Note: Descriptions are shown in the official language in which they were submitted.
112
LD 7951
STARTING AND OPERATING CIRCUIT FOR
GASEOUS DISC~ARGE hA~PS
The presen~ invention relates to discharge lamp
starting and operating circuits, and particularly
concerns such circuits or quickly re-starting
extinguished high intensity gaseous discharge lamps
while still hotO
Known types of circuits for starting and ballast-
ing high intensity discharge lamps have the disadvantage
that when power is briefly removed from the system, the
lamp rapidly de-ionizes and ceases to conduct current
upon re-application of power. This temporary outage may
las~ from 1 minute up to as much as 15 minutes depending
on lamp type and cause interruption of work operations
or other activities until the lamp is re-started~ In
the past, various devices for ~uickly re-starting the
lamp have been suggested, but known devices and circuits
of this type have generally been expensive, complicated
~: in structure or unreliable in operation.
It i~ object of the invention to provide an
improved device for starting and operating gaseous
discharge lamps.
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A particular object of the invention is to
provide a device of the above type for quickly
re~starting extinguished discharge lamps while still
hotO
S Another object o~ the invention is to provide a
device of the above type comprising a starting circuit
wherein provision is made for automatically reducing
power applied to the starting circuit when the lam~ is
inoperative or absent~
A further object of the invention is to provide a
device of the above type wherein the starting circui~
automatically ceases operation when the lamp turns on
and automatically begins operation when the lamp is
extinyuished.
Still another object of the invention is to
provide a device of the above type which is simple in
construction, relatively low in cost, and is efficient
and reliable in operation.
Other objects and advantages will become apparent
from the following description and the appended claims.
: With the above obj ects in view, the present
inve~tion in one of its aspects relates to a starting
and operating circuit for gaseous discharge lamps
comprising, in combination, a source of alternating
current, inductive ballast means connected at its input
side to the alternating current source, discharge lamp
means connected to the output side of the ballast means,
transformer means connected in series between the
discharge lamp means and the ballast means, sine wave
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oscillator means connected at its input side to the
alternating current source and at its output side to the
transformer means whereby the transformer means s~eps up
and applies to the discharge lamp means sine wave
voltage produced by the oscillator means for starting
and re-starting the discharge lamp means, and variable
impedance means connected between the alternating
current source and the oscillator means for reducing
power to the osci.llator means when the discharge lamp
means has ~een started or is inopera ive.
The invention will be better understood ~rom the
following description ta~en in conjunction with the
accompanying drawings, in whicho
FIGURE 1 is a circuit diagram o~ a discharge
lamp starting and operating circuit in accordance with
an embodiment of the invention; and
FIGURE 2 is a circuit diagram of a regulato~
ballast which may be employed in the circuit of FIGURE
1. .
Referring now to the drawings, and particularly
to FIGURE 1, there is shown a starting and operating
circuit for a high intensity gaseous discharge lamp 1,
typically a high pressure sodium vapor lamp or other
discharge lamp, which requires a relatively high voltage
pulse in order to be ignited and which thereafter
operates on a lower voltage. Lamp 1 is c3nnected by
conductors 5 and 6 to the output of balla t 7 which in
turn is connected to terminals 2 of a~ alternatiny
current source, typically 1~0 volts. Ballast 7, which
may be any of Xnown types of inductive ballast devices~
provides current limiting impedance as is conventional
in discharge lamp circuits. A preferred type is a
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magnetic regulator ballast such as shown in detail in
FIGURE 2 and described more fully below~
The ballast transformer shown in Figure 2
comprises primary winding 7a connected across supply
terminals 2, secondary winding 7b connected by
conductors 5 and 6 to the discharge lamp, and tertiary
winding 7c connected as shown to the oscillator circuit
by conductors 9 and 10, with regulating capacitor 13
connected in series with tertiary winding 7c, so as to
regulate the output of the oscillator within desired
limitsO
In accordance with the invention, a sine wave
oscillator circuit is employed to provide a high voltage
high frequency sine wave, e.g., in the range of 1600 to
200,000 Hz, for not only starting lamp 1 when cold but
also for quickly re-starting the extinguished lamp while
still hot, and there is further provided variable
impedance mean~ for reducing the voltage applied to the
oscillator circuit should the lamp be inoperative or be
absentv For these purposes there is provided in the
embodiment shown in FIGURE 1, sine wave oscillator
circuit 8 connected by conductors 9 and 10 to ballast 7
as shown and variable impedance means in the form of a
positive temperature coefficient resistor (PTCR) 11
connected in series between ballast 7 and oscillator
circuit 8. As well understood in the art, the PTCR has
low resistance when cool and as it gradually heats up
due ~.o passage of current therethrough, its resistance
correspondingly increases~ The particular oscillator
circuit illustrated is, in its main construction, of
known type, being shown, for example~ in U.S. Patent
4,202,031 ~ Hesler et al, (see particularly FIGURES l
a~d 7 of the patent and the description relating
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thereto), the patent being assigned to the same
assignee as the present invention. Oscillator circuit
8 co~prises full wave rectifier 12 serving as a direct
current source, filter capacitor 16, power transistor
17, transformer 18, diodes 19 and 20, resistors 21 and
30 and capacitor 22, the circuit components being
connected as shown to provide for turning on and
controlling the operation of the transistor, and the
combination functioning as a sine wave oscillator.
