U.S. patent application number 13/969690 was filed with the patent office on 2013-12-19 for fluorescent lamp power supply.
The applicant listed for this patent is William B. Sackett, Laurence P. Sadwick. Invention is credited to William B. Sackett, Laurence P. Sadwick.
Application Number | 20130336015 13/969690 |
Document ID | / |
Family ID | 44258031 |
Filed Date | 2013-12-19 |
United States Patent
Application |
20130336015 |
Kind Code |
A1 |
Sadwick; Laurence P. ; et
al. |
December 19, 2013 |
Fluorescent Lamp Power Supply
Abstract
Various embodiments of a fluorescent lamp power supply are
disclosed herein. In one embodiment, a power supply includes a
power input connected to a pulse generator. The power supply also
includes a filter connected to a variable pulse width output on the
pulse generator and to the power input. The filter is adapted to
substantially block at least one harmonic frequency component of
the variable pulse width output and to substantially pass a
fundamental frequency component of the variable pulse width output.
The power supply also includes a power output connected to the
filter, wherein an amplitude at the power output is related to the
pulse width at the variable pulse width output.
Inventors: |
Sadwick; Laurence P.; (Salt
Lake City, UT) ; Sackett; William B.; (Salt Lake
City, UT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sadwick; Laurence P.
Sackett; William B. |
Salt Lake City
Salt Lake City |
UT
UT |
US
US |
|
|
Family ID: |
44258031 |
Appl. No.: |
13/969690 |
Filed: |
August 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12837460 |
Jul 15, 2010 |
8536803 |
|
|
13969690 |
|
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Current U.S.
Class: |
363/21.01 |
Current CPC
Class: |
H05B 47/10 20200101;
H05B 41/2824 20130101; H05B 41/3927 20130101 |
Class at
Publication: |
363/21.01 |
International
Class: |
H05B 37/02 20060101
H05B037/02 |
Claims
1. A power supply, comprising: a power input; a power output; a
transformer having a primary winding connected to the power input
and a secondary winding connected to the power output; a switch
connected in series with the primary winding; a gate drive circuit
connected to the switch and operable to control a current through
the transformer; a feedback signal from a secondary winding side of
the power supply to the primary winding side of the power supply,
wherein the gate drive circuit is controlled at least in part based
on the feedback signal; and a dimming sense and control circuit
connected to the gate drive circuit, wherein the dimming sense and
control circuit is adapted to reduce a current to the power
output.
2. The power supply of claim 1, wherein the dimming sense and
control circuit comprises an external control signal input operable
to receive an external control signal to control a dimming
level.
3. The power supply of claim 2, wherein the external control signal
input comprises a wireless input.
4. The power supply of claim 2, wherein the external control signal
input comprises a wired input.
5. The power supply of claim 1, wherein the dimming sense and
control circuit is adapted to reduce the current to the power
output based at least in part on a power level at the power
input.
6. The power supply of claim 5, wherein the dimming sense and
control circuit is adapted to reduce the current to the power
output based at least in part on a power level at the power input
that as it is reduced by an external triac-based dimmer.
7. The power supply of claim 1, wherein the gate drive circuit is
operable to prioritize the feedback signal and a signal from the
dimming sense and control circuit.
8. The power supply of claim 1, further comprising at least one
transistor connected between the primary winding of the transformer
and the power input, a transformer driver connected to the at least
one transistor, and a rectifier connected between the power input
and the at least one transistor.
9. The power supply of claim 8, wherein the at least one transistor
comprises at least two transistors connected in a push-pull
configuration across the primary winding.
10. The power supply of claim 9, wherein the transformer driver is
operable to generate a pulse train to drive the primary
winding.
11. The power supply of claim 1, further comprising a high/low
driver connected between the secondary winding and the power
output.
12. The power supply of claim 1, further comprising a voltage level
feedback signal connected to the gate drive, operable to measure a
voltage across the primary winding.
13. The power supply of claim 1, wherein the power output comprises
an alternating current at a higher frequency than at the power
input.
14. The power supply of claim 1, wherein the power output comprises
an alternating current sine wave.
15. The power supply of claim 1, further comprising a rectifier
connected between the secondary winding and the power output,
wherein the power output comprises half sine wave pulses.
16. A method of supplying power, the method comprising: rectifying
a power input to yield a rectified power input; generating a pulse
train from the rectified power input; driving a primary winding of
a transformer with the pulse train; driving a power output from a
secondary winding of the transformer with an alternating current at
a higher frequency than a frequency of the power input; and
switching the rectified power input based on a measurement at the
power output.
17. The method of claim 16, further comprising switching the
rectified power input to set a dimming level at the power
output.
