Primary side control device and flyback switching power supply system

Abstract

The application relates to a primary side control device and a flyback switching power supply system. The primary side control device comprises a switching control module, a delay unit, a sampling circuit, a comparison unit and a clamping circuit. The switching control module is used for outputting a switching control signal. The delay unit is connected to the switching control module. After the switching control signal is turned on and an interval time elapses, the delay unit generates a sampling signal and a judgment enable signal. The sampling circuit generates a sampling voltage value according to a real-time voltage of a demagnetization terminal. The switching control module generates the switching control signal according to a judgment logic signal. The switching control signal and the judgment enable signal are responded to by the clamping circuit, and a clamping effect is generated on the real-time voltage of the demagnetization terminal, so that a demagnetization capacitor for the demagnetization terminal needs not to be set, power conversion efficiency is prevented from being reduced, and design cost and debugging cost caused by debugging of the demagnetization capacitor are avoided.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, and in particular to a primary-side control device and a flyback switching power supply system. Background Technology

[0002] A flyback switching power supply typically includes a transformer, a power switch, and a primary-side controller. The power switch is connected in series with the primary winding of the transformer. The primary-side controller sends a switching drive signal to the power switch, causing it to switch on and off, allowing magnetic flux energy to be transferred from the primary winding to the secondary winding.

[0003] To prevent core saturation in the transformer, the primary-side controller is equipped with a demagnetizing terminal. The transformer has an auxiliary winding, the voltage of which can reflect the magnitude of the magnetic flux in the core to a certain extent. Externally to the primary-side controller, the demagnetizing terminal and the auxiliary winding are connected in series via a voltage divider resistor.

[0004] The primary-side controller internally includes a sampling circuit and a comparison unit. Under certain conditions, the sampling circuit samples the real-time voltage of the demagnetizing terminal, generates a sampled voltage value, and outputs it to the comparison unit. The comparison unit determines whether there is an abnormality in the magnetic core based on the sampled voltage value. If the sampled voltage value exceeds a safety threshold, it will trigger a protection action or affect the control of the power switch.

[0005] In the PCB layout of a flyback switching power supply, a parasitic capacitance forms between the output terminal of the auxiliary winding and the demagnetizing terminal. This parasitic capacitance causes an upward jump in the voltage waveform at the demagnetizing terminal (e.g., Figure 1 (The solid arrow B in the diagram indicates the location). Because the voltage waveform of the demagnetizing terminal did not drop to the normal level in time at the sampling time, the sampling voltage value generated by the sampling circuit exceeded the safety threshold.

[0006] In traditional technology, to reduce the impact of parasitic capacitance between the output terminal of the auxiliary winding and the demagnetizing terminal, a demagnetizing capacitor is typically placed between the demagnetizing terminal and ground. This reduces the interference of parasitic capacitance on the voltage waveform of the demagnetizing terminal (the waveform improvement effect of the demagnetizing capacitor is as follows). Figure 1 (As indicated by the dashed arrow in the diagram). However, the installation of demagnetizing capacitors not only reduces the power conversion efficiency of flyback switching power supplies, but also requires significant debugging time to determine the appropriate capacitance value due to the influence of parasitic capacitance values ​​on PCB layout and routing. Utility Model Content

[0007] Based on this, the present invention provides a primary-side control device and a flyback switching power supply system that can solve or at least alleviate the above-mentioned technical problems.

[0008] This utility model provides a primary-side control device, which includes a demagnetizing terminal and an output terminal. The primary-side control device includes:

[0009] A switch control module, used to output switch control signals;

[0010] Delay unit; after the conduction time of the switch control signal ends and an interval time has elapsed, the delay unit generates a sampling signal and a judgment enable signal;

[0011] The sampling circuit is electrically connected to the demagnetizing terminal. When the sampling signal is received, it generates a sampling voltage value based on the real-time voltage of the demagnetizing terminal.

