CN105099194B - Tool improves the direction flyback converter and its control circuit of overcurrent protection - Google Patents
Tool improves the direction flyback converter and its control circuit of overcurrent protection Download PDFInfo
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- CN105099194B CN105099194B CN201410190331.6A CN201410190331A CN105099194B CN 105099194 B CN105099194 B CN 105099194B CN 201410190331 A CN201410190331 A CN 201410190331A CN 105099194 B CN105099194 B CN 105099194B
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Abstract
It is a kind of to have the direction flyback converter for improving overcurrent protection and its control circuit.Direction flyback converter includes first side winding, couples switch element, secondary side winding and the assists winding of first side winding.Assists winding detects output voltage, and exports first voltage.Circuit is controlled according to first voltage output control signal, with the switching for the switch element for controlling direction flyback converter.Circuit is controlled to include over-current judging unit and output voltage detection unit.Over-current judging unit couples switch element, according to current sensing signal and setting voltage output control signal.Current sensing signal corresponds to the electric current of first side winding.Output voltage detection unit couples assists winding and over-current judging unit, according to first voltage adjustment setting voltage, so that control signal does accommodation according to first voltage.The direction flyback converter and its control circuit of the present invention can automatically adjust setting voltage, and direction flyback converter is more effectively protected to reach.
Description
Technical field
The present invention provides a kind of direction flyback converter and its control circuit, and improves over current protection especially with regard to one kind tool
The direction flyback converter and its control circuit of shield.
Background technology
Because direction flyback converter (flyback converter) has high efficiency, low-loss, small size and lightweight etc.
Advantage, therefore it has been widely used to the power supply change-over device as various electronic products.To ask direction flyback converter normal
And stable running, the protection mechanism of direction flyback converter is very part and parcel, such as excess current protective function.
Traditional direction flyback converter is only using detecting primary side current (primary peak current) as output
The protection mechanism of overcurrent.Traditionally, the over-current protection point of primary side current is fixed, so can be realized more in output end
Low-voltage, more high current determine power (Constant Power) protection mechanism.However, when the output voltage of direction flyback converter
When causing the voltage to decline because of overcurrent, during, the power consumption (input of excessive protective current not only input power
Power dissipation) it can increase therewith, and unnecessary power consumption is caused, and need to use more high current specified
Power component, and the burden of cost is significantly increased.
The content of the invention
The present invention provides a kind of control circuit, for having the direction flyback converter for improving overcurrent protection.Flyback is changed
Device includes first side winding, couples switch element, secondary side winding and the assists winding of first side winding.Assists winding detection is defeated
Go out voltage, and accordingly export first voltage.Control circuit according to first voltage with accordingly output control signal to control to return
The switch element of formula of speeding converter.Circuit is controlled to include over-current judging unit and output voltage detection unit.Overcurrent is sentenced
Disconnected unit coupling switch element, according to current sensing signal and setting voltage output control signal.Current sensing signal corresponds to
The electric current of first side winding.Output voltage detection unit is coupled between assists winding and over-current judging unit.Output voltage is examined
Survey unit and setting voltage is accordingly adjusted according to first voltage, so that control signal does accommodation according to first voltage.
In an embodiment of the control circuit of the present invention, the output voltage detection unit includes：
One first diode, the anode tap of first diode is coupled to the assists winding；
One first resistor, one end of the first resistor couples the cathode terminal of first diode；
One first electric capacity, first electric capacity is coupled between the other end of the first resistor and an earth terminal；
One second resistance, the second resistance is coupled between the other end of the first resistor and the earth terminal；And
One second diode, one end of second diode couples one end of the second resistance, second diode it is another
One end couples the over-current judging unit.
In another embodiment of the control circuit of the present invention, the over-current judging unit includes：
One first comparator, with a first input end, one second input and one first output end, the first input end
The setting voltage is received, second input receives the current sensing signal, first output end is according to the current sensing signal
The control signal is exported with the setting voltage comparative result, to control the switching of the switch element, wherein this sets voltage as one
Reference voltage.
