A passive device resonant drive circuit and its design method

Abstract

This invention belongs to the field of power electronics technology and relates to a fully passive device resonant drive circuit and its design method, including: an LLCCDX main circuit and a fully passive device resonant drive circuit; the fully passive device resonant drive circuit adds a drive winding to the transformer of the LLCCDX main circuit, and the number of turns of the drive winding is N. d The voltage across the drive winding is a trapezoidal wave; the passive device resonant drive circuit includes: drive winding N d Resonant inductor L d Resonant capacitor C d1 C d2 C d3 C d4 The passive device resonant drive circuit of the present invention only includes passive devices such as windings, inductors and capacitors, and does not include power semiconductors. Therefore, compared with the resonant drive circuit that includes power semiconductors, the losses on the power semiconductors can be avoided, thereby reducing the overall loss of the drive circuit.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology and relates to a fully passive device resonant drive circuit and its design method. Background Technology

[0002] Series resonant converters (LLCs) have advantages such as high efficiency and simple control methods, and are widely used in data centers, energy storage, photovoltaics and other fields. Figure 1 The diagram shown is of an LLC converter circuit. LLC converters have two application modes: one is to change the voltage ratio through pulse frequency modulation (PFM); the other is to fix the switching frequency, allowing the LLC to always operate at its resonant point, fully utilizing the efficiency advantage of the LLC. This mode of operation is called a DC converter (DCX) in fixed-ratio scenarios. In many applications, the DCX is required to have a high side-to-side ratio and high current characteristics. This requires its secondary output side to withstand a large current. To cope with this condition, the secondary side often uses multi-phase synchronous rectification in parallel. Figure 2 The circuit diagram of a parallel multi-phase synchronous (full-wave) rectifier on the secondary side is shown. It is clear that the increase in the number of synchronous rectifier phases leads to an increase in the number of synchronous rectifier MOSFETs.

[0003] MOSFETs are voltage-driven and are typically driven using push-pull circuits. Figure 3 and Figure 4 The diagrams and waveforms of the push-pull circuit are shown below. When the MOSFET is turned on, the push-pull drive circuit charges the gate capacitor; when it is turned off, it discharges the gate capacitor. The energy loss during this process is: E dr =NF s V g Q g Where N is the number of MOSFETs, F s V is the switching frequency. g Q is the driving voltage. g This represents the gate charge.

[0004] However, as the switching frequency and power of DCX increase, N and F s It is constantly increasing, while the Q of the MOSFET is... g The Q of a MOSFET increases as the drain-source voltage decreases; therefore, the Q of a MOSFET in low-voltage applications... g It is also relatively large. Therefore, from formula E dr =NF s V g Q g It can be seen that if traditional drive technology is used, the drive loss on the secondary side of the DCX is relatively high, and as the power of the DCX increases, the drive loss on the secondary side will become increasingly larger, which will seriously affect the overall efficiency of the DCX, especially the improvement of efficiency under light load.

[0005] In recent years, scholars have proposed various resonant gate drive circuits to solve the problem of excessive drive losses, such as... Figure 5 As shown. The principle of the resonant gate drive circuit is to add a resonant cavity (composed of an inductor and a capacitor) to the drive circuit. The energy on the MOSFET gate capacitor is stored in the resonant cavity (i.e., the inductor and capacitor), which plays a role in recovering the energy of the MOSFET gate capacitor.

[0006] Existing resonant drive circuits all require power semiconductor devices (MOSFETs and their drivers in the drive circuit) and a power supply. Power semiconductor devices introduce additional losses, and external power supply complicates the design. The principle of existing resonant drive circuits can be roughly summarized as follows: when the resonant drive circuit is powered on, the MOSFETs in the drive circuit generate a specific waveform to drive the resonant cavity. The resonant cavity then outputs a drive voltage to drive the MOSFETs in the main circuit, such as... Figure 6 As shown. The switching frequency of LLCDCX is fixed, and the drive waveform of the synchronous rectifier MOSFET is also always fixed, while the transformer voltage waveform of the LLCDCX circuit is a trapezoidal wave with a frequency equal to its switching frequency.

