Energy efficient reactance ballast with electronic start circuit for the operation of fluorescent lamps of various wattages at standard levels of light output as well as at increased levels of light output

A ballast and control circuit for use with fluorescent lights. The circuit aids energy efficiency by removing heater current flow once the lamp has ignited. The circuit also uses time delayed inductive storage to allow delivery to the lamps of increased operating current without a concurrent increase in power utilization.

TECHNICAL FIELD 
This invention relates generally to fluorescent lamp control circuits. 
BACKGROUND OF THE INVENTION 
Electric discharge lamps, such as fluorescent lamps, operate by applying an 
electric current through a gas such that at least some of the gas atoms 
become ionized. When enough atoms are ionized, the gas becomes an electric 
conductor and light radiation results. 
Several circuits have been devised for starting and operating fluorescent 
lamps with the intent of conserving energy while maintaining correct lamp 
operation. The most successful methods thus far incorporate high frequency 
(20 KH to 30 KH) lamp excitation. Examples include U.S. Pat. No. 4,477,748 
to Grubbs; U.S. Pat. No. 4,398,128 to Wollank; U.S. Pat. No. 4,251,752 to 
Stolz; U.S. Pat. No. 4,055,335 to Perper; U.S. Pat. No. 4,109,307 to 
Knoll; U.S. Pat. No. 4,329,627 to Holmes; U.S. Pat. No. 4,220,896 to 
Paice; U.S. Pat. Nos. 3,648,196 and 3,753,071 to Engel et al.; U.S. Pat. 
No. 3,890,537 to Park et al.; U.S. Pat. No. 3,710,177 to Ward; U.S. Pat. 
No. 3,701,925 to Nozawa et al.; U.S. Pat. No. 3,573,544 to Zonis and 
others. 
Dimming the lamps by reducing the frequency of excitation within a high 
frequency circuit has been presented as another means of reducing the 
power requirements. Examples include U.S. Pat. Nos. 4,207,497 and 
4,210,846 to Capewell et al.; U.S. Pat. No. 3,936,696 to Gray; U.S. Pat. 
No. 3,422,309 to Spira; and U.S. Pat. No, 3,514,668 to Johnson et al. High 
frequency excitation does reduce the amount of power consumed 
(approximately 11% to 25% depending upon the design used). High frequency 
designs, however, have not been well received by the industry or used in 
large quantities because of the high failure rates encountered. As an 
example, one recent high frequency design produced in quantities of 
several thousand yielded a failure rate so severe that the product was 
taken off the market by the manufacturer. 
Further, all high frequency designs suffer from one or more of the 
following problems; they can be damaged by transient voltages from the 
incoming AC line; they generate R.F.I. (Radio Frequency Interference); 
they shorten lamp life by causing premature failure of the filaments 
inside many lamps; they produce frequency variations due to heating of the 
active power components used (SCR's, Triacs, transistors or FET's); they 
require many more components thereby increasing costs of production; and 
operation can vary from one unit to another due to sensitivity to 
variations in tolerances of the components used. 
Because of the above problems, low frequency, core and coil ballast units 
have prevailed. Nevertheless, when the high frequency ballast were 
introduced, attention was focused on energy conservation within the 
lighting industry. The increased interest resulted in low frequency 
ballast designs that incorporated various means of reducing the amount of 
power consumed. This combination of events led to strong differences of 
opinion in the industry. On the one hand, the high frequency designs 
reduced operating cost as much as 25%, but they were not reliable enough 
to use in large quantities. On the other hand, the low frequency designs 
were reliable, but offered little energy savings. In the great majority of 
cases, minimizing the cost of production prevailed, with the low frequency 
core and coil designs being less expensive than the high frequency 
ballast. 
Presently, the core and coil ballast account for approximately 98% of all 
ballast sales. In order to maintain this market share, the manufacturers 
of low frequency core and coil ballast have devised means of making their 
products more energy efficient. In almost every case, this invites turning 
off the heater current to the filaments of the lamp after the lamp has 
ignited. 
Examples of this method are found in U.S. Pat. No. 4,399,391 to Hammer et 
al. using a SIDAC connected in a series circuit with the primary of the 
filament transformer and a capacitor. In Hammer's design, the voltage 
differential needed to make the SIDAC perform its switching function is 
derived directly from one of the lamp filaments and phase shifted through 
a capacitor. This method of switching could very easily result in unstable 
operation (lamp oscillations) due to the current differential realized 
through lamps connected in series. The problem would become more 
significant when different wattage lamps are used, since the current 
characteristics of 40 watt lamps are much different from 34 watt lamps. 