In another embodiment of the control circuit of the present invention, the over-current judging unit includes：
One first comparator, with a first input end, one second input and one first output end, the first input end
The setting voltage is received, second input receives the current sensing signal, first output end is according to the current sensing signal
The control signal is exported with the setting voltage comparative result, to control the switching of the switch element, wherein this sets voltage as one
The voltage of feedback signal.
In another embodiment of the control circuit of the present invention, the voltage of the feedback signal by a photo-coupler according to
Produced according to the output voltage of the direction flyback converter.
The present invention, which provides a kind of direction flyback converter for having improvement overcurrent protection, includes transformer, switch element, electric current
Sensing unit and control circuit.Transformer has first side winding, secondary side winding and assists winding, and wherein assists winding is used
To detect an output voltage of direction flyback converter, and accordingly export first voltage.Switch element couples first side winding.Electricity
Influenza lateral circuit is coupled between switch element and earth terminal, and the electric current of first side winding is converted into current sensing signal.Control
Circuit is according to first voltage and accordingly exports a control signal with controlling switch element, wherein control circuit is sentenced including overcurrent
Disconnected unit and output voltage detection unit.Over-current judging unit couples switch element, according to current sensing signal and setting
Voltage output control signal.Output voltage detection unit is coupled between assists winding and over-current judging unit.Output voltage is examined
Survey unit and setting voltage is accordingly adjusted according to first voltage so that control signal does accommodation electric current according to first voltage
Transducing signal.
In an embodiment of the direction flyback converter of the present invention, the output voltage detection unit includes：
One first diode, the anode tap of first diode is coupled to the assists winding；
One first resistor, one end of the first resistor couples the cathode terminal of first diode；
One first electric capacity, first electric capacity is coupled between the other end of the first resistor and an earth terminal；
One second resistance, the second resistance is coupled between the other end of the first resistor and the earth terminal；And
One second diode, one end of second diode couples one end of the second resistance, second diode it is another
One end couples the over-current judging unit.
In an embodiment of the direction flyback converter of the present invention, the over-current judging unit includes：
One first comparator, with a first input end, one second input and one first output end, the first input end
The setting voltage is received, second input receives the current sensing signal, first output end is according to the current sensing signal
The control signal is exported with the setting voltage comparative result, to control the switching of the switch element, wherein this sets voltage as one
Reference voltage.
In an embodiment of the direction flyback converter of the present invention, the over-current judging unit includes：
One first comparator, with a first input end, one second input and one first output end, the first input end
The setting voltage is received, second input receives the current sensing signal, first output end is according to the current sensing signal
The control signal is exported with the setting voltage comparative result, to control the switching of the switch element, wherein this sets voltage as one
The voltage of feedback signal.
In an embodiment of the direction flyback converter of the present invention, the voltage of the feedback signal passes through a photo-coupler
The output voltage according to the direction flyback converter is produced.
In summary, the embodiment of the present invention provides direction flyback converter and its control circuit that tool improves overcurrent protection
The mode of output voltage is detected according to assists winding, setting voltage can be automatically adjusted, flyback is more effectively protected to reach
Formula converter.In other words, when output voltage because overcurrent and caused by voltage step-down when, output voltage detection unit according to auxiliary around
Output voltage that group is detected and the first voltage that produces accordingly adjust setting voltage so that over-current judging unit can be with
Act ahead of time, to limit bigger energy transmission to output end.Therefore, direction flyback converter overall power can be not only reduced,
And without the use of the specified power component of more high current, will not more be added to this burden.
In order to be able to be further understood that the present invention, to reach technology, method and effect that set purpose is taken, is referred to
Below in connection with detailed description of the invention, accompanying drawing, it is believed that the purpose of the present invention, feature and feature, when can thus be able to deeply and
It is specific to understand, but appended accompanying drawing is only provided with annex and used with reference to explanation, not for the present invention person of being any limitation as.
Brief description of the drawings
Fig. 1 is a kind of direction flyback converter for controlling circuit to be used for tool improvement overcurrent protection provided in an embodiment of the present invention
Schematic diagram.
