Note: Descriptions are shown in the official language in which they were submitted.
6~
HIGH FREQUENCY CIRCUIT FOR OPERATING
A HIGH-INTENSITY, GASEOUS DISCHARGE L~P
BACXGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention relates to a circuit for operating a high
intensity, gaseous-discharge lamp without requiring a large
ballast transformer, and more specifically, for operating such
a lamp at a frequency higher than acoustic resonance for such
lamps.
DESCRIPTION OF THE PRIOR ART
Conventional ballasting of high intensity discharge lamps,
such as metal-additive arc lamps, employ transformer-like coils,
capacitors, or inductor coils in various combinations to pro-
vide proper voltage for starting and limiting the current during
operation. Such ballasts are large, relatively expensive, and
not efficient at low cost. Simple inductor ballasts are avail-
able; however, they provide poor regulation for line voltage
variations.
Regulating solid state ballasts have been developed, but
heretofore no commercial ballasts have been developed which is
suitable for the operating conditions of high pressure mercury,
sodium and metal halide lamps to give proper control of lamp
wattage for high ranges of lamp voltages, line fluctuations
and temperatures.
Although theoretically a lamp may be operated on a com-
bination of applied dc and ac, which would give lower noise than
ac alone, it has been discovered that the application of dc is
bad for lamp efficiency and life. The application of low audio
frequency ac causes noisy ballast conditions. The application
of medium frequency ac causes noisy and unstable lamp conditions.
In fact, the high pitch whine of lamps operated under such
conditions is extremeIy unpleasant. Therefore, it has not
been recognized that high frequency ac may be used with regard
to lamps; however, life tests and lumen tests have revealed
that high frequency operation beyond a certain range is per-
fectly satisfactory, both as to providing acceptab~e lamp
operating stability and an absence of audible noise.
Therefore, it is a feature of this invention to provide
an improved operating circuit for a high intensity gaseous
discharge lamp that provides a high frequency mode of operation.
SUMMARY OF THE INVENTION
The invention in one broad aspect pertains to a circuit
for operating a high frequency, gaseous-discharge lamp,
comprising a ballast impedance connectable to the lamp, and
an oscillator operating at a frequency above the acoustic
resonances of the lamp connectable thereto, the oscillator
providing the lamp with high power and high frequency current.
In another aspect the invention pertains to a circuit
for operating a high frequency, gaseous-discharge lamp including
a ballast connected to receive a DC source voltate and a base-
driven triode transistor for supplying at least a portion ofthe high frequency current to the ballast. The improvement
comprises regulating means connected to the ballast and the
base-driven triode transistor for changing the conduction time
of the transistor when the voltage applied to the ballast
exceeds a predetermined value.
,~ .
A still further aspect of the invention comprehends a
circuit for operating a high frequency, gaseous-discharge lamp,
comprising a push-pull, Class C oscillator having a resonant
circuit including a high-Q coil connected to a first operating
electrode of the lamp, the oscillator being connected to a
power source and the resonant circuit establishing an operating
frequency for the oscillator at a frequency above the acoustic
resonant frequence of the lamp. A ballast impedance is
connected to a second operating electrode of the lamp and
the high-Q coil in the resonant circuit provides the lamp
with high power and high frequency current.
A preferred embodiment of the present invention includes
a drive circuit having a push-pull, Class C oscillator employ-
ing a high efficiency transformer, the center tap of the trans-
former being connected to a dc power source. The oscillator
halves are driven in such a fashion so that the application
of current provides high frequency at high efficiency to a
tank-and-lamp network, which from lamp starting, normal
operation, to lamp failure may exhibit a wide range of load
impedances to the drive circuit.
--3--
' . .
6~&~
Also disclosed is a coil configuration used in the tank-
andwlamp network for providing an unloaded high-Q of approxi-
mately 300 in conjunction with the operating conditions existing
for mèrcury, metal halide and high pressure sodium lamps.
Finally, a stable power supply including emergency fea-
tures for operation with the circuit is also described, such
circuit being capable of removing transients from the applied
line voltage. The circuit may incorporate a battery connected
through diode connec-tions when the nominal output, dc-line
voltage from the power supply varies beyond predetermined
limits, either high or low.
BRIEF DESCRIPTION OF TIIE DRAWING
So that the manner in which the above-recited features,
advantages and objects of the invention, as well as others
which will become apparent, are attained and can be understood
in detail, more particular description of the invention briefly
summarized above may be had by reference to the embodiments
thereof which are illustrated in the drawings, which drawings
form a part of this specification. It is to be noted, however,
that the appended drawings illustrate only typical embodiments
of the invention and are therefore not to be considered limit-
ing of its scope, for the invention may admit to other equally
effective embodiments.
IN THE DRAWINGS:
FIG. 1 is a simplified schematic diagram of the present
invention showing a preferred embodiment of a push-pull, Class
C oscillator connected for driving a high frequency, gaseous-
discharge lamp.
FIG. 2 are wave form diagrams illustrating the operation
of the preferred circuit illustrated in Fig. 1.
f \ ~-~
FIG. 3 diagramatically illus~ratcs in three dimensional
form, high-Q for a preferred high-Q coil confic3uration embodi-
ment.
FIG. ~ illustrates a cross section of a preferred higll-
Q coil configuration.
FIG. 5 is a par~ial schematic diagram of a regulating
circuit that may be connected as part of the circuit show
in Fig. 1.
FIG. 6 illustrates in simplified block-a}ld-scllematic-
diagram form a preferred power supply for operation with the
preferred circuit illustrated in Fig. 1.
FIG. 7 is a schematic diagram of a preferred power
supply for operation with the preferred circuit illustrated
in Fig. 1.
FIG. 8 is a schematic diagram of a preferred embodiment
of the ~ network shown in Fig. 7, appearing with Fig. l.
FIG. 9 is a schematic diagram of an alternate preferred
embodiment of the ~ network shown in Fig. 7, with Fig. 1.
FIG. 10 is a partial schematic diagram of an alternate
preferred embodiment of a regulating circuit that may be
connected as part of the circuit shown in Fig. l.
FIG. 11 is a partial schematic diagram of an alternate
preferred embodiment of a power supply for operation with the
r circuit illustrated in Fig. 1.
DESCRIPTION OF PR~I;'ERRED EMBODIMENTS
-
Now referring to the drawings and first to Fig. 1, a
high frequency, gaseous-discharge lamp operating circuit is
shown in~accordance with the present invention. Lamp 10 in-
-cludes two operating electrodes. One is connected to capa-
citor 12, WhiCIl may be characterized as a mica ballastcapacitor. Capacitor 12 is connected in series with trans-
6~
former winding 14, which is then connected to the other op-
erati~g electrode of lamp 10 to complete a ballast-like con-
nection thereto. As will be explained, this completes a
current source connection to a tank-and-lamp network. Con-
nected in shunt with transformer winding 14 is a resonant or
tank circuit comprising the parallel combination of capacitor
16 and high-Q coil 18. These components aid in stahilizing
the frequency of operation of the current applied to lamp 10
at a high frequency above the acoustic resonance of the lamp,
preferably in the range between 60 and 100 kHz.
Transformer winding 14 has a center tap Z0 for application
of a dc voltage via connecting terminal 22. Transformer winding
14 is part of a push-pull, Class C oscillator having alterna-
tively driving networks especially suited for providing alter-
nate current conduction to transformer winding 14 for efficient
high-frequency operation of lamp 10. Conduction time of the
drive circuit for transformer wlnding 14, as hereafter further
explained, is for about one-quarter or 90 degrees of the
operating cycle of the voltage across the lamp.
The frequency of operation of the curren-t and voltage
applied to lamp 10 is determined by the resonance of -the tank
circuit comprising coil 18 and capacitor 16, with capacitor
12 exerting some influence. Normally, capacitor 16 will have
at least twice the capacitance value as capacitor 12, although
it may have many times such value. Moreover, when lamp 10
represents a large load, the influence of capacitor 12 lessens
and hence, the frequency of operation is almost solely depen-
dent on the values of components 16 and 18.
Viewing the right side of the dra~ing, npn triode tran-
sistor 24 is connected with its collector terminal to the ad-
jacent end of transformer winding 14 and its emitter connected
. r~ k~
to ground. Alt}lough illustrated as an npn transistor, it is
understood that component 24 may be a pnp, an SCR or other
active device connected in a suitable circuit for functional
operation in accordance with the present invention. The base
of transistor 24 is connected to the drive circuit, the drive
voltage and current being principally derived from transformer
winding 26 and capacitor 28, as hereafter explained.
A fast recovery clamping diode 25 is connected across
the collector-emitter connection of transistor 24. ~ resistor
L0 30 connected in parallel with another fast acting diode 32
connects the base of transistor 24 to ground. A slow-acting
diode 34 is connected in series with capacitor 28 and the base
of transistor 24. Resistor 36 is connected across diode 34. '
In operation of transistor 24 and its related components,
an applied dc voltage on terminal 22 causes conduction of
transistor 24. The voltage drop across starter resistor 38
biases transistor 24 into its linear region of operation.
Positive feedback supplied by transformer isolation winding
26, which may be only a single turn magnetically coupled with
winding 14, causes conduction turn on to become greater with
each cycle. When the high gain region of transistor 24 is
reached, it then turns on hard and the oscillator will be
operating at full amplitude. Once full turn-on operation of
transistor 24 has been established, the currents through wind-
ing 14 and through the tank circuit comprising coil 18 and
capacitor 16 drive transistor 40 into conduction on alternate
half cycles from the conduction of transistor 24. Operation
is sustained for transistor 40 in a manner similar to that for
transistor 24, described more fully hereinafter.
Under steady operating conditions, fast turn-on of trans-
istor 24 at each cycle is influenced primarily by three factors.
First, previous to turn-on, the base emitter junction of trans-
istor 24 is barely reversed biased because diode 32 clamps the
reverse biasing voltage to a small value. This means that at
turn-on, there is only a small negative voltage on this base-
emitter junction that needs to be overcome.
Second, capacitor 2~, diode 34, and winding 26 in the base
circuit of transistor 24 for supplying the drive voltage are all
low impedance devices. Therefore, the drive source to trans-
istor 24 respcnds rapidly.
Third, diode 32 is a fast-acting diode. Diode 32 C~n-
ducts during turn-off. If it continued to conduct for a short
time during turn-on, then it would take current from the drive
circuit, but it does not, and therefore the full source is im-
mediately applied to turn on the transistor.
Turn off of transistor 24 is fast primarily because of the
slow action of series diode 34. As previously mentioned, diode
34 has a low impedance. Its slow recovery causes a fast
reverse current drain of transistor 24 during turn off, and
hence, causes transistor 24 to turn off rapidly. Note that
even though turn-off is rapid, it is not "hard" ~i.e., a large
base-emitter voltage is not developed) because of the clamping
action of diode 32.
Diode 25 is also a fast acting diode, primarily because
of operating conditions during start up and when the tank cir-
cuit becomes unloaded (such as with a failure of lamp 10). The
dlode clamps the voltage applied to it when the tank circuit
tries to force voltage VCe below ground and therefore keeps
transistor 24 from being overdriven. The reverse recovery
time is fast to prevent shorting out the tank.
Resistor 30 protects transistor 24 during build up of
oscillations at start up when the transistor is off by reducing
the collector-to-emitter leakage current.
Alternate transistor 40 operates in a similar manner to
that just described for transistor 24, but on alternate fre-
quency cycles of the developed current determined by the
resonant tank-and-lamp circuit. Variable resistors 36 and 42,
around the respective series capacitors, and variable capaci-
tors 28 and 44, in respective series therewith, are part of
the drive circuits for transistors 24 and 40 to provide ad-
justment for operation of the circuit.
"Q" or "Q factor" is a figure of merit for an energy-
storing device or a tuned circuit, which for the embodiment
disclosed herein would be coil 18. Q is equal to the reac-
tance of such device divided by its resistance. The Q deter-
mines the rate of decay of stored energy and hence the higher
the Q the more efficient the device. Therefore, high Q opera-
tion in a gaseous-discharge lamp circuit is highly desirable.
Diagrammatically, and assuming core, frequency, voltage
and temperature to be constant, high-Q for a given coil may be
represented by Fig. 3 which shows a three-dimensional rela-
tionship between number of turns and air gap to achieve ahigh-Q operation. This Q curve is arrived at experimentally
by the following procedure. A selected number of turns is
chosen for a given size pot core. A wire size is selected and
bundled with other similar wires to form a litz wire combina-
tion so that the core may be wound to nearly completely fill
the bobbin and thereby minimize copper loss. Then a gap is
selected and a point on the Q "mountain" is measured. Other
gap spacings are then made and other points at that number of
turns measured. The entire process is then repeated for other
numbers of turns. By this process the "peak" of the Q mountain
6~
is determined, as illustrated in Fig. 3. A coil for operating
as coil 18 for providing high voltage and high frequency to
gaseous-discharge lamp 10 may be made on a pot core made of
ferrite material.
Following the above described procedure and using No. 40
insulated wire, a bundle of such wire comprising 85 strands
twisted together was wound on a No. 2616 FERROXCUB ~ nylon
bobbin in such a manner as to form five layers of eig~it turns
each. Each layer was insulated from the adjoining layers by
MYLAR~ tape. The two parts of the core (with a wound bobbin
in between) were separated so as to form an air gap of approxi-
mately 65 thousandths of an inch. A nylon screw through the
two parts of the core was used to secure them together. It is
important that a metallic screw not be used. It is important
that both the bobbin and the screw be of materials having a
low dielectric loss at high fequency.
A coil made in the above manner is nominally rated for a
Q of 300 at 240 volts rms, 100 kHz. Such a coil is illustrated
in cross section in Fig. 4.
In a similar fashion, a twisted bundle of 189 No. 44
insulated wire strands was found acceptable in making a similar
coil. Further, to achieve a higher voltage rating, a coil of
60 turns was made for operating in conjunction with multi-
vapor lamp operation.
Note that the tank circuit is connected to lamp 10 and
hence the reactance and resistance of lamp 10 influence the
Q of the entire tank-and-lamp circuit. The efficiency of the
tank or resonant circuit may be represented by the following
formula:
Efficiency : Qu Ql
Qu
-- 10 --
wherein: Qu = ~ of tank circuit only without
other components
Ql = Q of circuit under load
Hence, when unloaded Qu is high, the efficiency of the
tank circuit may be very high on the order of 97-99 percent.
An efficiency of about 85 percent is achievable for the over-
all circuit shown in Fig. 1 with the coil structure herein
disclosed.
The operation of the tank-and-lamp circuit may be ana-
- logized to the operation of a mechanical swing with little
friction. At the end of each arc of the swing, a small push
is provided. The more the friction (load), the more the power
consumption and hence the more the push necessary to make the
swing make the same arc. Hence, as seen in Fig. 2, Ic is for
a short duration and the transistor is slightly over driven
(beyond a sine wave drive).
The transformer comprising winding 14 and isolation wind-
ing 26 and its alternate may be made identically to coil 14,
except in this case, the air gap may be eliminated.
Transformer winding 14 may also include taps 46 and 48
spaced equal distance from center tap 20 toward the two res-
pective ends of the winding. Such taps provide connection of
the transistors to provide a higher voltage to the lamp than
with the end connections, as shown. This is particularly ad-
vantageous in operating a multivapor lamp 10.
Fig. 5 illustrates a regulation circuit acting in conjunc-
tion with the circuit shown in Fig. 1. There are two identical
.
networks 100 and 102 operating in conjunction with the respec-
tive alternate halves of the oscillator. For simplicity of
illustration, only the half operating in conjunction with
-- 11 --
6C"~
.
transistor 40 is illustrated in detail.
' Connected across capacitor 44 and its accompanyin(J trans-
former isolation windiny 111 is the followinc; series conl-ection:
diode 104, collector-emitter of pnp transistor 106 and resistor
108. Connected to the high side of the winding is the cathode
of diode 110 and conneeted to the anode thereof to ground is
capacitor 112. Connected across capacitor 112 is the series
combination of Zener diode 114, variable resistor 116 and diode
118 for matching the base-emitter drop of transistor 120. l'he
variable tap on resistor 116 is connected to the base of pnp
transistor 120. The emitter of transistor 120 is connected to
ground throuyh resistor 122 and the collector thereof is
connected to the anode of 2ener diode 114 via resistor 124. The
collector of transistor 120 is connected to terminal 126, other-
wise designated VRl and the base of transistor 106 is con~lected
through resistor 128 to terminal 130, otherwise designated Bl.
In operation of ~he regulation cireuit of Fig. 5, the
voltage on the base winding, designated with numeral 111, charges
eapaeitor 112 throug}l 110. When the eharge on eapacitor 112
exeeeds the voltage thresholds of Zener diode 114 and diode
118, eurrent flows aeross resistor 116. This turns on trans-
istor 120 as an amplifier. As the voltage on resistor 122
inereases, the voltage on r,esistor 124 increases and the voltage
at terminal 126 decreases with respect to ground. Assume that
terminal 126 is conneeted to terminal 130, an alternative con-
neetion thereof as explained hereinafter, as the voltage on
resistor 108 decreases eurrent through transistor lO6 decreases,
henee redueing the amount of discharge f~rom capacitor 44.
The voltage on base winding 111 plus capacitor 44 appears across
,the series eonneetion of resistors 326 and 108, transistor 106 and
diode 104. When transistor 106 conducts less, the less
capacitor 44 discharges. I~ence, on the next half-cycle of
voltage operation of transistor 40, the less current capacitor
44 can deliver before charge up. On Fig. 2, this may be seen
as a higher intersection of V~l with the curve of VBl and hence
the delay in starting of IBl.
Hence, it may be seen that when the voltage on base winding
111 exceeds a predetermined value, diode 110 conducts to cause
a regulation voltage signal VRl to occur at terminal 126. The
adjustment of resistor 116 determines the value of the output.
Although regulating voltage signal VRl may be attached to
terminal 130, its preferred connection is to alternate terminal
B2 of regulating network 102 and terminal 130 is preferably
connected to receive the alternate regulating voltage signal
VR2 from network 102. This is because when transistor 40 is
conducting, base winding 111 is loaded. It is best to sense
the unloaded winding voltage for regulation purposes, WhiC]l
would indicate the preference for the connections shown in
Fig. 5.
In any event, when there is a regulating signal applied to
terminal 130, there is conduction of transistor 106 to partly
discharge capacitor 44 and to thereby regulate the circuit.
This protects transistor 40 from overheating by preventing an
extensive overdrive condition. In similar fashion transistor
24 is also protected.
Although one regulation circuit is shown, many alternative
arrangements are also available. For example, an alternate pre-
ferred embodiment is illustra-ted in Fig. 10.
The embodiment which is illustrated is a partial schematic
diagram which assumes a similar network is connected to the
opposite end of transformer winding 14 so that the complete
circuit operates as a push-pull, Class C oscillator as previously
descrlbed. The exception is that with this ernbodiment, only
one regulating circuit is necessary, to be described hereinafter.
- 13 -
Components numbered less than 200 in the Fig. 10 embodim~nt
identify similar components to those illustrated in Figs. 1
and 5, which are connected similar fashion.
Resistor 310 is connected between capacitor 312, across
which the dc input from the power supply is applied, and cir-
cuit common which may be a floating ground. This is also true
for the common connectors illustrated with a ground symbol in
other drawings. Diode 314 is connected in parallel across
resistor 310. The cathode of diode 314 is connected throuyh
current limiting resistor 316 to the anode of light emitting
diode (L.E.D.) 318. The cathode of L.E.D. 318 is connected to
common. L.E.D. 318 is packaged in an opto-isolator with photo-
transistor 320. Phototransistor 320 is connected betweell the
anode of diode 110 and the base of npn transistor 120.
Base resistor 322 is connected to the base of transistor 120
and capacitor 324 is connected to its collector. The output
from transistor 120 is taken from its collector and is labelled
''Vc''. Connection of this output 126 is made to points or
terminals "Bl" (130) and "B2", previously described.
Connected across capacitor 44 and its accompanying trans-
former isolation winding 111 is the following series connection:
variable resistor 326, diode 104, collector-emitter of Darling-
ton pair transistors 106 and resistor 108. The base of Dar-
lington pair transistors 106 is connected through resistor
128 to point 130 (Bl), which point is connected to point 126,
where Vc is present.
The circuit will regulate and operate in a satisEactory
- manner without further connection. Ilowever, to ensure smoot}
operation with both halves of the push-pull oscillator, the
junction point between diode 110 and capacitor 112 can be
connected to an anode of a diode 330, the cathode of which is
connected to transEormer isolation winding 26. In this event,
- 14 -
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capacitor 112 is charged up eacll half cycle of oscillator
operation.
In operation, this regulation circuit senses the presence
of too much base drive by sensing the ne~ative current through
power device or transistor 40 with resistor 310. Negative
current through device 40 causes a positive voltage across
resistor 310. Thls voltage causes current to flow througll
L.E.D. 318, and hence phototransistor 320 conducts current.
When this occurs, the base drive to tL-ansistor 120 is reduced
to cause Vc to decrease and to allow less current to flow
through Darlington pair 106. Thus, capacitor 44 discharges
less and the next cycle of base drive to transistor 40 is less
than before.
The base drive increase is controlled by the time con-
stant of the R of resistor 124 and the C of capacitor 324. The
base drive decrease is controlled by the time constant of C o~
capacitor 324 and the R of resistor 128 (and its counterpart
at terminal B2). So that an HID lamp being ignited will not
cause tank circuit oscillations to die out, the time constant
of resistor 124 and capacitor 324 is a shorter time constant of
the two.
Transistor 106 is preferably a Darlington pair in the
Fig. 10 embodiment for greater amplification. This permits
capacitor 324 to be smaller and allows regulation Witll less
conduction by transistor 120.
It may also be noted that a variable resistor 326 is
present in the collector-emitter series connection of transis-
tor 106 to provide a variable control for the base drive to
power device 40 when the HID lamp or lamps connected to the
circuit warms up. As the lamp or lamps warm up, transistor 106
begins to conduct. The rate of conduction is not linear, how-
ever. When the lamp is approximately one-third brightness,
6~
.
.
transistor 106 is substantially completely turned on and hence
the current therethrough controls the base drive. Therefore,
resistor 42 provides control for the base drive current during
start up and resistor 326 provides control for the base drive
current after the lamp or lamps have reached a certain warm
up condition.
Now turning to a suitable power supply, reference is made
to the circuit illustrated in Fig. 6. The applied ac source
imput is connected to the illustrative power supply at termi-
nals 50 and 52. Input coils 54 and 56 connected to these
terminals, respectively, and varistor 58, connected in parallel
with resistor 60 and capacitor 62, are connected across the ac
input line to perform a transient clipping operation.
Triac 64 is a power control device connected in serieswith one side of the ac line and controlled by variable con-
duction phase control 66 to provide ac power control over a
wide range of applied power.
Device 64 may also be an SCR or other active device having
a controllable gate for regulating conduction through the device
for only a part of each half cycle of the applied voltage.
~hen the detected dc output from rectifier 6~ is too high,
control circuit 66 connected thereto triggers the gate to
lessen the conduction time, and hence the effective output.
The control circuit may include a convenient timing network
having an RC time constant circuit to provide this function.
A more complete circuit is illustrated in Fig. 7.
The output from the power control device 64 is applied
to rectifier 68. The output from the rectifier is nominally
the dc line voltage. However, transients may be present and
therefore capacitor 70, together with yet another transient
circuit to be described, is connected to prevent such tran-
sients from being applied to the output.
- 16 -
Nominal output from -the rectifier appears on output line
72. The anode of diode 74 is connected thereto with its cath-
ode connected to the top of battery 76. Also connected to the
cathode of diode 74 is resistor 78, which, in turn, is con-
nected to a small dc power supply 80, the other side of which
is connec-ted to line 72. For illustration purposes, this
supply is shown as providing 10 volts. Therefore, the connec-
tion to resistor 78 is at a level 10 volts higher than the
voltage on line 72.
By example, the voltage on line 72 may be nominally 170
volts. This would make the output of power supply 80 at l80
volts. Assuming a 5-volt drop across reslstor 78, the voltage
at the cathode of diode 74 is at 175 volts. When the line vol-
tage exceeds a predetermined value slightly above 175 volts,
the same as the cathode voltage on diode 74 (175 volts),
diode 74 conducts and reduces the line voltage to 175 volts.
The batteries also effectively clips any transients that still
may occur on the output from the rectifier, but because of the
other transient attentuators, the batteries are not required
for this purpose.
Battery 76 as illustrated includes many cells and pro-
vides a voltage at a predetermined level slightly below the
nominal line voltage. In any event, connected near.the top
side of the battery, but just below the top, is the anode of
diode 82. The cathode of diode 82 is connected to output
line 72. Hence, when the line voltage falls below a pre-
determined level, battery 76 completely takes over through
diode 82 and the output therefrom is applied as the line
voltage to the output.
Note that low voltage power supply 80 also provides a
trickle charge to battery 76.
A low voltage sensing and cutout circuit 84 may be
connected to the battery so that when there is battery failure
(output drops below an acceptable predetermined level), the
battery will be disconnected from the circuit and not be a
drain on low voltage power supply 80. Additionally, sensing
circuit 84 may also detect an extended power outage of the ac
source, which would cause the lamp module(s) to put a drain
on the batteries over a long period of time. In this event,
a switch in line 72, for example at terminal 90, would bc
opened to disconnect the load from the batteries.
Note that the battery circuits are principally for
emergency operation and not required when the output from
rectifier 68 is within acceptable limits or to suppress
transients.
A so-called crow bar circuit 86 may be used to protect
the circuit from sudden extreme surges, such as might be
caused by lightning. One such device may merely be a vol-
tage amplitude sensing device that shorts out, and therefore
places a short across the input line, to blow a fuse or cir-
cuit breaker (not shown). Because replacing fuses or re-
setting circuit breakers is a nuisance, a preferred crow bar
arrangement is shown in Fig. 6. Such a preferred device 86
includes a voltage sensing element and a relay coil connected
to normally closed relay contacts 88 in the input line to
rectifier 68. When the voltage on this line exceeds a pre-
determined value, an internal relay coil in device 86 is
energized to open contacts 88. When the applied line voltage
returns to a more normal level, the sensing element de-
energizes the internal relay coil and closes contacts 88.
Crow bar circuit 86 may also be sensitive to rate-of-voltage
change so as to operate faster than just with an amplitude
change. This device is strictly a safety device and not
required for circuit operation. A detail preferred network
- 18 -
is shown in Fig. 7.
The output on line 72 is filtered from remaining tran-
sients by-capacitor 70, as previously mentioned. It also may
be seen that with a low line voltage condition requiring
switching to the battery, as above explained, the voltage on
capacitor 70 helps prevent the lamp connection from being in-
terrupted and therefore the possible loss of light.
Control circuit 66 connected to control the conduction
through power control device 64 may take the form of a circuit
for monitoring the output dc level on line 72 including a
light emitting diode. That is, the higher the voltage above
a preset level (such às determined by a series-connected Zener
diode), the brighter the produced light. This produced light
is detectable by a photo-sensitive device in an RC network
for controlling the angle of conduction (time of conduction)
through device 64. A detail network operating in this manner
is shown in Fig. 7.
The output is applied to output terminals 90 and 92.
These terminals, one of which may be grounded, such as illus-
trated at 92, are applied as the dc input to terminal 22 inFig. 1.
Now referring to Fig. 7, it may be seen that a detail
circuit operating in the manner just described for Fig. 1 is
illustrated. For example, rectifier 68 is illustrated by the
conventional diode bridge comprising diodes 68a, 68b, 68c and
68d. Varistor 58 and the filter including resistor 60 and
capacitor 62 in the simplified circuit of Fig. 1 are expanded
to include varistors 58a, 58b and 58c and there are two tran-
sient filters, one including resistor 60b and capacitor 62a
and the other including resistor 60b and capacitor 62b.
Inductors 54 and 56 are expanded to include inductors 54a
and 54b and 56a and 56b. Inductors 54a and 56a at the input
are preferably ferrite core inductors. These inductors and
. ~ r~ 6.~
the first stage varistors and transient filters attenuate
fast transients and reduce their frequencies so that subse-
quent tape-wound, steel-core inductors 54a and 54b and varis-
tor 58c, resistor 60b, and capacitor 62b can at;tenuate the
existing transients still further.
The crow bar circuit 86 is shown in Fiy. 7 as including
many components. Relay contacts 88 are actuated by coil 200,
connected in parallel with resistor 202 and in series with
triac 204. Connected from resistor 202 to the gate terminal
of the triac is box Z circuit 206, which is explained more
fully below. The gate resistor is resistor 208. This cir-
cuit forms a load-disconnecting, transient-shunting, non-fuse
blowing protection circuit.
Box Z circuit 206 may take the form of either of the
circuits shown in Figs. 8 and 9, or their equivalents. For
example, the Fig. 8 circuit includes two opposite facing
Zener diodes 210 and 212 connected in parallel with capacitor
214. Fig. 9 shows a parallel combination of Zener diode 216
and capacitor 218 connected to diodes 220, 222, 224 and 226.
These diodes form two paths around the parallel combination,
each path comprising two diodes. The connections to the cir-
cuit of Fig. 7 are made to the juncture between the two diodes
in each of the paths. In operation, the Zener diodes operate
as amplitude sensing devices and the capacitors in the re-
spective circuits are sensitive to rate of voltage change.
When the gate voltage on the triac exceeds about 1 volt,
caused by either sensing a large voltage amplitude or a fast
voltage increase, then the triac conducts. This energi7.es
relay coii 200 to open normally closed contacts 88. The re-
moval of the triggering condition will cause the contacts to
re-close.
Control circuit 66 may be characterized as a soft-start
20 -
, ~ ' f~ 7~
circuit for the operation of the power supply. Ultimately,
the application of source voltage to the rectifier bridge
shown in Fig. 7 is controlled by triac 230, the conduction
time of which is determined by the operation of pulse trans-
former 232. Windiny 232 is magnetically linked to winding
234 in the cathode circuit of programmable unijunction
transistor (PUT) 236. The control of the operation of PUT
236 is described below.
The gate connection to PUT 236 is connected to a rec-
tified dc voltage via variable resistor 238. The rectifiedvoltage is derived from bridge rectifier 240 connected
across the ac source line through current limiting resistors
239 and 241 just ahead of triac 230. The timing of the con-
duction of PUT 236 is determined by the voltage difference
between the voltage applled via resistor 238 and the voltage
applied to the anode of PUT 236. Both the voltage applied
to the anode and to the gate of PUT 236 are important to its
conduction.
That is, conduction is dependent on the arithmetic
difference between the voltage applied to the anode and gate.
