CA1283166C - Flyback power supply - Google Patents
Flyback power supplyInfo
- Publication number
- CA1283166C CA1283166C CA000520853A CA520853A CA1283166C CA 1283166 C CA1283166 C CA 1283166C CA 000520853 A CA000520853 A CA 000520853A CA 520853 A CA520853 A CA 520853A CA 1283166 C CA1283166 C CA 1283166C
- Authority
- CA
- Canada
- Prior art keywords
- power supply
- terminal
- transformer
- output terminal
- output
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Lifetime
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Classifications
-
- 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
-
- 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
- H02M3/33507—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 with automatic control of the output voltage or current, e.g. flyback converters
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
FLYBACK POWER SUPPLY
ABSTRACT
A flyback power supply (10) is disclosed which includes a sample and hold feedback path. A pulse width modulation circuit (23) provides control signals for a drive device (20) that determines current excitation pulses for a primary winding (17) of a transformer (16).
A secondary winding (19) of the transformer is connected to a rectifier circuit (21, 22) and provides a DC voltage signal at an output terminal (12). A selective feedback path (40 - 49) is provided between the output terminal and a sense input terminal (24) of the pulse width modulation circuit. The selective feedback path comprises a sample and hold circuit (40) which provides for effectively coupling the output terminal to the sense input terminal at time during the storage of energy in the transformer, corresponding to an increase in transformer flux, and wherein at other times when the transformer flux is decreasing and energy is being transferred from the transformer to the rectifier circuit the feedback path effectively disconnects the output terminal from the sense input. The sample and hold circuit comprises a series pass transistor (41) and a holding capacitor (42). The series pass transistor is selectively turned on and off in accordance with the control output signal of the pulse width modulation circuit (23) that determines the primary winding current pulses.
ABSTRACT
A flyback power supply (10) is disclosed which includes a sample and hold feedback path. A pulse width modulation circuit (23) provides control signals for a drive device (20) that determines current excitation pulses for a primary winding (17) of a transformer (16).
A secondary winding (19) of the transformer is connected to a rectifier circuit (21, 22) and provides a DC voltage signal at an output terminal (12). A selective feedback path (40 - 49) is provided between the output terminal and a sense input terminal (24) of the pulse width modulation circuit. The selective feedback path comprises a sample and hold circuit (40) which provides for effectively coupling the output terminal to the sense input terminal at time during the storage of energy in the transformer, corresponding to an increase in transformer flux, and wherein at other times when the transformer flux is decreasing and energy is being transferred from the transformer to the rectifier circuit the feedback path effectively disconnects the output terminal from the sense input. The sample and hold circuit comprises a series pass transistor (41) and a holding capacitor (42). The series pass transistor is selectively turned on and off in accordance with the control output signal of the pulse width modulation circuit (23) that determines the primary winding current pulses.
Description
3~i6 FLYBACK POWER SUPPLY
Backqround o~ the Invention The present invention i9 related to the ~ield o~
~lyback power supplies. ~ore particularly, the present invention i~ related to stable ~lyback power ~uppli8s which include an output sensing ~eedback control loop and wherein the power supply remains stable even when operated in a continuous excitation mode with respect to current excitation of the primary winding oi a flyback trans~oxmer in the power supply.
In known flyback power supplies, pulsed current excitation is ~upplied to the primary winding o~ a flyback transformer and a secondary winding of the trans~ormer is couple~, typically through a rectifier, to a load. The recti~ied output i~ sensed and provided by a ~eedback path as an input to a drive circuit which provides drive signals that determine the primary winding current excitation pulses. The drive signals vary in accordance with the sensed output ~o as to maintain the output at a desired 18vel, thus regulating the output.
Typiaally these ~lyback power supplies are operated in a discontinuous mode ~or ~tability reasons.
~k - 2 ~ 00612 In a discontinuous mode, magnetic flux will increase in the transformer during primary winding currenk pulses, and between primary winding current pulses the flux decreases to a substantially zero value~ Typically the decrease of ~lux to zero i8 abrupt, and ~lyback trans~ormers operated in the discontinuous mode typically generate sub~tantial radio ~requency inter~erence (RF~).
In addition, typically large primary winding current pulses mu~t be utilized in order to ~tore a substantial amount o~ energy for 3ubsequent tran~er to the secondary winding, or else the ~requency o~ the primary excitation pulses must be increased.
If the flyback power supply i5 ope~ated in a continuous mode such that the transformer ~lux has a substantial non-zero magnitude prior to the drive circuit causing an increase in flux to store additional energy, less primary current can be utilized and less RF
interference is generated. Alqo a lower excitation frequency can be used i~ desired. However~ operating in a continuous mode typically results in stability problems for the power supply, thu~ preventing the utilization of a continuous mode flyback power supply or requiring tight controls on ~he system gain, the input signal magnitude and the ~requency o~ primary current excitation in order to maintain limited stability. However, due to load variation, typically this stability cannot be maintained.
There~ore, substantially all ~lyback power ~upplies are operated in the discontinuous mode.
Summary o~ the Invention An ob~ect o~ the present invention is to provide an improved ~lyback power supply which overcomes the above-mentioned de~iciencie~ of prior ~lyback power supplies.
Backqround o~ the Invention The present invention i9 related to the ~ield o~
~lyback power supplies. ~ore particularly, the present invention i~ related to stable ~lyback power ~uppli8s which include an output sensing ~eedback control loop and wherein the power supply remains stable even when operated in a continuous excitation mode with respect to current excitation of the primary winding oi a flyback trans~oxmer in the power supply.
