Synchronous rectifier controller and related charging methods

Abstract

This invention provides a synchronous rectifier controller and a related charging method. In an embodiment of the invention, a charging method is provided for an operating power supply of a synchronous rectifier controller. The operating power supply can power the synchronous rectifier controller. The synchronous rectifier controller switches the synchronous rectifier switch according to a channel signal of the synchronous rectifier switch to generate a plurality of synchronous switch on times and a plurality of synchronous switch off times. The charging method includes: detecting whether the channel signal oscillates during a first synchronous switch off time and generating an oscillation record; and, based on the oscillation record, during a second synchronous switch off time, using the resonant energy that caused the channel signal to oscillate to charge the operating power supply. The second synchronous switch off time is later than the first synchronous switch off time.

Description

Technical Field

[0001] This invention generally relates to synchronous rectifier controllers, and more particularly to an apparatus and control method for charging the operating power supply of a synchronous rectifier controller. Background Technology

[0002] Synchronous rectification is a very popular technology in power management. Synchronous rectification uses a combination of a synchronous rectifier switch and a synchronous rectifier controller to simulate and replace a diode that carries a large current, thereby reducing the considerable power loss caused by the diode's fixed forward voltage.

[0003] Figure 1 This displays an AC-to-DC power supply 10. The transformer TF has a primary winding LP and a secondary winding LS, located on the phase-isolated primary side and secondary side, respectively.

[0004] On the primary side, the bridge rectifier 12 provides full-wave rectification of the AC input power supply, and provides the input voltage source V at the input power line IN. IN Input ground wire 26 provides input ground. Power controller 13 provides PWM signal S. PRI The power switch N1 is controlled to change the current flowing through the main winding LP and the voltage across the main winding LP.

[0005] On the secondary side, relative to the voltage / current changes in the primary winding LP, the secondary winding LS generates an induced voltage / current. Through the sensing terminal DET and the sensing resistor RC, the synchronous rectifier controller 14 detects the channel signal V of the synchronous rectifier switch SWSR. D Based on which to provide synchronization signal S SEC The synchronous rectifier controller 14 controls the synchronous rectifier switch SWSR. Essentially, the synchronous rectifier controller 14 enables the secondary side current I... SEC The values ​​are mostly positive, which charge the output capacitor 17 and establish the output power supply V. OUT It supplies power to load 16. On the secondary side, the operating power supply V is connected across the power supply capacitor 30. CC This is used to provide the electrical energy required for the operation of the synchronous rectifier controller 14.

[0006] Figure 2A and Figure 2B show Figure 1The power supply operates in discontinuous-conduction mode (DCM) and continuous-conduction mode (CCM) respectively. The PWM signal S... PRI With channel signal V D The wave pattern. Figure 2A The data shows that in the PWM signal S PRI Demagnetization time T after power switch N1 is turned off DMG Internal, channel signal V D From a negative value, it gradually changes to 0V. This means that the current flowing through the transformer TF returns to zero, hence this operating mode is called DCM. Demagnetization time T DMG Subsequently, due to the LC oscillation circuit formed by the parasitic capacitance and the windings of the transformer TF, the channel signal V... D The oscillation continues until the next turn-on time T of power switch N1. ON-P Begin. In Figure 2B In the middle, the demagnetization time T DMG In channel signal V D Before the voltage reaches 0V, meaning the current in transformer TF has not completely returned to zero, the circuit is activated for time T. ON-P It was forced to end because it was supposed to start. Therefore, this operating mode is called CCM.

[0007] Figure 2A and 2B The text specifically notes a special situation: operating power supply V CC It is higher than the output power supply V OUT In other words, the output power supply V OUT It is impossible to step down the voltage to directly charge the power supply capacitor 30. Operating power supply V CC We must find a way to replenish the energy, otherwise it will be depleted as the synchronous rectifier controller 14 operates.

