Synchronous rectifier controller for power converter and start-up method thereof during start-up phase

Abstract

The application discloses a synchronous rectification controller applied to a power converter and a starting method of the synchronous rectification controller in a starting stage. The synchronous rectification controller is coupled with a rectification switch of a secondary side of the power converter, and the rectification switch comprises a rectification switch control end, a rectification switch first end and a rectification switch second end. The synchronous rectification controller comprises a driving signal end, a power supply receiving end, a transistor and a starting control module. The power supply receiving end receives a working voltage, and when the working voltage is higher than a working voltage threshold value, the synchronous rectification controller can output a driving signal for driving the rectification switch through the driving signal end. The starting control module limits a cross voltage between the rectification switch control end and the rectification switch second end to be lower than a first threshold voltage of the rectification switch based on the working voltage being lower than the working voltage threshold value through conduction of the transistor.

Description

Technical Field

[0001] This invention relates to a synchronous rectifier controller and its startup method, and more particularly to a synchronous rectifier controller applied to a power converter and its startup method during the startup phase. Background Technology

[0002] Due to the rapid development of the information industry in recent years, power supplies play a crucial role, especially as the power requirements of large-scale information equipment have gradually increased. Consequently, the output power of power supplies has also increased to meet load demands. The main circuitry within a power supply that performs power conversion is the power converter. The power converter primarily functions to convert input voltage into output voltage and provide a stable output voltage to supply the load. Internally, a power converter typically contains several switches and at least one power inductor. An internal controller alternately turns the switches on and off, allowing the power inductor to store and release energy, thereby controlling the power converter's conversion of input voltage into output voltage.

[0003] like Figure 1 The diagram shows a circuit block diagram of a conventional power converter. Power converter 100 includes an isolated primary side circuit 100-1, a secondary side circuit 100-2, a transformer 100-3, a main controller 1, a rectifier switch SR, and a synchronous rectifier controller 2. The main controller 1 controls the switching of the power switch Q to convert the input voltage Vin, and the synchronous rectifier controller 2, based on the switching of the power switch Q, synchronously controls the switching of the rectifier switch SR so that the power converter 100 provides an output voltage Vo to power the load 200. When the power converter 100 is in the startup state after receiving the input voltage Vin, and the internal components of the power converter 100 are in an ideal state, the synchronous rectifier controller 2 does not output a drive signal S_DR to turn on the rectifier switch SR. However, when the internal components of the power converter 100 are in a non-ideal state, there is a parasitic capacitance Cgd between the drain D and gate G of the rectifier switch SR. Therefore, when part of the energy of the primary circuit 100-1 is coupled to the secondary circuit 100-2 through the transformer 100-3, the parasitic capacitance Cgd may be charged, causing the voltage at the control terminal G of the rectifier switch to rise. This leads to the power converter 100 being in the startup state after receiving the input voltage Vin, and the rectifier switch SR being mis-turned due to the influence of the parasitic capacitance Cgd.

[0004] Therefore, to prevent the rectifier switch SR from being mis-turned due to the parasitic capacitance Cgd when the power converter 100 is in the startup state immediately after receiving the input voltage Vin, existing methods to prevent mis-turning of the rectifier switch SR are nothing more than adjusting the dead time using a predetermined voltage to lock the rectifier switch SR within the dead time. Alternatively, a current source can be used to charge the energy storage element to lock the rectifier switch SR before the energy storage element is charged to a predetermined voltage. However, the above-mentioned dead time adjustment or current source charging of the energy storage element requires that the synchronous rectifier controller 2 is already operational (or partially operational). Therefore, existing methods to prevent mis-turning of the rectifier switch SR may still result in mis-turning of the rectifier switch SR even if the synchronous rectifier controller 2 is not yet operational.

[0005] Therefore, how to design a synchronous rectifier controller for a power converter and its startup method during the startup phase, so that even when the synchronous rectifier controller 2 is not yet in operation, it can still control the voltage across the gate and source of the rectifier switch to be locked in the off state during the startup state of the power converter, thus avoiding the rectifier switch from being mis-energized due to the influence of parasitic capacitance, is a major research topic that the creators of this project intend to conduct. Summary of the Invention

[0006] To address the aforementioned problems, this invention provides a synchronous rectification controller for power converters, thereby overcoming the limitations of existing technologies.

[0007] Therefore, the synchronous rectification controller of the present invention is coupled to the rectifier switch on the secondary side of the power converter. The rectifier switch includes a rectifier switch control terminal, a first rectifier switch terminal, and a second rectifier switch terminal. The synchronous rectification controller includes a drive signal terminal, a power receiving terminal, a transistor, and a startup control module. The drive signal terminal is coupled to the rectifier switch control terminal, and the power receiving terminal receives the operating voltage. When the operating voltage is higher than the operating voltage threshold, the synchronous rectification controller can output a drive signal through the drive signal terminal. The transistor includes a first transistor terminal, a second transistor terminal, and a transistor control terminal. The first transistor terminal is coupled to the rectifier switch control terminal, and the second transistor terminal is coupled to the second rectifier switch terminal. The startup control module is coupled to the transistor control terminal, and based on the operating voltage being lower than the operating voltage threshold, limits the voltage across the rectifier switch control terminal and the second rectifier switch terminal to be lower than the first threshold voltage of the rectifier switch by the conduction of the transistor.

[0008] When the operating voltage is higher than the operating voltage threshold, the normally closed transistor is turned off.

[0009] The transistor is a P-channel transistor, and the startup control module is a driving circuit. The driving circuit is coupled to the rectifier switch control terminal through the driving signal terminal, and is used to provide the driving signal to drive the rectifier switch to turn on when the operating voltage is higher than the operating voltage threshold.