In known flyback power supplies, pulsed current excitation is ~upplied to the primary winding o~ a flyback transformer and a secondary winding of the trans~ormer is couple~, typically through a rectifier, to a load. The recti~ied output i~ sensed and provided by a ~eedback path as an input to a drive circuit which provides drive signals that determine the primary winding current excitation pulses. The drive signals vary in accordance with the sensed output ~o as to maintain the output at a desired 18vel, thus regulating the output.
Typiaally these ~lyback power supplies are operated in a discontinuous mode ~or ~tability reasons.
~k - 2 ~ 00612 In a discontinuous mode, magnetic flux will increase in the transformer during primary winding currenk pulses, and between primary winding current pulses the flux decreases to a substantially zero value~ Typically the decrease of ~lux to zero i8 abrupt, and ~lyback trans~ormers operated in the discontinuous mode typically generate sub~tantial radio ~requency inter~erence (RF~).
In addition, typically large primary winding current pulses mu~t be utilized in order to ~tore a substantial amount o~ energy for 3ubsequent tran~er to the secondary winding, or else the ~requency o~ the primary excitation pulses must be increased.
If the flyback power supply i5 ope~ated in a continuous mode such that the transformer ~lux has a substantial non-zero magnitude prior to the drive circuit causing an increase in flux to store additional energy, less primary current can be utilized and less RF
interference is generated. Alqo a lower excitation frequency can be used i~ desired. However~ operating in a continuous mode typically results in stability problems for the power supply, thu~ preventing the utilization of a continuous mode flyback power supply or requiring tight controls on ~he system gain, the input signal magnitude and the ~requency o~ primary current excitation in order to maintain limited stability. However, due to load variation, typically this stability cannot be maintained.
There~ore, substantially all ~lyback power ~upplies are operated in the discontinuous mode.
Summary o~ the Invention An ob~ect o~ the present invention is to provide an improved ~lyback power supply which overcomes the above-mentioned de~iciencie~ of prior ~lyback power supplies.
- 3 ~ AP-00612 A more speci~ic ob~ect of the present invention is to provide a stable flyback powçr supply which can be operated in a continuou~ mode.
In one embodiment of the present invention a ~lyback power supply i~ provided. The ~lyback power supply comprises- terminal mean~ for receiving a DC
power supply voltage input ~ignal having a magnitude which may vary over a ranga o~ magnitudes; trans~ormer means having a primary winding coupled to said terminal mean~ and a secondary winding; drive circuit means having at least a sense signal input and providing, as an output, a control input signal to a control electrode o~
a drive devia~ coupled to said primary winding ~or controlling primary current therein provided by said power supply voltage input signal; rectifier means coupled to said secondary winding ~or rectifying signals induced in said secondary winding and providing, at an output terminal, a DC power supply output voltage in response thereto; ~eedhack path means connected between said output terminal and said sense input for controlling said drive circuit means to maintain said power supply output signal at a desired level; wherein the improvement comprises; said feedback path means comprising a sample and hold circuit comprising a controllable gate device provided between said output terminal and a holding capacitor connected to said sen~e input, a control terminal o~ said gate device receiving switching signals, wherein said gate device i9 alternately opened and closed such that said power supply output ~ignal is e~eatively sampled by said holding capacitor whan said control device causes primary windlng current ~low causing a ~lux increase in said trans~ormer means so as to store energy therein, and wherain said holding capacitor is e~ectively disconnected ~rom said output terminal at all other time~ when ~lux in said krans~ormer mean~ decreases ' .
3~
In one embodiment of the present invention a ~lyback power supply i~ provided. The ~lyback power supply comprises- terminal mean~ for receiving a DC
power supply voltage input ~ignal having a magnitude which may vary over a ranga o~ magnitudes; trans~ormer means having a primary winding coupled to said terminal mean~ and a secondary winding; drive circuit means having at least a sense signal input and providing, as an output, a control input signal to a control electrode o~
a drive devia~ coupled to said primary winding ~or controlling primary current therein provided by said power supply voltage input signal; rectifier means coupled to said secondary winding ~or rectifying signals induced in said secondary winding and providing, at an output terminal, a DC power supply output voltage in response thereto; ~eedhack path means connected between said output terminal and said sense input for controlling said drive circuit means to maintain said power supply output signal at a desired level; wherein the improvement comprises; said feedback path means comprising a sample and hold circuit comprising a controllable gate device provided between said output terminal and a holding capacitor connected to said sen~e input, a control terminal o~ said gate device receiving switching signals, wherein said gate device i9 alternately opened and closed such that said power supply output ~ignal is e~eatively sampled by said holding capacitor whan said control device causes primary windlng current ~low causing a ~lux increase in said trans~ormer means so as to store energy therein, and wherain said holding capacitor is e~ectively disconnected ~rom said output terminal at all other time~ when ~lux in said krans~ormer mean~ decreases ' .
3~
and said stored energy is provided to ~aid secondary winding and to said recti~ier ~eans, whereby stability o~
said powsr supply is provided by discontinuous feedback path sampling at times other than the times at which energy i9 txan~ferred from said primary to secondary windings.
More particularly, in the preferred embodiment of the pre~ent invention, ths driva device will implement a continuou~ mode o~ excitation ~or the ~lybaak transformer such that the trans~ormer ~lux ha~ a ~ubstantial non-zero magnitud~ prior to the drive device initiating primary winding current ~low causing the ~lux to increase. The preferred embodiment of the present invention utilizes a pulse width modulation circuit as the drive circuit means and provides for alternately opening and closing the gate device in accordance with an output of the pulse width modulation circuit that is provided as the control input signal to the drive device t~at determines the primary winding excitation. This insures the proper synchronization of the controllable gate device with respect to primary winding excitation. In addition, preferably the gate device comprises a series pass device connected between the output terminal and the pulse width modulation sense input. Pre~erably the drive device comprises an FET transistor.