U.S. Pat. No. 4,010,399 to Bessone et al. discloses a method of turning off 
the heater current (filament current) using independent circuits 
consisting of a Triac connected in parallel with a resistor divider. The 
Triac/resistor networks are then connected in series with each lamp 
filament (2 networks per lamp). Thermal switches have also been used to 
open the filament circuit inside the lamp after reaching a specified 
temperature. Examples of this method are found in U.S. Pat. No. 2,354,421 
to Pennybacker; U.S. Pat. No. 2,462,335 to Reinhardt; and U.S. Pat. No. 
4,097,779 to Latassa. The same method was also used within a ballast by 
locating a thermal switch next to the transformer core in U.S. Pat. No. 
2,317,602 to Hall. A relay with two sets of contacts was used by Bessone 
in U.S. Pat. No. 4,146,820 and a magnetizable core (forming a relay type 
switch) was used by Raney in U.S. Pat. No. 2,330,312. magnetic reed 
switches were used by Latassa in U.S. Pat. No. 4,009,412 that were 
energized by the magnetic field generated around the transformer core. 
This method required that the reed switches be oriented in a specific 
direction and located, within critical tolerances, in that portion of the 
magnetic field with the highest gauss levels. In addition, the problems 
were compounded due to variations from one reed switch to another. As a 
result, this method was never used in high volume production. A less 
effective method was used by Sammis in U.S. Pat. No. 3,525,901 whereby the 
heater voltage was controlled rather than being turned completely off. 
Turning heater current off does conserve energy during normal lamp 
operation, but the amount of energy saved is limited to the amount of 
current required to operate the filaments; usually 8% to 10%. 
Several methods of starting fluorescent lamps have been tried to yield a 
means of reducing the amount of energy used during the start process. For 
example, U.S. Pat. No. 3,982,153 to Burdick et al. used a surge current to 
achieve a rapid warm-up of the heaters. U.S. Pat. No. 3,582,709 to Furui 
used an unignited lamp as a ballast component in the circuit. U.S. Pat. 
No. 4,145,638 to Kaneda used series start circuits that operated 
sequentially causing one lamp to ignite before the other. U.S. Pat. No. 
2,697,801 to Hamilton used a thermal switch to operate a relay which 
controlled the amount of current going to the heaters. U.S. Pat. No. 
3,866,088 to Kaneda used a backswing voltage generated by an oscillator. 
U.S. Pat. No. 3,720,861 to Kahanic used a time delay circuit comprised of 
a SCR that generated a transient spike voltage to the heaters. U.S. Pat. 
No. 3,588,592 to Brandstadter used a SCR to control the voltage to the 
heaters. U.S. Pat. No. 3,851,209 to Murakami et al. used a pulse 
generating circuit consisting of a pulse transformer and bi-directional 
diodes. U.S. Pat. No. 2,668,259 to Stutsman used gas discharge tubes 
within the circuit to start the fluorescent lamps. U.S. Pat. No. 4,053,813 
to Kornrumpf used a transistorized inverter circuit to control the voltage 
by controlling the frequency of the applied power. 
Presuming, however, that a fluorescent fixture will be switched on and off 
five times a day, that the start process takes three seconds from 
beginning to end, and that a normal day of operation is eight hours. The 
total amount of time that the start circuit is in operation over a one 
year period would then be 1.52 hours, or 0.05% of the total lamp operation 
time. When the amount of energy saved due to improved starting circuits is 
compared to the amount of energy consumed to operate the lamps, it seems 
apparent that improved starting methods contribute very little to the 
over-all energy efficiency of fluorescent ballast operation. 
Other proposed methods of controlling the operation of fluorescent lamps 
will also affect the amount of energy used. U.S. Pat. No. 3,753,040 to 
Quenelle describes a strobing circuit using a Triac as the means of 
control. U.S. Pat. No. 3,449,629 to Wigert et al. uses a variable 
frequency oscillator circuit that can be controlled externally by heat or 
light sensors. Another example is found in U.S. Pat. No. 3,317,789 to 
Nuckolls which stabilizes lamp operation in response to variations in 
either heat or light. U.S. Pat. No. 3,611,021 to Wallace uses a feedback 
signal to reference comparator to achieve stabilization. Reversing the 
flow of current through fluorescent lamps have been thought to balance the 
light output. Examples of this method of control are found in U.S. Pat. 