[0010] Specifically, the transistor is turned on when a control voltage between the first terminal and the control terminal of the transistor is lower than a second threshold voltage of the transistor.

[0011] One end of the driving circuit is coupled to the power receiving end and the transistor control end, so that when the operating voltage is higher than the operating voltage threshold, the operating voltage drives the control voltage to always be higher than the second threshold voltage, thereby turning off the normally closed transistor.

[0012] The first threshold voltage is a rectifier switch critical voltage, and the transistor critical voltage is less than the rectifier switch critical voltage.

[0013] The transistor is an N-channel transistor, and the synchronous rectification controller further includes a drive circuit. The drive circuit is coupled to the rectifier switch control terminal through the drive signal terminal, and is used to provide the drive signal to drive the rectifier switch to turn on when the operating voltage is higher than the operating voltage threshold.

[0014] The startup control module includes a voltage control circuit with an input terminal and an output terminal. The input terminal is coupled to the first terminal of the rectifier switch, and the output terminal is coupled to the control terminal of the transistor. The input terminal receives a drain voltage, and the output terminal provides a control voltage corresponding to the drain voltage. When the operating voltage is lower than the operating voltage threshold, and the control voltage rises to make a control voltage across the control terminal and the second terminal of the transistor higher than a second threshold voltage, the transistor is turned on. When the operating voltage is lower than the operating voltage threshold, and the control voltage drops to make the control voltage across the control terminal lower than the second threshold voltage, the voltage control circuit controls the transistor to turn off.

[0015] The voltage control circuit limits a maximum value and a minimum value of the control voltage, and the maximum value and the minimum value are based on the specifications of the transistor.

[0016] The startup control module includes a potential judgment circuit, one end of which is coupled to the control terminal of the transistor, and the other end of which is coupled to the power receiving terminal. When the potential judgment circuit determines that the operating voltage is higher than the operating voltage threshold, the potential judgment circuit causes the control voltage to drop and controls the control voltage to be lower than the second threshold voltage, so that the normally closed transistor is turned off.

[0017] To address the aforementioned problems, this invention provides a rectifier switch startup method for a power converter during the startup phase, overcoming the limitations of existing technologies. Therefore, the rectifier switch of this invention is coupled to the secondary side of the power converter and includes a rectifier switch control terminal, a first rectifier switch terminal, and a second rectifier switch terminal. The rectifier switch startup method includes the following steps: (a) receiving an operating voltage, and when the operating voltage is lower than an operating voltage threshold, limiting the voltage across the rectifier switch control terminal and the second rectifier switch terminal to be lower than a first threshold voltage of the rectifier switch by turning on a transistor. (b) when the operating voltage is higher than the operating voltage threshold, turning off the normally closed transistor. (c) providing a drive signal through a drive circuit to drive the rectifier switch to turn on.

[0018] Wherein, the transistor is a P-channel transistor, and the rectifier switch start-up method further includes the following steps: when the operating voltage is lower than the operating voltage threshold, and a control voltage across the first terminal and the control terminal of the transistor is lower than a second threshold voltage of the transistor, the transistor is turned on; and when the operating voltage is higher than the operating voltage threshold, the operating voltage drives the control voltage across the transistor to always be higher than the second threshold voltage, thereby causing the normally closed transistor to be turned off.

[0019] Wherein, the transistor is an N-channel transistor, and the rectifier switch startup method further includes the following steps: receiving a drain voltage at a first terminal of the rectifier switch and providing a control voltage corresponding to the drain voltage; when the operating voltage is lower than the operating voltage threshold and the control voltage rises to make a control voltage across the control terminal of the transistor and the second terminal of the transistor higher than a second threshold voltage, controlling the transistor to turn on; and when the operating voltage is lower than the operating voltage threshold and the control voltage drops to make the control voltage across the control voltage lower than the second threshold voltage, controlling the transistor to turn off.

[0020] This includes the following steps: limiting a maximum and a minimum value of the control voltage based on the transistor's specifications.

[0021] The process further includes the following steps: determining whether the operating voltage is higher than the operating voltage threshold; and based on the fact that the operating voltage is higher than the operating voltage threshold, causing the control voltage to decrease and controlling the control voltage to be lower than the second threshold voltage, so as to turn off the normally closed transistor.

[0022] The main objective and effect of this invention is that, based on the operating voltage being lower than the operating voltage threshold, by turning on the transistor to limit the voltage across the rectifier switch control terminal and the second terminal of the rectifier switch to be lower than the first threshold voltage of the rectifier switch, the voltage across the rectifier switch can be locked in the off state during the power converter's startup state, thus avoiding the rectifier switch from being mis-turned due to the influence of parasitic capacitance.

[0023] To gain a deeper understanding of the techniques, means, and effects employed by this invention to achieve its intended purpose, please refer to the following detailed description and accompanying drawings. It is believed that the purpose, features, and characteristics of this invention can be understood in a thorough and specific manner from these drawings. However, the accompanying drawings are provided for reference and illustration only and are not intended to limit the scope of this invention. Attached Figure Description

[0024] Figure 1 The circuit block diagram of an existing power converter;

[0025] Figure 2 This is a circuit block diagram of the power converter with synchronous rectification controller of the present invention;

[0026] Figure 3A This is a circuit block diagram of a first embodiment of the synchronous rectifier controller for a power converter according to the present invention;

[0027] Figure 3B This is a waveform diagram of the first embodiment of the synchronous rectifier controller for a power converter according to the present invention;

[0028] Figure 4A This is a circuit block diagram of a second embodiment of the synchronous rectifier controller for a power converter according to the present invention;

[0029] Figure 4B This is a waveform diagram of a second embodiment of the synchronous rectifier controller for a power converter according to the present invention;

[0030] Figure 5A This is a circuit diagram of a first embodiment of the voltage control circuit of the present invention;

[0031] Figure 5B This is a circuit diagram of a second embodiment of the voltage control circuit of the present invention; and

[0032] Figure 6 This is a flowchart of the rectifier switch startup method for the power converter of this invention during the startup phase.