[0012] The comparison unit, electrically connected to the delay unit, generates a judgment logic signal based on the magnitude of the sampled voltage value upon receiving the judgment enable signal; the switch control module generates the switch control signal based on the judgment logic signal; and

[0013] A clamping circuit is electrically connected to the delay unit, the demagnetizing terminal, and the sampling circuit. When the switch control signal is in the off-time and the judgment enable signal stops, the voltage of the demagnetizing terminal is clamped by the clamping circuit to the sampled voltage value generated by the sampling circuit in the previous control cycle. In one control cycle of the switch control signal, the appearance of the judgment enable signal is later than the conduction time of the switch control signal. During the time period from the end of the conduction time of the switch control signal to the appearance of the judgment enable signal, the clamping circuit clamps the real-time voltage of the demagnetizing terminal to the sampled voltage value currently output by the sampling circuit, so that the real-time voltage of the demagnetizing terminal is locked in a range lower than the reference voltage.

[0014] The primary-side control device of this application responds to the switch control signal and the enable signal through a clamping circuit, and clamps the real-time voltage of the demagnetizing terminal. This avoids the need to set up a demagnetizing capacitor for the demagnetizing terminal, prevents a decrease in power conversion efficiency, and avoids design and debugging costs due to the adjustment of the demagnetizing capacitor.

[0015] In one embodiment, the clamping circuit includes a clamping control unit and a voltage clamping unit; the clamping control unit is electrically connected between the demagnetizing terminal and the voltage clamping unit; the clamping control unit is also electrically connected to the switch control module and the delay unit; the voltage clamping unit is electrically connected to the output terminal of the sampling circuit; when the switch control signal is in the off-time and the judgment enable signal stops, the clamping control unit is in a conducting state between the demagnetizing terminal and the voltage clamping unit, and the voltage clamping unit clamps the real-time voltage of the demagnetizing terminal to the sampled voltage value.

[0016] In one embodiment, the clamping control unit includes a switch S and a NOR gate; the switch S is electrically connected between the demagnetizing terminal and the voltage clamping unit; one input of the NOR gate is used to receive the switch control signal, and the other input is used to receive the judgment enable signal; when the switch control signal is in the off-time and the judgment enable signal stops, the NOR gate outputs an enable clamping signal; when the enable clamping signal is received, the switch S is in the on state.

[0017] In one embodiment, the voltage clamping unit includes an operational amplifier AMP; the non-inverting input of the operational amplifier AMP is used to receive the sampled voltage value; the clamping control unit is electrically connected between the demagnetizing terminal and the output of the operational amplifier AMP; and the inverting input of the operational amplifier AMP is electrically connected to the output of the operational amplifier AMP.

[0018] In one embodiment, the voltage clamping unit includes a comparator COMP0 and a switch M1; the non-inverting input of the comparator COMP0 is electrically connected to the demagnetizing terminal; the inverting input of the comparator COMP0 is used to receive the sampled voltage value; the output of the comparator COMP0 is electrically connected to the control terminal of the switch M1; the clamping control unit is electrically connected between the demagnetizing terminal and one of the current-carrying terminals of the switch M1; the other current-carrying terminal of the switch M1 is grounded.

[0019] In one embodiment, a drive circuit is further included; the drive circuit is electrically connected between the switch control module and the output terminal; the drive circuit generates a switch drive signal according to the switch control signal, and the switch drive signal is output from the output terminal.

[0020] In one embodiment, the output of the sampling circuit is electrically connected to the clamping circuit and the comparison unit, respectively.

[0021] In one embodiment, a current feedback terminal and a compensation terminal are also provided; the switch control module is electrically connected to the current feedback terminal and the compensation terminal respectively.

[0022] In one embodiment, the switch control module performs logical operations based on the current information of the power switch obtained from the current feedback terminal, the output load control information obtained from the compensation terminal, and the judgment logic signal output by the comparison unit to generate the switch control signal.

[0023] This utility model provides a flyback switching power supply system, including the primary-side control device of any of the above embodiments. Attached Figure Description

[0024] Figure 1 The diagram shows the voltage waveform of the demagnetizing terminal and other related waveforms in a traditional flyback switching power supply.

[0025] Figure 2 This is a schematic diagram of the circuit structure of a flyback switching power supply system according to an embodiment of this application.