By providing a discontinuous ~eedback path in accordance with the keachings o~ the present invention, a ~lyback power supply has been provided which i8 unconditionally stable regardless o~ variations in power supply load and regardless o~ variations in the magnitude o~ the DC power supply voltage input signal. This mean~
less expensive, looser tolerance circuit components can be used. When ~he power supply is operated in a continuous mode, this results in less radio ~requency ~3~L6~
said powsr supply is provided by discontinuous feedback path sampling at times other than the times at which energy i9 txan~ferred from said primary to secondary windings.
More particularly, in the preferred embodiment of the pre~ent invention, ths driva device will implement a continuou~ mode o~ excitation ~or the ~lybaak transformer such that the trans~ormer ~lux ha~ a ~ubstantial non-zero magnitud~ prior to the drive device initiating primary winding current ~low causing the ~lux to increase. The preferred embodiment of the present invention utilizes a pulse width modulation circuit as the drive circuit means and provides for alternately opening and closing the gate device in accordance with an output of the pulse width modulation circuit that is provided as the control input signal to the drive device t~at determines the primary winding excitation. This insures the proper synchronization of the controllable gate device with respect to primary winding excitation. In addition, preferably the gate device comprises a series pass device connected between the output terminal and the pulse width modulation sense input. Pre~erably the drive device comprises an FET transistor.
By providing a discontinuous ~eedback path in accordance with the keachings o~ the present invention, a ~lyback power supply has been provided which i8 unconditionally stable regardless o~ variations in power supply load and regardless o~ variations in the magnitude o~ the DC power supply voltage input signal. This mean~
less expensive, looser tolerance circuit components can be used. When ~he power supply is operated in a continuous mode, this results in less radio ~requency ~3~L6~
- 5 - AP-00~12 inter~erence being generated by the ~lyback power supply and can result in utilization of lower magnitude primary wind~ng current excitation pulses. In addition, the present invention provide~ greater de3ign flexibility with regard to determining the frequency of operation o~
the pulse width modulakion circuit such that eithar high or low ~requencies can be selected for the period of the signal that determine~ the primary winding current excitation pulses. If a high frequency of operation is 5elected, which i5 now pos3ible sinco less RF
inter~erence is produced, less expen~ive, smaller size circuit components can be utilized ~or the power supply.
These and other advantages of the present invention are best under~tood by reference to the more detailed description of the present invention which follows.
Brie~ Description of the Drawinq For a more complete understanding o~ the present invention, reference should be made to the drawing in which:
Figure 1 comprises a schematic diagram of a flyback power supply constructed in accordance with the teachings of the present lnvention.
Description of the Preferred Embodiments o~ the Invention Referring to the drawing, a flyhack power supply 10 is illustrated. The power supply include~ an input terminal 11 at which a DC power supply voltage input signal Vin is received wherein the magnitude o~ this 35 signal may vary over a wide range of magnitudes. In e~sence, the ~lyback power supply raceives a DC input ~ignal Vin and provides, in responRe thereto, a well regulatQd DC output signal VOUt at an output terminal 12. It is contemplated that various load~, shown schematically in the Figure ag load 13, may be connected to the output terminal 12. Thus the flyback power supply perform~ a regulating and pow~r transfer function so as to yenerate the desired regulated ~ignal Vout~
The input terminal 11 is connected to a terminal 14 through a ~ilter network 15 shown dashed ln the Figure. The Pilter network per~orms an initial voltage smoothing ~unction ~or the signal Vin 80 as to provide a DC signal at the terminal 14 with somewhat le88 ripple.
The flyback power supply 10 includes a tran~ormer 16 having a primary winding 17 having one end dir~ctly connected to the termlnal 14 and another end directly connected to the drain terminal of an FET transistor 20.
The transformer 16 include~ a transformer core 18, in which trAnsformer flux is created by excitation of the primary winding 17, and a secondary winding lg coupled to th~ transformer core and primary winding. One end of the secondary windiny 19 is connected to ground, and another end is connected through a rectifying diode 21 to the output terminal 12 while a capacitor 22 is aonnected between the terminal 12 and ground. Essentially, the diode 21 and capacitor 22 ~orm a rectifying means coupled to the secondary winding 19 Por rectifying signals induced in the secondary winding and provi~ing a DC power supply output voltage in response there~o at the output terminal 12.
The FET tran~istor 20 essentially controls the current excitation o~ the pri~ary winding 17 by being periodically dr:Lven on and o~f. A ~ource terminal o~ the FET transistor is directly connected to ground and a gate or control electrode terminal oP the FET transistor 33~3l6~
the pulse width modulakion circuit such that eithar high or low ~requencies can be selected for the period of the signal that determine~ the primary winding current excitation pulses. If a high frequency of operation is 5elected, which i5 now pos3ible sinco less RF
inter~erence is produced, less expen~ive, smaller size circuit components can be utilized ~or the power supply.
These and other advantages of the present invention are best under~tood by reference to the more detailed description of the present invention which follows.
Brie~ Description of the Drawinq For a more complete understanding o~ the present invention, reference should be made to the drawing in which:
Figure 1 comprises a schematic diagram of a flyback power supply constructed in accordance with the teachings of the present lnvention.
