LLC converter and associated control method

Abstract

The invention provides an LLC converter and a related control method. The LLC converter comprises a square wave generator, an LLC resonance circuit, a first synchronous rectification switch, an operation power supply capacitor and a synchronous rectification controller. The square wave generator comprises two power switches which are connected between an input power line and an input grounding line and provide square wave input at an input end. The LLC resonant circuit is connected to the input end and comprises a primary side winding of a transformer and a resonant capacitor which are connected in series. The transformer includes a first secondary side winding. The first synchronous rectification switch is provided with a first detection end. The first synchronous rectification switch is connected with the first secondary side winding and the output ground wire. The first secondary side winding is connected between the first detection end and the output power line. The operation power capacitor is used for providing operation power. The synchronous rectification controller controls the first synchronous rectification switch according to the first detection voltage of the first detection end. The synchronous rectification controller is provided with a power supply controller, and the power supply controller is configured to draw current from the first detection end so as to establish an operation power supply for supplying power to the synchronous rectification controller.

Description

Technical Field

[0001] This invention relates generally to synchronous rectification of LLC converters, and more particularly to the establishment of the operating power supply for the synchronous rectification controller in an LLC converter. Background Technology

[0002] LLC converters are a type of resonant converter, which typically offers a smooth output waveform, high conversion efficiency, and high output power. Generally, a resonant converter converts a DC input power supply into a sinusoidal signal. This conversion is achieved through a switch network architecture, providing a square-wave voltage to a resonant tank. After filtering by the resonant tank, the fundamental frequency of the square-wave voltage is roughly retained, thus approximating a sinusoidal input current. Due to the inductive effect, an alternating current is generated on the secondary side of the LLC converter, which, after rectification, can be used to establish the output power supply.

[0003] LLC converters are generally used for high-current output. To improve conversion efficiency, synchronous rectification can be used on the secondary side of the LLC converter. This involves replacing the traditional rectifier diode with a synchronous rectifier switch and a synchronous rectifier controller. This reduces or eliminates the high power consumption caused by the approximately fixed forward bias of the rectifier diode when conducting high currents.

[0004] Although synchronous rectification may increase conversion efficiency, it may also introduce other problems that require special handling. Summary of the Invention

[0005] This invention provides an LLC converter comprising a square wave generator, an LLC resonant circuit, a first synchronous rectifier switch, an operating power supply capacitor, and a synchronous rectifier controller. The square wave generator includes at least two power switches connected between an input power line and an input ground line to provide a square wave input at an input terminal. The LLC resonant circuit is connected to the input terminal and includes a primary winding of a transformer connected in series and a resonant capacitor. The transformer includes a primary winding. The first synchronous rectifier switch has a first detection terminal. The first synchronous rectifier switch can be connected to the primary winding and an output ground line. The primary winding is connected between the first detection terminal and an output power line. The operating power supply capacitor provides an operating power supply. The synchronous rectifier controller controls the first synchronous rectifier switch based on a first detected voltage at the first detection terminal. The synchronous rectifier controller includes a power controller architecture configured to draw current from the first detection terminal to establish the operating power supply and power the synchronous rectifier controller.

[0006] This invention provides a control method for an LLC converter, comprising: providing a square wave voltage to an input terminal of a resonant circuit, wherein the resonant circuit is connected between the input terminal and a power supply line, and includes a primary winding of a transformer connected in series and a resonant capacitor, the transformer including a primary winding; providing a first synchronous rectifier switch and a synchronous rectifier controller, wherein the first synchronous rectifier switch is connected between a first detection terminal and an output ground line and is controlled by the synchronous rectifier controller, the primary winding being connected between the first detection terminal and the output power supply line; and drawing current from the first detection terminal, passing it through the synchronous rectifier controller, charging an operating power supply capacitor to establish an operating power supply, and supplying power to the synchronous rectifier controller. Attached Figure Description

[0007] Figure 1 Display an LLC converter.

