CN104539167A - Synchronous rectification control method of push-pull converter and control chip - Google Patents
Synchronous rectification control method of push-pull converter and control chip Download PDFInfo
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- CN104539167A CN104539167A CN201410804413.5A CN201410804413A CN104539167A CN 104539167 A CN104539167 A CN 104539167A CN 201410804413 A CN201410804413 A CN 201410804413A CN 104539167 A CN104539167 A CN 104539167A
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- synchronous rectification
- comparator
- switch pipe
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- triode
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
- H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
- H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
- H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
- H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/337—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only in push-pull configuration
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Abstract
The invention provides a synchronous rectification circuit of a push-pull converter and a control method thereof. The voltage on a vice-side winding of a push-pull circuit transformer is detected to achieve synchronous rectification control. The synchronous rectification circuit of the push-pull converter and the control method thereof can effectively solve the countercurrent flow problem of output energy of synchronous rectification under the light load condition, and while it is guaranteed that synchronous rectification improves the product full load efficiency, the light load efficiency of products can also be improved. A synchronous rectification switch tube is connected in advance through the design, the current flowing through a rectification tube body parasitic diode is effectively reduced, and the connecting loss is reduced. Meanwhile, the detection precision can be effectively improved through the method of detecting winding voltages, it is guaranteed that the working state of a synchronous rectification tube is not affected by the magnitude of the current flowing through the rectification tube any more, the reliability of products is improved, and the application range of the synchronous rectification circuit is also greatly increased due to the simple design to the greater limit.
Description
Technical field
The present invention relates to a kind of synchronous rectification control method and control chip, particularly a kind of synchronous rectification control method and control chip being applied to push-pull converter.
Background technology
Along with the development of power electronics industry, traditional linear power supply gradually by there is switching characteristic Switching Power Supply gradually substitute, it is high that Switching Power Supply has efficiency, the characteristic such as controlled, through years development, also there is different circuit topology in Switching Power Supply, comprising forward topology, flyback topologies etc., and the push-pull topology, bridge type topology etc. that are developed out by forward topology, different topologys has respective advantage.Wherein push-pull circuit has symmetry characteristic, and its drive singal is symmetrical expression, the alternation of two master power switch pipes, by transformer alternative expression to Load transportation energy, magnetic core is operated in first and third quadrant, effectively can reduce volume of transformer, thus reduces Switching Power Supply volume.Due to the characteristic of its Transformer Winding alternation, make it in micropower open loop type Switching Power Supply, be provided with more application, the simplicity of micropower Switching Power Supply in order to design, its output filter inductance saves when designing by people.
Royer circuit is also a kind of simple push-pull circuit, and its basic functional principle utilizes magnetic saturation characteristic to realize self-oscillation, realizes the work of two triode alternative expressions, realize the effect of energy transferring.In actual design and debug process, there is debug difficulties problem in Royer circuit, is unfavorable for that design is produced.In order to the people that solve the problem bring into use the control IC with self-oscillation function to remove to control the power tube of push-pull circuit, triode is replaced with the lower metal-oxide-semiconductor of conduction impedance simultaneously, improve circuit debugging efficiency on the one hand, also improve the reliability of product on the other hand.
In order to improve the efficiency of circuit further, people start the rectifier diode that metal-oxide-semiconductor that choice for use has a low conduction impedance substitutes fixed pressure drop, thus improve the efficiency of circuit, but also problem served by band simultaneously, as the driven management problem of devices, that relatively commonly uses at present has two kinds of drive schemes:
Scheme one, transformer is utilized to export winding self-driven mode, physical circuit is shown in Fig. 1, its basic functional principle is described below: when transformer primary side switching tube Q10 drives as high level, switching tube Q10 is open-minded, now switching tube Q20 drives as low level, switching tube Q20 turns off, now input voltage is added on transformer primary side winding 21, transformer Same Name of Ends is negative, on transformer secondary winding, voltage is distributed as: 4 ends are higher than 5 ends, 5 ends are higher than 6 ends, and switching tube Q31 conducting, Transformer Winding 56 provides energy to output loading.With should transformer primary side switching tube Q20 open time, Q10 turn off time, transformer secondary switching tube Q41 conducting, Transformer Winding 45 provides energy to load.
But following two shortcomings of the fairly simple existence of the program: 1, the drive singal of synchronous rectification switch pipe is the voltage on another symmetric winding, and the driving voltage maximum of switching tube is 20V, that is the ceiling voltage difference of transformer secondary winding 4 to 6 higher than 20V, can not so just limit the extensive use of circuit; 2, when circuit working is in underload, because synchronous rectification drives winding by clamper, easily there is energy reflux phenomenon in output, easy like this when causing underload, product efficiency is low, and time especially unloaded, loss increases, cause product to generate heat serious, affect the useful life of product.
Scheme two, to be realized synchronous rectification by special control IC and control, existing market has much such control IC, its general principle is all detect rectifier switch both end voltage in real time to fall realization control, but the program is generally used only in the larger product of output current, in small area analysis output products, the program cannot realize, and program control IC general cost is higher, volume is unfavorable for that more greatly non-voltage stabilizing small size series products is applied.
Summary of the invention
An object of the present invention is: the synchronous rectification control method that a kind of push-pull converter is provided, it is characterized in that: the voltage magnitude being detected transformer secondary winding by synchronous rectification control chip, control transformer secondary synchronous rectification switch pipe open sequential, service time and turn-off time, realize synchronous rectification work.
