阅读说明：本技术 基于磁通相消的同步整流占空比丢失补偿方法与变换器 (Synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and converter ) 是由 何良宗 陈嘉哲 于 2020-02-25 设计创作，主要内容包括：本发明涉及一种基于磁通相消的同步整流占空比丢失补偿方法与具备占空比丢失补偿的LLC谐振变换器,利用磁通相消原理,在同步整流控制器的电压检测环路中引入互感,并产生特定的感应电动势,抵消检测环路中由于寄生电感或寄生互感产生的误差电压,最终解决了LLC变换器中副边同步整流电路中的同步整流管提前关断的问题,提高了变换器效率。与其他的补偿方法相比,本发明在实施上仅需要在检测环路中串入一个线圈或一匝导线,甚至无需调整PCB结构,只需要PCB上印制导线,即可以改善同步整流电路存在占空比丢失问题,进而本发明所述的LLC谐振变换器具有所需器件数量少,易于实施,适用于多种型号同步整流控制器等优点。(The invention relates to a synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation and an LL C resonant converter with duty cycle loss compensation, which utilize the magnetic flux cancellation principle to introduce mutual inductance into a voltage detection loop of a synchronous rectification controller and generate specific induced electromotive force to counteract error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop, and finally solve the problem of early turn-off of a synchronous rectification tube in a secondary synchronous rectification circuit in a LL C converter, thereby improving the efficiency of the converter.)

1. A synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation is characterized in that a magnetic flux cancellation principle is utilized, mutual inductance is introduced into a voltage detection loop of a synchronous rectification controller, a specific induced electromotive force is generated, error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop is offset, and synchronous rectification duty cycle loss is compensated.

2. The method of claim 1, wherein the flux cancellation based synchronous rectification duty cycle loss compensation method is characterized in that a synchronous rectification controller is used to adjust the turn-off timing of the synchronous rectification tube by using a flux cancellation principle; according to the electromagnetic induction law, an alternating magnetic field generated by a secondary winding of a transformer of an isolation converter is coupled through a compensator, and an induced electromotive force satisfying the following relation is generated:

V_offset＝-I_DS(jwM₁+jwL_package)；

wherein, I_DSFor current between drain and source of MOSFET of synchronous rectifier tube, M₁Self-inductance L of voltage detection loop for synchronous rectification controller₁Secondary side leakage inductance L with transformer₂Coupled inductances produced by mutual induction, L_packageIs parasitic inductance in a synchronous rectifier MOSFET.

3. The method of claim 2, wherein the compensator has a self-inductance L₃And is coupled with secondary side leakage inductor L of transformer₂Coupling inductance M generated by mutual inductance₃，M₃The magnitude of the sensitivity value satisfies the following relation:

M₁-M₃+L_package＝0。

4. the flux cancellation based synchronous rectification duty cycle loss compensation method of claim 3, wherein the compensator is at I_DSBefore the current drops to zero, the current passes through a coupling inductor M₃The resulting negative induced voltage compensates for the parasitic inductance L_packageAnd self-inductance L of voltage detection loop₁The generated positive error voltage enables the synchronous rectification controller to accurately detect the current zero crossing point and generate a turn-off signal without duty ratio loss.

5. The method of claim 4, wherein the duty cycle loss is compensated for by parasitic inductance L_packageOr a coupling inductor M₁The generated error voltage causes the synchronous rectification controller to generate a turn-off signal in advance to cause the MOSFET of the synchronous rectification tube to be in I_DSThe current is turned off in advance when not passing zero; after MOSFET of synchronous rectifier is turned off, I_DSElectric currentFreewheeling occurs through the body diode of the synchronous rectifier MOSFET, creating losses.

6. The method of any of claims 2 to 5, wherein the compensator is a coil or wire of one turn or a printed wire on a PCB, one end of the compensator is connected to the drain of the synchronous rectifier MOSFET, and the other end of the compensator is connected to the synchronous rectifier controller.

7. The method of flux cancellation based synchronous rectification duty cycle loss compensation according to claim 6, wherein the compensator is connected in series in the voltage detection loop for providing the compensation voltage.

