a sampling module and a high-precision voltage restoration module, including: The voltage sampling module respectively collects the auxiliary winding voltage V aux and the primary current i p , the sampled signal is transmitted to the high-precision voltage restoration module; The input of the high-precision voltage restoration module is the primary current i p and the auxiliary winding voltage V aux By predicting the voltage correction of the auxiliary winding voltage slope mutation point and the first zero-crossing point of the primary current, the corrected output voltage V is output. oc .

2. The high-precision output voltage sampling circuit of an active clamp flyback converter according to claim 1, characterized in that: The high-precision voltage restoration module performs voltage correction prediction, specifically including: When the circuit works in the intermittent conduction mode, after the main circuit is turned off, the output diode is first turned on at t1 and first turned off at t2. The secondary diode current i d Reach peak I speak The time is t peak , determine the slope ratio relationship between the rising and falling phases of the secondary diode current; Based on the slope proportional relationship, the auxiliary winding sampling voltage difference at time t1 and time t2 is calculated; Based on the voltage difference, determine the corrected output voltage V oc .

3. The high-precision output voltage sampling circuit of an active clamp flyback converter according to claim 2, characterized in that: The slope ratio of the secondary diode current during the rising and falling phases is: Among them, k up is the secondary diode current i d Slope of the rising phase, k down is the slope of the descending phase.

4. The high-precision output voltage sampling circuit of an active clamp flyback converter according to claim 3, characterized in that: The auxiliary winding sampling voltage difference is: Among them, L sk is the secondary side leakage inductance, V aux1 、V aux2 They are the sampling voltages at time t1 and time t2 respectively.

5. The high-precision output voltage sampling circuit of an active clamp flyback converter according to claim 4, characterized in that: Corrected output voltage V oc for: Among them, V f is the secondary side diode voltage drop.

6. A control system for an active clamp flyback converter, characterized in that: The invention comprises the output voltage high-precision sampling circuit, the output control module and the switch tube driving module according to any one of claims 1 to 5, wherein the input of the output control module is the corrected output voltage V oc and the target voltage V ref , adjust the duty cycle of the output tube according to the output voltage, and the output tube conduction time T on , Auxiliary tube conduction time T sr and dead time t dead The switch tube drive module input is the next cycle main conduction time T on , Auxiliary tube conduction time T sr and dead time t dead , output as the driving signal of the main switch tube M1 and the auxiliary switch tube M2 for the next cycle.

7. The control system of an active clamp flyback converter according to claim 1, characterized in that: The output control module specifically includes: the current switching cycle starts at time t0, the current cycle ends at time t0+Ts, and the next switching cycle begins; in the current switching cycle, when the main switch tube is turned on at time t0, the current cycle ends at time t0+Ts, and the next switching cycle begins; on During this phase, the main circuit is turned on, i.e. the main circuit control signal duty_main is set to 1. During the rest of the current switching cycle, the main circuit is turned off, i.e. the main circuit control signal duty_main is set to 0. At t0+T on +t dead to t0+T on +t dead +T sr Stage, T s -t dead -T sr To T s -t dead During the current switching cycle, the auxiliary tube is turned on and its control signal duty_sr is set to 1. During the rest of the current switching cycle, the auxiliary tube is turned off and its control signal duty_sr is set to 0.

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