WO2016177189A1

WO2016177189A1 - Synchronous rectification drive circuit used in llc resonant converter

Info

Publication number: WO2016177189A1
Application number: PCT/CN2016/077578
Authority: WO
Inventors: 李俊凯; 颜毅; 王陶; 周华敏
Original assignee: 中兴通讯股份有限公司
Priority date: 2015-08-31
Filing date: 2016-03-28
Publication date: 2016-11-10
Also published as: CN106487228A

Abstract

A synchronous rectification drive circuit used in an LLC resonant converter comprises: a power circuit, a main control circuit and a synchronous rectification control circuit. The power circuit comprises a primary LLC resonant circuit and a secondary LLC rectification circuit. An end of the main control circuit is connected to main switching transistors (Q1, Q2, Q3, Q4) in the power circuit, and the other end is connected to the synchronous rectification control circuit, and is configured to generate a first control signal for controlling the main switching transistor and a second control signal (B) for controlling the synchronous rectification control circuit. An end of the synchronous rectification control circuit is connected to synchronous switching transistors (Q5, Q6, Q7, Q8), and is configured to perform anti-interference protection with respect to the synchronous rectification circuit through a combination of an inductive module and a capacitive module, and perform processing on a third control signal (D) and the second control signal to obtain a signal (C) for driving the synchronous switching transistor, wherein the third control signal is required by the synchronous switching transistor and is obtained when performing detection on current flowing through the synchronous switching transistor.

Description

Synchronous rectification drive circuit for LLC resonant converter

Technical field

The present invention relates to the field of circuits, and in particular to a synchronous rectification drive circuit for an LLC resonant converter.

Background technique

In order to meet high efficiency and high power density requirements, synchronous rectification technology is widely used in low voltage and high current applications. The basic principle of synchronous rectification technology is to replace the rectifier diode with a low on-resistance switching tube to reduce the conduction loss of the rectifier circuit. The output rectification of the LLC resonant converter has two modes: continuous current mode (CCM) and discontinuous current mode (DCM). When the rectifier circuit operates in the CCM mode, the control signal of the main power tube is the same as or opposite to the control signal of the corresponding synchronous rectifier tube. Therefore, the control signal of the synchronous rectifier tube is easily acquired in the CCM mode. When the rectifier circuit works in the DCM mode, the control signal of the synchronous rectifier tube is lower than the control signal of the corresponding main power tube, and the control signal of the synchronous rectifier tube needs to be delayed or turned off in advance, and the control signal of the synchronous rectifier tube is difficult to obtain. In this regard, some synchronous rectification dedicated chips appear on the market to directly detect the voltage across the source and the drain of the synchronous rectifier, and control the on/off of the synchronous rectifier through the voltage signal. Since the on-resistance of the synchronous rectifier is small, the detected voltage signal is weak, and the voltage signal is easily disturbed, and the circuit operates abnormally. Especially in the multi-channel interleaved LLC resonant converter, the mutual interference between the various paths causes this problem to be particularly serious.

In view of the related art, the on-resistance of the synchronous rectifier tube is small, and the detected voltage signal is weak, which causes the voltage signal to be easily disturbed. Currently, an effective solution has not been proposed.

Summary of the invention

The embodiment of the invention provides a synchronous rectification driving circuit for an LLC resonant converter, so as to at least solve the related art, the on-resistance of the synchronous rectifier tube is small, the detected voltage signal is weak, and the voltage signal is easily disturbed. problem.

