U.S. patent number 3,590,316 [Application Number 04/807,659] was granted by the patent office on 1971-06-29 for phase-controlled universal ballast for discharge devices.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Robert T. Elms, Robert T. both of Elms, Joseph C. Engel.
United States Patent |
3,590,316 |
Engel , et al. |
June 29, 1971 |
PHASE-CONTROLLED UNIVERSAL BALLAST FOR DISCHARGE DEVICES
Abstract
Apparatus for ballasting any of a plurality of discharge devices
having varying voltage and current operating characteristics in
order to operate a discharge device at about a predetermined
wattage rating. A ballasting impedance limits the maximum current
through the operating device and a semiconductor switch is closed
in response to a triggering signal to vary the average wattage
consumed by an operating device. The circuit includes a solid-state
wattmeter having an input portion which develops a signal which is
proportional to the current drawn by an operating device, as well
as a signal which is proportional to the voltage drop across an
operating device. These signals are combined to generate a signal
which represents the logarithm of their product. The logarithmic
signal is then converted into an antilogarithmic signal which in
turn is averaged. The resulting averaged signal controls the
triggering of the semiconductor switch to maintain the wattage
input to an operating device at about its predetermined desired
value.
Inventors: |
Engel; Joseph C. (Pittsburgh,
PA), Elms; Robert T. (Pittsburgh, PA), Elms; Robert T.
both of (Pittsburgh, PA) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
25196891 |
Appl.
No.: |
04/807,659 |
Filed: |
March 17, 1969 |
Current U.S.
Class: |
315/209R;
315/308; 324/142 |
Current CPC
Class: |
H05B
41/3922 (20130101) |
Current International
Class: |
H05B
41/392 (20060101); H05B 41/39 (20060101); H05b
037/02 () |
Field of
Search: |
;315/209,225,293,299,306,307,308 ;324/142 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hossfeld; Raymond F.
Claims
We claim as our invention:
1. An apparatus for ballasting any of a plurality of discharge
devices having varying voltage and current operating
characteristics in order to operate a ballasted device at about a
predetermined wattage rating, said apparatus comprising:
a. output terminals adapted to have connected thereacross any of
said discharge devices, and input terminals adapted to be connected
across a source of energizing potential;
b. impedance means forming a part of said apparatus to limit the
maximum current therethrough;
c. semiconductor switching means connected between said input
terminals and said output terminals and having a high impedance
open position and a low impedance closed position, said
semiconductor switching means responsive to a control signal to
effect a closing of said semiconductor switching means, and the
relative proportion of time said semiconductor switching means is
closed varying the average wattage consumed by an operating device
connected across said output terminals;
d. wattage-measuring means comprising a semiconductor wattmeter,
said wattmeter having a voltage-responsive input portion connected
in said apparatus to continuously generate a varying signal which
is proportional to the varying voltage developed across said
operating device, said wattmeter having a current-responsive input
portion connected in said apparatus to continuously generate a
varying signal which is proportional to the varying current through
said operating device, means for combining said varying signal
outputs of said voltage-responsive input portion and said current
responsive input portion to generate a varying electric signal
which represents the logarithm of the product of said varying
signal outputs, said wattmeter having an output section into which
said varying logarithmic signal is fed to generate a signal which
varies according to the antilogarithm of said varying logarithmic
signal, and said wattmeter output section including a
signal-averaging means for averaging said varying antilogarithmic
signal to produce a composite signal having a magnitude which
varies in accordance with the average wattage input to said
operating device; and
e. control signal generating means electrically connected to said
wattage-measuring means and said switching means to receive and be
actuated by said composite averaged signal from said
wattage-measuring means and to generate a controlling signal for
closing said switching means, said controlling signal varying the
relative proportion of time said switching means is closed in
accordance with whether said composite averaged signal from said
wattage-measuring means indicates an average wattage input to said
operating device as equal to that wattage desired, or greater than
or less than that wattage desired, to maintain the average wattage
input to said operating device at about its predetermined desired
value.
2. The apparatus as specified in claim 1, wherein said input
terminals are adapted to be connected across a source of AC
energizing potential, said impedance means is an inductor, said
switching means is an AC switch, and said control signal generating
means generates a controlling signal in response to said composite
averaged signal from said wattage-measuring means once each half
cycle of energizing AC potential.
3. The circuit as specified in claim 2, wherein said
wattage-measuring means measures the wattage input to said
operating device throughout each half cycle of AC energizing
potential, said composite signal output of said wattage-measuring
means comprises a continuing series of signals each succeeding half
cycle of AC energizing potential with each signal representing the
average wattage input to said operating device during several half
cycles of energizing potential, and said control signal generating
means is actuated by said composite average signal from said
wattage-measuring means during each half cycle of AC energizing
potential.
4. The circuit as specified in claim 3, wherein said semiconductor
AC switching means is gate controlled and is gated to a closed
position by said controlling signal from said control signal
generating means once during each half cycle of AC energizing
potential.
5. The circuit as specified in claim 4, wherein said semiconductor
switching means is gated to a closed position at varying times
during each half cycle of energizing potential, said semiconductor
switching means being gated to a closed position in a later portion
of a half cycle when said composite averaged signal indicates an
average wattage input to said operating device greater than
desired, and said semiconductor switching means being gated to a
closed position in an earlier portion of a half cycle when said
composite averaged signal indicates an average wattage input to
said operating device less than desired.