Fig. 2 is the specific electricity for the direction flyback converter that a kind of tool that another embodiment of the present invention is provided improves overcurrent protection
Lu Tu.
Fig. 3 is that the tool for showing Fig. 2 improves the output voltage and output current relation of the direction flyback converter of overcurrent protection
Figure.
Fig. 4 is the specific electricity for the direction flyback converter that a kind of tool that another embodiment of the present invention is provided improves overcurrent protection
Lu Tu.
Wherein, description of reference numerals is as follows：
1、2、3：Direction flyback converter
10：Transformer
20：Switch element
30：Current sensing unit
40：Control circuit
50：Secondary side circuit
60、80：Bleeder circuit
410、710：Output voltage detection unit
420、720：Over-current judging unit
510；Current rectifying and wave filtering circuit
520：Feedback circuit
521a：Light emitting diode
521b：Optotransistor
U1：Photo-coupler
U2：Three-terminal shunt regulator
D1：First diode
D2：Second diode
D3：Commutation diode
R1：First resistor
R2：Second resistance
C1：First electric capacity
R3、R4、R5、R6、R7、R8：Resistance
C2、C3：Electric capacity
V1：First voltage
V2：Set voltage
VG：Control signal
VB：Dc bias
IN：Input voltage
OUT、VOUT：Output voltage
IOUT：Output current
GND：Earth terminal
NP：First side winding
NA：Assists winding
NS：Secondary side winding
VCS：Current sensing signal
VFB：The voltage of feedback signal
RCS：Sensing resistor
OCP_Vref：Reference voltage
COMP1：First comparator
Embodiment
Various exemplary embodiments will be more fully described referring to annexed drawings below, will be shown in annexed drawings
Exemplary embodiments.However, concept of the present invention may embody in many different forms, and it should not be construed as limited by institute herein
The exemplary embodiments of elaboration.Specifically the present invention is caused to be detailed and complete there is provided these exemplary embodiments, and will
The category of concept of the present invention is fully passed on to those of ordinary skill in the art.In all accompanying drawings, can be lavished praise on oneself in order to clear layer and
The size and relative size in area.Similar numeral indicates similar component all the time.
Although it should be understood that term first, second, third, etc. may be used to describe various elements, these yuan herein
Part should not be limited by these terms.These terms are to distinguish an element and another element.Therefore, first yuan be discussed herein below
Part can be described as teaching of second element without departing from concept of the present invention.As used herein, term "or" can depending on actual conditions
Any one of project or all combinations of many persons can be listed including associated.
[tool improves the embodiment of the direction flyback converter of overcurrent protection]
First, Fig. 1 is refer to, Fig. 1 is that a kind of flyback for having improvement overcurrent protection provided in an embodiment of the present invention turns
The schematic diagram of parallel operation.As shown in figure 1, direction flyback converter 1 includes transformer 10, switch element 20, current sensing unit 30, control
Circuit 40 processed and secondary side circuit 50.Transformer 10 has first side winding NP, secondary side winding NS and assists winding NA.
The coupling first side winding of switch element 20 NP.Current sensing unit 30 is coupled between switch element 20 and earth terminal GND.Control
Circuit 40 includes output voltage detection unit 410 and over-current judging unit 420.Secondary side circuit 50 couples secondary side winding
NS, to form output voltage VO UT, and is powered to load (not shown).
In the present embodiment, sensing resistor RCS can be as current sensing unit 30, and is coupled to switch element 20 and ground connection
Between the GND of end.When switch element 20 turns on (turn on), sensing resistor RCS can be used for sensing and flow through first side winding NP
Primary side current, and produce and represent the current sensing signal VCS of primary side current.However, in other embodiment, electric current is passed
The circuit framework of sense unit 30 can have different circuit frameworks, and those of ordinary skill in the art can enter according to actual use situation
Row design, therefore the present invention is not any limitation as.
In addition, in the present embodiment, switch element 20 is a mos field effect transistor (MOSFET),
The grid G coupling over-current judging unit 420 of switch element 20, the drain D coupling first side winding NP of switch element 20, and open
Close the source S coupling overcurrent sensing unit 30 of element 20.However, in other embodiment, switch element 20 can be using double
Polarity junction transistor (BJT), other kinds of transistor or other kinds of switch, therefore the present invention is not any limitation as.