According to an aspect of an embodiment of the present invention, a synchronous rectification driving circuit for an LLC resonant converter includes: a power circuit, a main control circuit, and a synchronous rectification control circuit, wherein the synchronous rectification circuit includes a filtering network, The filter network is composed of an inductive module with an overall impedance and a capacitive module with an overall impedance; the power circuit is composed of a primary side LLC resonant circuit and a secondary side LLC rectifier circuit, wherein the primary side LLC resonance The circuit is composed of a main switching tube, a resonant inductor, a resonant capacitor and a primary winding of the transformer; the secondary side LLC rectifier circuit is composed of a secondary winding of the transformer and a synchronous switching tube; one end of the main control circuit and the a main switch tube in the power circuit is connected, and the other end is connected to the synchronous rectification control circuit, configured to generate a first control signal for controlling the main switch tube, and generate a second control signal for controlling the synchronous rectification control circuit; One end of the synchronous rectification circuit is connected to the synchronous switch tube, and is disposed through the inductive module and the capacitive module Performing anti-interference protection on the synchronous rectification circuit, and processing the third control signal and the second control signal required by the synchronous switch tube obtained when detecting the current flowing through the synchronous switch tube Driving a signal of the synchronous switch tube, wherein one end of the inductive module is connected in series with one end of the capacitive module, and the other end of the inductive module is connected to a drain of the synchronous switch tube, the capacitive Mode The other end of the block is connected to the source of the synchronous switch.

Optionally, when the operating frequency is not less than the resonant frequency, the second control signal is consistent with the first control signal, and when the operating frequency is less than the resonant frequency, the first control signal is The conduction pulse width of the second control signal is half of the resonance period.

Optionally, the inductive module consists of one or more inductors connected in series or in parallel.

Optionally, the capacitive module consists of one or more capacitors connected in series or in parallel.

Optionally, the synchronous rectification circuit further includes: a synchronous rectification integrated processing circuit and a logic AND gate; wherein an input end of the sampling signal of the synchronous rectification integrated processing circuit is a series connection of the inductive module and the capacitive module An output of the point, an output end of the sampling signal of the synchronous rectification integrated processing circuit is connected to one end of the logic AND gate, and is set to be a sampling generated when the synchronous rectification circuit detects a current flowing through the synchronous switching tube Converting a signal into a driving signal corresponding to the third control signal; the logic AND gate is configured to pass the second control signal and the third control signal through a driving circuit to obtain the synchronous switching transistor Four control signals.

Optionally, the synchronous rectification circuit further includes: a synchronous rectification integrated processing circuit and a diode; wherein an input end of the sampling signal of the synchronous rectification integrated processing circuit is connected to a series connection point of the inductive module and the capacitive module The output end of the sampling signal of the synchronous rectification integrated processing circuit is connected to the anode of the diode, and is configured to convert the sampling signal generated by the synchronous rectification circuit when detecting the current flowing through the synchronous switch tube into a a driving signal corresponding to the third control signal; a cathode of the diode is connected to one end of the main control circuit, and is configured to be processed by processing the second control signal and the third control signal Synchronous switch tube fourth control signal.

Optionally, the LLC resonant converter comprises one of the following: a full-bridge LLC resonant converter, a half-bridge LLC resonant converter, and a multi-way interleaved LLC resonant converter.

Optionally, when the LLC resonant converter is a multi-way interleaved LLC resonant converter, the primary side LLC resonant circuit of the LLC resonant converter is connected in series or in parallel, and the secondary resonant circuit of the LLC resonant converter is connected in series or in parallel.

Optionally, when the LLC resonant converter is a two-way interleaved LLC resonant converter, the main control circuit interleaves 90° to control two main switches in the primary side LLC resonant circuit.

Optionally, the main switch tube and the synchronous switch tube are field effect transistors.

In the embodiment of the present invention, a filtering network composed of an inductive module with an overall impedance and a capacitive module with an overall impedance is used in the synchronous rectification circuit, so that the interference signal cannot trigger the synchronous rectification circuit when there is an interference signal. The turn-off threshold can only be controlled by the second control signal and the third control signal after the processed drive signal, thereby solving the related art, the on-resistance of the synchronous rectifier is small, the detected voltage The signal is weak, which causes the voltage signal to be easily disturbed, and the driving signal for driving synchronous rectification is effectively obtained.

DRAWINGS

The drawings described herein are provided to provide a further understanding of the invention, which form a part of this application, The illustrative embodiments and the description thereof are illustrative of the invention and are not to be construed as limiting the invention. In the drawing:

1 is a block diagram showing the structure of a synchronous rectification driving circuit for an LLC resonant converter according to an embodiment of the present invention;

2 is a schematic diagram of a synchronous rectification control circuit in accordance with an alternative embodiment of the present invention;

3 is a schematic diagram of a synchronous rectification drive circuit in accordance with an alternative embodiment of the present invention;

4 is a circuit schematic diagram of Embodiment 1 of a synchronous rectification control circuit in accordance with an alternative embodiment of the present invention;

5 is a circuit schematic diagram of Embodiment 2 of a synchronous rectification control circuit in accordance with an alternative embodiment of the present invention.

detailed description

The invention will be described in detail below with reference to the drawings in conjunction with the embodiments. It should be noted that the embodiments in the present application and the features in the embodiments may be combined with each other without conflict.