18. The method of claim 17, further comprising switching the
rectified power input to set a dimming level based on a wired
external dimming control signal.
19. The method of claim 17, further comprising switching the
rectified power input to set a dimming level based on a wireless
external dimming control signal.
20. The method of claim 17, further comprising switching the
rectified power input to set a dimming level based on a power level
at the power input as controlled by a triac-based dimmer.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to U.S. Patent
Application No. 61/226,193 entitled "Cold Cathode Fluorescent Lamp
Power Supply", filed Jul. 16, 2009, and to U.S. patent application
Ser. No. 12/837,460 entitled "Fluorescent Lamp Power Supply", filed
Jul. 15, 2010. The entirety of all of the aforementioned
applications is incorporated herein by reference for all
purposes.
BACKGROUND
[0002] Fluorescent lamps are used in a variety of applications,
such as for general purpose lighting in commercial and residential
locations, in backlights for liquid crystal displays in computers
and televisions, etc. Fluorescent lamps generally include a glass
tube, circle, spiral or other shaped bulb containing a gas at low
pressure, such as argon, xenon, neon, or krypton, along with low
pressure mercury vapor. A fluorescent coating is deposited on the
inside of the lamp. As an electrical current is passed through the
lamp, mercury atoms are excited and photons are released, most
having frequencies in the ultraviolet spectrum. These photons are
absorbed by the fluorescent coating, causing it to emit light at
visible frequencies.
[0003] A number of different types of fluorescent lamps exist, such
as cold cathode fluorescent lamps (CCFLs) and compact fluorescent
lamps (CFLs), traditional full size fluorescent lamps, etc. In
general, the various types of fluorescent lamps share a requirement
for a high voltage current-limited AC power supply. A very high
voltage is initially applied to strike or light the lamp. Once the
lamp is lit, the electrical resistance in the lamp drops and the
voltage is reduced to avoid high currents. As current passes
through the fluorescent lamp, the electrical resistance of the lamp
drops, allowing more current to flow. Traditionally, relatively
expensive and bulky ballasts are used to limit the current through
the fluorescent lamp, as well as to provide the voltage needed to
strike the lamp. However, traditional fluorescent lamp ballasts, in
addition to being relatively expensive and bulky, can be noisy and
prone to failure, and are not dimmable using TRIAC-based dimmers.
Often, for low power and self ballasting applications including
CFLs, traditional ballasts have electrical characteristics that are
undesirable including low power factor values and performance.
SUMMARY
[0004] The present invention provides a fluorescent lamp power
supply that may be used to dimmably power any of a number of types
of fluorescent lamps and also maintain a high power factor.
[0005] In one embodiment, a power supply for a fluorescent lamp
includes a power input connected to a pulse generator. The power
supply also includes a filter connected to a variable pulse width
output on the pulse generator and to the power input. The filter is
adapted to substantially block at least one harmonic frequency
component of the variable pulse width output and to substantially
pass a fundamental frequency component of the variable pulse width
output. The power supply also includes a power output connected to
the filter, wherein an amplitude at the power output is related to
the pulse width at the variable pulse width output.
[0006] An embodiment of the power supply also includes a dimming
sense and control circuit connected to the pulse generator. The
dimming sense and control circuit is adapted to controllably alter
the pulse width at the variable pulse width output.
[0007] An embodiment of the power supply also includes a load
current controller connected to the dimming sense and control
circuit and to the power output.
[0008] In an embodiment of the power supply, the power supply is
adapted to increase a power factor by controlling the pulse
generator.
[0009] In an embodiment of the power supply, the filter comprises a
transformer connected between the power input and the power
output.
[0010] An embodiment of the power supply also includes a load
current detector connected to the power output, and a load current
feedback signal from the load current detector to the variable
pulse generator.
[0011] An embodiment of the power supply also includes a reference
current signal and a comparator connected to the load current
feedback signal and the reference current signal.
[0012] An embodiment of the power supply also includes an isolator
connected in series with the load current feedback signal.
[0013] An embodiment of the power supply also includes a rectifier
connected between the power output and the load current
detector.
[0014] An embodiment of the power supply also includes a partial
rectifier connected between the power output and the load current
detector.
[0015] An embodiment of the power supply also includes a load
voltage detector connected to the power output, and a load voltage
feedback signal from the load voltage detector to the variable
pulse generator.
[0016] An embodiment of the power supply also includes a rectifier
connected between the power input and the filter.
[0017] An embodiment of the power supply also includes an input
current detector connected in series with the filter.
[0018] An embodiment of the power supply also includes an input
voltage detector connected to the power input.
[0019] In an embodiment of the power supply, the filter comprises a
transformer, wherein the pulse generator comprises a transformer
driver connected to the transformer.
