Off-line flyback converter system and its synchronous rectifier controller

Abstract

Embodiments of the present application disclose an off-line flyback converter system and a synchronous rectification controller thereof. According to the synchronous rectification controller provided by the embodiments of the present application, the conduction and turn-off of a synchronous rectification switch tube are controlled, and the synchronous rectification controller comprises an adaptive turn-off threshold control module configured to detect a demagnetization time of a previous switching period of the synchronous rectification switch tube, set a turn-off control threshold based on a time length comparison relationship between a conduction time of a current switching period of the synchronous rectification switch tube and the demagnetization time of the previous switching period of the synchronous rectification switch tube, and control the synchronous rectification switch tube to change from a conduction state to a turn-off state when a voltage difference between a drain voltage and a source voltage of the synchronous rectification switch tube is greater than the turn-off control threshold.

Description

Technical Field

[0001] Embodiments of the present invention relate to the field of integrated circuits, and more particularly to an offline flyback converter system and its synchronous rectifier controller. Background Technology

[0002] In traditional synchronous rectifier controllers, primary-side pulse width modulation (PWM) controllers typically have power factor correction (PFC) functionality for higher power system applications. This is to meet the power factor requirements of higher power applications and thus reduce the converter's pollution to the power grid.

[0003] Furthermore, for systems requiring multiple output voltages, a DC-DC converter stage is typically added after the output of the power converter system to obtain a different fixed output voltage than the system output stage.

[0004] However, in PFC or DC-DC converter applications, there is a high-frequency switch (whose operating frequency is greater than the maximum operating frequency of the PWM controller). The opening or closing of this high-frequency switch will generate interference. This interference will affect the normal operation of the Synchronous Rectification (SR) controller through the transformer or ground wire, causing the SR switch in the SR controller to be turned off prematurely. The SR switch cannot maintain the conducting state throughout the entire demagnetization time. The SR switch can be a MOSFET (Silicon Field Effect Transistor) or GaN (Gallium Nitride Field Effect Transistor), which seriously affects the system efficiency. Summary of the Invention

[0005] The embodiments of the present invention provide an offline flyback converter system and its synchronous rectifier controller, which can set a turn-off control threshold based on the comparison between the conduction time of the current switching cycle of the SR switch and the demagnetization time of the previous switching cycle of the SR switch, so as to prevent the SR switch from being turned off accidentally.

[0006] On one hand, embodiments of the present invention provide a synchronous rectification controller for controlling the on and off states of a synchronous rectification switch, and include an adaptive turn-off threshold control module configured to: detect the demagnetization time of the synchronous rectification switch in the previous switching cycle; set a turn-off control threshold based on a time comparison between the on-time of the synchronous rectification switch in the current switching cycle and the demagnetization time of the synchronous rectification switch in the previous switching cycle; and control the synchronous rectification switch to change from an on state to an off state when the voltage difference between the drain voltage and the source voltage of the synchronous rectification switch is greater than the turn-off control threshold.

[0007] On the other hand, embodiments of the present invention provide an offline flyback power converter system, including a synchronous rectifier controller as described in the first aspect. Attached Figure Description

[0008] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0009] Figure 1 A schematic diagram of a conventional offline flyback power converter system 100 is shown.

[0010] Figure 2 It shows Figure 1 A schematic diagram of one implementation of the system output stage 116 is shown.

[0011] Figure 3 It shows Figure 1 A schematic diagram of another implementation of the system output stage 116 shown;

[0012] Figure 4 It shows Figure 2 and Figure 3 The diagram shown is a structural schematic of the SR controller 120.

[0013] Figure 5 The diagram shows the waveform of the difference between the drain voltage and the source voltage, Vds, and the gate drive signal, gate, of a conventional SR switch.

[0014] Figure 6 The diagram shows the waveform of the difference between the drain voltage and the source voltage Vds of the SR switch and the gate drive signal gate when subjected to high-frequency switching interference in PFC.

[0015] Figure 7 A schematic diagram of the structure of the SR controller provided in an embodiment of the present invention is shown;

[0016] Figure 8 The diagram shows the waveform of the corresponding signal of the adaptive shutdown threshold control module provided in an embodiment of the present invention.

[0017] Figure 9 A schematic diagram of the adaptive shutdown threshold control module provided in an embodiment of the present invention is shown.

[0018] Figure 10 The diagram shows waveforms of corresponding signals from the self-recovery control module provided in this embodiment of the invention; and

[0019] Figure 11 A schematic diagram of the drive self-recovery control module provided in an embodiment of the present invention is shown. Detailed Implementation

[0020] The features and exemplary embodiments of various aspects of the present invention will now be described in detail. To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only configured to explain the present invention and are not configured to limit the present invention. For those skilled in the art, the present invention can be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the present invention by illustrating examples of the invention.

[0021] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0022] To better understand the offline flyback converter system and its SR controller provided in the embodiments of the present invention, the structure and working principle of the SR controller provided in the prior art are first introduced below.

[0023] like Figure 1 As shown, Figure 1 A schematic diagram of a conventional offline flyback power converter system 100 is shown, where VAC is the input AC power.

[0024] The system 100 may include components such as: an EMI filter 110; a full-wave rectifier 112; a PFC-PWM controller (a PWM controller with power factor correction (PFC) function) 114 to meet the system power factor requirements in high-power applications; a transformer T; a system output stage (secondary side stage) 116, which includes four ports (e.g., port 1, port 2, port 3, and port 4), which may consist of an SR controller, SR switching transistors (e.g., SR MOSFETs), filter capacitors, etc., and whose output is a fixed voltage; and a DC-DC converter 118, which may be a buck or boost DC-DC converter that can output another different fixed voltage to meet the application requirements of multiple outputs.