It is to be understood that the terms "first", "second" and the like in the specification and claims of the present invention are used to distinguish similar objects, and are not necessarily used to describe a particular order or order.

In this embodiment, a synchronous rectification driving circuit for an LLC resonant converter is provided. FIG. 1 is a schematic structural diagram of a synchronous rectification driving circuit for an LLC resonant converter according to an embodiment of the present invention, as shown in FIG. The circuit comprises: a power circuit, a main control circuit and a synchronous rectification control circuit, wherein the synchronous rectification control circuit comprises a filtering network, wherein the filtering network is composed of an inductive module with an overall impedance and a capacitive module with an overall impedance;

The power circuit is composed of a primary side LLC resonant circuit and a secondary side LLC rectifier circuit, wherein the primary side LLC resonant circuit is composed of a main switching tube, a resonant inductor, a resonant capacitor and a primary winding of the transformer; the secondary side LLC rectifier circuit is composed of a transformer. The secondary winding and the synchronous switching tube are configured;

One end of the main control circuit is connected to the main switch tube in the power circuit, and the other end is connected to the synchronous rectification control circuit, and is configured to generate a first control signal for controlling the main switch tube, and generate a control for the synchronous rectification control circuit. Second control signal;

One end of the synchronous rectification circuit is connected to the synchronous switch tube, and is configured to perform anti-interference protection on the synchronous rectification circuit through a combination of the inductive module and the capacitive mode, and is required for the synchronous switch tube obtained when detecting the current flowing through the synchronous switch tube. The third control signal and the second control signal are processed to obtain a signal for driving the synchronous switch tube, wherein one end of the inductive module is connected in series with one end of the capacitive module, and the other end of the inductive module is connected to the drain of the synchronous switch tube. The other end of the sex module is connected to the source of the synchronous switch.

In the above-mentioned synchronous rectification circuit, the filtering network composed of the inductive module with the overall impedance and the capacitive module with the overall impedance is made, so that the interference signal cannot trigger the synchronization rectification circuit when there is an interference signal. The threshold value can be controlled only by the second control signal and the third control signal after the processed driving signal, thereby solving the related art, the on-resistance of the synchronous rectifier tube is small, and the detected voltage signal is compared. Weak, causing the voltage signal to be easily disturbed, effectively obtaining the synchronous rectification drive signal.

For the first control signal involved in this embodiment, the first control signal is consistent with the first control signal when the operating frequency is not less than the resonant frequency, the first The control signal has a conduction pulse width of half of the resonance period when the operating frequency is less than the resonance frequency. Wherein, the working frequency refers to the operating frequency of the main switching tube, and the working frequency is given by the loop control in the main control circuit, and the loop is automatically given according to factors such as input voltage, output voltage, output load, etc. The resonant frequency is determined by the inductance of the resonant inductor and the capacitance of the resonant capacitor. Once these two parameters are determined, the resonant frequency is fixed. Consistent with the main switch tube means that the conduction pulse width is the same as that of the main switch tube.

In addition, the inductive module in this embodiment is composed of one or more inductors connected by series or parallel, and the capacitive module is composed of one or more capacitors connected by series or parallel connection.

The synchronous rectification circuit in this embodiment may further include: a synchronous rectification integrated processing circuit and a logic AND gate; wherein, the input end of the sampling signal of the synchronous rectification integrated processing circuit is an output of a series point of the inductive module and the capacitive module, and is synchronized. The output end of the sampling signal of the rectification integrated processing circuit is connected to one end of the logic AND gate, and is configured to convert the sampling signal generated by the synchronous rectification circuit when detecting the current flowing through the synchronous switching tube into a driving signal corresponding to the third control signal; The logic AND gate is configured to pass the second control signal and the third control signal through the driving circuit to obtain a fourth control signal for driving the synchronous switching transistor.