[0033] In the attached figures, the following labels are used:

[0034] 100… power converter

[0035] 100-1… Primary circuit

[0036] Q…Power Switch

[0037] 1…Main Controller

[0038] 100-2…Secondary circuit

[0039] SR… rectifier switch

[0040] D…Drawing the Extreme

[0041] G…Rectifier switch control terminal, gate

[0042] S…Source

[0043] SR1(D)... First terminal of rectifier switch

[0044] SR2(S)...Second terminal of rectifier switch

[0045] Cgd…parasitic capacitance

[0046] 2…Synchronous Rectifier Controller

[0047] DR…drive signal terminal

[0048] IN…Power receiver

[0049] VDD…Power supply side

[0050] Cs… Energy storage circuit

[0051] M… transistor

[0052] M1(S), M1(D)... First terminal of transistor

[0053] M2(D), M1(S)... the second terminals of transistors

[0054] M3(G)...Transistor control terminal

[0055] 22…Start control module

[0056] 220…Voltage control circuit

[0057] 220-1…Input Terminal

[0058] 220-2… Output terminal

[0059] SW1…First Switch

[0060] ZD… Voltage Regulator

[0061] 222… Potential Detection Circuit

[0062] Cc…comparator

[0063] SW2…Second Switch

[0064] R…resistance

[0065] 24…Driver Circuit

[0066] C…capacitor

[0067] 100-3…Transformer

[0068] 200…load

[0069] Vin…Input Voltage

[0070] Vo…output voltage

[0071] Vdd…working voltage

[0072] Vgs_SR…Transpressure

[0073] Vth_SR…First threshold voltage

[0074] Vgs… controls transpressure

[0075] Vth_M…Second threshold voltage

[0076] Vd_SR…Drain Voltage

[0077] Vc…control voltage

[0078] V_max…maximum value

[0079] V_min…minimum value

[0080] Vref…reference voltage

[0081] S_DR…drive signal

[0082] Waveforms I, II...

[0083] t1~t2…time

[0084] (S100)~(S300)…Steps Detailed Implementation

[0085] The technical content and detailed description of the present invention are explained below with reference to the accompanying drawings:

[0086] Please see Figure 2 This is a circuit block diagram of a power converter with a synchronous rectification controller according to the present invention. The power converter 100 receives an input voltage Vin and is coupled to a load 200. The power converter 100 includes an isolated primary-side circuit 100-1, a secondary-side circuit 100-2, a transformer 100-3, and a main controller 1, with the transformer 100-3 coupled between the primary-side circuit 100-1 and the secondary-side circuit 100-2. The main controller 1 is coupled to a power switch Q of the primary-side circuit 100-1, and the main controller 1 controls the switching of the power switch Q to convert the input voltage Vin, so that the energy converted by the primary-side circuit 100-1 is provided to the secondary-side circuit 100-2 through the transformer 100-3. The power converter 100 further includes a synchronous rectification controller 2, and the secondary-side circuit 100-2 includes a rectifier switch SR.

[0087] A rectifier switch SR is coupled between the transformer 100-3 and the output terminal of the power converter 100, and a synchronous rectifier controller 2 is coupled to the rectifier switch SR. The synchronous rectifier controller 2 synchronously controls the switching of the rectifier switch SR based on the switching of the power switch Q, converting the energy of the transformer 100-3 into an output voltage Vo, which is then supplied by the secondary circuit 100-2 to power the load 200. Specifically, the rectifier switch SR is generally a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and includes a rectifier switch control terminal G, a first rectifier switch terminal SR1, and a second rectifier switch terminal SR2. These three terminals can correspond to the gate, drain, and source, respectively. The synchronous rectifier controller 2 includes a drive signal terminal DR, a power receiving terminal IN, a power supply terminal VDD, and an energy storage circuit Cs, with the drive signal terminal DR coupled to the rectifier switch control terminal G.

[0088] The power receiving terminal IN is coupled to the output terminal of the power converter 100 and receives the output voltage Vo. The energy storage circuit Cs is coupled to the power receiving terminal IN and the power supply terminal VDD, and converts the output voltage Vo into the operating voltage Vdd. The power supply terminal VDD is coupled to the energy storage circuit Cs and the capacitor C, and the capacitor C stores the operating voltage Vdd to provide the operating voltage Vdd required for the operation of the synchronous rectifier controller 2. The energy storage circuit Cs can be, for example, but not limited to, a low-dropout regulator (LDO). Furthermore, the configuration of the power receiving terminal IN and the energy storage circuit Cs is solely for charging the capacitor C to establish the operating voltage Vdd. Therefore, it is not intended to... Figure 2 The scope of this embodiment is limited to the circuit architecture (shown by dashed lines). Any circuit configuration that can charge capacitor C to establish the operating voltage Vdd should be included in the scope of this embodiment.

[0089] When the power converter 100 does not receive the input voltage Vin, the operating voltage Vdd required for the synchronous rectifier controller 2 to operate has not been established, and the power converter 100 has not yet started operating. During the instant the power converter 100 begins to receive the input voltage Vin, the energy storage elements within the power converter 100 begin to store energy, causing the voltage of the energy storage elements to rise (e.g., from 0V to 12V). However, at this instant, the voltage of each energy storage element is still gradually rising, and a stable operating voltage Vdd has not yet been established. Therefore, the power supply terminal VDD of the synchronous rectifier controller 2 has not yet received a sufficiently high operating voltage Vdd and cannot operate normally, but the input voltage Vin has been supplied to the primary side circuit 100-1, and some energy can also be coupled to the secondary side circuit 100-2 through the transformer 100-3. Therefore, this instant is also called the startup state of the power converter 100. Once all energy storage components have established a stable and normal operating voltage Vdd, the main controller 1 and the synchronous rectifier controller 2 can be fully driven. The main controller 1 and the synchronous rectifier controller 2 can then control the power converter 100 to convert the input voltage Vin into the output voltage Vo. Therefore, this steady state is also referred to as the normal operating state of the power converter 100.