[0026] Figure 3 This is a schematic diagram of the circuit structure of a primary-side control device according to an embodiment of this application.

[0027] Figure 4 This is a schematic diagram of the clamping circuit in a primary-side control device according to an embodiment of this application.

[0028] Figure 5 This is a schematic diagram of the circuit structure of a clamping circuit according to another embodiment of this application.

[0029] Figure 6 The voltage waveform of the demagnetizing terminal and other related waveforms are for the flyback switching power supply system or control method of this application.

[0030] Reference numerals: 100, Flyback switching power supply system; 20, Primary-side control device; DEM, Demagnetizing terminal; GATE, Output terminal; CS, Current feedback terminal; COMP, Compensation terminal; 21, Switching control module; ON, Switching control signal; 22, Delay unit; Sample, Sampling signal; ENcomp, Judgment enable signal; 23, Sampling circuit; DEMsmpl, Sampling voltage value; VREFdem[n:1], Reference voltage; 24, Comparison unit; DEMov, Overvoltage warning signal; 25, Clamping circuit; 251, Clamping control unit; NOR, NOR gate; ENclamp, Enable clamping signal; 252, Voltage clamping unit; 26, Drive circuit; 30, Secondary-side control device. Detailed Implementation

[0031] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application 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 this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0033] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, integral connections, mechanical connections, electrical connections, direct connections, indirect connections via an intermediate medium, or internal connections between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0034] The technical solutions provided by the embodiments of this application are described below with reference to the accompanying drawings.

[0035] Combination Figure 2 As shown, this application provides a flyback switching power supply system 100. Understandably, the flyback switching power supply system 100 is used to provide DC power to electronic products. Exemplarily, the flyback switching power supply system 100 can be at least a mobile phone charger, an LED driver power supply, or a home appliance adapter.

[0036] Specifically, in combination Figure 2 As shown, the flyback switching power supply system 100 includes a transformer, a power switch M0, and a primary-side control device 20. The transformer has a primary winding NP, a secondary winding NS, and an auxiliary winding NA that are coupled together. The primary-side control device 20 has an output terminal GATE and a demagnetizing terminal DEM. The primary-side control device 20 also has a current feedback terminal CS and a compensation terminal COMP.

[0037] Combination Figure 2 As shown, power switch M0 is electrically connected between one end of the primary winding NP and ground. The output terminal GATE of the primary control device 20 is used to output a switch drive signal to the control terminal of power switch M0. Upon receiving the switch drive signal, power switch M0 alternately switches between the on and off states.

[0038] Combination Figure 2As shown, the flyback switching power supply system 100 also includes a voltage divider branch. The voltage divider branch is electrically connected between the two ends of the auxiliary winding NA. The voltage divider node of the voltage divider branch is electrically connected to the demagnetizing terminal DEM of the primary-side control device 20. Exemplarily, the voltage divider branch includes resistors RH and RL, which are connected in series between the two ends of the auxiliary winding NA.

[0039] Furthermore, resistor RH is electrically connected to the same-name terminal of auxiliary winding NA, and resistor RL is electrically connected to the opposite-name terminal of auxiliary winding NA. The opposite-name terminal of auxiliary winding NA is grounded. A parasitic capacitance Cpar is formed between the same-name terminal of auxiliary winding NA and demagnetizing terminal DEM.

[0040] The flyback switching power supply system 100 also includes a resistor RS. One current-carrying terminal of the power switch M0 is electrically connected to the corresponding terminal of the primary winding NP. The resistor RS is electrically connected between the other current-carrying terminal of the power switch M0 and ground. The current feedback terminal CS of the primary control device 20 is electrically connected to the other current-carrying terminal of the power switch M0. Understandably, the voltage input to the current feedback terminal CS is approximately proportional to the current through the resistor RS, thereby allowing the magnitude of the current through the primary winding NP to be determined based on the input voltage to the current feedback terminal CS.

