CN107517006A - A LLC resonant converter with hybrid control and overcurrent protection - Google Patents

Abstract

The invention discloses a kind of LLC resonant converter with mixing control and overcurrent protection measure, it includes power supply A, power supply A is just, the negative pole source electrode with first switch pipe Q1 respectively, second switch pipe Q2 drain electrode is connected, first switch pipe Q1 drain electrode and second switch pipe Q2 source electrode are connected with the input of resonance circuit respectively, the output end of resonance circuit and power supply A negative pole are connected with the input of transformer respectively, the output end of transformer passes through rectifier and load parallel connection, the input of control circuit is respectively by detecting circuit, voltage comparator circuit and resonance circuit, load is connected, the output end of control circuit respectively with first switch pipe Q1, second switch pipe Q2 grid is connected.The present invention, which realizes LLC resonant converter and automatically switches PWM or PFM according to load change, mixes control model, improve its underloading or it is unloaded when operating efficiency, overload or it is short-circuit when overcurrent protection and startup when dash current limitation.

Description

A LLC resonant converter with hybrid control and overcurrent protection

technical field

The invention belongs to the technical field of electronic circuits, and in particular relates to an LLC resonant converter with hybrid control and overcurrent protection measures.

Background technique

In recent years, modularization, miniaturization, high frequency, high efficiency, and high power density have become the research and development trends of switching power supplies. The traditional topology and control methods of switching power supplies can no longer meet the requirements. Therefore, soft switching technology has emerged as the times require. The resonant converter uses the principle of resonance to make the current or voltage of the switching tube of the switching converter change according to the law of sinusoidal or quasi-sinusoidal. When the current naturally crosses zero, the switching tube is turned off, or when the voltage is zero, the switching tube is turned on. So that the switch tube loss is reduced to close to zero. Therefore, the purpose of reducing the switching loss and improving the efficiency of the switching converter is achieved.

The advantages of the LLC resonant converter include:

(1) It has ZVS function in the range from zero to full load, and the MOSFET has low turn-off current and turn-off loss,

(2) It has high efficiency under high input voltage, and can optimize the design of the converter under normal working conditions.

(3) There is no filter inductor in the secondary of the converter, and the voltage stress of the output rectifier diode is low, which can be reduced to twice the output voltage.

(4) The magnetic devices of the transformer can be easily integrated into a magnetic core. And the magnetizing inductance and leakage inductance of the transformer can also be utilized.

However, since the LLC resonant converter adopts variable frequency PFM control, in order to keep the output voltage constant under light load and no load, the switching converter must be in the BUCK mode. At this time, the frequency of the switching tube is very high, and the equivalent primary side The impedance is very large, resulting in very low efficiency of the switching converter.

In the case of overload and short circuit, unlike the traditional PWM converter, the duty ratio can limit the current when the current is overcurrent, and the LLC resonant converter works at the resonant frequency. Reach high in a short time.

Contents of the invention

According to the deficiencies in the prior art above, the technical problem to be solved by the present invention is to propose a kind of LLC resonant converter with hybrid control and overcurrent protection measures. The efficiency of the LLC resonant converter is very low at no load and the resonant cavity current of the LLC resonant converter reaches a high level in a short time under overload and short-circuit conditions. It has the ability to realize the automatic control circuit of the LLC resonant converter according to the load change. Switching adopts PWM or PFM hybrid control mode to improve the working efficiency of the LLC resonant converter at light load or no load, the overcurrent protection of the LLC resonant converter current during overload or short circuit, and the limitation of the inrush current at startup.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

The present invention provides an LLC resonant converter with hybrid control and overcurrent protection measures, which includes a power supply A, and also includes a first switching tube Q1, a second switching tube Q2, a resonant circuit, a transformer, a rectifier, a load, and a detection circuit , a voltage comparison circuit and a control circuit, the positive and negative poles of the power supply A are respectively connected to the source of the first switching tube Q1 and the drain of the second switching tube Q2, and the drain of the first switching tube Q1 and the source of the second switch tube Q2 are respectively connected to the positive input end of the resonant circuit, the negative output end of the resonant circuit and the negative electrode of the power supply A are respectively connected to the input end of the transformer, The output end of the transformer is connected in parallel with the load through the rectifier, the input end of the control circuit is connected with the resonant circuit and the load through the detection circuit and the voltage comparison circuit respectively, and the output of the control circuit Terminals are respectively connected to the gates of the first switching transistor Q1 and the second switching transistor Q2.