[0090] Similarly, when the power converter 100 is in the startup state, although the operating voltage Vdd gradually increases, it is lower than the operating voltage threshold set by the synchronous rectifier controller 2. Therefore, the synchronous rectifier controller 2 is not fully driven and cannot operate normally. Conversely, when the power converter 100 is in the normal operating state, the operating voltage Vdd is higher than the operating voltage threshold. Therefore, the synchronous rectifier controller 2 can be fully driven, and the drive signal S_DR can be output from the drive signal terminal DR to the rectifier switch control terminal G to control the rectifier switch SR to turn on. Preferably, the operating voltage threshold can be set at the undervoltage protection (UVP) point of the synchronous rectifier controller 2. This is because the synchronous rectifier controller 2 can usually operate normally when the operating voltage Vdd is higher than the undervoltage protection (UVP) point. Conversely, the synchronous rectifier controller 2 usually enters the undervoltage protection (UVP) protection program when the operating voltage Vdd is lower than the undervoltage protection (UVP) point. However, this is not the limitation; it can be set, for example but not limited to, above the undervoltage protection (UVP) point, so that the synchronous rectifier controller 2 has the ability of dual protection.

[0091] Therefore, to avoid the aforementioned situation, the main feature and effect of this invention is that the synchronous rectification controller 2 further includes a transistor M and a startup control module 22. The transistor M includes a first transistor terminal M1, a second transistor terminal M2, and a control transistor terminal M3. The first transistor terminal M1 is coupled to the rectifier switch control terminal G, and the second transistor terminal M2 is coupled to the second rectifier switch terminal SR2 (source S). The startup control module 22 is coupled to the transistor control terminal M3 and the power supply terminal VDD. Based on the fact that the operating voltage Vdd is lower than the operating voltage threshold, the transistor M is turned on to limit the voltage across the rectifier switch control terminal G and the second rectifier switch terminal SR2, Vgs_SR, to be lower than the first threshold voltage Vth_SR of the rectifier switch SR (i.e., the critical voltage Vth of the rectifier switch SR). In this way, the voltage across the rectifier switch SR, Vgs_SR, will not exceed the first threshold voltage Vth_SR during the startup state of the power converter 100, thus locking it in the off state and preventing the rectifier switch SR from being mis-turned due to the parasitic capacitance Cgd. Conversely, when the power converter 100 is in normal operation, the operating voltage Vdd is higher than the operating voltage threshold. Therefore, the synchronous rectification controller 2 turns off the normally closed transistor M to prevent the transistor M from being mistakenly turned on, which could cause the rectifier switch SR to be incorrectly turned on / off. Simultaneously, the synchronous rectification controller 2 can typically provide a drive signal S_DR based on the voltage difference between the first terminal SR1 and the second terminal SR2 of the rectifier switch SR to selectively turn on the rectifier switch SR, thereby synchronously controlling the switching of the rectifier switch SR.

[0092] Please see Figure 3A This is a circuit block diagram of the first embodiment of the synchronous rectification controller for a power converter according to the present invention. Figure 3B This is a waveform diagram of the first embodiment of the synchronous rectification controller for a power converter according to the present invention, and can be further referenced. Figure 2 And consulted repeatedly Figures 3A-3B .exist Figure 3A In this circuit, transistor M is a P-type channel transistor, and the startup control module 22 is the drive circuit 24 that provides the drive signal S_DR. The first terminal M1 (source S) of the transistor is coupled to the rectifier switch control terminal G, and the second terminal M2 (drain D) of the transistor is coupled to the second terminal SR2 (source S) of the rectifier switch. The drive circuit 24 is coupled to the rectifier switch control terminal G through the drive signal terminal DR, and one end of the drive circuit 24 is coupled to the power supply terminal VDD and the transistor control terminal M3 (gate G). When the operating voltage Vdd is lower than the operating voltage threshold, the drive circuit 24 cannot provide the drive signal S_DR to drive the rectifier switch SR to conduct. Conversely, when the operating voltage Vdd is higher than the operating voltage threshold, the drive circuit 24 can provide the drive signal S_DR to drive the rectifier switch SR to conduct.

[0093] On the other hand, when the operating voltage Vdd is lower than the operating voltage threshold, transistor M turns on / off automatically based on the voltage difference between its terminals. When part of the energy of the input voltage Vin is coupled to the secondary circuit 100-2, causing the voltage at the first terminal SR1(D) of the rectifier switch to rise, and the voltage at the control terminal G of the rectifier switch rises through the parasitic capacitance Cgd of the rectifier switch SR, the voltage at the first terminal M1 (source S) of the transistor rises. When the control voltage Vgs (i.e., Vg-Vs) between the control terminal M3 (gate G) of the transistor and the first terminal M1 (source S) of the transistor is lower than the second threshold voltage Vth_M (i.e., the critical voltage Vth of the P-type channel transistor M), transistor M turns on, causing the control terminal G of the rectifier switch to be bypassed to the second terminal SR2 (source S) of the rectifier switch. This causes the voltage at the control terminal G of the rectifier switch to drop, thus preventing the voltage across the control terminal G of the rectifier switch and the second terminal SR2(S) of the rectifier switch from being incorrectly higher than the first threshold voltage Vth_SR of the rectifier switch SR, which would cause the rectifier switch SR to mis-turn on.