[0020] In an embodiment of the power supply, the power input to the
pulse generator comprises an unrectified alternating current
supply, and the pulse generator comprises a pair of transistors
controlled by a gate drive circuit.
[0021] Other embodiments provide a method of supplying power. In
one such embodiment, the method includes providing a pulse train
from a power input, filtering the pulse train to substantially
block at least one harmonic frequency component of the pulse train
while substantially passing a fundamental frequency component of
the pulse train, and providing the resulting filtered waveform at a
power output. The amplitude of the filtered waveform is related to
a pulse width in the pulse train.
[0022] An embodiment of the method also includes adjusting the
pulse width in the pulse train to control the amplitude for
dimming.
[0023] An embodiment of the method also includes controlling the
pulse train to increase power factor.
[0024] An embodiment of the method also includes limiting the pulse
width based in part on at least one of a load current feedback
signal, a load voltage feedback signal, and an input current
feedback signal.
[0025] This summary provides only a general outline of some
particular embodiments. Many other objects, features, advantages
and other embodiments will become more fully apparent from the
following detailed description. Nothing in this document should be
viewed as or considered to be limiting in any way or form.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] A further understanding of the various exemplary embodiments
may be realized by reference to the figures which are described in
remaining portions of the specification. In the figures, like
reference numerals may be used throughout several drawings to refer
to similar components.
[0027] FIGS. 1A-1D depict input and output waveforms from example
embodiments of a fluorescent lamp power supply.
[0028] FIG. 2 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with isolated
voltage and current feedback.
[0029] FIG. 3 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with
rectified load current and isolated voltage feedback.
[0030] FIG. 4 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with filtered
load current and fully rectified current feedback.
[0031] FIG. 5 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with filtered
load current and partially rectified current feedback.
[0032] FIG. 6 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with filtered
load current and partially rectified current feedback.
[0033] FIG. 7 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with
unrectified AC input.
[0034] FIG. 8 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with a
high/low driver controlling high frequency alternating current to
the load.
[0035] FIG. 9 depicts a block diagram of an example embodiment of a
power supply that may be used for a fluorescent lamp, with a
primary side dimming controller, transformer driver and direct load
current control.
[0036] FIG. 10 depicts a block diagram of an example embodiment of
a power supply that may be used for a fluorescent lamp, with
unrectified AC input, a primary side dimming controller and direct
load current control.
[0037] FIG. 11 depicts a block diagram of an example embodiment of
a power supply that may be used for a fluorescent lamp, with
unrectified AC input, a primary side dimming controller and direct
load current control, and a single diode powering primary side
controllers.
[0038] FIG. 12 depicts and example method of powering a fluorescent
lamp.
DESCRIPTION
[0039] Brief definitions of terms used throughout this document are
given below. The phrases "in one embodiment," "according to one
embodiment," and the like generally mean the particular feature,
structure, or characteristic following the phrase is included in at
least one embodiment of the present invention, and may be included
in more than one embodiment of the present invention. Importantly,
such phrases do not necessarily refer to the same embodiment.
[0040] If the specification states a component or feature "may",
"can", "could", or "might" be included or have a characteristic,
that particular component or feature is not required to be included
or have the characteristic.
[0041] A power supply is disclosed herein that may be used to power
fluorescent lamps such as CFLs and CCFLs and other types of loads.
High frequency pulses are generated from a typical AC line voltage
and filtered in a transformer or other device to produce a high
frequency AC sine wave output to drive a CCFL or other load while
also having high power factor correction (PFC) and power factor.
The filtered signal may be further processed if desired, for
example to rectify the signal to the load. Some embodiments of the
power supply may be dimmed with conventional external dimmers such
as TRIAC-based dimmers and/or with internal dimming circuitry
including, but not limited to, remote control via wired or
wireless, digital to analog conversion, etc.
[0042] A pulse train is formed from an input power source, and the
pulse train is filtered using, for example, a transformer and/or
inductor, filter or other device to substantially limit the output
to the fundamental frequency and block harmonics. For example, the
pulse train could be a square wave at 50% on/50% off, although the
pulse train is not limited to this waveform or duty cycle. By
filtering the pulse train, it is transformed to a sine wave for
which the amplitude is dependent on the pulse duration or width.
