High-precision output voltage sampling system of primary side feedback active clamping flyback converter

Abstract

The invention provides a high-precision output voltage sampling system of a primary side feedback active clamping flyback converter, input signals are a main switch tube switching signal and an auxiliary winding feedback voltage of the primary side feedback active clamping flyback converter, and the high-precision output voltage sampling system mainly comprises a slope generation module, a sampling time judgment module and an output voltage acquisition module; the output signal is a sampling voltage value, and the sampling voltage value is transmitted to the control loop, thereby achieving the closed-loop control of the converter. The slope generation module generates a voltage signal in direct proportion to the change slope of the feedback voltage of the auxiliary winding; the sampling time judgment module determines an output voltage sampling time based on the voltage signal representing the slope; and the output voltage acquisition module acquires an auxiliary winding feedback voltage at an output voltage sampling moment, and transmits the auxiliary winding feedback voltage as an output voltage value to the control loop for closed-loop control. According to the invention, high-precision output voltage sampling of the primary side feedback active clamping flyback converter can be realized.

Description

Technical Field

[0001] This invention belongs to the field of switching power supplies, specifically relating to a high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter. Background Technology

[0002] With the iterative updates of electronic information technology, consumer electronics products, represented by mobile phones, have developed rapidly, and their performance has been greatly improved. However, this performance improvement also means increased power consumption, causing mobile phones to drain their batteries faster. Therefore, to improve mobile phone charging speed and meet people's usage needs, researching higher-power mobile power adapters has become a key focus for researchers. Currently, most mobile power adapters are flyback converters. Flyback converters have the advantages of simple topology, low cost, and high reliability, and are widely used in the field of switching power supply design. Flyback converters with active clamping structures can further increase the converter's output power, reduce its size, and improve its efficiency. While meeting the design requirements of higher-power power adapters, they can also improve the portability of the adapter.

[0003] However, active clamp flyback converters typically use optocouplers as the core of their feedback circuit. Optocouplers suffer from drawbacks such as aging, temperature drift, and nonlinearity, leading to low converter stability. To eliminate the optocoupler, primary-side feedback control technology can be used. The sampling time for primary-side feedback is usually determined to be the moment the output diode begins to conduct and the moment it begins to turn off. At this time, the output voltage and the auxiliary winding feedback voltage have a fixed proportional relationship. However, due to sampling errors introduced by the output diode voltage, the parasitic inductance voltage of the secondary winding, and the parasitic resistance voltage, using the moment the output diode begins to turn off as the sampling time results in low sampling accuracy. This makes it impossible to achieve high-precision constant voltage output control of the converter, and unstable charging voltage will have serious safety implications for devices such as mobile phones. Summary of the Invention

[0004] To address the aforementioned problems and technical requirements, this invention proposes a high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter. This system performs precise sampling at the moment the output diode just begins to conduct, thereby achieving high-precision output voltage sampling for the primary-side feedback active clamp flyback converter.

[0005] The technical solution to achieve the purpose of this invention is as follows:

[0006] A high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter is disclosed. The input signals are the main switch signal of the primary-side feedback active clamp flyback converter and the auxiliary winding feedback voltage. The system includes a slope generation module, a sampling time determination module, and an output voltage acquisition module.

[0007] The slope generation module generates a voltage signal that is proportional to the slope of the change in the auxiliary winding feedback voltage.

[0008] The sampling time determination module determines the output voltage sampling time based on the voltage signal representing the slope;

[0009] The output voltage acquisition module acquires the auxiliary winding feedback voltage at the time of output voltage sampling and transmits it as the output voltage value to the control loop of the primary-side feedback active clamp flyback converter for closed-loop control, thereby realizing the closed-loop control of the converter.

[0010] Furthermore, the slope generation module is a differential operation circuit unit, consisting of an operational amplifier, a first resistor R, a second resistor R', and a capacitor. The capacitor C is connected to the positive terminal of the operational amplifier, the two ends of the first resistor R are connected to the positive terminal and the output terminal of the operational amplifier respectively, and the second resistor R' is connected to the negative terminal of the operational amplifier. The output is V. p .