No. 2,810,862 to Smith using a relay and U.S. Pat. No. 3,904,922 to Webb 
et al. using a SCR bridge circuit. The amount of flickering encountered 
with fluorescent lamps is controlled with parallel connected capacitors in 
U.S. Pat. No. 2,487,092 to Bird, while U.S. Pat. No. 2,588,858 to Lehmann 
solves the problem by connecting the lamps in phase relationships through 
multiple series connections. 
With the exception of external control options, the stabilization of light 
output has been greatly improved through the use of more efficient 
coatings on the inside surfaces of the lamps. Many of the problems 
discussed above have now been completely eliminated through improved lamp 
technology. 
As a result of changing markets within the lighting industry, two 
independent efforts are now in process. The manufacturers of high 
frequency ballast are directing their efforts toward reducing the price of 
their products while improving reliability and performance, and the 
manufacturers of the low frequency ballast are seeking to improve the 
energy efficiency of their products without increasing price. A need 
clearly exists for a ballast unit that offers the price and reliability of 
the low frequency units along with the energy efficiencies of the high 
frequency units. 
DISCLOSURE OF THE INVENTION 
This need and others are substantially met through provision of the ballast 
circuit disclosed herein. Objects of the invention are to provide energy 
efficient ballast circuits for starting and operating fluorescent lamps, 
of various wattages, at standard light output levels as well as at 
increased light output levels from a low frequency power source such as a 
60 Hz source. 
A particular object of the invention is to provide ballast circuits that 
reduce the amount of power required for operation while maintaining full 
light output from fluorescent lamps using an inductive current storage 
method. 
Additional objects of this invention are to provide ballast circuits with 
improved operational characteristics such as: reduced lamp current crest 
factor; lower operating temperature; increased power factor; and more 
efficient lamp starting at various temperatures.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring now to the drawings and particularly to FIG. 1, one embodiment of 
the ballast apparatus can be seen as depicted generally by the numeral 1. 
The apparatus (1) includes an inductor assembly (2) that is comprised of 
four bobbin wound coils (3 through 6) assembled on an irregular shaped 
common core (7). Two of the coils (3 and 4) are serially connected to form 
a first coil grouping (9) and the remaining two coils (5 and 6) are 
serially connected to form a second coil grouping (10). Each coil grouping 
(9 or 10) can be individually considered as the electrical equivalent of 
one continuous coil wound on the irregular shaped common core (7). The two 
coil groupings (9 or 10) are serially connected at a common node (8) with 
the outermost ends of each coil grouping being connected to a 60 Hz power 
source by two terminals (11 and 12), with the outermost end of the first 
coil grouping (9) being serially connected through a thermal switch (13) 
to one terminal (11) and the outermost end of the second grouping (10) 
being directly connected to the remaining terminal (12). One terminal (11) 
is the hot side of the AC power source and the remaining terminal (12) is 
the neutral side of the AC power source. 
When the inductor assembly (2) is connected to a source of 60 Hz AC power, 
it functions as an inductive current storage device that also regulates 
current flow with an efficiency dependent upon the interaction of the 
reactance of the coil grouping (9 and 10) in combination with the 
reluctance of the cross sectional area of the core (7). Since an inductor 
cannot release reactive power instantaneously, a short delay will occur 
between the coil groupings (9 and 10) that is dependent upon the vector 
sums of the reactive powers released from the coil groupings (9 and 10). 
The delayed response, or storage, of the inductive reactances provides the 
current regulation. 
The inductor assembly (2) can be viewed as the electrical equivalent of the 
two coil groupings (9 and 10) wound on the irregular shaped core (7), with 
the first coil grouping (9) being the line inductor and the second coil 
grouping (10) being the load inductor. The significance of the second coil 
grouping (10) being connected in parallel with the output load sections of 
the apparatus (1) will be discussed in detail below. 
The connection node (8) between the coil groupings (9 and 10) connects to 
two capacitors (14 and 15). One capacitor (14) also connects to one end of 
a first fluorescent lamp (26) through a wire (18). The other end of this 
lamp (26) connects to the neutral terminal (12) of the AC line through 
appropriate wires (25 and 30). In a like manner, the second capacitor (15) 
connects to a second lamp (27) through a wire (20) with the other end of 
the lamp (27) being connected to the neutral terminal (12) of the AC line 
through appropriate wires (22 and 30). 