[0008] Figure 2 show Figure 1 The square wave signal V at the endpoint SW SW Control signal S G1 Detection voltage V DT1 Inductor current I LS1 Control signal S G2 Detection voltage V DT2 and inductor current I LS2 The signal waveform.

[0009] Figure 3 An example is shown in the illustration of a synchronous rectifier switch.

[0010] Figure 4 This illustrates an LLC converter implemented according to the present invention.

[0011] Figure 5 This invention demonstrates a synchronous rectifier controller according to the present invention.

[0012] [Symbol Explanation]

[0013] 100, 200 LLC converter

[0014] 102 load

[0015] 104, 204, 304 Synchronous Rectifier Controller

[0016] 205 Power Controller

[0017] 206 Linear Regulator

[0018] BVD1 and BVD2 bias detectors

[0019] CGD1 drain gate capacitance

[0020] CI Input Capacitor

[0021] CO output capacitor

[0022] CR resonant capacitor

[0023] CVCC operating power supply capacitor

[0024] D1 and D2 rectifier diodes

[0025] DB1 body diode

[0026] DP rectifier diode

[0027] DR1 and DR2 drive circuits

[0028] DT1 and DT2 detection terminals

[0029] G1, G2 control terminals

[0030] GNDI input ground wire

[0031] GNDO output ground wire

[0032] HI Upper Arm Control Signal

[0033] HS upper arm switch

[0034] I LS1 I LS Inductor current

[0035] IN Input power line

[0036] I R Alternating current

[0037] LO lower arm control signal

[0038] LP primary winding

[0039] LR resonant inductor

[0040] LS lower arm switch

[0041] LS1 and LS2 secondary windings

[0042] OUT output power line

[0043] S G1 S G2 control signals

[0044] SR1 and SR2 synchronous rectifier switches

[0045] SW input endpoint

[0046] Time points t11, t12, and t13

[0047] TF Transformer

[0048] TNK LLC resonant circuit

[0049] V CC Operating power supply

[0050] V DT1 V DT2 Detection voltage

[0051] V IN Input power

[0052] V OUT Output power

[0053] V SW Square wave signal Detailed Implementation

[0054] 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.

[0055] Figure 1 To illustrate the LLC converter 100, it is used to convert the input power supply V located on the primary side. IN Converted to output power V located on the secondary side OUT The LLC converter 100 employs synchronous rectification, using two synchronous rectifier switches SR1 and SR2 to rectify the inductor current I output from the two secondary windings LS1 and LS2, respectively. LS1 with ILS .

[0056] On the primary side, the upper arm switch HS and the lower arm switch LS are connected in series between the input power line IN and the input ground line GNDI via the input terminal SW, forming a half-bridge structure, which can be regarded as a square wave generator. The input capacitor CI acts as a filter capacitor, connected between the input power line IN and the input ground line GNDI, which can stabilize the input power supply V. IN The voltage. The upper arm switch HS and the lower arm switch LS are controlled by the upper arm control signal HI and the lower arm control signal LO, respectively.

[0057] The resonant inductor LR, the primary winding LP of the transformer TF, and the resonant capacitor CR are connected in series between the input terminal SW and the input ground line GNDI, forming an LLC resonant tank TNK. In one embodiment, the resonant inductor LR may not be an independent component, but rather a leakage inductance in the primary winding LP that is not inductively coupled to the secondary windings LS1 and LS2.

[0058] The upper arm switch HS and the lower arm switch LS are alternately turned on, providing a square wave voltage to the input terminal SW of the resonant circuit, causing the LLC resonant circuit TNK to resonate. An alternating current I is generated across the resonant inductor LR. R Through the inductive coupling of transformer TF, corresponding inductive currents I will also be generated in the secondary windings LS1 and LS2. LS1 with I LS2 The secondary-side synchronous rectifier switches SR1 and SR2 provide full-wave rectification. Synchronous rectifier switch SR1 is connected between the output ground line GNDO and the sensing terminal DT1, while synchronous rectifier switch SR2 is connected between the output ground line GNDO and the sensing terminal DT2. The output capacitor CO provides low-pass filtering, generating the output power V across the output power line OUT and the output ground line GNDO. OUT It is used to supply power to load 102.