[0025] Specifically, see Figure 2 and Figure 3 ,in, Figure 2 It shows Figure 1 The diagram shown is a structural schematic of one implementation of the system output stage 116. Figure 3 It shows Figure 1 The diagram shows another implementation of the system output stage 116.

[0026] like Figure 2 and Figure 3 As shown, the output stage 116 of this system may include an output capacitor Cout, an SR controller 120, and an SR switch (labeled MS). The SR controller 120 and the SR switch MS together constitute an SR module to replace the Schottky rectifier diode in a traditional flyback converter. The SR controller 120 can be used to control the on and off of the SR switch MS. Since the SR switch MS has a low on-state voltage drop, it can effectively reduce the heat loss of the system, thereby improving efficiency and increasing the output current capability of the system. As a result, the SR module can be widely used in systems with large output current.

[0027] Specifically, see Figure 4 , Figure 4 It shows Figure 2 and Figure 3 The diagram shows the structure of the SR controller 120.

[0028] like Figure 4As shown, the SR controller 120 may include various components such as: a high-voltage switch MNH, a module for generating the on-state control threshold Vt(on), a module for generating Vt(off), a regulator 1202, a voltage / current reference module 1204, an SR on-state comparator (Comp_srron) 1206, an SR off-state comparator (Comp_sroff) 1208, an SR on-state control module 1210, a minimum on-time control module 1212, a NOR gate 1214, a NOR gate 1216, a latch 1218, and / or a driver 1220, etc.

[0029] The input signals Vd and Vin can be used to power the voltage regulator 1202. The voltage regulator 1202 can generate the internal power supply AVDD and provide it to the high-voltage switch MNH and the voltage / current reference module 1204. The voltage / current reference module 1204 can be used to generate the reference voltage vref and the reference current iref.

[0030] Specifically, Vd generates a signal Vd_in via the high-voltage switch MNH. This signal Vd_in can be input to the first input terminal (e.g., non-inverting input terminal) of the SR turn-on comparator 1206 via the turn-on control threshold Vt(on) generation module, and can also be input to the first input terminal (e.g., inverting input terminal) of the SR turn-off comparator 1208 via the Vt(off) generation module. The second input terminals (e.g., inverting input terminal) of the SR turn-on comparator 1206 and the second input terminal (e.g., non-inverting input terminal) of the SR turn-off comparator 1208 can be grounded. The SR turn-on comparator 1206 can be used to generate an on det signal based on the signals Vd_in and Vt(on), and the SR turn-off comparator 1208 can be used to generate an off det signal based on the signals Vd_in and Vt(off). The SR turn-on control module 1210 can be used to generate the on det signal. The minimum on-time control module 1212 can be used to generate the minimum on-time signal min_ton of the SR switch. The NOR gate 1214 can be used to output a turn on signal to control the SR switch from the off state to the on state based on the on ctrl signal and the on det signal. The NOR gate 1216 can be used to output a turn off signal to control the SR switch from the on state to the off state based on the off det signal and the min_ton signal. The latch 1218 can be used to generate a synchronous rectifier switch signal sr based on the turn on signal and the turn off signal. The driver 1220 can be used to generate a gate signal to drive the SR switch to turn on and off based on the synchronous rectifier switch signal sr.

[0031] Figure 5The waveform schematic diagram of the voltage difference Vds between the drain voltage and the source voltage of the traditional SR switching transistor MS and the gate drive signal gate is shown. Among them, Vds is the pressure difference across the two ends of the SR switching transistor MS (corresponding to the difference between the drain voltage and the source voltage of the SR switching transistor), gate is the gate drive signal used to control the on and off of the SR switching transistor MS, Vt(slp) is the reference voltage (for example, 2V), Vt(on) is the turn-on control threshold of the SR switching transistor (for example, -200 mV), Vt(reg) is the Vds voltage adjustment value (for example, -20 mV), Vt(off) is the turn-off control threshold of the SR switching transistor (for example, 0 mV), and ts is the time taken for Vds to drop from Vt(slp) to Vt(on).

[0032] Among them, the turn-on condition of the SR switching transistor can be: t s <t ref (for example, 100 ns); and (2) Vds < Vt(on); if conditions (1) and (2) are satisfied simultaneously, the SR switching transistor MS can be turned on.

[0033] In some embodiments, as Figure 5 shown, during the normal operation of the system, the primary switch of the transformer T (controlled by the PWM signal) is in the off state, and the voltage difference Vds between the drain voltage and the source voltage of the SR switching transistor MS on the secondary side starts to drop from the plateau voltage, passing through Vt(slp), 0, Vt(on) in sequence, and continues to drop from Vt(on). Since the SR switching transistor MS is not turned on at this time, the demagnetizing current flows through the body diode of the SR switching transistor MS for freewheeling. When it is detected that the turn-on condition of the SR switching transistor MS is satisfied, it is considered that this is a valid turn-on of the SR switching transistor MS. When it is detected that the voltage Vds < Vt(on), the internal SR turn-on comparator 1206 (see Figure 4 ) flips to pull up the gate drive signal gate through the driver 1220 to turn on the SR switching transistor MS.

[0034] Next, as the demagnetizing current gradually decreases, when the voltage drop Vds generated by the demagnetizing current on the on-resistance of the SR switching transistor MS is slightly greater than Vt(reg), the internal control circuit will pull down the gate drive signal gate, so that the on-resistance of the SR switching transistor MS increases, and the value of the voltage difference Vds between the drain voltage and the source voltage of the SR switching transistor MS will stabilize near Vt(reg). This process is called the Vds voltage adjustment process.