Description of the Preferred Embodiments o~ the Invention Referring to the drawing, a flyhack power supply 10 is illustrated. The power supply include~ an input terminal 11 at which a DC power supply voltage input signal Vin is received wherein the magnitude o~ this 35 signal may vary over a wide range of magnitudes. In e~sence, the ~lyback power supply raceives a DC input ~ignal Vin and provides, in responRe thereto, a well regulatQd DC output signal VOUt at an output terminal 12. It is contemplated that various load~, shown schematically in the Figure ag load 13, may be connected to the output terminal 12. Thus the flyback power supply perform~ a regulating and pow~r transfer function so as to yenerate the desired regulated ~ignal Vout~
The input terminal 11 is connected to a terminal 14 through a ~ilter network 15 shown dashed ln the Figure. The Pilter network per~orms an initial voltage smoothing ~unction ~or the signal Vin 80 as to provide a DC signal at the terminal 14 with somewhat le88 ripple.
The flyback power supply 10 includes a tran~ormer 16 having a primary winding 17 having one end dir~ctly connected to the termlnal 14 and another end directly connected to the drain terminal of an FET transistor 20.
The transformer 16 include~ a transformer core 18, in which trAnsformer flux is created by excitation of the primary winding 17, and a secondary winding lg coupled to th~ transformer core and primary winding. One end of the secondary windiny 19 is connected to ground, and another end is connected through a rectifying diode 21 to the output terminal 12 while a capacitor 22 is aonnected between the terminal 12 and ground. Essentially, the diode 21 and capacitor 22 ~orm a rectifying means coupled to the secondary winding 19 Por rectifying signals induced in the secondary winding and provi~ing a DC power supply output voltage in response there~o at the output terminal 12.
The FET tran~istor 20 essentially controls the current excitation o~ the pri~ary winding 17 by being periodically dr:Lven on and o~f. A ~ource terminal o~ the FET transistor is directly connected to ground and a gate or control electrode terminal oP the FET transistor 33~3l6~
- 7 - ~P-00612 receives periodic variable duty cycle pul~e~ fro~ a pulse width modulation (PWM) circuit 23 shown in the Figure.
The pulse width modulation circuit 23 ha~ a sense input terminal 24 ~or receiving signal~ generally related to the magnitude o~ the output signal Vout~ Tha PWM
circuit 23 also includes a reference terminal 25 at which an external predetermined re~erence voltage may be provided. Alternatively, the circuit 23 may internally generate the re~erence voltage at terminal 25. In response to the di~erence between the output r~lated sen~e voltage at the terminal 24 and the reference voltage at the terminal 25, the pulse width modulation circu~t 23 provides, ae an output at a terminal 26, a control input signal which is applied to tho gate of the FET transistor 20. The FET 20 serves as a drive device for the primary winding 17 of the trans~ormer 16. In this manner, the output of the pulse width modulation circuit, via the dri~e device 20, controls the primary winding current which i~ provided by the voltage at the terminal 14 that is determined in accordance with the voltage input signal Vin It should be noted that preferably the pulse width modulation circuit 23 shown in the Figure can comprise a Motorola integrated circuit MC34060 which is re~ponsive to DC sense signals so as to provide a variable duty cycle pulse width modulated output signal in accordance with the di~ference between the sensed signal magnitude and a re~erence voltage maintained at the terminal 25. The ~inal output device o~ the pulsa width modulation circuit 23 is ~hown in the Figure as an NPN transistor 27 having its collector connected to the terminal 26. Due to this con~iguration, a biasing/load resistor 28 is coupled betwaen the terminal 26 and the terminal 1~. In addition, the ~lyback power supply 10 shown in the Figure includes a conventional "snubber"
The pulse width modulation circuit 23 ha~ a sense input terminal 24 ~or receiving signal~ generally related to the magnitude o~ the output signal Vout~ Tha PWM
circuit 23 also includes a reference terminal 25 at which an external predetermined re~erence voltage may be provided. Alternatively, the circuit 23 may internally generate the re~erence voltage at terminal 25. In response to the di~erence between the output r~lated sen~e voltage at the terminal 24 and the reference voltage at the terminal 25, the pulse width modulation circu~t 23 provides, ae an output at a terminal 26, a control input signal which is applied to tho gate of the FET transistor 20. The FET 20 serves as a drive device for the primary winding 17 of the trans~ormer 16. In this manner, the output of the pulse width modulation circuit, via the dri~e device 20, controls the primary winding current which i~ provided by the voltage at the terminal 14 that is determined in accordance with the voltage input signal Vin It should be noted that preferably the pulse width modulation circuit 23 shown in the Figure can comprise a Motorola integrated circuit MC34060 which is re~ponsive to DC sense signals so as to provide a variable duty cycle pulse width modulated output signal in accordance with the di~ference between the sensed signal magnitude and a re~erence voltage maintained at the terminal 25. The ~inal output device o~ the pulsa width modulation circuit 23 is ~hown in the Figure as an NPN transistor 27 having its collector connected to the terminal 26. Due to this con~iguration, a biasing/load resistor 28 is coupled betwaen the terminal 26 and the terminal 1~. In addition, the ~lyback power supply 10 shown in the Figure includes a conventional "snubber"
circuit 29 shown dashed as comprising a dioda 30, a resistor 31 and a capacitor 32 connacted between the drain terminal of the FET 20 and ground. The function of the snubber circuit i3 essentially ko protect the FET
device from high reverse bias voltages which may be generated by abruptly interrupting the current flow in the primary winding 17 when the ~ET transistor is turned o~. The snubber circuit 29 e~sentially ~unctions to limit the magnituda o~ the reverse bias voltages produced at the drain terminal o~ the FET. The operation of the snubber circuit is not particularly significant with respect to the present invention.