Therefore, the setting of resistor 238 "programs" what anode
voltage is required to produce conduction. The dc voltage
applied to resistor 238 is developed by bridge rectifier 240.
A Zener diode 242 and bleeder resistor 244 insures that the
voltage applied to resistor 238 never exceeds a predetermined
value.
The output from bridge rectifier 240 is also connected
through resistors 246 to a time constant control network con-
nected to the anode of PUT 236. This time constant network
includes capacitors 248 and 250 and resistors 246 and 252.
Basically, the charging of capacitor 248 through resistor
246 determines the soft start or the ultimate speed of
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r 1 ~
conduction or angle advancement in the conduction of triac
230 and the charging of capacitor 250 through resistor 252
determines the phase or conduction angle of triac 230. The
RC time constants of these networks and the voltages applied
to them, as explained below, are important in the operation
of this regulation circuit.
The photo transistor voltage is determined by the
brightness of the light emitting diode connected in series
with resistor 262 and Zener diode 264 across dc line 72.
10 The resistor and Zener diode protect L.E.D. 260 against an
overload condition.
By this operation, it may be seen that the L.E.D~ and
photo transistor regulate the dc output voltage and that
there is really no regulation of the ac input. A too high
dc voltage causes Zener diode 264 and L.E.D. 260 to conduct,
turning photo transistor 258 partly on and retards the phase
or firing angle of triac 230 to thus lower the dc output to
about the voltage for causing conduction of Zener diode 264
and L.E.D. 260.
Fuses 270 and 272 at the input and 274 and 276 provide
further safety to the circuit.
Now referring to Fig. 11, an alternate embodiment of a
suitable power supply is illustrated, the primary differences
to the circuit shown in Fig. 7 being in the network associated
triac 204 operating as a crow bar power device. The transient
clipping and attenuation circuit 63 preceding this network
is the same as that illustrated for Fig. 7. Triac 230 for
ultimately controlling the application of source voltage to
rectifier bridge 68 is connected in the-positive line. Its
gate voltage for determining the time of its conduction is
controlled by the operation of pulse transformer 232, as with
the Fig. 7 embodimen.t. The main terminals of triac 230 are
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connected to rectifier 6~, wllich is precede-l by bleedel-
resistor 2~9.
Connected across the line just ahead of resistor 219
is the RC network comprising resistor 215 and capacitor 217.
Back-to-back Zener dio~es 209 are connected to the high side
of capacitor 217 and, through resistor 207, to the gate ter-
minal of triac 204. The main terminals of a triac 205 are
connected between the high side of capacitor 217 and the
gate of triac 204. The gate of triac 205 is connected to
the junction between resistor 207 and back-to-back Zener
diodes 209. Gate resistor 211 to triac 204 completes the
network.
In operation, crow bar power device 204 is turned on
only when the voltage across capacitor 217 exceeds the Zener
voltage across Zener diodes 209~ Transients occurriny wllen
triac 230, which may be functionally characterized as a soft-
start/regulation circuit po~er device, is off, are not applied
to the ac input of rectifier bridge 68. ~ence, capacitor 217
is not charged up and the crow bar is not activated. When
triac 230 is on and a transient occurs that is large enougll
to endanger the electronic ballast or ballasts connected to
the dc output, the transients remaining after treatment by
transient suppression circuit 63 are applied to the ac side
of rectifier bridge 68 and to RC network comprising resistor
215 and capacitor 217. If the voltage on capacitor 217 is
great enough, triac 204 is triggered as a result of back-
to-back Zener diode 209 triggering triac 205. Since the
transient can be either positive or negative, one or the
other of the two Zener diodes will conduct to initiate the
triggering action.
It should be also noted that resistor 215 and capacitor
217, in combination with capacitor G2b, form a ~nubber for
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;~
13i.1~i ~ ~r~
in-line triac 230.
While particular embodiments of the invention have been
shown and described, it will be understood that the invention
is not limited thereto, since modifications may be made and
will become apparent to those skilled in the art. ~or exam-
ple, the operation of a single lamp module as illustrated in
Figs. 1 and 5 has been described. It is understood that the
preferred embodiment will include a plurality of such modules
connected to a common power supply, such as illustrated in
Figs. 6 and 7.
Furthermore, it may be recognized that the dc power
supply which has been described is a preferred embodiment
with somewhat elaborate features for ensuring highly stable
dc output to the high frequency operating circuit for the
lamp. Such an elaborate supply may not be desirable for
installation not having extremely important stability re-
quirements.
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