Since the capacitors (14 and 15) will pass AC current, the fluorescent 
lamps (26 and 27) are effectively connected in parallel between the common 
node (8) of the inductor assembly (2), and the neutral terminal (12) of 
the AC power source. Two resistors (16 and 17) are connected in parallel 
across the capacitors (14 and 15), respectively, to provide a means of 
discharging the capacitors (14 and 15) when the AC power source is 
deactivated in accordance with the safety requirements listed in 
Underwriters Laboratories safety standard number UL-935, seventh edition. 
Another resistor (28) is connected between the input to the lamps (26 and 
27) through appropriate wires (18 and 20), respectively, to balance the 
current going to the lamps (26 and 27). (Since the resistance of a 
fluorescent lamp in operation is the effective resistance of the ignited 
gas within the lamp operating at a controlled current a fluorescent lamp 
is said to have a negative resistance.) 
The above noted resistor (28) compensates for variations in negative 
resistance in different fluorescent lamps by causing the current going to 
the lamps (26 and 27) to be shared more evenly. The balancing of current 
going to the lamps (26 and 27) by this resistor (28) helps to reduce the 
crest factor of the lamps (26 and 27) during normal operation. 
A filament transformer (29) is used to supply heater voltage to the 
filaments inside the lamps (26 and 27) as a necessary condition to start 
the lamps (26 and 27). The filament transformer (29) is comprised of one 
primary winding terminated at pins P1 and P2 and is wound on a common core 
with three secondary windings denoted as B1 and B2 for the first 
secondary, R1 and R2 for the second secondary, and Y1 and Y2 for the third 
secondary. The primary winding is connected to the hot side of the AC line 
by connection of pin P1 of the filament transformer (29) to one side of 
the thermal switch (13). The other end of the primary winding P2 is 
connected to terminal MT2 of a Triac (31) as explained below. 
The first secondary of the filament transformer (29) connects to the lamp 
filament inside the second lamp (27) through appropriate wires (20 and 
21), respectively. The second secondary connects to the lamp filament 
inside the first lamp (26) through appropriate wires (19 and 18), 
respectively. Finally, the third secondary connects to the lamp filaments 
inside both lamps (26 and 27) in parallel by connecting secondary Pin Y1 
to the lamps (26 and 27) through a first set of wires (23 and 24), 
respectively and by connecting secondary Pin Y2 to the lamps (26 and 27) 
through a second set of wires (25 and 22,), respectively. The latter 
electrical point also connects to the neutral terminal (12) of the AC 
power source through a wire (30). 
Certain start conditions must be met to cause the fluorescent lamps (26 and 
27) to light when a source of 60 Hz AC power is applied to the terminals 
(11 and 12). The required start conditions are created by a start circuit 
denoted generally by the reference numeral 60. 
The start circuit (60) is a digital circuit that operates from a +8 volt DC 
power source. The DC power source is derived from an AC voltage tap (61) 
located in one coil (6) of the second coil grouping (10). The output 
voltage of this tap (61) is 16 vac when measured between the tap (61) and 
the neutral terminal (12). The AC voltage at this tap (61) connects to the 
anode of a rectifier (50) that converts the AC voltage to half wave 
rectified DC. The cathode of this rectifier (50) connects to the input of 
an 8 volt positive voltage regulator (52) and also to the positive side of 
a capacitor (51). The negative side of this capacitor (51) and the 
negative terminal of the voltage regulator (52) are connected to the 
neutral terminal (12), which serves as both the neutral side of the AC 
power source and the ground side of the +8 vdc power supply. The capacitor 
(51) removes the ripple voltage coming through the rectifier (50) thus 
filtering the input voltage to the regulator (52). The output of the 
regulator (52) provides a regulated DC voltage of +8 vdc as the source of 
power to operate the start circuit (60). 
The start circuit (60) is controlled by two Hall effect solid state 
magnetic switches (53 and 54) that are located at the end of the core (7) 
near the first coil grouping (9). Hall effect switches operate in a 
digital manner providing a low output in the presence of a south pole 
magnetic field and a high output in either a north pole magnetic field or 
no magnetic field at all. 
