CA2103542A1 - Power supply having high power factor with control that tracks the input alternating supply - Google Patents
Power supply having high power factor with control that tracks the input alternating supplyInfo
- Publication number
- CA2103542A1 CA2103542A1 CA002103542A CA2103542A CA2103542A1 CA 2103542 A1 CA2103542 A1 CA 2103542A1 CA 002103542 A CA002103542 A CA 002103542A CA 2103542 A CA2103542 A CA 2103542A CA 2103542 A1 CA2103542 A1 CA 2103542A1
- Authority
- CA
- Canada
- Prior art keywords
- voltage
- power supply
- control
- producing
- control signal
- 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.)
- Abandoned
Links
- 230000005669 field effect Effects 0.000 claims description 4
- 230000008878 coupling Effects 0.000 claims description 2
- 238000010168 coupling process Methods 0.000 claims description 2
- 238000005859 coupling reaction Methods 0.000 claims description 2
- 230000001965 increasing effect Effects 0.000 abstract description 5
- 239000003990 capacitor Substances 0.000 description 9
- 230000001939 inductive effect Effects 0.000 description 2
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000002674 ointment Substances 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
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
- H02M1/00—Details of apparatus for conversion
- H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
- H02M1/4208—Arrangements for improving power factor of AC input
- H02M1/4225—Arrangements for improving power factor of AC input using a non-isolated boost converter
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Circuit Arrangements For Discharge Lamps (AREA)
- Inverter Devices (AREA)
Abstract
2103542 9216085 PCTABS00016 A voltge boost power supply, for use in a fluorescent lamp ballast (100), having: an inductance (170) coupled between an alternating supply voltage input (108, 110) and an output (134, 136), a switch (128) for controlling the current carried by the inductance, and a current-mode control IC (144) for producing a PWM control signal to control the switch so as to control the current carried by the inductance and thereby control the voltage across the inductance. The current-mode control IC is coupled (138) to the input so that the frequency of the control signal is modulated in accordance with the alternating supply voltage whereby the frequency of the control signal has a maximum value when the magnitude of the alternating supply voltage is a maximum. The power supply thus exhibits reduced harmonic distortion and increased power factor.
Description
2 1 0 3 S 4 2 PCT~592/~1752 POWER SUPPLY HAVING HIGH POWE~ FACTOR WITH CONTRQL THAT
TRACKS THE INPUT ALTERNATING SUPPLY
~ ,''; `` ~
Fleld of the Invention This invention relates to power supplies, and particularly, though not exclusively, to voltage boost power supplies for use in driving gas discharge lamps such as fluorescent lamps.
: .
Backaround of ~he Invention 15Gas discharge lamps are non-linear, negative resistance loads and so need to be driven from a ballast circuit Such a ballast circuit typicaLly incorporates a ~ -power s~lpply which is itself supplied from a low frequency supply (e.g. a 60Hz utility mains).
Such a ballast circuit should ideally exhibit a high :
power factor ~the ratio of the output power and input power, i.e. the ratio of the power delivered to the lamps and the power taken from the mains) and low harmonic distortion (introduction into the~mains of frequencies : ~ .
different from the mains frequency).
It is~known in such ballast circuits to use a power ;
; supply which boosts the mains voltage, e.g. at lamp ; ~.
30~start-up, by employing a boost inductor whose current is ;~
`~ cont~rolled by a switch (e.g. a field-effect transistor) whlch~is in turn~controlled by a pulse-width-modulated `;~
~(PWM) signal. When, at the~end of each PWM pulse, the switch turns OFF, the inductive current in the boost :
inductor generates an lncreased voltage. The PWM signal is typically generated in a current-mode control ~::i ,. :
...~ . : ~
: :: :
~ .
:: : : :
SUB~TITl~E StlH~T
WOg2~16~8~ ~ PCT/US92/01752 i~grated circuit ~IC). Such current-mode control IC's are well known in the art. ~---:~: . . :- -It is known in such power supplies to sense the 5 output voltage, the lnductor current and the line current ;;~
and to generate therefrom a control signal to control (e.g. via a multiplier circuit) the PWM signal in order to improve the circuit's power factor~ However, such known arrangements typically require special IC's to accomplish this additional control ~unction.
Summary of the Iny~iQn lS In accordance with a first aspect of the invention there is provided a power supply comprising~
- an input for receiving an alternating supply `~
voltage;
an output for producing a voltage derived from the ~ :
supply voltage;
voltage producing means coupled bet~een the input and the output for carrying a current and for producing a voltage therefrom;
.
switch means for controlling the current carried by the voltage producing means; and control signal generating means for producing a pulsed control signal to control the switch means so as to control the current carried by the voltage producing means and thereby control the voltage produced thereby, ! , ' '""' the improvement comprising modulating means coupled between the input and the control signal generating means for modulating the frequency of the control ;~
signal in accordance with the alternating supply -voltage whereby the frequency of the control signal has a maximum value when the magnitude of the "'':'::
"'' ' WO92/16085 ~ ~ 0 3 ~ 4 2 PcT/us92/ut7s2 ~ !