[0094] exist Figure 3B The diagram shows the voltage Vgs_SR between the rectifier switch control terminal G and the second terminal SR2(S). The dashed waveform I represents the voltage Vgs_SR of the rectifier switch before the start-up control module 22 is added, when the rectifier switch control terminal G is affected by the parasitic capacitance Cgd, potentially causing the rectifier switch SR to mis-turn on. The solid waveform II represents the voltage Vgs_SR of the rectifier switch before the start-up control module 22 is added. Figure 3A After the start control module 22 is activated, the waveform of the rectifier switch control terminal G is as follows. Time t1 to t2 is when the operating voltage Vdd has not yet been established, and the voltage across the rectifier switch SR is affected by the operation of the primary circuit 100-1 (e.g., but not limited to the on / off state of power switch Q), and rises due to the coupling of some energy from transformer 100-3. To avoid the rectifier switch SR turning on when the control voltage across transistor M Vgs is not yet lower than the second threshold voltage Vth_M of transistor M, the second threshold voltage Vth_M (absolute value) of transistor M must be less than the first threshold voltage Vth_SR of rectifier switch SR. Figure 3B During time t1, the difference between the second threshold voltage Vth_M (absolute value) and the first threshold voltage Vth_SR can prevent the rectifier switch SR from turning on first.

[0095] For example, the second threshold voltage Vth_M of the P-type channel transistor M can be selected as -2V, and the first threshold voltage Vth_SR of the rectifier switch SR can be selected as 3V. When the operating voltage Vdd and the second terminal SR2(S) of the rectifier switch are both 0V, and the voltage at the control terminal G of the rectifier switch rises to 2.2V as the voltage at the first terminal SR1(D) of the rectifier switch rises: the control voltage Vgs_M of the P-type channel transistor M is -2.2V, which is already lower than -2V, causing the P-type channel transistor M to conduct; thus, the control voltage Vgs_SR of the rectifier switch SR will only rise to a maximum of 2.2V, and will gradually decrease as the P-type channel transistor M conducts, remaining below 3V throughout, thus keeping the rectifier switch SR off.

[0096] On the other hand, since transistor M is a P-type channel transistor, when the operating voltage Vdd is lower than the operating voltage threshold, for example, close to 0V, and transistor M is on for the time t1 to t2, although transistor M remains on, causing the control voltage Vgs_SR of the rectifier switch SR to decrease, when the voltage at the rectifier switch control terminal G, i.e., the voltage at the source S of the first terminal M1 of the P-type channel transistor M, approaches 0V at the drain D of the second terminal M2 of transistor M, causing the control voltage Vgs_M of the P-type channel transistor M to no longer be lower than the second threshold voltage Vth_M, for example, rising from -2.2V to -2V, the P-type channel transistor M will turn off, and it will be unable to further reduce the voltage at the rectifier switch control terminal G. Therefore, although the voltage at the rectifier switch control terminal G will decrease between time t1 and t2, it will not decrease to 0, but will decrease to the minimum voltage level that keeps the control voltage Vgs_M of the P-type channel transistor M below the second threshold voltage Vth_M.

[0097] When the power converter 100 is in normal operation, it means that the operating voltage Vdd is higher than the operating voltage threshold. When the operating voltage Vdd is higher than the operating voltage threshold, it means that the control voltage Vgs of the P-type channel transistor M is always higher than the second threshold voltage Vth_M. Therefore, when the power converter 100 is in normal operation, the P-type channel transistor M is naturally and uncontrolled to be normally closed and turned off.

[0098] Specifically, since one end of the driving circuit 24 is coupled to the power supply terminal VDD and the transistor control terminal M3, the voltage at the transistor control terminal M3 will gradually rise to the steady-state value of the operating voltage Vdd (i.e., the voltage value after setup). Thus, as long as the driving signal S_DR provided by the driving circuit 24 is less than the operating voltage Vdd plus the second threshold voltage Vth_M, the control voltage Vgs of the P-type channel transistor M will always be lower than the second threshold voltage Vth_M, thereby preventing the transistor M from turning on.

[0099] Please see Figure 4AThis is a circuit block diagram of the second embodiment of the synchronous rectification controller for a power converter according to the present invention. Figure 4B This is a waveform diagram of a second embodiment of the synchronous rectification controller for a power converter according to the present invention, with reference to other diagrams. Figures 2-3B And consulted repeatedly Figures 4A-4B .exist Figure 4A In this circuit, transistor M is an N-type channel transistor, and the driving circuit 24 is located outside the startup control module 22. The first terminal M1 (drain D) of the transistor is coupled to the rectifier switch control terminal G, and the second terminal M2 (source S) of the transistor is coupled to the second terminal SR2 (source S) of the rectifier switch. When the operating voltage Vdd is higher than the operating voltage threshold, the driving circuit 24 can output a driving signal S_DR to the rectifier switch control terminal G to selectively drive the rectifier switch SR to conduct. When the operating voltage Vdd is lower than the operating voltage threshold, the driving circuit 24 cannot output the driving signal S_DR to drive the rectifier switch SR to conduct.

[0100] The start-up control module 22 includes a voltage control circuit 220 and a potential judgment circuit 222. The voltage control circuit 220 includes an input terminal 220-1 and an output terminal 220-2. The input terminal 220-1 is coupled to the first terminal SR1 (drain D) of the rectifier switch, and the output terminal is coupled to the transistor control terminal M3 (gate G). One end of the potential judgment circuit 222 is coupled to the transistor control terminal M3 (gate G), and the other end of the potential judgment circuit 222 is coupled to the power supply terminal VDD.