[0041] Combination Figure 2 As shown, the flyback switching power supply system 100 also includes a secondary-side control device 30, a switch M1, and a capacitor Cout. The secondary-side winding NS, the switch M1, and the capacitor Cout are connected in series in the same circuit. The secondary-side control device 30 controls the conduction of the switch M1. The circuit structure on the NS side of the secondary-side winding feeds back load control information to the compensation terminal COMP through an optocoupler.

[0042] Specifically, in combination Figure 3 and Figure 6As shown, the primary-side control device 20 includes: a switch control module 21, a delay unit 22, a sampling circuit 23, a comparison unit 24, and a clamping circuit 25. The switch control module 21 outputs a switch control signal ON. The delay unit 22 is connected to the switch control module 21. After the conduction time in any control cycle of the switch control signal ON ends and an interval time has elapsed, the delay unit 22 generates a sampling signal Sample and a judgment enable signal ENcomp. The sampling circuit 23 is electrically connected to the delay unit 22 and the demagnetizing terminal DEM. Upon receiving the sampling signal Sample, the sampling circuit 23 generates a sampling voltage value DEMsmpl based on the real-time voltage of the demagnetizing terminal DEM. The comparison unit 24 is electrically connected to the delay unit 22. Upon receiving the judgment enable signal ENcomp, the comparison unit 24 generates a judgment logic signal based on the magnitude of the sampling voltage value DEMsmpl. The switch control module 21 generates the switch control signal ON based on the judgment logic signal. The clamping circuit 25 is electrically connected to the delay unit 22, the demagnetizing terminal DEM, and the sampling circuit 23. When the switch control signal ON is in the off time and the judgment enable signal ENcomp stops, the clamping circuit 25 clamps the voltage of the demagnetizing terminal DEM to the sampling voltage value DEMsmpl generated by the sampling circuit 23.

[0043] The primary-side control device 20 of this application includes a switch control module 21 that generates a switch control signal ON to trigger the power switch M0 to periodically turn on and off. After the ON conduction time within the control cycle ends, the power switch M0 turns off, and the magnetic flux of the transformer gradually decreases. The delay unit 22 starts delaying according to the start or end of the ON conduction time. Under the delay, the sampling signal Sample and the judgment enable signal ENcomp appear after the ON conduction time ends and an interval has elapsed, allowing the sampling circuit 23 to sample the real-time voltage of the demagnetizing terminal DEM only after the transformer's magnetic flux has decreased to a certain extent.

[0044] The occurrence time of the sampling signal Sample corresponds to the occurrence time of the judgment enable signal ENcomp. When triggered by the sampling signal Sample, the sampling circuit 23 generates a sampling voltage value DEMsmpl based on the real-time voltage of the demagnetizing terminal DEM. After the sampling signal Sample stops, the sampling circuit 23 continuously outputs the sampling voltage value DEMsmpl to provide feedback to the comparison unit 24. The judgment enable signal ENcomp enables the comparison unit 24, causing it to feed back a judgment logic signal to the switch control module 21 based on the magnitude of the sampling voltage value DEMsmpl. The switch control module 21 then controls the switch control signal ON based on the judgment logic signal.

[0045] Combination Figure 6As shown, the voltage at the same terminal of the auxiliary winding jumps when the direction of the transformer's magnetic flux changes, and this voltage jump is transmitted to the demagnetizing terminal DEM. The change in the direction of the transformer's magnetic flux corresponds in time to the end of the conduction time of the switch control signal ON. In one control cycle of the switch control signal ON, the occurrence of the enable signal ENcomp is determined to be later than the end of the conduction time of the switch control signal ON. During the time period from the end of the conduction time of the switch control signal ON to the occurrence of the enable signal ENcomp, the clamping circuit 25 clamps the real-time voltage of the demagnetizing terminal DEM to the sampling voltage value DEMsmpl currently output by the sampling circuit 23, locking the real-time voltage of the demagnetizing terminal DEM to a range lower than the reference voltage VREFdem[n:1], thereby preventing the real-time voltage of the demagnetizing terminal DEM from being affected by the upward jump of the voltage waveform during sampling, avoiding triggering protection actions or affecting the closed-loop control of the power switch M0.