The course of work of described synchronous rectification control chip is:
When the input port V1 of synchronous rectification control chip detects that input voltage is negative voltage, synchronous rectification control chip internal timing circuit starts timing, now input port V2 detects that input voltage is positive voltage, synchronous rectification control chip drive singal port G22 output low level, drive singal port G11 exports high level, the conducting of transformer secondary the 3rd synchronous rectification switch pipe, transformer secondary the 4th synchronous rectification switch pipe turns off, and provides energy by transformer first vice-side winding to load; After elapsed time t1, drive singal port G11 output low level, turns off transformer secondary the 3rd synchronous rectification switch pipe;
After elapsed time t22, input port V1 detects that input voltage is positive voltage, when input port V2 detects that input voltage is negative voltage, synchronous rectification control chip internal timing circuit restarts timing, synchronous rectification control chip drive singal port G22 exports high level, drive singal port G11 output low level, the conducting of control transformer secondary the 4th synchronous rectification switch pipe, now transformer secondary the 3rd synchronous rectification switch pipe is still in off state, provides energy by transformer secondary second winding to load; After elapsed time t2, drive singal port G22 output low level, turns off transformer secondary the 4th synchronous rectification switch pipe; Now transformer secondary the 3rd synchronous rectification switch pipe and the 4th synchronous rectification switch pipe are all in off state;
After elapsed time t11, input port V1 detects that input voltage is negative voltage, repeats the above-mentioned course of work, alternate conduction transformer secondary the 3rd synchronous rectification switch pipe and transformer secondary the 4th synchronous rectification switch pipe.
Described t1, t2 are the ON time of transformer secondary the 3rd synchronous rectification switch pipe and transformer secondary the 4th synchronous rectification switch pipe respectively, according to the setting of synchronous rectification control chip inner parameter, and t1=t2.
Described t1, t2 are all less than driving high level time t and the Dead Time △ t sum of the control chip output of push-pull converter former limit, and before achieving the switching tube conducting of former limit, secondary synchronous rectification switch pipe is in off state, there will not be energy reflux phenomenon.
Another object of the present invention is to provide a kind of synchronous rectification control chip of push-pull converter.This object is achieved through the following technical solutions:
A synchronous rectification control chip for push-pull converter, comprises input port V1 and V2, drive singal port G11 and G22, feeder ear VCC, earth terminal GND.
Described input port V1 and V2 connects transformer respectively and exports non-voltage stabilizing end; Described drive singal port G11 and G22 connects the grid of transformer secondary the 3rd synchronous rectification switch pipe and the grid of transformer secondary the 4th synchronous rectification switch pipe respectively, driving transformer secondary the 3rd synchronous rectification switch pipe and transformer secondary the 4th synchronous rectification switch pipe alternate conduction.
Described power supply side VCC meets transformer secondary positive output port Vo.
Described earth terminal GND ground connection.
Preferably, the synchronous rectification control chip of described a kind of push-pull converter, also comprises the first comparator, the second comparator, the 3rd comparator, the 4th comparator, the 5th comparator, the 6th comparator, the first triode, the second triode, the 3rd triode, the 4th triode, the first constant-current source, the second constant-current source, the first electric capacity, the second electric capacity, the first gate-controlled switch, the second gate-controlled switch.
The positive input port of the first described comparator meets input port V1, negative input port ground connection, and output port connects the base stage of the first triode; The positive input port of the second described comparator meets input port V1, and negative input port connects reference voltage V 22, and output port meets the base stage of the second triode and the control end SW1 of the first gate-controlled switch; The emitter of the first triode is connected with 1 end of the first constant-current source, and the collector electrode of the first triode is connected with the collector electrode of the second triode; 0 termination feeder ear VCC of the first constant-current source; The emitter of the second triode connects 0 end of the second constant-current source, 1 end ground connection of the second constant-current source; The collector electrode of one termination second triode of the first electric capacity and 1 end of the first gate-controlled switch, 1 end of another termination second constant-current source of the first electric capacity; The positive input terminal of 0 termination the 3rd comparator of the first gate-controlled switch, the output termination drive singal port G22 of negative input termination reference voltage V the 11, three comparator of the 3rd comparator;
The positive input port of the 4th described comparator meets input port V2, negative input port ground connection, and output port connects the base stage of the 3rd triode; The positive input port of the 5th described comparator meets input port V2, and negative input port connects reference voltage V 22, and output port meets the base stage of the 4th triode and the control end SW2 of the second gate-controlled switch; The emitter of the 3rd triode is connected with 1 end of the first constant-current source, and the collector electrode of the 3rd triode is connected with the collector electrode of the 4th triode; The emitter of the 4th triode connects 0 end of the second constant-current source; The collector electrode of one termination the 4th triode of the second electric capacity and 1 end of the second gate-controlled switch, 1 end of another termination second constant-current source of the second electric capacity; The positive input terminal of 0 termination the 6th comparator of the second gate-controlled switch, the output termination drive singal port G11 of negative input termination reference voltage V the 11, six comparator of the 6th comparator;
Preferably, the synchronous rectification control chip of described a kind of push-pull converter, also comprises the 5th synchronous rectification switch pipe and the 6th synchronous rectification switch pipe, replaces the synchronous rectification switch pipe of transformer secondary, simplifies external circuit; The grid of the 5th synchronous rectification switch pipe and the grid of the 6th synchronous rectification switch pipe connect the output of the 3rd comparator and the output of the 6th comparator respectively, the drain electrode of the 5th synchronous rectification switch pipe connects detection port V1, the positive input terminal of the first comparator and the positive input terminal of the second comparator respectively, the drain electrode of the 6th synchronous rectification switch pipe connects detection port V2, the positive input terminal of the 4th comparator and the positive input terminal of the 5th comparator respectively, the source electrode of the 5th synchronous rectification switch pipe and the source ground of the 6th synchronous rectification switch pipe.