[0101] The voltage control circuit 220 receives the drain voltage Vd_SR from input terminal 220-1 and provides a control voltage Vc corresponding to the drain voltage Vd_SR at its output terminal. The magnitude of the control voltage Vc is the same as or positively correlated with the drain voltage Vd_SR. Furthermore, the voltage control circuit 220 limits the maximum value V_max and the minimum value V_min of the control voltage Vc to prevent excessively high / low voltage surges that could damage the transistor M. Therefore, the default maximum and minimum values ​​V_max and V_min of the voltage control circuit 220 are based on the specifications of the transistor M.

[0102] When the operating voltage Vdd is lower than the operating voltage threshold, and part of the energy of the input voltage Vin is coupled to the secondary circuit 100-2, causing the voltage at the first terminal SR1 (drain D) of the rectifier switch to rise, the voltage at the control terminal G of the rectifier switch will rise accordingly through the parasitic capacitance Cgd of the rectifier switch SR. The voltage control circuit 220 receives the drain voltage Vd_SR from the input terminal 220-1 and provides a control voltage Vc, which is positively correlated with the drain voltage Vd_SR, to the control terminal M3 (gate G) of the transistor at the output terminal. Therefore, the control voltage Vc also shows an upward voltage waveform. When the rise of the control voltage Vc causes the control voltage Vgs (i.e., Vg-Vs) between the control terminal M3 (gate G) and the second terminal M2 (source S) of the transistor to be higher than the second threshold voltage Vth_M (i.e., the critical voltage Vth of the N-type channel transistor M), the transistor M turns on, causing the control terminal G of the rectifier switch to be bypassed to the grounded second terminal SR2 (source S) of the rectifier switch. This causes the voltage at the rectifier switch control terminal G to drop, preventing the rectifier switch SR from malfunctioning and turning on due to the voltage at G exceeding the first threshold voltage Vth_SR. When the control voltage Vc drops, causing the control voltage Vgs (i.e., Vg-Vs) between the transistor control terminal M3 (gate G) and the transistor's second terminal M2 (source S) to fall below the second threshold voltage Vth_M (i.e., the critical voltage Vth of the N-type channel transistor M), transistor M turns off, making the path between the rectifier switch control terminal G and the rectifier switch's second terminal SR2 (source S) an open circuit.

[0103] Since the control voltage Vc of the transistor control terminal M3 (gate G) is positively correlated with the drain voltage Vd_SR, when the power converter 100 is in the startup state, the energy transmitted from the transformer 100-3 to the first terminal SR1 (drain D) of the rectifier switch, combined with the effect of the parasitic capacitance of the rectifier switch SR, may cause a surge in the drain voltage Vd_SR (e.g., Figure 4B The voltage control circuit 220 can prevent transistor M from being damaged by excessively high positive voltage surges by limiting the maximum value V_max of the control voltage Vc (e.g., but not limited to, time t1). Similarly, the voltage control circuit 220 can prevent transistor M from being damaged by excessively low negative voltage surges by limiting the minimum value V_min of the control voltage Vc (e.g., but not limited to, time t2).

[0104] exist Figure 4B The image shows the voltage Vgs_SR between the rectifier switch control terminal G and the second terminal SR2(S). The dashed waveform I represents the voltage Vgs_SR waveform before the start-up control module 22 is added, where the rectifier switch control terminal G is affected by the parasitic capacitance Cgd, potentially causing the rectifier switch SR to mis-turn on. The solid waveform II represents the voltage Vgs_SR waveform after the start-up control module 22 is added. Figure 4A After the start-up control module 22, the waveform of the rectifier switch control terminal G is as follows. During time t1 to t2, the operating voltage Vdd has not yet been established, and the voltage across the rectifier switch SR, Vgs_SR, is affected by the operation of the primary side circuit 100-1 (e.g., but not limited to the on / off state of the power switch Q), and rises due to the coupling of some energy from the transformer 100-3. Since transistor M is an N-channel transistor, when the power converter 100 is in the start-up state, the potential point in the entire secondary side circuit 100-2 may be at the first terminal SR1 (drain D) of the rectifier switch, and the potential at the grounded second terminal SR2 (source S) of the rectifier switch is 0.

[0105] With a drain voltage Vd_SR, the voltage control circuit 220 outputs a control voltage Vc to the transistor control terminal M3 (gate G), and the potential of the transistor's second terminal M2 (source S) is 0. Thus, when the operating voltage Vdd is below the operating voltage threshold and transistor M is turned on, the rectifier switch control terminal G is coupled to the transistor's first terminal M1 (drain D). Even if the voltage at the rectifier switch control terminal G drops to 0V, it will not affect the control voltage Vgs of the N-channel transistor M, and transistor M will continue to conduct. Therefore, compared to... Figures 3A-3B , Figures 4A-4B The N-channel transistor can remain on after transistor M is turned on until the voltage at the rectifier switch control terminal G drops to 0 (e.g., ...). Figure 4B (After time t1 in the middle).

[0106] When the power converter 100 is in normal operation, the operating voltage Vdd is higher than the operating voltage threshold. When Vdd is higher than the operating voltage threshold, the potential judgment circuit 222 determines that Vdd is above the threshold. When the potential judgment circuit 222 determines that Vdd is higher than the threshold, it lowers the voltage at the control terminal G of transistor M, so that the control voltage Vgs of transistor M is lower than the second threshold voltage Vth_M (i.e., the critical voltage Vth of the N-type channel transistor M), thus turning off the normally closed transistor M. This is to prevent transistor M from being mistakenly turned on, which could cause the rectifier switch SR to be incorrectly turned on / off.