[0046] When the enable signal ENcomp is detected, the clamping circuit 25 releases the clamping effect on the real-time voltage of the demagnetizing terminal DEM, allowing the real-time voltage of the demagnetizing terminal DEM to change with the voltage at the output of the auxiliary winding. At this time, the sampling circuit 23 is triggered by the sampling signal Sample to sample and generate a new sampled voltage value DEMsmpl, and continuously outputs this new sampled voltage value DEMsmpl for the comparison unit 24 and the switch control module 21 to perform overall loop control and protection monitoring, as well as for voltage clamping before the next sampling.

[0047] The clamping circuit 25 responds to the switch control signal ON and the enable signal Encomp, and clamps the real-time voltage of the demagnetizing terminal DEM. This avoids the need to set up a demagnetizing capacitor for the demagnetizing terminal DEM, prevents a decrease in power conversion efficiency, and avoids design and debugging costs due to the debugging of the demagnetizing capacitor.

[0048] Understandably, combined Figure 6 As shown, the sampling signal Sample can be a pulse signal. The sampling signal Sample can also be a short-duration high-level signal. Understandably, the sampling circuit 23 does not continuously generate a sampling voltage value DEMsmpl based on the real-time voltage of the demagnetizing terminal DEM at all times. Instead, during the duration of the sampling signal Sample, the sampling circuit 23 generates a new sampling voltage value DEMsmpl based on the real-time voltage of the demagnetizing terminal DEM. For example, when the pulse signal corresponding to the sampling signal Sample occurs once, the sampling circuit 23 performs an update of the sampling voltage value DEMsmpl as a response to the sampling signal Sample.

[0049] After responding to the sampling signal Sample, the sampling circuit 23 continuously outputs the sampling voltage value DEMsmpl generated by the most recent update. The sampling voltage value DEMsmpl will not change until the sampling signal Sample is received again.

[0050] Combination Figure 2 As shown, when not subjected to clamping, the voltage at the demagnetizing terminal DEM is determined by the voltage V of the transformer auxiliary winding. AUX The voltage V generated after voltage division is the voltage of the auxiliary winding at this time. AUX This corresponds to a multiple relationship with the system output voltage Vout. For example, the voltage corresponding to the demagnetizing terminal DEM is... By sampling the voltage of the demagnetizing terminal DEM, the obtained sampled voltage value DEMsmpl can contain information about the system output voltage Vout.

[0051] Understandably, for the switch control module 21 to generate the switch control signal ON based on the judgment logic signal, for example, the switch control module 21 may adjust the duty cycle of the switch control signal ON according to the content of the judgment logic signal, thereby changing the voltage, current, or power output by the secondary winding NS. For example, the switch control module 21 may continuously stop outputting the switch control signal ON after detecting an abnormal situation according to the judgment logic signal.

[0052] Combination Figure 3 and Figure 6 As shown, exemplarily, the enable signal Encomp is set to a high level. Upon receiving the enable signal Encomp, the comparison unit 24 compares and processes the sampled voltage value DEMsmpl with the reference voltage VREFdem[n:1] using its internal comparator, generating a corresponding judgment logic signal. This judgment logic signal includes an overvoltage warning signal DEMov. When the sampled voltage value DEMsmpl is greater than the reference voltage VREFdem[n:1], the overvoltage warning signal DEMov remains high; when the sampled voltage value DEMsmpl is not greater than the reference voltage VREFdem[n:1], the overvoltage warning signal DEMov remains low.

[0053] Optionally, the judgment logic signal also includes a voltage high / low level indicator signal to provide feedback on the level of the sampled voltage value DEMsmpl.

[0054] Optionally, the judgment logic signal may also include a demagnetization cycle completion signal to provide feedback on the demagnetization status of the transformer.

[0055] For example, the switch control module 21 performs logical operations based on the current information of the power switch M0 obtained from the current feedback terminal CS, the output load control information obtained from the compensation terminal COMP, and the judgment logic signal output by the comparison unit 24, to generate a switch control signal ON, thereby regulating and controlling the output voltage and output power of the flyback switching power supply system 100. More specifically, the judgment logic signal includes an overvoltage warning signal DEMov, a voltage high / low level indication signal, and a demagnetization cycle completion signal.