Described reference voltage V 22 can regulate according to design, setting answer the low Δ Vo of specific output voltage, the scope that arranges of Δ Vo is 0V-0.7V.Can realize before synchronous rectification switch body parasitic diode opens, the second comparator or the 5th comparator overturn in advance, make drive singal port G11 or G22 export high level in advance, realize opening the synchronous rectification switch pipe driven in advance.
Basic thought of the present invention is: in open loop type push-pull circuit, and former limit switching tube drive control signal is produced by former limit control chip U1, and the pulsewidth of control signal is t, there is Dead Time △ t between two path control signal.Secondary synchronous rectification control chip U2 detects the voltage on winding by special detection pin, record corresponding winding low level time t11 and t22, when this winding voltage becomes positive level, export drive control signal by control chip U2 and open synchronous rectifier, and synchronous rectifier is turned off after t1 or the t2 time, so alternately record the negative pressure time on corresponding winding, the ON time of control synchronization rectifying tube, make former limit switching tube Q1 or Q2 open front secondary synchronous rectification switch pipe Q3 and Q4 and be all in off state, effectively avoid output energy reflux, improve underloaded efficiency, this control program is by detecting Transformer Winding voltage simultaneously, do not limit by output current size, can reliably also can realize when small area analysis reliably controlling.
Beneficial effect of the present invention is as follows:
The present invention effectively can solve synchronous rectification in underloaded situation, export energy reflux phenomenon, while ensureing that synchronous rectification improves product full load efficiency, also can improve the light load efficiency of product.Synchronous rectification switch pipe can also be realized by design open-minded in advance, effectively reduce the electric current flowing through rectification body parasitic diode, reduce conduction loss.Simultaneously by detecting the method for winding voltage, effectively can improve accuracy of detection, ensure that synchronous rectifier operating state no longer by the impact of size of current flowing through rectifying tube, improve the reliability of product, because simplicity of design also adds the range of application of this invention to a greater extent.
Accompanying drawing explanation
Fig. 1 is self-driving type synchronous rectification push-pull circuit in prior art;
Fig. 2 synchronous rectification control chip of the present invention is applied to the circuit diagram of push-pull converter;
The circuit diagram of synchronous rectification control chip in Fig. 3 embodiment of the present invention;
Coherent signal sequential chart t<t12<t+ △ t in Fig. 4 embodiment of the present invention;
Coherent signal sequential chart t>t12 in Fig. 5 embodiment of the present invention;
Synchronous rectifier is integrated in the circuit diagram of synchronous rectification control chip inside by Fig. 6 the present invention.
Embodiment
Embodiment one
Fig. 2 is the circuit diagram that the present invention applies in push-pull converter, and the course of work that composition graphs 2 couples of the present invention realize synchronous rectification control method is explained.
BT is direct-current input power supplying, its negativing ending grounding, anode is connected with electric capacity C1 one end, and be connected with the VCC pin of control chip U1, be connected with the common tap point 2 of the second winding 23 with transformer first winding 12, the other end ground connection of electric capacity C1, the GND pin ground connection of control chip U1, G1 pin is connected with the grid of switching tube Q1, G2 pin is connected with switching tube Q2 grid, transformer T1 has four windings, be respectively winding 12, winding 23, winding 45, winding 56, wherein winding 12, 23 have a common tap point 2, winding 45, 56 have a common tap point 5, the drain electrode of 1 termination switching tube Q1 of winding 12, the drain electrode of 3 termination switching tube Q2 of winding 23, common tap point 2 connects the forward output of power supply BT, switching tube Q1, the source grounding of Q2, diode D1 and D2 is the body parasitic diode of switching tube Q1 and Q2 respectively.The common tap point 5 of transformer T1 vice-side winding 45 and 56 meets secondary positive output Vo and holds, the drain electrode of 4 termination switching tube Q4 of winding 45 and synchronous rectification control chip U2 detection signal input V2, the drain electrode of 6 termination switching tube Q3 of winding 56 and synchronous rectification control chip U2 detection signal input V1, the source electrode of switching tube Q3 with Q4 is connected with output filter capacitor C2 one end, connect load R one end simultaneously, the grid of switching tube Q3 with Q4 is connected with G22 pin with the G11 pin of synchronous rectification control chip U2 respectively, output filter capacitor C2 is connected with load R one end and is connected with output plus terminal Vo, diode D3 and D4 is switching tube Q3 and Q4 body parasitic diode respectively.