[0011] Furthermore, the output V p for:

[0012] ;

[0013] Where k1, k2, and k3 are the drain-source voltages V of the main switch M1 at different stages. ds1 The slope of the change, t1 is the moment when the main switch M1 of the active clamp flyback converter is turned off, and t2 is the drain-source voltage V of M1. ds1 When the voltage rises to the set value, t3 is the voltage across the magnetizing inductor when it is greater than nV. o Time R.

[0014] Furthermore, k1 is:

[0015] ;

[0016] Where, N p For the primary winding, N s For the secondary winding and N a For auxiliary winding, i p For the primary current, C oss1 R1 and R2 are the parasitic capacitances across the main switch transistor M1, and the output voltage sampling voltage divider resistors.

[0017] Furthermore, k2 is:

[0018] ;

[0019] Among them, C r This is a clamping capacitor.

[0020] Furthermore, k3 is:

[0021] ;

[0022] Among them, I s This represents the diode current.

[0023] Furthermore, the sampling time determination module is a voltage comparator, and the negative input of the voltage comparator is the voltage signal V. p The positive input terminal is the reference voltage V. k ; the reference voltage V k Set to less than greater than During the time interval t1 to t3, V p Greater than V k The voltage comparator signal COMP outputs a low level during the time period t3 to t4, V p Less than V k The comparator signal COMP outputs a high level, and K is the slope amplification factor of the slope generation module.

[0024] Furthermore, the output voltage acquisition module receives the main switch duty cycle signal duty1, the sampling time determination module output signal COMP, and the auxiliary winding feedback voltage V. aux After the main switch is turned off, i.e., after the falling edge of duty1, the first rising edge of COMP at time t3 is the precise sampling time T. sample At this time, the output voltage acquisition module feeds back the auxiliary winding voltage V. aux Perform sampling and record it as V. aux (T sample V aux (T sample ) and output voltage V o It satisfies a fixed ratio relationship and is transmitted as the output signal of the output voltage acquisition module to the control loop for closed-loop control.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] 1. This application proposes a method for achieving high-precision sampling with primary-side feedback in an active clamp flyback converter, and designs a sampling circuit without the need for a traditional optocoupler.

[0027] 2. The control strategy proposed in this application determines the sampling time by calculating the slope of the change in the feedback voltage of the auxiliary winding, thereby reducing the complexity and cost of the overall system;

[0028] 3. This invention can be extended to other primary-side feedback sampling circuit designs, such as primary-side feedback designs of LLC and AHB flyback circuits. Attached Figure Description

[0029] Figure 1 This is a diagram of the high-precision output voltage sampling module proposed in this invention.

[0030] Figure 2 This is the basic topology diagram of a primary-side feedback active clamp flyback converter.

[0031] Figure 3 This is a control loop module diagram of the present invention.

[0032] Figure 4 This is a key waveform diagram of the present invention.

[0033] Figure 5 This is the equivalent circuit diagram of the transformer operating at the sampling time of this invention.

[0034] Figure 6 This is a sampling circuit design diagram of the present invention.

[0035] Figure 7 This is a schematic diagram of the sampling waveform of the present invention. Detailed Implementation

[0036] To provide a high-precision sampling solution, a high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter is presented. This invention can be applied to applications requiring high-precision control of active clamp flyback converters; such as... Figure 1 The high-precision output voltage sampling system for the primary-side feedback active clamp flyback converter includes a slope generation module, a sampling time determination module, and an output voltage acquisition module. The output signal is a sampled voltage value, which is transmitted to the control loop to achieve closed-loop control of the converter. The input signals are the main switch signal of the primary-side feedback active clamp flyback converter and the auxiliary winding feedback voltage. The slope generation module outputs the slope of the auxiliary winding feedback voltage change as a voltage signal. The sampling time determination module determines the output voltage sampling time based on this voltage signal representing the slope. The output voltage acquisition module acquires the auxiliary winding feedback voltage at the output voltage sampling time and transmits it as the output voltage value to the control loop for closed-loop control. This invention enables high-precision output voltage sampling of the primary-side feedback active clamp flyback converter.