[0059] exist Figure 1 In the middle, the output power supply V OUT It also serves as the operating power supply V for the synchronous rectifier controller 104. CC This supplies the electrical energy required for the operation of the synchronous rectifier controller 104. The synchronous rectifier controller 104 operates based on the detected voltage V on the detection terminals DT1 and DT2. DT1 With V DT2 Control signals S are generated at control terminals G1 and G2. G1 With S G2 These control the synchronous rectifier switches SR1 and SR2 respectively. For example, the bias detector BVD1 controls the voltage V based on the detected voltage. DT1This controls the drive circuit DR1, which can generate a control signal S with an appropriate voltage. G1 This is used to control the synchronous rectifier switch SR1. Figure 2 show Figure 1 The square wave signal V at the endpoint SW SW Control signal S G1 Detection voltage V DT1 Inductor current I LS1 Control signal S G2 Detection voltage V DT2 and inductor current I LS2 The signal waveform. In Figure 2 In this process, time point t11 ​​to time point t12 can be considered as half a switching cycle, while time point t12 to time point t13 can be considered as the other half of a switching cycle.

[0060] Taking half a switching cycle from time point t11 ​​to time point t12 as an example, near time point t11, the detected voltage V DT2 The voltage across the primary winding LP drops as the sensing voltage decreases. Once the sensing voltage V... DT2 The synchronous rectifier controller 104 changes the control signal S to negative, thus converting it to negative. G2 For a logical "1", the synchronous rectifier switch SR2 is turned on, clamping the detection voltage V. DT2 Approximately 0V, while the inductor current I LS2 The voltage also oscillates and rises with the resonance of the LLC resonant circuit TNK, then oscillates and falls before approximately time point t12. Around time point t11, the voltage V is detected due to inductive induction. DT1 It will start rising from a negative value very close to 0V. Once the detected voltage V... DT1 The synchronous rectifier controller 104 converts the control signal S to positive, and the synchronous rectifier controller 104 makes the control signal S G1 To set the logic value to "0", turn off the synchronous rectifier switch SR1, and allow the inductor current I to... LS1 Maintained at 0A, while the detection voltage V DT1 It will continue to rise, and then stabilize at approximately twice the output power V. OUT ,as Figure 2 As shown.

[0061] Figure 2 The signal waveforms during the other half of the switching cycle, from time t12 to time t13, can be found in the previous explanation of the first half of the switching cycle, and will not be repeated here.

[0062] Figure 2 The signal waveform is at the output power supply V. OUT The system is ready, meaning the output power supply V is in a state of readiness. OUT It has stabilized at the preset target voltage V TARFor example, 5V. However, during the power-on process, that is, the output power V... OUT From 0V to the target voltage V TAR Previously, the synchronous rectifier switches SR1 and SR2 could experience slight conduction when they should be off due to capacitive coupling, leading to leakage. In the worst-case scenario, this could cause the output power supply V... OUT The voltage simply cannot be raised to the target voltage V. TAR .

[0063] Figure 3 The example shows the synchronous rectifier switch SR1. Figure 3 It also shows two components parasitic on the synchronous rectifier switch SR1: the drain-to-gate capacitor CGD1 connected between the control terminal G1 and the detection terminal DT1, and the body diode DB1 connected between the output ground line GNDO and the detection terminal DT1. When the output power supply V... OUT When the voltage is not high enough, Figure 1 The synchronous rectifier controller 104 in the middle lacks operating power supply V. CC The synchronous rectifier switch SR1 cannot be controlled to open or close. In this situation, theoretically, the synchronous rectifier switch SR1 should remain closed, with rectification provided by the body diode DB1. In other words, when the output power supply V... OUT The voltage is not high enough, control signal S G1 With S G2 They should all be logically maintained as "0". However, in Figure 2 Around time point t11, the detected voltage V DT1 There is a rising edge. This rising edge may, through capacitive coupling of the drain-gate capacitor CGD1, slightly raise the voltage at the control terminal G1, causing the synchronous rectifier switch SR1, which should be turned off, to conduct slightly and leak current. Therefore, Figure 1 In the LLC converter 100, the output power supply V OUT It may take a long time for the voltage to rise to the target voltage V. TAR In the worst-case scenario, the output power supply might be V. OUT The voltage simply cannot be raised to the target voltage V. TAR .