For pulses that are on less than 50% of the period, the amplitude
of the output fundamental sine wave increases in amplitude with an
increase in pulse width with the amplitude of the sine wave
reaching a maximum at 50% on/50% off. Above 50% on-time, the
amplitude of the output sine wave decreases. By generating the
pulse in an appropriate range of frequencies, such as 100 kHz
(which is only an example frequency, with higher and lower
frequencies also working depending on the characteristics of the
transformer/filter and load requirements), high power factor and
efficiency can be achieved with a substantially pure sine wave
output that supports dimming, both internal and external. Universal
voltage output can also be realized. The output can be isolated in
embodiments using a transformer to process the pulse train. By
using a rectifier or rectifier bridge, a DC rectified sine wave
output can be obtained. By employing appropriate filters, other
waveforms can be obtained at the output of, for example, the
transformer from the input pulse Fourier series waveform and terms.
In addition, for a number of applications, where appropriate, the
pulse can be riding on a waveform or waveforms (for example, the
pulse train could be riding on top of a 50 or 60 Hz AC sine
wave).
[0043] The relationship between input pulse width and output
amplitude is illustrated in FIGS. 1A-1D. In FIG. 1A, a pulse train
10 with a duty cycle of about 20% is processed by a power supply 12
to form an alternating current output 14. In this embodiment, the
output 14 of the power supply 12 has the same frequency as the
input 10, although other embodiments may be adapted to produce an
output 14 at a different frequency. In FIG. 1B, the pulse train 16
has a duty cycle of about 40%, and this doubling of the duty cycle,
from 20% to 40%, while remaining under 50% doubles the amplitude of
the alternating current output 20. Once the duty cycle of the pulse
train exceeds 50% on-time, the output amplitude will decrease with
increasing duty cycle. Although in this embodiment the output
amplitude is linearly proportional to input duty cycle, other
embodiments may be adapted to implement non-linear functions. The
embodiments of FIGS. 1A and 1B generate full sine wave outputs. As
illustrated in FIGS. 1C and 1D, a power supply 22 may have a
rectified output, while maintaining the same relationship between
the duty cycle of the input pulse trains 24 and 26 and the
amplitude of the rectified sine wave outputs 30 and 32.
[0044] The frequency and amplitude of the alternating current
output from a power supply may thus be controlled by adjusting the
frequency and duty cycle of an input pulse train. An example
embodiment of a power supply 40 that may be used for fluorescent
lamps or other loads is illustrated in FIG. 2. In this embodiment,
the power supply 40 supplies a load 42 such as a CCFL, CFL, or
other type of fluorescent lamp, from an alternating current (AC)
input 44. A rectifier 46 and optional capacitor 50 rectify the AC
input to produce a direct current (DC) supply 52. The AC input 44
may be connected through a fuse 54 and electromagnetic interference
(EMI) filter 56, if desired. The DC supply 52 is converted to a
pulse train by a switch, such as an n-channel metal-oxide
semiconductor (NMOS) field effect transistor (FET) 60, bipolar
junction transistor (BJT), insulated gate bipolar transistor
(IGBT), junction FET (JFET), unijunction transistor, or other type
of transistor, to produce a pulse train. Other non-limiting
examples of suitable switch devices include a bipolar transistor or
field effect transistor of any type and material including but not
limited to metal oxide semiconductor FET (MOSFET), junction FET
(JFET), etc, and can be made of any suitable material including
silicon, gallium arsenide, gallium nitride, silicon carbide, etc.
The transistor 60 is rated to operate at the voltages that appear
at the DC supply 52, or at the AC input 44 if no rectifier 46 is
used at the input.
[0045] The transistor 60 is controlled by a pulse train at an
output 62 of a variable pulse generator 64. The variable pulse
generator 64 is adapted to generate a pulse train at the desired
frequency for the load 42, which for a fluorescent lamp may be, for
example, about 100 kHz, or any other suitable frequency including a
variable frequency or a frequency with intentional dither, etc. The
variable pulse generator 64 is also adapted to adjust the pulse
width or duty cycle of the pulses at the variable pulse generator
output 62 to provide the desired voltage and/or current amplitude
to the load 42. The variable pulse generator 64 may comprise any
suitable device or circuit for generating a pulse train, including
using digital logic, digital, circuits, state machines,
microelectronics, microcontrollers, microprocessors, field
programmable gate arrays (FPGAs), complex logic devices (CLDs),
analog circuits, discrete components, band gap generators, timer
circuits and chips, ramp generators, half bridges, full bridges,
level shifters, difference amplifiers, error amplifiers, logic
circuits, comparators, operational amplifiers, flip-flops,
counters, AND, NOR, NAND, OR, exclusive OR gates, etc. or various
combinations of these and other types of circuits.