Operation principle and the course of work of this circuit are described below, suppose transformer T1 tetra-windings 12,23,45,56 turn ratioes are 1:1:1:1, and former limit is recommended chip U1 output and driven high level time to be t, Dead Time △ t is there is between two drive singal G1 and G2, and △ t is much smaller than drive singal high level time t, △ t+t=T/2, wherein T is the push-pull circuit drive singal work period.It is high level that control chip U1 output drive signal G1 is recommended on former limit, and G2 is low level, then switching tube Q1 grid is high level, switching tube Q2 grid is low level, switching tube Q1 is open-minded, and power supply BT voltage-drop loading is in Transformer Winding 21, and in Transformer Winding 21, voltage rises to V gradually by zero
bT, final V
21=V
bT, switching tube Q2 turns off, and according to Faraday's law of induction, on other winding of transformation T1, induced voltage is respectively to be reached by a certain uncertain magnitude of voltage and finally determines state, is respectively: V
23=-V
bT, V
45=V
bT, V
56=V
bT, in winding voltage change procedure, in the 6 pin voltages reduction process gradually of Transformer Winding 56, when 6 pin voltage ratio output ground GND1 voltages are low, then the body parasitic diode D of synchronous rectification switch pipe Q3
3conducting, now the drive singal output G11 of synchronous rectification control chip U2 exports high level, Q3 is open-minded for driving switch pipe, when the input pin V1 of synchronous rectification control chip U2 detects that transformer 6 pin is negative, chip U2 internal timing circuit starts timing, drive singal output G22 now output low level, input pin V2 does not now do any detection.Now transformer provides energy by Transformer Winding 56 to load, charges to electric capacity C2 simultaneously.
After elapsed time t, former limit control IC output drive signal G1 is by high step-down, and switching tube Q1 turns off, and now drive singal G2 is also low level, then former limit switching tube Q1 and Q2 is in off state simultaneously.Secondary synchronous rectification control chip U2 drive singal output pin G11 after t1 after a while exports and becomes low level from high level, and synchronous rectification switch pipe Q3 turns off, then now secondary synchronous rectification switch pipe Q3 and Q4 is in off state.Time, t1 was not more than T/2, if t1 is less than t, after then switching tube Q3 turns off, the still conducting of Q3 body parasitic diode, winding 56 continues to provide energy to output, until Transformer Winding 56 terminal voltage is higher than output GND1 voltage, Q3 body parasitic diode ends, so just can realize secondary-side switch pipe Q3 and Q4 when switching tube Q2 opens is in off state simultaneously, there will not be and exports energy reflux phenomenon; If t1 is greater than t, but when being less than t+ △ t, then, when Q3 turns off, namely Q3 body parasitic diode ends, and can be implemented in secondary-side switch pipe Q3 and Q4 when switching tube Q2 opens so equally and is in off state simultaneously, there will not be energy reflux phenomenon.The input pin V1 closing the chip U2 that has no progeny at switching tube Q3 detects that positive level stops detecting, and the detection time that tracer signal is detected pin V1 by chip U2 internal timer is t22.After switching tube Q1 turns off after Dead Time △ t, the driver output pin G2 output level of former limit control chip U1 is uprised by low, and former limit switching tube Q2 is open-minded, then Transformer Winding 23 two ends gradually become positive level by zero level, and is finally V
23=V
bT, and other winding voltage of transformer T1 also changes, the voltage of winding 12 becomes V from zero
bT, and winding 45 and 56 is gradually varied to final stable level by zero level too gradually: V
45=-V
bT, V
56=-V
bT, in the process of winding 45 change in voltage, but switching tube Q4 body parasitic diode is open-minded when winding 4 terminal voltage specific output ground GND1 is low, and the driver output pin G22 of the control chip of synchronous rectification simultaneously U2 exports high level, switching tube Q4 is open-minded, Transformer Winding 45 provides energy to secondary load R, charge to electric capacity C2 simultaneously, the input pin V2 opening chip U2 simultaneously at Q4 starts to detect Transformer Winding 4 end low level, after elapsed time t2, synchronous rectification control chip U2 driver control driver output pin G22 drive level is by high step-down, on-off switching tube Q4, time, t2 was not more than T/2, if t2 is less than t, after then switching tube Q4 turns off, the still conducting of Q4 body parasitic diode, winding 45 continues to provide energy to output, until Transformer Winding 45 terminal voltage is higher than output GND1 voltage, Q4 body parasitic diode ends, so just can realize secondary-side switch pipe Q3 and Q4 when switching tube Q1 opens is in off state simultaneously, there will not be and export energy reflux phenomenon, if t1 is greater than t, but when being less than t+ △ t, then, when Q4 turns off, namely Q4 body parasitic diode ends, and can be implemented in secondary-side switch pipe Q3 and Q4 when switching tube Q1 opens so equally and is in off state simultaneously, there will not be energy reflux phenomenon.Stop detecting when the input pin V2 that switching tube Q4 closes the chip U2 that has no progeny detects positive level, the detection time that tracer signal is detected pin V2 by U2 internal timer is t11.
Above-mentioned synchronous rectification control chip U2 has following characteristic, input pin V1 or V2 is when detecting that input voltage is negative value, namely U2 inside start timing, U2 output pin G11 or G22 also exports high level simultaneously, after certain hour t1 or t2, the corresponding driver output pin G11 of control chip U2 or G22 output low level, on-off switching tube Q3 or Q4, input pin V1 or V2 detects that incoming level stops timing when being positive level, synchronous rectification switch pipe service time t1 or t2 is all less than T/2, can ensure that secondary rectifier switch pipe Q3 and Q4 is all in off state before arbitrary switching tube Q1 or Q2 in former limit opens like this, thus ensure that output storage capacitor C2 energy can not reflux thus cause energy dissipation, improve the efficiency of power supply.