It should be noted that an FET transistor is utilized to control the switching of the primary winding current since suc~ transistors have good high ~requency and temperature characteriatics thus enabling operation of the flyback power ~upply over wide temperature ranges and enabling tha selection of a relatively high ~requency, if desired, ~or the periodic s~itching on and o~ of the FET transistor which results in the generation of periodic current pulses for the primary winding 17.
A feedback path is provided between the output terminal 12 and the sense input terminal 24 o~ the pulse width modulation clrcuit 23. The function o~ this feedback path is to provide, at the sense terminal 24, a signal related to the magnitude o~ the output voltage VOUt. Typically this ~eedback path can comprise either a direct connection or a trans~ormer couplad conneation between the output terminal 12 and the sense terminal 24.
However, the provision in prior ~lyback transformers o~
this feedback path generally resulted in stability problems ~or the ~lyback pow~r supply, particularly i~
the power ~upply was operated in a continuous mode wherein the transformer ~lux had a substantially non-zero 33~
device from high reverse bias voltages which may be generated by abruptly interrupting the current flow in the primary winding 17 when the ~ET transistor is turned o~. The snubber circuit 29 e~sentially ~unctions to limit the magnituda o~ the reverse bias voltages produced at the drain terminal o~ the FET. The operation of the snubber circuit is not particularly significant with respect to the present invention.
It should be noted that an FET transistor is utilized to control the switching of the primary winding current since suc~ transistors have good high ~requency and temperature characteriatics thus enabling operation of the flyback power ~upply over wide temperature ranges and enabling tha selection of a relatively high ~requency, if desired, ~or the periodic s~itching on and o~ of the FET transistor which results in the generation of periodic current pulses for the primary winding 17.
A feedback path is provided between the output terminal 12 and the sense input terminal 24 o~ the pulse width modulation clrcuit 23. The function o~ this feedback path is to provide, at the sense terminal 24, a signal related to the magnitude o~ the output voltage VOUt. Typically this ~eedback path can comprise either a direct connection or a trans~ormer couplad conneation between the output terminal 12 and the sense terminal 24.
However, the provision in prior ~lyback transformers o~
this feedback path generally resulted in stability problems ~or the ~lyback pow~r supply, particularly i~
the power ~upply was operated in a continuous mode wherein the transformer ~lux had a substantially non-zero 33~
- 9 - AP~00612 magnitude at and immediately prior to the turning on of the drive device that then requlted in causing primary winding current 80 as to increase the trans~ormer ~lux.
In such situations, substantial stability problem~
existed which typically resulted in all prior ~lyback trans~ormers being operated in the discontinuous mode despite the fact that in such a mode high primary current pulse~ wero required and substantial RF inter~erence was generated. These disadvantages have been overcome by the present invention.
In the ~lyback power supply 10, a selective discontinuous ~eedback path 40 is provided between the outpu~ terminal 12 and the input sense terminal 24. This ~eedback path 40 is shown dashed in the Figure and comprises a PNP series pass transistor 41 having its emitter terminal directed connected to the output terminal 12 and lts collector terminal directly connected to one electrode of a holding capacitor 42 having its other electrode connected to ground. The transistor 41 forms a controllable gate device. The base o~ the transistor 41 is connected to the terminal 12 through a biasing resistor 43. An NPN control transistor 44 i provided in the feedback path 40 and has its emitter connected to ground, its collector connected to the base of the transistor 41 through a resistor 45 and its base connected to ground through a capacitor 46 and connected to the terminal 26 through a resistor 47. The collector o~ the transistor 41 is directly connected to the sensed terminal 24 through a series resistor 48 wherein a resistor 49 connected bekween the terminal 24 and ground and performs a vol~age divider ~unction in combination wlth the resistor 48. Essentially the components 41 through ~9 comprise the selective ~eedback path 40 o~ the present lnvention. The path 40 comprises a DC circuit ~2~33~i ~ 10 - AP-00612 path between the serie~ pa~ device 41 and terminal~ 12 and 24.
Essentially, the selectiva feedback path 40 implements a sample and hold function by v.irtue of the selsctive conduction o~ the serie~ pass device 41 and the holding capacitor 42 such that an effective direct connection between the terminal 12 and the sense terminal 24 is only provided at certain times. In the present invention, these time~ occur during the existence o~
primary winding current pulse~ which cause an increase in the transformer ~lux so as to store energy in the transformer. This occurs by virtue of the periodic pulse width modulation control input signal provided at the terminal 26 functioning a~ a switching signal. This switching signal cause~ the FET transistor 20 to turn on and, at the æame time, turns on the transistor 4~ which results in turning on the transistor 41. Thus during primary winding current pulses causing an increase in transformer flux, the series pass transistor 41 couples the voltage at the terminal 12 to the holding capacitor 42. This effectively ~amples the signal Vout~ When the pulse width modulation control signal at the terminal 26 turns off the FET drive device 20, current effectively ceases in the primary winding 17 and flux in the transformer 16 will decrease resulting in the transfer of the stored energy in the transformer to the secondary winding 19 and to the rectifier circuit comprising ths components 21 and 22. At this time, the transistors 44 and 41 are turned of~, thus preventing any transient signals at the tsrminal 12 from reaching th~ holding capacitor 42 and the sense input terminal 24. Because o~
thi~, the ~tability of the ~lyback power supply 10 is mainkained since instability typically results from providing a continuous feedback path between the output and sense terminals during the time that energy is ~ ~3~
~ransf2rred from the trans~ormer to the recti~ier circuit.