[0008] A sort of Figure 1 The method for charging the power supply capacitor 30 is as follows: Figure 2A Or Figure 2B The on-time T of power switch N1 in the middle ON-P Inside, the linear regulator (low dropout, LDO) (not shown) in the synchronous rectifier controller 14 is turned on, drawing current from the high-voltage power supply terminal HVR to supply the operating power supply V connected to the power supply terminal VCC. CC Charging. However, like... Figure 2A and 2B As shown, at the opening time T ON-P At that time, the channel signal V on the high-voltage power supply terminal HVR D Higher than the operating power supply V CCThe amount is very large, so the LDO will consume a considerable amount of electrical energy. Especially when the load 16 is unloaded or lightly loaded, it will significantly reduce the power conversion efficiency of the power supply 10. Summary of the Invention

[0009] This invention provides a method for charging an operating power supply for a synchronous rectifier controller. The operating power supply powers the synchronous rectifier controller. The synchronous rectifier controller switches the synchronous rectifier switch according to a channel signal of the synchronous rectifier switch to generate a plurality of synchronous switch on-times and a plurality of synchronous switch off-times. The charging method includes: detecting whether the channel signal oscillates during a first synchronous switch off-time and generating an oscillation record; and, based on the oscillation record, during a second synchronous switch off-time, using the resonant energy that caused the channel signal to oscillate to charge the operating power supply. The second synchronous switch off-time is later than the first synchronous switch off-time.

[0010] This invention provides a synchronous rectification controller, powered by an operating power supply on a power capacitor, for controlling a synchronous rectification switch. The synchronous rectification controller includes a switch controller, a charging switch, an oscillation detector, and a charging time setter. Based on a channel signal from the synchronous rectification switch, the switch controller switches the synchronous rectification switch on and off to generate several synchronous switch on-times and several synchronous switch off-times. When the charging switch is on, it provides a charging path. The oscillation detector detects whether the channel signal oscillates during a first synchronous switch off-time and provides an oscillation record. When the oscillation record indicates that the channel signal is oscillating, the charging time setter activates the charging switch during a second synchronous switch off-time, allowing the resonant energy of the channel signal oscillation to charge the operating power supply through the charging path. The second synchronous switch off-time is later than the first synchronous switch off-time. Attached Figure Description

[0011] Figure 1 Displays an AC-to-DC power supply 10.

[0012] Figure 2A and Figure 2B show Figure 1 The power supply operates in discontinuous conduction mode and continuous conduction mode respectively. The PWM signal S PRI With channel signal V D The wave pattern.

[0013] Figure 3 This shows the synchronous rectifier controller 100 implemented according to the present invention.

[0014] Figure 4 Control method 600 applicable to synchronous rectifier controller 100.

[0015] Figure 5 for Figure 1 Some signal waveforms when the AC to DC power supply 10 uses the synchronous rectifier controller 100.

[0016] Figure 6 An example is shown in oscillation detector 108.

[0017] Figure 7 Example shows charging time setter 112.

[0018] Figure 8 Roughly similar Figure 5 However, it increased Figure 6 and Figure 7 The signal CNT, oscillation recording MOD, and voltage V in the data are mentioned. D-OFF V REC V RAT The signal waveform of signal SAV.

[0019] [Symbol Explanation]