[0035] Then, as the demagnetizing current further decreases, the increase in the on-resistance of the SR switch MS is no longer sufficient to maintain the voltage Vds near Vt(reg), and the voltage Vds begins to increase. When it is detected that the voltage Vds > Vt(off), the internal SR turn-off comparator 1208 (see...) is turned off. Figure 4 The gate drive signal is flipped to pull low via driver 1220, so that the SR switch MS is turned off.

[0036] Among them, the Vds voltage adjustment process can pull the gate drive signal gate to a lower value in advance, shorten the pull-down time of the gate drive signal gate, speed up the turn-off of the SR switch MS, and reduce the spike on Vds in continuous conduction mode (CCM).

[0037] In high-power system applications, the PWM controller on the primary side of transformer T generally has PFC functionality (e.g., Figure 1 As shown in 114), this is to meet the system power factor requirements in high-power applications, thereby reducing the pollution of the power grid by the converter; and, in systems with multiple output voltage requirements, a DC-DC converter (such as...) is generally added after the output of the power converter system. Figure 1 As shown in 118), a different fixed output voltage is obtained, which is different from the output voltage of the system output stage 116.

[0038] However, in PFC or DC-DC converter applications, there is a high-frequency switch (whose operating frequency is greater than the maximum operating frequency of the PWM controller). The opening or closing of this high-frequency switch will generate interference. The interference will affect the normal operation of the SR controller through the transformer or ground wire, causing the SR switch MS to be turned off prematurely. The SR switch cannot maintain the conducting state throughout the entire demagnetization time, which seriously affects the system efficiency.

[0039] refer to Figure 6 , Figure 6 The diagram shows the waveforms relating the voltage difference Vds between the drain and source voltages of the SR switch MS, the gate drive signal gate of the SR switch MS, the minimum on-time min_ton, and the gate drive signal PFC gate of the high-frequency switch in the PFC when subjected to interference from the high-frequency switch in the PFC.

[0040] Specifically, PFC gate is the waveform of the control signal on the gate of the high-frequency switch in PFC, whose switching frequency is greater than the maximum operating frequency of PWM; Vds is the voltage difference across the two ends (drain and source terminals) of the SR switch MS; gate is the gate drive signal used to control the turn-on and turn-off of the SR switch MS; and min_ton is the minimum on-time control module (e.g., ...). Figure 4 The output signal of 1212 shown is given, where Ton-min is the minimum on-time of the SR switch MS. Within the time Ton-min, the SR switch MS will remain on and cannot be turned off.

[0041] from Figure 6 As can be seen, at each falling edge of the PFC gate signal, the interference affects the ground line or equivalently generates a voltage spike on the voltage Vds. The peak value of this voltage spike on Vds is greater than Vt(off), which causes the internal SR to turn off the comparator Comp_sroff (e.g., Figure 4 The 1208 shown is mistakenly flipped, which in turn causes the driver (such as...) to... Figure 4 The gate drive signal gate (as shown in 1220) is pulled low, causing the SR switch MS to be mistakenly turned off.

[0042] Specifically, such as Figure 6 As shown, in the first switching cycle, the falling edge of the PFC gate signal falls within the minimum on-time Ton-min of the SR switch MS. Due to the shielding effect of this time, the SR switch MS will remain on, thus preventing false turn-off. However, in the second switching cycle, the falling edge of the PFC gate signal falls after the minimum on-time Ton-min of the SR switch MS, so shielding is not possible. Furthermore, since the peak value of the voltage spike Vds is greater than Vt(off), this will cause the internal SR turn-off comparator Comp_sroff (as shown in the image) to fail. Figure 4 The 1208 shown is mistakenly flipped, which in turn causes the driver (such as...) to... Figure 4 As shown in Figure 1220, pulling down the gate drive signal gate causes the SR switch MS to be mistakenly turned off. During the subsequent demagnetization time, the demagnetizing current can only flow through the body diode of the SR switch MS, increasing power consumption and reducing system efficiency.

[0043] It is understandable that the switching action of the high-frequency switch in the DC-DC converter (characterized by the DC-DC gate) interferes with the SR switch MS. Figure 6The interference of the PFC gate signal to the SR switch MS is similar, except that the PFC gate signal generates interference on the falling edge, i.e. when the PFC switch is turned off, while the DC-DC gate signal generates interference on the rising edge, i.e. when the DC-DC switch is turned on. For ease of description, this paper will not introduce the interference of the DC-DC converter.

[0044] To address at least one of the problems in the prior art, embodiments of the present invention provide an SR controller. The SR controller provided by embodiments of the present invention will be described in detail below. For example, see... Figure 7 , Figure 7 A schematic diagram of the structure of the SR controller provided in an embodiment of the present invention is shown.

[0045] It should be noted that, Figure 7 and Figure 4 The same or similar components in the SR controller shown are labeled with the same reference numerals. Figure 7 The SR controller shown is similar to Figure 4 The SR controller shown is illustrated below, and for ease of description, the differences between the two will be described in detail below.

[0046] Similar to Figure 4 The SR controller shown Figure 7 The SR controller shown may include various components such as: a high-voltage switch MNH, a module for generating the turn-on control threshold Vt(on), a voltage regulator 1202, a voltage / current reference module 1204, an SR turn-on comparator 1206, an SR turn-off comparator 1208, an SR turn-on control module 1210, a minimum on-time control module 1212, a NOR gate 1214, a NOR gate 1216, and / or a driver 1220, etc.