[0107] The voltage control circuit in the second embodiment of the synchronous rectifier controller of the present invention basically provides waveform tracking and voltage control functions. Please refer to [link / reference needed]. Figure 5A This is a circuit diagram of the first embodiment of the voltage control circuit of the present invention. Figure 5B This is a circuit diagram of a second embodiment of the voltage control circuit of the present invention, which can be further referenced. Figures 2-4B .exist Figure 5AIn the circuit, voltage control circuit 220 includes a first switch SW1 and a voltage regulator ZD. When the first terminal SR1 (drain D) of the rectifier switch has a drain voltage Vd_SR, the drain voltage Vd_SR is partially coupled to the output terminal 220-2 through the first switch SW1. This allows the voltage control circuit 220 to provide a control voltage Vc from the output terminal 220-2, whose waveform changes follow the drain voltage Vd_SR but has a smaller voltage variation range, to the transistor control terminal M3 (gate G). Because the drain voltage Vd_SR may vary significantly, the voltage regulator ZD clamps and limits the maximum value V_max and the minimum value V_min of the control voltage Vc to prevent the control voltage Vc from exceeding the input voltage range that the gate of the transistor control terminal G can withstand. The connection relationship between the first switch SW1 and the voltage regulator ZD is as follows: Figure 5A As shown, it will not be elaborated further here.

[0108] The potential judgment circuit 222 includes a comparator Cc and a second switch SW2. The comparator Cc compares the operating voltage Vdd with the reference voltage Vref, and controls the second switch SW2 to turn on / off based on the comparison result. Therefore, the transistor control terminal M3 (gate G) can be grounded through the conduction of the second switch SW2, thereby causing the control voltage Vc to decrease. The connection relationship between the comparator Cc and the second switch SW2 is as follows... Figure 5A As shown, it will not be elaborated further here.

[0109] Figure 5B and Figure 5A The main difference in voltage control circuit 220 is that... Figure 5A The first switch SW1 is an N-channel transistor. Figure 5B The second switch SW2 is a P-channel transistor. Therefore, the circuit connection depends on the type of switch SW, but the main principles are the same, and will not be elaborated further here. On the other hand, Figure 5B and Figure 5A The main difference in the potential judgment circuit 222 is the addition of a resistor R to limit the current flowing through the second switch SW2 when it is turned on. It is worth noting that in one embodiment of the present invention, the voltage control circuit 220 and the potential judgment circuit 222 are only two examples of numerous circuit implementations. Therefore, any electronic circuit, logic circuit, or software-controlled controller that achieves the operation and function of the voltage control circuit 220 and the potential judgment circuit 222 of this embodiment should be included within the scope of this embodiment.

[0110] Please see Figure 6 This is a flowchart of the rectifier switch startup method for the power converter of this invention during the startup phase. Please refer to the attached diagram for further details. Figures 2-5BThe startup method of the rectifier switch SR in the power converter 100 during the startup phase is mainly to prevent the rectifier switch SR from being mis-turned due to the parasitic capacitance Cgd when some energy from the primary circuit 100-1 is coupled to the secondary circuit 100-2 through the transformer 100-3. Therefore, the startup method of the rectifier switch SR includes receiving the operating voltage, and when the operating voltage is lower than the operating voltage threshold, limiting the voltage across the rectifier switch control terminal and the second terminal of the rectifier switch to be lower than the first threshold voltage of the rectifier switch by turning on the transistor (S100). In a preferred embodiment, the startup control module 22, based on the operating voltage Vdd being lower than the operating voltage threshold, limits the voltage across the rectifier switch control terminal G and the second terminal SR2 of the rectifier switch to be lower than the first threshold voltage Vth_SR of the rectifier switch SR (i.e., the critical voltage Vth of the rectifier switch SR) by turning on the transistor M. In this way, the voltage across the rectifier switch SR, Vgs_SR, will not exceed the first threshold voltage Vth_SR during the startup state of the power converter 100, and will be locked in the off state, thus avoiding the rectifier switch SR from being mis-turned due to the influence of parasitic capacitance Cgd.

[0111] Then, when the operating voltage is higher than the operating voltage threshold, the normally closed transistor is turned off (S200). A preferred embodiment utilizes the startup control module 22 to turn off the normally closed transistor M when the operating voltage Vdd is higher than the operating voltage threshold, to prevent the transistor M from being mis-turned on, causing the rectifier switch SR to be erroneously turned on / off. Finally, a drive signal is provided by the drive circuit to drive the rectifier switch to turn on (S300). A preferred embodiment utilizes the synchronous rectification controller 2 to provide a drive signal S_DR to turn on the rectifier switch SR when the operating voltage Vdd is higher than the operating voltage threshold, based on the switching of the power switch Q, to synchronously control the switching of the rectifier switch SR. It is worth mentioning that, in one embodiment of the present invention, the detailed process steps of the rectifier switch SR startup method of the power converter 100 during the startup phase can be referred to in conjunction with... Figures 3A-5A The details will not be elaborated here.

[0112] However, the above description is only a detailed description and drawings of preferred embodiments of the present invention. The features of the present invention are not limited thereto and are not intended to limit the present invention. The scope of the present invention should be determined by the following claims. All embodiments that are in line with the spirit of the claims and similar variations thereof should be included in the scope of the present invention. Any variations or modifications that can be easily conceived by those skilled in the art within the field of the present invention can be covered by the following patent scope.