Each logic gate used in the start circuit (60) appears individually (36, 
39, 41 and 44), although all four gates may be physically contained in one 
component package. Each gate (36, 39, 41 and 44) comprises a digital 
C-MOS, 2 input, NAND, Schmitt trigger gate (Part #4093). Schmitt trigger 
gates produce a clean output signal when operating in an electrically 
noisy environment. 
Each Hall effect switch (53 and 54) connects to the +8 vdc power source and 
to the neutral terminal (12). The output of the first Hall effect switch 
(53) connects to the cathode of a diode (57) and the output of the second 
Hall effect switch (54) connects to the cathode of a second diode (58). 
The anodes of these diodes (57 and 58) are connected together through a 
wire (55) and then serially connect through a resistor (46) to one side of 
a capacitor (37) and to pin 2 of one gate (41) and to pin 8 of another 
gate (36). The other side of the capacitor (37) connects to ground. A 
voltage divider consisting of two resistors (49 and 47) also connects to 
Pin 2 of the first gate (41) with the capacitor (48) being connected in 
parallel with a resistor (47). Pin 1 of this gate (41) connects to the +8 
vdc to allow the gate (41) to function as an inverter. A capacitor (35) 
connects between ground and Pin 9 of the second gate (36) in combination 
with a resistor (34) that connects between Pins 9 and 10 of the second 
gate (36) to function as a 115 Hz oscillator that is controlled by Pin 8 
of the second gate (36). 
When a source of 60 Hz power is first applied to the terminals (11 and 12), 
only a small amount of power flows through the inductor assembly (2) which 
generates a magnetic field around the core (7) that is directly 
proportional to the amount of power flowing through the inductor assembly 
(2). Since the magnetic field is not yet strong enough to activate the 
Hall effect switches (53 and 54), their outputs are held high by the 
resistors (49 and 47) of the resistor divider network. The same high 
signal is applied to Pin 8 of the second gate (36) and Pin 2 of the first 
gate (41). As a result, Pin 3 of the first gate (41) goes low and 
transfers the low signal to Pin 6 of the third gate through a resistor 
(42). Pin 6 of the third gate (44) was already low prior to receiving a 
signal from the first gate (41) due to the time required to charge the 
capacitor (43) that connects between Pin 6 of the third gate (44) and 
ground. 
The low signal created by the time period required to charge the capacitor 
(43), combined with the low signal being transferred from Pin 3 of the 
first gate, (41) guarantees that Pin 6 of the third gate (44) will be low 
the instant that AC power is applied to the terminals (11 and 12). When 
Pin 6 of the third gate (44) goes low, Pin 4 of this gate (44) will go 
high, causing a voltage to be applied to the gate terminal G of a Triac 
(31) through a resistor (45). The voltage applied to the gate terminal G 
causes the Triac (31) to switch on, which activates the filament 
transformer (29), thereby causing the filaments inside each lamp (26 and 
27) to heat up. One second after the filaments inside the lamps (26 and 
27) have been activated, an oscillator comprised of the second gate (36), 
a resistor (34), and a capacitor (35) begins to oscillate at the rate of 
115 Hz. The delay before oscillation begins is due to the initial time 
period required to charge the capacitor (35). Pin 10 of the second gate 
(36) begins pulsing Pin 12 of the fourth gate (39) at a 115 Hz rate which 
causes Pin 11 of the fourth gate (39) to provide voltage pulses to the 
gate terminal G of the Triac (56) through a capacitor (40). 
A resistor (59) connects between the gate terminal G of the Triac (56) and 
ground to discharge the capacitor (40) immediately after each positive 
pulse has passed through the capacitor (40). The Triac (56) is pulsed on 
and off by the positive pulses going to the gate terminal G. When the 
Triac (56) conducts, it temporarily shorts a capacitor (14) through two 
rectifiers (32 and 33), causing a controlled pulse voltage to be generated 
through a wire (18) to the hot side of the first lamp (26). Because the 
amplitude of the pulsed voltage is higher than the normal line voltage, 
the gas inside this lamp (26) responds by igniting during the negative 
transition of the pulse, which causes this lamp (26) to turn on. When this 
lamp (26) turns on, the negative resistance of the lamp (26) changes the 
load impedence which allows the voltage pulses to be coupled to the 
remaining lamp (27) through two capacitors (14 and 15), and to some extent 
through the sharing resistor (28) until the second lamp (27) switches on. 
