Note: Descriptions are shown in the official language in which they were submitted.
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FLUO~ESCENT LAMP BRIGHTNESS CONTROL
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S~MM~RY OF HE INVENTION
The present invention relates generally to lighting control
systems and more particularly to intensity or illumination level
control circuits for fluorescent lights. In a particular
disclosed preferred embodiment, a phase or duty cycle control is
incorporated into a rapid start type fluorescent lamp system
having a conventional ballast or autotransformer.
A wide variety of brightness controls are known for electric
lighting systems. For incandescent lights, a simple rheostat is
a common expedient. Fluorescent lights, while more economical to
operate than incandescent lamps, are not readily controlled by
thls simple expedient. Dimming control arrangements for
fluorescent lamps typically employ special and more costly
ballasts in conjunction with other circuitry to achieve a range
of illumination levels.
Illustrative of such special ballast arrangements is U.S.
Patent 4,464,610 where the ballas~ includes three separate
windings for filament heating purposes, two capacitors, and what
appears to be a pair of magnetically coupled iron cores. Such a
balla~t is not standard in the sense o~ being of a type widely
used and produced in such large numbers as to be readily and
cheaply available. The truly standard or conventlonal ballast iS
~ormed as an autotransformer on an iron core wlth a multiply
tapped ~ingle winding the full extent of which provides the high
voltage necessary to initiate lamp operation while the taps
comprise the input or primary circuit and two filament ~cathode~
heating clrcults.
A dimmer arrangement for a ~luorescent lamp uslng a standard
ballast haY boon proposed ln u.s. Patent 3,~35,50~. In this
pat~nted device, the control clrcuitry is entirely on the line
side of the ballast, that ls, the lamp and ballast are
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interconnected ln the conventional manner and the control
circuitry is interposed in one of the lines leading ~rom the
autotransformer primary winding to the source of line voltage.
With this arrangement, filament voltage is lowered as the
intensity is diminished placing an undesirably high lower bound
on the intensity level as well as causing instability forcing
the patentee to employ a negative feedback circui~ for
compensation. The circuit require~ post installation adjustment
of a trimmer resistance, and a sequential switch which allows
the lamp to heat up before being dimmed. Further, switching noise
created by operation of the circuit may be introduced into the
voltage supply and thus into other devices connected to the
supply. This patented arrangement as well as that of the earlier
mentioned 4,464,610 patent are sufficiently complex and costly as
to preclude their widespread use.
Among the several ob~ects o~ the present invention may be
noted the provision of a simplistic and economical fluorescent
lamp dimmer control; the provision of a fluorescent lamp dimmer
control employed in a lamp system using a conventional ballast;
the provision of a load side phase con~rol circuit for
fluorescent lamps utilizing a 1:1 transformer to isolate the
phase control circuit from the fila~ent ener~izing circult; the
provision of an intensity control for a fluorescent lamp used as
a task light, receiving power ~rom a conventional outlet and
fused at the plug location; the provision of a fluorescent la~p
circuit requiring but a single thermal protector associated with
a conventional ballast; and the provision of a dimmer control for
fluorescent lamps which is readily assembled on a printed circuit
board and then connected by a crlmp operation to the remainder of
the lamp system. The~e as well as othor ob~ects ~nd advantageous
~eatures of the pre~ent invention will be in part apparent and in
part pointed out her~ina~t~r.