[0113] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A synchronous rectification controller for a power converter, characterized in that, The synchronous rectification controller is coupled to a rectifier switch on the primary and secondary sides of the power converter. The rectifier switch includes a rectifier switch control terminal, a rectifier switch first terminal, and a rectifier switch second terminal. The synchronous rectification controller includes: One drive signal terminal is coupled to the control terminal of the rectifier switch; A power receiving terminal receives a working voltage, and when the working voltage is higher than a working voltage threshold, the synchronous rectifier controller can output a drive signal through the drive signal terminal. A transistor includes a first terminal, a second terminal, and a control terminal, wherein the first terminal is coupled to the control terminal of the rectifier switch, and the second terminal is coupled to the second terminal of the rectifier switch; and A startup control module is coupled to the control terminal of the transistor, and based on the operating voltage being lower than the operating voltage threshold, limits a voltage across the rectifier switch control terminal and the second terminal of the rectifier switch to be lower than a first threshold voltage of the rectifier switch by turning on the transistor, and the startup control module includes: A voltage control circuit includes an input terminal and an output terminal, the input terminal being coupled to the first terminal of the rectifier switch, and the output terminal being coupled to the control terminal of the transistor; The input terminal receives a drain voltage from the first terminal of the rectifier switch, and the output terminal provides a control voltage corresponding to the drain voltage. The magnitude of the control voltage is the same as or positively correlated with the drain voltage. When the operating voltage is lower than the operating voltage threshold, and the control voltage rises to make the control voltage across the transistor control terminal and the second terminal of the transistor higher than a second threshold voltage, the transistor is turned on. When the operating voltage is lower than the operating voltage threshold, and the control voltage drops to make the control voltage across the transistor lower than the second threshold voltage, the voltage control circuit controls the transistor to turn off.

2. The synchronous rectifier controller according to claim 1, characterized in that, When the operating voltage is higher than the operating voltage threshold, the normally closed transistor is turned off.

3. The synchronous rectification controller according to claim 1, characterized in that, The transistor is a P-channel transistor, and the startup control module is a driving circuit. The driving circuit is coupled to the rectifier switch control terminal through the driving signal terminal, and is used to provide the driving signal to drive the rectifier switch to turn on when the operating voltage is higher than the operating voltage threshold.

4. The synchronous rectification controller according to claim 3, characterized in that, The transistor turns on when a control voltage between the first terminal and the control terminal of the transistor is lower than a second threshold voltage of the transistor.

5. The synchronous rectification controller according to claim 4, characterized in that, One end of the driving circuit is coupled to the power receiving terminal and the transistor control terminal, so that when the operating voltage is higher than the operating voltage threshold, the operating voltage drives the control voltage to always be higher than the second threshold voltage, thereby turning off the normally closed transistor.

6. The synchronous rectification controller according to claim 5, characterized in that, The first threshold voltage is a rectifier switch critical voltage, and the transistor critical voltage is less than the rectifier switch critical voltage.

7. The synchronous rectifier controller according to claim 1, characterized in that, The transistor is an N-channel transistor, and the synchronous rectification controller further includes a drive circuit; the drive circuit is coupled to the rectifier switch control terminal through the drive signal terminal, and is used to provide the drive signal to drive the rectifier switch to turn on when the operating voltage is higher than the operating voltage threshold.

8. The synchronous rectifier controller according to claim 1, characterized in that, The voltage control circuit limits a maximum value and a minimum value of the control voltage, and the maximum value and the minimum value are based on the specifications of the transistor.

9. The synchronous rectification controller according to claim 7, characterized in that, The startup control module includes: A potential determination circuit, one end of which is coupled to the control terminal of the transistor, and the other end of which is coupled to the power receiving terminal; Specifically, when the potential judgment circuit determines that the working voltage is higher than the working voltage threshold, the potential judgment circuit causes the control voltage to drop and controls the control voltage to be lower than the second threshold voltage, so that the normally closed transistor is turned off.

10. A rectifier switch startup method for a power converter during the startup phase, characterized in that, The rectifier switch is coupled to the primary and secondary sides of the power converter and includes a rectifier switch control terminal, a rectifier switch first terminal, and a rectifier switch second terminal. The rectifier switch start-up method includes the following steps: The rectifier receives an operating voltage, and when the operating voltage is lower than an operating voltage threshold, it limits a voltage across the rectifier control terminal and the second terminal of the rectifier to be lower than a first threshold voltage of the rectifier by turning on a transistor. When the operating voltage is higher than a certain operating voltage threshold, the normally closed transistor is turned off. A driving signal is provided by a driving circuit to drive the rectifier switch to turn on. The rectifier receives a drain voltage at the first terminal of the rectifier switch and provides a control voltage corresponding to the drain voltage, the magnitude of which is the same as or positively correlated with the drain voltage. When the operating voltage is lower than the operating voltage threshold, and the control voltage rises to make a control voltage across the control terminal of the transistor and the second terminal of the transistor higher than a second threshold voltage, the transistor is controlled to turn on; and When the operating voltage is lower than the operating voltage threshold, and the control voltage drops so that the control voltage drops below the second threshold voltage, the transistor is controlled to turn off. This transistor is an N-channel transistor.

11. The rectifier switch starting method according to claim 10, characterized in that, The transistor is a P-channel transistor, and the rectifier switch startup method further includes the following steps: When the operating voltage is lower than the operating voltage threshold, and the control voltage between the first terminal and the control terminal of the transistor is lower than a second threshold voltage of the transistor, the transistor is turned on; and When the operating voltage is higher than the operating voltage threshold, the operating voltage drives the control voltage to always be higher than the second threshold voltage, thereby turning off the normally closed transistor.

12. The rectifier switch starting method according to claim 10, characterized in that, It also includes the following steps: The control voltage has a maximum and a minimum value based on the transistor's specifications.

13. The rectifier switch starting method according to claim 10, characterized in that, It also includes the following steps: Determine whether the operating voltage is higher than the operating voltage threshold; and Based on the fact that the operating voltage is higher than the operating voltage threshold, the control voltage is reduced to control the control voltage to be lower than the second threshold voltage, so that the normally closed transistor is turned off.

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