Automatically tuned synchronous rectifier controller

Abstract

A device includes a high-pass filter circuit configured to receive a drain-source voltage from a drain node of a synchronous rectifier switch at a secondary side of a power converter and generate a filtered drain-source voltage using the received drain-source voltage. A current comparison circuit of the device is configured to receive a current indicative of a current flowing through the synchronous rectifier switch and generate a current comparison signal using the received current. An auto-tuning controller of the device is configured to turn on the synchronous rectifier switch upon determining that a body diode of the synchronous rectifier switch is conducting, initiate an auto-tuning delay upon determining that the current flowing through the synchronous rectifier switch has changed direction, turn off the synchronous rectifier switch upon expiration of the auto-tuning delay, and update the duration of the auto-tuning delay based on the filtered drain-source voltage during a detection time window.

Description

[0001] Related applications

[0002] This application claims priority to U.S. non-provisional patent application No. 16 / 811,827, filed on March 6, 2020, and entitled “Auto-Tuned Synchronous Rectifier Controller,” the entire contents of which are incorporated herein for all purposes. Background Art

[0003] Switched mode power supplies (SMPS) (“power converters”) are widely used in consumer, industrial, and medical applications to provide well-regulated power to the load while maintaining high power handling efficiency, tight output voltage regulation, and reducing conducted and radiated electromagnetic interference (EMI).

[0004] Some power converters, such as flyback converters, include a transformer that galvanically isolates the primary side of the power converter from the secondary side of the power converter. In this type of power converter, a primary-side switch of the power converter controls the flow of current through the primary-side winding of the transformer to charge the magnetizing inductance of the transformer. A synchronous rectifier switch (e.g., a diode or an actively controlled switch) on the secondary side of the power converter controls the flow of current from the secondary-side winding of the transformer to release the energy stored in the magnetizing inductance of the transformer, thereby transferring power to the load of the power converter.

[0005] Some power losses in the primary-side switch are related to the voltage across the primary-side switch and the current flowing through the primary-side switch when the primary-side switch transitions to the on state. The power handling efficiency of the power converter can be improved by minimizing the voltage across the primary-side switch before the primary-side switch turns on. Summary of the Invention

[0006] In some embodiments, a device includes a high-pass filter circuit configured to receive a drain-source voltage from a drain node of a synchronous rectifier switch at a secondary side of a power converter and generate a filtered drain-source voltage using the received drain-source voltage. A current comparison circuit of the device is configured to receive a current indicative of a current flowing through the synchronous rectifier switch and generate a current comparison signal using the received current. An auto-tuning controller of the device is configured to turn on the synchronous rectifier switch when it is determined using the current comparison signal that a body diode of the synchronous rectifier switch is conducting, start an auto-tuning delay when it is determined using the current comparison signal that the current flowing through the synchronous rectifier switch has changed direction, turn off the synchronous rectifier switch when the auto-tuning delay expires, and update the duration of the auto-tuning delay based on the filtered drain-source voltage during a detection time window.

[0007] In some embodiments, a method involves receiving, at a high-pass filter circuit, a drain-source voltage from a drain node of a synchronous rectifier switch on a secondary side of a power converter. The high-pass filter circuit uses the received drain-source voltage to generate a filtered drain-source voltage. A current indicating a current flowing through the synchronous rectifier switch is received at a current comparison circuit. The current comparison circuit uses the received current to generate a current comparison signal. When an auto-tuning controller determines, using the current comparison signal, that body diode conduction of the synchronous rectifier switch has occurred, the synchronous rectifier switch is turned on. When the current comparison signal determines that the current flowing through the synchronous rectifier switch has changed direction, the auto-tuning controller initiates an auto-tuning delay. When the auto-tuning delay expires, the synchronous rectifier switch is turned off, and the auto-tuning controller updates the duration of the auto-tuning delay based on the filtered drain-source voltage during a detection time window. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a simplified circuit schematic of a power converter according to some embodiments.

[0009] Figure 2 Demonstrating the Figure 1 A simplified graph of signals relevant to the operation of the power converter is shown.

[0010] Figure 3 According to some embodiments, Figure 1 A simplified circuit diagram of a synchronous rectifier controller in a power converter is shown.

[0011] Figure 4 According to some embodiments, Figure 3 A portion of an exemplary process of operation of a synchronous rectifier controller is shown.

[0012] Figures 5A to 5B Demonstrating the Figure 1 A simplified graph of signals relevant to the operation of the power converter is shown.

[0013] Figure 6 According to some embodiments, Figure 3 The operation of the synchronous rectifier controller is shown in Figure 4 Part of an exemplary process.

[0014] 7A to 7B Demonstrating the Figure 1 A simplified graph of signals relevant to the operation of the power converter is shown. DETAILED DESCRIPTION

[0015] According to some embodiments, a synchronous rectifier controller on the secondary side of a power converter automatically adjusts the duration of a negative magnetizing inductance current formed at a primary-side switch of the power converter, thereby releasing energy stored by the parasitic capacitance of the primary-side switch to reduce the drain-source voltage of the primary-side switch. Thereafter, the primary-side switch transitions to an on-state having a zero voltage or near-zero voltage formed across the primary-side switch, thereby advantageously reducing switching losses of the power converter.

[0016] A power converter, such as a flyback converter, typically includes a transformer that galvanically isolates the primary side of the power converter from the secondary side of the power converter. In these power converters, a primary-side switch of the power converter controls the flow of current through the primary-side winding of the transformer to charge the magnetizing inductance of the transformer. A synchronous rectifier switch on the secondary side of the power converter controls the flow of output current from the secondary-side winding of the transformer to release energy stored in the magnetizing inductance of the transformer, thereby transferring power to the load of the power converter. Generally speaking, the synchronous rectifier switch is in the off-state during the time period when the primary-side switch is in the on-state, and the synchronous rectifier switch is typically in the on-state during a portion of the time when the primary-side switch is in the off-state.