[0056] In some implementations, combined Figure 3 As shown, the output terminal of sampling circuit 23 is electrically connected to clamping circuit 25 and comparison unit 24, respectively. Understandably, the output terminal of sampling circuit 23 is used to output the sampled voltage value DEMsmpl to clamping circuit 25 and comparison unit 24, respectively.

[0057] In some implementations, combined Figure 3 As shown, the switch control module 21 is electrically connected to the current feedback terminal CS and the compensation terminal COMP, respectively. Understandably, in addition to controlling the switch control signal ON according to the judgment logic signal, the switch control module 21 also controls the switch control signal ON in conjunction with the magnitude of the current in the primary winding NP and the abnormal output voltage of the secondary winding NS, thereby ensuring that the switch control module 21 has comprehensive control logic.

[0058] In some implementations, combined Figure 3 As shown, the primary-side control device 20 also includes a drive circuit 26. The drive circuit 26 is electrically connected between the switch control module 21 and the output terminal GATE. The drive circuit 26 generates a switch drive signal based on the switch control signal ON, and the switch drive signal is output from the output terminal GATE. Understandably, the switch control signal ON has a certain power limitation and cannot directly drive the power switch M0 to the ON state. By setting up the drive circuit 26, the drive circuit 26 generates a switch drive signal with higher driving capability based on the switch control signal ON, thereby reliably realizing the state control of the power switch M0.

[0059] For example, the delay unit 22 performs delay and logic processing on the switch control signal ON to generate a sampling signal Sample and a judgment enable signal ENcomp that acts on the comparison unit 24.

[0060] In some implementations, combined Figure 4 and Figure 5As shown, the clamping circuit 25 includes a clamping control unit 251 and a voltage clamping unit 252. The clamping control unit 251 is electrically connected between the demagnetizing terminal DEM and the voltage clamping unit 252. The clamping control unit 251 is also electrically connected to the switch control module 21 and the delay unit 22. The voltage clamping unit 252 is electrically connected to the output terminal of the sampling circuit 23. When the switch control signal ON is in the off-time and the judgment enable signal ENcomp stops, the clamping control unit 251 is in a conducting state between the demagnetizing terminal DEM and the voltage clamping unit 252, and the voltage clamping unit 252 clamps the real-time voltage of the demagnetizing terminal DEM to the sampled voltage value DEMsmpl. Understandably, when the enable signal ENcomp is detected, the clamping control unit 251 is disconnected between the demagnetizing terminal DEM and the voltage clamping unit 252, thereby ensuring electrical isolation between the demagnetizing terminal DEM and the voltage clamping unit 252. This prevents the real-time voltage of the demagnetizing terminal DEM from being affected by the voltage clamping unit 252 during sampling by the sampling circuit 23. During the conduction time of the switch control signal ON, the clamping control unit 251 is disconnected between the demagnetizing terminal DEM and the voltage clamping unit 252, preventing short circuits between the voltage divider node of the voltage divider branch and the voltage clamping unit 252 under conditions of large voltage differences.

[0061] In some implementations, combined Figure 4 As shown, the clamping control unit 251 includes a switch S and a NOR gate. The switch S is electrically connected between the demagnetizing terminal DEM and the voltage clamping unit 252. One input of the NOR gate is used to receive the switch control signal ON, and the other input is used to receive the judgment enable signal ENcomp. When the switch control signal ON is in the off-time and the judgment enable signal ENcomp stops, the NOR gate outputs the enable clamping signal ENclamp. When the enable clamping signal ENclamp is received, the switch S is in the on state.

[0062] For example, during the on-time, the ON signal of the switch control signal can be understood as a high level at the output of the switch control module 21, and the power switch M0 is in the on state accordingly. During the off-time, the ON signal of the switch control signal is a low level at the output of the switch control module 21, and the power switch M0 is in the off state accordingly. The ENcomp signal of the determination enable signal can be understood as a high level at one of the outputs of the delay unit 22. When the ENcomp signal of the determination stops, one of the outputs of the delay unit 22 is at a low level. Therefore, when the switch control signal is ON and the ENcomp signal of the determination stops, the NOR gate outputs a high-level enable clamp signal ENclamp. The switch S switches to the on state under the trigger of the high level.