When both lamps switch on, the magnetic field created around the core (7) 
becomes strong enough to cause the Hall effect switches (53 and 54) to 
turn on and off at a 60 Hz rate. When the outputs of the Hall effect 
switches (53 and 54) go low (at a 60 Hz rate), the low pulses pass through 
two diodes (57 and 58) to an integrator network comprised of three 
resistors (46, 47 and 49) and two capacitors (37 and 48). The low pulses 
coming from the Hall effect switches (53 and 54) cause one capacitor (48) 
to discharge enough to lower the voltage going to Pin 8 of the second gate 
(36) and Pin 2 of the first gate (41) to a value that appears as a low 
signal, thereby reversing the start process which causes Pin 11 of the 
fourth gate (39) to go low and remain low as long as the Hall effect 
switches (53 and 54) continue to produce low pulses. It is important to 
note that the Triac (56) stops producing start pulses the instant that the 
Hall effect switches (53 and 54) sense that the lamps have turned on. 
The same is not true of another Triac (31) which supplies power to the 
filament transformer (29). This Triac (31) remains on for one second after 
the first Triac (56) has turned off. This is due to the time period 
required for a capacitor (43) to discharge through a resistor (42) in 
response to the output signal from Pin 3 of the first gate (41). Pin 4 of 
the third gate (44) will go low when the capacitor (43) discharges, 
thereby turning Triac (31) off, which removes power to the filament 
transformer (29). Lamp filament power is allowed to continue for one 
second after the start pulses have stopped to assure that the lamps (26 
and 27) remain on. 
Immediately after the one second delay, the filament transformer (29) is 
turned off to conserve energy. The lamps (26 and 27) will continue to 
operate even though the power to the filaments inside the lamps (26 and 
27) has been removed. The above description details only one of several 
means of producing time delays and switching functions using digital IC 
circuits, variations are possible without affecting the actual functions 
achieved, provided that solid state Hall effect switches are used to sense 
the change in the magnetic field when the lamps (26 and 27) turn on. 
The ballast apparatus (1) may be made to accommodate 120 volt or 277 volt 
operation of either single lamp or dual lamp fixtures by simply adjusting 
the turns ratio of the first coil grouping (9) to the second coil grouping 
(10). Additionally, the amount of light output may be increased or 
decreased by increasing or decreasing respectively the values of the two 
coupling capacitors (14 and 15). Increasing the capacitance of these 
capacitors (14 and 15) will cause more current to be passed to the lamps 
(26 and 27). (In a single lamp configuration, one capacitor (15) one 
resistor (28) and one lamp (27) may be removed from the circuit). The 
ballast apparatus (1) will operate either 40 watt or 34 watt (energy 
saver) fluorescent lamps in any of the above configurations without any 
additional circuit changes. 
The physical construction of the inductor assembly (2) may be modeled after 
an existing construction method. For specific details, reference is made 
to pending application Ser. No. 594,458 filed on Mar. 28, 1984 in the name 
of Gerald D. Boyd, as assigned to a common assignee. It is important to 
note that the physical construction (not the electrical or magnetic values 
or operation) may be incorporated in the construction of the inductor 
assembly (2). The sole purpose of using this particular construction 
method is to allow manufacture of an inductor assembly (2) in a small 
physical form. The ballast apparatus (1) will in fact, operate exactly the 
same when configured on separate and individual cores. It should be noted 
that the ballast apparatus (1) conserves energy in two ways. First, it 
removes the voltage going to the filaments inside the lamps (26 and 27) 
after they have turned on. Second, it provides more current to operate the 
lamps (26 and 27) than is currently available from 60 Hz ballast units. 
Now, referring to FIGS. 2 and 3, the inductor assembly (2) can be seen as 
generally represented to include a line inductor (the first coil grouping 
(9)) and a load inductor (the second coil grouping (10)). Upon the 
application of the AC power to the inductor assembly (2) an inductive 
reactance is impressed upon the source impedence of the AC line that 
prevents the inductor assembly (2) from becoming a short circuit across 
the AC line voltage. In the example shown in FIG. 2, the inductance of the 
line inductor (9) is 398 mh and the inductance of the load inductor (10) 
is 1.51 h. Expressed in ratiometric terms, the load inductor (10) is 3.8 
times more inductive than the line inductor (9). (Inductance is defined as 
the property of an electric circuit by virtue of which a varying current 
induces an electromotive force in that circuit or in a neighboring 
circuit.) 
