Higher efficiency incandescent lighting unit having an improved ballast unit

An improved general service incandescent lamp having an improved capacitive ballast circuit for operating a low voltage filament of the lamp is disclosed. Various embodiments of an improved capacitive ballast circuit that substantially eliminates unwanted stored energy and unwanted resistive dissipation are disclosed.

BACKGROUND OF THE INVENTION 
This invention relates to general service incandescent lighting units, and 
more particularly, to a higher efficiency general service incandescent 
lighting unit having an improved capacitive ballast circuit. 
The continuing pursuit of improving the efficiency of lamps is of 
increasing importance due to the increasing cost of energy. One of the 
family of lamps in which efficiency is desired to be improved is the 
incandescent lamp. Incandescent lamps, although having efficiency ratings 
lower than those of fluorescent and high intensity discharge lamps, have 
many attractive features, such as, low cost, compact size, instant light, 
dimmability, convenience, pleasing spectral distribution, and millions of 
existing sockets in the homes of the users who have become accustomed to 
the pleasing incandescent type lighting. 
The efficiencies of the incandescent lamp have recently been improved and 
such improvements are described in U.S. patent application Ser. No. 
519,162 and U.S. Pat. Nos. 4,517,491; 4,535,269; and 4,524, 302 all filed 
Aug. 1, 1983 and assigned to the same assignee as the present invention. 
The hereinabove referenced U.S. patent application Ser. No. 519,165 
discloses a filament operated at a low voltage while maintaining the 
wattage and even increasing the efficacy of the general service 
incandescent lamp containing the filament. 
The operation of a filament at a low voltage may be accomplished by the use 
of a capacitive ballast circuit. One such ballast circuit is described in 
my U.S. patent application Ser. No. 379,411, now U.S. Pat. No. 4,516,056 
filed May 18, 1982 and assigned to the same assignee as the present 
invention. In such a ballast circuit a first and a second capacitive 
element reduce the voltage applied across a low voltage filament. 
I have determined that in the use of capacitive elements to reduce the 
voltage across the filament, certain disadvantages can exist in the event 
the capacitive elements should be inadvertently left in their charged 
state. The disadvantages resulting from inadvertently charged capacitive 
elements are (1) if the plug of the lamp fixture, housing the lamp, is 
suddenly removed from the wall receptacle, the potential of the charged 
capacitive elements may be present at the prongs of the plug, and (2) if 
the lamp is quickly removed from the socket of the fixture, the potential 
of the charged capacitive elements may be present at the base of the lamp. 
Additionally, if the power applied to the lamp is suddenly interrupted and 
then quickly reapplied, the voltage potential across the capacitive 
elements may be of a value, such as 440 volts, which if allowed to 
discharge across the filament may damage the filament. 
Various means such as a resistor placed in a parallel arrangement with the 
capacitive elements such as to bleed off the charge stored in the 
capacitive elements can be a solution to the disadvantage of the 
capacitive ballast circuits. However, in order for the bleed-off time to 
be less than, for example two seconds, a resistor in the order of 20K ohms 
is typically required. Such a resistor is disadvantageous in that it 
dissipates about 0.5 watts during a steady-state operation which degrades 
the efficacy of the improved general service lamp. It is desired to 
operate a capacitor ballast circuit having means to prevent inadvertently 
charged capacitive elements without the need of providing devices which 
degrade the efficacy of the improved general service incandescent lamp. 
Accordingly, an object of the present invention is to provide an improved 
general service incandescent lamp having a capacitor ballast circuit for a 
low voltage filament and having means to reduce substantially or even to 
eliminate the efficacy degradation of the capacitive ballast circuits. 
This and other objects of the present invention will become apparent upon 
consideration of the following description of the invention. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved general service 
incandescent lamp having an improved capacitor ballast circuit for 
operating a low voltage filament. 