8. The flux cancellation based synchronous rectification duty cycle loss compensation method according to claim 1, wherein the synchronous rectification controller and the synchronous rectification tube are connected in series through a pair of voltage detection lines to form a voltage detection loop; the synchronous rectification controller has at least one pair of voltage detection pins for detecting V of synchronous rectification MOSFET_DSA voltage; one pin is connected with the source electrode of the synchronous rectifier tube MOSFET, and the other pin is connected with the drain electrode of the synchronous rectifier tube MOSFET.

9. An LL C resonant converter with duty cycle loss compensation is characterized by comprising an input voltage source, a controllable switch network, a LL C resonant network, a transformer, a synchronous rectification unit provided with a compensator, a filter capacitor and a load, wherein the synchronous rectification unit comprises a synchronous rectification controller and a synchronous rectification MOSFET, and based on the synchronous rectification duty cycle loss compensation method of any one of claims 1 to 8, mutual inductance is introduced into a voltage detection loop of the synchronous rectification controller through the compensator, a specific induced electromotive force is generated, an error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop is counteracted, and the synchronous rectification duty cycle loss is compensated.

10. The LL C resonant converter with duty cycle loss compensation of claim 9, wherein the compensator is external to the synchronous rectification unit and is connected in series in a voltage detection loop of the synchronous rectification controller.

Technical Field

The invention relates to the technical field of large-current synchronous rectification on a secondary side of a resonant DC-DC converter, in particular to a synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation and an LL C resonant converter with duty cycle loss compensation.

Background

The low-voltage large-current DC-DC converter usually adopts a synchronous rectification technology to reduce the output impedance of a rectification part so as to achieve the aim of improving the efficiency of the converter. Taking the 14V converter as an example, if the diode full-wave rectification is adopted, the voltage drop of the diode is assumed to be 0.7V, and the power of the loss of the rectification part at least accounts for more than 5% of the input power under the premise of not considering the reverse recovery loss. If synchronous rectification is used and the diode is replaced by the controlled MOSFET, the on-state voltage drop generated on the MOSFET on-resistance can be reduced to below 50 mV. Then the loss of the rectifying part is only 0.3%. Therefore, the synchronous rectification technology is applied to the low-voltage high-current converter, and the efficiency of the converter can be effectively improved.

However, in the actual voltage detection type synchronous rectification application, the phenomenon of duty ratio loss often occurs. The voltage detection type synchronous rectification is realized according to the V of the MOSFET_DSThe voltage (the voltage at the drain terminal versus the source terminal) determines the operating state of the MOSFET. Ideally, when the MOSFET is turned on, if the package parasitic inductance of the MOSFET is neglected, the turned-on MOSFET can be equivalently formed by only using one on-resistance R_{DS_ON}Instead. Since it is a purely resistive branch, V_DSVoltage and I_DSThe currents (between drain and source) are in phase.

In general, a MOSFET is equivalent to an on-resistance R when turned on_{DS_ON}And a packaged inductor L_packageIn series. Due to the existence of the packaging inductor, the branch circuit is a resistance-inductance type branch circuit, and the voltage phase and the current phase are firstly conducted. Thus, at this time V_DSThe phase of the voltage will precede I_DSThe phase of the current. When current I_DSAt the beginning of descent, V_DSDue to phase advance, V_DSWill precede I_DSZero crossing. When the synchronous rectification controller detects V_DSAnd after the voltage crosses zero, the MOSFET is controlled to be switched off. And then I_DSDoes not cross zero, after being turned off, I_DSThe current flows through the body diode of the MOSFET, and a large amount of conduction loss is generated due to the conduction voltage drop (much larger than 50mV) of about 0.4V existing in the body diode.

On the other hand, in the application of high-current rectification, the influence of package parasitic inductance exists, and the mutual inductance of loops is detectedThe feeling is not negligible. According to the decoupling equivalent circuit of the synchronous rectification circuit, the mutual inductance M on the decoupled branch₁And self-inductance L_packageThe series relationship, i.e., mutual inductance and self-inductance, can interfere with the normal operation of the synchronous rectification controller.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, provides a synchronous rectification duty ratio loss compensation method based on magnetic flux cancellation and an LL C resonant converter with duty ratio loss compensation, solves the problem that a synchronous rectification tube in a secondary synchronous rectification circuit in a LL C converter is turned off in advance, and improves the efficiency of the converter.

The technical scheme of the invention is as follows:

a synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation utilizes a magnetic flux cancellation principle to introduce mutual inductance into a voltage detection loop of a synchronous rectification controller, generate specific induced electromotive force, cancel error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop, and compensate loss of a synchronous rectification duty cycle.