[0047] In some embodiments, Figure 7 The SR controller shown may further include an adaptive turn-off threshold control module 1222, which can be configured to: detect the demagnetization time of the SR switch in the previous switching cycle; set a turn-off control threshold based on the duration comparison between the on-time of the SR switch in the current switching cycle and the demagnetization time of the SR switch in the previous switching cycle; and control the SR switch to change from the on state to the off state when the voltage difference Vds between the drain voltage and the source voltage of the SR switch is greater than the turn-off control threshold.

[0048] Specifically, a turn-off control threshold can be set based on the comparison between the conduction time of the SR switch in the current switching cycle and the demagnetization time of the SR switch in the previous switching cycle to prevent the SR switch from being turned off accidentally.

[0049] In other embodiments, Figure 7 The SR controller shown may further include a drive self-recovery control module 1224, which can be configured to: during a period of time, starting from the moment the SR switch changes from the off state to the on state, and lasting for a duration equal to a preset proportion of the demagnetization time of the previous switching cycle of the SR switch: detect whether the difference Vds between the drain voltage and the source voltage of the SR switch is less than a turn-on control threshold; when the duration for which the difference Vds between the drain voltage and the source voltage of the SR switch is less than the turn-on control threshold is greater than a preset duration Th (see below) Figure 10 When ), the SR switch is controlled to change from the off state to the on state.

[0050] Specifically, by detecting the relationship between the difference Vds between the drain voltage and source voltage of the SR switch and the turn-on control threshold, the SR switch can be turned on again after a short delay after being mistakenly turned off.

[0051] like Figure 7 As shown, the adaptive turn-off threshold control module 1222 can be used to receive the Vd_in signal and the demagnetizing dem signal, and output the Vd_os signal. The Vd_os signal can be input to the first input terminal (e.g., the inverting input terminal) of the SR turn-off comparator 1208. The drive self-recovery control module 1224 can be used to receive the turn-on, turn-off, and Vd_in signals, and output the dem and sr signals. The dem signal can be input to the input terminals of the SR turn-on control module 1210, the minimum conduction time control module 1212, and the adaptive turn-off threshold control module 1222. The sr signal can be input to the input terminal of the driver 1220. The output terminal of the driver 1220 can be connected to the Gate terminal of the SR controller. The Vd_in signal is the voltage difference between the drain voltage and the source voltage of the clamped SR switch clamped by the high-voltage switch MNH.

[0052] like Figure 7As shown, the first terminal of the voltage regulator 1202 can be connected to the first terminal (e.g., Vd terminal) of the SR controller, the second terminal can be connected to the second terminal (e.g., Vin terminal) of the SR controller, and the third terminal can be connected to the first terminal of the voltage / current reference module 1204. The second terminal of the voltage / current reference module 1204 can output a reference voltage Vref and a reference current Iref. The first terminal of the SR turn-on control module 1210 can be connected to the first terminal of the SR controller. The first terminal of the high-voltage switch MNH can be connected to the first terminal of the SR controller. The first terminal of the turn-on control threshold Vt(on) generation module can be connected to the second terminal of the high-voltage switch MNH, and the third terminal of the high-voltage switch MNH can receive AVDD. The first terminal (e.g., non-inverting input) of the SR turn-on comparator 1206 can be connected to the second terminal of the turn-on control threshold Vt(on) generation module, and the second terminal (e.g., inverting input) can be grounded. The first terminal of the NOR gate 1214 can be connected to the second terminal of the SR turn-on control module 1210 to receive the on signal from the SR turn-on control module 1210. The first terminal of the adaptive turn-off threshold control module 1222 can be connected to the second terminal of the high-voltage switch MNH. The first terminal (e.g., the inverting input terminal) of the SR turn-off comparator 1208 can be connected to the second terminal of the adaptive turn-off threshold control module 1222. The second terminal (e.g., the non-inverting input terminal) of the SR turn-off comparator 1208 can be grounded. The first terminal of the NOR gate 1216 can be connected to the third terminal of the SR turn-off comparator 1208 to receive the off-det signal from the SR turn-off comparator 1208. The second terminal can be connected to the first terminal of the minimum on-time control module 1212 to receive the min_ton signal from the minimum on-time control module 1212. The turn-on signal provided to the drive self-recovery control module 1224 is generated based on the off-det signal and the min_ton signal. The first terminal of the self-recovery control module 1224 can be connected to the third terminal of the NOR gate 1214 to receive the turn-on signal from the NOR gate 1214. The second terminal can be connected to the third terminal of the NOR gate 1216 to receive the turn-off signal from the NOR gate 1216. The third terminal can be connected to the third terminal of the SR turn-on control module 1210, the second terminal of the minimum on-time control module 1212, and the third terminal of the adaptive turn-off threshold control module 1222 to provide them with the DEM signal. The fourth terminal can be connected to the first terminal of the driver 1220 to provide the driver 1220 with the SR signal. The second terminal of the driver 1220 can be connected to the third terminal of the SR controller (e.g., the Gate terminal).A gate drive signal (gate) is provided to the gate of the SR switch to control its on / off state.

[0053] As can be seen, in the case of less severe interference, the embodiments of the present invention can prevent the SR switch from being accidentally turned off due to system interference by setting the adaptive turn-off threshold control module 1222. In the case of more severe interference, the drive self-recovery control module 1224 can turn the SR switch back on after a short delay after it is turned off. The purpose of both is to ensure that the SR switch remains in the conducting state for most of the entire demagnetization period.