Hold above-mentioned, after direction flyback converter 1 receives input voltage VIN, by controlling the controlling switch element of circuit 40
20 switching, and then input voltage VIN is sent to the first side winding NP of transformer 10, so that transformer 10 is by input voltage
VIN is converted into output voltage VO UT to be powered to load (not shown).Further say, when direction flyback converter 1 is in opening
When pass element 20 turns on (turn on), energy will be stored in transformer 10, and according to the primary side electricity for flowing through switch element 20
The size of stream and change situation and corresponding output current transducing signal VCS are to over-current judging unit 420.In addition, once opening
When pass element 20 ends (turn off), the energy stored by transformer 10, which will be discharged via secondary side winding NS to flyback, to be turned
The output end OUT of parallel operation 1, while the output voltage that the assists winding NA of transformer 10 can be exported according to direction flyback converter 1
VOUT and accordingly produce first voltage V1, and first voltage V1 is inputted to output voltage detection unit 410.
Over-current judging unit 420 couples switch element 20, to compare the setting voltages of current sensing signal VCS and one
V2, and control signal VG is produced come the switching of controlling switch element 20 according to comparative result.On the other hand, output voltage detection is single
Member 410 couples assists winding NA and over-current judging unit 420, to receive first voltage V1, and according to V1 pairs of first voltage
Ground adjustment setting voltage V2 is answered, so that control signal VG can do accommodation according to first voltage V1, with further
The switching of ground controlling switch element 20.
For example, because assists winding NA is to detect output voltage VO UT and accordingly export first voltage V1, because
This, when tool improve overcurrent protection direction flyback converter 1 output end OUT because overcurrent and caused by output voltage VO UT decline
When, the first voltage V1 produced by assists winding NA also can be with decline.Accordingly, output voltage detection unit 410 can be according to drop
Low first voltage V1 sets voltage V2 accordingly to adjust, that is to say, that will setting voltage V2 reductions.In other words, due to setting
Determine voltage V2 reduction, the running that over-current judging unit 420 can be ahead of time is with the switching of controlling switch element 20, to limit more
Big energy transmission to direction flyback converter 1 output end OUT, and reach protection direction flyback converter 1 effect.
[tool improves the embodiment of the flyback converter circuit of overcurrent protection]
Fig. 2 is refer to, Fig. 2 is a kind of direction flyback converter for having improvement overcurrent protection provided in an embodiment of the present invention
Circuit diagram.Direction flyback converter 2 in Fig. 2 is similar to both outer direction flyback converters 1 in Fig. 1 structure, and below will be to two
Similar elements included by person are represented with identical label, and are further illustrated, output voltage detection unit 410 and overcurrent
The circuit framework of the thin portion of judging unit 420.
In the present embodiment, output voltage detection unit 410 includes the first diode D1, first resistor R1, the first electric capacity
C1, second resistance R2 and the second diode D2.First diode D1 anode tap coupling assists winding NA.First resistor R1's
One end couples the first diode D1 cathode terminal.Between first electric capacity C1 coupling first resistors the R1 other end and earth terminal GND.
Between second resistance R2 coupling first resistors the R1 other end and earth terminal GND.Second diode D2 anode tap coupling second
Resistance R2 one end, the second diode D2 cathode terminal coupling over-current judging unit 420.
Over-current judging unit 420 includes first comparator COMP1, and wherein first comparator COMP1 has the first input
End, the second input and the first output end.First input end couples the second diode D2 cathode terminal, to receive first voltage
V1.Second input couples the source terminal S of switch element 20, to receive current sensing signal VCS.First output end is according to electric current
Transducing signal VCS and setting voltage V2 comparative result carrys out the switching of controlling switch element 20 with output control signal VG, wherein
Voltage V2 is set as a reference voltage OCP_Vref.