[0017] During the period when the synchronous rectifier switch is in the on state, the output current from the secondary winding flows to the output of the power converter. In response to this flow of output current, the transformer's magnetizing inductance current decreases to zero as the energy stored in the magnetizing inductance is released. If the synchronous rectifier switch remains in the on state after the magnetizing inductance current reaches zero, the magnetizing inductance current becomes negative, at which point it begins to discharge the primary-side switch's parasitic output capacitance, Coss. As the primary-side switch's output capacitance is discharged, the drain-source voltage of the primary-side switch decreases. By controlling the duration of the negative magnetizing inductance current flowing through the primary winding before the synchronous rectifier switch transitions to the off state, the primary-side switch can advantageously achieve zero volt switching (ZVS) or near-ZVS. By utilizing ZVS or near-ZVS in the primary-side switch, switching losses in the primary-side switch are reduced, and the power handling efficiency of the power converter is improved, compared to power converters that do not implement ZVS or near-ZVS.

[0018] As disclosed herein, a synchronous rectifier controller advantageously automatically adjusts the duration that the synchronous rectifier switch remains in the on state after the magnetizing inductor current has transitioned to negative current flow to control the discharge amount of the output capacitor Coss of the primary-side switch, without requiring a priori information about the inductance of the transformer, without requiring voltage or current measurements on the primary side, and without requiring control signals from the primary-side controller of the power converter. Because the synchronous rectifier controller is advantageously isolated from communication with the primary side of the power converter, the design of the power converter is simplified, and existing power converter designs can utilize the synchronous rectifier controller disclosed herein without requiring modifications to the primary-side controller.

[0019] Furthermore, compared to conventional solutions, some embodiments disclosed herein advantageously transition the primary-side switch to the on state before the drain-source voltage reaches zero volts, thereby enabling near-zero-volt switching of the primary-side switch. By utilizing near-ZVS switching, such embodiments advantageously mitigate the risk of negative current flowing through the primary-side switch, thereby reducing the risk of damaging the primary-side switch.

[0020] Figure 1 is a simplified circuit diagram of a flyback power converter ("power converter") 100 according to some embodiments. Some components of the power converter 100 have been removed from Figure 1 106. The primary side is coupled to the secondary side by a transformer 102. The transformer 102 transfers power from the primary side of the power converter 100 to the secondary side of the power converter 100 and typically includes a primary winding 104 and a secondary winding 106. The primary side of the power converter 100 typically includes a primary winding 104 of the transformer 102, an input voltage filter block 115, a rectifier block 116 (in the case of an AC input), an input voltage buffer capacitor C1, a primary side switch M1 directly electrically connected to a node 110 of the primary winding 104, and a power converter controller ("controller") 118. The magnetizing inductance L of the transformer 102 M105. The compensator 117 is part of the control / feedback path from the secondary side of the power converter 100 to the primary side of the power converter 100 and is therefore part of both the primary and secondary sides. The secondary side of the power converter 100 generally includes the secondary winding 106 of the transformer 102, an output buffer circuit 112, a synchronous rectifier switch M2 having a body diode, and a synchronous rectifier controller 120. The synchronous rectifier switch M2 is electrically connected directly to the secondary winding 106 at node 121. As shown, the output of the power converter 100 is configured to be connected to the load R L The feedback path of the compensator 117 provides a measurement of the output voltage Vout to the controller 118. Nodes 107, 111, 122, and 123 are also shown. Figure 1 The signals related to the operation of the power converter 100 shown include the primary side switch control signal GATE M1 , power converter feedback signal FB, input voltage Vin′, buffered, filtered or otherwise regulated input voltage Vin at node 111, magnetizing inductor current i LM , primary side switching current i M1 , the drain-source voltage V at the drain node of the primary side switch M1 (at node 110 ) M1 , the output current iout of the power converter 100, the synchronous rectifier switch control signal GATE M2 , the synchronous rectifier switch drain-source voltage V at the drain node of the synchronous rectifier switch M2 M2 , the synchronous rectifier switch current i through the synchronous rectifier switch M2 SR , and indicates the synchronous rectifier switch current i SR The received, indicated or sampled synchronous rectifier switch current i M2 .

[0021] The voltage Vin' is received at the power converter 100 as an alternating current (AC) or direct current (DC) voltage. The input voltage filter block 115, the rectifier block 116, and the input buffer capacitor C1 provide the filtered, buffered, rectified, or otherwise regulated input voltage Vin to the transformer 102 at node 111. The primary winding 104 receives the input voltage Vin at node 111. The primary winding 104 is directly electrically connected in series to the drain node of the primary side switch M1, and the source node of the primary side switch M1 is electrically coupled to a voltage bias node (such as ground). The primary side switch M1 is controlled at the gate node by the primary side switch control signal GATE generated by the controller 118. M1 (eg, a pulse width modulation (PWM) signal) is controlled. The primary side switch M1 responds to the primary side switch control signal GATE M1Control the current i flowing through the primary winding 104 M1 The magnetizing inductance L of the transformer 102 is calculated during the first portion of the switching cycle of the power converter 100 (ie, during the on-time of the primary-side switch M1). M 105 (such as magnetizing inductance current i LM The synchronous rectifier switch M2 controls the current flow through the secondary winding 106 to release the energy stored by the transformer 102 to the output buffer circuit 112 and the load R during the subsequent part of the switching cycle (i.e., during the off time of the primary side switch M1). L middle.

[0022] Specifically, when the primary side switch M1 is enabled by the controller 118 during the first portion of the switching cycle, current flows through the primary winding 104 to the voltage bias node. The current flowing through the primary winding 104 causes energy to be stored in the magnetizing inductance L of the transformer 102. M 105 and leakage inductance L L When the primary side switch M1 is disabled in the subsequent portion of the switching cycle, an output voltage Vout is generated at the output buffer circuit 112 and provided to the load R L The compensator 117 receives the generated output voltage Vout at the node 107 and uses the output voltage Vout to generate a feedback signal FB for adjusting the on-time of the primary-side switch M1 .