Preferably, the turn-off time sequence of the synchronous rectifier tube is adjusted by utilizing a magnetic flux cancellation principle and matching with the synchronous rectifier controller; according to the electromagnetic induction law, an alternating magnetic field generated by a secondary winding of a transformer of an isolation converter is coupled through a compensator, and an induced electromotive force satisfying the following relation is generated:

V_offset＝-I_DS(jwM₁+jwL_package)；

wherein, I_DSFor current between drain and source of MOSFET of synchronous rectifier tube, M₁Self-inductance L of voltage detection loop for synchronous rectification controller₁Secondary side leakage inductance L with transformer₂Coupled inductances produced by mutual induction, L_packageFor synchronous rectificationParasitic inductance in the pipe MOSFET.

Preferably, the compensator has a self-inductance L₃And is coupled with secondary side leakage inductor L of transformer₂Coupling inductance M generated by mutual inductance₃，M₃The magnitude of the sensitivity value satisfies the following relation:

M₁-M₃+L_package＝0。

preferably, the compensator is in_DSBefore the current drops to zero, the current passes through a coupling inductor M₃The resulting negative induced voltage compensates for the parasitic inductance L_packageAnd self-inductance L of voltage detection loop₁The generated positive error voltage enables the synchronous rectification controller to accurately detect the current zero crossing point and generate a turn-off signal without duty ratio loss.

Preferably, the duty cycle loss is caused by parasitic inductance L_packageOr a coupling inductor M₁The generated error voltage causes the synchronous rectification controller to generate a turn-off signal in advance to cause the MOSFET of the synchronous rectification tube to be in I_DSThe current is turned off in advance when not passing zero; after MOSFET of synchronous rectifier is turned off, I_DSCurrent freewheels through the body diode of the synchronous rectifier MOSFET, creating losses.

Preferably, the compensator is a coil or a lead wire with one turn or a printed lead wire on a PCB, one end of the compensator is connected with the drain electrode of the synchronous rectifier MOSFET, and the other end of the compensator is connected with the synchronous rectifier controller.

Preferably, the compensator is connected in series in the voltage detection loop for providing the compensation voltage.

Preferably, the synchronous rectification controller and the synchronous rectification tube are connected in series through a pair of voltage detection lines to form a voltage detection loop; the synchronous rectification controller has at least one pair of voltage detection pins for detecting V of synchronous rectification MOSFET_DSA voltage; one pin is connected with the source electrode of the synchronous rectifier tube MOSFET, and the other pin is connected with the drain electrode of the synchronous rectifier tube MOSFET.

An LL C resonant converter with duty ratio loss compensation comprises an input voltage source, a controllable switch network, a LL C resonant network, a transformer, a synchronous rectification unit provided with a compensator, a filter capacitor and a load, wherein the synchronous rectification unit comprises a synchronous rectification controller and a synchronous rectification MOSFET.

Preferably, the compensator is externally arranged on the synchronous rectification unit and is connected in series in a voltage detection loop of the synchronous rectification controller.

The invention has the following beneficial effects:

compared with other compensation methods, the synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation and the LL C resonant converter with duty cycle loss compensation utilize a magnetic flux cancellation principle to introduce mutual inductance into a voltage detection loop of a synchronous rectification controller and generate specific induced electromotive force to counteract error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop, and finally solve the problem that a synchronous rectification tube in a secondary synchronous rectification circuit in a LL C converter is turned off in advance, so that the efficiency of the converter is improved.

Drawings

FIG. 1 is a schematic circuit diagram of an LL C resonant converter according to the present invention;

FIG. 2 is a circuit schematic of a synchronous rectification unit;

FIG. 3 is a schematic diagram of an equivalent circuit with synchronous rectification unit decoupling;

FIG. 4 is a duty cycle loss diagram;

FIG. 5 is a circuit schematic of a synchronous rectification unit with a compensator;

fig. 6 is a schematic of a decoupled equivalent circuit of a synchronous rectification circuit with a compensator.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

The invention provides a synchronous rectification duty cycle loss compensation method based on magnetic flux cancellation and an LL C resonant converter with duty cycle loss compensation, aiming at solving the problems in the prior art.