[0037] During the t0 to t1 stage: the main switch M1 is turned on (drive signal duty1 is high), the auxiliary switch M2 is turned off (drive signal duty2 is low), and the secondary diode D... r Reverse cutoff. Input DC voltage V in Applied to the magnetizing inductor L m Resonant inductor L k At both ends, the primary current i p Flowing through M1 and N p Linear increase.

[0038] During the t1 to t2 phase: the main switch M1 is turned off (drive signal duty1 is low), and the drain-source voltage V of the main switch M1... ds1 Rapid rise, V ds1 The slope of change, k1, is relatively rapid. Simultaneously, the drain-source voltage V of the auxiliary switch M2... ds2 Rapid decline.

[0039] t2 to t3 stage: when V ds2 After the voltage drops to 0, the auxiliary switch M2 is turned on (drive signal duty2 is high), at which point the secondary diode D... r Still reverse cutoff. Magnetizing inductance L m and resonant inductance L k For clamping capacitor C r Charging. Due to C r The capacitance value is much larger than the parasitic capacitance, at which point the drain-source voltage V of M1 is... ds1 The slope of change, k2, is less than k1.

[0040] Stages t3 to t4: When the clamping capacitor C r When the voltage rises to a certain value, the secondary winding N s The induced voltage causes the secondary diode D r When the circuit is turned on, only the resonant inductor L is conducting. k For clamping capacitor C r Charging, M1 drain-source voltage V ds1 The slope of change, k3, decreases further.

[0041] During the t4 to t5 stage: both the main switch M1 and the auxiliary switch M2 are turned off, and the clamping capacitor voltage remains unchanged.

[0042] From t5 to t6: Auxiliary switch M2 turns on, clamping capacitor discharges, thus achieving charge balance of the clamping capacitor, and secondary diode D... r The circuit is turned on. More importantly, if the turn-on time of the auxiliary switch M2 is controlled properly, the drain-source voltage V of the main switch M1 can be reduced. ds1 There are three waveform changes with varying slopes within the time interval t1-t4.

[0043] During the t6 to t7 stage: both the main switch M1 and the auxiliary switch M2 are turned off, and the drain-source voltage V of the main switch M1 is... ds1 The rapid drop creates conditions for the main switch M1 to achieve ZVS (zero voltage turn-on).

[0044] (1)

[0045] Where V s For secondary winding N sVoltage across both terminals. Sampling is achieved through the secondary diode D. r V during conduction aux The signal is compared with the reference voltage inside the error amplification module. Through the pulse width modulation (PWM) or pulse frequency modulation (PFM) algorithm of the compensation module and the dynamic adjustment of the conduction time of the main switch M1 and the auxiliary switch M2, as well as their phase relationship, the output voltage V is ultimately achieved. out Stable regulation.

[0046] The output voltage sampling mechanism of this invention: The clamping capacitor value of the primary-side feedback active clamp flyback converter is relatively small. From the time the main switch M1 is turned off until the primary-side current drops to zero, the drain-source voltage V of M1 is... ds1 The charging process is divided into three stages.