In one embodiment of the present invention a general service incandescent 
lighting unit comprises (a) a base having an electrically conductive 
screw-in section, (b) an outer envelope mounted on the base, (c) an inner 
envelope coaxially disposed within the outer envelope and containing a 
halogen gas atmosphere along with a high pressure fill-gas, (d) a low 
voltage filament coaxially disposed within the inner envelope, and (e) a 
capacitive ballast circuit having a capacitive element of a preselected 
value and serially connected with the filament. The ballast circuit 
further comprises a sensing means for sensing the active condition of the 
capacitive element and developing in response to the active condition a 
control signal which is applied to a switching means so as to be rendered 
conductive and provide a resistive discharge path to cause the capacitive 
element to be substantially discharged. 
The particular features of the invention believed to be novel are set forth 
with particularity in the appended claims. The invention itself, however, 
both as to its organization and operation, together with further objects 
and advantages thereof may best be understood by reference to the 
following description taken in conjunction with the accompanying drawing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
A general service incandescent lighting unit 10 is shown in FIG. 1 as 
comprising a base 14 having an electrically conductive screw-in section. 
An outer envelope 12 is attached to the base 14. The lighting unit 10 
further comprises an inner envelope 30 coaxially disposed and supported 
within the outer envelope 12 and which contains a halogen gas atmosphere 
along with a high pressure fill-gas. Coaxially disposed and supported 
within the inner envelope 30 is a low voltage tungsten filament 32 
operated in the range of 24 to 36 volts. 
The inner envelope 30 may be comprised of a glass or quartz material. The 
filament 32 is arranged within the inner envelope 30 across lead-in 
conductors 24 and 26. The filament 32 along with the inner envelope 30 may 
each be of the type described in the previously mentioned U.S. patent 
application having Ser. No. 519,165, assigned to the same assignee as the 
present invention and herein incorporated by reference. The lead-in 
conductors 24 and 26 are connected to inleads 16 and 18 via cross members 
20 and 22, respectively. The filament 32 is operated by one of the ballast 
circuit arrangements of FIG. 2 or FIG. 3 each shown in FIG. 1 as located 
in the housing 15 of the lamp 10. 
FIG. 2 is a block diagram representative of a capacitive ballast circuit 40 
in accordance with one embodiment of the present invention. The circuit 40 
has a capacitive element C1 arranged in a serial manner with the FILAMENT. 
The capacitive element C1 has connected across it a sensing means 31 for 
sensing the active condition of the capacitive element C1 and developing 
in response to the active condition a control signal which is applied to a 
switching means 33 so as to be rendered conductive and cause the 
capacitive element C1 to be discharged by a path provided by resistor R1. 
A second embodiment of a ballast circuit 50 is shown in FIG. 3 and operates 
in a manner similar to that of FIG. 2 except that its sensing means 34 is 
in a serial arrangement with the capacitive element C1 and FILAMENT. 
In order that both embodiments of the present invention may be more readily 
understood, reference is made to FIG. 4 showing an arrangement of a 
capacitor ballast circuit. 
The circuit of FIG. 4 included means for having an alternating current 
(A.C.) voltage V.sub.AC, having a typical value of 120 volts at a 
frequency 60 Hz, applied to its inputs. One side of the A.C. voltage 
V.sub.AC is connected to one side of the filament via an appropriate 
electrical contact, shown as P2 of the lamp, whereas, the other side of 
the A.C. voltage is connected to the other side of the FILAMENT via a 
serially arrangement of (1) a switch S1, (2) an appropriate contact P1, 
shown as P1 of the lamp, and (3) a parallel arrangement of a capacitive 
element C2 and a resistor R2. The capacitive element C2 provides a 
predetermined series reactance path to the applied A.C. voltage V.sub.AC 
so that the portion of the voltage V.sub.AC applied across the filament is 
reduced from 120 volts to a desired value in the range of 24 to 36 volts. 
The resistor R2 connected across the capacitive element C2 is used to 
provide a path to discharge the unwanted energy that may be inadvertently 
stored in the capacitive element C2. 
As discussed in the "Background" section, the inadvertently stored unwanted 
energy of the capacitive element C2 may be created if the lamp (not having 
resistor R2) is removed from its socket with the capacitive element in the 
charged state thereby presenting unwanted energy at P1 and P2 of the lamp. 