TRACKS THE INPUT ALTERNATING SUPPLY
~ ,''; `` ~
Fleld of the Invention This invention relates to power supplies, and particularly, though not exclusively, to voltage boost power supplies for use in driving gas discharge lamps such as fluorescent lamps.
: .
Backaround of ~he Invention 15Gas discharge lamps are non-linear, negative resistance loads and so need to be driven from a ballast circuit Such a ballast circuit typicaLly incorporates a ~ -power s~lpply which is itself supplied from a low frequency supply (e.g. a 60Hz utility mains).
Such a ballast circuit should ideally exhibit a high :
power factor ~the ratio of the output power and input power, i.e. the ratio of the power delivered to the lamps and the power taken from the mains) and low harmonic distortion (introduction into the~mains of frequencies : ~ .
different from the mains frequency).
It is~known in such ballast circuits to use a power ;
; supply which boosts the mains voltage, e.g. at lamp ; ~.
30~start-up, by employing a boost inductor whose current is ;~
`~ cont~rolled by a switch (e.g. a field-effect transistor) whlch~is in turn~controlled by a pulse-width-modulated `;~
~(PWM) signal. When, at the~end of each PWM pulse, the switch turns OFF, the inductive current in the boost :
inductor generates an lncreased voltage. The PWM signal is typically generated in a current-mode control ~::i ,. :
...~ . : ~
: :: :
~ .
:: : : :
SUB~TITl~E StlH~T
WOg2~16~8~ ~ PCT/US92/01752 i~grated circuit ~IC). Such current-mode control IC's are well known in the art. ~---:~: . . :- -It is known in such power supplies to sense the 5 output voltage, the lnductor current and the line current ;;~
and to generate therefrom a control signal to control (e.g. via a multiplier circuit) the PWM signal in order to improve the circuit's power factor~ However, such known arrangements typically require special IC's to accomplish this additional control ~unction.
Summary of the Iny~iQn lS In accordance with a first aspect of the invention there is provided a power supply comprising~
- an input for receiving an alternating supply `~
voltage;
an output for producing a voltage derived from the ~ :
supply voltage;
voltage producing means coupled bet~een the input and the output for carrying a current and for producing a voltage therefrom;
.
switch means for controlling the current carried by the voltage producing means; and control signal generating means for producing a pulsed control signal to control the switch means so as to control the current carried by the voltage producing means and thereby control the voltage produced thereby, ! , ' '""' the improvement comprising modulating means coupled between the input and the control signal generating means for modulating the frequency of the control ;~
signal in accordance with the alternating supply -voltage whereby the frequency of the control signal has a maximum value when the magnitude of the "'':'::
"'' ' WO92/16085 ~ ~ 0 3 ~ 4 2 PcT/us92/ut7s2 ~ !
- 3 - -~ :
alternating supply voltage is a maximum so as to cause the current carried by the voltage producing ~ :~
means to have a waveform which approximates to that of the alternating supply voltage.
S : ~
It will be appreciated that by causing the current ::
carried by the voltage producing means to vary in accordance with the alternating supply voltage in this . . .
way, thereby causing the voltage producing means to l0 present a load which varies in accordance with the ~
alternating supply voltage, the power supply produces low ; -harmonic distortion and exhibits a high power factor.
In accordance with a second aspect of the inventlon ;;~
15 there is provided a power supply for converting an AC .
voltage into a DC voltage, said power supply having~
a full wave rectifier coupled to said AC voltage, means for producing a pulse width modulated signal, said means having a control input, and means .;: ~ :
controlled by said signal for producing said DC
voltage, the improvement comprising means for coupling said control input to the full wave rectifier to cause ~.
the frequency of said pulse width modulated signal ;~
to vary in accordance with the magnitude of said AC
;. . ~ .
: ~ voltage whereby the frequency of said pulse width modulated slgnal has~a maximum value when the ;~
magnitude of said AC voltage is~a maximum, thereby obtaining high power factor and low harmonic ~:~
30 : : distortion.
.~: , . :.:
.
rief Descri~tion_of t~ rawinas -~
~ One circuit for driving fluorescent lamps and : incorporating a power supply in accordance with the .
.
WO92/16085 -i~ PCT/US92/01752 . - - ~:~
~ 2 - 4 -present invention will now be described, by way of example only, with reference to the accompanying :~
drawings, in which~
FIG. 1 shows a partially block-schematic circuit diagram of the fiuorescent lamp drive circuit , ~ .
FIG. 2 shows the waveform of the supply line voltage ~ ~ .
applied to the circuit; ~ ~
1 0 , . . .
FIG. 3 shows the waveform o~ the line current drawn ~ ~-by the circuit; and FIG. 4 shows the waveform of line current drawn by a mo~ified form of the circuit, not incorporating the present invention.