The inductive reactance of the load inductor (10) is converted to reactive 
power because the product of voltage and the out-of-phase component of 
alternating current is reactive power. In a passive network, reactive 
power represents the alternating exchange of stored energy (in this case 
inductive energy) between two areas. Expressed in simpler terms, the load 
inductor (10) releases power at a slower rate than the line inductor (9) 
because the load inductor (10) is 3.8 times more inductive than the line 
inductor (9). As a result of this difference in inductance, the current 
waveform of the load inductor (10), shown as waveform "C" in FIG. 3, is 
138 degrees out-of-phase (lagging) from the waveform of the line inductor 
(9), shown as waveform "B". Or, expressed another way, waveform "C": is 
out-of-phase 42 degrees (leading) waveform "B". 
The vector sum of waveform "B" plus waveform "C" equals waveform "A", which 
is the amount of current being delivered to the fluorescent lamps (26 and 
27). Waveforms "D" and "E" represent the amount of energy stored (delayed) 
in the load inductor (10). By causing the energy stored in the load 
inductor (10) to be released in approximately the same phasing attitude as 
the energy in the line inductor (9) (only 42 degrees out-of-phase) the 
inductive power in the circuit is phase shifted to a point where it 
becomes usable power instead of being dissipated in the form of heat. As a 
result, the ballast apparatus (1) operates at a greatly reduced 
temperature of 34 degrees C. as compared to a standard ballast operating 
temperature of 90 degrees C. It thus becomes apparent that the ballast 
apparatus (1) takes advantage of stored inductive power within an 
alternating magnetic field in a much more efficient manner than has 
heretofore been done. 
This method of storage could be defined as either "inductive storage" or 
"magnetic storage". Whichever term is used, the storage method can only 
occur in the presence of a circuit employing an alternating current with a 
changing magnetic field. 
Referring again to FIG. 2, actual rms current measurements of the ballast 
apparatus (1) during normal operation for the embodiment described above 
is shown. A first meter (62) indicates that the system is drawing 552 ma 
from the incoming AC line. A second meter (63) indicates that the load 
inductor (10) has a circulating current of 239 ma. A third meter (64), 
however, indicates that 619 ma flows to the lamps (26 and 27). This meter 
(64) reflects the vector sum of the waveform currents "B" and "C" for a 
total of 619 ma which equals waveform "A". It is immportant to note that 
new power has not been created; rather, power already existing in the 
system has been phase shifted into a usable region of the AC waveform. 
Additional meters (65 and 66) indicate that the lamps (27 and 26) are 
drawing 311 ma and 308 ma, respectively. The difference between the 
current readings going to the lamps (26 and 27) is due to the difference 
in the negative resistance of each lamp. If the position of the lamps (26 
and 27) were reversed, the respective current readings would follow. The 
sharing resistor (28) across the lamps (26 and 27) reduces the effects of 
the varying negative resistance within different lamps by causing the 
lamps (26 and 27) to share (or balance the load current more evenly. 
The capacitors (14 and 15) couple the output of the inductor assembly (2) 
(at the common node 8) to the lamps (26 and 27). Increasing the value of 
these capacitors (14 and 15) allows more current to be coupled to the 
lamps (26 and 27) which will generally cause the lamps to increase in 
brightness. One embodiment of the ballast apparatus (1) can use this 
method to increase the amount of light output for the specific reason of 
compensating for a normal loss in light when used with fluorescent 
fixtures containing reflective materials that create multiple images of 
the lamps used. 
The capacitors (14 and 15) also balance the phasing between the inductor 
assembly (2) and the lamps (26 and 27). At a point in time when the 
inductor assembly (2) is trying to release as much reactive power as 
possible, the capacitors (14 and 15) are trying to charge to their fullest 
potential. As a result, the inductor assembly (2) is pushing power out at 
the same point in time when the capacitors (14 and 15) are trying to pull 
power in. The total efficiency of the ballast apparatus (1) is dependent 
upon this relationship. 
If the ballast apparatus (1) were allowed to establish a resonant 
frequency, a short circuit through the negative resistance of the lamps 
(26 and 27) would result. Since the capacitors (14 and 15) are between the 
inductor assembly (2) and the lamps (26 and 27) in a series circuit, a 
resonant circuit condition from either direction would cause damage to the 
lamps (26 and 27). The phase shift of waveform "C" combined with the 
appropriate values of the capacitors (14 and 15) assures that a resonant 
circuit condition is avoided. 
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.