[0023] The synchronous rectifier switch M2 provides rectification on the secondary side of the power converter 100. When the primary side switch M1 is in the on state, the synchronous rectifier switch M2 is in the off state. After the primary side switch M1 transitions to the off state, the synchronous rectifier switch M2 transitions to the on state. During the period when the synchronous rectifier switch M2 is in the on state, the output current iout flows from the secondary winding 106 to the output buffer circuit 112 and the load R L . Corresponding to the flow of output current iout, the synchronous rectifier switching current i SR Flows through the synchronous rectifier switch M2. As the output current iout flows out of the secondary winding 106, the magnetizing inductor current i LM flow decreases to zero. If the magnetizing inductance current i LM After reaching zero, the synchronous rectifier switch M2 remains in the on state, and the magnetizing inductor current i LM becomes negative, at this time the magnetizing inductance current i LM The parasitic output capacitance Coss of the primary side switch M1 will begin to discharge. As the output capacitance Coss of the primary side switch M1 is discharged, the drain-source voltage V M1Therefore, by controlling the negative magnetizing inductance current i LM During the time that the current flows through the primary winding 104 before the synchronous rectifier switch M2 turns to the off state, when the drain-source voltage V M1 When the voltage is zero volts or close to zero volts, the primary-side switch M1 can be advantageously turned on, thereby achieving zero volt switching (ZVS) or close to ZVS of the primary-side switch M1. By using ZVS or close to ZVS of the primary-side switch M1, the switching loss of the primary-side switch M1 is reduced, and the power processing efficiency of the power converter 100 is improved, compared to a power converter that does not implement ZVS or close to ZVS.

[0024] Compared to conventional solutions, some embodiments disclosed herein advantageously provide a low drain-source voltage V M1 The primary side switch M1 is turned on before reaching zero volts, thereby achieving near zero volt switching of the primary side switch M1. By utilizing near ZVS switching, such embodiments advantageously mitigate the risk of negative current forming through the primary side switch M1, which reduces the risk of damaging the primary side switch M1 compared to conventional solutions. In addition, as disclosed herein, the synchronous rectifier controller 120 advantageously automatically tunes the magnetizing inductor current i LM The duration for which the synchronous rectifier switch M2 remains in the on state after the current has switched to negative current flow controls the discharge amount of the output capacitor Coss of the primary side switch M1 .

[0025] As shown, synchronous rectifier controller 120 is communicatively isolated from the primary side of power converter 100, including controller 118 and primary-side switch M1. Because synchronous rectifier controller 120 is communicatively isolated from the primary side of power converter 100, synchronous rectifier controller 120 does not receive timing signals, control signals, voltage indications, or current indications from the primary side of power converter 100. Therefore, as disclosed herein, synchronous rectifier controller 120 advantageously does not use primary-side measurements or primary-side control signals to perform automatic tuning of synchronous switch M2.

[0026] Figure 2 Shows the sampling period during time t according to some embodiments Figure 1 A simplified graph 200 of signals related to the operation of the power converter 100 is shown. Graph 202 includes the drain-source voltage V of the primary side switch M1 during time t. M1 203 and the first region of interest 204. Graph 205 includes the primary side switch control signal GATE during time t. M1 206 and synchronous rectifier switch control signal GATE M2207. Graph 208 includes the primary side switch current i in time t M1 209 curve and magnetizing inductance current i LM Graph 210. Graph 212 includes the synchronous rectifier switch current i during time t SR 213 and a second region of interest 214. Also shown is the automatically tuned delay t 延迟 215 and the duration of the negative magnetizing inductance current 216 .

[0027] At the beginning of the sampling period shown at the leftmost end of the graph 200, the primary side switch M1 is in the on state, as shown by the primary side switch control signal GATE. M1 At the same time, the synchronous rectifier switch M2 is in the off state, as shown by the effective level of the synchronous rectifier switch control signal GATE. M2 During the time when the primary side switch M1 is turned on and the synchronous rectifier switch M2 is turned off, the primary side switch current i M1 209 and magnetizing inductance current i LM 210 As the magnetizing inductance L of the transformer 102 M 105 is charged and increases. When the primary side switch control signal GATE M1 When 206 is invalid, the primary side switch M1 turns to the off state, and the primary side switch current i M1 209 quickly drops to zero. Shortly thereafter, the body diode conduction of the synchronous rectifier switch M2 occurs, as shown in the second region of interest 214. When the synchronous rectifier controller 120 detects that the body diode conduction of the synchronous rectifier switch M2 is occurring or has occurred, the synchronous rectifier controller 120 turns the synchronous rectifier switch M2 into the conducting state, as shown in the graph 205. Therefore, as the magnetizing inductance L stored in the transformer 102 M The energy in 105 is released to the load R L In the synchronous rectifier switching current i SR 213 increases and magnetizing inductance current i LM During the period when the synchronous rectifier switch M2 is kept in the on state, the magnetizing inductor current i LM 210 continues to decrease. In region 216, the magnetizing inductance current i LM 210 and synchronous rectifier switch current i SR 213Both become negative. When the synchronous rectifier switching current i SR 213 When the current changes to negative (i.e., changes direction), the delay t of the automatic tuning 延迟215 is started by the synchronous rectifier controller 120. When the magnetizing inductor current i LM During the time period when 210 is negative, the charge stored by the parasitic capacitance Coss of the primary side switch M1 is discharged as shown in region 216. As shown at the first region of interest 204, discharging the parasitic capacitance Coss of the primary side switch M1 ultimately reduces the drain-source voltage V M1 203. Delay t in automatic tuning 延迟 After 215 expires, the synchronous rectifier switch M2 is turned off. Thereafter, the primary side switch M1 is turned back on. Thus, by advantageously controlling the delay t 延迟 215 duration, negative magnetizing inductance current i LM The corresponding forced duration of 210 (within region 216) releases the energy stored by the parasitic capacitance Coss of the primary side switch M1. Before the primary side switch M1 is turned on, the drain-source voltage V M1 203 decreases to zero or near zero (ie, a value greater than zero volts), as shown at a first region of interest 204 .

[0028] If the auto-tuning delay t 延迟 215 is shorter than the optimum value, then when the drain-source voltage V M1 203 is still substantially greater than zero, the primary side switch M1 may transition to an on state, thereby causing switching losses that reduce the power handling efficiency of the power converter 100. However, if the auto-tuning delay t 延迟 If the duration of 215 is too long, a negative current may form through the primary side switch, which may potentially damage the primary side switch M1. Therefore, as disclosed herein, the synchronous rectifier controller 120 advantageously automatically tunes the automatically tuned delay t 延迟 215 duration for optimal duration.