Further, the detection circuit includes a voltage detection circuit and a current detection circuit, the voltage detection circuit is connected between the load and the control circuit, the current detection circuit includes a resonant current detection circuit and a load current detection circuit, The resonance current detection circuit is connected between the resonance circuit and the control circuit, and the load current detection circuit is connected between the load and the control circuit.

Further, the resonant circuit includes a resonant capacitor Cr and an equivalent inductance Lr connected in series in sequence, the transformer includes an excitation inductance Lm and a transformer body, the excitation inductance Lm is connected in parallel with the input end of the transformer body, and the load It includes an output capacitor C0 and a load resistor R0, the output capacitor C0 is connected in parallel with the load resistor R0.

Further, the control circuit includes a micro control unit MCU and a control information output module, the micro control unit MCU includes an AD acquisition module, a PI adjustment module, a PWM module and a PFM module, and the input terminals of the AD acquisition module are respectively connected to the The output end of the resonant current detection circuit, the output end of the load current detection circuit, and the output end of the voltage detection circuit are connected, the input end of the PI adjustment module is connected with the output end of the voltage comparison circuit, and the PWM module and The output terminals of the PFM module are respectively connected to the input terminals of the control information output module, and the output terminals of the control information output module are respectively connected to the gates of the first switching transistor Q1 and the second switching transistor Q2.

Further, the voltage comparison circuit includes a current transformer T1, a bridge uncontrolled rectifier LN and a comparator LM, and the input terminals CT+ and CT- of the current transformer T1 correspond to the positive and negative poles of the load resistor R0 respectively connected, the output end of the current transformer T1 is connected to the input end of the bridge uncontrolled rectifier LN, and the output end of the bridge uncontrolled rectifier LN is respectively connected to the comparator through the output capacitor C2 and the resistor Req The inverting input terminal of the LM is connected, the non-inverting input terminal of the comparator LM is connected to the power supply VCC through the output capacitor C1, the output resistor R2, and the output resistor R1 in turn, and the output terminal of the comparator LM is connected through the output resistor R4 in sequence , the output resistor R5, and the output capacitor C4 are connected to the input end of the PI adjustment module.

Further, an output resistor R3 and an output capacitor C3 are sequentially connected between the output terminal of the bridge uncontrolled rectifier LN and the inverting input terminal of the comparator LM for filtering the output voltage.

Further, the first switching tube Q1 and the second switching tube Q2 are both N-channel MOSFET switching tubes, and the transformer is a center-tapped transformer with the same number of secondary turns.

The beneficial effects of the present invention are: through detection circuit, voltage comparison circuit and control circuit, solve the very low efficiency of LLC resonant converter when light load and no-load and the resonant cavity current of LLC resonant converter is very low under the condition of overload and short circuit The problem of reaching a high level in a short time realizes that according to the load change, the control circuit of the LLC resonant converter automatically switches and adopts the PWM or PFM hybrid control mode, which improves the work of the LLC resonant converter at light load or no load Efficiency and overcurrent protection of LLC resonant converter current during overload or short circuit and limitation of inrush current at start-up. In addition, the invention has simple circuit connection, convenient integrated control and long service life.

Description of drawings

The following is a brief description of the content expressed in the drawings of this specification and the marks in the drawings:

Fig. 1 is a control block diagram of an LLC resonant converter with hybrid control and overcurrent protection measures according to a specific embodiment of the present invention.

Fig. 2 is a block diagram of the hybrid control and over-current protection algorithm algorithm of the LLC resonant converter with hybrid control and over-current protection measures according to the specific embodiment of the present invention.

Fig. 3 is a hardware circuit diagram of the overcurrent protection of the LLC resonant converter with hybrid control and overcurrent protection measures according to the specific embodiment of the present invention.