Embodiment two
Figure tri-is a kind of simplified models of control chip U2 internal circuit in the present invention, the input pin V1 of control chip U2 is connected with the positive input of comparator 1 with comparator 2 respectively, the negative input of comparator 1 is connected with the output ground GND1 of control chip U2, the output of comparator 1 is connected with the base stage of triode TR1, the emitter of triode TR1 is connected with 1 end of constant-current source 1, the collector electrode of triode TR1 is connected with electric capacity Cap1 one end, be connected with 1 end of gate-controlled switch 1 with the collector electrode of triode TR2 simultaneously, 0 end of gate-controlled switch 1 is connected with the positive input of comparator 3, gate-controlled switch 1 control end 2 end SW1 is connected with the output SW1 of comparator 2.0 end of constant-current source 1 is connected with the feeder ear VCC of U2.The negative input of comparator 2 is connected with reference level V22, the output of comparator 2 is connected with the base stage of triode TR2, the emitter of triode TR2 is connected with 0 end of constant-current source 2,1 end of constant-current source 2 is connected with the output ground GND1 of control chip U2, be connected with the other end of electric capacity Cap1 simultaneously, the negative sense input of comparator 3 is connected with reference level V11, and the output of comparator 3 is held with the G22 of control chip and is connected.The input pin V2 of control chip U2 is connected with the positive input of comparator 4 with comparator 5 respectively, the negative input of comparator 4 and the output ground GND1 of control chip U2, the output of comparator 4 is connected with the base stage of triode TR3, the emitter of triode TR3 is connected with 1 end of constant-current source 1, the collector electrode of triode TR3 is connected with electric capacity Cap2 one end, simultaneously with the collector electrode of triode TR4, 1 end of gate-controlled switch 2 is connected, 0 end of gate-controlled switch 2 is connected with the positive input of comparator 6, gate-controlled switch 2 control end 2 end SW2 is connected with the output SW2 of comparator 5.0 end of constant-current source 1 is connected with the feeder ear VCC of chip U2.The negative input of comparator 5 is connected with reference level V22, the output of comparator 5 is connected with the base stage of triode TR4, the emitter of triode TR4 is connected with 0 end of constant-current source 2,1 end of constant-current source 2 is connected with the output ground GND1 of control chip U2, be connected with the other end of electric capacity Cap2 simultaneously, the negative sense input of comparator 6 is connected with reference level V11, and the output of comparator 6 is held with the G11 of control chip U2 and is connected.Wherein reference level V11 and V22 is the internal reference level of U2 respectively, just be, specific design is carried out according to circuit parameter, constant-current source 1 and constant-current source 2 are U2 internal reference constant-current source equally, according to design parameter specific design, gate-controlled switch 1 and gate-controlled switch 2 respectively suspension control signal SW1 and SW2 control, and during high level, switch is open-minded.
Circuit working principles illustrated is as follows: composition graphs 2 and Fig. 3, when former limit control chip U1 drive output G1 output level by low raise gradually time, switching tube Q1 is open-minded gradually, and the winding 21 two ends level of transformer T1 becomes V from 0 gradually
bT, then Transformer Winding 45,56 two ends level also becomes V from 0 gradually
bTbecause transformer 4 end level is higher than 5 ends, so secondary synchronous rectifier Q4 body parasitic diode can not be opened, and transformer 5 end level is higher than 6 ends, and 5 ends are just connected with exporting, and transformer 5 end level uprises, then transformer 6 end level reduces gradually, when transformer 6 end level specific output ground GND1 is low, then synchronous rectifier Q3 body parasitic diode D3 conducting, Transformer Winding 56 provides energy by synchronous rectifier Q3 body parasitic diode D3 to secondary.And in the process of Transformer Winding change in voltage, following action is done: V1 end detects that transformer 6 end level is lower than after output ground GND1 after two test side V1 and V2 of control chip U2 detect corresponding signal respectively, the level of comparator 1 positive input is lower than negative sense input, then comparator 1 output low level, triode TR1 is open-minded, and constant-current source 1 charges to electric capacity Cap1.The level of the positive input of comparator 2 is lower than negative input, comparator 2 output SW1 output low level, gate-controlled switch 1 turns off, triode TR2 turns off, then the positive input level of comparator 3 is lower than negative input, comparator 3 output G22 output low level, synchronous rectifier Q4 turns off.And winding 45 both end voltage is just in time contrary with winding 56, the level of transformer 4 end raises gradually, then the input pin V2 of control chip U2 is input as positive level, then the level of comparator 4 positive input is higher than negative input, comparator 4 exports high level, and three grades of TR3 are in off state.The level of comparator 5 positive input is higher than negative input, the output SW2 of comparator 5 is high level, triode TR4 is open-minded, then electric capacity Cap2 is discharged by constant-current source 2, because SW2 is high level, then gate-controlled switch 2 is open-minded, the level of the positive input of comparator 6 is higher than negative input, then comparator 6 output G11 is high level, and Q3 is open-minded for synchronous rectification switch pipe, realize synchronous rectifier work, realize Transformer Winding 56 and power to secondary.After t1 after a while, electric capacity Cap2 makes both end voltage reach comparator 6 negative sense reference level V11 through constant-current source electric discharge, then comparator 6 output G11 will become low level, and synchronous rectification Q3 turns off.If time t1 is less than former limit switching tube service time t, then switching tube Q3 closes Transformer Winding 6 end of having no progeny is still low level, according to upper surface analysis, constant-current source 1 also continues to charge to electric capacity Cap1, constant-current source 2 continues to charge to electric capacity Cap2, until former limit drive singal turns off, drive singal enters Dead Time, the 6 end level of transformer T1 become GND1, and 4 ends are still high level, zero is input as according to upper surface analysis V1, V2 is input as height, then comparator 1 exports as high level, triode TR1 turns off, electric capacity Cap1 stops charging, and comparator 5 still exports high level, electric capacity Cap2 continues electric discharge until be zero.If t1 is greater than former limit switching tube service time t, but must be less than t+ △ t, then Q3 closes and has no progeny, and the 6 end level of transformer T1 become GND1, and 4 ends are still high level, be input as zero, V2 according to upper surface analysis V1 and be input as high level, then comparator 1 exports as high level, triode TR1 pipe turns off, electric capacity Cap1 stops charging, and comparator 5 still exports high level, and electric capacity Cap2 continues electric discharge until be zero.Time t1 is determined by current value I2, the reference level V1 of electric capacity Cap2 original levels Vcap2 and capacitor's capacity C2, constant-current source 2.The 6 end vanishing level of transformer T1 after t22 after a while, comparator 1 exports high level, and triode TR1 stops charging to electric capacity Cap1, then now electric capacity Cap1 voltage is Vcap1=I1 × t22/C1, wherein C1 is the capacitance of electric capacity Cap1, and I1 is the size of current of constant-current source 1.