Similarly, if the plug coupling the A.C. voltage V.sub.AC to the lamp, is 
removed from its wall receptacle, unwanted energy is present at the prongs 
(not shown) of the plug. 
The capacitive element C2 may be of a relatively large value, for example, 
50 microfarads for a 60 watt-24 volt incandescent lamp. In order to 
provide a relatively fast discharge time, for example, two (2) seconds, 
for the unwanted stored energy of the 50 microfarad capacitive element C2, 
a resistor R2 of 20K may be used. This 20K ohm resistor R2 typically 
dissipates about 0.5 watts of wasted energy during steady state operation 
of the prior art circuit arrangement of FIG. 4, which unwanted dissipation 
degrades the efficacy of the lamp in which the resistor R2 is implemented. 
A further related disadvantage of the prior art circuit arrangement of FIG. 
4 related to damaging the filament may exist if the voltage applied to or 
removed from the filament is not accomplished in an orderly desired manner 
and may be described with reference to FIG. 5. 
FIG. 5 is segmented into, (1) FIG. 5(a) showing the waveform of the applied 
A.C. voltage V.sub.AC,(2) FIG. 5(b) showing the waveshape of the current 
I.sub.L flowing in the circuit arrangement of FIG. 4, (3) FIG. 5(c) 
showing the voltage V.sub.C2 across the capacitive element C2, and (4) 
FIG. 5(d) showing the arc voltage V.sub.gap that may appear at P1, P2 or 
S1 of FIG. 4. A comparison between FIGS. 5(a), 5(b) and 5(c) reveal that 
the steady state current I.sub.L (FIG. 5(b)) leads the voltage V.sub.AC 
(FIG. 5(a)) by nearly 90.degree. and the voltage V.sub.AC is nearly in 
phase with the voltage V.sub.C2 (FIG. 5(c)). The voltages V.sub.AC and 
V.sub.C2 are essentially in-phase quantities because for the value 
previously given for the capacitor C2 of 50 microfarads and for a typical 
filament resistance of 9.6 ohms, the impedance X.sub.C2 significantly 
exceeds that of the resistance of the filament. 
For this condition, if either switch S1, contact P1 or contact P2 begins to 
open for example, at time t.sub.d of FIG. 5(a), an arc between the 
contacts of switch S1 or between contacts P1 or P2 and their mating 
contacts in the socket of the lamp fixture will most likely occur. The 
conductive or arcing condition of the switch S1, contact P1 or P2 is shown 
in FIG. 5(d) as the duration "gap closed," whereas, the non-conductive or 
non-arcing condition of switch S, contact P1 or P2 is shown in FIG. (d) as 
the duration "gap open." The transition from the durations gap closed to 
gap open is shown by the initiation of the negative going waveshape of 
V.sub.gap of FIG. 5(d). The arc voltage V.sub.gap maintains current flow 
I.sub.L within the lamp until the zero-crossing condition of I.sub.L 
(shown as t.sub.o in FIG. 5(b)), at which time the arc will extinguish. 
For this condition the capacitive element C2 is charged to a peak voltage 
V.sub.C2 of approximately 170 volts for a typical V.sub.AC of 120 volts. 
The peak voltage of V.sub.C2 is shown in FIG. 5(c) by event t.sub.p and 
corresponds to the +170 voltage value of V.sub.AC of FIG. 5(a). The 
voltage V.sub.C2 of FIG. 5(c) remains at this peak condition because 
I.sub.L of FIG. 5(b) is zero, the arc having extinguished. As the line 
voltage V.sub.AC begins to swing to its negative polarity, a voltage of up 
to twice the peak voltage e.g. 340 volts (shown in FIG. 5(d) by event 
t.sub.p1), may appear across the device S1, P1 or P2 that was initially 
opened (event t.sub.d of FIG. 5(a)). If the device S1, P1 or P2 has not 
opened (shown by the duration, gap open of FIG. 5(d)) sufficiently in 
one-half cycle of the V.sub.AC voltage, e.g. approximately 8 milliseconds, 
since the arc extinction (event t.sub.o of FIG. 5(b)), the arc will 
restrike at some time later (shown as event t.sub.BD related to FIGS. 