[0007] Therefore, a passive resonant drive circuit with simple structure, low loss, and high efficiency is needed to solve the above technical problems. Summary of the Invention

[0008] The technical solution adopted by this invention to solve the technical problem is: a fully passive device resonant drive circuit, comprising: an LLCCDX main circuit and a fully passive device resonant drive circuit; the fully passive device resonant drive circuit is formed by adding a drive winding to the transformer of the LLCCDX main circuit, the number of turns of the drive winding being N. d The voltage across the drive winding is a trapezoidal wave;

[0009] The passive device resonant drive circuit includes: drive winding N d Resonant inductor L d Resonant capacitor C d1 C d2 C d3 C d4 The connection method of the passive device resonant drive circuit is as follows: drive winding N d One end is connected in series with a resonant inductor L d Resonant capacitor C d1 C d2 C d3 C d4 Resonant capacitor C d4 The other end is connected back to the drive winding N. d The other end; resonant capacitor C d1 Cd2 C d3 C d4 C d1 =C d4 C d2 =C d3 Resonant capacitor C d2 and C d3 The connection midpoint is connected to the output GND of the LLCDCX, and the resonant capacitor C is connected. d2 The upper end is connected to the gate of one half of the synchronous rectifier MOSFET, and the resonant capacitor C d3 The lower end is connected to the gate of the other half of the synchronous rectifier MOSFET.

[0010] Preferably, the resonant capacitor C d2 C d3 The specific connection method for the synchronous rectifier MOSFET gate is as follows: the gate capacitance of each synchronous rectifier MOSFET in the synchronous rectifier MOSFET gate is C. g Resonant capacitor C d2 and C d3 respectively with C g N SR / 2 parallel, where N is the number of parallel connections. SR C represents the number of synchronous rectifier MOSFETs. g N SR / 2 is the sum of the capacitances of half of the gate capacitances of the synchronous rectifier MOSFETs.

[0011] More preferably, in the fully passive resonant drive circuit, the total capacitance C after all capacitors are equivalent is... d Represented as:

[0012]

[0013] The transfer function G(s) of a fully passive resonant drive circuit is expressed as:

[0014]

[0015] The resonant frequency f of a fully passive resonant drive circuit r_drive Represented as:

[0016]

[0017] Among them, v s L is the winding voltage; d It is a resonant inductor.

[0018] This invention also discloses a design method for a completely passive device resonant drive circuit. The design method is used in the above-mentioned completely passive device resonant drive circuit and includes the following steps:

[0019] Step 1: The resonant frequency of the all-passive resonant drive circuit is the resonant frequency. The phase of the transfer function to the left of the resonant frequency is 0°, and the phase of the transfer function to the right of the resonant frequency is 180°. The resonant frequency of the drive circuit is designed to be at the winding voltage v. s Between the first harmonic frequency and the third harmonic frequency;

[0020] Step 2, add capacitor C d2 and C d3 voltage v ga and v gb The maximum value is represented by V. m The critical value is represented by V. th Indicates; total capacitance C d voltage v d The maximum value is represented by V. m ' indicates that the critical value is represented by V. th ' represents; their relationship is represented as:

[0021]

[0022] In equation (4), K c For v ga or v gb With v d The ratio;

[0023] Step 3: Calculate the specified f according to the formula in Step 2. r_drive V m 'and V th The value of ';

[0024] Step 4, let V th This is equal to the gate threshold voltage of the synchronous rectifier MOSFET, thus yielding K. c Thus, V is derived. m ;

[0025] Step 5, change f r_drive Choose the appropriate V m Finally, f was determined. r_drive ;

[0026] Step 6: Select a larger L d Calculate C d1 C d2 C d3 C d4 The value of .

[0027] Preferably, in step 2, V m 'and V th ' is represented as:

[0028] v g (t)≈vg(1) (t)+v g(3) (t) (5)

[0029] v g(i) (t)=A (i) G (i) sin(2πif s t) (6)

[0030]

[0031] V m =max(v d (9)

[0032]

[0033] In the above formula, f r_drive t is the resonant frequency of the drive circuit. d It is the dead time of LLCDCX, f s It is the switching frequency of LLCDCX.

[0034] The beneficial effects of this invention are:

[0035] 1. The passive device resonant drive circuit of the present invention only includes passive devices such as windings, inductors and capacitors, and does not include power semiconductors. Therefore, compared with the resonant drive circuit that includes power semiconductors, the loss on the power semiconductors can be avoided, thereby reducing the overall loss of the drive circuit.

[0036] 2. This invention does not contain power semiconductors, but only passive devices, thus its structure is simple; this invention avoids losses on power semiconductors, thus its efficiency is high.

[0037] 3. The device of this invention has a small footprint: it only contains passive components such as inductors and capacitors, and the windings are integrated on the transformer of LLC DCX. Therefore, it has a small footprint on the PCB, which is beneficial to improving the overall power density of the prototype.

[0038] 4. This invention is simple to apply and can be used with only reasonable parameter design, without the need for an external controller driver. Attached Figure Description

[0039] Figure 1 This is a circuit diagram of an existing LLC resonant converter;

[0040] Figure 2 This is a circuit diagram of a parallel multiphase synchronous rectifier on the secondary side of an existing LLC resonant converter;

[0041] Figure 3 This is a circuit diagram of a push-pull circuit in the prior art;

[0042] Figure 4 This is a waveform diagram of the operation of a push-pull circuit in the prior art;

[0043] Figure 5 This is a waveform diagram of the existing push-pull structure drive circuit.

[0044] Figure 6 This is a block diagram of the resonant drive circuit principle in the prior art;

[0045] Figure 7 This invention relates to a fully passive device resonant drive circuit and its design method, and includes a schematic diagram of the main circuit of an LLC DCX.

[0046] Figure 8 This is a schematic diagram of the passive device resonant drive circuit of the present invention;

[0047] Figure 9 This is a schematic diagram of the equivalent circuit of the passive device resonant drive of the present invention;

[0048] Figure 10 This is a schematic diagram of the simplified passive device resonant drive circuit of the present invention;

[0049] Figure 11 This is the Bode diagram of the fully passive device resonant drive circuit of the present invention;

[0050] Figure 12 This is a key waveform diagram of the fully passive device resonant drive circuit of the present invention;

[0051] Figure 13 These are photographs of the prototype of this invention;

[0052] Figure 14 This is a measured waveform diagram of the present invention;

[0053] Figure 15 This is a comparison chart of the efficiency of the present invention.

[0054] In the diagram: 1. LLCCDX main circuit; 2. Passive device resonant drive circuit; 3. Passive device resonant drive circuit winding voltage v. s 4. Resonant inductance L d 5. Resonant capacitor C d1 6. Resonant capacitor C d2 7. Synchronous rectifier MOSFET; 8. Gate capacitance C of synchronous rectifier MOSFET g 9. Resonant capacitor C d3 10. Resonant capacitor C d4 11. Parasitic resistance R d 12. C d2 The total gate capacitance in parallel; 13, C d3Parallel total gate capacitance; 14. Equivalent total capacitance C d ;15, v s First harmonic frequency; 16. Resonant frequency of a fully passive resonant drive circuit; 17. v s Third harmonic frequency; 18. Design range of resonant frequency for a fully passive resonant drive circuit; 19. Winding voltage V of a fully passive resonant drive circuit. s Waveform; 20. Equivalent total capacitance C d Voltage waveform v d 21. C d3 Voltage waveform v gb 22. C d2 Voltage waveform v ga 23. Current i in a fully passive resonant drive circuit d Waveform; 24. Fully passive device resonant drive circuit; 25. Traditional drive chip. Detailed Implementation

[0055] The related technologies of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0056] refer to Figures 1-15 The passive device resonant drive circuit of this embodiment is as follows: Figure 7 As shown in the figure (the LLC DCX in the figure includes a 2-phase synchronous (full-wave) rectifier as an example; in practice, this invention is applicable to LLC DCXs with synchronous rectification of any number of phases), a drive winding with N turns is added to the transformer of the LLC DCX. d The voltage across the winding is a trapezoidal wave, such as... Figure 12 The winding voltage v of the fully passive resonant drive circuit in the middle s Waveform 19 is shown. A resonant inductor L is connected after the winding. d Four resonant capacitors C d1 C d2 C d3 C d4 C d1 =C d4 C d2 =C d3 C d2 and C d3 The midpoint of the CLC is connected to the output GND of the LLCDCX. d2 The upper end is connected to the gate of half (simultaneously turned on) of the synchronous rectifier MOSFET, C d3The lower end of the MOSFET is connected to the gate of the other half (which is also conducting), and the gate capacitance of each synchronous rectifier MOSFET is C. g ,like Figure 8 As shown.

[0057] Figure 9 The equivalent schematic diagram of a fully passive resonant drive circuit is shown, where C d2 and C d3 respectively with C g N SR / 2 parallel, where N is the number of parallel connections. SR To represent the number of synchronous rectifier MOSFETs, C g N SR / 2 is the sum of half the gate capacitance of the synchronous rectifier MOSFET.

[0058] Figure 10 A simplified schematic diagram of a fully passive resonant drive circuit is shown, where C d The total capacitance, after considering all capacitors in the circuit as equivalent, can be expressed as:

[0059]

[0060] As can be seen, the simplified circuit is a typical inductor-capacitor series circuit, and its transfer function is:

[0061]

[0062] The resonant frequency is:

[0063]

[0064] Figure 11 The Bode plot of the transfer function is shown. The resonant frequency of the passive device resonant drive circuit is 16. It can be seen that the phase of the transfer function is 0° to the left of the resonant frequency and the phase of the transfer function is 180° to the right of the resonant frequency. Figure 11 v in s First harmonic frequency 15 and V s The third harmonic frequency 17 represents the winding voltage V. s The first and third harmonic frequencies are used to design the resonant frequency of the drive circuit at v. s Between the first harmonic frequency and the third harmonic frequency, such a v s The first harmonic input to the resonant drive circuit will be amplified in phase, v s The third harmonic input to the resonant drive circuit will be amplified in reverse phase, and the sum of the two will increase the output voltage v of the drive circuit. d The amplitude decreases near the zero crossing point, such as Figure 12 As shown. Capacitor C d2and C d3 voltage v ga and v gb like Figure 12 C in d3 Voltage waveform v gb 21 and C d2 Voltage waveform v ga As shown in Figure 22, both and C d voltage v d There is a proportional relationship, and they are 180° out of phase. ga and v gb and v d Two points are particularly important: the maximum value and the critical value. The critical value refers to the values ​​of the three voltages mentioned above when the synchronous rectifier MOSFET is turned on and off. ga and v gb The maximum value is represented by V. m The critical value is represented by V. th Indicate; v d The maximum value is represented by V. m ' indicates that the critical value is represented by V. th ' represents. Their relationship can be represented as:

[0065]

[0066] Where K c For v ga (v gb ) and v d The ratio of V m 'and V th 'Can be represented as:

[0067] v g (t)≈v g(1) (t)+v g(3) (t) (5)

[0068] v g(i) (t)=A (i) G (i) sin(2πif s t) (6)

[0069]

[0070] V m =max(v d (9)

[0071]

[0072] Where f r_drive t is the resonant frequency of the drive circuit. d It is the dead time of LLCDCX, fs This is the switching frequency of the LLCCDX. The specified f can be calculated using the formula above. r_drive V m 'and V th The value of '. Then, let V... th This is equal to the gate threshold voltage of the synchronous rectifier MOSFET, from which K can be derived. c Thus, V is derived. m ; Change f r_drive Choose the appropriate V m Finally, f was determined. r_drive .

[0073] The resonant frequency f of the drive circuit r_drive After confirming, L d The larger the value of L, the smaller the current in the drive circuit. Since the majority of losses in the drive circuit are due to parasitic resistance in the loop, L... d The larger the value, the lower the loss. Choose a larger L. d C can be calculated according to formulas (1), (3), and (4). d1 C d2 C d3 C d4 The value of .

[0074] The fully passive resonant drive circuit proposed in this embodiment only includes passive components such as windings, inductors, and capacitors, and does not include power semiconductors. Therefore, compared with resonant drive circuits that include power semiconductors, the losses on the power semiconductors can be avoided, thereby reducing the overall losses of the drive circuit.

[0075] To verify the effectiveness of this solution, two prototype LLCDCX devices were fabricated: one using a fully passive resonant drive circuit and the other using a traditional drive chip. Figure 13 As shown. Figure 14 The measured waveforms of the prototype using a resonant circuit with all passive components are shown. Figure 15 The efficiency comparison of the two prototypes is shown, and it can be seen that the prototype using a fully passive resonant circuit is significantly higher, with a peak efficiency improvement of 0.83%.

[0076] In summary, the passive device resonant drive circuit of this invention only includes passive components such as windings, inductors, and capacitors, and does not contain power semiconductors. Therefore, compared with resonant drive circuits that include power semiconductors, losses on the power semiconductors can be avoided, thereby reducing the overall loss of the drive circuit. Therefore, this invention has broad application prospects in the field of series resonant converters.

[0077] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A design method for a fully passive device resonant drive circuit, applicable to fully passive device resonant drive circuits, wherein the drive circuit is applied to an LLC DCX main circuit, and the drive circuit consists of adding a drive winding to the transformer of the LLC DCX main circuit, wherein the voltage across the drive winding is a trapezoidal wave; the drive circuit includes: drive winding N d Resonant inductor L d Resonant capacitor C d1 , C d2 , C d3 , C d4 The drive circuit is connected as follows: drive winding N d One end is connected in series with a resonant inductor L d Resonant capacitor C d1 , C d2 , C d3 , C d4 The resonant capacitor C d4 The other end is connected back to the drive winding. N d The other end; the resonant capacitor C d1 , C d2 , C d3 , C d4 middle C d1 = C d4 , C d2 = C d3 The resonant capacitor C d2 and C d3 The midpoint of the connection is connected to the output GND of the LLC DCX, and the resonant capacitor is connected to... C d2 The upper end is connected to the gate of half of the synchronous rectifier MOSFET, and the resonant capacitor C d3 The lower end is connected to the gate of the other half of the synchronous rectifier MOSFET; The resonant capacitor C d2 , C d3 The specific connection method with the gate of the synchronous rectifier MOSFET is as follows: the gate capacitance of each synchronous rectifier MOSFET in the synchronous rectifier MOSFET gate is... C g The resonant capacitor C d2 and C d3 respectively with C g N SR / 2 Parallel connection, among which N SR The total number of the synchronous rectifier MOSFETs, the C g N SR / 2 The equivalent total capacitance is half of the gate capacitance of the synchronous rectifier MOSFET connected in parallel; the equivalent total capacitance is the sum of all capacitances. C d Represented as: （1）； The design method includes the following steps: Step 1: Design the resonant frequency of the drive circuit to be the voltage across the drive winding. v s Between the first harmonic frequency and the third harmonic frequency; The resonant frequency f r_driver Represented as: （3）； Step 2, add capacitors C d2 and C d3 voltage v ga and v gb The maximum value is used V m The critical value is represented by... V th Indicates total capacitance. C d voltage v d The maximum value is used V m ’ The critical value is represented by... V th ’ The relationship is represented as follows: （4）； in, K c for v ga or v gb and v d The ratio, （9）； （10）； （5）； （6）； （7）； （8）； In the above formula, t d It is the dead time of LLC DCX. f s It is the switching frequency of the LLC DCX. N d The number of turns in the drive winding; Step 3: Calculate the specified value according to the formula in Step 2. f r_driver of V m ’ and V th ’ The value; Step 4, let V th This is equal to the gate threshold voltage of the synchronous rectifier MOSFET, thus yielding... K c Therefore, we can conclude that V m ; Step 5: Traverse f r_driver Select one that meets the driving requirements. V m Finally determined f r_driver ; Step 6: Select the most feasible option that minimizes both drive current and drive circuit losses. L d Calculate C d1 , C d2 , C d3 , C d4 The value of .

2. The design method of a fully passive device resonant driving circuit according to claim 1, characterized in that, The transfer function G( of the passive device resonant drive circuit) s ) is represented as: （2）。

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