[0054] To better understand the embodiments of the present invention, as provided below Figure 7 The adaptive shutdown threshold control module 1222 shown below, in conjunction with the following Figure 8 and Figure 9 The adaptive shutdown threshold control module 1222 and its control principle are introduced through specific examples. Figure 8 The diagram shows a waveform of the corresponding signal of the adaptive shutdown threshold control module provided in an embodiment of the present invention. Figure 9 A schematic diagram of the adaptive shutdown threshold control module provided in an embodiment of the present invention is shown.

[0055] As an example, the adaptive turn-off threshold control module 1222 can be further configured to: when the conduction time TON(n) of the current switching cycle of the SR switch is greater than a preset proportion K*Tdem(n-1) of the demagnetization time of the previous switching cycle of the SR switch: during the period from the moment the SR switch changes from the off state to the on state, and the duration is equal to the preset proportion K*Tdem(n-1) of the demagnetization time of the previous switching cycle of the SR switch, the turn-off control threshold is set to the first control threshold Vth(off); during other periods when the SR switch is in the on state, the turn-off control threshold is set to the second control threshold Vt(off), where the second control threshold Vt(off) is less than the first control threshold Vth(off).

[0056] Specifically, the adaptive turn-off threshold control module 1222 can detect the demagnetization time (Tdem(n-1), see [reference]) of the previous (i.e., the (n-1)th) switching cycle of the SR switch. Figure 8 ), and take a certain proportion K (for example, K = 0.75), calculate the product of the demagnetization time of the previous switching cycle of the SR switch and the proportion k, K*Tdem(n-1), as a reference.

[0057] refer to Figure 8During the current switching cycle (i.e., the (n)th) conduction time TON(n) of the SR switch, if the conduction time TON(n) of the current switching cycle of the SR switch is greater than K*Tdem(n-1) (e.g.) Figure 8 As shown), during the time period (corresponding to the time period from t1 to t2) that begins when the SR switch changes from the off state to the on state (corresponding to time t1) and lasts for a duration equal to K*Tdem(n-1), the turn-off control threshold is set to the first control threshold Vth(off). During the time period other than the above period (corresponding to the time period from t2 to t3) in the on-time TON(n) of the current switching cycle of the SR switch, the turn-off control threshold is set to the second control threshold Vt(off). Figure 8 As shown, the first control threshold Vth(off) is greater than the second control threshold Vt(off).

[0058] In some embodiments, the first control threshold Vth(off) may be set to, for example, +50mV, and the second control threshold Vt(off) may be set to, for example, 0mV, or any other suitable value less than the first control threshold Vth(off), without limitation by this application.

[0059] As can be seen, although the spike of the difference between the drain voltage and the source voltage of the SR switch caused by interference is greater than Vt(off), it is less than Vth(off). Therefore, the adaptive turn-off threshold control module 1222 provided in this embodiment increases the turn-off control threshold by setting the turn-off control threshold to Vth(off), so that the SR switch will not be mistakenly turned off. This implementation method is effective for some systems with less severe interference. However, for systems with more severe interference, such as those where the spike of the difference between the drain voltage and the source voltage of the SR switch is greater than Vth(off), the self-recovery control module 1224 can be driven to enable the SR switch to be turned on again after a short delay after being mistakenly turned off.

[0060] As an example, the adaptive turn-off threshold control module 1222 can be further configured to: when the conduction time of the current switching cycle (i.e., the (n)th switching cycle) of the SR switch is not greater than a preset proportion K*Tdem(n-1) of the demagnetization time of the previous switching cycle (i.e., the (n-1)th switching cycle) of the SR switch: during the entire period when the SR switch is in the conducting state, the turn-off control threshold is set to a first control threshold Vth(off), wherein the first control threshold Vth(off) is greater than the spike of the difference between the drain voltage and the source voltage of the SR switch.

[0061] Specifically, if the on-time TON(n) of the current switching cycle of the SR switch is less than or equal to K*Tdem(n-1), then the turn-off control threshold can be kept constant at the first control threshold Vth(off) during the entire on-time TON(n) of the current switching cycle of the SR switch. For ease of description, this threshold is not shown in the figure.

[0062] See Figure 9 , Figure 9 The diagram illustrates the structure of an adaptive shutdown threshold control module 1222 provided in an embodiment of the present invention. The adaptive shutdown threshold control module 1222 may include: an adaptive shutdown threshold detection module, with its first terminal connected to the first terminal of the adaptive shutdown threshold control module 1222; a second terminal and a third terminal respectively used to output a first switch control signal (e.g., ctrl) and a second switch control signal (e.g., ctrlb), wherein the second switch control signal is the inverted signal of the first switch control signal; and a first switch (e.g., Sh), the first terminal of which may be connected to the second terminal of the adaptive shutdown threshold control module 1222, the second terminal being used to connect to... The system includes: a module for receiving a first switch control signal (e.g., ctrl); a module for generating a first control threshold Vth(off), the first end of which can be connected to the third end of the first switch, and the second end of which can be connected to the third end of the adaptive off-threshold control module 1222; a second switch (e.g., Sb), the first end of which can be connected to the second end of the adaptive off-threshold control module 1222, the second end being used to receive a second switch control signal (e.g., ctrlb); and a module for generating a second control threshold Vt(off), the first end of which can be connected to the third end of the second switch, and the second end of which can be connected to the third end of the adaptive off-threshold control module 1222.

[0063] Specifically, the first terminal of the adaptive turn-off threshold control module 1222 can be used to receive the dem signal, the second terminal of the adaptive turn-off threshold control module 1222 can be used to receive the difference between the drain voltage and the source voltage of the clamped SR switch, and the third terminal of the adaptive turn-off threshold control module 1222 can be used to output the Vd_os signal.