[0029] Figure 3 is a simplified circuit diagram providing details of the synchronous rectifier controller 120 of the power converter 100 according to some embodiments. Some components of the synchronous rectifier controller 120 have been removed from Figure 3306 (e.g., timing and control logic, counter circuits, general purpose processors, programmable logic circuits, lookup tables, and / or other circuits), a high-pass filter circuit 308, a current comparison circuit 310, a voltage comparison circuit 312, and a gate driver circuit 314. Figure 1 Nodes 121 , 122 , and 123 are depicted. In some embodiments, all or a portion of one or more of components 308 , 310 , 312 , and / or 314 are external to the integrated circuit implementing synchronous rectifier controller 120 .

[0030] Signals related to the operation of the synchronous rectifier controller 120 include the sampled synchronous rectifier switch current i at node 122. M2 , the synchronous rectifier switch drain-source voltage V at node 121 M2 , the synchronous rectifier switch control signal GATE at node 123 M2 , the current threshold i at the non-inverting node of the current comparison circuit 310 sw th , the voltage threshold V at the inverting node of the voltage comparison circuit 312 sw th , the high-pass filtered drain-source voltage V generated by the high-pass filter circuit 308 M2 HPF , the current comparison signal C generated by the current comparison circuit 310 电流检测 , the voltage comparison signal C generated by the voltage comparison circuit 312 incDelay and the gate control signal C generated by the automatic tuning controller 302 栅极 .

[0031] In some implementations, the sampled synchronous rectifier switch current i received at the inverting input of the current comparison circuit 310 is M2 Equal to the synchronous rectifier switch current i SR In other embodiments, the sampled synchronous rectifier switch current i M2 and the synchronous rectifier switch current i SR In yet other embodiments, the sampled synchronous rectifier switch current i M2 Is the synchronous rectifier switching current i SR The current threshold i sw th is used to sample the synchronous rectifier switch current i M2In some embodiments, the current threshold i sw th Equal to, proportional to, or representing zero amperes.

[0032] The high-pass filter circuit 308 is configured to receive the synchronous rectifier switch drain-source voltage V M2 Or indicate the synchronous rectifier switch drain-source V M2 The high pass filter circuit 308 is operable to substantially attenuate the synchronous rectifier switch drain-source voltage V below a non-zero frequency cutoff value (e.g., 5 MHz). M2 frequency components and pass the synchronous rectifier switch drain-source voltage V greater than the non-zero frequency cutoff value M2 Therefore, the high-pass filtered drain-source voltage V received at the non-inverting input of the voltage comparison circuit 312 M2 HPF The signal represents the drain-source voltage V of the synchronous rectifier switch at frequencies above the non-zero frequency cutoff value. M2 frequency component of the instantaneous voltage.

[0033] In some embodiments, the high-pass filtered drain-source voltage V M2 HPF signal is compared to the voltage threshold V sw th The value of is chosen based on the desired near-ZVS valley voltage as seen on the secondary side, i.e., Where n is the turns ratio of the primary to secondary transformer. In some embodiments, the voltage threshold V sw th Equivalent to 2 to 5 volts, this is equivalent to a valley voltage of 10 to 30V.

[0034] In some embodiments, the gate control signal C generated by the automatic tuning controller 302 is 栅极 is a digital signal configured to control the output of the gate driver circuit 314. The gate driver circuit 314 responds to the gate control signal C 栅极 Level shifting, buffering, amplification, or other conditioning to generate the synchronous rectifier switch control signal GATE M2 .

[0035] According to some embodiments, the operation of the synchronous rectifier controller 120 is determined by Figure 4 The exemplary process 400 shown is described at a high level. Figure 4Specific steps, orders of steps, and combinations of steps are shown in the examples. Other embodiments may implement different specific steps, orders of steps, and combinations of steps to achieve similar functions or results. Figure 1 The power converter 100, Figure 2 The graph 200 shows the correlation signal and Figure 3 The details of the synchronous rectifier controller 120 are shown in FIG. Figure 4 steps.

[0036] At step 401, as an initial starting condition for process 400, the synchronous rectifier switch M2 is in the off state and the primary side switch M1 has transitioned from the on state to the off state. At step 402, it is determined whether the body diode conduction of the synchronous rectifier switch M2 is detected or has been detected, for example, using the current comparison circuit 310. For example, if the synchronous rectifier switch current i SR transitions from a non-zero or zero current level to a negative current level, such as Figure 2 As shown in the first region of interest 214 in FIG, the sampled synchronous rectifier switch current i M2 will correspondingly reach a value less than the current threshold i sw th value.

[0037] If the body diode conduction of the synchronous rectifier switch M2 is not detected or has been detected at step 402, the flow of process 400 remains at step 402. However, after determining that the sampled synchronous rectifier switch current i M2 Less than the current threshold i sw th When the current comparison circuit 310 generates an effective current comparison signal C 电流检测 When the synchronous rectifier switch M2 is in the off state, the effective current comparison signal C is received at the automatic tuning controller 302. 电流检测 , it is determined at step 402 that body diode conduction of the synchronous rectifier switch M2 has occurred and the flow proceeds to step 404 .

[0038] At step 404, by setting the active gate control signal C 栅极 The gate driver circuit 314 transmits the signal to the automatic tuning controller 302, which turns the synchronous rectifier switch M2 into the on state. 栅极 When the gate driver circuit 314 level-shifts, buffers, amplifies or otherwise adjusts the synchronous rectifier gate control signal Gate M2 is transmitted to the gate node of the synchronous rectifier switch M2 to turn the synchronous rectifier switch M2 into the on state.

[0039] During the time when the synchronous rectifier switch M2 is in the on state, the primary side switch M1 is kept in the off state, and the magnetizing inductance L stored in the transformer 102 M The energy in 105 is released (as shown in graph 208). When the output current iout flows from transformer 102 to output buffer circuit 112 and load R L When the corresponding synchronous rectifier switching current i SR flows through the synchronous rectifier switch M2 (as shown in graph 212 ), and receives a proportional, representative, or identical sampled synchronous rectifier switch current i at the inverting node of the current comparison circuit 310 . M2 .