,. :: ::...
~escription Q~:~he ~ferred Embodim~n~
Referring now to FIG. 1, a circuit 100, for driving three fluorescent lamps 102, 104, 106, has two input ~ ~;.`.
terminals 108, 110 for receiving thereacross an AC supply -:
voltage of approximately 277V at a frequency of 60Hz. A
full-wave rectifying bridge circuit 112 has two input nodes 114, 116 connected respec~ively to the input terminals 108, llO, and has two output nodes 118, 120.
~The;output node~118 of the bridge 112 is connected to a ground voltage rail 122.
: 30 ~A cored inductor 124 (having an indoctance of~
approximately 4.5mH) has one end connected to the output node 120 of the bridge ~112, and has its~other end : :~:~
connected to a;node 126. A field effect transistor (FET) .
128 (of the type BUZ90) has its drain electrode connected -~
: to the node 126. The field effect transistor (FET) 128 .~ :
.
WO92/1608~ 21 ~ PCI/US92/01752 -~
~ 5 ~
has its source electrode connected, via a resistor 130 (having a value of approximately 1.6Q)r to the ground : -. -voltage rail 122. A diode 132 (of the type MUR160) has a ' its anode connected to the node 126 and has its cathode 5 connected to an output terminal 139. The ground voltage rail 122 is connected to an output terminal 136. An integrating capacitor 137 is connected between the outpu~
terminals 134 and 136.
A resistor 138 (having a resistance of approximately ~: .
2MQ) is connected between the output node 120 of the bridge 112 and a node 140. A capacitor 142 (having a capacitance of approximately 0.0039,UF) is connected between the node 140 and the ground voltage rail 122.j A :~
current:-mode control integrated circuit ( IC) 144 (of the .
type A';3845, available from ASTEC Semiconductor) has its~
RT/C~ input (pin 4) connected to the node 140. The current: mode control IC 144 has itS VREG output (pin 8) . ~:`
connect:ed, via a resistor 146 (having a resistance of : .`.
approximately loKQ)l to the node 140 and connected, via a : :~
capacitor 143 (having a capacitance of approximately ....
O.22~lF) to the ground volta~e rail 122. The current mode ;
control IC 194 has its control signal output (pin 6) : .
connected, via a resistor 150 (having a resistance of .
~25 approximately 20Q), to the gate electrode of the FET 128.
~:The gate electrode~of the FET 128 is also connectéd, via ~a resistor 1S2 (having~a~ r~sistance of approximately ~ ~
: 22KQ), :to the :ground volta~e rail 122. ~ :
: 30 ~Two resistors 154,:156 (having respecti~7e ~.:
resistances of approximately 974KQ and 5.36KQ) are ~ ~ ~
connected in series, via an intermediate node 158, :: :
between the output terminal 134 :and the ground voltage rail 122. The current mode control IC 144: has itS VFB --input (pin 2) connected to the node 158 via a resistor ; -~
160 (having a resistance of approximately 97KQ). The :: ~
W092/1608~ PCT/US92~017S2 - 6 - `
current mode control IC 144 has its COMP output (pin connected to its VFB input (pin 2) via a series-connected :~
resistor 162 (having a resistance of approximately looKQ) .
and capacitor 164 (having a capacitance of approximately 0.1~F). The current mode control IC 144 has its current sense input (pin 3) connected to the ground voltage rail 122 via a capacitor 166 (having a capacitance of .
approximately 470pF) and to the source electrode of the FET 128 via a resistor 168 (having a resistance of approximately lKQ).
~:~ .,' The current mode control IC 149 has its Vcc input (pin 7) connected to the bridge rectifier output node 120 ~ ~
via a resistor 170 (having a resistance of approximately ~:-24oKQ) ~nd connected to the ground voltage rail 122 via a capacitor 172 (having a capacitance of approximately ; ;` --:
100~F). The current mode control IC 144 has its GND ..
input (pin 5) connected to the ground voltage rail 122.
The power supply output terminals 134 and 136 are . ~ -connected to a half-bridge inverter 174, whose output is ,- :~
connected to a series-resonant tank circuit 176. The :
output of the tank circuit is connected, via a transformer~178, to the three fluorescent lamps which are 25 connected in series. The composition and operation of .:
.. . ..
ballast sub-components 174, 176 and 178 are well-known in the art and need not be further described herein. Such ~ . : .. :
: ~sub-components are described more fully in, for example, . -~
U.S. patent application no. 07/636,833, which is assigned :~
30 ~to the same assignee as the present application, and the ~:
:disclosure of which is hereby incorporated by~reference. :
:
: In operation of the circuit of FI~. 1, with a voltage of 277V, 60Hz (as shown in FIG. 2~ applied across the input terminals 108 and 110, the bridge 112 produces between the node 120 and the ground voltage rail 122 a . -WO92/1608~ : 21 0 3 ~ ~ ~ PCT/US92/0l752 . - ~ , . :. .