~ In general, a rapid start type fluorescen-t lamp
system comprises: an elongated fluorescent lamp with low
voltage filaments at opposite ends thereof; a step-up
autotransformer having a primary circuit and a plurality of
secondary circuits, the primary circuit adapted to be
energized by line voltage, one secondary circuit for provid-
ing a high voltage between lamp ends to initiate lamp
operation and thereafter providing an inductive impedance
limiting lamp curren-t, a second secondary circuit for
energizing one of the low voltage filaments~ and a third
secondary circuit for energizing the other low voltage
filament; a thermal protection device responsive to auto-
transformer temperature for opening the primary circuit whenthe autotransformer temperature exceeds a predetermined
value; a phase control circuit connecting the lamp to the one
secondary circuit for selectively controlling lamp current
and, therefor, also controlling lamp intensity; isolating
means for coupling the second secondary circuit and the one
low voltage filament without shunting the phase control
circuit; a printed circuit board having a plurality of leads
extending thererom to be crimp connected to other leads in
the lamp system including at least leads to the lamp and
leads to the autotransformer; and an on-off switch to be
connected in series with the primary circuit, the phase
control circuit, on-off switch, and isolating means being
permanently connected to the printed circuit board.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic diagram of a rapid start
type fluorescent lamp system utilizing a conventional ballast
and illustrating the invention in one form;
Figure 2 is a side elevation view of a fused plug
for connecting a task light embodiment oE the invention to a
conventional outlet; and
Figure 3 is a simplified one cycle depiction of
lamp current illustrating the effect of the con-trol circui-t.
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Corresponding reference characters indicate
corresponding parts throughout the several views of the
drawing.
The exemplifications set out herein illustrate a
preferred embodiment of the invention in one form thereof and
such exemplifications are not to be construed as limiting the
scope of the disclosure or the scope of the invention in any
manner.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In Figure 1 there is illustrated a rapid start
tcontinuously
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heated cathode) type fluorescent lamp system having an elongated
~luorescent lamp 11 with low voltage filaments 1~ and 19 at
opposite ends thereof and a step-up autotransformer or ballast 13
having a single multiply tapped winding 21 including a primary
circuit between leads 2~ and 31, and a plurality of secondary
circuits. The primary circuit is adapted ~o be energized by line
voltage by way of closed switch 45 from plug 33 while one
secondary circuit across the extreme ends of winding 21 between
lines 2~ and 29 is for providing a high voltage between lamp ends
to initiate lamp operation and thereafter providing an inductive
impedance limiting lamp current. A second secondary circuit
including winding segment 25 i5 for energizing one of the low
voltage filaments 19, and a third secondary circui~ including
winding segment 23 is for energizing the other low voltage
~ilament 17. A phase control circuit including the solid state
switching device 53 connects the lamp to the one secondary
circuit for selectively controlling lamp current and, there~or,
also controlling lamp intensity. Transformer 51 provides
isolation for coupling the second secondary circuit 25 and the
one low voltage filament l9 w~thout shunting the phase control
circuit.
The circuit of Figure 1 has particular, but not exclusive,
utility when the lamp is employed as a task light where the
~luorescent lamp 11 is mounted relatlvely close to an underlying
work area as described more completely, for example. in U.S.
Patent 4,562,515 and the system receives power from a
conventional outlet. The system includes a plug 33 having blades
35 and 37 along with ground pron~ 41 which are mateable with a
conventional outlet and connected to supply power ta the primary
circuit between llnes 27 and 31. The plu~ lncludes a replaceable
plug-ln ~USQ 39 ~or c~rr0nt overload protection. ~his particular
posltioning o~ ~use 39 a~ords maximum current overload
protection for the illustrated circuitry. When compared to
(optional) fuse 40 ~or example, a short in line cord 42 will trip
fuse 39, but would fail to trip fuse 40.
When line voltage, say 115 volts, is applied to the primary
circuit as by closing the on-o~f switch 45, a voltage step-up
action occurs so that the ~oltage across the complete winding 21
is around 300 ~olts. This high voltage is impressed across the
region 15 of lamp 11 to initiate conduction through and
illumination of the lamp~ Once conduction is established. the
voltage drop between the cathodes 17 and 19 drops markedly and
current limiting is provided by the inductive effect of winding
21. This description of the start up action assumes that the
high voltage is actually applied across the cathodes 17 and 19
of the lamp as will be the case if the phase control circuit is
conducting as, for example, when variable resistor 61 is set at
its minimum value or lf lines 43 and 27 were to be directly
connected together e~fectively removing the phase control
circuit from the system.