The synchronous rectification duty cycle loss compensation method based on the magnetic flux cancellation introduces mutual inductance into a voltage detection loop of a synchronous rectification controller by utilizing the magnetic flux cancellation principle, generates specific induced electromotive force, cancels error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop, and compensates the loss of the synchronous rectification duty cycle.

Based on the synchronous rectification duty cycle loss compensation method, the invention also provides an LL C resonant converter with duty cycle loss compensation, as shown in fig. 1, comprising an input voltage source U_iA controllable switch network (in this embodiment, including high-low-side switching tubes S1 and S2), and a LL C resonant network (including a resonant capacitor C)_rResonant capacitor L_pResonant capacitor L_r) Transformer T₁A synchronous rectification unit with a compensator (one end of the compensator is connected with the drain electrode of the synchronous rectification MOSFET, the other end of the compensator is connected with the synchronous rectification controller), a filter capacitor C_outLoad R_L(ii) a The synchronous rectification unit comprises a synchronous rectification controller and synchronous rectification MOSFETs (in the embodiment, the synchronous rectification unit comprises two synchronous rectification units, namely two synchronous rectification controllers and two synchronous rectification transistors SR1 and SR 2); mutual inductance is introduced into a voltage detection loop of the synchronous rectification controller through the compensator, specific induced electromotive force is generated, error voltage generated by parasitic inductance or parasitic mutual inductance in the detection loop is offset, and loss of a synchronous rectification duty ratio is compensated. In this embodiment, the compensator is connected in series in the voltage detection loop for providing the compensation voltage.

In the invention, a synchronous rectification controller and a synchronous rectification tube are connected in series through a pair of voltage detection lines to form a voltage detection loop; the synchronous rectification controller has at least one pair of voltage detection pins for detecting V of synchronous rectification MOSFET_DSVoltage (voltage of drain versus source); one pin is connected with the source electrode of the synchronous rectifier tube MOSFET, and the other pin is connected with the drain electrode of the synchronous rectifier tube MOSFET.

The invention utilizes the principle of magnetic flux cancellation and is matched with a synchronous rectification controller to adjust the turn-off time sequence of a synchronous rectification tube; coupling of transformer T by isolating converter by compensator according to law of electromagnetic induction₁The secondary winding generates an alternating magnetic field and an induced electromotive force which satisfies the following relation:

V_offset＝-I_DS(jwM₁+jwL_package)；

wherein, I_DSFor current between drain and source of MOSFET of synchronous rectifier tube, M₁Self-inductance L of voltage detection loop for synchronous rectification controller₁And transformer T₁Secondary edge leakage L₂Coupled inductances produced by mutual induction, L_packageIs parasitic inductance in a synchronous rectifier MOSFET.

As shown in fig. 2, in the synchronous rectification unit, the inductor L₁、L₂Respectively, parasitic inductances on the conductors of the voltage detection loop and the transformer T₁Secondary side leakage inductance L due to the self-inductance of the voltage sense loop of the synchronous rectifier controller₁And transformer T₁Secondary edge leakage L₂There is a coupling relationship, i.e. the coupling inductance is produced by the mutual inductance, denoted M₁For inductance L₁And L₂The interaction between them. Use of AC current source for equivalent transformer T₁The primary part and the inverter circuit part are used for simplifying analysis. For high frequency currents, the filter capacitor C_outIs approximately 0, so that it can be considered that the filter capacitance C is a high frequency current ripple_outShort-circuited load R_LAnd is shown in dashed lines.

Decoupling mutual inductance in the synchronous rectification unit shown in fig. 2, e.g.FIG. 3 shows the detected V of the synchronous rectification controller_DSThe voltage satisfies the following relationship:

wherein, V_SR1Voltage is I_DSThe voltage drop produced when current flows through the synchronous rectifier MOSFET is due in part to the on-resistance R_{DS_ON}Another part is the parasitic inductance L due to packaging_packageAnd (4) generating. Among the commonly used synchronous rectification controllers, there is a V of the synchronous rectification controller_DSThe input impedance of the voltage input end is very large, taking the synchronous rectification controller NCP4303 as an example, under the condition that 200V bias voltage is applied to the D end and the S end of the controller, the I flowing into the chip₂The current is only 1uA, corresponding to an equivalent input impedance of 200M Ω. Due to I₂<<I_DSTherefore, it can be approximated that the self-inductance L on the voltage detection loop₁And a coupling inductor M₁The resulting pressure drop is 0. Further, V_DSThe voltages can be simplified to the following relationship:

V_DS＝I_DS(jwM₁+jwL_package+R_{DS_ON})。

from the above formula, V_DSThe voltage being parasitic mutual inductance (i.e. coupling inductance M)₁) Parasitic inductor L_packageAnd an on-resistance R_{DS_ON}The sum of the voltages on. Wherein the coupling inductance M₁And parasitic inductance L_packageThe resulting voltage will result in a detected V_DSThe phase of the voltage leading I_DSThe phase of the current, in turn, increases the off current threshold.

The loss of duty cycle is caused by parasitic inductance L_packageOr a coupling inductor M₁The generated error voltage causes the synchronous rectification controller to generate a turn-off signal in advance to cause the MOSFET of the synchronous rectification tube to be in I_DSThe current is turned off in advance when not passing zero; after MOSFET of synchronous rectifier is turned off, I_DSCurrent freewheels through the body diode of the synchronous rectifier MOSFET, creating losses. As shown in fig. 4, since the synchronous rectification controllerUpon detection of V_DSAfter the voltage crosses zero, a turn-off signal is generated and sent to the synchronous rectifier MOSFET; therefore, if V without compensation is adopted_DSThe voltage signal is directly used to generate the driving signal, which results in an early turn-off of the synchronous rectifier MOSFET, i.e. a loss of duty cycle. After MOSFET of synchronous rectifier is turned off, I_DSCurrent will freewheel through the body diode of the synchronous rectifier MOSFET, resulting in a large amount of conduction losses.

As shown in FIG. 5, the compensator is externally disposed on the synchronous rectification unit and is serially connected to the voltage detection loop of the synchronous rectification controller₃Transformer T₁Secondary edge leakage L₂Self-inductance with compensator L₃There is a coupling relation between them, transformer T₁Secondary edge leakage L₂Self-inductance with compensator L₃The coupling inductance, denoted M, being generated by mutual inductance₃. Wherein M is₃Can be changed by changing the transformer T₁Secondary edge leakage L₂Self-inductance with compensator L₃Is adjusted, and at the same time, the self-inductance L of the voltage detection loop₁Self-inductance with compensator L₃There is also a coupling relation between them, the self-inductance L of the voltage detection loop₁Self-inductance with compensator L₃The coupling inductance, denoted M, being generated by mutual inductance₂。

Decoupling the mutual inductance in the synchronous rectification unit shown in fig. 5, as shown in fig. 6, can obtain a coupled inductance M₃Is decoupled at I_DSThe branch through which the current flows, and the parasitic inductor L_packageCoupled inductor M₁And an on-resistance R_{DS_ON}In a serial relationship. Thus, the coupling inductance M can be made by inserting an external compensator of suitable size₃Satisfies the following relationship:

M₁-M₃+L_package＝0。

compensator in_DSBefore the current drops to zero, the current passes through a coupling inductor M₃The resulting negative induced voltage compensates for the parasitic inductance L_packageAnd voltage detectionSelf-inductance of the measurement loop L₁The generated positive error voltage enables the synchronous rectification controller to accurately detect the current zero crossing point and generate a turn-off signal without duty ratio loss. I.e. by introducing a coupling inductance M₃And the whole branch circuit is converted into a pure resistive branch circuit, and the pure resistive branch circuit meets the relation of voltage and current in the same phase. Therefore, the problem of duty ratio loss can not be caused by detecting the voltage on the branch circuit as the trigger signal of the synchronous rectification controller.

Due to parasitic parameters (i.e. coupling inductance M generated by mutual inductance present in the voltage detection loop₁) Generally small, and in practice, the compensator may be implemented as a coil or wire of one turn, or as a section of printed wiring on a PCB, sufficient to generate a coupling inductance M of the order nH₃. Compared with other compensation methods, the method can solve the problem of duty ratio loss at the turn-off time of the synchronous rectification circuit only by serially connecting a turn of coil in the voltage detection loop or even without adjusting a PCB structure, and has the advantages of less required devices, easiness in implementation, suitability for various types of synchronous rectification controllers and the like.

The above examples are provided only for illustrating the present invention and are not intended to limit the present invention. Changes, modifications, etc. to the above-described embodiments are intended to fall within the scope of the claims of the present invention as long as they are in accordance with the technical spirit of the present invention.