[0020] 10 Power Supply

[0021] 12 Bridge rectifier

[0022] 13 Power Controller

[0023] 14 Synchronous Rectifier Controller

[0024] 16 Load

[0025] 17 Output capacitor

[0026] 26 Input grounding wire

[0027] 28 Output grounding wire

[0028] 30 Power supply capacitor

[0029] 100 Synchronous Rectifier Controller

[0030] 102 Constant Current Circuit

[0031] 104, 106 Charging Switch

[0032] 107 Logic Gates

[0033] 108 Oscillation Detector

[0034] 110 comparator

[0035] 112 Charging Time Setter

[0036] 120 Switch Controller

[0037] 130 comparator

[0038] 132 Turn off the time register

[0039] 134 Selector

[0040] 136 Constant Current Source

[0041] 138 switch

[0042] 140 comparator

[0043] 600 Control Method

[0044] Steps 602, 604, and 606

[0045] CNT signal

[0046] CSA capacitors

[0047] CSP sampling capacitor

[0048] DF1, DF2, DF3 D flip-flops

[0049] DET detection end

[0050] HVR high voltage power supply terminal

[0051] IN Input power line

[0052] I SEC Secondary side current

[0053] LP main winding

[0054] LS secondary winding

[0055] MOD Oscillation Recording

[0056] N1 power switch

[0057] PK area

[0058] PTH charging path

[0059] Voltage divider resistors R1 and R2

[0060] RC sensing resistor

[0061] SAV signal

[0062] S ON1 S ON2 short pulse

[0063] S PRI PWM signal

[0064] SR-OFF1 and SR-OFF2 synchronous switch closing time

[0065] SR-ON1 and SR-ON2 Synchronous Switch On-Time

[0066] S SEC S DRV Synchronization signal

[0067] SWSR Synchronous Rectifier Switch

[0068] T DMG Demagnetization time

[0069] TF Transformer

[0070] T ON-P Opening time

[0071] T SAV Charging period

[0072] T SR-OFF Synchronous switch off time

[0073] T SR-ON Synchronous switch on time

[0074] V CC Operating power supply

[0075] VCC power supply

[0076] V D Channel signal

[0077] V IN Input voltage source

[0078] V D-OFF V REC V RAT Voltage

[0079] V OUT Output power

[0080] V REF-CC Reference voltage

[0081] V RES-OS Reference voltage Detailed Implementation

[0082] In this specification, some identical symbols are used to represent elements having the same or similar structure, function, or principle, which can be inferred by those skilled in the art based on the teachings of this specification. For the sake of brevity, elements with the same symbols will not be repeated.

[0083] One embodiment of the present invention is a charging method applicable to a synchronous rectifier controller. The synchronous rectifier controller is applicable to a power supply. The synchronous rectifier controller switches the synchronous rectifier switch according to a channel signal of the synchronous rectifier switch to generate a plurality of synchronous switch on times and a plurality of synchronous switch off times. The charging method includes detecting whether the channel signal oscillates during a first synchronous switch off time and generating an oscillation record. Based on the oscillation record, during a second synchronous switch off time following the first synchronous switch off time, the resonant energy that caused the channel signal to oscillate is used to charge the operating power supply.

[0084] In one embodiment, the charging method first determines whether the power supply is currently operating in DCM. If so, during the next synchronous switch off time, approximately when the channel signal generates a peak value, the resonant energy is used to charge the operating power supply.

[0085] One embodiment of the present invention is a synchronous rectification controller, powered by an operating power supply on a power capacitor, for controlling a synchronous rectification switch. The synchronous rectification controller includes a switch controller, a charging switch, an oscillation detector, and a charging time setter. The switch controller switches the synchronous rectification switch on and off according to a channel signal of the synchronous rectification switch to generate a plurality of synchronous switch on times and a plurality of synchronous switch off times. The charging switch provides a charging path. The oscillation detector detects whether the channel signal oscillates during a first synchronous switch off time and provides an oscillation record. The charging time setter turns on the charging switch during a second synchronous switch off time later than the first synchronous switch off time, so that the resonant energy of the channel signal oscillation charges the operating power supply through the charging path.

[0086] In one embodiment, the oscillation detector detects whether a power supply containing the synchronous rectification controller is currently operating in DCM. If it is operating in DCM, the charging time setter turns on the charging switch during a charging period in the second synchronous switch off time, so that the resonant energy charges the operating power supply approximately when the channel signal generates a peak value.

[0087] Please also refer to Figure 3 , Figure 4 and Figure 5 . Figure 3 The synchronous rectification controller 100 implemented according to the present invention is shown, which in the embodiments can replace... Figure 1 The synchronous rectifier controller 14 in the middle. Figure 4 Control method 600 applicable to synchronous rectifier controller 100. Figure 5 for Figure 1Some signal waveforms when the AC to DC power supply 10 uses the synchronous rectifier controller 100.

[0088] as Figure 3 As shown, the synchronous rectifier controller 100 includes a switch controller 120, an oscillation detector 108, a charging switch 104, a charging time setter 112, a comparator 110, and a charging switch 106.