5(a), (b), (c) and (d)) and allow capacitive element C2 (event t.sub.p2 of 
V.sub.C2 of FIG. 5(c)) to discharge into the filament. The stored energy 
of the capacitive element C2 may be expressed by the relationship given in 
Joules: 
EQU W=1/2CV.sup.2 (1) 
where C has a value of 50 microfarads and V has a value of 340 volts so 
that expression (1) yields the following results: 
##EQU1## 
A discharge of 2.89 Joules is an excessive amount of energy to be delivered 
to the low voltage filament and can cause damage to the filament 
especially if delivered repeatedly. The disadvantage of the prior art 
circuit arrangement of FIG. 4 having waveshapes of FIG. 5 are 
substantially reduced or even eliminated by the present invention. 
In general, the circuit arrangements of FIGS. 2 and 3 which have switching 
means 33 and 36, respectively, connected across the capacitive element C1, 
cause the capacitive element C1 to be discharged in a relatively quick 
manner, via the bleed-off resistor R1 having a relatively small value such 
as 60 ohms, if the voltage of the capacitor C2 does not change for a 
predetermined duration such as 1.0 milliseconds. It should be noted that 
the 1.0 millisecond duration is determined even in the absence of the 
applied V.sub.AC voltage by virtue of the stored energy typically 
available in the power supply energizing the sensing means 34 of FIG. 7 
and 31 of FIG. 8. 
The discharging of the capacitive element C1, in response to this unchanged 
1.0 millisecond duration voltage, quickly eliminates the unwanted energy 
present at the prongs of a plug removed from a wall receptacle or at the 
base of the lamp removed from its fixture. Further, the quick discharge of 
the capacitive element C1, via resistor R1, reduces or substantially 
eliminates the possible damage to the filament by preventing the 
relatively high stored energy, e.g., 2.89 Joules, from being discharged 
into the filament. The circuit arrangements of FIGS. 2 and 3 provide the 
improvement without the need of a continuous power dissipation resistor 
which would otherwise reduce the efficacy of the lamp unit. The operation 
of the circuit arrangements 40 and 50 of FIGS. 2 and 3 may be described 
with reference to FIG. 6. 
FIG. 6 is similar to FIG. 5 and is segmented into, (1) FIG. 6(a) showing 
the AC line voltage V.sub.AC, (2) FIG. 6(b) showing the current (I.sub.L) 
flowing in the lamp, (3) FIG. 6(c) showing the voltage V.sub.Cl across the 
capacitor C1, and (4) FIG. 6(d) showing the arc voltage V.sub.gap that may 
appear across P1, P2 or S1 of FIGS. 2 and 3. FIG. 6 shows events t.sub.d 
(FIG. 6(a)), t.sub.o (FIGS. 6(b)), and t.sub.p (FIG. 6(c)), all previously 
described with regard to FIG. 5. 
FIG. 6(c) further shows a duration dt.sub.e, having an initial quantity of 
t.sub.p, and is meant to represent an elapsed time which is indicative 
that the charged state of the capacitive element C1 remains unchanged for 
the previously discussed predetermined duration of approximately 1.0 
millisecond. If this duration dt.sub.e expires, the discharge of the 
capacitive element C2 is initiated, and V.sub.C1 decays from its peak 
value at t.sub.p of about 170 volts toward its zero condition. The stored 
energy of V.sub.C1 for this 170 volt condition may be determined by 
expressions (1) and (2) and has a value of about 0.72 Joules which is 
substantially less than the 2.89 Joules discharge previously discussed 
with regard to FIG. 5. 
The time duration in which V.sub.C1 is discharged, shown in FIG. 6(c) as 
occurring in less than one-half cycle (4.0 milliseconds), is determined by 
the values selected for the capacitive element C1 and the bleed-off 
resistor R1. For the circuit arrangement of FIGS. 2 and 3, C1 has a value 
of 50 microfarads and R1 has a value of 60 so that C1 is substantially 
discharged in about 4.0 milliseconds. 
The circuit arrangements of FIGS. 2 and 3, having the bleed-off resistor 
R1, substantially reduces the likelihood of the gap to break over and 
conduct which may be described with reference to FIG. 6(d). 