[0047] Phase 1: At the turn-off time t1 of the main switch M1, the magnetizing inductance L of the active clamp flyback converter... m and resonant inductance L k Parasitic capacitance C across the main switch transistor M1 oss1 During charging, the drain-source voltage V of M1 is... ds1 The slope of change is relatively rapid. k1 has the following relationship (2):

[0048] (2)

[0049] Phase 2: When the drain-source voltage V of M1 ds1 When the voltage rises to a certain value at time t2, the auxiliary switch M2 turns on, and the magnetizing inductor L... m and resonant inductance L k For clamping capacitor C r Charging, due to C r The capacitance value is much larger than the parasitic capacitance, at which point the drain-source voltage V of M1 is... ds1 The slope of change, k2, is less than k1. k2 has the following relationship (3):

[0050] (3)

[0051] Stage 3: When the voltage across the magnetizing inductor is greater than nV o (n is the turns ratio of the primary and secondary sides of the transformer, V) o At time t3 (for the output voltage), the secondary diode is turned on (at this time, the sampled V...). aux The signal voltage value most accurately reflects the output voltage. At this time, the drain-source voltage V of M1... ds1 The slope of change, k3, decreases further. k3 has the following relationship (4):

[0052] (4)

[0053] The voltage change slopes mentioned above all reflect the voltage change slopes across the magnetizing inductor, with k1>k2>k3. Figure 2 The time t3 in the figure is the sampling time T. sample .

[0054] (5)

[0055] Depend on Figure 4 It can be seen that in T sample At time t, the output diode current I s (t3)=0 and the current rise slope I s '(t3)=0. Therefore, T sample The forward voltage drop R of the secondary diode at time t dr I s (t3), Parasitic resistance voltage R of secondary winding f I s (t3) and parasitic inductance voltage L ks I s '(t3) are all zero. Combining with equation (5), we can obtain T sample Secondary winding voltage V at time t s Strictly equal to the output voltage V out T was successfully eliminated. sample The output voltage sampling error caused by parasitic effects at time T. sample Feedback voltage V at time aux The sampling voltage V can be obtained aux (T sample Combining equation (5) and equation (1), we can obtain T. sample Sample voltage V at any time aux (T sample Satisfying equation (6):

[0056] (6)

[0057] V out The output voltage V can be established using equation (8). out With sampling voltage V aux The equation relationship between them, with the help of V aux (T sample High-precision constant voltage output control can be achieved through analysis and calculation.

[0058] The slope generation module consists of an operational amplifier, resistors (R and R'), and a capacitor (C). The connection method is as follows: Figure 6 As shown. Capacitor C is connected to the positive input of the operational amplifier, resistor R is connected to the positive input and output of the operational amplifier respectively, and resistor R' is connected to the negative input of the operational amplifier. The auxiliary winding feedback voltage V... auxThe slope generation module outputs V. p The following relationship exists:

[0059] (7)

[0060] (8)

[0061] The magnification factor depends on the values ​​of R and C. Therefore, V... p Directly proportional to V aux The slope of the change. And there is

[0062] (9)

[0063] Where RC corresponds to the slope amplification factor K of the slope generation module.

[0064] The sampling timing determination module is a voltage comparator. The negative input of the comparator is the voltage signal V. p The positive input terminal is the reference voltage V. k The reference voltage V k Set to less than greater than During the time interval from t1 to t3, V p Greater than V k The comparator signal COMP outputs a low level. During the time period t3 to t4, V... p Less than V k The comparator signal COMP outputs a high level. That is, COMP has a rising edge at time t3, as shown below. Figure 7 As shown.

[0065] The output voltage acquisition module receives the duty cycle signal "duty1" from the main switch and the output signal "COMP" from the sampling time determination module. As can be seen from the above, after the main switch is turned off, i.e., after the falling edge of "duty1", the first rising edge of "COMP" is the precise sampling time "T". sample (To avoid multiple rising edges from COMP interfering with the sampling timing judgment logic). At this time, the output voltage acquisition module feeds back the auxiliary winding voltage V. aux Perform sampling and record it as V. aux (T sample V aux (T sample ) and output voltage V o It satisfies a fixed ratio relationship and is transmitted as the output signal of the output voltage acquisition module to the control loop for closed-loop control.