[0089] Switch controller 120 detects the channel signal V of synchronous rectifier switch SWSR. D Based on which to provide synchronization signal S SEC This controls the synchronous rectifier switch (SWSR). For example, when the channel signal V... D When the signal is positive and greater than the output ground voltage of output ground line 28 (considered as 0V on the secondary side), the switch controller 120 causes the synchronization signal S to... SEC / S DRV A logical zero indicates that the synchronous rectifier switch SWSR is off. Conversely, when the channel signal V... D When the voltage is negative and less than the output ground voltage of output ground wire 28, the switch controller 120 causes the synchronization signal S to... SEC / S DRV The logical value is 1, which enables the synchronous rectifier switch SWSR. The synchronous rectifier switch SWSR is enabled for the synchronous switch on-time T. SR-ON At that time, the synchronous rectifier switch SWSR provided a very small on-resistance, which roughly short-circuited the channel signal V. D To output ground wire 28; when the synchronous rectifier switch SWSR is closed, it is the synchronous switch closing time T. SR-OFF At that time, the synchronous rectifier switch SWSR largely isolated the channel signal V. D Output ground wire 28. Synchronization signal S SEC With S DRV These can be considered as signals with the same logic value. In some embodiments, the synchronization signal S SEC It may have varying voltage or current to drive the synchronous rectifier switch SWSR; while the synchronization signal S DRV It is used for internal control of the synchronous rectifier controller 100 and has a fixed digital voltage level. Like... Figure 5 As shown, with the PWM signal S PRI This causes a change in the voltage / current of the main winding LP, and the switch controller 120 then responds according to the channel signal V. D Provide synchronization signal S SECThe switching synchronous rectifier switch (SWSR) can generate several synchronous switch on times (SR-ON1, SR-ON2, etc.) and synchronous switch off times (SR-OFF1, SR-OFF2, etc.). Each synchronous switch on time is between two synchronous switch off times, and each synchronous switch off time is between two synchronous switch on times.

[0090] Oscillation detector 108 can perform Figure 4 In step 602, the channel signal V is detected. D Is it during the closing time T of a synchronous switch? SR-OFF It oscillates and provides an oscillation recording MOD. The oscillation detector 108 will be explained in detail later with examples. Figure 5 This shows the channel signal V during the synchronous switch off time SR-OFF1. D There is obvious oscillation; therefore, when the synchronous switch closing time SR-OFF1 ends, the oscillation detector 108 will set the oscillation record MOD to a logical 1. If the oscillation detector 108 does not determine the channel signal V... D During the closing time T of a synchronous switch SR-OFF If there is oscillation, then the oscillation record MOD will be logically 0.

[0091] Charging switches 104 and 106 are connected in series. When both charging switches 104 and 106 are turned on, a charging path PTH can be provided, allowing the channel signal V to... D Along the charging path PTH, through the high-voltage power supply terminal HVR, the constant current circuit 102, and the charging switches 104 and 106, the operating power supply V connected to the power supply terminal VCC is activated. CC Charge.

[0092] The charging time setter 112 can achieve Figure 4 In step 604, record the closing time T of a synchronous switch. SR-OFF The duration of the time interval is determined, and a signal SAV is generated based on this duration to indicate the next synchronous switch closing time T. SR-OFF During the charging period T SAV The charging time setter 112 will be explained in detail with examples. Figure 5 During the charging period T within the synchronous switch off time SR-OFF2, SAV It roughly starts around the same time as the synchronous switch closing time SR-OFF2, while the charging period T SAV The length is determined by the synchronous switch closing time SR-OFF1. For example, Figure 5 During the charging period T SAV It is approximately half the synchronous switch off time SR-OFF1.

[0093] The oscillation detector 108, the charging time setter 112, and the logic gate 107 can be implemented Figure 4 Step 606. When the oscillation record MOD is logically 1, the charging time setter 112 sets the charging time during the charging period T. SAV The internal charging switch 104 can be activated using channel signal V. D The resonant energy of the oscillation, through the charging path PTH, affects the operating power supply V. CC Charge until the operating power supply V CC The voltage reaches the reference voltage V REF-CC Until then. Like Figure 5 As shown, because the channel signal V is within the synchronous switch off time SR-OFF1... D There is oscillation, so during the charging period T of the synchronous switch off time SR-OFF2. SAV Channel signal V D The resonant energy can affect the operating power supply V. CC Charge. Figure 5 In the region PK, the original channel signal V is displayed. D The oscillation peaks that should have appeared were reduced because of the channel signal V. D Exceeding the operating power supply V CC Start operating power supply V CC Charge. Figure 5 It also shows that the oscillation amplitude of the synchronous switch off time SR-OFF2 is significantly smaller than that of the synchronous switch off time SR-OFF1, because part of the channel signal V D The resonant energy, when region PK appears, has already been used to power the operating power supply V. CC Charge.