In addition, resistance R3 and resistance R4 constitutes a bleeder circuit 60, it is electric to produce a reference to partial pressure Dc bias VB
OCP_Vref is pressed, and reference voltage OCP_Vref is inputted to comparator COMP1 first input end.
Followed by the operation principle for further illustrating direction flyback converter 2.Specifically, when operation, flyback turns
Parallel operation 1 is received after input voltage VIN, and the first comparator COMP1 in over-current judging unit 420 is sensed by electric current
Signal VCS produces control signal VG with setting voltage V2 comparative result, and switches switch element 20 according to control signal VG,
So that input voltage VIN is converted to output voltage VO UT to be powered to a load (not shown) by transformer 10.
However, when direction flyback converter 1 output end because overcurrent and caused by output voltage VO UT decline when, it is now, auxiliary
Help winding NA accordingly to produce first voltage V1 according to detected output voltage VO UT, and by the first diode D1 with
And the resistance R1 and resistance R2 bleeder circuit that is formed adjusts first voltage V1, to form relatively low first voltage V1, wherein
Noises of the first electric capacity C1 to filter out first voltage V1.
Then, relatively low first voltage V1 is again via the second diode D2 to be injected into the first of first comparator COMP1
Input, thereby reduces setting voltage V2 (the i.e. reference voltage OCP_ positioned at first comparator COMP1 first input end
Vref).In other words, can suitably it be adjusted positioned at the first defeated of first comparator COMP1 via output voltage detection unit 410
Enter the setting voltage V2 at end.Therefore, because setting voltage V2 (i.e. reference voltage OCP_Vref) reduction so that first comparator
When COMP1 compares current sensing signal VCS and setting voltage V2 (i.e. reference voltage OCP_Vref), current sensing signal VCS is high
Can occur ahead of time in setting voltage V2 (i.e. reference voltage OCP_Vref), that is to say, that what first comparator COMP1 can be ahead of time is defeated
Go out the switching that running carrys out controlling switch element 20 with output control signal VG.Accordingly, the size of primary side current is reduced, one is gone forward side by side
Bigger energy transmission is limited to step to output end, to reach the effect of protection direction flyback converter 2.
In other words, reference picture 3, Fig. 3 is the output electricity of the direction flyback converter for the tool improvement overcurrent protection for illustrating Fig. 2
Pressure and output current graph of a relation.In Fig. 3, the longitudinal axis represents output voltage VO UT, and transverse axis represents output current IO UT.Curve C1
Represent the output voltage VO UT and output current IO UT of traditional direction flyback converter relation curve.Curve C2 represents the present embodiment
Direction flyback converter 1 output voltage VO UT and output current IO UT relation curve.
By Fig. 3 it is known that when the direction flyback converter 1 of traditional direction flyback converter and the present embodiment is simultaneously in output
When the situation of overcurrent occurs for end, the over-current judging unit 420 in the direction flyback converter 1 of the present embodiment is compared to traditional
The action that direction flyback converter can do sth. in advance, to limit bigger energy transmission to output end.In addition, curve C1 and C2 can be obtained
Know, when the situation of overcurrent occurs for output end, the direction flyback converter 1 of the present embodiment is compared to traditional direction flyback converter
The output voltage VO UT exported is relatively low, and output current IO UT is relatively low.Therefore, examined through output voltage detection unit 410
The setting voltage V2 for the first output end for surveying output voltage VO UT accordingly to adjust first comparator COMP1 mode, can be with
Outside the power consumption for reducing input power, also without the use of the specified power component of more high current.
[tool improves another embodiment of the flyback converter circuit of overcurrent protection]
Fig. 4 is refer to, Fig. 4 is that a kind of tool that another embodiment of the present invention is provided improves the flyback conversion of overcurrent protection
The circuit diagram of device.Direction flyback converter 3 in Fig. 4 is similar to both direction flyback converters 1,2 in Fig. 1,2 structure, and following
Similar elements included by the two will be represented with identical label.The difference of both direction flyback converters 2,4 is：Output voltage
The coupling mode of the second diode D2 in detection unit 410,710 is simultaneously differed.In addition, over-current judging unit 420,720
In the first comparator COMP1 setting voltage V2 that is received of the first output end also differ.In addition, in this embodiment,
Further illustrate, the circuit framework of the thin portion of secondary side circuit 50.
In detail, as shown in figure 4, output voltage detection unit 710 includes the first diode D1, first resistor R1, the
One electric capacity C1, second resistance R2 and the second diode D2.First diode D1 anode tap coupling assists winding NA.First electricity
The one end for hindering R1 couples the first diode D1 cathode terminal.The first electric capacity C1 coupling first resistors R1 other end and earth terminal
Between GND.Between second resistance R2 coupling first resistors the R1 other end and earth terminal GND.Second diode D2 cathode terminal
Couple second resistance R2 one end, the second diode D2 anode tap coupling over-current judging unit 720.
Over-current judging unit 720 includes first comparator COMP1, wherein, first comparator COMP1 has the first input
End, the second input and the first output end.First input end couples the second diode D2 anode tap.The coupling of second input is opened
The source terminal S of element 20 is closed, to receive current sensing signal VCS.First comparator COMP1 the first output end is passed according to electric current
Signal VCS is felt with setting voltage V2 comparative result with output control signal VG, carrys out the switching of controlling switch element 20, wherein,
In this embodiment, voltage VFBs of the voltage V2 as a feedback signal is set.
On the other hand, the coupling of secondary side circuit 50 secondary side winding NS, to form output voltage VO UT, and is loaded to one
(not shown) is powered.Secondary side circuit 50 includes current rectifying and wave filtering circuit 510 and feedback circuit 520.Current rectifying and wave filtering circuit
510 include commutation diode D3 and electric capacity C2.Commutation diode D2 anodes couple secondary side winding NS, and commutation diode D2 is cloudy
Pole coupling capacitance C2 wherein one end, and between electric capacity C2 couplings commutation diode D2 and earth terminal GND.Current rectifying and wave filtering circuit
510 voltage to be exported to secondary side winding NS carries out rectification and filtering.
Feedback circuit 520 to sample output voltage VO UT to produce the voltage VFB of feedback signal corresponding with loading, its
In, it is in parallel steady that feedback circuit 520 includes resistance R5~R7, electric capacity C3, photo-coupler U1 light emitting diode 521a and three ends
Depressor U2 (Three-Terminal Shunt Regulator), three-terminal shunt regulator U2 have anode tap A, cathode terminal K and
Reference edge R.It is noted that photo-coupler U1 optotransistor 521b is disposed in a lateral circuit, and with resistance R8
Series connection is to form a bleeder circuit 80, the voltage VFB to form feedback signal, and inputs to the of first comparator COMP1
One input.
Further say, feedback circuit 520 is then, defeated after sampling through resistance R6 and R7 sampling output voltage VO UT
Go out control source to three-terminal shunt regulator U2 reference edge R, and three-terminal shunt regulator U2 passes through its internal circuit and then production
The raw corresponding electric current If for flowing through resistance R5.It follows that electric current If size corresponds to the size of load.In addition, electric current If
During by photo-coupler U1 light emitting diode 521a, the optotransistor 521b of the photo-coupler U1 in a lateral circuit also can
Produce corresponding electric current.Therefore, load capacity is also corresponded in the photo-coupler U1 optotransistor 521b size of current produced,
Can as feedback signal voltage VFB.
Followed by the operation principle for further illustrating direction flyback converter 3.In detail, direction flyback converter 1 is received
After input voltage VIN, first comparator COMP1 in over-current judging unit 720 through electric current obtain transducing signal VCS with
Voltage V2 (i.e. the voltage VFB of feedback signal) comparative result is set to produce control signal VG, and is cut according to control signal VG
Switch element 20 is changed, so that input voltage VIN is converted to output voltage VO UT to a load (not shown) to enter by transformer 10
Row power supply.Therefore, when normal operating, the first voltage V1 that assists winding NA is accordingly produced according to output voltage VO UT,
Then, after bleeder circuits of the first voltage V1 by the first diode D1 and resistance R1 and resistance R2 formation, now the
One voltage V1 voltage quasi position is above the voltage VFB of feedback signal, that is to say, that the now electricity of the second diode D2 cathode terminals
Level is pressed to be higher than the voltage quasi position of the second diode D2 anode taps, and due to the characteristic of diode, electric current can only be toward single direction
Flowing.That is, electric current can only flow to negative electrode from anode, and anode can not be flowed to from negative electrode.Therefore, direction flyback converter 3
When normal operating, output voltage detection unit 710 can not export first voltage V1 first defeated to first comparator COMP1
Enter end.