- 7 ~
unipolar, full-wave rectified, DC voltage having a frequency of 120Hz. When the FET 128 is enabled to conduct, substantially the whole of this unipolar DC
voltage appears across the inductor 124, and causes 5 current to flow through the inductor. When the FET 128 .
is disabled from conducting, this inductive current causes the voltage across the inductor to increase. This increased voltage is applied through the diode 132 to the .~ :
output terminal 134. The increased voltage between the .. :~
output terminals 134 and 136 charges the capacitor 137 which powers the inverter 174, the series-resonant tank circuit 176 and the transformer 178 to drive the three series-connected fluorescent lamps 102, 104, 106.
The switching between enablement and disablement of .
~, ..: . :
the FET 128 is controlled by the control signal (output from pin 5) of the current mode control IC 144. The IC's ::.
control signal output is in the form of a pulse-width ..
modulated signal, during whose mark intervals the FET is switched ON to enable conduction of current and during whose space i~tervals the FET is switched OFF to disable conduction of curre~t. The IC's pulse-width modulated : control signal at pin 6 has a nominal mark/space ratio of unity, producing a nominal 50% duty cycle. The frequency .:
25 of the IC's pulse-width modulated control siqnal and the ~ :
voltage at the node 120 determine the current drawn from :the supply line. .
In the circuit 100 the nominal frequency of the PWM - ~
30 control signal produced at pin 6 of the IC 144, which is . -determined by the product of the values of the resistor ~ -~
146 and the capacitor 142, is approximately 23KHz.
However, by applying the 120Hz unipolar waveform 35 output from the.bridqe 112 through the resistor 138 to .
the input at pin 4 of the current mode control IC 144, . . ~.
: :
, :..: :.: ~.
:~ : . ' ', ': . .
W092/1608~ - PCT/US92/01752 ~
~a3~ 8 -the frequency of the pulse-width modulated control signal produced at pin 6 of the IC is forced to vary in response to the AC line voltage (whose waveform is shown in FIG. 2) applied across the input terminals 108 and 110.
As the instantaneous value of the unipolar bridge output voltage increases, the curxent applied to pin 4 of the IC
144 increases and causes the frequency of the PWM control ;~
signal output at pin 6 of the IC to increase. Thus the -frequency of the PWM control signal output at pin 6 of - ;
the IC has its minimum, nominal value of approximately 23KHz when the bridge output voltage has its minimum, zero value, and the frequency of the PWM control signal output at pin 6 of the IC has its maximum value of approximately 43KHz when the bridge output voltage has its pea]c value. At intermediate values of the bridge output voltage the frequency of the IC's PWM control signal :is proportionately reduced.
,., Th,e frequency of the pulse-width modulated control ~ -~
signal produced at pin 6 of the IC 144 determines the current drawn from the bridge 112 and hence from the AC
supply line. By forcing the line current (whose waveform is shown in FIG. 3) to vary in accordance with the applied line voltage in this way, the line current is forced to become sinusoidal, endowing the circuit 100 with a near-unity power factor and low harmonic distortion.
As referred to above, the line current is caused to ~vary in this way by the connection provided between the node 120 and the node 140 by the resistor 138, which causes a modulating signal from the output of the rectifier bridge 112 to be applied to the ~requency determining input RT/CT at pin 4 of the IC 144. If the 35 resistor 138 were removed, the frequency of the PWM ;;~
output signal produced at pin 6 of the IC 144 would ;
~,.'- ' , WO92/16085 21 ~ 3 ~ 4 ~ PCT/US92/01752 ~ ~
_ g _ remain constant at approximately 23KHz, and the line current drawn by the circuit would be of the form shown in FIG. 4.
: , . -:
As can be seen from comparing the waveforms of FIG. 3 and 4, the waveform of FIG. 4 is noticeably less sinusoidal than that of FIG. 3, particularly in the regions marked 180 around the zero-crossings of the waveform. These deviations from sinusoidal shape in the ~ -waveform of FIG. 4 would manifest themselves as increased THD and decreased power factor, both of which are `~
substantially avoided in the circuit 100 whose line ::
current waveform is shown in FIG. 3.
Calculations and measurements have shown that the power factor and THD figure associated with the waveform of FIG. 4 are approximately 0.95 and 15% respectively, whereas the power factor and THD figure produced by the circuit 100 are approximately 0.99 and 5% respectively.
.
It will be appreciated the degree of modulation provided of the PWM output signal of the IC 144 could be ;
varied by varying the value of the resistor 138 and additlonally or alternatively by inserting a resistor ~ -(not shown) in parallel with~the capacitor 142 between the node 140 and ground voltage rail. Such variation could be used to provide greatex or lesser compensation for the non-sinusoidal regions 180 shown in FIG. 4, as , ~
desired.