Because o~ the configuration o~ the present invention, the ~lyback power supply 10 is unconditionally stable, thus allowing the power supply t4 be operated in a continuous mode, whereas previously operating a flyback power ~upply in a continuous mode would nok be possible since the power supply would not remain stable and would produce undesired signal 09cillation~. In the continuous mode o~ operation, the period o~ the control signal provided at the terminal 26 by the pulse width modulator circuit 23 i~ such that the trans~ormer ~lux, while decreasing during the off time o~ the FET transistor 20, never reaches a substantially zero magnitud~ prior to the occurrence of the next primary winding current pulse.
Thus pre~erably the flyback transformer 10 is operated in a continuous mode such that flux in the transformer will have a substantial non-zero magnitude at and immediately prior to the time the FET transistor inltiates primary winding current ~low pulses which cause the transformer flux to increase. Because of this, the ef~ective inductance of the primary winding 17 is increased such that a larger amount of energy is storable in the trans~ormer 16 while a smaller amount o~ current can be utili~ed to provide this larger amount of stored energy.
In addition, operation in the continuous mode reduces RF
interference which may be produced by the switching on and o~ o~ the primary current.
It should be noted tha~ while the present invention is described in terms o~ a ~lyback power supply designed to operate in a continuous mode, the present invention is also applicable to ~lyback power supplies that are des.igned to operate in a discontinuous mode, but may occasionally be inadvertently opcrated in a ~3~
continuous mode dua to variations in the load 13. Thus the present invention provides for unconditional stability of flyback power supply 10 regardless of what kype o~ mode it is dasigned to be operated in. This stability i8 achieved despite any variations in the load 13. In addition, this stability is also maintained despite wide variation~ in the magnitudQ o~ the input signal Vin While specific embodiments of the present invention have beQn shown and described, further modi~ications and improvements will occur to those skilled ln th~ art. All such modi~ication~ which retain the basic underlying principles di~closed and claimed herein are within the scope o~ this invention.
In such situations, substantial stability problem~
existed which typically resulted in all prior ~lyback trans~ormers being operated in the discontinuous mode despite the fact that in such a mode high primary current pulse~ wero required and substantial RF inter~erence was generated. These disadvantages have been overcome by the present invention.
In the ~lyback power supply 10, a selective discontinuous ~eedback path 40 is provided between the outpu~ terminal 12 and the input sense terminal 24. This ~eedback path 40 is shown dashed in the Figure and comprises a PNP series pass transistor 41 having its emitter terminal directed connected to the output terminal 12 and lts collector terminal directly connected to one electrode of a holding capacitor 42 having its other electrode connected to ground. The transistor 41 forms a controllable gate device. The base o~ the transistor 41 is connected to the terminal 12 through a biasing resistor 43. An NPN control transistor 44 i provided in the feedback path 40 and has its emitter connected to ground, its collector connected to the base of the transistor 41 through a resistor 45 and its base connected to ground through a capacitor 46 and connected to the terminal 26 through a resistor 47. The collector o~ the transistor 41 is directly connected to the sensed terminal 24 through a series resistor 48 wherein a resistor 49 connected bekween the terminal 24 and ground and performs a vol~age divider ~unction in combination wlth the resistor 48. Essentially the components 41 through ~9 comprise the selective ~eedback path 40 o~ the present lnvention. The path 40 comprises a DC circuit ~2~33~i ~ 10 - AP-00612 path between the serie~ pa~ device 41 and terminal~ 12 and 24.
Essentially, the selectiva feedback path 40 implements a sample and hold function by v.irtue of the selsctive conduction o~ the serie~ pass device 41 and the holding capacitor 42 such that an effective direct connection between the terminal 12 and the sense terminal 24 is only provided at certain times. In the present invention, these time~ occur during the existence o~
primary winding current pulse~ which cause an increase in the transformer ~lux so as to store energy in the transformer. This occurs by virtue of the periodic pulse width modulation control input signal provided at the terminal 26 functioning a~ a switching signal. This switching signal cause~ the FET transistor 20 to turn on and, at the æame time, turns on the transistor 4~ which results in turning on the transistor 41. Thus during primary winding current pulses causing an increase in transformer flux, the series pass transistor 41 couples the voltage at the terminal 12 to the holding capacitor 42. This effectively ~amples the signal Vout~ When the pulse width modulation control signal at the terminal 26 turns off the FET drive device 20, current effectively ceases in the primary winding 17 and flux in the transformer 16 will decrease resulting in the transfer of the stored energy in the transformer to the secondary winding 19 and to the rectifier circuit comprising ths components 21 and 22. At this time, the transistors 44 and 41 are turned of~, thus preventing any transient signals at the tsrminal 12 from reaching th~ holding capacitor 42 and the sense input terminal 24. Because o~
thi~, the ~tability of the ~lyback power supply 10 is mainkained since instability typically results from providing a continuous feedback path between the output and sense terminals during the time that energy is ~ ~3~
~ransf2rred from the trans~ormer to the recti~ier circuit.
Because o~ the configuration o~ the present invention, the ~lyback power supply 10 is unconditionally stable, thus allowing the power supply t4 be operated in a continuous mode, whereas previously operating a flyback power ~upply in a continuous mode would nok be possible since the power supply would not remain stable and would produce undesired signal 09cillation~. In the continuous mode o~ operation, the period o~ the control signal provided at the terminal 26 by the pulse width modulator circuit 23 i~ such that the trans~ormer ~lux, while decreasing during the off time o~ the FET transistor 20, never reaches a substantially zero magnitud~ prior to the occurrence of the next primary winding current pulse.