[0040] As shown in graphs 208 and 212, the magnetizing inductance current i LM and the synchronous rectifier switch current i SR The amplitude of the transformer 102 increases with the magnetizing inductance L M 105 are released and each decreases to zero, eventually reaching and crossing the zero amplitude at the beginning of region 216, thereby changing direction. At step 406, the synchronous rectifier switch current i is determined using the current comparison circuit 310. SR Has changed direction (ie, has a negative amplitude). If the synchronous rectifier switch current i SR has changed direction, the flow of process 400 remains at step 406. However, if it is determined at step 406 that the sampled synchronous rectifier switch current i M2 Less than the current threshold i sw th , the current comparison circuit 310 generates an effective current comparison signal C 电流检测 When the synchronous rectifier switch M2 is in the on state, upon receiving the effective current comparison signal C 电流检测 , the flow of process 400 continues to step 408.

[0041] At step 408, the auto-tuning controller 302 begins the auto-tuning delay (eg, Figure 2 The t shown 延迟 215). In some embodiments, the delay t to start automatic tuning 延迟 This involves initializing one or more timing or delay modules in the delay module 304 of the auto-tuning controller 302. In some embodiments, the auto-tuning delay t is initiated by initializing one of the delay modules in the delay module 304 to zero. 延迟 , and when the delay module in the delay module 304 determines a delay equal to the automatic tuning delay t 延迟 When the time has passed, the auto-tuning delay t 延迟In other embodiments, by initializing one of the delay modules 304 to a delay t corresponding to the auto-tuned delay 延迟 The value of the delay t to start the automatic tuning 延迟 , and when the delay module determines that the delay is equal to the automatic tuning delay t 延迟 When the time has passed, the automatic tuning of t 延迟 maturity.

[0042] The delay t 延迟 After the auto-tuning delay t 延迟 Before the expiration of the current, the synchronous rectifier switch M2 remains in the on state and forces the negative magnetizing inductor current i LM Advantageously, the energy stored by the parasitic capacitance Coss of the primary side switch M1 is released, as in Figure 2 The delay t of the automatic tuning 延迟 215 area shown.

[0043] At step 410, the auto-tuning controller 302 determines (eg, using the delay module 304) the auto-tuning delay t 延迟 If the automatic tuning delay t is not determined at step 410, 延迟 If the auto-tuning delay t is determined by the auto-tuning controller 302 at step 410, the process 400 remains at step 410 and the synchronous rectifier switch M2 remains in the on state. 延迟 If the timeout period has expired, the process proceeds to step 412. At step 412, the auto-tuning controller 302 turns the synchronous rectifier switch M2 to an off state (eg, by generating an invalid C 栅极 At step 414, the delay t 延迟 Indicates the delay duration to update (i.e., "tune") the auto-tuning delay t 延迟 .

[0044] Generally speaking, after the synchronous rectifier switch M2 turns to the off state, based on the drain-source voltage V M2 The rate of change of the auto-tuning delay t 延迟 As mentioned above, the drain-source voltage V M2 The instantaneous voltage component is composed of the high-pass filtered drain-source voltage V M2 HPF If the drain-source voltage V M2 The instantaneous voltage component increases rapidly to a peak value, then the delay t 延迟Indicates the duration of the delay in order to increase the negative magnetizing inductance current i LM , thereby increasing the amount of energy released from the parasitic capacitance Coss of the primary side switch M1 during the next switching cycle. In contrast, if the drain-source voltage V M2 The instantaneous voltage component increases slowly to the peak value, then the delay t 延迟 Indicates the duration of the delay. By reducing the delay t 延迟 The duration of the delay indicated corresponds to a decrease in the negative magnetizing inductance current i LM The duration of the forced magnetizing inductor current i is determined by the synchronous rectifier controller 120 to reduce the amount of energy released from the parasitic capacitance Coss of the primary-side switch M1, so that the maximum discharge amount of the parasitic capacitance Coss is less than the full discharge amount (for example, to prevent a potentially harmful negative current from flowing through the primary-side switch M1). LM The optimal duration of synchronous rectifier controller 120 is determined to achieve ZVS or near ZVS of primary-side switch M1 without receiving primary-side measurements or control signals of power converter 100 and without requiring an a priori indication of the inductance of transformer 102. Thus, existing power converter designs can be easily and economically modified to include synchronous rectifier controller 120.

[0045] refer to Figures 5A to 6 Additional details regarding step 414 are described. Figure 5A Demonstrating that according to some embodiments Figure 1 The signals related to the operation of the power converter 100 are shown and Figure 3 A simplified graph 500 is shown showing details of the synchronous rectifier controller 120. The graph 500 includes the voltage comparison signal C during time t. incDelay 502 curve, synchronous rectifier switching current i SR 504 curve diagram, voltage threshold V sw th 506, the high-pass filtered drain-source voltage V M2 HPF 508 curve, synchronous rectifier switch drain-source voltage V M2 510 and the synchronous rectifier switch M2 gate control signal C 栅极 512. Also shown is the auto-tuning delay t 延迟 Graph of exemplary durations of 514 and detection windows t 检测The example shown in graph 500 generally illustrates a portion of a switching cycle of the synchronous rectifier switch M2 occurring at step 414 of process 400, wherein after the synchronous rectifier switch M2 transitions to the off state, the drain-source voltage V M2 The instantaneous voltage component of 510 (ie, V M2 HPF 508) increases rapidly to a peak value, thereby 检测 516 exceeds the voltage threshold V before the expiration sw th 506. Therefore, as shown by the voltage comparison signal C incDelay 502 active level trigger, increase the delay t by automatic tuning 延迟 Indicates the duration of the delay in order to increase the forced negative magnetizing inductance current i LM duration.