[0094] Figure 6 For example, an oscillation detector 108 is shown, which has a comparator 130, D flip-flops DF1, DF2, and DF3, connected to each other as shown in the figure. Figure 7 Example shows charging time setter 112. Figure 8 Roughly similar Figure 5 However, it increased Figure 6 and Figure 7 The signal CNT, oscillation recording MOD, and voltage V in the data are mentioned. D-OFF V REC V RAT The signal waveform of signal SAV.

[0095] Figure 6 This is merely illustrative and not intended to limit the scope of the invention. In other embodiments, the oscillation detector 108 may employ different methods. Figure 6 The method described above is used to detect the closing time T of a synchronous switch. SR-OFFInternal, channel signal V D Is there any oscillation? Please also refer to... Figure 6 and Figure 8 Simply put, Figure 6 The oscillation detector 108 in the middle detects the channel signal V. D During the closing time T of a synchronous switch SR-OFF Within, is there a rise that exceeds the reference voltage V? RES-OS Twice. The D flip-flops DF1 and DF2 act as shift registers. The signal CNT will only be logically 1 when the output of comparator 130 has two rising edges, as... Figure 8 As shown. When the synchronization signal S SEC / S DRV When the logic changes from 0 to 1, the D flip-flop DF3 copies the signal CNT to generate the oscillation record MOD. Simultaneously, D flip-flops DF1 and DF2 are reset, as if... Figure 8 As shown. Channel signal V D During the closing time T of a synchronous switch SR-OFF If the rise exceeds the reference voltage V RES-OS Two or more occurrences indicate that the AC-to-DC power supply 10 is currently operating in DCM mode. If the AC rise exceeds the reference voltage V... RES-OS This means that the AC-to-DC power supply 10 may be operating in either DCM or CCM. Therefore, Figure 6 In the oscillation record, when MOD is logically 1, it indicates that during the previous synchronous switch closing time T... SR-OFF Inside, the AC-to-DC power supply 10 is determined to operate in DCM, channel signal V D There is oscillation.

[0096] Figure 7 Example shows charging time setter 112. Figure 7 This is merely illustrative and not intended to limit the invention. In other embodiments, the charging time setter 112 may employ different methods. Figure 7 The approach described above involves a synchronous switch closing time T. SR-OFF Within, set the charging period T SAV . Figure 7 The charging time setter 112 includes a shutdown time register 132, a selector 134, and voltage divider resistors R1 and R2.

[0097] Please refer to the following at the same time Figure 7 and Figure 8 When the synchronous switch is closed for time T SR-OFF Initially, the voltage V D-OFF Approximately 0V. With the synchronous switch closing for time T...SR-OFF As the current continues, the constant current source 136 continuously charges the capacitor CSA, so the voltage V... D-OFF This can be approximately represented by the current synchronous switch closing time T. SR-OFF- The duration of time. When the synchronous switch is closed for time T... SR-OFF After it ends, short pulse S ON1 This causes the sampling capacitor CSP to first measure the voltage V D-OFF The voltage V generated by sample / hold is REC Then short pulse S ON2 Make the voltage V D-OFF It was reset to 0V by switch 138. Therefore, the voltage V D-OFF It roughly has a triangular waveform, and the voltage V across the sampling capacitor CSP is... REC The peak of the triangular wave was recorded. Voltage V REC It is equivalent to recording the closing time T of the previous synchronous switch. SR-OFF The length of time, like Figure 8 As shown. The voltage V divided by resistors R1 and R2. REC To generate voltage V RAT For example, voltage V RAT Fixed as voltage V REC 1 / 2, like Figure 8 As shown in the example.