[0046] The pulse train is converted and/or filtered to produce a
sine wave using a transformer 66 in this embodiment, also isolating
the load 42 from the AC input 44. In other embodiments, the pulse
train may be filtered by an inductor or any suitable filter to
substantially remove at least one harmonic frequency component of
the pulse train while substantially passing the fundamental
frequency component of the pulse train. Any desired waveform may be
generated at the output by this filtering or other processing. In
this example embodiment, all harmonic frequency components are
substantially removed by the transformer 66 and filtering
capacitors 70 and 72 and inductor 74, of which some or all may not
be needed or used, substantially passing only the fundamental
frequency component, resulting in a relatively pure to pure sine
wave to the load 42. Filtering capacitors 70 and 72 and inductor 74
are merely examples and may be omitted, placed in other locations
in the power supply 40, or replaced with other types of filters as
desired.
[0047] The variable pulse generator 64 may be adapted to control
the pulse width, frequency, and/or other characteristics based on
one or more feedback signals representing various aspects of the
power supply 40. For example, the variable pulse generator 64 may
be adapted to limit inrush current through the transformer 66 or to
protect against over-current situations on the input or primary
side 76 of the power supply 40, based for example on a current
measurement in the primary side 76 by an input current detector. In
one embodiment, an input current sensing resistor 80 is placed at
any suitable location in the primary side 76, and the current
through the input current sensing resistor 80 is measured for
example by an input current feedback signal 82. The variable pulse
generator 64 interprets the voltage level on the input current
feedback signal 82 as an indication of the current through the
input current sensing resistor 80. If the current through the input
current sensing resistor 80 reaches a threshold level, the variable
pulse generator 64 is adapted to reduce the pulse width as
established by the on-time of the transistor 60, or even to turn
off the transistor 60 altogether. The power supply 40 is not
limited to any particular method of measuring the input current in
the primary side 76. Furthermore, the input current may be limited
or turned off in other ways, rather than or in addition to using
the variable pulse generator 64 to reduce pulse width.
[0048] The variable pulse generator 64 may also be adapted to
control the load current in the secondary side 84 of the power
supply 40. In some embodiments, load current may be controlled
based in part on the voltage across the load 42, measured for
example by a load voltage detector comprising a voltage divider
made of resistors 86 and 90, capacitors, or using another voltage
sensor. Resistors 86 and 90 are rated to withstand the voltage
across the load 42 and have a relatively high resistance to
minimize their impact on the load current. The load voltage may be
compared with a reference voltage signal 92 in a comparator or
operational amplifier (op-amp) 94 or any other suitable device, or
may be fed directly into the variable pulse generator 64 for
analysis before adjusting the pulse width at the transistor 60.
Load current may also be used by the variable pulse generator 64
when controlling the pulse width at the transistor 60. In some
embodiments, load current is measured using a load current detector
or load current sensing resistor 96 placed in series with the load
42, using a relatively low value resistor to minimize impact on
load current. As with the load voltage detection, the load current
may be compared with a reference current signal 100 in an op-amp
102 or other device. Feedback signals may be combined if desired
outside of the variable pulse generator 64 in an OR gate, a summer,
or any other type of digital, analog or digital and analog
combining circuit 104. The feedback signals may be further
processed as desired in a feedback signal processing circuit 106,
or may be passed directly on toward the variable pulse generator
64. The feedback signal or signals may be isolated and/or level
shifted, if desired, using an optocoupler 110, optoisolator,
transistor, transformer, or other device. The variable pulse
generator 64 may be adapted to begin controlling the pulse width in
the pulse train at the transistor 60 when the load voltage and/or
load current reaches a threshold level.
[0049] Note that the terms "primary side" and "secondary side" are
applicable not only to embodiments using a transformer 66 to
convert a pulse train to a sine wave or other waveform, in which
the term "primary side" refers to the circuit on the primary
winding of the transformer 66 and the term "secondary side" refers
to the circuit on the secondary winding of the transformer 66 but
also in embodiments using an inductor, filter or other devices. In
these embodiments, the term "primary side" refers to the pulse
train side of the power supply and the term "secondary side" refers
to the filtered sine wave side of the power supply.
[0050] It is also important to note that features shown in the
drawings may be combined in various different ways, including
combining features illustrated in different figures. Furthermore,
additional embodiments of the invention may be formed by
selectively omitting features shown in the drawings. For example,
embodiments of the invention may include or omit various filtering
components, primary side current feedback, secondary side voltage
feedback, secondary side current feedback, etc, to form a wide
number of different embodiments based on the requirements for the
power supply 40. The combinations of features illustrated in the
drawings are merely examples and have been selected in part to
limit the number of drawings for clarity by including a wide range
of elements that may or may not be included in any particular
embodiment. Additional components may also be included as required
by the load 42 or to fulfill other requirements of the power supply
40, such as a bypass capacitor or ballast capacitor 112 that may be
connected in parallel with some types of fluorescent lamps.