Thus pre~erably the flyback transformer 10 is operated in a continuous mode such that flux in the transformer will have a substantial non-zero magnitude at and immediately prior to the time the FET transistor inltiates primary winding current ~low pulses which cause the transformer flux to increase. Because of this, the ef~ective inductance of the primary winding 17 is increased such that a larger amount of energy is storable in the trans~ormer 16 while a smaller amount o~ current can be utili~ed to provide this larger amount of stored energy.
In addition, operation in the continuous mode reduces RF
interference which may be produced by the switching on and o~ o~ the primary current.
It should be noted tha~ while the present invention is described in terms o~ a ~lyback power supply designed to operate in a continuous mode, the present invention is also applicable to ~lyback power supplies that are des.igned to operate in a discontinuous mode, but may occasionally be inadvertently opcrated in a ~3~
continuous mode dua to variations in the load 13. Thus the present invention provides for unconditional stability of flyback power supply 10 regardless of what kype o~ mode it is dasigned to be operated in. This stability i8 achieved despite any variations in the load 13. In addition, this stability is also maintained despite wide variation~ in the magnitudQ o~ the input signal Vin While specific embodiments of the present invention have beQn shown and described, further modi~ications and improvements will occur to those skilled ln th~ art. All such modi~ication~ which retain the basic underlying principles di~closed and claimed herein are within the scope o~ this invention.
Claims (12)
1. A flyback power supply comprising:
terminal means for receiving a DC power supply voltage input signal having a magnitude which may vary over a range of magnitudes;
transformer means having a primary winding coupled to said terminal means and a secondary winding;
drive circuit means having at least a sense signal input and providing, as an output, a control input signal to a control electrode of a drive device coupled to said primary winding for controlling primary current therein provided by said power supply voltage input signal;
rectifier means coupled to said secondary winding for rectifying signals induced in said secondary winding and providing, at an output terminal, a DC power supply output voltage in response thereto;
feedback path means connected between said output terminal and said sense input for controlling said drive circuit means to maintain said power supply output signal at a desired level:
wherein the improvement comprises;
said feedback path means comprising a sample and hold circuit comprising a controllable gate device provided between said output terminal and a holding device connected to said sense input, a control terminal of said gate device receiving a switching signal, wherein said gate device is alternately opened and closed such that said power supply output signal is effectively sampled by said holding device when said drive device causes primary winding current flow causing a flux increase in said transformer means so as to store energy therein, and wherein said holding device is effectively disconnected from said output terminal at all other times when flux in said transformer means decreases and said stored energy is provided to said secondary winding and to said rectifier means, whereby stability of said power supply is provided by discontinuous feedback path sampling at times other than the times at which energy is transferred from said primary to secondary windings.
terminal means for receiving a DC power supply voltage input signal having a magnitude which may vary over a range of magnitudes;
transformer means having a primary winding coupled to said terminal means and a secondary winding;
drive circuit means having at least a sense signal input and providing, as an output, a control input signal to a control electrode of a drive device coupled to said primary winding for controlling primary current therein provided by said power supply voltage input signal;
rectifier means coupled to said secondary winding for rectifying signals induced in said secondary winding and providing, at an output terminal, a DC power supply output voltage in response thereto;
feedback path means connected between said output terminal and said sense input for controlling said drive circuit means to maintain said power supply output signal at a desired level:
wherein the improvement comprises;
said feedback path means comprising a sample and hold circuit comprising a controllable gate device provided between said output terminal and a holding device connected to said sense input, a control terminal of said gate device receiving a switching signal, wherein said gate device is alternately opened and closed such that said power supply output signal is effectively sampled by said holding device when said drive device causes primary winding current flow causing a flux increase in said transformer means so as to store energy therein, and wherein said holding device is effectively disconnected from said output terminal at all other times when flux in said transformer means decreases and said stored energy is provided to said secondary winding and to said rectifier means, whereby stability of said power supply is provided by discontinuous feedback path sampling at times other than the times at which energy is transferred from said primary to secondary windings.
2. A flyback power supply according to claim 1 wherein said drive device implements a continuous mode of excitation for said transformer such that flux in said transformer means has a substantial non-zero magnitude at the time the drive device initiates primary winding current flow causing said flux increase.
3. A flyback power supply according to claim 1 wherein said gate device comprises a controllable series pass device connected between said output terminal and said drive circuit means sense input.
4. A flyback power supply according to claim 3 wherein said feedback path means comprises a DC circuit path between said series pass device and said output terminal and a DC circuit path between said series pass device and said drive circuit means sense input.
5. A flyback power supply according to claim 1 wherein said drive device comprises a FET transistor.
6. A flyback power supply according to claim 1 wherein said gate device comprises a transistor and wherein said control terminal comprises a base electrode of said transistor.
7. A flyback power supply comprising:
terminal means for receiving a DC power supply voltage input signal having a magnitude which may vary over a range of magnitudes;
transformer means having a primary winding coupled to said terminal means and a secondary winding;
drive circuit means comprising a pulse width modulation (PWM) circuit having at least a sense signal input and providing, as an output, a control input signal to a control electrode of a drive device coupled to said primary winding for periodically controlling primary current therein provided by said power supply voltage input signal;
rectifier means coupled to said secondary winding for rectifying signals induced in said secondary winding and providing, at an output terminal, a DC power supply output voltage in response thereto;
feedback path means connected between said output terminal and said PWM input for controlling said PWM
circuit to maintain said power supply output signal at a desired level;
wherein the improvement comprises;
said feedback path means comprising a sample and hold circuit comprising a controllable gate device provided between said output terminal and a holding device connected to said PWM sense input, a control terminal of said gate device receiving switching signals determined in accordance with said PWM output, wherein said gate device is alternately opened and closed in accordance with said PWM output such that said power supply output signal is effectively sampled by said holding device when said drive device causes primary winding current flow causing a flux increase in said transformer means so as to store energy therein, and wherein said holding device is effectively disconnected from said output terminal at all other times when flux in said transformer means decreases and said stored energy is provided to said secondary winding and to said rectifier means, whereby stability of said power supply is provided by discontinuous feedback path sampling at is times other than the times at which energy is transferred from said primary to secondary windings.