:
It will also be~appreciated that although the invention has been described above with respect to a :~
power supply employing a boost inductor and incorporated ln a ballast circuit for driving fluorescent lamps, the - ;
invention may be advantageously used in other types of power supplies for use in any application where THD and ~ -.'~.,,~...,...' y ::: : :.~
WO92/1608~ ~ : , .,f PCT/US92/01752 3~ o power factor are significant factors in power supply performance. ---It will also be appreciated that various other ~
5 modifications or alternatives to the above ~;~.. :`
described embodiment wilI be apparent to the person skilled in the art without departing from the inventive concept of providing modulation, in accordance with an applied supply voltage, of a ~ :~
lO control signal which determines the line current : ;
drawn by a power supply, thereby reducing harmonic `
distortion and increasing power factor ~.
:''-." .
.. .: -:
: :.
..
~, : . :
::
: . :
.
. ~ .
, ~.: . . ,:
: : ~ : . ~:: . . .
. .-
alternating supply voltage is a maximum so as to cause the current carried by the voltage producing ~ :~
means to have a waveform which approximates to that of the alternating supply voltage.
S : ~
It will be appreciated that by causing the current ::
carried by the voltage producing means to vary in accordance with the alternating supply voltage in this . . .
way, thereby causing the voltage producing means to l0 present a load which varies in accordance with the ~
alternating supply voltage, the power supply produces low ; -harmonic distortion and exhibits a high power factor.
In accordance with a second aspect of the inventlon ;;~
15 there is provided a power supply for converting an AC .
voltage into a DC voltage, said power supply having~
a full wave rectifier coupled to said AC voltage, means for producing a pulse width modulated signal, said means having a control input, and means .;: ~ :
controlled by said signal for producing said DC
voltage, the improvement comprising means for coupling said control input to the full wave rectifier to cause ~.
the frequency of said pulse width modulated signal ;~
to vary in accordance with the magnitude of said AC
;. . ~ .
: ~ voltage whereby the frequency of said pulse width modulated slgnal has~a maximum value when the ;~
magnitude of said AC voltage is~a maximum, thereby obtaining high power factor and low harmonic ~:~
30 : : distortion.
.~: , . :.:
.
rief Descri~tion_of t~ rawinas -~
~ One circuit for driving fluorescent lamps and : incorporating a power supply in accordance with the .
.
WO92/16085 -i~ PCT/US92/01752 . - - ~:~
~ 2 - 4 -present invention will now be described, by way of example only, with reference to the accompanying :~
drawings, in which~
FIG. 1 shows a partially block-schematic circuit diagram of the fiuorescent lamp drive circuit , ~ .
FIG. 2 shows the waveform of the supply line voltage ~ ~ .
applied to the circuit; ~ ~
1 0 , . . .
FIG. 3 shows the waveform o~ the line current drawn ~ ~-by the circuit; and FIG. 4 shows the waveform of line current drawn by a mo~ified form of the circuit, not incorporating the present invention.
,. :: ::...
~escription Q~:~he ~ferred Embodim~n~
Referring now to FIG. 1, a circuit 100, for driving three fluorescent lamps 102, 104, 106, has two input ~ ~;.`.
terminals 108, 110 for receiving thereacross an AC supply -:
voltage of approximately 277V at a frequency of 60Hz. A
full-wave rectifying bridge circuit 112 has two input nodes 114, 116 connected respec~ively to the input terminals 108, llO, and has two output nodes 118, 120.
~The;output node~118 of the bridge 112 is connected to a ground voltage rail 122.
: 30 ~A cored inductor 124 (having an indoctance of~
approximately 4.5mH) has one end connected to the output node 120 of the bridge ~112, and has its~other end : :~:~
connected to a;node 126. A field effect transistor (FET) .
128 (of the type BUZ90) has its drain electrode connected -~
: to the node 126. The field effect transistor (FET) 128 .~ :
.
WO92/1608~ 21 ~ PCI/US92/01752 -~
~ 5 ~
has its source electrode connected, via a resistor 130 (having a value of approximately 1.6Q)r to the ground : -. -voltage rail 122. A diode 132 (of the type MUR160) has a ' its anode connected to the node 126 and has its cathode 5 connected to an output terminal 139. The ground voltage rail 122 is connected to an output terminal 136. An integrating capacitor 137 is connected between the outpu~
terminals 134 and 136.
A resistor 138 (having a resistance of approximately ~: .
2MQ) is connected between the output node 120 of the bridge 112 and a node 140. A capacitor 142 (having a capacitance of approximately 0.0039,UF) is connected between the node 140 and the ground voltage rail 122.j A :~
current:-mode control integrated circuit ( IC) 144 (of the .
type A';3845, available from ASTEC Semiconductor) has its~
RT/C~ input (pin 4) connected to the node 140. The current: mode control IC 144 has itS VREG output (pin 8) . ~:`
connect:ed, via a resistor 146 (having a resistance of : .`.
approximately loKQ)l to the node 140 and connected, via a : :~
capacitor 143 (having a capacitance of approximately ....