Furthermore, circuitry may be added to power elements of the power
supply 40 internally from the DC supply 52 or from other sources,
for example to power the variable pulse generator 64, optocoupler
110, feedback signal processing circuit 106, op-amps 94 and 102,
etc., and some examples of internal power circuits will be
illustrated and described in figures below. Variable frequency,
variable on time, variable off time, etc. may be employed in the
present invention. The circuit could consist, but is not limited
to, of one or more of the following: boost, buck, boost-buck,
buck-boost, SEPIC, Cuk, etc. Discontinuous conduction mode,
continuous conduction mode, critical conduction mode, resonant
conduction mode, etc. can be used to implement the present
invention.
[0051] Referring now to FIG. 3, another embodiment of a power
supply 120 has a rectified output as illustrated in FIGS. 1C and
1D. In this embodiment, a diode bridge or other rectifier 122
inverts negative portions of the sine wave (or other waveform) from
the transformer 66, producing a series of half sine wave pulses to
the load 42. Note that the power supply 120 may be applied to loads
in any suitable manner. For example, fluorescent lamps may be
negatively impacted by power supplied with a DC offset which could
force mercury to collect at one end of the lamp. In such a case,
the fluorescent lamp could be driven by two power supplies 120 from
opposite ends of the lamp, with suitable phase and/or polarity
differences to power the lamp. In other embodiments, a DC bias may
be applied to the output of the rectifier 122 to counteract the DC
offset of the rectified sine wave. In one particular embodiment, no
rectification of the waveform across the CFL, CCFL, FL, etc. is
performed which results in an AC output waveform. Any of the above
and other methods can be used to produce a zero DC or appropriate
waveform for a particular application or need.
[0052] As illustrated in FIG. 4, another embodiment of a power
supply 130 provides a non-rectified sine wave or other desired
waveform to the load 42, while rectifying the load current feedback
signal 132 using a rectifier 134 below or after the load 42. In
this embodiment, the load current sensing resistor 96 is connected
between the positive DC node at the common cathode point of a diode
bridge rectifier 134 and the DC ground node at the common anode
point of a diode bridge rectifier 134. The load current feedback
signal 132 is placed to convey the voltage drop across the load
current sensing resistor 96, such as at the positive DC node at the
common cathode point of a diode bridge rectifier 134. The load
current feedback signal 132 may be referenced to the AC return line
136 on the secondary side 84 as illustrated in FIG. 4, or to the DC
ground node at the common anode point of the diode bridge rectifier
134, or to other reference points as desired. This embodiment
leaves the load current in an optimal unrectified state for
fluorescent lamps, while providing a rectified feedback signal.
Note that voltage feedback signals may be similarly rectified if
desired. Rectified feedback signals may further be filtered to
provide DC feedback signals or time or frequency averaged signals.
The above is only meant to suggest some example exemplary
embodiments of the present invention. Any combination of the above
or of circuits and approaches not described here may be used to
realize the present invention.
[0053] As illustrated in FIG. 5, feedback signals in other
embodiments may be partially rectified rather than fully rectified,
reducing size, cost and complexity of a power supply 150. For
example, a diode 152 may be connected in parallel with the load
current sensing resistor 96, with another diode 154 connected in
opposite polarity to the top of the load current sensing resistor
96 as shown in FIG. 5. Time constants may be added as desired to
feedback signals in various locations in the power supply 150, and
feedback signals may be filtered if desired, such as in a filter
156 in the load current feedback signal 132. In still other
embodiments, the feedback circuitry may be further simplified by
omitting the diode 154 in the load current feedback signal 132. In
another example embodiment illustrated in FIG. 6, the diode 154 is
placed in series with the load current sensing resistor 96 rather
than in parallel with the load current sensing resistor 96 in the
load current feedback signal 132.
[0054] Filters 156 and 160 may be placed in the power supply 162 as
desired, for example to control the pulse width based on average
voltage and/or current values rather than instantaneous values.
Combinations of average and instantaneous feedback values may also
be used. In the embodiment illustrated in FIG. 6, the load 42 is a
CFL with a cathode heater, although the power supply 162 is not
limited to use with any particular type of load. The primary side
76 and secondary side 84 may be isolated by the transformer 66 and
an optocoupler 110, allowing them to float independently, or may be
coupled through the feedback signals as illustrated in FIG. 6.
Control circuitry 164 may also be added to process the load current
feedback signal 132 and control the variable pulse generator 64.
For example, the variable pulse generator 64 may comprise a simple
gate pulse driver and the control circuitry 164 may comprise a
timer or oscillator, comparator, etc, with internal isolation as
needed for protection.