[0066] This invention enables high-precision sampling of primary-side feedback active clamp flyback converters through a novel sampling scheme. This invention avoids the need for optocouplers and ADCs in traditional sampling, and can achieve high-precision output voltage sampling of primary-side feedback active clamp flyback converters, which can significantly improve the accuracy of the system and reduce the overall system complexity and cost.

[0067] The above description, in conjunction with the accompanying drawings and specific embodiments, provides a further detailed explanation of the technical solution of the present invention, but should not be construed as limiting the scope of implementation of the invention in any way. The core idea of ​​this invention is to achieve high-precision constant voltage through novel digital sampling combined with adaptive hysteresis control, which can be used in other isolated and non-isolated topologies. These variations and extensions do not depart from the core innovation of this invention and should all be included within the scope of these claims.

Claims

1. A high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter, wherein the input signals are the main switch signal and the auxiliary winding feedback voltage of the primary-side feedback active clamp flyback converter, characterized in that, It includes a slope generation module, a sampling time determination module, and an output voltage acquisition module; among which, The slope generation module generates a voltage signal that is proportional to the slope of the change in the auxiliary winding feedback voltage. The sampling time determination module determines the output voltage sampling time based on the voltage signal representing the slope; The output voltage acquisition module acquires the auxiliary winding feedback voltage at the time of output voltage sampling and transmits it as the output voltage value to the control loop of the primary-side feedback active clamp flyback converter for closed-loop control, thereby realizing the closed-loop control of the converter.

2. The high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter according to claim 1, characterized in that, The slope generation module is a differential operation circuit unit, consisting of an operational amplifier, a first resistor R, a second resistor R', and a capacitor. The capacitor C is connected to the positive input of the operational amplifier. The two ends of the first resistor R are connected to the positive input and the output of the operational amplifier, respectively. The second resistor R' is connected to the negative input of the operational amplifier. The output is V. p .

3. The high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter according to claim 1, characterized in that, The output V p for: ； Where k1, k2, and k3 are the drain-source voltages V of the main switch M1 at different stages. ds1 The slope of the change, t1 is the moment when the main switch M1 of the active clamp flyback converter is turned off, and t2 is the drain-source voltage V of M1. ds1 When the voltage rises to the set value, t3 is the voltage across the magnetizing inductor when it is greater than nV. o Time R.

4. A high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter according to claim 3, characterized in that, The k1 is: ； Where, N p For the primary winding, N s For the secondary winding and N a For auxiliary winding, i p For the primary current, C oss1 R1 and R2 are the parasitic capacitances across the main switch transistor M1, and the output voltage sampling voltage divider resistors.

5. A high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter according to claim 3, characterized in that, The k2 is: ； Among them, C r This is a clamping capacitor.

6. A high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter according to claim 4, characterized in that, The k3 is: ； Among them, I s This represents the diode current.

7. A high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter according to claim 1, characterized in that, The sampling time determination module is a voltage comparator, and the negative input of the voltage comparator is the voltage signal V. p The positive input terminal is the reference voltage V. k ; the reference voltage V k Set to less than greater than During the time interval t1 to t3, V p Greater than V k The voltage comparator signal COMP outputs a low level during the time period t3 to t4, V p Less than V k The comparator signal COMP outputs a high level, and K is the slope amplification factor of the slope generation module.

8. A high-precision output voltage sampling system for a primary-side feedback active clamp flyback converter according to claim 1, characterized in that, The output voltage acquisition module is input to the main switch duty cycle signal (duty1), the sampling time determination module output signal (COMP), and the auxiliary winding feedback voltage (V). aux After the main switch is turned off, i.e., after the falling edge of duty1, the first rising edge of COMP at time t3 is the precise sampling time T. sample At this time, the output voltage acquisition module feeds back the auxiliary winding voltage V. aux Perform sampling and record it as V. aux (T sample V aux (T sample ) and output voltage V o It satisfies a fixed ratio relationship and is transmitted as the output signal of the output voltage acquisition module to the control loop for closed-loop control.

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