[0064] Figure 4 This illustrates an LLC converter 200 implemented according to the present invention, used to convert the input power supply V located on the primary side... IN Converted to output power V located on the secondary side OUTThe LLC converter 200 is similar to the LLC converter 100; their similarities can be found in the previous tutorial on the LLC converter 100, and will not be repeated here. Compared to Figure 1 Medium LLC converter 100, Figure 4 The LLC converter 200 additionally includes a rectifier diode DP and an operating power capacitor CVCC. The operating power capacitor CVCC is used to provide the operating power V. CC Compared to Figure 1 The synchronous rectifier controller 104 in the middle, Figure 4 The synchronous rectifier controller 204 in the middle has an additional power controller 205, which has a rectifier diode D1 and a linear regulator 206.

[0065] exist Figure 4 In the middle, the operating power supply V on the operating power supply capacitor CVCC CC Power is supplied to the synchronous rectifier controller 204. Operating power supply V CC It can be powered by the output power supply V OUT The current can be established by powering the rectifier diode DP, or by the power controller 205 drawing current from the detection terminal DT1.

[0066] In one embodiment, the operating power supply V CC As long as the voltage is above 4.5V, the synchronous rectifier controller 204 can normally control the synchronous rectifier switches SR1 and SR2; and the linear regulator 206 is designed to draw current from the detection terminal DT1 to charge the operating power supply capacitor CVCC, thereby increasing the operating power supply voltage V. CC The voltage is boosted to 4.5V. When the operating power supply V... CC When the voltage exceeds 4.5V, the linear regulator 206 stops drawing current from the sensing terminal DT1. Please refer to [link / reference]. Figure 2 During the power-on process, as long as the output power V is available... OUT When the voltage is above 2.25V, during the half-switching cycle from time point t11 ​​to t12, the detection voltage V on the detection terminal DT1 is... DT1 At approximately 4.5V, a sufficiently high voltage can be provided through diode D1 and linear regulator 206 to charge the operating power supply capacitor CVCC, thus supplying the operating power supply V. CC The voltage is pulled up to 4.5V, allowing the synchronous rectifier controller 204 to properly control the synchronous rectifier switches SR1 and SR2.

[0067] Assume the output power supply V OUT Target voltage V TAR It is 5V. When Figure 4 The LLC converter 200 in the middle will output power supply V OUT When the voltage is adjusted to 5V, the output power supply V OUT The operating power supply V is maintained by the rectifier diode DP.CC- At approximately 5V, the linear regulator 206 will stop drawing current from the sensing terminal DT1. In other words, at the output power supply V... OUT It has been regulated to the target voltage V TAR At this time, the linear regulator 206 will hardly generate any energy loss.

[0068] During the power-on process, Figure 4 The LLC converter 200 can control the synchronous rectifier switches SR1 and SR2 relatively early and normally. As... Figure 4 In accordance with the teachings of the relevant instructions, Figure 4 The synchronous rectifier controller 204 only needs to be in the output power supply V OUT Normal operation can begin once the voltage is above 2.25V, because the operating power supply voltage is at this level. CC It will be approximately 4.5V. Conversely, from... Figure 1 As can be seen from the relevant explanations, if Figure 1 The synchronous rectifier controller 104 also requires a 4.5V operating power supply. CC To proceed with normal operation, then Figure 1 The output power supply V in OUT The voltage must be higher than 4.5V for the synchronous rectifier controller 104 to operate normally. Therefore, compared to Figure 1 During the power-on process, Figure 4 The LLC converter 200 controls the synchronous rectifier switches SR1 and SR2 normally from an early stage, and the start-up process will be relatively stable.

[0069] Figure 5 The synchronous rectification controller 304 is shown, which in one embodiment can replace... Figure 4 The synchronous rectifier controller 204 is included. Compared to the power controller 205, the power controller 305 additionally has a rectifier diode D2, connected between the linear regulator 206 and the sensing terminal DT2, as... Figure 5 As shown.

[0070] Synchronous rectifier controller 304 can not only Figure 2 During the first half of the switching cycle (time points t11 to t12), current is drawn from the detection terminal DT1 to establish the operating power supply V. CC ; or you can Figure 2 During the latter half of the switching cycle (time points t12 to t13), current is drawn from the detection terminal DT2 to establish the operating power supply V. CC .

[0071] 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. An LLC converter, comprising: A square wave generator includes at least two power switches connected between the input power line and the input ground line to provide a square wave input at the input terminal. An LLC resonant circuit, connected to the input terminal, includes a primary winding of a transformer connected in series and a resonant capacitor, wherein the transformer includes a primary winding; and A first synchronous rectifier switch has a first detection terminal for connecting the first primary winding to the output ground line, wherein the first primary winding is connected between the first detection terminal and the output power line; Operating power capacitor, used to provide operating power; and A synchronous rectification controller controls the first synchronous rectification switch based on the first detected voltage at the first detection terminal. The synchronous rectification controller includes: The power controller is designed to draw current from the first detection terminal to establish the operating power supply and supply power to the synchronous rectifier controller.

2. The LLC converter as described in claim 1, wherein, The transformer also includes a secondary winding, and the LLC converter also includes: The second synchronous rectifier switch has a second detection terminal for connecting the second secondary winding to the output ground line, wherein the second secondary winding is connected between the second detection terminal and the output power line; The synchronous rectifier controller controls the second synchronous rectifier switch based on the second detection voltage on the second detection terminal.

3. The LLC converter as described in claim 2, wherein, The power controller architecture draws current from the second sensing terminal to establish the operating power supply.

4. The LLC converter as claimed in claim 1 further includes a rectifier diode connected between the output power line and the operating power capacitor.

5. The LLC converter as described in claim 1, wherein, The power controller architecture is based on the principle that when the operating power supply exceeds a first preset voltage, it stops drawing current from the first detection terminal.

6. The LLC converter as described in claim 5, wherein, The LLC converter regulates the output power on the output power line to a second preset voltage, and the first preset voltage is lower than the second preset voltage.

7. The LLC converter as claimed in claim 1, wherein, The power controller is a low dropout regulator.

8. The LLC converter as claimed in claim 1, wherein, This square wave generator has a half-bridge structure.

9. A control method for an LLC converter, comprising: A square wave voltage is provided to the input terminal of the resonant circuit, wherein, The resonant circuit is connected between the input terminal and the power line and includes the primary winding of a transformer connected in series and a resonant capacitor. The transformer includes the primary winding. A first synchronous rectifier switch and a synchronous rectifier controller are provided, wherein the first synchronous rectifier switch is connected between a first detection terminal and an output ground line and is controlled by the synchronous rectifier controller, and the first primary winding is connected between the first detection terminal and the output power line; as well as Current is drawn from the first detection terminal and used to charge the operating power supply capacitor through the synchronous rectifier controller to establish the operating power supply and supply power to the synchronous rectifier controller.

10. The control method as described in claim 9, wherein, The transformer includes a secondary winding, and the control method includes: A second synchronous rectifier switch is provided, connected between the second detection terminal and the output ground line, and controlled by the synchronous rectifier controller. The second stage winding is connected between the second detection terminal and the output power line. as well as Current is drawn from the second detection terminal and used to charge the operating power supply capacitor through the synchronous rectifier controller.

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