Said process records transformer 6 end low level time by electric capacity Cap1, and transformer 6 end low level time is identical with former limit switching tube service time, then record former limit control chip U1 by Cap1 and export the time driving G1.Detect transformer 4 end level by comparator 5, Q3 is open-minded for control synchronization rectifier switch pipe, and is discharged by constant-current source 2 couples of electric capacity Cap2, control synchronization rectifier switch pipe switching time.
When former limit control chip U1 drive output G2 output level by low raise gradually time, switching tube Q2 is open-minded gradually, and the winding 23 two ends level of transformer T1 becomes V from 0 gradually
bT, then Transformer Winding 45,56 two ends level is also gradually by V
bTbecome-V
bTbecause transformer 6 end level is higher than 5 ends, so secondary synchronous rectifier Q3 body parasitic diode can not be opened, and transformer 5 end is higher than 4 ends, and 5 ends are just connected with exporting, and transformer 5 end level uprises, then transformer 4 end level reduces gradually, when transformer 4 end level specific output ground GND1 is low, then synchronous rectifier Q4 body parasitic diode D4 conducting, Transformer Winding 45 provides energy by synchronous rectifier Q4 body parasitic diode D4 to secondary.And in the process of Transformer Winding change in voltage, following action is done: V2 end detects that transformation 4 end level is lower than after output ground GND1 after two test side V1 and V2 of control chip U2 detect corresponding signal respectively, comparator 4 positive input level is lower than negative sense input, then comparator 4 output low level, triode TR3 is open-minded, and constant-current source 1 charges to electric capacity Cap2.The level of the positive input of comparator 5 is lower than negative input, comparator 5 output SW2 output low level, gate-controlled switch 2 turns off, triode TR4 turns off, then the level of the positive input of comparator 6 is lower than negative input, comparator 6 output G11 output low level, synchronous rectifier Q3 turns off.And winding 45 both end voltage is just in time contrary with winding 56, the level of transformer 6 end raises gradually, then the input pin V1 of control chip U2 is input as positive level, then the level of comparator 1 positive input is higher than negative input, comparator 1 exports high level, and triode TR1 is in off state.The level of comparator 2 positive input is higher than negative input, the output SW1 of comparator 2 is high level, triode TR2 is open-minded, then electric capacity Cap1 is discharged by constant-current source 2, because SW1 is high level, then gate-controlled switch is open-minded, the positive input of comparator 3 is higher than negative input, then comparator 3 output G22 is high level, and Q4 is open-minded for synchronous rectification switch pipe, realize synchronous rectifier work, realize Transformer Winding 45 and power to secondary.After t2 after a while, electric capacity Cap1 makes both end voltage reach comparator 3 negative sense reference level V11 through constant-current source electric discharge, then comparator 3 output G22 will become low level, and synchronous rectification Q4 turns off.If time t2 is less than former limit switching tube service time t, then switching tube Q4 closes Transformer Winding 4 end of having no progeny is still low level, according to upper surface analysis, constant-current source 1 also continues to charge to electric capacity Cap2, constant-current source 2 continues to charge to electric capacity Cap1, until former limit drive singal turns off, drive singal enters Dead Time, the 4 end level of transformer T1 become GND1, and 6 ends are still high level, zero is input as according to upper surface analysis V2, V1 is input as high level, then comparator 4 exports as high level, triode TR3 pipe turns off, electric capacity Cap2 stops charging, and comparator 2 still exports high level, electric capacity Cap1 continues electric discharge until be zero.If t2 is greater than former limit switching tube service time t, but must be less than t+ △ t, then Q1 closes and has no progeny, and the 4 end level of transformer T1 become GND1, and 6 ends are still high level, be input as zero, V2 according to upper surface analysis V1 and be input as height, then comparator 4 exports as high level, triode TR3 turns off, electric capacity Cap2 stops charging, and comparator 2 still exports high level, and electric capacity Cap1 continues electric discharge until be zero.Time t2 is determined by current value I2, the reference level V11 of electric capacity Cap1 original levels Vcap1 and capacitor's capacity C2, constant-current source 2.The 4 end vanishing level of transformer T1 after t11 after a while, comparator 4 exports high level, and triode TR3 stops charging to electric capacity Cap2, then now electric capacity Cap2 voltage is Vcap2=I1 × t11/C2, wherein C2 is the capacitance of electric capacity Cap2, and I1 is the size of current of constant-current source 1.