[0046] Figure 5B Demonstrating that according to some embodiments Figure 1 The signals related to the operation of the power converter 100 are shown and Figure 3 A simplified graph 520 is shown showing details of the synchronous rectifier controller 120. The graph 520 includes the voltage comparison signal C during time t. incDelay 522 curve, synchronous rectifier switching current i SR 524 curve, voltage threshold V sw th 526 curve, high-pass filtered drain-source voltage V M2 HPF 528 curve, synchronous rectifier switch drain-source voltage V M2 The curve of 530 and gate control signal C 栅极 532. Also shown is the auto-tuning delay t 延迟 Graph of exemplary durations of 534 and detection windows t 检测 The example shown in graph 520 generally illustrates a portion of a switching cycle of the synchronous rectifier switch M2 occurring at step 414 of process 400, wherein after the synchronous rectifier switch M2 transitions to the off state, the drain-source voltage V M2 The instantaneous voltage component of 530 (ie, V M2 HPF 528) does not increase rapidly to the peak value, and therefore in the detection window t 检测 536 before the expiration of the voltage threshold V sw th526. Therefore, as shown by the voltage comparison signal C incDelay 522 active level trigger, reducing the delay caused by automatic tuning t 延迟 534 indicates the duration of the delay in order to reduce the forced negative magnetizing inductance current i LM duration.

[0047] The details of step 414 of process 400 are as follows: Figure 6 For illustration and explanation purposes only, Figure 6 Specific steps, orders of steps, and combinations of steps are shown in the examples. Other embodiments may implement different specific steps, orders of steps, and combinations of steps to achieve similar functions or results. Figure 1 The power converter 100, Figure 3 The details of the synchronous rectifier controller 120 are shown and Figures 5A to 5B The graphs 500 and 520 are used to describe the related signals Figure 6 steps.

[0048] At step 602, as an initial starting condition for step 414, the primary side switch M1 is in the off state, and the synchronous rectifier switch M2 has transitioned from the on state to the off state (i.e., Figure 4 At step 412). At step 604, a time detection window is started (e.g., t 检测 516 / 536). In some embodiments, the detection window t 检测 This involves initializing one or more timing or delay modules in the delay module 304 of the automatic tuning controller 302. In some embodiments, the detection window t is started by initializing one of the delay modules in the delay module 304 to zero. 检测 , and when the delay module determines that it is equal to the detection window t 检测 When the time has passed, the detection window t 检测 In other embodiments, by initializing one of the delay modules 304 to correspond to the detection window t 检测 The value of the detection window t 检测 , and when the delay module determines that it is equal to the detection window t 检测 When the time has passed, the detection window t 检测 Typically, the detection window (e.g., t 检测 516 / 536) is set to a value based on the maximum quasi-resonant half cycle. In some embodiments, the detection window t 检测 Equal to 100ns (eg, for >= 300Mhz switching frequency) or 1000us (eg, for < 300kHz switching frequency).

[0049] At step 606, the detection window t is determined. 检测 If the detection window t is determined to have expired at step 606 检测 If the timeout period has not expired, the process proceeds to step 608. At step 608, the synchronous rectifier switch drain-source voltage V M2 (i.e., the instantaneous voltage component) of the high-pass filtered drain-source voltage V M2 HPF Is it greater than the voltage threshold V sw th If the synchronous rectifier switch drain-source voltage V M2 The high-pass filtered drain-source voltage V M2 HPF Greater than the voltage threshold V sw th (For example, as shown in graph 500, where the high-pass filtered drain-source voltage V M2 HPF 508 crosses the voltage threshold V sw th 506), the voltage comparison circuit 312 generates an effective voltage comparison signal C incDelay 502, as shown in the graph 500, and the process proceeds to step 610. At step 610, the automatic tuning controller 302 responds to receiving the effective voltage comparison signal C incDelay 502 and increase the delay t by automatic tuning 延迟 If the synchronous rectifier switch drain-source voltage V is not determined at step 608, M2 The high-pass filtered drain-source voltage V M2 HPF Greater than the voltage threshold V sw th , the process returns to step 606. At step 606, if it is determined that the detection window t 检测 has expired (i.e., before the synchronous rectifier switch drain-source voltage V M2 The high-pass filtered drain-source voltage V M2 HPF Greater than the voltage threshold V sw th In the case of automatic tuning), the automatic tuning controller 302 reduces the delay t 延迟 Flow proceeds from either step 610 or 614 to step 616 , which ends the illustrated portion of process 400 at step 414 .

[0050] Figure 7ADemonstrates the use of an automatic tuning method similar or identical to process 400 according to some embodiments. Figure 1 The experimental results 700 of the power converter 100 are similar to those of the power converter 100. The experimental results 700 include the primary side switch drain-source voltage V M1 Graph 702 of FIG. 703 , a dashed line 704 indicating the lowest switching voltage of the primary side switch M1 during time t, and a first region of interest 705 . Graph 706 shows the synchronous rectifier switch control signal GATE during time t M2 707, and the primary side switch control signal GATE M1 708. Graph 709 includes the magnetizing inductance current i in time t LM 710 and the primary side switch current i M1 711 curve chart. Figure 7B Continue according to some embodiments Figure 7A The experimental results 700 are shown in FIG. 722. The graph 722 includes the synchronous rectifier switch current i during time t. SR Graph 723. Graph 724 includes the synchronous rectifier switch drain-source voltage V during time t M2 725, a dashed line 726 indicating the primary side switch valley voltage, and a second region of interest 727 corresponding to the first region of interest 705 of the graph 702. The closer the dashed line 726 is to the synchronous rectifier switch drain-source voltage V M2 The lower the peak voltage of 725, the closer the power converter 100 is to zero voltage switching of the primary side switch M1. Figure 7A As shown in the region of interest 705, the synchronous rectifier controller 120 automatically tunes the forced negative magnetizing current i LM The duration of the switching operation is to achieve zero voltage switching or near zero voltage switching of the primary side switch M1.

[0051] Reference has been made in detail to embodiments of the present invention, one or more examples of which have been shown in the accompanying drawings. Each example has been provided as an explanation of the present technology, not as a limitation of the present technology. In fact, although this specification has been described in detail with respect to specific embodiments of the present invention, it should be understood that those skilled in the art, after understanding the foregoing, can easily conceive of alternatives, variations and equivalents of these embodiments. For example, a feature shown or described as part of one embodiment can be used together with another embodiment to produce yet another embodiment. Therefore, it is intended that this subject matter covers all such modifications and variations within the scope of the appended claims and their equivalents. These and other modifications and variations may be made to the present invention by those skilled in the art without departing from the scope of the present invention, the scope of the present invention being more particularly set forth in the appended claims. In addition, it will be understood that the foregoing description is by way of example only and is not intended to limit the present invention.

Claims

1. A device for automatic tuning, comprising: a high-pass filter circuit configured to receive a drain-source voltage from a drain node of a synchronous rectifier switch at a secondary side of the power converter and generate a filtered drain-source voltage using the received drain-source voltage; a current comparison circuit configured to receive a current indicative of a current flowing through the synchronous rectifier switch and to generate a current comparison signal using the received current; as well as An auto-tuning controller configured to: When it is determined using the current comparison signal that the body diode of the synchronous rectifier switch is turned on, turning on the synchronous rectifier switch; a delay for initiating auto-tuning upon determining, using the current comparison signal, that the current flowing through the synchronous rectifier switch has changed direction; When a delay of the automatic tuning expires, turning off the synchronous rectifier switch; and During a detection time window, a duration of the auto-tuned delay is updated based on the filtered drain-source voltage.

2. The apparatus of claim 1, wherein: When the synchronous rectifier switch turns on, the voltage at the drain node of the primary side switch of the power converter decreases by an amount corresponding to the duration of the auto-tuning delay.

3. The apparatus of claim 2, wherein: A maximum duration of the auto-tuning delay corresponds to a drain-source voltage at the drain node of the primary side switch being greater than zero volts.

4. The apparatus of claim 2, wherein: The auto-tuning controller is isolated in communication with a signal representative of the voltage at the drain node of the primary side switch.

5. The apparatus of claim 1 , wherein the automatic tuning controller is further configured to: updating the duration of the auto-tuned delay by increasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage exceeds a voltage threshold during the detection time window; and Upon determining that the filtered drain-source voltage does not exceed the voltage threshold during the detection time window, the duration of the auto-tuned delay is updated by reducing the duration of the auto-tuned delay.

6. The apparatus of claim 5, further comprising: a voltage comparison circuit configured to generate a voltage comparison signal based on a comparison of the filtered drain-source voltage and the voltage threshold; wherein the auto-tuning controller is further configured to: upon receiving a first level of the voltage comparison signal, determining that the filtered drain-source voltage exceeds the voltage threshold; and Upon receiving the second level of the voltage comparison signal, it is determined that the filtered drain-source voltage does not exceed the voltage threshold.

7. The apparatus of claim 1 , wherein the current comparison circuit is further configured to: generating the current comparison signal by comparing the current indicative of the current flowing through the synchronous rectifier switch to a current threshold; wherein the auto-tuning controller is further configured to: When the synchronous rectifier switch is in an off state, upon receiving a first level of the current comparison signal, determining that the body diode of the synchronous rectifier switch has been turned on; and When the synchronous rectifier switch is in an on state, upon receiving the first level of the current comparison signal, it is determined that the current flowing through the synchronous rectifier switch has changed direction.

8. The apparatus of claim 7, wherein: The current threshold corresponds to a current of approximately zero amperes.

9. The apparatus of claim 1, wherein: The power converter includes a transformer having a primary side winding on a primary side of the power converter and a secondary side winding on the secondary side of the power converter; and The synchronous rectifier switch is configured to be directly electrically connected to the secondary side winding.

10. The apparatus of claim 9, wherein: A primary-side switch is directly electrically connected to the primary-side winding; and The duration of the forced negative magnetizing inductance current at the drain node of the primary side switch corresponds to the duration of the auto-tuning delay.

11. The apparatus of claim 10, wherein: The auto-tuning controller is communicatively isolated from each of the drain, source, and gate nodes of the primary side switch.

12. The apparatus of claim 10, wherein: The increase in the duration of the auto-tuning delay corresponds to an increased discharge amount of the parasitic capacitance of the primary side switch; and The reduction in the duration of the auto-tuning delay corresponds to a reduced discharge amount of the parasitic capacitance of the primary-side switch.

13. The apparatus of claim 12, wherein: The maximum duration of the delay of the automatic tuning corresponds to a maximum discharge amount of the parasitic capacitance of the primary side switch; and The maximum discharge amount of the parasitic capacitance of the primary-side switch is less than a full discharge amount of the parasitic capacitance of the primary-side switch.

14. A method for automatic tuning, comprising: receiving a drain-source voltage at a high pass filter circuit from a drain node of a synchronous rectifier switch at a secondary side of the power converter; generating, by the high pass filter circuit, a filtered drain-source voltage using the received drain-source voltage; receiving, at a current comparison circuit, a current indicative of a current flowing through the synchronous rectifier switch; generating, by the current comparison circuit, a current comparison signal using the received current; When an automatic tuning controller determines, using the current comparison signal, that body diode conduction of the synchronous rectifier switch has occurred, turning on the synchronous rectifier switch; a delay for initiating auto-tuning by the auto-tuning controller upon determining, using the current comparison signal, that the current flowing through the synchronous rectifier switch has changed direction; When a delay of the automatic tuning expires, turning off the synchronous rectifier switch; as well as During a detection time window, a duration of the auto-tuned delay is updated by the auto-tuning controller based on the filtered drain-source voltage.

15. The method of claim 14, wherein: When the synchronous rectifier switch turns on, the voltage at the drain node of the primary side switch of the power converter decreases by an amount corresponding to the duration of the auto-tuning delay.

16. The method of claim 15, wherein: A maximum duration of the auto-tuning delay corresponds to a drain-source voltage at the drain node of the primary side switch being greater than zero volts.

17. The method of claim 15, wherein: The auto-tuning controller is isolated in communication with a signal representative of the voltage at the drain node of the primary side switch.

18. The method of claim 14, further comprising: updating the duration of the auto-tuned delay by increasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage exceeds a voltage threshold during the detection time window; as well as Upon determining that the filtered drain-source voltage does not exceed the voltage threshold during the detection time window, the duration of the auto-tuned delay is updated by reducing the duration of the auto-tuned delay.

19. The method of claim 14, wherein: The duration of the auto-tuning delay corresponds to a duration of a forced negative magnetizing inductor current at a drain node of a primary-side switch of the power converter.

20. The method of claim 19, wherein: The auto-tuning controller is communicatively isolated from each of the drain, source, and gate nodes of the primary side switch.

21. A device for automatic tuning, comprising: a high-pass filter circuit configured to receive a drain-source voltage from a drain node of a synchronous rectifier switch at a secondary side of the power converter and generate a filtered drain-source voltage using the received drain-source voltage; as well as An auto-tuning controller configured to: When detecting that the body diode of the synchronous rectifier switch is turned on, turning on the synchronous rectifier switch; a delay for initiating auto-tuning upon determining that current flowing through the synchronous rectifier switch has changed direction; When a delay of the automatic tuning expires, turning off the synchronous rectifier switch; and During a detection time window, a duration of the auto-tuned delay is updated based on the filtered drain-source voltage.

22. The apparatus of claim 21, wherein: When the synchronous rectifier switch turns on, the voltage at the drain node of the primary side switch of the power converter decreases by an amount corresponding to the duration of the auto-tuning delay.

23. The apparatus of claim 22, wherein: A maximum duration of the auto-tuning delay corresponds to a drain-source voltage at the drain node of the primary side switch being greater than zero volts.

24. The apparatus of claim 22, wherein: The auto-tuning controller is isolated in communication with a signal representative of the voltage at the drain node of the primary side switch.

25. The apparatus of claim 21 , wherein the auto-tuning controller is further configured to: updating the duration of the auto-tuned delay by increasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage exceeds a voltage threshold during the detection time window; and Upon determining that the filtered drain-source voltage does not exceed the voltage threshold during the detection time window, the duration of the auto-tuned delay is updated by reducing the duration of the auto-tuned delay.

26. The apparatus of claim 25, further comprising: a voltage comparison circuit configured to generate a voltage comparison signal based on a comparison of the filtered drain-source voltage and the voltage threshold; wherein the auto-tuning controller is further configured to: upon receiving a first level of the voltage comparison signal, determining that the filtered drain-source voltage exceeds the voltage threshold; and Upon receiving the second level of the voltage comparison signal, it is determined that the filtered drain-source voltage does not exceed the voltage threshold.

27. The apparatus of claim 21, further comprising: The current comparison circuit is configured to: generating a current comparison signal by comparing the current indicative of the current flowing through the synchronous rectifier switch to a current threshold; wherein the auto-tuning controller is further configured to: When the synchronous rectifier switch is in an off state, upon receiving a first level of the current comparison signal, determining that the body diode of the synchronous rectifier switch has been turned on; and When the synchronous rectifier switch is in an on state, upon receiving the first level of the current comparison signal, it is determined that the current flowing through the synchronous rectifier switch has changed direction.

28. The apparatus of claim 27, wherein: The current threshold corresponds to a current of approximately zero amperes.

29. The apparatus of claim 21, wherein: The power converter includes a transformer having a primary side winding on a primary side of the power converter and a secondary side winding on the secondary side of the power converter; and The synchronous rectifier switch is configured to be electrically coupled to the secondary side winding.

30. The apparatus of claim 29, wherein: a primary-side switch electrically coupled to the primary-side winding; and The duration of the forced negative magnetizing inductance current at the drain node of the primary side switch corresponds to the duration of the auto-tuning delay.

31. The apparatus of claim 30, wherein: The auto-tuning controller is communicatively isolated from each of the drain, source, and gate nodes of the primary side switch.

32. The apparatus of claim 30, wherein: The increase in the duration of the auto-tuning delay corresponds to an increased discharge amount of the parasitic capacitance of the primary side switch; and The reduction in the duration of the auto-tuning delay corresponds to a reduced discharge amount of the parasitic capacitance of the primary-side switch.

33. The apparatus of claim 32, wherein: The maximum duration of the delay of the automatic tuning corresponds to a maximum discharge amount of the parasitic capacitance of the primary side switch; and The maximum discharge amount of the parasitic capacitance of the primary-side switch is less than a full discharge amount of the parasitic capacitance of the primary-side switch.

34. A method for automatic tuning, comprising: receiving a drain-source voltage at a high pass filter circuit from a drain node of a synchronous rectifier switch at a secondary side of the power converter; generating, by the high pass filter circuit, a filtered drain-source voltage using the received drain-source voltage; When the automatic tuning controller determines that the body diode of the synchronous rectifier switch has been turned on, turning on the synchronous rectifier switch; a delay for initiating auto-tuning by the auto-tuning controller upon determining that current flowing through the synchronous rectifier switch has changed direction; When a delay of the automatic tuning expires, turning off the synchronous rectifier switch; as well as During a detection time window, a duration of the auto-tuned delay is updated by the auto-tuning controller based on the filtered drain-source voltage.

35. The method of claim 34, wherein: When the synchronous rectifier switch turns on, the voltage at the drain node of the primary side switch of the power converter decreases by an amount corresponding to the duration of the auto-tuning delay.

36. The method of claim 35, wherein: A maximum duration of the auto-tuning delay corresponds to a drain-source voltage at the drain node of the primary side switch being greater than zero volts.

37. The method of claim 35, wherein: The auto-tuning controller is isolated in communication with a signal representative of the voltage at the drain node of the primary side switch.

38. The method of claim 34, further comprising: updating the duration of the auto-tuned delay by increasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage exceeds a voltage threshold during the detection time window; as well as Upon determining that the filtered drain-source voltage does not exceed the voltage threshold during the detection time window, the duration of the auto-tuned delay is updated by reducing the duration of the auto-tuned delay.

39. The method of claim 34, wherein: The duration of the auto-tuning delay corresponds to a duration of a forced negative magnetizing inductor current at a drain node of a primary-side switch of the power converter.

40. The method of claim 39, wherein: The auto-tuning controller is communicatively isolated from each of the drain, source, and gate nodes of the primary side switch.

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