Fig. 4 is the graph of output gain under different quality factors and switching frequencies when L _n is constant.

detailed description

Referring to the accompanying drawings, through the description of the embodiments, the specific embodiments of the present invention include the shape, structure, mutual position and connection relationship of each part, the function and working principle of each part, and the manufacturing process of the various components involved. And the method of operation and use, etc., are described in further detail to help those skilled in the art have a more complete, accurate and in-depth understanding of the inventive concepts and technical solutions of the present invention.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

Under the traditional PFM control method, the voltage gain of the LLC resonant converter is only affected by the switching frequency of the switching device when the circuit parameters are determined, and the expression formula is as follows:

Where L _n is the ratio of the resonant inductance to the leakage inductance of the transformer, f _n is the normalized switching frequency, and Q is the quality factor.

According to this, when L _n is constant, the output gain curves under different quality factors and switching frequencies can be obtained, as shown in Fig. 4 .

It can be seen that at light load, that is, when Q is large, the input voltage remains unchanged. In order to maintain the output voltage unchanged, f _n should be far away from 1 at this time, which will cause the efficiency of the LLC resonant converter to be very low. Therefore, the hybrid control method of PWM and PFM is introduced, and the output voltage gain expression is as follows:

Among them, t _d is the conduction time of the switching device, and T _s is the cycle time of the switching device.

It can be obtained that under the condition that the on-off frequency remains unchanged, the output gain increases with the increase of the duty cycle.

Based on the above theory, the LLC resonant converter with hybrid control and overcurrent protection measures provided by the present invention includes a power supply A, and also includes a first switching tube Q1, a second switching tube Q2, a resonant circuit, a transformer, a rectifier, a load, Detection circuit, voltage comparison circuit and control circuit, the positive and negative poles of the power supply A are respectively connected to the source of the first switching tube Q1 and the drain of the second switching tube Q2, and the drain of the first switching tube Q1 is connected to the second switching tube The source of the tube Q2 is respectively connected to the positive input terminal of the resonant circuit, the negative output terminal of the resonant circuit and the negative terminal of the power supply A are respectively connected to the input terminal of the transformer, and the output terminal of the transformer is connected in parallel with the load through a rectifier, and the control circuit The input terminals are respectively connected to the resonant circuit and the load through the detection circuit and the voltage comparison circuit, and the output terminals of the control circuit are respectively connected to the gates of the first switching tube Q1 and the second switching tube Q2.

The present invention solves the problem that the efficiency of the LLC resonant converter is very low at light load and no load and that the resonant cavity current of the LLC resonant converter reaches the peak in a short time under the condition of overload and short circuit through the detection circuit, the voltage comparison circuit and the control circuit. The problem is very high. According to the load change, the control circuit of the LLC resonant converter can automatically switch to the PWM or PFM hybrid control mode, which improves the working efficiency of the LLC resonant converter under light load or no load and under overload. Or the overcurrent protection of the LLC resonant converter current during short circuit and the limitation of the inrush current during startup. In addition, the invention has simple circuit connection, convenient integrated control and long service life.

Specifically, the detection circuit includes a voltage detection circuit and a current detection circuit. The voltage detection circuit is connected between the load and the control circuit. The current detection circuit includes a resonant current detection circuit and a load current detection circuit. The resonant current detection circuit is connected between the resonant circuit and the control circuit. Between the circuits, the load current detection circuit is connected between the load and the control circuit.

Specifically, the resonant circuit includes a resonant capacitor Cr and an equivalent inductance Lr in series in sequence, the transformer includes an excitation inductance Lm and a transformer body, the excitation inductance Lm is connected in parallel with the input end of the transformer body, the load includes an output capacitor C0 and a load resistance R0, and the output The capacitor C0 is connected in parallel with the load resistor R0.

Specifically, the control circuit includes a micro control unit MCU and a control information output module. The micro control unit MCU includes an AD acquisition module, a PI adjustment module, a PWM module and a PFM module. The input terminals of the AD acquisition module are respectively connected with the output terminals of the resonance current detection circuit , the output terminal of the load current detection circuit and the output terminal of the voltage detection circuit are connected, the input terminal of the PI adjustment module is connected with the output terminal of the voltage comparison circuit, the output terminals of the PWM module and the PFM module are respectively connected with the input terminals of the control information output module The output terminals of the control information output module are respectively connected to the gates of the first switching transistor Q1 and the second switching transistor Q2.