O.22~lF) to the ground volta~e rail 122. The current mode ;
control IC 194 has its control signal output (pin 6) : .
connected, via a resistor 150 (having a resistance of .
~25 approximately 20Q), to the gate electrode of the FET 128.
~:The gate electrode~of the FET 128 is also connectéd, via ~a resistor 1S2 (having~a~ r~sistance of approximately ~ ~
: 22KQ), :to the :ground volta~e rail 122. ~ :
: 30 ~Two resistors 154,:156 (having respecti~7e ~.:
resistances of approximately 974KQ and 5.36KQ) are ~ ~ ~
connected in series, via an intermediate node 158, :: :
between the output terminal 134 :and the ground voltage rail 122. The current mode control IC 144: has itS VFB --input (pin 2) connected to the node 158 via a resistor ; -~
160 (having a resistance of approximately 97KQ). The :: ~
W092/1608~ PCT/US92~017S2 - 6 - `
current mode control IC 144 has its COMP output (pin connected to its VFB input (pin 2) via a series-connected :~
resistor 162 (having a resistance of approximately looKQ) .
and capacitor 164 (having a capacitance of approximately 0.1~F). The current mode control IC 144 has its current sense input (pin 3) connected to the ground voltage rail 122 via a capacitor 166 (having a capacitance of .
approximately 470pF) and to the source electrode of the FET 128 via a resistor 168 (having a resistance of approximately lKQ).
~:~ .,' The current mode control IC 149 has its Vcc input (pin 7) connected to the bridge rectifier output node 120 ~ ~
via a resistor 170 (having a resistance of approximately ~:-24oKQ) ~nd connected to the ground voltage rail 122 via a capacitor 172 (having a capacitance of approximately ; ;` --:
100~F). The current mode control IC 144 has its GND ..
input (pin 5) connected to the ground voltage rail 122.
The power supply output terminals 134 and 136 are . ~ -connected to a half-bridge inverter 174, whose output is ,- :~
connected to a series-resonant tank circuit 176. The :
output of the tank circuit is connected, via a transformer~178, to the three fluorescent lamps which are 25 connected in series. The composition and operation of .:
.. . ..
ballast sub-components 174, 176 and 178 are well-known in the art and need not be further described herein. Such ~ . : .. :
: ~sub-components are described more fully in, for example, . -~
U.S. patent application no. 07/636,833, which is assigned :~
30 ~to the same assignee as the present application, and the ~:
:disclosure of which is hereby incorporated by~reference. :
:
: In operation of the circuit of FI~. 1, with a voltage of 277V, 60Hz (as shown in FIG. 2~ applied across the input terminals 108 and 110, the bridge 112 produces between the node 120 and the ground voltage rail 122 a . -WO92/1608~ : 21 0 3 ~ ~ ~ PCT/US92/0l752 . - ~ , . :. .
- 7 ~
unipolar, full-wave rectified, DC voltage having a frequency of 120Hz. When the FET 128 is enabled to conduct, substantially the whole of this unipolar DC
voltage appears across the inductor 124, and causes 5 current to flow through the inductor. When the FET 128 .
is disabled from conducting, this inductive current causes the voltage across the inductor to increase. This increased voltage is applied through the diode 132 to the .~ :
output terminal 134. The increased voltage between the .. :~
output terminals 134 and 136 charges the capacitor 137 which powers the inverter 174, the series-resonant tank circuit 176 and the transformer 178 to drive the three series-connected fluorescent lamps 102, 104, 106.
The switching between enablement and disablement of .
~, ..: . :
the FET 128 is controlled by the control signal (output from pin 5) of the current mode control IC 144. The IC's ::.
control signal output is in the form of a pulse-width ..
modulated signal, during whose mark intervals the FET is switched ON to enable conduction of current and during whose space i~tervals the FET is switched OFF to disable conduction of curre~t. The IC's pulse-width modulated : control signal at pin 6 has a nominal mark/space ratio of unity, producing a nominal 50% duty cycle. The frequency .:
25 of the IC's pulse-width modulated control siqnal and the ~ :
voltage at the node 120 determine the current drawn from :the supply line. .
In the circuit 100 the nominal frequency of the PWM - ~
30 control signal produced at pin 6 of the IC 144, which is . -determined by the product of the values of the resistor ~ -~
146 and the capacitor 142, is approximately 23KHz.
However, by applying the 120Hz unipolar waveform 35 output from the.bridqe 112 through the resistor 138 to .
the input at pin 4 of the current mode control IC 144, . . ~.
: :
, :..: :.: ~.
:~ : . ' ', ': . .
W092/1608~ - PCT/US92/01752 ~
~a3~ 8 -the frequency of the pulse-width modulated control signal produced at pin 6 of the IC is forced to vary in response to the AC line voltage (whose waveform is shown in FIG. 2) applied across the input terminals 108 and 110.