Said process records transformer 4 end low level time by electric capacity Cap2, and transformer 4 end low level time is identical with former limit switching tube service time, then record former limit control chip U1 by Cap2 and export the time driving G2.Detect transformer 6 end level by comparator 2, Q4 is open-minded for control synchronization rectifier switch pipe, and is discharged by constant-current source 2 couples of electric capacity Cap1, control synchronization rectifier switch pipe switching time.
By analyzing whole circuitry processes above, can find out that above-mentioned two processes are symmetrical, so foregoing circuit is in the design in order to the consistency of parameter, in circuit design, triode TR1 with TR3 can the consistent triode of Selection parameter, the triode that triode TR2 is consistent with TR4 Selection parameter, electric capacity Cap1 and electric capacity Cap2 equally can the consistent electric capacity of Selection parameter, synchronous rectification switch pipe Q3 and Q4 service time t1=t2, electric capacity Cap1 and electric capacity Cap2 charging interval t11=t22 can be realized like this.Synchronous rectification switch pipe ON time t1 or t2 can be realized by circuit design and be less than former limit switching tube service time t, thus ensure that secondary synchronous rectifier there will not be energy reflux phenomenon completely, while improving product efficiency, improve the reliability of product.Synchronous rectifier switching tube can be realized by the negative input reference voltage V 22 arranging comparator 2 and comparator 5 open-minded in advance, reduce the conduction loss of synchronous rectification switch body diode, thus improve power-efficient.
Fig. 4 and Fig. 5 be in the present invention correlation time sequential chart, wherein t is former limit switching tube service time, △ t is that former limit switching tube Q1 and Q2 opens Dead Time, within this time, switching tube Q1 and Q2 drive singal are low level, t1, t2 are secondary synchronous rectifier switching time respectively, make t1=t2=t12.T11, t22 are respectively electric capacity Cap1 and electric capacity Cap2 charging interval, make t11=t22.
Embodiment three
Fig. 6 is the circuit theory diagrams of the synchronous rectification control chip of the embodiment of the present invention three, with embodiment one unlike: be integrated with synchronous rectification switch pipe Q5 and Q6 in synchronous rectification control chip, instead of synchronous rectifier switch Q3 and Q4 of transformer secondary respectively, the circuit layout of push-pull converter can be simplified like this, compared with synchronous rectification control IC existing on market, not only simplify the complexity of circuit, and highly integratedly also reduce cost, reduce the volume of product, improve consistency and the reliability of product.Its annexation is: the grid of Q5 and Q6 connects the output of comparator 3 and the output of comparator 6 respectively, and the drain electrode of Q5 and Q6 connects V1 pin and the V2 pin of synchronous rectification control chip respectively, and the source electrode of Q5 and Q6 meets the ground GND1 of synchronous rectification control chip.Its course of work is identical with embodiment one, does not repeat them here.
Embodiments of the present invention are not limited thereto according to foregoing of the present invention; utilize ordinary technical knowledge and the customary means of this area; do not departing under the present invention's above-mentioned basic fundamental thought prerequisite; in the present invention, concrete implementing circuit can also make the amendment of other various ways, replacement or change, all drops within rights protection scope of the present invention.
Claims (8)
1. the synchronous rectification control method of a push-pull converter, the voltage magnitude of transformer secondary winding is detected by synchronous rectification control chip, control transformer secondary synchronous rectification switch pipe open sequential, service time and turn-off time, realize synchronous rectification work, it is characterized in that: the course of work of described synchronous rectification control chip is as follows:
When the input port V1 of synchronous rectification control chip detects that input voltage is negative voltage, synchronous rectification control chip internal timing circuit starts timing, now input port V2 detects that input voltage is positive voltage, synchronous rectification control chip drive singal port G22 output low level, drive singal port G11 exports high level, the conducting of transformer secondary the 3rd synchronous rectification switch pipe, transformer secondary the 4th synchronous rectification switch pipe turns off, and provides energy by transformer first vice-side winding to load; After elapsed time t1, drive singal port G11 output low level, turns off transformer secondary the 3rd synchronous rectification switch pipe;
After elapsed time t22, input port V1 detects that input voltage is positive voltage, when input port V2 detects that input voltage is negative voltage, synchronous rectification control chip internal timing circuit restarts timing, synchronous rectification control chip drive singal port G22 exports high level, drive singal port G11 output low level, the conducting of control transformer secondary the 4th synchronous rectification switch pipe, now transformer secondary the 3rd synchronous rectification switch pipe is still in off state, provides energy by transformer secondary second winding to load; After elapsed time t2, drive singal port G22 output low level, turns off transformer secondary the 4th synchronous rectification switch pipe; Now transformer secondary the 3rd synchronous rectification switch pipe and the 4th synchronous rectification switch pipe are all in off state;
After elapsed time t11, input port V1 detects that input voltage is negative voltage, repeats the above-mentioned course of work, alternate conduction transformer secondary the 3rd synchronous rectification switch pipe and transformer secondary the 4th synchronous rectification switch pipe.