FIG. 6(d) shows V.sub.gap as having a dashed line and solid line 
waveshapes. The dashed line waveshape indicates the voltage waveshape 
which could appear between the gap, previously discussed as contacts of 
switch S1 or between contact P1 or P1 and their mating contact in the 
socket, if capacitor C1 is not discharged. If C1 remains charged to 170 
volts, then as much as 340 V could appear across the gap making breakdown, 
that is, an arc condition, a probable occurrence. 
The present invention reduces this probability as shown by the solid line 
waveshape of FIG. 6(d). The solid waveform shows the V.sub.gap which 
exists by causing the previously described discharge of capacitor C1. The 
V.sub.gap for the present invention is simply that of V.sub.AC (FIG. 6(a)) 
varying between peaks of about -170 volts to +170 volts. For this peak 
voltage the break-over condition of the gap is substantially reduced and 
possibly eliminated. 
The bleed-off resistor R1 is interconnected to the capacitive element C1, 
so as to provide a discharge path, in circuit arrangements 40 and 50 by 
switching means 33 and 36, respectively. The current conducted through the 
switching means 33 and 36 is typically 3.0 amps for a duration of less 
than 4.0 milliseconds. The switching means 33 along with its related 
sensing means 31 for sensing the unchanged charged state of the capacitive 
element C1 are shown in detail in FIG. 8, whereas, the switching means 36 
along with the related sensing means 34 for sensing the unchanged charged 
state of the capacitive element C1 are shown in detail in FIG. 7. 
FIG. 7 shows the switching means 36 as comprised of two metal-oxide 
semiconductor field-effect transistors (MOS/FET) 40 and 42 having inherent 
parasitic diodes and available from International Rectifier Co. of El 
Segundo, CA. The field effect transistors provide a high impedance between 
the capacitor C1 and the resistive discharge path of R1. The switching 
means 36 further comprises diodes D1 and D2, a zener diode Z.sub.1, a 
resistor RF having a typical value of 47K ohms, and a capacitor CF having 
a typical value of 10 microfarads. The sensing means 34 is of a current 
sensing type and may be comprised of a plurality of elements having the 
reference number, circuit function and of the type all given in Table 1. 
TABLE 
______________________________________ 
Element 
Reference 
Number Circuit Type 
______________________________________ 
RS Sensing Resistor 
1 ohm 
44 Rectifying Plurality of four (4) 
Means diodes arrangement in a 
full-wave configuration 
or a conventional dif- 
ferential amplifier 
rectifier circuit con- 
figuration 
46 Comparator A differential amplifier 
of the type (CA3130) 
available from RCA of 
Somerville, NJ. 
48 One-Shot An astable multi-vibrator 
of the type ICM7555 avail- 
able from Intersil of 
Cupertino, CA. 
50 Transistor Semiconductor device of 
the type 2N5223 available 
from GE of Syracuse, NY. 
52 Optical Coupler 
Light-emitting device of 
the type H11G2 
available from GE of 
Syracuse, NY. 
______________________________________ 
The devices 40 and 42 each have a source (S), drain (D) and gate (G) 
electrode. The source (S) and drain (D) electrodes of each device 40 and 
42 are shunted by an inherent parasitic diode as shown in FIG. 7. The 
diodes D1 and D2 together with the inherent diodes of devices 40 and 42 
form a full-wave rectifier, as shown in FIG. 7, for operating the optical 
coupler 52. The source (S) electrodes of devices 40 and 42 are 
interconnected and connected to a common ground point 41 which is floating 
with respect to either side of the V.sub.AC voltage having the potential 
present at P1 and P2 of lamp unit 10. The drain (D) electrode of device 40 
is connected to one end of resistor R1 and to the anode of diode D1, 
whereas, the drain (D) electrode of device 42 is connected to one end of 
capacitive element C1 and to the anode of diode D2 all as shown in FIG. 7. 