terminal means for receiving a DC power supply voltage input signal having a magnitude which may vary over a range of magnitudes;
transformer means having a primary winding coupled to said terminal means and a secondary winding;
drive circuit means comprising a pulse width modulation (PWM) circuit having at least a sense signal input and providing, as an output, a control input signal to a control electrode of a drive device coupled to said primary winding for periodically controlling primary current therein provided by said power supply voltage input signal;
rectifier means coupled to said secondary winding for rectifying signals induced in said secondary winding and providing, at an output terminal, a DC power supply output voltage in response thereto;
feedback path means connected between said output terminal and said PWM input for controlling said PWM
circuit to maintain said power supply output signal at a desired level;
wherein the improvement comprises;
said feedback path means comprising a sample and hold circuit comprising a controllable gate device provided between said output terminal and a holding device connected to said PWM sense input, a control terminal of said gate device receiving switching signals determined in accordance with said PWM output, wherein said gate device is alternately opened and closed in accordance with said PWM output such that said power supply output signal is effectively sampled by said holding device when said drive device causes primary winding current flow causing a flux increase in said transformer means so as to store energy therein, and wherein said holding device is effectively disconnected from said output terminal at all other times when flux in said transformer means decreases and said stored energy is provided to said secondary winding and to said rectifier means, whereby stability of said power supply is provided by discontinuous feedback path sampling at is times other than the times at which energy is transferred from said primary to secondary windings.
8. A flyback power supply according to claim 7 wherein said drive device implements a continuous mode of excitation for said transformer such that flux in said transformer means has a substantially non-zero magnitude at the times the drive device periodically initiates primary winding current flow causing said flux increase.
9. A flyback power supply according to claim 7 wherein said gate device comprises a controllable series pass device connected between said output terminal and said drive circuit means sense input.
10. A flyback power supply according to claim 9 wherein said feedback path means comprises a DC circuit path between said series pass device and said output terminal and a DC circuit path between said series pass device and said drive circuit means sense input.
11. A flyback power supply according to claim 7 wherein said drive device comprises a FET transistor.
12. A flyback power supply according to claim 7 wherein said gate device comprises a transistor and wherein said control terminal comprises a base electrode of said transistor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79967785A | 1985-11-19 | 1985-11-19 | |
| US799,677 | 1985-11-19 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1283166C true CA1283166C (en) | 1991-04-16 |
Family
ID=25176487
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000520853A Expired - Lifetime CA1283166C (en) | 1985-11-19 | 1986-10-20 | Flyback power supply |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JPS63501400A (en) |
| KR (1) | KR950013352B1 (en) |
| CN (1) | CN86107801A (en) |
| CA (1) | CA1283166C (en) |
| WO (1) | WO1987003150A1 (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN1062694C (en) * | 1993-04-30 | 2001-02-28 | 东芝株式会社 | Pulse modulated circuit |
| IT1269736B (en) * | 1994-05-10 | 1997-04-15 | Sits Soc It Telecom Siemens | DC / DC CONVERTER INCLUDING A HIGH INSULATION CHARGE TRANSFER FEEDBACK NETWORK |
| DE59404962D1 (en) * | 1994-07-18 | 1998-02-12 | Siemens Ag | DC converter with current limitation |
| DE19732766C2 (en) | 1997-07-30 | 2000-11-30 | Mirow Georg Dieter | Power supply for one sensor |
| US6429709B1 (en) * | 1998-12-14 | 2002-08-06 | Semiconductor Components Industries Llc | Power converter circuit and method for controlling |
| JP2009283401A (en) | 2008-05-26 | 2009-12-03 | Panasonic Electric Works Co Ltd | Power supply device, lamp fitting, and vehicle |
| JP2013016855A (en) * | 2012-09-25 | 2013-01-24 | Panasonic Corp | Electric power unit and lighting fixture, vehicle |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4301497A (en) * | 1980-06-16 | 1981-11-17 | International Business Machines Corporation | Flyback converter control with feed forward |
| US4326244A (en) * | 1980-12-18 | 1982-04-20 | Astes Components, Ltd. | Flyback power supply booster circuit |
| US4458112A (en) * | 1981-10-29 | 1984-07-03 | Telefonaktiebolaget L M Ericsson | Floating subscriber loop interface circuit |
| US4489369A (en) * | 1983-06-28 | 1984-12-18 | The United States Of America As Represented By The Secretary Of The Navy | Control circuit for a flyback stepcharger |
-
1986
- 1986-10-20 CA CA000520853A patent/CA1283166C/en not_active Expired - Lifetime
- 1986-10-23 JP JP61505728A patent/JPS63501400A/en active Pending
- 1986-10-23 KR KR1019870700618A patent/KR950013352B1/en active IP Right Grant
- 1986-10-23 WO PCT/US1986/002282 patent/WO1987003150A1/en unknown
- 1986-11-19 CN CN198686107801A patent/CN86107801A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| KR880701035A (en) | 1988-04-22 |
| JPS63501400A (en) | 1988-05-26 |
| KR950013352B1 (en) | 1995-11-02 |
| WO1987003150A1 (en) | 1987-05-21 |
| CN86107801A (en) | 1987-08-19 |
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| MKLA | Lapsed |