[0055] Turning now to FIG. 7, another embodiment of the power
supply 180 omits the rectifier 46 on the primary side 76, including
back to back source-connected transistors 60 and 182, both
controlled in concert by the variable pulse generator 64. In this
embodiment, when the pulse train runs at a relatively high
frequency such as on the order of 100 kHz for fluorescent lamp
applications, the pulse train comprises a series of substantially
square or rectangular pulses that follows the envelope of the input
AC waveform, such as a 50 Hz or 60 Hz AC sine wave. When the AC
input 44 is positive and the transistors 60 and 182 are both
switched on by the variable pulse generator 64, current flows
through the channel of the transistor 60 and through the parasitic
diode of the transistor 182. When the AC input 44 is negative and
the transistors 60 and 182 are both switched on by the variable
pulse generator 64, current flows through the channel of the
transistor 182 and through the parasitic diode of the transistor
60.
[0056] Turning now to FIG. 8, in another embodiment the variable
pulse generator 64 may be used to control the power factor of the
power supply 190 on the primary side 76 while a high/low driver 192
and high/low controller 194 are used on the secondary side 84 to
control load voltage and/or current. The high/low driver 192
drives, for example, a pair of NFET transistors 200 and 202 (or any
other suitable types of transistors, switches or alternative
circuitry), to alternately connect an unfiltered output node 204 to
the output 206 of the transformer 66 and to the return line 210 of
the transformer secondary 66. (In embodiments with an inductor or
other filter in place of the transformer 66, the unfiltered output
node 204 would be alternately connected to the output and ground
lines from the filter.) In this embodiment, the variable pulse
generator 64 and high/low driver 192 may be operated at or near the
same frequency, or at very different frequencies and may also be
used for dimming. The high/low driver 192 samples the sine wave
output from the output 206 of the transformer 66. Filtering
capacitors 212, 72 and inductors (e.g., 74) may be used to smooth
the sampled sine wave to provide a waveform suitable for the load
42.
[0057] Turning to FIG. 9, a transformer driver 220 may be used, for
example, in a power supply 222 to drive a pair of transistors 222
and 224 to control the current through the transformer 66 in a
push-pull configuration using, for example, a non-center tapped
transformer or a center tapped transformer. A center tapped
transformer may be used on the primary or secondary side or both
sides. A capacitor 230 may be connected in series with the
transformer 66. The transformer 66 may also be connected in a
center tap configuration. The transformer driver 220 may be powered
from the DC supply 52 by a series inductor 232 and diode 234
connected in parallel with the transformer driver 220 and with a
capacitor 236. The voltage across the transformer driver 220 may be
measured by voltage divider resistors 240 and 242 and provided as
feedback to a gate drive circuit 244 to limit or turn off the
current through the transformer 66 in the event of an over-voltage
condition. The gate drive circuit 244 may also be provided with
feedback from the secondary side 84, such as with the load current
and voltage feedback illustrated in FIG. 9, either with or without
reference level comparisons. In this embodiment, the pulse train
may be generated by the transformer driver 220, with the variable
pulse generator 64 being replaced by a gate drive circuit 244 to
turn off the current through the transformer driver 220 in the
event of over-voltage or over-current conditions at various
locations in the power supply 222. With, for example, the
transformer driver 220 referenced to the DC supply 52 and the gate
drive circuit 244 referenced to the primary side ground 246, the
transformer driver voltage feedback signal 250 may be passed
through any suitable level shifter 252 if needed.
[0058] A dimming sense and control circuit 254 may be used to
internally dim the power supply 222 based on an external control
signal, whether obtained in a wired or wireless manner, or based on
voltage and/or current levels at the DC supply 52, or based on duty
cycle, waveform, phase information, etc. of the DC supply 52 or of
the AC input 44. The dimming sense and control circuit 254 may
provide a pulse width modulated (PWM) output signal or other type
of output signal, using any suitable circuitry such as, for
example, digital logic, digital, circuits, state machines,
microelectronics, microcontrollers, microprocessors, field
programmable gate arrays (FPGAs), complex logic devices (CLDs),
analog circuits, discrete components, band gap generators, timer
circuits and chips, ramp generators, half bridges, full bridges,
level shifters, difference amplifiers, error amplifiers, logic
circuits, comparators, operational amplifiers, flip-flops,
counters, AND, NOR, NAND, OR, exclusive OR gates, etc. or various
combinations of these and other types of circuits. The dimming
sense and control circuit 254 may reduce the current to the load 42
in one or more of a number of manners, including controlling the
transformer driver 220 and/or the gate drive circuit 244 to reduce
current through the transformer 66, or by providing a current level
control signal 256 used to directly modify the load current by a
load current controller 260 on the secondary side 84. Note that the
current level control signal 256 may be directly connected, or may
be isolated, level shifted, and/or filtered as desired or needed
between the dimming sense and control circuit 254 and load current
controller 260. The load current controller 260 may comprise any
device or circuit capable of adjusting or limiting the load
current, such as a current mirror or variable impedance, etc. In
some embodiments, the dimming may be based in part on current
and/or voltage measurements from devices such as sense resistors
(e.g., 262). Additional components may be added as needed, such as
a DC-blocking or filtering capacitor 264 connected in series with
the load 42.