Alternatively, the synchronous rectification circuit may further include: a synchronous rectification integrated processing circuit and a diode; wherein, the input end of the sampling signal of the synchronous rectification integrated processing circuit is connected with the series connection point of the inductive module and the capacitive module, and the sampling of the synchronous rectification integrated processing circuit The output end of the signal is connected to the positive pole of the diode, and is configured to convert the sampling signal generated by the synchronous rectifying circuit when detecting the current flowing through the synchronous switching tube into a driving signal corresponding to the third control signal; the negative pole of the diode and the main control circuit One end is connected, and is configured to obtain a fourth control signal for driving the synchronous switch by processing the second control signal and the third control signal.

The LLC resonant converter includes one of the following: a full-bridge LLC resonant converter, a half-bridge LLC resonant converter, and a multi-way interleaved LLC resonant converter, wherein when the LLC resonant converter is a multi-channel interleaved LLC resonant converter, The primary side LLC resonant circuit of the LLC resonant converter is connected in series or in parallel, and the secondary side rectifying circuits of the LLC resonant converter are connected in series or in parallel. For example, when the LLC resonant converter is a two-way interleaved LLC resonant converter, the main control circuit interleaves 90° to control the main switching tubes in the two-way primary-side LLC resonant circuit.

It should be noted that the main switch tube and the synchronous switch tube in this embodiment may be selected as field effect transistors.

The invention is exemplified below in conjunction with an alternative embodiment of the invention;

The present embodiment provides a synchronous rectification driving circuit for an LLC resonant converter. By the optional embodiment, interference between multiple channels can be eliminated, and a synchronous rectified driving signal can be effectively obtained. To achieve the above object, the present optional embodiment adopts the following measures and technical solutions. The circuit includes: a power circuit, a main control circuit, and a synchronous rectification control circuit.

The power circuit refers to the power circuit of the LLC resonant converter, and includes a main switch tube, a resonant inductor, a resonant capacitor, a transformer, and a synchronous switch tube. The main switch tube, the resonant inductor, the resonant capacitor, and the primary winding of the transformer constitute a primary side LLC. The resonant circuit, and the secondary winding of the transformer and the synchronous switching transistor constitute a secondary rectifier circuit.

The main control circuit is connected to the main switch tube, and is set to control the main switch tube to maintain the operation of the primary side LLC resonant circuit; is connected to the synchronous rectification control circuit, and participates in the synchronous rectification circuit control.

The main control circuit participates in the synchronous rectification control signal (ie, the signal B corresponds to the first control signal in the above embodiment), and when the operating frequency is not less than the resonance frequency, the control signal is consistent with the main switch tube corresponding to the primary side; When the resonance frequency is smaller than the resonance frequency, the conduction pulse width of the control signal is half of the resonance period.

a synchronous rectification control circuit configured to detect a current flowing through the synchronous switching tube to generate a driving signal required for the synchronous switching tube. FIG. 2 is a schematic diagram of a synchronous rectification control circuit according to an alternative embodiment of the present invention, as shown in FIG. The synchronous rectification control circuit comprises: a filtering network, a synchronous rectification integrated processing circuit, and a logic AND gate.

The filter network is connected at one end to the DS end of the corresponding synchronous switch tube, and is set to detect the DS terminal voltage of the synchronous switch tube; one end is connected to the detection end of the synchronous rectification integrated processing circuit, and sends the detection signal to the integrated processing circuit; the structure includes Inductive module, capacitive module. The inductive module is a module that is connected by series or parallel connection by one or more components, and the overall impedance is inductive; the capacitive module is connected by series or parallel by one or more components, and the overall impedance is presented. Sexual module.

One end of the inductive module is connected in series with one end of the capacitive module, the other end of the inductive module is connected to the drain of the corresponding synchronous switch tube, and the other end of the capacitive module is connected to the source of the corresponding synchronous switch tube.

The synchronous integrated processing circuit refers to processing the sampled signal through an integrated circuit and converting it into a corresponding driving signal (ie, the signal D corresponding to the second control signal in the above embodiment). The output of the inductive module and the capacitive module's series point is used as the input of the sampling signal of the synchronous integrated processing circuit.