2. the synchronous rectification control method of a kind of push-pull converter according to claim 1, it is characterized in that: described t1, t2 are the ON time of transformer secondary the 3rd synchronous rectification switch pipe and transformer secondary the 4th synchronous rectification switch pipe respectively, according to the setting of synchronous rectification control chip inner parameter, and t1=t2.
3. the synchronous rectification control method of a kind of push-pull converter according to claim 2, it is characterized in that: described t1, t2 are all less than driving high level time t and the Dead Time △ t sum of the control chip output of push-pull converter former limit, before achieving the switching tube conducting of former limit, secondary synchronous rectification switch pipe is in off state, there will not be energy reflux phenomenon.
4. a synchronous rectification control chip for push-pull converter, is characterized in that: comprise input port V1 and V2, drive singal port G11 and G22, feeder ear VCC, earth terminal GND;
Described input port V1 and V2 connects transformer respectively and exports non-voltage stabilizing end, is used for detecting the voltage magnitude of transformer output port; Described drive singal port G11 and G22 connects the grid of transformer secondary the 3rd synchronous rectification switch pipe and the grid of transformer secondary the 4th synchronous rectification switch pipe respectively, driving transformer secondary the 3rd synchronous rectification switch pipe and transformer secondary the 4th synchronous rectification switch pipe alternate conduction; Described power supply side VCC meets transformer secondary positive output port Vo; Described earth terminal GND ground connection.
5. the synchronous rectification control chip of a kind of push-pull converter according to claim 4, is characterized in that: also comprise the first comparator, the second comparator, the 3rd comparator, the 4th comparator, the 5th comparator, the 6th comparator, the first triode, the second triode, the 3rd triode, the 4th triode, the first constant-current source, the second constant-current source, the first electric capacity, the second electric capacity, the first gate-controlled switch, the second gate-controlled switch;
The positive input port of the first described comparator meets described input port V1, the negative input port ground connection of the first described comparator, and the output port of the first described comparator connects the base stage of the first described triode; The positive input port of the second described comparator meets input port V1, the negative input port of the second described comparator connects reference voltage V 22, and the output port of the second described comparator meets the base stage of the second described triode and the control end SW1 of the first described gate-controlled switch; The emitter of the first described triode is connected with 1 end of the first described constant-current source, and the collector electrode of the first described triode is connected with the collector electrode of the second described triode; 0 termination feeder ear VCC of the first described constant-current source; The emitter of the second described triode connects 0 end of the second described constant-current source, 1 end ground connection of the second described constant-current source; The collector electrode of the second triode described in one termination of the first described electric capacity and 1 end of described first gate-controlled switch, 1 end of the second constant-current source described in another termination of described first electric capacity; The positive input terminal of the 3rd comparator described in 0 termination of described first gate-controlled switch, the negative input termination reference voltage V 11 of described 3rd comparator, the drive singal port G22 described in output termination of described 3rd comparator;
The positive input port of the 4th described comparator meets described input port V2, the negative input port ground connection of the 4th described comparator, and the output port of the 4th described comparator connects the base stage of described 3rd triode; The positive input port of the 5th described comparator meets described input port V2, the negative input port of the 5th described comparator connects reference voltage V 22, and the output port of the 5th described comparator meets the base stage of described 4th triode and the control end SW2 of described second gate-controlled switch; The emitter of the 3rd described triode is connected with 1 end of the first described constant-current source, and the collector electrode of the 3rd described triode is connected with the collector electrode of the 4th described triode; The emitter of the 4th described triode connects 0 end of the second described constant-current source; The collector electrode of the 4th triode described in one termination of the second described electric capacity and 1 end of the second described gate-controlled switch, 1 end of second constant-current source described in another termination of the second described electric capacity; The positive input terminal of the 6th comparator described in 0 termination of the second described gate-controlled switch, the negative input termination reference voltage V 11 of the 6th described comparator, the drive singal port G11 described in output termination of the 6th described comparator.
6. the synchronous rectification control chip of a kind of push-pull converter according to claim 5, it is characterized in that: also comprise the 5th synchronous rectification switch pipe and the 6th synchronous rectification switch pipe, replace the 3rd synchronous rectification switch pipe and the 4th synchronous rectification switch pipe of transformer secondary, simplify external circuit, the grid of the 5th described synchronous rectification switch pipe and the grid of the 6th described synchronous rectification switch pipe connect the output of the 3rd described comparator and the output of the 6th described comparator respectively, the drain electrode of the 5th described synchronous rectification switch pipe meets detection port V1 respectively, the positive input terminal of the first described comparator and the positive input terminal of the second described comparator, the drain electrode of the 6th described synchronous rectification switch pipe meets detection port V2 respectively, the positive input terminal of the 4th described comparator and the positive input terminal of the 5th described comparator, the source electrode of the 5th described synchronous rectification switch pipe and the source ground of the 6th described synchronous rectification switch pipe.
7. the synchronous rectification control chip of a kind of push-pull converter according to claim 5, it is characterized in that: described reference voltage V 22 can regulate according to design, its value answers the low Δ Vo of specific output voltage Vo, realize before synchronous rectification switch body parasitic diode opens, the second described comparator or the 5th described comparator are overturn in advance, and then make described drive singal port G11 or G22 export high level in advance, realize opening the synchronous rectification switch pipe driven in advance.
8. the synchronous rectification control chip of a kind of push-pull converter described in requiring according to comprehensive 7, is characterized in that: the described general interval of Δ Vo is 0V to 0.7V.
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