[0059] In an embodiment illustrated in FIG. 10, the unrectified AC
signal from the AC input 44 is passed through the transformer 66 as
in the previously described embodiment of FIG. 7. In this
embodiment, a dimming sense and control circuit 254 is included,
powered by a rectifier 270. A DC ground 272 is connected between
the primary side 76 and secondary side 84, although in other
embodiments the DC grounds from the primary and secondary side
rectifiers 270 and 134 are left separate to allow them to float
independently. Again, various elements of the example embodiments
disclosed herein may be selectively combined in any of a number of
ways, such as including voltage and current feedback from the
secondary side 84 to the gate drive circuit 244, isolating or not
isolating feedback signals and grounds, comparing voltage and
current levels to threshold values as with the load current
feedback signal 132 in FIG. 10 or not as with the load voltage
feedback signal 274. Feedback signals may be combined outside of
the gate drive circuit 244 or supplied independently to the gate
drive circuit 244 and used in a variety of ways in the gate drive
circuit 244, for example giving priority to particular feedback
signals, etc. The voltage level at the common source node of the
transistors 60 and 182 may be provided as feedback to the gate
drive circuit 244, with the voltage level referenced to the DC
ground 272 through resistor 276 or not, as desired. The size and
cost can thus be balanced against the desired features and
operating characteristics of the power supply 280.
[0060] Turning now to FIG. 11, in another embodiment of the power
supply 290 the power circuitry supplying the dimming sense and
control circuit 254 and the gate drive circuit 244 from the AC
input 44 is simplified from the rectifier 270 to a single diode
292. One or more diodes may be used for this particular example
embodiment where, for example, the number of diodes can typically
be from 1 to N, where N may typically equal 1, 2, 3, 4 or a number
larger than 4. Depending on the specific circuitry used in the
dimming sense and control circuit 254 and gate drive circuit 244,
they may require more regulated power or may be able to run with
partially rectified and unfiltered power from the AC input 44. In
this embodiment, the dimming sense and control circuit 254 and gate
drive circuit 244 are allowed to float within the AC power from the
AC input 44, by enclosing them within resistors 294 and 296. By
selecting values for the resistors 294 and 296, the dimming sense
and control circuit 254 and gate drive circuit 244 can be caused to
float closer to either the upper rail 300 or lower rail 302. Sense
resistors (e.g., 304) may be included and placed in various
locations based upon the control scheme to be implemented by the
dimming sense and control circuit 254 and gate drive circuit
244.
[0061] An example of a method for supplying power to a fluorescent
lamp or other load is illustrated in the flowchart of FIG. 12.
Based on a power input, whether unrectified AC, rectified AC, DC,
or any other power input, a pulse train is provided. (Block 310)
The pulse train is filtered to substantially block at least one
harmonic frequency component of the pulse train while substantially
passing a fundamental frequency component of the pulse train.
(Block 312) The power supply is not limited to producing any
particular type of output waveform, but in an embodiment for
powering a fluorescent lamp, the output waveform is a pure or
substantially pure sine wave with substantially no DC offset. The
resulting filtered waveform is then provided at a power output,
wherein an amplitude of the filtered waveform is related to the
pulse width in the pulse train. (Block 314) As discussed above, the
power to the load may be dimmed under the control of an external
dimmer or by a control signal provided to an internal dimming sense
and control circuit. The dimming may be accomplished by varying the
width or duty cycle of the pulses in the pulse train, or by
directly controlling the load current using a current mirror,
variable impedance or any other suitable method, etc. The width or
duty cycle of the pulses in the pulse train may be controlled
during dimming and/or during over-current or over-voltage
conditions using one or more feedback signals to a variable pulse
generator (e.g., 64), transformer driver (e.g., 220), gate drive
circuit (e.g., 244), high-low side driver, push-pull, center tapped
transformer, etc.
[0062] The power supply disclosed herein in its various embodiments
provides a dimmable, controllable, relatively simple and
inexpensive circuit and device for powering loads such as
fluorescent lights, and for dimming those loads, while controlling
and providing an excellent power factor.
[0063] While illustrative embodiments have been described in detail
herein, it is to be understood that the concepts disclosed herein
may be otherwise variously embodied and employed.
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