6. The apparatus as specified in claim 5, wherein said control
signal generating means comprises a timing circuit and a trigger
circuit, said timing circuit connected to the output of said
wattmeter and said trigger circuit connected to the gate of said AC
switch, said timing circuit including a capacitor which is charged
at a rate which varies with the magnitude of the composite signal
output from said wattage-measuring means, the charging rate of said
capacitor serving to control the point at which said trigger
circuit gates said AC switch, with a greater-than-desired wattage
input to said operating device causing said AC switch to be gated
at a relatively later period of time in each half cycle of
energizing potential, and vice versa.
7. The apparatus as specified in claim 6, wherein each time the AC
energizing potential passes through zero, a discharging circuit is
actuated to discharge said capacitor preparatory to being recharged
during the next half cycle of energizing potential.
8. The circuit as specified in claim 5, wherein said wattmeter
comprises a first transistor having an emitter, base and collector
with its base and collector connected, and a second transistor
having an emitter, base and collector with its base and collector
connected, said transistors connected to each other in series
additive relationship, said voltage-responsive input portion of
said wattmeter having an output connected across the base and
emitter of one of said transistors, said current-responsive input
portion of said wattmeter having an output connected across the
base and emitter of the other of said transistors, and said
serially connected transistors having developed across the
unconnected base and emitter thereof a voltage signal which is
proportional to the instantaneous value of the log of the product
of the current outputs of said voltage-responsive input portion and
said current-responsive input portion, an output transistor having
an emitter, base and collector, an additional transistor having an
emitter, base and collector with the base and collector connected,
the base of said additional transistor connected with the emitter
of said output transistor, and the base of said output transistor
and the emitter of said additional transistor having applied
thereacross the voltage output signal of said serially connected
transistors, a constant current generator having an output
connected to the collector of said output transistor with the
resulting current through said output transistor proportional to
the instantaneous wattage input to said operating device, and a
capacitor connected across the collector and emitter of said output
transistor to filter the signal developed thereacross.
9. The apparatus as specified in claim 2, wherein a warmup current
regulator for said device is connected to said current-responsive
input portion and also to the output section of said wattmeter,
said warmup current regulator having a maximum current detector
portion which is responsive to a maximum predetermined current
passing through said operating device to actuate a signal bypass
impedance to decrease the composite signal output of said
wattage-measuring means and limit the current which can pass
through said operating device during warmup thereof to said
predetermined maximum.
10. An apparatus for ballasting a discharge device having varying
voltage and current operating characteristics in order to operate
the ballasted device at about a predetermined wattage rating, said
apparatus comprising:
a. output terminals adapted to have connected thereacross said
discharge device, and input terminals adapted to be connected
across a source of energizing potential;
b. impedance means forming a part of said apparatus to limit the
maximum current therethrough;
c. switching means connected between said input terminals and said
output terminals and having a high impedance open position and a
low impedance closed position, said switching means responsive to a
control signal to effect a closing thereof, and the relative
proportion of time said switching means is closed varying the
average wattage consumed by an operating device connected across
said output terminals;
d. wattage-measuring means having a voltage-responsive input
portion connected in said apparatus to generate a varying signal
which is proportional to the varying voltage developed across said
operating device, said wattage-measuring means having a
current-responsive input portion connected in said apparatus to
generate a varying signal which is proportional to the varying
current through said operating device, means for multiplying said
varying signal outputs of said voltage-responsive input portion and
said current responsive input portion to produce a composite signal
having a magnitude which varies in accordance with the average
wattage input to said operating device; and
e. control signal generating means electrically connected to said
wattage-measuring means and said switching means to receive and be
actuated by said composite signal from said wattage-measuring means
and to generate a controlling signal for closing said switching
means, said controlling signal varying the relative proportion of
time said switching means is closed in accordance with whether said
composite signal from said wattage-measuring means indicates an
average wattage input to said operating device as equal to that
wattage desired, or greater than or less than that wattage desired,
to maintain the average wattage input to said operating device at
about its predetermined desired value.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
In copending application Ser. No. 807,710, filed concurrently
herewith by Joseph C. Engel, Robert T. Elms and George A.
Kappenhagen, and owned by the present assignee, now U.S. Pat. No.
3,519,88l is disclosed a starting and operating apparatus which
facilitates starting and operation of discharge lamps having
different starting and operating characteristics. This apparatus
applies to the lamp a very high voltage pulse, which is followed by
an intermediate voltage, high energy pulse. Such an apparatus is
particularly adapted to be used in conjunction with the apparatus
of the present invention.
In copending application Ser. No. 807, 711, filed concurrently
herewith, by Joseph C. Engel, and owned by the present assignee,
and now abandoned is disclosed a solid-state photocontrol apparatus
which eliminates the use of movable contacts which are subject to
wear and failure. Such a photocontrol apparatus is particularly
adapted to be used in conjunction with the apparatus of the present
invention.
BACKGROUND OF THE INVENTION
The usual discharge device operates with a negative volt-ampere
characteristic and some form of current limiting ballasting is
required to prevent a runaway discharge. In recent years there have
been developed several new types of discharge devices which have
achieved some limited commercial success for applications such as
outdoor flood lighting and similar uses, and these discharge
devices have promise for use in interior lighting. Such devices are
commercially marketed under various trade designations, but broadly
can be categorized as mercury-metal halide, high-pressure,
discharge devices and sodium or mercury-sodium discharge devices
which utilize a light-transmitting refractory envelope formed of
polycrystalline alumina or similar material. Various combinations
of such devices are also known. These devices, together with the
well-known high-pressure mercury-vapor discharge devices, are used
for high-bay factory lighting, highway and floodlighting, and
stadium lighting to name a few of the applications.
One of the problems with the use of such discharge lamps is that
each type has different voltage and operating characteristics, even
though the wattage ratings might be the same. The effect of this is
that each type of lamp requires a different ballast which is
specially tailored to start and operate the lamp. The problem is
further complicated by the fact that in the field of mercury-metal
halide lamps, a myriad of different metal-halide additives can be
used to achieve different illumination effects, and each different
combination of metal halide additives often changes the lamp
starting and operating characteristics sufficiently to require a
different lamp starting and operating ballast. Since the ballast
represents a substantial portion of cost of the fixture, once the
user is committed to one specific type of lamp, he cannot readily
change lamp types without incurring substantial expense in changing
the lamp starting and operating ballast.
It is known in the art to ballast a discharge device by actuating a
bilateral switch to vary the input to a lamp so that the average
lamp input is maintained at about a predetermined value. Such an
apparatus is disclosed in U.S. Pat. No. 3,222,572 dated Dec. 7,
1965. In this disclosed apparatus, the bilateral switch is actuated
by sensing a lamp operating condition, such as current or
brightness. Such an apparatus is designed to be operable with only
one specific type of lamp which has predetermined voltage and
current and operating characteristics. A circuit which functions in
a generally similar fashion is disclosed in U.S. Pat. No. 3,265,930
dated Aug. 9, 1966.
In U.S. Pat. No. 2,486,068 dated Oct. 25, 1949 is described a
tube-type wattmeter as well as a circuit which can effect
multiplication and division of independent quantities. More
recently, semiconductor circuits which function in a similar
fashion have been disclosed in U.S. Pats. Nos. 3,152,250 dated Oct.
6, 1954 and 3,197,626 dated July 27, 1965.
SUMMARY OF THE INVENTION
It is the general object of the invention to provide a ballast
apparatus for starting and operating any of a plurality of
discharge devices having varying voltage and current operating
characteristics.
It is another object to provide a ballast apparatus which can be
readily and easily modified to operate lamps having different
wattage ratings, as well and varying voltage and current operating
characteristics.
It is a further object to provide a ballast apparatus which is
readily adapted to have a solid-state photocontrol operate in
conjunction therewith.
It is an additional object to provide a ballast apparatus which is
independent of line voltage variations and which continuously
monitors lamp wattage and regulates the average lamp power in a
closed loop system.
It is yet another object to provide a ballast apparatus which is of
solid-state design and can supply a lamp voltage in excess of
instantaneous line voltage to facilitate operation of different
types of lamps.
It is still another object to provide a solid-state universal type
of ballast which regulates lamp current to a maximum permissible
value during the lamp warmup to limit the warmup time required.
The foregoing objects of the invention, and other objects which
will become apparent as the description proceeds, are achieved by
providing a ballast apparatus which comprises an impedance means,
preferably an inductor, connected between the input terminals and
output terminals of the apparatus, along with a semiconductor
switch. The switch is responsive to a control signal to close and
the relative proportion of time the switch is closed determines the
average wattage consumed by an operating lamp which is connected
across the output terminals. A solid-state-wattmeter has a
voltage-responsive input portion which continuously generates a
varying signal which is proportional to the voltage developed
across the operating lamp, and the wattmeter also has a
current-responsive input portion which continuously generates a
varying signal which is proportional to the current through the
operating lamp. These signals are combined to produce a signal
which is proportional to the logarithm of their product. The
logarithmic signal is then converted to a varying signal which
varies in accordance with the antilogarithm of the logarithmic
signal and the antilogarithmic signal is then averaged to provide a
composite signal which varies in accordance with the average
wattage consumed by the operating lamp. This averaged composite
signal actuates a control signal generator which in turn actuates
the closing of the semiconductor switch in order to maintain the
average wattage of the operating lamp at about its predetermined
desired value.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the present invention, reference is
made to the accompanying drawings wherein:
FIG. 1 is a block diagram of the present ballast apparatus;
FIGS. 2A and 2B show a detailed comprehensive circuit diagram of
the present ballast;
FIGS. 2C and 2D correspond to FIGS. 2A and 2B with the specific
values of the circuit components shown;
FIG. 3 is a graphic representation of voltage vs. time setting
forth the line voltage and lamp voltage relationships encountered
during operating conditions;
FIG. 4 is a circuit diagram of the voltage-responsive input portion
of the semiconductor wattmeter portion of the apparatus with the
various current relationships shown thereon;
FIG. 5 is a circuit diagram of the current-responsive input portion
of the semiconductor wattmeter portion of the apparatus with the
various current relationships shown thereon;
FIG. 6 is a circuit diagram of the constant current generator used
to provide a constant current signal for use with the semiconductor
wattmeter;
FIG. 7 is a circuit diagram of the multiplier section of the
wattmeter wherein the varying current signal and varying voltage
signal are multiplied and then averaged;
FIG. 8 is a circuit diagram of the logic and timing circuit which
constitutes a part of the control signal generating means for
triggering the semiconductor switching means;
FIG. 9 is a graph of voltage vs. both current and time illustrating
the phase sequence relationships used to trigger the semiconductor
switch;
FIG. 10 is a circuit diagram of the gate drive portion of the
signal generating means which controls the switching means;
FIG. 11 is a circuit diagram of the zero voltage reset which
operates with the logic and timing circuit to insure that the AC
switch is turned off at the start of each half cycle;
fIG. 12 is a circuit diagram of the lamp warmup current
regulator;
FIG. 13 is a circuit diagram of the solid-state photocontrol which
is particularly adapted to be operated with the present
ballast;
FIGS. 14A and 14B are graphs of the ballast operating
characteristics wherein voltage and current relationships are
plotted vs. time showing the operation with the photocontrol
actuated and the photocontrol not actuated;
FIG. 15 is a circuit diagram of the high voltage pulse recycler
used to start a sodium-mercury high-pressure discharge device;
FIG. 16 is a graph of voltage vs. time setting forth the various
relationships present when starting a sodium-mercury high-pressure
discharge lamp from the present apparatus; and
FIG. 17 is a circuit diagram of the low-voltage regulator of the
present apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As noted hereinbefore, present conventional ballasting techniques
for controlling present day high-pressure vapor lamps require a
specially designed ballast for each type of lamp. The ballast of
the present invention will operate all types of such lamps at a
predetermined power rating with no changes in the circuitry, with
the operation being independent of line voltage variations since
the lamp wattage is maintained substantially constant. All that is
required is to replace a lamp of one type with a lamp of a
different type and the present ballast will automatically
compensate for the different voltage and current operating
characteristics. In addition, some types of lamps change their
operating characteristics throughout their life. The present
ballast automatically compensates for such changes and maintains
the desired lamp wattage constant.
The basic block diagram of the present ballast apparatus is shown
in FIG. 1, and each of the blocks will be explained separately in
the following discussion. FIGS. 2A--2D set forth a circuit diagram
of the complete ballast and each component thereof will be
described in detail. In the diagram in FIGS. 2A--2D, all resistors
are 0.5 watt unless otherwise marked, capacitors are 30 volt unless
otherwise marked, transistors are NPN 2N1711 and PNP 2N2905 unless
otherwise designated, and diodes are 1N457 unless marked.
POWER CIRCUITRY
This circuitry is shown in FIGS. 2A and 2C and comprises a 5A, 600
volt AC switch, S, Cla, C1, C13, C14, R5, R35, L.sub.1 and L.sub.2.
This circuit functions as follows. Because the specific ballast is
designed to operate a 400 w. lamp 10 connected across output
terminals 12 and 14, from a 210 to 270 volt AC line to which the
input terminals 16 and 18 are adapted to be connected, a 5 ampere,
600 switch is used. Inductor L.sub.2 is selected to yield the
required lamp current for either the highest voltage lamp at the
lowest line or the lowest voltage lamp at the lowest line,
whichever produces the lowest value of inductance. This inductor
normally will be about 27 ohms at 60 hz.
Resistor R5 and capacitor C1 are used to limit the rate at which
the voltage across the AC switch rises and this prevents dv./dt.
turn-on of the AC switch. The switch has a dv./dt. rating in excess
of 20 bolts/microsecond. Winding 1-2 of L.sub.2 and capacitor C13
are used to produce a high voltage pulse across the lamp 10. When
the AC switch first turns on, C13 is at 0 bolts. Thus for (+)
values of line voltage, the total line voltage appears across
winding 1-2. At this instant of time the voltage across winding 2-3
is:
V.sub.s = instantaneous value of line voltage when AC switch turns
on. A representative value for this starting pulse is 2500
volts.
Network C14, L.sub.1, L.sub.2 and R35 provide the capability to
supply a lamp voltage in excess of the instantaneous line voltage
when the AC switch first turns on during lamp operation. In
explanation, when the AC switch is first turned on, C14 is at a low
voltage due to the discharging action of R35. Thus all the line
voltage is applied across L.sub.1 and L.sub.2. If the lamp is not
in a low impedance state, L.sub.1, L.sub.2 and C14 form a series LC
circuit which is underdamped. Under these circumstances the voltage
across C14 can rise to almost twice the instantaneous line voltage,
as shown in FIG. 3. This voltage pulse is sufficient to cause an
operating lamp to strike each half cycle and go into a low
impedance state. This basic operating circuit is described more
fully in the aforementioned copending application Ser. No. 807,710,
filed concurrently herewith, now U.S. Pat. No. 3,519,881. C.sub.la
provides power factor correction. Zener diodes D.sub.la and
resistor R.sub.la protect the AC switch S from excess voltage
transients.
TRANSISTORIZED WATTMETER
The wattmeter comprises C.sub.3, CR1, CR3, CR5, CR6, CR7, CR8, CR9,
D.sub.1, D.sub.3, Q.sub.1, Q.sub.2, Q.sub.3, Q.sub.6, Q.sub.7,
Q.sub.8, Q.sub.9, R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.4a,
R.sub.9, R.sub.14 and R.sub.36. Since the wattmeter is essentially
a current operated device, currents proportional to instantaneous
lamp current and voltage are provided. The circuit in FIG. 4
provides a current proportional to instantaneous lamp voltage
V.sub.1 . This circuit constitutes a voltage-responsive wattmeter
input portion which continuously generates a varying signal which
is proportional to the varying voltage developed across the lamp 10
as operated. By way of further explanation, when V.sub.1 is
positive I.sub.11 is equal to I.sub.2 and both are proportional to
V.sub.1 /(R.sub.3 +R.sub.36). Under these conditions, CR3 is
forward-biased and both Q.sub.1 and Q.sub.2 are in a nonconducting
state. When V.sub.1 is negative I.sub.13 is equal to -V.sub.1
/(R.sub.3 +R.sub.36) which is equal to V.sub.1 /(R.sub.3 +R.sub.36)
since -V.sub.1 = V.sub.1 at this time. Since Q.sub.1 has a high
beta, I.sub.13 is equal to I.sub.14. Current I.sub.15 equals
since the diode drop of CR1 cancels out the emitter-base junction
drop of Q.sub.2. Also, I.sub.15 is equal to I.sub.2 since CR3 is
now reverse-biased. Thus, for negative values of V.sub.1, I.sub.2
is equal to
since R.sub.1 =R.sub.2. As a result,
for all values of V.sub.1 and when the AC switch S is conducting,
V.sub.1 =V.sub.lamp. Thus the circuit as shown in FIG. 4 is
essentially a full wave rectifier wherein I.sub.2 is proportional
to the magnitude of V.sub.L, wherein V.sub.L represents the
instantaneous voltage drop across the operating lamp 10.
Current proportional to load current is provided by the circuit
shown in FIG. 5. This circuit comprises a current-responsive
wattmeter input portion which continuously generates a varying
signal which is proportional to the varying current (I.sub.L)
through an operating lamp 10.
Current transformer T.sub.1 steps down the load current such that
I.sub.17 =I.sub.L /100. Diode bridge CR5, CR6, CR7 and CR8 full
wave rectify I.sub.17 so that I.sub.18 = I.sub.17 . Components CR9,
Q.sub.6, R.sub.9 and R.sub.14 form a current divider. The result is
that I.sub.1 is equal to
when the voltage across CR9 cancels the voltage across the
base-emitter junction of Q.sub.6. Thus, current I.sub.1 =K.sub.1
I.sub.L where K.sub.1 =R.sub.9 /100(R.sub.14 +R.sub.9). The circuit
shown in FIG. 5 is a full wave current sensor wherein I.sub.1 is
proportional to the magnitude of the lamp current. If the circuit
is designed to operate a lamp 10 with a predetermined wattage of
400 watts, the resistor R.sub.14 has a resistance of
.apprxeq.10,000 ohms. This value of resistance can be preselected
to vary the average current, and thus the power, at which the lamp
10 is to be operated. Alternatively, R.sub.14 can be provided with
a series of taps so that the wattage at which the lamp 10 will
operate can be readily varied to accommodate a plurality of lamp
types which are designed to operate at different wattages.
The constant current generator is shown in FIG. 6 and provides a
bias for Q.sub.7. The collector current I.sub.16, of Q.sub.3 is
maintained constant in the following manner. The voltage of D1
appears across R.sub.7, and the emitter current of Q.sub.3 is
Neglecting the base current of Q.sub.3 its collector current will
then be 1 ma. and is independent of the supply voltage. This
constant current represents the power reference signal as will be
discussed hereinafter.
The multiplier portion of the wattmeter circuit is pg,11 shown in
FIG. 7. The current I.sub.1 in Q.sub.6 is proportional to the
magnitude of the instantaneous lamp current and the current I.sub.2
is proportional to the magnitude of the instantaneous lamp voltage
when the AC switch is "on." Since the external drains on the
collector current of Q.sub.3 are negligible, the current I.sub.5 in
Q.sub.9 is equal to the constant current I.sub.16. Owing to the
exponential relationship between voltage and current in a
forward-biased diode, the product of the currents in Q.sub.6 and
Q.sub.8 is proportional to the product of the currents in Q.sub.7
and Q.sub.9. Thus the current in Q.sub.7 is proportional to the
instantaneous value of lamp power. Capacitor C.sub.3 filters this
current so that the average current drawn by the collector of
Q.sub.7 is proportional to average load power. The voltage V.sub.4
is equal to the difference of I.sub.16 minus I.sub.3 (average)
times the input impedance (R.sub.IN .apprxeq.120K) of the reset of
the circuitry connected to that diode. This is true for a range of
V.sub.4 voltages from 1 to about 10.5 volts. At 10.5 volts Zener
D.sub.3 starts to conduct and clamps V.sub.4. Thus, for the
foregoing voltage range, each voltage corresponds to a range of
powers. This range is determined by the accuracy of the wattmeter
which is about 1 percent. To illustrate if V.sub.4 is 5 volts and
the nominal power for 5 volts is 400 watts, then lamp power will be
400 w. .+-.1 percent when V.sub.4 =5 volts. Briefly, summarizing
the circuit as shown in FIG. 7, the varying signal outputs of the
voltage-responsive wattmeter input portion (FIG. 4) and the
current-responsive wattmeter input portion (FIG. 5) are combined to
generate a varying electric signal (i.e., the voltage across the
collector and emitter of serially connected Q.sub.6 and Q.sub.8)
which represents the logarithm of the product of the varying signal
outputs. This logarithmic signal is fed into the wattmeter output
section to generate a signal (the current in Q.sub.7) which varies
according to the antilogarithm of the varying logarithmic signal.
The wattmeter output section also includes a signal averaging means
for averaging the antilogarithmic signal to produce a composite
signal (V.sub.4) which represents the average wattage input to the
operating lamp 10 with reference to a desired average wattage.
Also, the "average wattage" composite signal V.sub.4 is actually
averaged over several half cycles of energizing potential.
LOGIC, TIMING CIRCUIT
The timing circuit shown in FIG. 8 consists of components C.sub.5,
CR10, D.sub.4, Q.sub.5, Q.sub.13, Q.sub.14, Q.sub.16, R.sub.11,
R.sub.12, R.sub.15, R.sub.21, R.sub.22, R.sub.24 and R.sub.29. The
current I.sub.6 in R.sub.22 is equal to V.sub.4 less a diode drop
divide by R.sub.22 or approximately V.sub.4 /R.sub.22. Since
Q.sub.13 has a high beta (about 100), I.sub.7 =I.sub.6. The voltage
across CR10 cancels the base emitter voltage of Q.sub.5, and the
voltage across R.sub.11 and the combination D.sub.4, R.sub.15 is
R.sub.12 I.sub.7. The current I.sub.8 therefore equals (R.sub.12
/R.sub.11) I.sub.7 and the current I.sub.9 is zero for R.sub.12
I.sub.7 values less than the Zener voltage. For R.sub.12 I.sub.7
values greater than the Zener voltage,
Current I.sub.10 is approximately equal to I.sub.8 plus I.sub.9.
Thus for each DC voltage V.sub.4, there is a unique value of
current I.sub.10, see FIG. 9. Current I.sub.10 flows into C.sub.5
(Q.sub.14 and Q.sub.16 are "off" as will be described hereinafter)
causing the voltage V.sub.5 on capacitor C.sub.5 to rise linearly.
When V.sub.5 reaches about 8 volts the trigger circuit Q.sub.14,
Q.sub.16, R.sub.24 and R.sub.29 trips in the following manner. At 8
volts, the reverse-biased base-emitter junction of Q.sub.14
avalanches permitting a current to flow into the base of Q.sub.16.
This base current allows Q.sub.16 to draw collector current through
the base Q.sub.14 and regenerative turn-on occurs. Transistor
Q.sub.14 and Q.sub.16 are not turned off until V.sub.5 is reduced
to less than a volt or reset to zero. FIG. 9 illustrates a plot of
the time necessary for C.sub.5 to charge up to the trigger voltage
with respect to the wattmeter output voltage V.sub.4. Resistors
R.sub.24 and R.sub.29 prevent Q.sub.14 and Q.sub.16 from operating
in an open base condition. In summary, the charging rate of C.sub.5
controls the time at which the trigger circuit trips, with the
greater the average wattage input to the operating lamp 10, the
later the tripping time, and vice versa. The logic-timing circuit,
together with the gate drive and zero voltage reset, as described
hereinafter, constitute a control signal generating means which is
actuated by the composite signal output of the wattmeter means to
generate a controlling signal for closing the AC switch. This
varies the proportion of time the AC switch is closed in accordance
with whether the composite averaged signal from the wattmeter
indicates an average wattage input to the operating lamp 10 as that
wattage desired, or greater or less than that wattage desired, so
that the average wattage input to the operating lamp 10 is
maintained at about its predetermined desired value, for example,
400 watts.
GATE DRIVE
Components C.sub.6, C.sub.12, CR15, CR16, CR17, CR18, Q.sub.17,
R.sub.10, R.sub.23 and R.sub.33 form the gate drive circuit shown
in FIG. 10. Capacitor C.sub.6 is charged up to about 9 volts by
transformer T.sub.2. When the trigger circuit Q.sub.14 and Q.sub.16
turn on, base drive is applied to Q.sub.17 causing Q.sub.17 to
saturate. With Q.sub.17 saturated all the voltage across C.sub.6 is
applied to the R, RC network C.sub.12, R.sub.10, R.sub.33 and the
gate cathode junction of the AC switch. This voltage causes a
current to flow out of the gate of the AC switch. This current has
an initial peak value of about 4 times the DC value for about 5 to
10 microseconds. The DC drive current is equal to the voltage
across C.sub.6 less the cathode to gate voltage of the AC switch,
divided by R.sub.10. Gate current is applied while Q.sub.14 and
Q.sub.16 are "on." When C5 and the trigger circuit are reset, gate
drive is removed. Resistor R.sub.23 improves the turnoff
characteristic of Q.sub.17 and prevents Q.sub.17, from operating in
an open base condition.
SYNCHRONIZING OR ZERO VOLTAGE RESET
Since the AC switch is required to be turned on at a specific time
in each half cycle, capacitor C.sub.5 must be reset at a specific
time in each half cycle. Moreover, resetting must occur before the
current in the AC switch goes to zero or the AC switch will not
turn off. In order to satisfy the above requirements, resetting of
C.sub.5 is chosen to occur at line voltage zero. This provides a
very stable reference which will occur before current zero because
of the inductive nature of the power circuitry. This function is
performed by components C.sub.7, CR13, CR14, Q.sub.15, Q.sub.18,
R.sub.25, R.sub.26, R.sub.27, and R.sub.28, as shown in FIG. 11.
Resistors R.sub.25, R.sub.27 and R.sub.28 divide the voltage
V.sub.8, which is an unfiltered full-wave rectified sine wave, and
apply about one-third of V.sub.8 to the base of Q.sub.15. As long
as V.sub.8 is above about 3 volts, Q.sub.15 will be conducting and
all the current in R.sub.26 will flow into the collector of
Q.sub.15. When V.sub.8 is below about 3 volts, Q.sub.15 will become
nonconducting and the current in R.sub.26 will be allowed to flow
through CR14 into the base of Q.sub.18. When Q.sub.18 receives base
drive, current is allowed to flow from C.sub.5 through R.sub.21
into the collector of Q.sub.18 to ground. This current flow decays
the voltage across C.sub.5 to zero in about 200 microseconds. Thus,
every time the line voltage goes to zero, Q.sub.18 resets the
voltage of C.sub.5 to zero. Capacitor C.sub.7 is used to filter out
voltage transients appearing on the line.
WARMUP CURRENT REGULATOR
Due to the universal nature of the present phase-controlled
ballast, the inductor reactance is sufficiently low (about 27
.OMEGA.) that during lamp warmup, it would normally pass too much
current (about 10A for a 400 watt lamp) at high line voltage. For
this reason the logic is designed to maintain the lamp current at a
preselected maximum value until the logic begins to regulate power.
Components C.sub.2, C.sub.9, CR4, CR24, D2, D7 R.sub.8, R.sub.13,
R.sub.30 and Q.sub.4 as shown in FIg. 12 perform this regulating
function. The voltage V.sub.9 at the cathode of CR.sub.6 is equal
to I.sub.L (R.sub.9 /100), assuming R.sub.14 >>R.sub.9 (see
the description of the transistorized wattmeter). Once this voltage
rises above the knee voltage of D.sub.2, any further increase in
this voltage V.sub.9 must appear across R.sub.8. The voltage across
R.sub.8 causes Q.sub.4 to conduct a current I.sub.19 through
R.sub.13. Current I.sub.19 causes voltage V.sub.4 to decrease, and
as shown in FIG. 9, a decrease in V.sub.4 causes the ballast to
phase-back or reduce the conduction time. If the conduction time is
reduced, the average voltage across L.sub.2, is reduced and thus
I.sub.L is reduced. Phasing-back continues until an equilibrium
condition of the warmup current regulator occurs in which the peak
current is reduced to the point where it is just sufficient to
enable Q.sub.4 to conduct such current as required to maintain
V.sub.4 constant at the particular equilibrium value. Capacitor
C.sub.9 is used to provide additional filtering of V.sub.4 and
components CR24 and R30 are used to isolate C.sub.9 from the
wattmeter circuitry when the operating lamp 10 is stabilized and
current control is no longer needed. Thus the warmup current
regulator is connected to the current responsive wattmeter input
portion and also to the output section of the wattmeter. When a
maximum predetermined current through the lamp 10 is sensed, a
bypass impedance decreases the composite signal output of the
wattmeter and limits the maximum current which can pass through the
operating lamp 10 during warmup. With this warmup circuit, a
typical time required for warmup of the operating lamp 10 is about
20 percent of the total time required with usual lamp ballasts.
PHOTOCONTROL
A ballast which is intended for such applications such as street
lighting must automatically turn on at an ambient light level of
about 1 foot-candle and turn off at an ambient light level of about
5 foot-candles. Shown in FIG. 13 is the photocontrol circuit which
performs this function. This circuit consists of components
C.sub.4, CR11, CR12, Q.sub.11, Q.sub.12, R.sub.16, R.sub.17,
R.sub.18, R.sub.19 and photocell R .lambda.. If the ambient light
level is below 1 foot-candle the photocell resistance is high
causing base drive to flow into Q.sub.12. If Q.sub.12 is "on," then
Q.sub.11 is "off" and the ballast is phase controlling as shown in
FIGS. 14A and 14B. When the illumination level rises to 5
foot-candles, the photocell resistance has dropped to such a low
value (about 7000 ohms) that Q.sub.12 is starved of base drive and
is turned "off." With Q.sub.12 "off," Q.sub.11 receives base drive
and is turned "on." When Q.sub.11 is "on," voltage V.sub.4 is
reduced to about 2 volts and at this level the gate of the AC
switch does not receive drive current. With no gate drive to the AC
switch the ballast is "off." The ballast turns on again when the
illumination level drops to about 1 foot-candle. At this level the
photocell resistance is about 15,000 ohms and Q.sub.12 is turned
"on" causing Q.sub.11 to become nonconducting. The following
formulas can be used to calculate R.lambda. at the two switching
points: ##SPC1##
The foregoing photocontrol is generally described in the
aforementioned copending application Ser. No. 807,711, filed
concurrently herewith, now abandoned.
HIGH VOLTAGE PULSE RECYCLER
The high-pressure sodium-mercury lamp is the most difficult to
start. In order to strike such a lamp, the ballast should produce a
series of 2500 to 4000 volt pulses of a 10 to 2 microseconds
duration until the lamp is struck. The circuit performing this
function is shown in FIG. 15 and is constructed from components
C.sub.10, CR25, CR26, D.sub.5, Q.sub.19, Q.sub.20, R.sub.31,
R.sub.32 and R.sub.34. When the illumination level drops
sufficiently for the photocontrol to switch the ballast to the "on"
state, V.sub.4 immediately starts rising towards 10.5 volts at a
rate of about 0.1 v./ms., as shown in FIG. 16. As V.sub.4 rises,
the AC switch turns on at a different phase angle each cycle (see
FIG. 16). Every other time the AC switch turns on, a pulse of
voltage is produced across the lamp. Each voltage pulse is equal to
about 11 times the instantaneous line voltage at that time. These
pulses occur only on the (+) half cycle as was discussed in the
section POWER CIRCUITRY. If, however, the lamp does not strike
before V.sub.4 reaches 10.5 volts, V.sub.4 is reset to about 2
volts and recycled to 10.5 volts. Voltage V.sub.4 should be reset
due to the fact that when V.sub.4 =10.5 v., the voltage pulse
across the lamp is less than 1000 volts. Resetting occurs when
V.sub.4 reaches about 10v., the voltage across C.sub.11 rises to
about 9.5 v. and D.sub.5 starts to conduct. The current in D.sub.5
flows through R.sub.32 into the base of Q.sub.20. This base current
causes Q.sub.20 to conduct the current in R.sub.17 away from the
base of Q.sub.12 resetting the photocontrol to the "off" state.
With the photocontrol in the "off" state, Q.sub.11 is "on" state.
With the photocontrol in the "off" state, Q.sub.11 is "on" and
V.sub.4 decays down to about 2 volts. When V.sub.4 drops to about 2
volts the photocontrol changes to the "on" state and V.sub.4 starts
rising towards 10.5 volts. This recycling continues until the lamp
strikes. When the lamp is struck, its current produces a voltage of
about 12 volts peak across R.sub.9. This 12 volt peak charges
C.sub.10 to 12 volts and causes about 30 .mu. a to flow through
R.sub.31 into the base of Q.sub.19. Transistor Q.sub.19 is thus
turned "on" and all the current in R.sub.32 flows into the
collector of Q.sub.19. Under these conditions, Q.sub.20 does not
receive base drive and the photocontrol is no longer reset to the
"off" state. The lamp current is then regulated by the warmup
current regulator until the wattmeter starts to regulate power.
LOW VOLTAGE REGULATOR
The voltage regulator circuit shown in FIG. 17 consists of
components C.sub.8, D.sub.6, Q.sub.10 and R.sub.20. The voltage
V.sub.7 on C.sub.8 can range anywhere from 20 to 40 volts depending
on the line voltage and the turns ratio of transformer T.sub.2.
This voltage is then applied across the series circuit R.sub.20,
D.sub.6. Due to Zener action the voltage across D.sub.6 is
regulated to 19 volts. Since the base of Q.sub.10 is connected
directly to D.sub.6, the base voltage of Q.sub.10 must also be 19
volts. Since the emitter of Q.sub.10 can be only about 1 volt below
the base of Q.sub.10, V.sub.3 is thus regulated to 18 v.
It will be recognized that the objects of the invention have been
achieved by providing a ballast apparatus for starting and
operating any of a plurality of different discharge devices having
varying voltage and operating characteristics. If desired, the
wattage at which the lamps will operate can readily be modified to
accommodate different lamp types. The ballast apparatus is readily
adapted to operate in conjunction with a solid-state
photocontrol.
As an alternative embodiment, the main AC switch could be
paralleled by an inductor which would supplement the series
inductor to vary the value of impedance, when the switch is open
and closed, between two finite values. Also, the switch and
series-connected inductor can both be paralleled by an
inductor.
In further explanation of the operation of the photocontrol circuit
as shown in the graphs of FIGS. 14A and 14B, as related to the
block diagram as shown in FIG. 1, when the resistance of the
photocell is low, as is the case during daylight hours, the voltage
across V.sub.4 drops to about 2 volts and the photocell "operates"
to keep the circuit in an "off" condition. The voltage across
V.sub.5 never reaches the 8 volts required to trigger Q.sub.14 and
Q.sub.16, as shown in FIG. 8. In such case, as shown in FIG. 14B,
the gate current I.sub.G will always be "zero," and the lamp
current I.sub.L will be "zero." The supply voltage V.sub.S remains
the same. When the photocontrol is "not operating," which permits
the apparatus to be in an "on" condition the apparatus is phase
controlling, as shown in FIG. 14A. In this case, when V.sub.5
reaches about 8 volts, Q.sub.14 and Q.sub.16, see FIG. 8, are
triggered, which in turn causes the gate current I.sub.G to flow to
the switch S. Lamp current I.sub.L then flows and the supply
voltage V.sub.S of course remains constant.
In further explanation of the operation of the starting of a
sodium-mercury type lamp, as shown in the graphs of FIG. 16 and as
related to the block diagram shown in FIG. 1, if the lamp does not
strike initially, the pulse recycler causes V.sub.4 again to rise
to 10 volts over a period of many cycles thereby varying the time
in each cycle that V.sub.5 reaches the trigger level to turn on the
AC switch "S," with the representative voltages which appear across
the switch "S" shown as V.sub.2 in FIG. 16. This recycling is
repeated until the lamp 10 is struck.
* * * * *