Full-passive device resonance type driving circuit and design method

Abstract

The invention belongs to the technical field of power electronics, and relates to a full-passive device resonance type driving circuit and a design method, and the full-passive device resonance type driving circuit comprises an LLCDCX main circuit and a full-passive device resonance type driving circuit; according to the full passive device resonance type driving circuit, a driving winding is additionally arranged in a transformer of an LLCDCX main circuit, the number of turns of the driving winding is Nd, and voltages at the two ends of the driving winding are trapezoidal waves; the full-passive device resonance type driving circuit comprises a driving winding Nd, a resonance inductor Ld and resonance capacitors Cd1, Cd2, Cd3 and Cd4. The full-passive device resonance type driving circuit only comprises passive devices such as a winding, an inductor and a capacitor, and does not comprise a power semiconductor, so that compared with a resonance type driving circuit comprising the power semiconductor, the loss of the power semiconductor can be avoided, and the overall loss of the driving circuit can be reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics and relates to a fully passive device resonant drive circuit and a design method. Background Art

[0002] The series resonant converter (LLC) has the advantages of high efficiency and simple control method, and is widely used in data centers, energy storage, photovoltaics and other fields. Figure 1 The circuit diagram of LLC converter is shown. LLC converter has two application modes. One is to change the voltage ratio through pulse frequency modulation (PFM); the other is to fix the switching frequency so that LLC always works at the resonance point, giving full play to the efficiency advantage of LLC. This working mode is called DC transformer (DCX) in the fixed ratio scenario. In many applications, DCX is required to have the characteristics of high side ratio and large current, which requires that its secondary output side can withstand a large current. To cope with this working condition, the secondary side often adopts multi-phase synchronous rectification in parallel. Figure 2 The circuit diagram of secondary-side parallel multi-phase synchronous (full-wave) rectification is shown. It is obvious that the increase in the number of synchronous rectification phases leads to an increase in the number of synchronous rectification MOSFETs.

[0003] MOSFET is a voltage-type driver, usually driven by a push-pull circuit. Figure 3 and Figure 4 They are the circuit diagram and working waveform of the push-pull circuit. When the MOSFET is turned on, the push-pull drive circuit charges the gate capacitance, and when it is turned off, the gate capacitance is discharged. The energy loss in this process is: E dr =NF s V g Q g , where N is the number of MOSFETs, F s is the switching frequency, V g is the driving voltage, Q g is the gate charge.

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

[0005] In recent years, scholars have proposed a variety of resonant gate drive circuits to solve the problem of excessive drive loss, such as Figure 5 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 capacitance will be stored in the resonant cavity (that is, the inductor and the capacitor), which plays a role in recovering the energy of the MOSFET gate capacitance.

[0006] Existing resonant drive circuits all require power semiconductor devices (MOSFETs in the drive circuit and their drivers) and power supply. Power semiconductor devices will cause additional losses, and external power supply will make the design more complicated. The principle of the existing resonant drive circuit can be roughly summarized as follows: turn on the resonant drive circuit power supply, the MOSFET in the drive circuit generates a specific waveform to drive the resonant cavity, and the resonant cavity outputs a drive voltage to drive the MOSFET in the main circuit, such as Figure 6 As shown in the figure, the LLCDCX switching frequency is fixed, the driving waveform of the synchronous rectification MOSFET is also always fixed, and the transformer voltage waveform of the LLCDCX circuit is a trapezoidal wave with a frequency equal to its switching frequency.

[0007] Therefore, a fully passive device 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 the present invention to solve the technical problem is: a full passive device resonant drive circuit, including: LLCCCX main circuit, full passive device resonant drive circuit; the full passive device resonant drive circuit is to add a drive winding in the transformer of the LLCCCX main circuit, and the number of turns of the drive winding is N d , the voltage across the driving winding is a trapezoidal wave;

[0009] The fully passive device resonant drive circuit includes: a drive winding N d , resonant inductor L d , resonant capacitor C d1 , C d2 , C d3 , C d4 ; The connection method of the fully passive device resonant drive circuit is: drive winding N d One end of the series 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 of the resonant capacitor C d1 , Cd2 , C d3 , C d4 Middle C d1 =C d4 , C d2 =C d3 ; Resonant capacitor C d2 and C d3 The midpoint of the connection and the output GND of LLCCX are connected, and the resonant capacitor 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 of is connected to the gate of the other half of the synchronous rectification MOSFET.

[0010] Preferably, the resonant capacitor C d2 , C d3 The specific connection method connected to the gate of the synchronous rectifier MOSFET is: 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 in parallel, where N SR is the number of synchronous rectifier MOSFETs, C g N SR / 2 is half the sum of the capacitances of the synchronous rectifier MOSFET gates.

[0011] More preferably, in the all-passive device resonant drive circuit, the total capacitance C after all capacitors are equivalent is d It is expressed as:

[0012]

[0013] The transfer function G(s) of the all-passive device resonant drive circuit is expressed as:

[0014]

[0015] The resonant frequency f of the all-passive device resonant drive circuit r_drive It is expressed as:

[0016]

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

[0018] The present invention also discloses a design method for a fully passive device resonant drive circuit, the design method is used for the above-mentioned fully passive device resonant drive circuit, and the design method comprises the following steps:

[0019] Step 1: The resonant frequency of the fully passive device resonant drive circuit is the resonant frequency. The phase of the transfer function on the left side of the resonant frequency is 0°, and the phase of the transfer function on the right side 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: Connect capacitor C d2 and C d3 The voltage v ga and v gb The maximum value is V m Indicated by V th Indicates; total capacitance C d The voltage v d The maximum value is V m ', the critical value is V th ' indicates that the relationship is:

[0021]

[0022] In formula (4), K c v ga or v gb With v d The ratio of

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

[0024] Step 4: Let V th is equal to the gate threshold voltage of the synchronous rectifier MOSFET, which gives K c , and then we get V m ;

[0025] Step 5. Change f r_drive , choose the appropriate V m Finally, determine f r_drive ;

[0026] Step 6. Choose 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 expressed 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 is the resonant frequency of the driving circuit, t d is the dead time of LLCCX, f s is the switching frequency of LLCDX.

[0034] The beneficial effects of the present invention are:

[0035] 1. The all-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 including power semiconductors, the loss on the power semiconductors can be avoided, thereby reducing the overall loss of the drive circuit.

[0036] 2. The present invention does not include power semiconductors, but only includes passive devices, so the structure is simple; the present invention avoids the loss on the power semiconductors, so the efficiency is high.

[0037] 3. The device of the present invention occupies a small area: it only includes passive components such as inductors and capacitors, and the windings are integrated on the transformer of LLC DCX, so it occupies a small area on the PCB, which is conducive to improving the overall power density of the prototype.

[0038] 4. The present invention is simple to apply and can be used with only reasonable parameter design without the need for an external controller drive. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a circuit diagram of LLC resonant converter in the prior art;

[0040] Figure 2 It is a circuit diagram of the LLC resonant converter secondary-side parallel multi-phase synchronous rectification in the prior art;

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

[0042] Figure 4 It is the working waveform diagram of the push-pull circuit of the prior art;

[0043] Figure 5 It is a working waveform diagram of a push-pull structure driving circuit in the prior art;

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

[0045] Figure 7 It is a schematic diagram of a fully passive device resonant drive circuit and a design method of the present invention and an LLC DCX main circuit;

[0046] Figure 8 It is the principle diagram of the all-passive device resonant drive circuit of the present invention;

[0047] Fig. 9 It is a schematic diagram of the equivalent circuit of the fully passive device resonant drive of the present invention;

[0048] Fig.10 This is a simplified circuit diagram of the all-passive device resonant drive of the present invention;

[0049] Fig.11 It is the Bode diagram of the all-passive device resonant type driving circuit of the present invention;

[0050] Fig.12 It is the key waveform diagram of the all-passive device resonant drive circuit of the present invention;

[0051] Fig.13 It is a prototype photo of the present invention;

[0052] Fig.14 It is the measured waveform diagram of the present invention;

[0053] Fig.15 It is an efficiency comparison diagram of the present invention.

[0054] In the figure, 1. LLCDCX main circuit; 2. All-passive device resonant drive circuit; 3. All-passive device resonant drive circuit winding voltage v s ; 4. Resonant inductor 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 Total gate capacitance in parallel; 13, C d3Total gate capacitance in parallel; 14. Equivalent total capacitance C d ; 15, v s First harmonic frequency; 16. Resonant frequency of all-passive device resonant drive circuit; 17. v s Third harmonic frequency; 18. Design range of resonant frequency of all-passive device resonant drive circuit; 19. Winding voltage v of all-passive device 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. Full passive device resonant drive circuit current i d Waveform; 24. All-passive device resonant drive circuit; 25. Traditional drive chip. DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the relevant technologies in the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

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

[0057] Fig. 9 The equivalent schematic diagram of the all-passive device resonant drive circuit is shown, where C d2 and C d3 Respectively with C g N SR / 2 in parallel, where N SR is the number of synchronous rectifier MOSFETs, then C g N SR / 2 is half of the sum of the synchronous rectifier MOSFET gate capacitances.

[0058] Fig.10 The simplified schematic diagram of the all-passive device resonant drive circuit is shown, where C d is the total capacitance after all the capacitances in the circuit are equivalent, which can be expressed as:

[0059]

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

[0061]

[0062] The resonant frequency is:

[0063]

[0064] Fig.11 The transfer function Bode diagram is shown. In the diagram, the resonant frequency 16 of the all-passive device resonant drive circuit is the resonant frequency. It can be seen that the phase of the transfer function is 0° on the left side of the resonant frequency, and the phase of the transfer function is 180° on the right side of the resonant frequency. Fig.11 v s The first harmonic frequency is 15 and v s The third harmonic frequency 17 is the winding voltage v s The first harmonic frequency and the third harmonic frequency of the drive circuit are designed to have a resonant frequency of v s between the first harmonic frequency and the third harmonic frequency, so v s The first harmonic input to the resonant drive circuit will be amplified in phase, v s The third harmonic of the input to the resonant drive circuit will be inverted and amplified, and the addition of the two will make the output voltage of the drive circuit v d The amplitude near the zero crossing point of is reduced, such as Fig.12 As shown. Capacitor C d2and C d3 The voltage v ga and v gb like Fig.12 C d3 Voltage waveform v gb 21 and C d2 Voltage waveform v ga 22, both and C d The voltage v d There is a proportional relationship, and the phase difference is 180°. ga and v gb and v d Two points are more important, namely the maximum value and the critical value. The critical value refers to the values ​​of the above three voltages when the synchronous rectifier MOSFET is turned on and off. ga and v gb The maximum value is V m Indicated by V th indicates; v d The maximum value is V m ', the critical value is V th ' indicates that. The relationship can be expressed as:

[0065]

[0066] Where K c v ga (v gb ) and v d The ratio of V m ' and V th ' can be expressed 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 is the resonant frequency of the driving circuit, t d is the dead time of LLCCX, fs is the switching frequency of LLCDX. According to the above formula, the specified f r_drive V m ' and V th '. Then, let V th is equal to the gate threshold voltage of the synchronous rectifier MOSFET, which gives K c , and then we get V m ; Change f r_drive , choose the appropriate V m Finally, determine f r_drive .

[0073] Drive circuit resonant frequency f r_drive After confirming, L d The larger the L is, the smaller the current in the drive circuit is. Most of the loss in the drive circuit is the loss of the parasitic resistance of the loop. Therefore, L d The larger the L, the smaller the loss. Choose a larger L d According to formula (1)(3)(4), C can be calculated d1 , C d2 , C d3 , C d4 The value of .