[0063] In some implementations, combined Figure 4 As shown, the voltage clamping unit 252 includes an operational amplifier AMP. The non-inverting input of the operational amplifier AMP is used to receive the sampled voltage value DEMsmpl. The clamping control unit 251 is electrically connected between the demagnetizing terminal DEM and the output of the operational amplifier AMP. The inverting input of the operational amplifier AMP is electrically connected to the output of the operational amplifier AMP, which acts as a voltage follower, and the voltage at the output of the operational amplifier AMP is consistent with the sampled voltage value DEMsmpl. When the clamping control unit 251 is in the ON state, the output of the operational amplifier AMP is short-circuited with the demagnetizing terminal DEM, so that the real-time voltage of the demagnetizing terminal DEM is limited to the sampled voltage value DEMsmpl.

[0064] In some implementations, combined Figure 5 As shown, the voltage clamping unit 252 includes a comparator COMP0 and a switch M1. The non-inverting input of the comparator COMP0 is electrically connected to the demagnetizing terminal DEM. The inverting input of the comparator COMP0 is used to receive the sampled voltage value DEMsmpl. The output of the comparator COMP0 is electrically connected to the control terminal of the switch M1. The clamping control unit 251 is electrically connected between the demagnetizing terminal DEM and one of the current-carrying terminals of the switch M1, and the other current-carrying terminal of the switch M1 is grounded. When the clamping control unit 251 is in the ON state, when the voltage jump at the same-name terminal of the auxiliary winding NA is transmitted to the demagnetizing terminal DEM, the real-time voltage of the demagnetizing terminal DEM will be greater than the most recently generated sampled voltage value DEMsmpl. The output of the comparator COMP0 outputs a high level to the control terminal of the switch M1, making the two current-carrying terminals of the switch M1 conduct, causing the real-time voltage of the demagnetizing terminal DEM to be pulled down and discharged to ground until the real-time voltage of the demagnetizing terminal DEM drops below the most recently generated sampled voltage value DEMsmpl. Therefore, the voltage clamping unit 252 is able to clamp the real-time voltage of the demagnetizing terminal DEM to the sampled voltage value DEMsmpl.

[0065] In other embodiments, the clamping circuit 25 function can also be implemented using other circuit structures.

[0066] Optionally, the primary-side control device 20 can be in the form of an integrated package.

[0067] The primary-side control device of this application responds to the situation where the switch control signal ON is in the off time and the judgment enable signal ENcomp stops, and clamps the real-time voltage of the demagnetizing terminal DEM. During the period from the end of the conduction time of the switch control signal ON to the appearance of the judgment enable signal ENcomp, the real-time voltage of the demagnetizing terminal DEM is locked in a range lower than the reference voltage VREFdem[n:1], thereby preventing the real-time voltage of the demagnetizing terminal DEM from being affected by the upward jump of the voltage waveform during sampling, avoiding triggering protection action or affecting the closed-loop control of the power switch M0.

[0068] When the enable signal ENcomp appears, the clamping effect on the real-time voltage of the demagnetizing terminal DEM is released. The real-time voltage of the demagnetizing terminal DEM can change with the voltage of the auxiliary winding NA output terminal, so that a new sampling voltage value DEMsmpl can be generated in time based on the real-time voltage sampling of the demagnetizing terminal DEM for overall loop control and protection monitoring, as well as for voltage clamping before the next sampling.

[0069] The above embodiments are merely preferred embodiments of this application and are not intended to limit the scope of this application. Any modifications and improvements made by those skilled in the art to the technical solutions of this application without departing from the spirit of this application should fall within the protection scope defined by the claims of this application.