However, when direction flyback converter 3 output end because overcurrent and caused by output voltage VO UT decline when, it is now, auxiliary
Winding NA is helped also to be declined according to the detected output voltage VO UT first voltage V1 accordingly exported so that the second diode
The voltage quasi position of D2 cathode terminals is less than the voltage quasi position of the second diode D2 anode taps, now, and the voltage VFB of feedback signal can be saturating
Cross the second diode D2 to be discharged, thereby reduce the setting voltage V2 positioned at first comparator COMP1 first input end
(i.e. the voltage VFB of feedback signal).In other words, through the second diode D2 of conducting mode, suitably to adjust positioned at first
The setting voltage V2 (i.e. the voltage VFB of feedback signal) of comparator COMP1 first input end.
Accordingly, due to setting voltage V2 (i.e. the voltage VFB of feedback signal) reduction so that first comparator COMP1 ratios
During compared with current sensing signal VCS and setting voltage V2 (i.e. the voltage VFB of feedback signal), current sensing signal VCS is higher than setting
Voltage V2 (i.e. the voltage VFB of feedback signal) can occur ahead of time, that is to say, that first comparator COMP1 can be operated with defeated ahead of time
Go out the switching that control signal VG carrys out controlling switch element 20, further, since the progress that the switching of switch element 20 can be ahead of time is cut
Change, therefore, reduce the size of primary side current, and further limit bigger energy transmission to output end, to reach guarantor
Protect the effect of direction flyback converter 3.
[possible effect of the invention]
In summary, the embodiment of the present invention provides direction flyback converter and its control circuit that tool improves overcurrent protection
Output voltage, and the accordingly mode of adjustment setting voltage can be detected according to assists winding so that switch element 20 can be carried
Early running, more effectively to protect direction flyback converter.
In other words, when output voltage because of overcurrent and caused by voltage step-down when, output voltage detection unit can basis
Output voltage that assists winding is detected and accordingly adjust setting voltage so that over-current judging unit can be according to adjustment
Setting voltage does sth. in advance action and carrys out controlling switch element with output control signal, to limit bigger energy transmission to output end.Cause
This, can not only reduce direction flyback converter overall power, and without the use of the specified power component of more high current, will not more increase
The burden of addition sheet.
Sum it up, the tool that the embodiment of the present invention is provided improves the direction flyback converter and its control electricity of overcurrent protection
Road can utilize less element and the change of the circuit of minimum, you can reach power consumption (the input power of reduction input power
dissipation)。
It is described above, it is only the optimal specific embodiment of the present invention, but the feature of the present invention is not limited thereto, it is any
Those of ordinary skill in the art in the field of the invention, can think easily and change or modification, can all cover in following this case
Claim.
Claims (8)
1. one kind control circuit, for a direction flyback converter, the direction flyback converter includes a first side winding, a switch member
Part, a secondary side winding and an assists winding, the switch element couple the first side winding, and the assists winding is to detect that this is returned
One output voltage of formula of speeding converter, and a first voltage is accordingly exported, the control circuit exports one according to the first voltage
Control signal is to control the switching of the switch element, and the control circuit includes：
One over-current judging unit, is coupled to the switch element, and the over-current judging unit compares a current sensing signal and one
Voltage is set, to produce the control signal, the wherein current sensing signal corresponds to the electric current of the first side winding；And
One output voltage detection unit, is coupled to the assists winding and the over-current judging unit, the output voltage detection unit
The setting voltage is adjusted according to the first voltage, so that the control signal does accommodation according to the first voltage；
Wherein the output voltage detection unit includes：
One first diode, the anode tap of first diode is coupled to the assists winding；
One first resistor, one end of the first resistor couples the cathode terminal of first diode；
One first electric capacity, first electric capacity is coupled between the other end of the first resistor and an earth terminal；
One second resistance, the second resistance is coupled between the other end of the first resistor and the earth terminal；And
One second diode, one end of second diode couples one end of the second resistance, the other end of second diode
The over-current judging unit is coupled, and it is connecing as the offer setting voltage to couple one of over-current judging unit contact
Point；
Wherein the over-current judging unit includes：
One first comparator, with a first input end, one second input and one first output end, the first input end is received
The setting voltage, second input receives the current sensing signal, and first output end is according to the current sensing signal with being somebody's turn to do
Setting voltage comparative result exports the control signal, to control the switching of the switch element.
2. this of control circuit according to claim 1, wherein the over-current judging unit set voltage as a reference voltage.
3. this of control circuit according to claim 1, wherein the over-current judging unit set voltage as a feedback signal
Voltage.
4. control circuit according to claim 3, the wherein voltage of the feedback signal are by a photo-coupler according to the flyback
The output voltage of converter is produced.
5. a kind of have the direction flyback converter for improving overcurrent protection, it is characterised in that including：
One transformer, with a first side winding, a secondary side winding and an assists winding, wherein the assists winding is to detect
One output voltage of the direction flyback converter, and accordingly export a first voltage；
One switch element, couples the first side winding；
One current sensing unit, is coupled between the switch element and an earth terminal, and the electric current of the first side winding is converted into one
Current sensing signal；And
One control circuit, exports according to the first voltage and accordingly a control signal to control the switching of the switch element, its
In the control circuit include：
One over-current judging unit, is coupled to the switch element, and the over-current judging unit compare the current sensing signal with
One setting voltage, to produce the control signal；And
One output voltage detection unit, is coupled to the assists winding and the over-current judging unit, the output voltage detection unit
The setting voltage is accordingly adjusted according to the first voltage, to cause the control signal to do adaptability tune according to the first voltage
It is whole；
Wherein the output voltage detection unit includes：
One first diode, the anode tap of first diode is coupled to the assists winding；
One first resistor, one end of the first resistor couples the cathode terminal of first diode；
One first electric capacity, first electric capacity is coupled between the other end of the first resistor and an earth terminal；
One second resistance, the second resistance is coupled between the other end of the first resistor and the earth terminal；And
One second diode, one end of second diode couples one end of the second resistance, the other end of second diode
The over-current judging unit is coupled, and it is connecing as the offer setting voltage to couple one of over-current judging unit contact
Point；
Wherein the over-current judging unit includes：
One first comparator, with a first input end, one second input and one first output end, the first input end is received
The setting voltage, second input receives the current sensing signal, and first output end is according to the current sensing signal with being somebody's turn to do
Setting voltage comparative result exports the control signal, to control the switching of the switch element.
6. this of the direction flyback converter of tool improvement overcurrent protection according to claim 5, wherein the over-current judging unit
Voltage is set as a reference voltage.
7. this of the direction flyback converter of tool improvement overcurrent protection according to claim 5, wherein the over-current judging unit
Set voltage of the voltage as a feedback signal.
8. tool according to claim 7 improves the direction flyback converter of overcurrent protection, the voltage of the wherein feedback signal passes through
One photo-coupler is produced according to the output voltage of the direction flyback converter.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201410190331.6A CN105099194B (en) | 2014-05-07 | 2014-05-07 | Tool improves the direction flyback converter and its control circuit of overcurrent protection |
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|---|---|---|---|
| CN201410190331.6A CN105099194B (en) | 2014-05-07 | 2014-05-07 | Tool improves the direction flyback converter and its control circuit of overcurrent protection |
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| CN105099194B true CN105099194B (en) | 2017-10-24 |
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| CN107705763B (en) * | 2017-10-12 | 2020-04-28 | 深圳市华星光电技术有限公司 | Level conversion circuit and liquid crystal display device |
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| CN105099194A (en) | 2015-11-25 |
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