As the instantaneous value of the unipolar bridge output voltage increases, the curxent applied to pin 4 of the IC
144 increases and causes the frequency of the PWM control ;~
signal output at pin 6 of the IC to increase. Thus the -frequency of the PWM control signal output at pin 6 of - ;
the IC has its minimum, nominal value of approximately 23KHz when the bridge output voltage has its minimum, zero value, and the frequency of the PWM control signal output at pin 6 of the IC has its maximum value of approximately 43KHz when the bridge output voltage has its pea]c value. At intermediate values of the bridge output voltage the frequency of the IC's PWM control signal :is proportionately reduced.
,., Th,e frequency of the pulse-width modulated control ~ -~
signal produced at pin 6 of the IC 144 determines the current drawn from the bridge 112 and hence from the AC
supply line. By forcing the line current (whose waveform is shown in FIG. 3) to vary in accordance with the applied line voltage in this way, the line current is forced to become sinusoidal, endowing the circuit 100 with a near-unity power factor and low harmonic distortion.
As referred to above, the line current is caused to ~vary in this way by the connection provided between the node 120 and the node 140 by the resistor 138, which causes a modulating signal from the output of the rectifier bridge 112 to be applied to the ~requency determining input RT/CT at pin 4 of the IC 144. If the 35 resistor 138 were removed, the frequency of the PWM ;;~
output signal produced at pin 6 of the IC 144 would ;
~,.'- ' , WO92/16085 21 ~ 3 ~ 4 ~ PCT/US92/01752 ~ ~
_ g _ remain constant at approximately 23KHz, and the line current drawn by the circuit would be of the form shown in FIG. 4.
: , . -:
As can be seen from comparing the waveforms of FIG. 3 and 4, the waveform of FIG. 4 is noticeably less sinusoidal than that of FIG. 3, particularly in the regions marked 180 around the zero-crossings of the waveform. These deviations from sinusoidal shape in the ~ -waveform of FIG. 4 would manifest themselves as increased THD and decreased power factor, both of which are `~
substantially avoided in the circuit 100 whose line ::
current waveform is shown in FIG. 3.
Calculations and measurements have shown that the power factor and THD figure associated with the waveform of FIG. 4 are approximately 0.95 and 15% respectively, whereas the power factor and THD figure produced by the circuit 100 are approximately 0.99 and 5% respectively.
.
It will be appreciated the degree of modulation provided of the PWM output signal of the IC 144 could be ;
varied by varying the value of the resistor 138 and additlonally or alternatively by inserting a resistor ~ -(not shown) in parallel with~the capacitor 142 between the node 140 and ground voltage rail. Such variation could be used to provide greatex or lesser compensation for the non-sinusoidal regions 180 shown in FIG. 4, as , ~
desired.
:
It will also be~appreciated that although the invention has been described above with respect to a :~
power supply employing a boost inductor and incorporated ln a ballast circuit for driving fluorescent lamps, the - ;
invention may be advantageously used in other types of power supplies for use in any application where THD and ~ -.'~.,,~...,...' y ::: : :.~
WO92/1608~ ~ : , .,f PCT/US92/01752 3~ o power factor are significant factors in power supply performance. ---It will also be appreciated that various other ~
5 modifications or alternatives to the above ~;~.. :`
described embodiment wilI be apparent to the person skilled in the art without departing from the inventive concept of providing modulation, in accordance with an applied supply voltage, of a ~ :~
lO control signal which determines the line current : ;
drawn by a power supply, thereby reducing harmonic `
distortion and increasing power factor ~.
:''-." .
.. .: -:
: :.
..
~, : . :
::
: . :
.
. ~ .
, ~.: . . ,:
: : ~ : . ~:: . . .
. .-
Claims (10)
- Claims l. A power supply comprising:
an input for receiving an alternating supply voltage;
an output for producing a voltage derived from the supply voltage;
voltage producing means coupled between the input and the output for carrying a current and for producing a voltage therefrom;
switch means for controlling the current carried by the voltage producing means; and control signal generating means for producing a pulsed control signal to control the switch means so as to control the current carried by the voltage producing means and thereby control the voltage:
produced thereby, the improvement comprising modulating means coupled between the input and the control signal generating means for modulating the frequency of the control signal in accordance with the alternating supply voltage whereby the frequency of the control signal has a maximum value when the magnitude of the alternating supply voltage is a maximum so as to cause the current carried by the voltage producing means to have a waveform which approximates to that of the alternating supply voltage. - 2. A power supply according to claim 1 wherein the voltage producing means comprises an inductance.
- 3. A power supply according to claim 2 or 2 wherein the switch means comprises a field effect transistor.
- 4. A power supply according to claim 1, 2 or 3 wherein the control signal is a pulse-width modulated signal.
- 5. A power supply according to any preceding claim wherein the control signal generating means comprises a current-mode control integrated circuit.
- 6. A power supply according to any preceding claim wherein the modulating means comprises an impedance coupled between the input and the control signal generating means.