Specifically, the voltage comparison circuit includes a current transformer T1, a bridge uncontrolled rectifier LN, and a comparator LM. The input terminals CT+ and CT- of the current transformer T1 are respectively connected to the positive and negative poles of the load resistor R0. The current transformer T1 The output end of the bridge type uncontrolled rectifier LN is connected to the input end of the bridge type uncontrolled rectifier LN, and the output end of the bridge type uncontrolled rectifier LN is respectively connected to the inverting input end of the comparator LM through the output capacitor C2 and the resistance Req, and the positive phase of the comparator LM The phase input terminal is connected to the power supply VCC through the output capacitor C1, the output resistor R2, and the output resistor R1 in sequence, and the output terminal of the comparator LM is connected to the input terminal of the PI adjustment module through the output resistor R4, the output resistor R5, and the output capacitor C4 in sequence. Preferably, an output resistor R3 and an output capacitor C3 are sequentially connected between the output terminal of the uncontrolled bridge rectifier LN and the inverting input terminal of the comparator LM for filtering the output voltage. In the present invention, it can be seen from Fig. 3 Among them, CT+ and CT- are connected in series on the secondary side of the LLC resonant converter, through the current transformer T1 and the bridge uncontrolled rectifier LN, the AC current signal in the current signal is converted into a DC current signal, and through the output capacitor C2 and the resistor Req converts the current signal into a voltage signal, the output resistor R3 and the output capacitor C3 filter the output voltage, V _out is compared with V _ref , if V _out is less than V _ref , the comparator LM outputs a high level, and passes through the output resistor R4, The output filter of output resistor R5 and output capacitor C4 transmits the signal to the PI adjustment module in the MCU; if V _out is greater than V _ref , the comparator outputs a low level, OCP will be pulled down instantly, and the MCU will also act instantaneously until When V _out is less than V _ref , OCP will be at high level, and the over-current protection will be released.

Preferably, in the present invention, both the first switching tube Q1 and the second switching tube Q2 are N-channel MOSFET switching tubes, and the transformer is a center-tapped transformer with the same number of secondary turns.

The specific implementation is as follows: At the beginning, the PFM module outputs the switching signal until it reaches the preset value, and the duty cycle of the PWM module gradually increases to make the output of the LLC resonant circuit until it reaches the system preset value, and the system soft start is completed. During this period, the AD acquisition module timing The output voltage of the LLC resonant converter is sampled through the voltage detection circuit to determine whether it reaches the preset value. At the same time, the output current and the resonant cavity current are regularly sampled through the load current detection circuit and the resonance current detection circuit respectively. Through the output voltage and output The current value judges the output load condition. If the output resistance calculated by the output voltage and output current is large, or close to infinity, it is judged as light load or open circuit. If the output resistance is small, or close to zero, it is judged as overload or short circuit. If the output resistance is normal, it is judged as normal operation mode.

If the system is in normal mode, the voltage collected by the AD acquisition module is compared with the set reference value through the voltage comparison circuit, the error is amplified to the PI compensator, and the PFM module outputs signals to the control information output module to drive the power switch tubes Q1 and Q2.

If the system is in light-load or open-circuit mode, in order to maintain the output voltage unchanged, the switching frequency remains unchanged. At this time, the efficiency of the LLC resonant converter is the highest, and the duty cycle of the switching signal is reduced until it reaches the preset value. In the process Determine whether the output voltage meets the range, and if so, compare it with the reference value of the output voltage, and output the PWM waveform to the control information output module to drive the power switch tubes Q1 and Q2 through the PI compensator; if the voltage still cannot reach the expected voltage, change the switch at this time The frequency outputs the mixed waveform of PWM and PFM to the control information output module to drive the power switch tubes Q1 and Q2.

If the system is in overload and short-circuit mode, the switching frequency rises rapidly to the preset value, making the LLC resonant converter work in BUCK mode, and the resonant current detection circuit detects the current of the resonant cavity. If it is too large but still less than the V _ref reference value, this The PWM module reduces the output voltage and the current in the resonant cavity by reducing the duty cycle. If the current is still greater than V _ref , the PFM and PWM modules will no longer work, and the system will be shut down, so as to realize the overcurrent protection of the LLC resonant converter.