Claims

1. A primary-side control device, comprising a demagnetizing terminal and an output terminal, characterized in that, The primary-side control device includes: A switch control module, used to output switch control signals; Delay unit; after the conduction time of the switch control signal ends and an interval time has elapsed, the delay unit generates a sampling signal and a judgment enable signal; The sampling circuit is electrically connected to the demagnetizing terminal. When the sampling signal is received, it generates a sampling voltage value based on the real-time voltage of the demagnetizing terminal. The comparison unit, electrically connected to the delay unit, generates a judgment logic signal based on the magnitude of the sampled voltage value upon receiving the judgment enable signal; the switch control module generates the switch control signal based on the judgment logic signal; and A clamping circuit is electrically connected to the delay unit, the demagnetizing terminal, and the sampling circuit. When the switch control signal is in the off-time and the judgment enable signal stops, the voltage of the demagnetizing terminal is clamped by the clamping circuit to the sampled voltage value generated by the sampling circuit in the previous control cycle. In one control cycle of the switch control signal, the appearance of the judgment enable signal is later than the conduction time of the switch control signal. During the time period from the end of the conduction time of the switch control signal to the appearance of the judgment enable signal, the clamping circuit clamps the real-time voltage of the demagnetizing terminal to the sampled voltage value currently output by the sampling circuit, so that the real-time voltage of the demagnetizing terminal is locked in a range lower than the reference voltage.

2. The primary-side control device according to claim 1, wherein The clamping circuit includes a clamping control unit and a voltage clamping unit; the clamping control unit is electrically connected between the demagnetizing terminal and the voltage clamping unit; the clamping control unit is also electrically connected to the switch control module and the delay unit; the voltage clamping unit is electrically connected to the output terminal of the sampling circuit; when the switch control signal is in the off-time and the judgment enable signal stops, the clamping control unit is in a conducting state between the demagnetizing terminal and the voltage clamping unit, and the voltage clamping unit clamps the real-time voltage of the demagnetizing terminal to the sampled voltage value.

3. The primary-side control device according to claim 2, wherein The clamping control unit includes a switch S and a NOR gate; the switch S is electrically connected between the demagnetizing terminal and the voltage clamping unit; one input terminal of the NOR gate is used to receive the switch control signal, and the other input terminal is used to receive the judgment enable signal; when the switch control signal is in the off time and the judgment enable signal stops, the NOR gate outputs an enable clamping signal; when the enable clamping signal is received, the switch S is in the on state.

4. The primary-side control device according to claim 2, wherein The voltage clamping unit includes an operational amplifier AMP; the non-inverting input of the operational amplifier AMP is used to receive the sampled voltage value; the clamping control unit is electrically connected between the demagnetizing terminal and the output of the operational amplifier AMP; the inverting input of the operational amplifier AMP is electrically connected to the output of the operational amplifier AMP.

5. The primary-side control device according to claim 2, wherein The voltage clamping unit comprises a comparator COMP0 and a switch M1; a non-inverting input terminal of the comparator COMP0 is electrically connected to the demagnetization terminal; an inverting input terminal of the comparator COMP0 is configured to receive the sampling voltage value; an output terminal of the comparator COMP0 is electrically connected to a control terminal of the switch M1; the clamping control unit is electrically connected between the demagnetization terminal and one of current passing terminals of the switch M1; the other current passing terminal of the switch M1 is grounded.

6. The primary-side control device according to claim 1, wherein The drive circuit is further included; the drive circuit is electrically connected between the switch control module and the output terminal; the drive circuit generates a switch drive signal according to the switch control signal, and the switch drive signal is output by the output terminal.

7. The primary-side control device according to claim 1, wherein The output terminals of the sampling circuit are respectively electrically connected to the clamping circuit and the comparison unit.

8. The primary-side control device according to claim 1, wherein The current feedback terminal and the compensation terminal are further provided; the switch control module is respectively electrically connected to the current feedback terminal and the compensation terminal.

9. The primary side control device according to claim 8, wherein The switch control module performs logical operation processing according to current information of the power switch obtained from the current feedback terminal, output load control information obtained from the compensation terminal, and the judgment logic signal output by the comparison unit, to generate the switch control signal.

10. A flyback switching power supply system characterized by comprising: The primary side control device comprises the primary side control device according to any one of claims 1 to 9.

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