[0064] Return to reference Figure 7 One end of the high-voltage switch MNH can be used to receive the drain voltage Vd of the SR switch (equal to the difference Vds between the drain voltage and the source voltage of the SR switch), and the other end can provide the voltage Vd_in to the adaptive turn-off threshold control module 1222. The high-voltage switch MNH can be used to clamp the voltage Vd to obtain the clamped voltage Vd_in. Specifically, the high-voltage switch MNH can be used to clamp the part of the voltage Vd that is higher than a preset threshold to a certain fixed voltage, while the other voltages remain unchanged, thereby providing the clamped Vd_in for subsequent processing.

[0065] As an example, the adaptive shutdown threshold control module 1222 can be configured to: when the first switch control signal (e.g., ctrl) is high, output the difference between the voltage difference Vd_in between the drain voltage and the source voltage of the clamped SR switch and the first control threshold Vth(off); and when the second switch control signal (e.g., ctrlb) is high, output the difference between the voltage difference Vd_in between the drain voltage and the source voltage of the clamped SR switch and the second control threshold Vt(off).

[0066] Specifically, in Figure 9 In this circuit, the DEM signal can be input to the adaptive turn-off threshold detection module, generating a pair of complementary signals, namely the first switch control signal Ctrl and the second switch control signal CTRlb. The frequencies of the first switch control signal Ctrl and the second switch control signal CTRlb can be the same as the frequency of the DEM signal. The high-level width of the first switch control signal Ctrl or the low-level width of the second switch control signal CTRlb can be, for example, K times the high-level width of the DEM signal. The first switch control signal Ctrl and the second switch control signal CTRlb can be used to control the conduction and turn-off of a pair of complementary switches, namely the first switch Sh and the second switch Sb. The first control threshold Vth(off) and the second control threshold Vt(off) correspond to the two turn-off control thresholds of the SR switch.

[0067] When the first switch control signal ctrl is high, the second switch control signal ctrlb is low, the first switch Sh is turned on, and the second switch Sb is turned off. The output signal Vd_os of the adaptive turn-off threshold control module 1222 can be expressed as shown in the following formula (1):

[0068] Vd_os=Vd_in-Vth(off) (1)

[0069] When the first switch control signal ctrl is low, the second switch control signal ctrlb is high, the second switch Sb is turned on, and the first switch Sh is turned off. The output signal Vd_os of the adaptive turn-off threshold control module 1222 can be expressed as shown in the following formula (2):

[0070] Vd_os=Vd_in-Vt(off) (2)

[0071] To better understand the embodiments of the present invention, as provided below Figure 7 The drive self-recovery control module 1224 shown below, in conjunction with... Figure 10 and Figure 11 This paper introduces the self-recovery control module 1224 and its control principle through specific examples. Figure 10 It shows a waveform schematic diagram of the corresponding signals of the driving self - recovery control module provided by an embodiment of the present invention. Figure 11 It shows a schematic structural diagram of the driving self - recovery control module 1224 provided by an embodiment of the present invention.

[0072] As Figure 10 shown, if the system interference is relatively severe, the spike of the voltage difference Vds between the drain voltage and the source voltage of the SR switching transistor MS will be greater than the first control threshold Vth(off). During the current switching cycle of the SR switching transistor (i.e., the (n)th switching cycle), due to the gate drive signal gate of the SR switching transistor MS being interfered at the falling edge of the signal PFC gate or the rising edge of the signal DC - DC gate, the SR switching transistor MS is accidentally turned off. The demagnetizing current can only flow through the body diode of the SR switching transistor MS for freewheeling. Then, the voltage difference Vds between the drain voltage and the source voltage of the SR switching transistor MS will drop below the turn - on control threshold Vt(on) again. In this case, by detecting the duration of the voltage difference Vds < Vt(on) between the drain voltage and the source voltage of the SR switching transistor MS, if the duration is greater than the preset duration Th, and during the period starting from the moment when the SR switching transistor changes from the off state to the on state and lasting for a duration equal to K·Tdem(n - 1) (corresponding to Figure 10 the time period between the moment t1 and t2 shown), the interrupted drive will be triggered again, making the SR switching transistor MS be turned on again, that is, changing from the off state to the on state; in other cases, the SR switching transistor MS will not be turned on again.

[0073] As an example, the preset duration Th can be, for example, 200 ns. It is only provided as an example and should not be construed as restrictive.

[0074] Refer to Figure 11 , Figure 11 It shows a schematic structural diagram of the driving self - recovery control module 1224 provided by an embodiment of the present invention.

[0075] As an example, the drive self-recovery control module 1224 may include: a first inverter 210, the first terminal of which can be connected to the first terminal of the drive self-recovery control module 1224 to receive a turn-on signal; a drive self-recovery detection module 212, the first terminal of which can be connected to the second terminal of the drive self-recovery control module 1224 to receive a Vd_in signal, and the second terminal of which can be connected to the third terminal of the drive self-recovery control module 1224 to receive a dem signal; a first AND gate 214, the first terminal of which can be connected to the second terminal of the first inverter 210, and the second terminal of which can be connected to the third terminal of the drive self-recovery detection module 212 to receive an autor signal; a second inverter 216, the first terminal of which can be connected to the fourth terminal of the drive self-recovery control module 1224 to receive a turn-off signal; and a delay module 218, the first terminal of which can be connected to the fourth terminal of the drive self-recovery control module 1224 to receive a turn-off signal. The signal is off; the first flip-flop 220 has a first terminal that can be connected to the second terminal of the first inverter 210, a second terminal that can be connected to the second terminal of the delay module 218, and a third terminal that can be connected to the third terminal of the drive self-recovery control module 1224 to output the dem signal; the second flip-flop 222 has a first terminal that can be connected to the third terminal of the first AND gate 214, and a second terminal that can be connected to the second terminal of the second inverter 216; and the second AND gate 224 has a first terminal that can be connected to the third terminal of the first flip-flop 220, a second terminal that can be connected to the third terminal of the second flip-flop 222 to receive the sr_pre signal, and a third terminal that can be connected to the fifth terminal of the drive self-recovery control module 1224 to output the sr signal.