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

[0075] In order to verify the effect of this solution, an LLCCCX prototype using a fully passive device resonant drive circuit and an LLCCCX prototype using a traditional drive chip were made. Fig.13 shown. Fig.14 The waveforms measured using a prototype resonant circuit with all passive devices are shown. Fig.15 The efficiency comparison of the two prototypes is shown, and it can be seen that the prototype using the all-passive device resonant circuit is significantly higher, with the peak efficiency being increased by 0.83%.

[0076] In summary, the all-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 including power semiconductors, the loss on the power semiconductor can be avoided, thereby reducing the overall loss of the drive circuit. Therefore, the present invention has a wide range of application prospects in the field of series resonant converters.

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

Claims

1. A fully passive device resonant drive circuit, characterized in that: include: LLCDCX main circuit, full passive device resonant drive circuit; the full passive device resonant drive circuit is to add a drive winding to the transformer of the LLCDCX main circuit, and the voltage across the drive winding is a trapezoidal wave; The fully passive device resonant drive circuit comprises: a drive winding N d , resonant inductor L d , resonant capacitor C d1 , C d2 , C d3 , C d4 The connection mode of the fully passive device resonant drive circuit is: the drive winding N d One end of the series 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 of 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 and the output GND of LLCCX are connected, the resonant capacitor 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 rectification MOSFET.

2. The all-passive device resonant drive circuit according to claim 1, characterized in that: The resonant capacitor C d2 , C d3 The specific connection method connected to the gate of the synchronous rectification MOSFET is: the gate capacitance of each synchronous rectification MOSFET in the gate of the synchronous rectification MOSFET is C g ; The resonant capacitor C d2 and C d3 Respectively with C g N SR / 2 in parallel, where N SR is the number of the synchronous rectifier MOSFETs, the C g N SR / 2 is half of the sum of the capacitances of the gates of the synchronous rectifying MOSFETs.

3. The all-passive device resonant drive circuit according to claim 2, characterized in that: In the all-passive device resonant drive circuit, the total capacitance C after all capacitors are equivalent d It is expressed as: The transfer function G(s) of the all-passive device resonant drive circuit is expressed as: The resonant frequency f of the fully passive device resonant drive circuit is r_drive It is expressed as: Among them, v s is the winding voltage; L d is the resonant inductor.

4. A design method for a fully passive device resonant drive circuit, characterized in that: The design method is used for the all-passive device resonant drive circuit according to any one of claims 1 to 3, and the design method comprises the following steps: Step 1: Design the resonant frequency of the drive circuit to be at the winding voltage v s Between the first harmonic frequency and the third harmonic frequency; Step 2: Connect capacitor C d2 and C d3 The voltage v ga and v gb The maximum value is V m Indicated by V th Indicates; total capacitance C d The voltage v d The maximum value is V m ', the critical value is V th ' indicates that the relationship is: In formula (4), K c v ga or v gb With v d The ratio of Step 3: Calculate the specified f according to the formula in step 2 r_drive V m ' and V th 'value; Step 4: Let V th is equal to the gate threshold voltage of the synchronous rectifier MOSFET, which gives K c , and then we get V m ; Step 5. Change f r_drive , choose the appropriate V m Finally, determine f r_drive ; Step 6. Choose a larger L d , calculate C d1 , C d2 , C d3 , C d4 The value of .

5. The design method of a fully passive device resonant drive circuit according to claim 4, characterized in that: In step 2, V m ' and V th ' is expressed as: v g(i) (t)=A (i) G (i) sin(2πif s t) (6) V m '=max(v d ) (9) In the above formula, f r_drive is the resonant frequency of the driving circuit, t d is the dead time of LLCCX, f s is the switching frequency of LLCDX.

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