- 7. A power supply for converting an AC voltage into a DC voltage, said power supply having a full wave rectifier coupled to said AC voltage, means for producing a pulse width modulated signal, said means having a control input, and means controlled by said signal for producing said DC voltage, the improvement comprising:
means for coupling said control input to the full wave rectifier to cause the frequency of said pulse width modulated signal to vary in accordance with the magnitude of said AC voltage whereby the frequency of said pulse width modulated signal has a maximum value when the magnitude of said AC voltage is a maximum, thereby obtaining high power factor and low harmonic distortion. - 8. A power supply as set forth in claim 7 wherein said means for producing said pulse width modulated signal is powered from said full wave rectifier.
- 9. A power supply as set forth in claim 7 or 8 wherein said means for producing said DC signal comprises a voltage boost circuit.
- 10. A ballast for driving gas discharge lamps and incorporating a power supply according to any:
preceding claim.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US66583091A | 1991-03-07 | 1991-03-07 | |
| US665,830 | 1991-03-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2103542A1 true CA2103542A1 (en) | 1992-09-17 |
Family
ID=24671735
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002103542A Abandoned CA2103542A1 (en) | 1991-03-07 | 1992-03-06 | Power supply having high power factor with control that tracks the input alternating supply |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0577704A1 (en) |
| JP (1) | JPH06507777A (en) |
| KR (1) | KR970002285B1 (en) |
| CN (1) | CN1064955A (en) |
| BR (1) | BR9205729A (en) |
| CA (1) | CA2103542A1 (en) |
| MX (1) | MX9201010A (en) |
| WO (1) | WO1992016085A1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA2255732C (en) * | 1996-03-18 | 2004-10-19 | Gad Products, S.A. De C.V. | High-efficiency self-regulated electronic ballast with a single characteristic curve for operating high-pressure sodium vapour lamps |
| WO1999005776A1 (en) * | 1997-07-25 | 1999-02-04 | Siemens Ag Österreich | Switched-mode transformer |
| US6088754A (en) * | 1997-12-31 | 2000-07-11 | Cisco Technology, Inc. | Generic serial interface with automatic reconfigurability |
| DE19843678A1 (en) * | 1998-09-23 | 2000-03-30 | Patent Treuhand Ges Fuer Elektrische Gluehlampen Mbh | Method for providing an output signal with a desired value of a parameter at the output of a switching power supply and circuit for carrying out the method |
| GB0021763D0 (en) * | 2000-09-05 | 2000-10-18 | Minebea Electronics Uk Ltd | Active power factor correction |
| KR101142271B1 (en) * | 2010-01-08 | 2012-05-11 | (주) 트랜스마그넷 | Electronic stabilizer for channel sign adapting output voltage following loads |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| AT374653B (en) * | 1981-09-11 | 1984-05-25 | Zumtobel Ag | ELECTRONIC CONTROL UNIT FOR A FLUORESCENT OR GAS DISCHARGE TUBE WITH A RECTIFIER AND AN ACTIVE HARMONIC FILTER |
| US4677366A (en) * | 1986-05-12 | 1987-06-30 | Pioneer Research, Inc. | Unity power factor power supply |
| US4920302A (en) * | 1987-01-27 | 1990-04-24 | Zenith Electronics Corporation | Fluorescent lamp power supply |
| US4870327A (en) * | 1987-07-27 | 1989-09-26 | Avtech Corporation | High frequency, electronic fluorescent lamp ballast |
| GB8817684D0 (en) * | 1988-07-25 | 1988-09-01 | Astec Int Ltd | Power factor improvement |
| YU47882B (en) * | 1989-01-25 | 1996-05-20 | Siemens Ag. | WASHER SWITCH ASSEMBLY NETWORK PART WITH BLOCKING Oscillator |
-
1992
- 1992-03-06 KR KR1019930702696A patent/KR970002285B1/en not_active IP Right Cessation
- 1992-03-06 EP EP92908255A patent/EP0577704A1/en not_active Withdrawn
- 1992-03-06 WO PCT/US1992/001752 patent/WO1992016085A1/en not_active Application Discontinuation
- 1992-03-06 CA CA002103542A patent/CA2103542A1/en not_active Abandoned
- 1992-03-06 JP JP4507858A patent/JPH06507777A/en active Pending
- 1992-03-06 BR BR9205729A patent/BR9205729A/en unknown
- 1992-03-06 MX MX9201010A patent/MX9201010A/en active IP Right Grant
- 1992-03-07 CN CN92101494A patent/CN1064955A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| BR9205729A (en) | 1994-08-02 |
| MX9201010A (en) | 1992-09-01 |
| WO1992016085A1 (en) | 1992-09-17 |
| EP0577704A1 (en) | 1994-01-12 |
| JPH06507777A (en) | 1994-09-01 |
| KR970002285B1 (en) | 1997-02-27 |
| CN1064955A (en) | 1992-09-30 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued |