Synchronous rectification controller and related control method

Abstract

An embodiment of the present invention discloses a synchronous rectification controller for controlling a rectification switch. The synchronous rectification controller includes a full-open controller and a voltage regulator. The full-open controller can be triggered by a channel voltage of the rectification switch and, according to a preset condition, is used to fully open the rectification switch for a full-open time. The voltage regulator is disabled during the full-open time and enabled after the full-open time, and is used to turn on the rectification switch and maintain the channel voltage within a preset voltage range. The full-open controller adjusts the preset condition according to a performance record when the voltage regulator is enabled.

Description

[0001] This application is a divisional application. The filing date of the original application is: April 28, 2020;

[0002] The application number is: 202010348396.4; The invention title is: Synchronous rectification controller and related control method. Technical Field

[0003] The present invention relates to a synchronous rectification controller on the secondary side; in particular to a synchronous rectification controller on the secondary side of a flyback switching power supply and a related control method. Background Art

[0004] In addition to requiring accurate output voltage or output current, power conversion efficiency is often one of the specifications that the industry cares very much about.

[0005] A traditional flyback switching power supply separates the primary side and the secondary side with a transformer. Through the switching of a power switch, the voltage across the main winding on the primary side changes. Due to inductive coupling, an alternating current part is generated across the secondary winding, which can supply the load located on the secondary side after rectification.

[0006] For rectification on the secondary side, the simplest way is to use a rectifier diode. However, the forward voltage required for the rectifier diode to turn on makes the rectifier diode a component that constantly consumes energy. In order to reduce or eliminate the energy consumption of the rectifier diode and increase the energy conversion efficiency, the industry has developed a rectification switch to replace the rectifier diode. Such a technology is called secondary side synchronous rectification. However, how to control the rectification switch not only concerns the energy conversion efficiency but also concerns product safety. If the rectification switch turns on when it should not, it will not only damage the efficiency but also may pose a risk of explosion of the power supply. Summary of the Invention

[0007] Embodiments of the present invention disclose a synchronous rectification controller for controlling a rectification switch. The synchronous rectification controller includes a full-on controller, a voltage regulator, and a turn-off controller. The full-on controller can be triggered by a channel voltage of the rectification switch and, according to a preset condition, is used to fully turn on the rectification switch for a full-on time. The full-on controller also adjusts the length of the full-on time according to the preset condition, and the preset condition is related to a reference voltage. When the channel voltage is higher than the reference voltage, the full-on controller ends the full-on time. The voltage regulator is disabled during the full-on time and enabled after the full-on time, and is used to turn on the rectification switch and maintain the channel voltage within a preset voltage range. When the channel voltage is greater than a preset turn-off voltage, the turn-off controller turns off the rectification switch. The full-on controller adjusts the preset condition according to a performance record when the voltage regulator is enabled. The voltage regulator is enabled for a voltage regulation time after the full-on time. The preset voltage range is between two boundary voltages, both of which are less than the preset turn-off voltage and both of which are less than the reference voltage. The full-on controller records the number of times the channel voltage touches one of the two boundary voltages during the voltage regulation time and adjusts the preset condition according to the number of times of crossing.

[0008] Embodiments of the present invention also disclose a control method applicable to a synchronous rectification controller for controlling a rectification switch. The control method includes: fully turning on the rectification switch for a full-on time, where the full-on time is determined according to a preset condition that a channel voltage of the rectification switch is higher than a reference voltage. When the channel voltage is higher than the reference voltage, the full-on time ends; during a voltage regulation time after the full-on time, maintaining a channel voltage within a preset voltage range and generating a performance record. The preset voltage range is between two boundary voltages, both of which are less than the preset turn-off voltage and both of which are less than the reference voltage; when the channel voltage meets a turn-off condition, maintaining the rectification switch in the off state, and the turn-off condition is that when the channel voltage is greater than a preset turn-off voltage; when maintaining the channel voltage within the preset voltage range, recording the number of times the channel voltage touches one of the two boundary voltages; and adjusting the preset condition according to the performance record so that the performance record approaches a preset target.

[0009] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but it is not intended to limit the present invention. Description of the Drawings

[0010] Figure 1 Show a flyback switching power supply implemented according to the present invention.

[0011] Figure 2 Show Figure 1The synchronous rectification controller in

[0012] Figure 3 For example, it shows the control signal S in three switching cycles NP , the channel current I flowing through the rectification switch NS D , the channel voltage V D , and the signal waveforms of the gate signal V G .

[0013] Figure 4 It shows the control method 200 used in the synchronous rectification controller 10.

[0014] Figure 5 It shows the control method 300 used in the fully - on controller 104.

[0015] Among them, the reference numerals

[0016] 10: Synchronous rectification controller

[0017] 14: Power supply controller

[0018] 16: Load

[0019] 20: Flyback switching power supply

[0020] 26: Input ground

[0021] 28: Output ground

[0022] 102: State detector

[0023] 104: Fully - on controller

[0024] 106: Voltage regulator

[0025] 108: Comparator

[0026] 110: Shutdown controller

[0027] 112, 114: Switches

[0028] 116, 118: Current sources

[0029] 120, 122: Switches

[0030] 200, 300: Control methods

[0031] IN: Input power line

[0032] LP: Primary winding

[0033] LS: Secondary winding

[0034] NC: Number of crossings

[0035] NP: Power switch

[0036] NS: Rectifying switch

[0037] NSET: Preset number of times

[0038] OUT: Output power line

[0039] S10, S12, S14, S16, S18, S20, S22, S24, S26, S28: Steps

[0040] SF: Pulse

[0041] S NP : Control signal

[0042] t0, t1, t2, t3, t4, t5, ta, tb, tc: Time points

[0043] TF: Transformer

[0044] TFO: Fully open time

[0045] TR: Voltage stabilization time

[0046] VA, VB: Boundary voltages

[0047] VC: Preset voltage

[0048] V D : Channel voltage

[0049] V G : Gate signal

[0050] VMAX: Maximum voltage

[0051] V OUT : Output voltage

[0052] VTH NS : Threshold voltage Detailed implementation manners

[0053] In this specification, there are some identical symbols, which represent elements with the same or similar structures, functions, and principles, and can be inferred by those with general knowledge in the industry according to the teachings of this specification. For the sake of simplicity of the specification, the elements with the same symbols will not be restated.

[0054] In an embodiment of the present invention, the turn-on of the rectifying switch on the secondary side is divided into two times: the full-on time and the voltage-stabilizing time. During the full-on time, the rectifying switch is fully turned on. The voltage-stabilizing time immediately follows the full-on time. During the voltage-stabilizing time, the rectifying switch is partially turned on to maintain a channel voltage of the rectifying switch within a preset voltage range. The full-on time can be adaptively adjusted according to a performance record during the voltage-stabilizing time, so that the performance record can approach a preset target as the switching cycle progresses.

[0055] The full-on time being before the voltage-stabilizing time can reduce the energy loss of the rectifying switch during rectification and increase the conversion efficiency.

[0056] The voltage-stabilizing time can pre-pull down a gate signal of the rectifying switch, and can immediately and quickly turn off the rectifying switch when it is determined that the rectifying switch must be turned off later. The voltage-stabilizing time provides a relatively high turn-on resistance, which can prevent the risk of excessive reverse current that may occur when the rectifying switch is turned off too late.

[0057] Adaptively adjusting the full-on time according to the performance record during the voltage-stabilizing time can extend the full-on time as much as possible to enjoy a higher conversion efficiency.

[0058] Figure 1 Shows a flyback switching power supply 20 implemented according to the present invention. On the primary side, the flyback switching power supply 20 has an input power line IN, an input ground 26, a power controller 14, a main winding LP, and a power switch NP, and their electrical connection relationships are as Figure 1 shown. On the secondary side, the flyback switching power supply 20 has an output power line OUT, an output ground 28, a synchronous rectification controller 10, a secondary winding LS, and a rectifying switch NS, and their electrical connection relationships are as Figure 1 shown. The transformer TF has, but is not limited to, a main winding LP and a secondary winding LS, which are respectively located on the primary side and the secondary side and are inductively coupled to each other.

[0059] The power controller 14 controls the power switch NP with a control signal S NP so that the voltage across the main winding LP and the current flowing through the main winding LP change. Due to inductive coupling, an alternating voltage or current is generated in the secondary winding LS. The rectifying switch NS provides a rectifying function and is expected to generate an appropriate output voltage V OUT, to supply power to the load 16. The rectifying switch NS can provide a conducting path, electrically connecting the output ground 28 to the secondary winding LS. For example, the rectifying switch NS is an NMOS transistor, whose source terminal is connected to the output ground 28, whose drain terminal is connected to the secondary winding LS, and whose gate terminal is controlled by the synchronous rectification controller 10. There is a channel voltage V at the connection point between the rectifying switch NS and the secondary winding LS D , which can represent the voltage across the conducting path of the rectifying switch NS. Based on the channel voltage V D , the synchronous rectification controller 10 generates a gate signal V G , for controlling the rectifying switch NS. Briefly speaking, the synchronous rectification controller 10 determines whether the rectifying switch NS should be turned on at present based on the channel voltage V D , and decides the on state.

[0060] Figure 2 Shown Figure 1 The synchronous rectification controller 10 in

[0061] Based on the channel voltage V D , the state detector 102 determines whether the power switch NP has just turned off, so as to trigger the full-on controller 104. For example, the state detector 102 detects the falling edge slope of the channel voltage V D . When the falling edge slope of the channel voltage V D is greater than a certain degree, and the channel voltage V D is negative, the state detector 102 determines that the power switch NP on the primary side has just turned off, thus triggering the full-on controller 104.

[0062] After being triggered, the full-on controller 104 generates a pulse SF to turn on the switch 112. The turned-on switch 112 pulls the voltage value of the gate signal V G to a fixed maximum voltage VMAX, that is, fully turns on the rectifying switch NS. The pulse width of the pulse SF is the full-on time TFO. Therefore, the full-on controller 104 keeps the rectifying switch NS fully on within the full-on time TFO.

[0063] The voltage regulator 106 includes a comparator 108, several logic gates, current sources 116 and 118, and switches 120 and 122, and their connection relationship is as shown in Figure 2 . The voltage regulator 106 is disabled within the full-on time TFO, and the voltage regulator 106 does not drive the gate signal V G, because the pulse SF simultaneously turns off switches 120 and 122 in the voltage regulator 106. After the full-on time TFO, the voltage regulator 106 is enabled, not only maintaining the rectifying switch NS partially on, but also maintaining the channel voltage V D at approximately a preset negative voltage V REF , or causing the channel voltage V D to be approximately maintained between the boundary voltages VA and VB. In one embodiment, the preset negative voltage V REF , the boundary voltages VA and VB can be, but are not limited to, -0.3V, -0.25V, and -0.35V respectively. When the channel voltage V D is higher than the boundary voltage VA, the comparator 108 outputs "0", the switch 120 opens and the switch 122 shorts, and the current source 118 pulls down the gate signal V G , causing the channel voltage V D to tend to decrease. When the channel voltage V D is lower than the boundary voltage VB, the comparator 108 outputs "1", the switch 122 opens and the switch 120 shorts, and the current source 116 raises the gate signal V G , causing the channel voltage V D to tend to increase.

[0064] Taking the shutdown controller 110 as an example, it detects whether the channel voltage V D meets a shutdown condition. In Figure 2 , this shutdown condition is that the channel voltage V D is greater than the preset voltage VC. In one embodiment, the preset voltage VC is exemplified as, but not limited to, 0V. If the channel voltage V D is greater than the preset voltage VC, the shutdown controller 110 turns on the switch 114, making the gate signal V G 0V, forcing and maintaining the rectifying switch NS completely off.

[0065] Figure 3 Exemplarily shows the signal waveforms of the control signal S NP , the channel current I D flowing through the rectifying switch NS, the channel voltage V D , and the gate signal V G in three switching cycles.

[0066] In Figure 3 , at the time point t0 in the first switching cycle, the power switch NP has just turned off, so the channel current I D appears inductively and starts to linearly decrease as it discharges. At this time, the rectifying switch NS is off. The channel current I D instantly flows through the diode parasitic in the rectifying switch NS. At the time point t0, the channel voltage V Dit will quickly drop from a positive value to a voltage of -0.7V or lower, as shown in Figure 3 shown.

[0067] At time point t0, the state detector 102 detects that the falling edge slope is large enough and determines that the power switch NP has just turned off, thus triggering the full-on controller 104. Therefore, after a signal delay, the full-on controller 104 starts to fully turn on the rectifier switch NS at time point t1. The full-on controller 104 ends the full-on time TFO at time point t2. During the full-on time TFO, the voltage level of the gate signal V G is the highest voltage VMAX that the synchronous rectification controller 10 can provide to fully turn on the rectifier switch NS.

[0068] After time point t2, the full-on controller 104 stops controlling the rectifier switch NS, and the voltage regulator 106 takes over, causing the channel voltage V D to be maintained approximately between the boundary voltages VA and VB. Therefore, starting from time point t2, the channel voltage V D starts to vary between the boundary voltages VA and VB, and the gate signal V G also varies up and down until time point t3. The period during which the voltage regulator 106 takes over, from time point t2 to time point t3 in the first switching cycle, is called the voltage regulation time TR. Note that as shown in Figure 3 , during the voltage regulation time TR, the voltage value of the gate signal V G is still higher than the critical voltage VTH NS of the rectifier switch NS, so the rectifier switch NS remains on, but not fully on, because the voltage value of the gate signal V G is lower than the highest voltage VMAX during the full-on time TFO.

[0069] At time point t3, the control signal S NP starts to turn on the power switch NP to end the first switching cycle and start the second switching cycle. At this time, the channel current I D rapidly changes to a negative value due to inductance induction, which also causes the channel voltage V D to rapidly become positive. Figure 2 The turn-off controller 110 in D- detects that the channel voltage V

[0070] Please refer to Figure 2 . Figure 2 The full-on controller 104 in Figure 2In an embodiment, this performance record is the channel voltage V D The number of times NC that the boundary voltage VB is crossed, and the preset target is the preset number NSET. The fully-on controller 104 receives the output of the comparator 108 to record the channel voltage V D The number of times NC that -0.35V is crossed, and based on this, adjusts the length of the fully-on time TFO in the next switching cycle, so that the subsequent number of times NC of crossing can approach the preset number NSET. For example, this preset number is 2. In another embodiment, the performance record can be the channel voltage V D The number of times the boundary voltage VA is crossed, or it can also be the channel voltage V D The number of times the boundary voltages VA and VB are crossed, or any other result generated when the voltage regulator 106 is enabled.

[0071] Please refer to Figure 3 , within the regulated voltage time TR, the fully-on controller 104 calculates the channel voltage V D The number of times the boundary voltage VB is crossed within the regulated voltage time TR, and based on this, adjusts the fully-on time TFO of the next switching cycle. At time point t3, the number of times NC of crossing recorded in the fully-on controller 104 is 3, that is, the channel voltage V D Crosses the boundary voltage VB three times within the regulated voltage time TR, occurring at time points ta, tb, and tc respectively. Since the number of times NC of crossing is greater than the preset number NSET (assumed to be 2) at this time. Therefore, the fully-on controller 104 adjusts the preset condition for controlling the fully-on time TFO, resulting in a longer fully-on time TFO in the second switching cycle and a shorter regulated voltage time TR. At time point t4, the number of times NC of crossing recorded in the fully-on controller 104 is still 3, so the fully-on controller 104 adjusts the preset condition for controlling the fully-on time TFO again, making the fully-on time TFO in the third switching cycle even longer and the regulated voltage time TR even shorter. At time point t5, the number of times NC of crossing recorded in the fully-on controller 104 is 2, so the fully-on controller 104 keeps the preset condition for controlling the fully-on time TFO unchanged, expecting the fully-on time TFO in the next switching cycle to be approximately unchanged.

[0072] In an embodiment, the preset condition for the fully-on controller 104 to control the fully-on time TFO can be that when the channel voltage V D Is higher than the reference voltage V REF2 , the fully-on controller 104 ends the fully-on time TFO. It can be expected that the higher the reference voltage V REF2 , the closer it is to 0V, the longer the fully-on time TFO will be. In this embodiment, when the number of times NC of crossing recorded in the fully-on controller 104 is greater than the preset number NSET, the fully-on controller 104 increases the reference voltage V REF2, to increase the full-on time TFO in the next switching cycle. Thus, the full-on time TFO is related to the channel voltage V D and the reference voltage V REF2 , and the full-on controller 104 adjusts the reference voltage V according to the performance record during the regulation time TR REF2 .

[0073] In another embodiment, the preset condition for the full-on controller 104 to control the full-on time TFO can be that the current full-on time TFO is approximately equal to the product of the discharge time TDIS in a previous switching cycle and a proportionality constant K between 0 and 1. The discharge time TDIS refers to the time when the channel current I D is greater than 0A, as marked in Figure 3 . In this embodiment, when the number of crossings NC recorded in the full-on controller 104 is greater than the preset number NSET, the full-on controller 104 increases the proportionality constant K to increase the full-on time TFO in the next switching cycle. Therefore, the full-on time TFO is related to the discharge time TDIS and the proportionality constant K, and the full-on controller 104 adjusts the proportionality constant K according to the performance record during the regulation time TR

[0074] Figure 4 Shows the control method 200 used in the synchronous rectification controller 10

[0075] In step S10, the state detector 102 determines that the power switch NP has just turned off based on the falling slope of the channel voltage V D , thus triggering the full-on controller 104 to start turning on the rectification switch NS

[0076] In step S12, the full-on controller 104 fully turns on the rectification switch NS until a preset condition is met, ending the full-on time TFO

[0077] In step S14, the voltage regulator 106 controls the gate signal V G such that the channel voltage V D is maintained approximately between the boundary voltages VA and VB. At the same time, the full-on controller 104 generates a performance record. In one embodiment, this performance record is the number of crossings NC calculated and provided by the full-on controller 104, indicating the number of times the channel voltage V D reaches the boundary voltage VB within the regulation time TR

[0078] In step S16, since it is found that the channel voltage V D is greater than 0V, the shutdown controller 110 sets the gate signal V G to 0V, forcing and maintaining the rectification switch NS fully off

[0079] In step S18, the fully-open controller 104 adjusts the preset conditions used in step S12 according to the performance record, so that the performance record in the next switching cycle can approach a preset target.

[0080] Figure 5 Show the control method 300 used in the fully-open controller 104.

[0081] In step S20, the fully-open controller 104 provides the number of crossings NC.

[0082] In steps S22 and S26, the fully-open controller 104 compares the number of crossings NC with the preset number NSET.

[0083] When the number of crossings NC is greater than the preset number NSET, step S24 adjusts the preset conditions used in step S12 to increase the fully-open time TFO in the next switching cycle.

[0084] When the number of crossings NC is less than the preset number NSET, step S28 adjusts the preset conditions used in step S12 to reduce the fully-open time TFO in the next switching cycle.

[0085] Both steps S24 and S28 are used to make the number of crossings NC in the next switching cycle approach the preset number NSET.

[0086] Please refer to Figure 3 . It can be known from the previous teachings that the synchronous rectification controller 10 can approximately automatically adjust the length of the fully-open time TFO, so that the regulated voltage time TR is maintained at the number of crossings NC approximately equal to the preset number NSET. In other words, if the regulated voltage time TR in the current switching cycle is too short, the next fully-open time TFO will increase. Vice versa.

[0087] The fully-open time TFO is in a period with a relatively high channel current I D Because when the fully-open time TFO, the rectifier switch NS is fully open, so it has a relatively small on-resistance (R DS-ON ), which can reduce the conduction loss generated when the rectifier switch NS rectifies.

[0088] The regulated voltage time TR can pull down the gate signal V of the rectifier switch NS in advance G , as shown in Figure 3 . Therefore, at time point t3, when the shutdown controller 110 finds that the channel voltage V D- becomes positive, it can quickly and fully turn off the rectifier switch NS to avoid the channel current I D from being too large reverse current.

[0089] The adjustable length of the full-open time TFO adaptability can enjoy reduced conduction loss as much as possible, and at the same time, the rectifier switch NS can be quickly turned off.

[0090] The above are only the preferred embodiments of the present invention, and all equivalent changes and modifications made according to the claims of the present invention shall fall within the scope of the present invention.

Claims

1. A synchronous rectification controller for controlling a rectification switch, comprising: An all - on controller, triggered by a channel voltage of the rectification switch, according to a preset condition, used to fully turn on the rectification switch for an all - on time, and the all - on controller adjusts the length of the all - on time according to the preset condition, the preset condition is related to a reference voltage, when the channel voltage is higher than the reference voltage, the all - on controller ends the all - on time; A voltage regulator, disabled during the all - on time and enabled after the all - on time, used to turn on the rectification switch and maintain the channel voltage within a preset voltage range; And A turn - off controller, which turns off the rectification switch when the channel voltage is greater than a preset turn - off voltage; Wherein, the all - on controller adjusts the preset condition according to a performance record when the voltage regulator is enabled; and Wherein, the voltage regulator is enabled for a voltage - regulating time after the all - on time, the preset voltage range is between two boundary voltages, both of the two boundary voltages are less than the preset turn - off voltage, both of the two boundary voltages are less than the reference voltage, the all - on controller records the number of times of crossing when the channel voltage touches one of the two boundary voltages during the voltage - regulating time, and adjusts the preset condition according to the number of crossing times.

2. The synchronous rectification controller as claimed in claim 1, wherein, The all - on controller adjusts the preset condition to make the number of crossing times equal to a preset number.

3. A control method, applicable to a synchronous rectification controller for controlling a rectification switch, comprising: Fully turning on the rectification switch for an all - on time, wherein the all - on time is determined according to a preset condition that a channel voltage of the rectification switch is higher than a reference voltage, when the channel voltage is higher than the reference voltage, the all - on time ends; During a voltage - regulating time after the all - on time, maintaining the channel voltage within a preset voltage range and generating a performance record, the preset voltage range is between two boundary voltages, both of the two boundary voltages are less than a preset turn - off voltage, both of the two boundary voltages are less than the reference voltage; When the channel voltage meets a turn - off condition, maintaining the rectification switch off, and the turn - off condition is that when the channel voltage is greater than the preset turn - off voltage; When maintaining the channel voltage within the preset voltage range, recording the number of times of crossing when the channel voltage touches one of the two boundary voltages; And According to the performance record of the number of crossing times, adjusting the preset condition to make the performance record approach a preset target.

4. The control method according to claim 3, wherein, The preset condition is adjusted to make the number of crossing times equal to a preset number.

5. The control method according to claim 3, wherein, The all - on time is related to a discharge time and a proportionality constant, and the step of adjusting the preset condition adjusts the proportionality constant.

6. The control method according to claim 3, wherein, The all - on time is related to the channel voltage and a reference voltage, and the step of adjusting the preset condition adjusts the reference voltage.

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