[0076] The delay module 218 can be used to delay and invert the input signal turn off before outputting it to the first flip-flop 220. When the turn on signal at the first terminal of the self-recovery control module 1224 becomes high, a falling edge is generated by the first inverter 210 and input to the first AND gate 214. The first AND gate 214 also generates a falling edge. Therefore, the first flip-flop 220 and the second flip-flop 222 simultaneously output high levels, that is, the dem and sr_pre signals simultaneously become high levels. Then, the sr signal at the fifth terminal of the self-recovery control module 1224 becomes high level to control the SR switch from the off state to the on state.

[0077] When the turn off signal at the fourth terminal of the driving self - recovery control module 1224 becomes high, this signal becomes low after passing through the second inverter 216, setting the output of the second flip - flop 222 to low. That is, the output signal sr_pre of the second flip - flop 222 becomes low, and then sr at the fifth terminal of the driving self - recovery control module 1224 becomes low to control the SR switch tube to change from the conducting state to the off state. At the same time, the turn off signal is input to the delay module 218. If the time that the turnoff signal remains high is less than the delay time of the delay module 218 (for example, 300 ns), the output of the delay module 218 remains unchanged, and the output signal dem of the first flip - flop 220 will not become low and remains in the high - level state. Only when the time that the turn off signal remains high is greater than the delay time of the delay module 218 (for example, 300 ns), the output dem of the first flip - flop 220 will flip to low.

[0078] Therefore, when the voltage difference Vds between the drain voltage and the source voltage of the SR switch tube generates a spike due to PFC or DC - DC gate interference, the duration of the spike is generally very short. So even if the turn off signal becomes high, its duration will also be very short, and the output signal dem of the first flip - flop 220 will not flip and remains in the high - level state. However, the output signal sr_pre of the second flip - flop 222 will flip to low, and sr becomes low to control the SR switch tube to change from the conducting state to the off state. After that, the demagnetizing current can only flow through the body diode of the SR switch tube MS for freewheeling. Then the voltage difference Vds between the drain voltage and the source voltage of the SR switch tube MS will drop below the turn - on control threshold Vt(on) again. At this time, the driving self - recovery detection module 212 can compare Vd_in (which is equal to Vds at this time) with the turn - on control threshold Vt(on) and time. If the duration of Vds < Vt(on) is greater than Th (for example, Th = 200 ns) and within the time period starting from the moment when the SR switch tube changes from the off state to the on state and with a duration equal to K·Tdem(n - 1), the output signal autor of the driving self - recovery detection module 212 will flip to low, the first AND gate 214 outputs a falling edge, the output signal sr_pre of the second flip - flop 222 will flip to high. At this time, the signal dem remains in the high - level state, then the signal sr becomes high, and the interrupted driving will be triggered again, and the SR switch tube will conduct again.

[0079] In addition, an embodiment of the present invention further provides an offline flyback power converter system, including the SR controller as described in the specification.

[0080] In summary, the technical solutions provided by the embodiments of the present invention can improve the anti-interference capability of the SR controller. Specifically, the above technical solutions can ensure that the SR switch (SR MOSFET or GaN) remains in the conducting state for most of the entire demagnetization period, and is protected from being accidentally turned off by system interference (e.g., by setting an adaptive turn-off threshold control module), or can be turned on again after a short delay (Th, e.g., Th = 200ns) after being accidentally turned off (e.g., by setting a drive self-recovery control module). This greatly improves the stability of the SR switch and avoids system efficiency loss due to interference.

[0081] Specifically, for the adaptive turn-off threshold control module, the adaptive turn-off threshold control module detects the demagnetization time (Tdem(n-1)) of the SR switch in the previous switching cycle, takes a certain proportion K (for example, K = 0.75), and calculates the product K·Tdem(n-1) between the two to determine the relationship between the conduction time TON(n) of the SR switch in the current switching cycle and K·Tdem(n-1), where:

[0082] If TON(n) > K·Tdem(n-1), then during the period of time equal to K·Tdem(n-1) starting from the moment the SR switch changes from the off state to the on state, the turn-off control threshold for controlling the SR switch to change from the on state to the off state is set to Vth(off) (e.g., +50mV). During other periods when the SR switch is in the on state, the turn-off control threshold for controlling the SR switch to change from the on state to the off state is set to Vt(off) (e.g., 0mV), where Vth(off) > Vt(off).

[0083] If TON(n)≤K·Tdem(n-1), then the SR off control threshold Vth(off) will remain unchanged throughout the entire TON(n).

[0084] For the drive self-recovery control module, during a period of time equal to K·Tdem(n-1) starting from the moment the SR switch changes from the off state to the on state, it detects whether the difference Vds between the drain voltage and the source voltage of the SR switch is less than Vt(on) (e.g., -200mV). If the duration of Vds being less than Vt(on) is greater than the preset duration Th (e.g., Th = 200ns), the drive interrupted by the interference will be activated again, causing the SR switch to turn on again.

[0085] It should be clarified that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications, and additions, or change the order of steps, after understanding the spirit of the present invention.