The gate (G) electrodes are commoned together and connected to the output 
of the optical coupler 52 of sensing means 34. One side of capacitor CF 
and the anode of zener diode Z1 are connected to the common ground point 
41. The cathode of the zener diode Z1 is connected (1) to the other end of 
capacitor CF; (2) to the collector of the transistor of the optical 
coupler 52; and (3) to one end of resistor RF having its other end 
connected to each of the cathodes of diodes D1 and D2. The zener diode Z1, 
capacitor CF and resistor RF form a filter and voltage regulator network. 
Sensing means 34 has the sensing resistor RS serially arranged with the 
filament of the lamp unit 10 and provides the input signal 54 to the 
rectifying means 44. Rectifying means 44 rectifies the input signal 54 and 
develops signal 56 which is routed to an input of comparator 46. The 
rectified signal 56 along with signal 54 are indicative of the voltage 
condition of the capacitor C1. 
In general, the comparator 46 compares the rectified signal 56 against a 
predetermined reference voltage (V.sub.REF) established by a selectable 
potentiometer 45. In response to the comparison, the comparator 46 
generates a first pulse train signal 58 responding to a condition 
indicative that the voltage level of rectifier signal 56 is greater than 
the predetermined reference voltage (V.sub.REF) and terminates the first 
pulse train signal 58 at a predetermined voltage level in response to a 
condition that the voltage level of rectified signal 56 is less than the 
predetermined reference voltage (V.sub.REF). 
The comparator 46 in response to the input signal 56 and the predetermined 
reference (V.sub.REF) develops an output signal 58 which is routed to (1) 
the collector of transistor 50, (2) the input of the optical coupler 52 
functionally shown as comprising a light-emitting diode and a light 
sensitive transistor, and (3) to the input of the one-shot device 48, 
which, in turn, develops an output signal 60 which is applied to the gate 
of transistor 50 which has its emitter connected to a common 51, which, in 
turn, is connected to P2 of the lamp unit 10. 
In general, the transistor 50 and the optical coupler 52 comprise a 
detection means responsive to the first pulse train signal 58 and to a 
second pulse train signal 60, and generate the control signal to switching 
means 36 in response to the termination of the first pulse train signal 
58. 
The operation of the sensing means 34 is illustrated by the waveshapes of 
signals 54, 56, 58 and 60 of FIG. 7. The waveshapes of signals 54, 56, 58 
and 60 are each shown as having a NORMAL and a ZERO portion. The NORMAL 
portion corresponds to the condition in which the voltage across the 
capacitor C1 is experiencing a periodic normally occurring change. The 
ZERO portion corresponds to the condition in which the voltage across the 
capacitor C1 is not experiencing a periodic change and thus the energy 
stored across the capacitor C1 is to be discharged via the bleed-off 
resistor R1. 
The NORMAL conditions of signals 54, 56, 58 and 60, are respectively shown 
as (1) a periodic sinusoidal waveshape, (2) an A.C. rectified signal 
having a mid-portion corresponding to a reference voltage V.sub.REF which 
may be established by a selectable potentiometer 45 at the input to 
comparator 46, (3) a periodically occurring wavetrain comprised of pulses 
W1 having a typical pulse width of about 0.5 milliseconds, and (4) the 
periodically occurring second wavetrain signal comprised of pulses W2 
chosen to be wider than W1, and having a typical pulse width of about 1.0 
milliseconds. Normally, pulses W2 render transistor 50 conductive which 
prevents the actuation of optical coupler 52 by shorter pulses W1. 
The ZERO conditions of signals 54, 56, 58 and 60 are respectively shown as 
(1) a waveshape having an amplitude of approximately zero (0), (2) a 
waveshape having an amplitude approaching zero (0), (3) a positive D.C. 
level, and (4) a zero D.C. level. 