The phase control circuit comprises a bilateral solid state
ZO gate controlled switching device such as triac 55 connected in
series between the lamp and the one (hlgh voltage) secondary
circuit, and a relaxation oscillator including re~istor 63,
variable resistor 51 and capacitor 59 connected in controlling
relatlon to the gate of the swltching device by a threshold
device such as an A-C switching diode or diac 57.
Ballast 13 includes a thermal protection devlce 77, for
example, a bimetalic disk, which i9 located in close proximity
to and in good heat transfer relatlonship with the winding 21 so
as to be actuated to open the power supply line 31 in the event
o~ overheating o~ the ballast. The trans~ormer 51 is a low
voltage (about 6 volts) 1.1 trans~ormer having about the same
number oS turns ln the prlmary windlng ~7 and in the secondary
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winding 49. The trans~ormer operates at a very low current
level, for example, a 350 milliampere rating, and requires no
such thermal protection, hence, the thermal protector ~ is the
only thermal protection device in the system.
All of the components below the horiæontal line of crimp
connectors such as ~5 and 76 in Figure 1 are permanently
connected to a common printed circuit board including the
isolating transformer S1, on-off switch 45, fuse 40 if present
as well as the phase control and related components, and that
board has seven leads extending therefrom to be crimp connected
to the upper part o~ the circuit including to the lamp as by
crimp connector ~6 and to the ballast or autotransformer as by
crimp connector 75. Advantageously, these crimp connections are
accomplished using the MTA system available from Amp. Inc~ which
employs a simultaneous insulation piercing or displacing and
crimping ~or each connection.
Included on the printed circuit board are a resistor 65 and
capacitor 67 connected in series between the lamp 11 and
secondary high voltage winding of leads 2~ and 29. This series
resistor and capacitor are connected in parallel with the phase
control clrcult e~fectively bypasqing switchlng device 53 when
that device i9 nonconducting and supplying a low level
energlzation current to the lamp 11. The series circuit also
suppresses voltage surges when the phase control circuit is
switched to a conducting state and provid~s an impedance which
tends to prevent overvoltages across the triac 55. This low level
current is illustrated by the dotted sine wave ~9 in Figure 3. I~
the switching devlce were to be conductive at all times, the lamp
current would be as lllustrated by sine wave 81 in Figure 3. In
actual operatlon, the lamp current ~ollows the solid line ln
Fi~ure 3 with the n~arly vertical ~ump in current cccurring when
the switch 53 is gated to itq conducting state. The time ln each
cycle (earlier or later as indicated by the arrows) where this
jump occurs, and thus the energy supplied to the lamp and
resulting intensity level is controlled by the setting of
potentiometer 61 which determines the charging rate for capacitor
59. Each time diac 5~ conducts to discharge capacitor 59 through
the gate of triac 55, the diode bridge circuit 69 and matched
pair of resistors 71 and 73 thereafter function to reset the
initial capacitor charge to the same level thereby eliminating
any hysteresis effect and ensuring a balanced current flow, i.e.,
symmetry of the two hal~ cycles illustrated in Figure 3. There
would actually be a phase difference between the sine waves ~9
and 81 due to the presence of capacitor 67, but this has little
effect on the operation of the system and has been ignored for
the purposes of explaination.
One implementation of the invention which has been built
and tested successfully employed the ~ollowing illustrative
circult components. Resistors 71 and 73 were both 15,000 ohms.
Variable resistor 61 was 500,000 ohms. Resistor 63 was 6800
ohms. Capacitors 59 and 67 were .02 and.10 microfarads
respectively. Resistor 65 was 100 ohms. Diac 5~ and triac 55
were purchased as a single component 53 called a quadrac, Teccor
model number Q6004FT1.
From the forgoing, it is now apparent that a novel
arrangement has been disclosed meeting the obJects and
advantageous features set out hereinbefore as well as others,
and that numerous modifications as to the preci~e shapes,
con~lgurations and details may be made by those ha~ing ordinary
skill in the art wlthout departing from the spirit of the
lnventlon or the scope thereo~ as set out by the claims whlch
~ollow.