The present invention has been exemplarily described above in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above methods, as long as various insubstantial improvements are adopted in the method concept and technical solutions of the present invention, or there is no improvement Directly applying the conception and technical solutions of the present invention to other occasions falls within the protection scope of the present invention. The protection scope of the present invention should be determined by the protection scope defined in the claims.

Claims (7)

1. a kind of LLC resonant converter with mixing control and overcurrent protection measure, including power supply A, it is characterised in that also wrap Include first switch pipe Q1, second switch pipe Q2, resonance circuit, transformer, rectifier, load, detection circuit, voltage comparator circuit And control circuit, the positive and negative electrode drain electrode with the source electrode, second switch pipe Q2 of the first switch pipe Q1 respectively of the power supply A It is connected, the drain electrode of the first switch pipe Q1 and the source electrode positive pole with the resonance circuit respectively of the second switch pipe Q2 Input is connected, the cathode output end of the resonance circuit and the power supply A negative pole input with the transformer respectively End is connected, the output end of the transformer by the rectifier and the load parallel connection, the control circuit it is defeated Enter end respectively by the detection circuit, voltage comparator circuit with the resonance circuit, load to be connected, the control circuit Grid of the output end respectively with the first switch pipe Q1, second switch pipe Q2 is connected.

2. the LLC resonant converter with mixing control and overcurrent protection measure as claimed in claim 1, it is characterised in that The detection circuit includes voltage detecting circuit and current detection circuit, and the voltage detecting circuit is connected to the load and institute Between stating control circuit, the current detection circuit includes resonance electric current detection circuit and load current detection circuit, described humorous The current detection circuit that shakes is connected between the resonance circuit and the control circuit, and the load current detection circuit is connected to Between the load and the control circuit.

3. the LLC resonant converter with mixing control and overcurrent protection measure as claimed in claim 1 or 2, its feature exist In the resonance circuit includes the resonant capacitance Cr and equivalent inductance Lr being sequentially connected in series, and the transformer includes magnetizing inductance Lm And transformer body, the magnetizing inductance Lm and the transformer body input are connected in parallel, the load includes output Electric capacity C0 and load resistance R0, the output capacitance C0 are connected in parallel with the load resistance R0.

4. the LLC resonant converter with mixing control and overcurrent protection measure as claimed in claim 3, it is characterised in that The control circuit includes micro-control unit MCU and control information output module, and the micro-control unit MCU includes AD collection moulds Block, PI adjustment modules, PWM module and PFM modules, the input of the AD acquisition modules detect electricity with the resonance current respectively The output end on road, the output end of load current detection circuit, the output end of voltage detecting circuit are connected, the PI adjustment modules Input be connected with the voltage comparator circuit output end, the output end of the PWM module and PFM modules respectively with it is described The input of control information output module is connected, the output end of the control information output module respectively with the first switch Pipe Q1, second switch pipe Q2 grid are connected.

5. the LLC resonant converter with mixing control and overcurrent protection measure as described in claim 1 or 4, its feature exist In the voltage comparator circuit includes current transformer T1, bridge-type uncontrollable rectifier device LN and comparator LM, the current transformer T1 input CT+, CT- connections corresponding with the both positive and negative polarity of the load resistance R0 respectively, the output of the current transformer T1 End is connected with the input of the bridge-type uncontrollable rectifier device LN, and the output end of the bridge-type uncontrollable rectifier device LN is respectively by defeated The inverting input for going out electric capacity C2, resistance Req with the comparator LM is connected, and the normal phase input end of the comparator LM is successively It is connected by output capacitance C1, output resistance R2, output resistance R1 with power supply VCC, the comparator LM output ends are led to successively Output resistance R4, output resistance R5, output capacitance C4 is crossed with the input of the PI adjustment modules to be connected.

6. the LLC resonant converter with mixing control and overcurrent protection measure as claimed in claim 5, it is characterised in that Also it is connected with output electricity between the output end of the bridge-type uncontrollable rectifier device LN and the inverting input of the comparator LM in turn R3 and output capacitance C3 is hindered, for being filtered processing to output voltage.

7. the LLC resonant converter with mixing control and overcurrent protection measure as claimed in claim 1, it is characterised in that The first switch pipe Q1, second switch pipe Q2 are n-channel MOSFET switch pipe, and the transformer is secondary equal turn numbers Centre-tapped transformer.