[0086] The functional blocks shown in the above-described structural diagram can be implemented as hardware, software, firmware, or a combination thereof. When implemented in hardware, they can be, for example, electronic circuits, application-specific integrated circuits (ASICs), appropriate firmware, plug-ins, function cards, etc. When implemented in software, the elements of this invention are programs or code segments used to perform the required tasks. The programs or code segments can be stored in a machine-readable medium or transmitted over a transmission medium or communication link via data signals carried in a carrier wave. "Machine-readable medium" can include any medium capable of storing or transmitting information. Examples of machine-readable media include electronic circuits, semiconductor memory devices, ROM, flash memory, erasable ROM (EROM), floppy disks, CD-ROMs, optical disks, hard disks, fiber optic media, radio frequency (RF) links, etc.

[0087] It should also be noted that the exemplary embodiments mentioned in this invention describe methods or systems based on a series of steps or apparatus. However, this invention is not limited to the order of the steps described above; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0088] The above description is merely a specific embodiment of the present invention. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A synchronous rectifier controller, characterized in that, Used to control the on and off of synchronous rectifier switches, and including an adaptive turn-off threshold control module, configured as follows: The demagnetization time of the synchronous rectifier switch in the previous switching cycle is detected; Based on the comparison between the conduction time of the current switching cycle of the synchronous rectifier switch and the demagnetization time of the previous switching cycle of the synchronous rectifier switch, a turn-off control threshold is set. as well as When the voltage difference between the drain and source voltages of the synchronous rectifier switch exceeds the turn-off control threshold, the synchronous rectifier switch is controlled to change from the on state to the off state. The adaptive shutdown threshold control module is also configured to: When the conduction time of the current switching cycle of the synchronous rectifier switch is greater than a preset proportion of the demagnetization time of the previous switching cycle: During a period starting from the moment the synchronous rectifier switch changes from the off state to the on state, and lasting for a duration equal to a preset proportion of the demagnetization time of the previous switching cycle, the turn-off control threshold is set to a first control threshold; during other periods when the synchronous rectifier switch is in the on state, the turn-off control threshold is set to a second control threshold, where the second control threshold is less than the first control threshold. When the conduction time of the current switching cycle of the synchronous rectifier switch is not greater than a preset proportion of the demagnetization time of the previous switching cycle of the synchronous rectifier switch: during the entire period when the synchronous rectifier switch is in the conducting state, the turn-off control threshold is set to the first control threshold.

2. The synchronous rectifier controller according to claim 1, characterized in that, The first control threshold is 50 mV, and the second control threshold is 0 mV.

3. The synchronous rectification controller according to claim 1, characterized in that, The synchronous rectification controller further includes a drive self-recovery control module, configured to, within a time period starting from the moment the synchronous rectification switch changes from the off state to the on state, and lasting for a duration equal to a preset proportion of the demagnetization time of the previous switching cycle of the synchronous rectification switch: Detect whether the difference between the drain voltage and the source voltage of the synchronous rectifier switch is less than the turn-on control threshold; When the duration for which the difference between the drain voltage and the source voltage of the synchronous rectifier switch is less than the turn-on control threshold is greater than a preset duration, the synchronous rectifier switch is controlled to change from the off state to the on state.

4. The synchronous rectification controller according to claim 3, characterized in that, The preset duration is 200 ns.

5. The synchronous rectifier controller according to claim 1, characterized in that, The adaptive shutdown threshold control module includes: An adaptive shutdown threshold detection module has a first terminal connected to the first terminal of the adaptive shutdown threshold control module, and a second terminal and a third terminal used to output a first switch control signal and a second switch control signal, respectively, wherein the second switch control signal is the inverted signal of the first switch control signal; A first switch has a first end connected to a second end of the adaptive shutdown threshold control module, and the second end is used to receive the control signal of the first switch. The first control threshold generation module has its first end connected to the third end of the first switch and its second end connected to the third end of the adaptive shutdown threshold control module. The second switch has its first terminal connected to the second terminal of the adaptive off-threshold control module, and its second terminal is used to receive the control signal of the second switch; and The second control threshold generation module has its first end connected to the third end of the second switch, and its second end connected to the third end of the adaptive shutdown threshold control module.

6. The synchronous rectification controller according to claim 5, characterized in that, The adaptive shutdown threshold control module is configured as follows: When the first switch control signal is high, the difference between the drain voltage and source voltage of the clamped synchronous rectifier switch is the difference between the first control threshold. as well as When the second switch control signal is high, the difference between the drain voltage and source voltage of the clamped synchronous rectifier switch is output as the difference between the second control threshold.

7. The synchronous rectification controller according to claim 3, characterized in that, The drive self-recovery control module includes: The first inverter has its first terminal connected to the first terminal of the drive self-recovery control module; The self-recovery detection module is connected at its first end to the second end of the self-recovery control module, and at its second end to the third end of the self-recovery control module. The first AND gate has its first terminal connected to the second terminal of the first inverter, and its second terminal connected to the third terminal of the drive self-recovery detection module. The second inverter has its first terminal connected to the fourth terminal of the drive self-recovery control module; The delay module has its first end connected to the fourth end of the drive self-recovery control module; The first trigger has its first terminal connected to the second terminal of the first inverter, its second terminal connected to the second terminal of the delay module, and its third terminal connected to the third terminal of the drive self-recovery control module. The second flip-flop has its first terminal connected to the third terminal of the first AND gate, and its second terminal connected to the second terminal of the second inverter; and The second AND gate has its first terminal connected to the third terminal of the first trigger, its second terminal connected to the third terminal of the second trigger, and its third terminal connected to the fifth terminal of the drive self-recovery control module.

8. An offline flyback power converter system, characterized in that, Includes the synchronous rectifier controller as described in any one of claims 1 to 7.

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