[0098] In selector 134, comparator 140 compares voltage V. RAT With voltage V D-OFF During the closing time T of a synchronous switch SR-OFF Within this timeframe, a signal SAV is generated. During the charging period T... SAV For signal SAV during the logic 1 period, it is like... Figure 8 As shown. Therefore, the charging period T SAV The defined charging time, or charging period T SAV The length will be approximately the same as the previous synchronous switch closing time T. SR-OFF The duration of time has a fixed relationship. For example, Figure 8 In the middle, the charging period T of the synchronous switch off time SR-OFF2 SAV It is approximately half the duration of the synchronous switch closing time SR-OFF1.

[0099] Generally speaking, the channel signal V D The resonant energy is often naturally dissipated over time by the parasitic resistance in the LC oscillation circuit. However, a power supply according to the present invention can utilize this resonant energy to charge the operating power supply of a synchronous rectifier controller in a timely manner, maintaining its voltage level. Therefore, embodiments of the present invention may achieve better conversion efficiency.

[0100] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made in accordance with the claims of the present invention shall be within the scope of the present invention.

Claims

1. A method for charging an operating power supply for a synchronous rectifier controller, the operating power supply supplying power to the synchronous rectifier controller, the synchronous rectifier controller switching the synchronous rectifier switch according to a channel signal of the synchronous rectifier switch to generate a plurality of synchronous switch on times and a plurality of synchronous switch off times, the charging method comprising: Detect whether the channel signal oscillates during the first synchronous switch closing time, and generate an oscillation record; and Based on the oscillation record, during the closing time of the second synchronous switch, the resonant energy that caused the channel signal to oscillate is used to charge the operating power supply. in, The second synchronous switch closes later than the first synchronous switch.

2. The charging method as described in claim 1, further comprising: Record the duration of the first synchronous switch's closing time; and During the charging period when the second synchronous switch is closed, the resonant energy is used to charge the operating power supply. in, The charging period is determined based on the length of the time.

3. The charging method as described in claim 2, wherein, The charging time during this charging period is proportional to the length of this time.

4. The charging method as described in claim 1, comprising: The oscillation record is generated by detecting whether the channel signal crosses the preset reference voltage a preset number of times during the first synchronous switch closing time.

5. A synchronous rectification controller, powered by an operating power supply on a power supply capacitor, for controlling a synchronous rectification switch, the synchronous rectification controller comprising: The switch controller switches the synchronous rectifier switch on and off according to the channel signal of the synchronous rectifier switch, so as to generate a number of synchronous switch on times and a number of synchronous switch off times; The charging switch, when turned on, provides a charging path; An oscillation detector detects whether the channel signal oscillates during the first synchronous switch closing time and provides an oscillation record. as well as The charging time setter, when the oscillation record indicates that the channel signal oscillates, turns on the charging switch during the second synchronous switch closing time, so that the resonant energy of the channel signal oscillation charges the operating power supply through the charging path. The second synchronous switch closes later than the first synchronous switch.

6. The synchronous rectification controller as described in claim 5, wherein, The oscillation detector detects whether the channel signal crosses a preset reference voltage a preset number of times during the first synchronous switch closing time, in order to provide the oscillation record.

7. The synchronous rectification controller as described in claim 6, wherein, The oscillation detector detects whether the channel signal exceeds the preset reference voltage twice during the first synchronous switch closing time to provide the oscillation record.

8. The synchronous rectification controller as described in claim 5, wherein, The charging time setter includes: The closing time register records the duration of the first synchronous switch's closing time; and The selector determines the charging period within the off time of the second synchronous switch based on the time length, and turns on the charging switch during the charging period.

9. The synchronous rectification controller as described in claim 8, wherein, The charging time during this charging period has a fixed relationship with the length of this time.

10. The synchronous rectification controller as described in claim 5, wherein, When the channel signal is of the first polarity, the switch controller turns on the synchronous rectifier switch, generating one of the synchronous switch turn-on times; Furthermore, when the channel signal is a second polarity opposite to the first polarity, the switch controller turns off the synchronous rectifier switch, generating one of the synchronous switch off times.

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