Transformer 18 comprises primary winding 18a, demagnetizing
winding 18b and secondary winding 18c, the latter winding,
in accordance with the invention, being connected by
conductors 33 and 34 to a coupling transformer 32,
such as the autotransformer shown, connected to
conductor 5 in series with lamp 1. Capacitor 36
connected across transistor 17 serves to assure proper
transistor commutation over widely ranging load
conditions. Transformer 18 also comprises three
feedback windings 27, 28, 29 which serve to control the
operation of transistor 17. The base of transistor 17
is connected to a starting and control network
comprising resistor 30, diodes 19 and 20, feedback
windings 28, 29, resistor 21 and capacitor 22. Diode 23
connected to windings 18a, 18b serves to protect transistor
17 from high voltage surges.
Further details of the elements, arrangement
and operation of oscillator circuit 8 are set forth
in the aforementioned Hesler et al U.S. Patent No.
4,202,031.
In the illustrated embodiment, a turn off
mechanism comprising series connected diode 24 and
inductor 25 is provided in the oscillator circuit for
turning off the oscillator as more fully described
below. The particular turn-off mechanism illustrated,
which is not a part of the present invention, is
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disclosed and claimed in Canadian application Serial
Number 390,563 - Owen, filed November 20, 1981
and assigned to the same assignee as the
present invention. As there disclosed, the turn-
off mechanism comprises series-connected diode
24 and inductor 25 connected at one side to the
junction of the anode of diode 23 and transformer
demagnetizing winding 18b, and at the other side to
the junction of base feedback winding 29 and
capacitor 22. This device stops operation of the
oscillator during normal lamp operation without
interfering with normal restarting functions. This
is accomplished with the illustrated circuit by
supplying a negative current to capacitor 22
which is greater in magnitude than the positive
charging current supplied to capacitor 22 through
resistor 30. The described turn-off circuit utilizes
the high voltage transformer 32 as a lamp current
sensor during lamp operation. Transformer 32, which
steps up the high frequency voltage to start the
lamp is designed to saturate with the 60 Hz lamp current
during normal lamp operation to minimize its interference
with lamp current. However, normal transformer
action takes place until the current waveform reaches
a magnitude sufficient to saturate the core. This
produces a 60 Hz voltage on the normal primary of
transformer 32. This voltage, being applied to
transformer secondary winding 18c, induces a voltage
reduced by turns ratio in the other windings of
3Q transformer 18. In accordance with the present
invention, this voltage is rectified to obtain a
negative voltage and filtered, and is employed to turn
off transistor 17.
Inductor 25 serves as a high frequency blocking
filter to prevent the high frequency restart voltage
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from turning off transistor 17. Diode 24 serves to
block the posi ive pulse and pass the negative pulse~ so
as to produce a negative bias to the transistor base for
shutting off the transistor.
In the operation of the disclosed circuit, when
the circuit is energized, capacitor 16 charges up
through PTCR 11 and rectifier bridge 12. During such
charging of capacitor 16, PTCR 11 has a current limiting
function~ After capacitor 16 is fully charged, the
oscillator circuit turns on as hereinafter explained.
The RC time constant for capacitor 16 and PTCR 11 is
very short, and accordingly capacitor 16 becomes fully
charged very quic~lyl e.g., within one cycle. For
oscillator circuit 8 to turn on, capacitor 22 must
charge up to a small positive value, such charging being
controlled by the RC constant of resistor 30 and
capacitor 22 and requiring a number of cycles. The
charging capacitor 22 biases the base of transistor 17
posi~ive, and the transistor turns on with the collector
current flowing through transformer winding 18a.
Feedback windings 28, 29 generate a negative voltage
which turns off transistor 17. The energy stored in
transformer 18 is then reduced when current flows
through the demagnetizing winding 18b of the transformer
and diode 23. Oscillator 8 thus becomes free running,
as described in further de~ail in the aforemen~ioned
~esler et al patent, and the output of transformer 18 is
a high frequency sine wave. The voltage is then stepped
up by coupling autotransformer 32 for application to
lamp 1.
Capacitor 35 conn~cted across ballast 7 offers
very low impedance to the high voltage generated by
.
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transformer 32, and hence very little of the high
frequency voltage appears across the ballast.
If lamp l starts, the oscillator circuit is
turned off by operation of diode 24 and inductor 25, as
described previously. Normal starting of a cold lamp is
thus providedO
If lamp l becomes extinguished due to a dip in
the line voltage, the turn off mechanism of diode 24 and
inductor 25 ceases to function as a result of a lack of
lamp curren~ through transformer 32. Then, since
capacitor 16 is still fully charged, it starts to
re-charge capacitor 22~ which had been held with a small
neyative charge by the turn-off network, so that a small
positive charge is again placed on capacitor 22 and the
previously described procedure is repeated for starting
lamp 1.
In the event lamp 1 is absent or inoperative,
oscillator circuit 8 becomes partially disabled after a
predetermined period of operation. This occurs by PTCR
ll becoming heated and presenting a high resistance,
thus limiting the output power of the oscillator because
capacitor 16 does not become fully charged.
Capa~itor 26 shown connecte~ across transformer
secondary winding 18c forms a resonant circuit wi~h the
latter winding and the primary of autotransformer 32,
and serves to control the frequen~y o~ the sine wave
oscillator to the desired level.
While PTCR ll is shown connected between ballast
7 and rectifier 12, it may in another preferred
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embodiment ke connected instead between rectifier 12 and
transformer primary winding 18a.
While oscillator circuit 8 is shown connected to
supply terminals 2, 2 via ballast 7, it will be
understood that it may be directly connected to the
supply terminals, or it may be connected to a separate
supply source in appropriate conditions.
While the present invention has been described
with reference to particular embodiments thereof, it
will be understood that numerous modifications may be
made by those skilled in the art without actually
departing from the scope of the invention. Therefore,
the appended claims are intended to cover all such
equivalent variations as come within the true spirit and
scope of the invention.