The logic AND gate has its input terminal signal B and signal D respectively; its output terminal passes through the driving circuit to generate a signal C to drive the corresponding synchronous switching transistor.

The LLC resonant converter may be a full-bridge LLC resonant converter, may be a half-bridge LLC resonant converter, may be a multi-channel interleaved LLC resonant converter, wherein the multi-channel interleaved LLC resonant converter includes multiple combinations of various connections In the mode, the primary side LLC resonant circuit of the converter is connected in series or in parallel, and the secondary side rectifier circuit of the converter is connected in series or in parallel.

The present optional embodiment will be described in detail below through specific embodiments of the present exemplary embodiment;

Example 1

3 is a schematic diagram of a synchronous rectification driving circuit according to an alternative embodiment of the present invention. As shown in FIG. 3, a two-way interleaved half-bridge LLC resonant converter. Main switch tube (Q1, Q2), resonant inductor (Lr1), resonant capacitor (Cr1, Cr2) and the primary winding of transformer (T1) constitute one LLC resonant circuit; main switch tube (Q3, Q4), resonant inductor (Lr2 ), the resonant capacitor (Cr3, Cr4) and the primary winding of the transformer (T2) constitute another LLC resonant circuit; two LLC resonant circuits are connected in series. The synchronous switching tube (Q5, Q6) and the secondary winding of the transformer (T1) constitute a rectifier circuit; the synchronous switching transistor (Q7, Q8) and the secondary winding of the transformer (T2) constitute another rectifier circuit; the two rectifier circuits are connected in parallel connection. The main control circuit interleaves 90 degrees to control the main switching tubes of the two resonant circuits.

4 is a circuit schematic diagram of Embodiment 1 of a synchronous rectification control circuit according to an alternative embodiment of the present invention, as shown in FIG. L1 is an inductive module, C1 is a capacitive module, and point A and ground point are the source and drain of the corresponding synchronous switching tube. The output of the filtering network is used as an input of a synchronous processing IC (corresponding to the synchronous rectification integrated processing circuit), and the output of the synchronous processing IC (ie, signal D) and the signal B are logically and processed and output to the driving circuit, and then the driving circuit drives the corresponding synchronous switch. Tube (ie signal C).

When the LLC resonant circuit starts to work, the main control circuit waves and the signal B is high. The current flows through the body diode of the synchronous switch tube, and the synchronous processing IC detects the voltage of the DS terminal of the synchronous switch tube (ie, the turn-on voltage drop of the body diode), reaches the turn-on threshold of the synchronous processing IC, and the signal D turns to a high level. After signal B and signal D are logically ANDed, output signal C is at a high level, and the current in the synchronous switching transistor is transferred from the body diode to the channel. As time changes, another interleaved LLC resonant circuit switches, and a synchronous interfering circuit generates a pulsating interference signal. After the interference signal is processed by the filtering network, the shutdown threshold of the synchronous processing IC is not triggered until the signal B changes from the high level to the low level, the signal C also goes to the low level, and the synchronous switch tube drive is turned off. . If there is no filtering network, the interference signal will trigger the shutdown threshold of the synchronous processing IC, and the synchronous switching transistor will be turned off in advance to reduce the conversion efficiency of the synchronous rectifier circuit. However, after the filter network is added, it is difficult for the detection signal to reach the shutdown threshold of the synchronous processing IC, and the synchronous processing IC cannot be effectively turned off, so the signal B needs to be added to ensure reliable shutdown.

Example 2

5 is a circuit schematic diagram of Embodiment 2 of a synchronous rectification control circuit according to an alternative embodiment of the present invention. As shown in FIG. 5, unlike Embodiment 1, in the second embodiment, the diode D1 replaces the logic AND gate. .

In this alternative embodiment, the signal D can effectively control the turn-on time of the synchronous rectification; the signal B can effectively control the turn-off time of the synchronous rectification; the filter network can solve the mutual interference problem caused by the multi-way interleaving topology. This alternative embodiment can be applied to LLC resonant converters, particularly in multi-channel interleaved LLC resonant converters, with better results.

The above description is only an alternative embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes can be made to the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and scope of the present invention are intended to be included within the scope of the present invention.

Industrial applicability

Claims

A synchronous rectification driving circuit for an LLC resonant converter, comprising: a power circuit, a main control circuit and a synchronous rectification control circuit, wherein the synchronous rectification control circuit comprises a filtering network, wherein the filtering network is inductive by an overall impedance The inductive module and the capacitive module with capacitive impedance are formed;

The power circuit is composed of a primary side LLC resonant circuit and a secondary side LLC rectifier circuit, wherein the primary side LLC resonant circuit is composed of a main switching tube, a resonant inductor, a resonant capacitor and a primary winding of the transformer; the secondary side LLC The rectifier circuit is composed of a secondary winding of the transformer and a synchronous switch tube;

One end of the main control circuit is connected to the main switch tube in the power circuit, and the other end is connected to the synchronous rectification control circuit, and is arranged to generate a first control signal for controlling the main switch tube, and generate and control the synchronous rectification a second control signal of the control circuit;

One end of the synchronous rectification circuit is connected to the synchronous switch tube, and is configured to perform anti-interference protection on the synchronous rectification circuit through a combination of the inductive module and the capacitive module, and will detect the flow through the synchronization The third control signal required by the synchronous switch tube obtained by switching the current of the switch tube and the second control signal are processed to obtain a signal for driving the synchronous switch tube, wherein one end of the inductive module and the capacitor are One end of the capacitive module is connected in series, the other end of the inductive module is connected to the drain of the synchronous switch tube, and the other end of the capacitive module is connected to the source of the synchronous switch tube.
The circuit according to claim 1, wherein said first control signal is coincident with said first control signal when said operating frequency is not less than a resonant frequency, said first control signal being at an operating frequency When less than the resonant frequency, the conduction pulse width of the second control signal is half of the resonance period.
The circuit of claim 1 wherein said inductive module is comprised of one or more inductors connected in series or in parallel.
The circuit of claim 1 wherein said capacitive module is comprised of one or more capacitors connected in series or in parallel.
The circuit of claim 1 wherein said synchronous rectification circuit further comprises: a synchronous rectification integrated processing circuit and a logic AND gate;

An input end of the sampling signal of the synchronous rectification integrated processing circuit is an output of a series connection point of the inductive module and the capacitive module, and an output end of the sampling signal of the synchronous rectification integrated processing circuit and the logic AND gate Connected at one end, configured to convert a sampling signal generated by the synchronous rectifying circuit when detecting a current flowing through the synchronous switching tube into a driving signal corresponding to the third control signal;

The logic AND gate is configured to pass the second control signal and the third control signal through a driving circuit to obtain a fourth control signal for driving the synchronous switch.
The circuit of claim 1 wherein said synchronous rectification circuit further comprises: a synchronous rectification integrated processing circuit and a diode;

An input end of the sampling signal of the synchronous rectification integrated processing circuit and the inductive module and the capacitive module Connected at a series point, the output end of the sampling signal of the synchronous rectification integrated processing circuit is connected to the anode of the diode for converting the sampling signal generated by the synchronous rectifying circuit when detecting the current flowing through the synchronous switching tube And a driving signal corresponding to the third control signal;

A cathode of the diode is connected to one end of the main control circuit, and is configured to obtain a fourth control signal for driving the synchronous switch by processing the second control signal and the third control signal.
The circuit of claim 1 wherein said LLC resonant converter comprises one of: a full-bridge LLC resonant converter, a half-bridge LLC resonant converter, or a multi-way interleaved LLC resonant converter.
The circuit according to claim 7, wherein when said LLC resonant converter is a multi-way interleaved LLC resonant converter, said primary LLC resonant circuit of said LLC resonant converter is connected in series or in parallel, said LLC resonant converter The secondary side rectifier circuits are connected in series or in parallel.
The circuit according to claim 8, wherein said main control circuit interleaves 90° to control two main switches in said primary side LLC resonant circuit when said LLC resonant converter is a two-way interleaved LLC resonant converter tube.
The circuit of claim 1 wherein said main switching transistor and said synchronous switching transistor are field effect transistors.