In operation, the rectified signal 56 is continuously compared by the 
comparator 46 against the reference voltage V.sub.REF. When the value of 
the signal 56 becomes less and remains less than V.sub.REF, which is 
representative of a zero condition being sensed by sensing resistor RS, 
the comparator 46 develops the ZERO condition of its output signal 58 that 
is, a positive dc level. The one-shot 48 in response to the ZERO condition 
of signal 58 develops its ZERO condition of its output signal 60, that is, 
a zero D.C. level following the 1.0 millisecond pulse. The ZERO condition 
of signal 60 renders transistor 50 nonconductive while signal 58 is 
positive thus actuating optical coupler 52, which, in turn, causes a 
signal to be applied to the gate (G) electrodes of devices 40 and 42 so as 
to render both devices 40 and 42 conductive. The conductive devices 40 and 
42 corresponding to zero condition sensed by the sensing resistor RS, in 
turn, connect one side of capacitor C1 to the bleed-off resistor R1 so 
that the energy stored in capacitor C2 is essentially discharged. 
An alternate embodiment to supply the discharge path for the stored energy 
of the capacitive element C1 is shown in FIG. 8. The circuit arrangement 
of FIG. 8 is particularly advantageous in that it does not require a 
sensing resistor RS, arranged in series with the FILAMENT, to detect lamp 
current. The circuit of FIG. 8 is mainly comprised of switching means 33 
and sensing means 31. 
The switching means 33 may be comprised of (1) a metal-oxide-semiconductor 
field-effect transistor (MOS/FET) 38 which may be of the type previously 
given for devices 40 and 42 and (2) a plurality of diodes D3, D4, D5 and 
D6 arranged as shown in FIG. 8 in a full-wave rectifier configuration. The 
input node of the full-wave rectifier formed from diodes D4 and D6 is 
connected to one end of capacitor C1, whereas, the output node of the 
full-wave rectifier formed from diodes D3 and D5 is connected to one end 
of the resistive discharge path provided by resistor R1. The central nodes 
of diodes D3, D4, D5 and D6 have connected thereacross the device 38 and 
the node of diodes D3 and D4 is connected to the common 41. The gate (G) 
electrode of device 38 is connected to the output of optical coupler 52 
which provides the control signal of sensing means 31. 
The node formed by the cathodes of diodes D5 and D6 is connected via one 
end of the resistor RF as previously discussed with regard to FIG. 7. The 
other end of resistor RF is connected to; (1) the node formed by the 
cathode of zener diode Z1 and one end of capacitor CF; and (2) to the 
collector of the transistor of the optical coupler 52. The other end of 
capacitor CF and the anode of zener diode Z1 is connected to the common 
41. 
The sensing means 31 may utilize the optical coupler 52, the transistor 50, 
the rectifying means 44, the comparator 46, and the one-shot 48 all 
previously described with reference to FIG. 7. The sensing means 31 of 
FIG. 8 is of a voltage detecting type which is different than the current 
detecting sensing means 34 of FIG. 7. Further, unlike sensing means 34, 
sensing means 31 has a voltage divider network formed by RD and RE having 
respective typical values of 2.2K ohms and 100K ohms connected across 
capacitor C1 so that only a portion of the voltage V.sub.C1 appears at the 
input to the rectifier means 44. The node formed by resistors RD and RE is 
connected to the input of rectifier means 44. Still further, unlike 
sensing means 34, the common potential 51 of sensing means 31 is connected 
to the node formed between resistor RD and capacitor C1. The sensing means 
31 has signals 58 and 60 each having waveshapes including a NORMAL and a 
ZERO portion all of which are as described for FIG. 7. The sensing means 
31 has signals 62 and 64 not previously discussed with regard to FIG. 7. 
The signals 62 and 64 each have a NORMAL portion respectively represented 
as (1) a sinusoidal occurring waveshape, and (2) a rectified A.C. signal. 
The NORMAL portion of signal 64 has a peak value greater than the 
reference voltage V.sub.REF previously described with regard to FIG. 7. 
In general, the comparator 46 compares the rectified signal 64 against the 
predetermined reference voltage (V.sub.REF) . In response to the 
comparison, the comparator 46 generates the first pulse train signal 58 
responding to a condition indicative that the peak value of the rectified 
signal 64 is greater than the predetermined reference voltage (V.sub.REF) 
and terminates the first pulse train signal 58 at a predetermined voltage 
level in response to a condition that the voltage level of the rectified 
signal 64 remains greater than the predetermined reference voltage 
(V.sub.REF) for a typical predetermined duration of 1.0 milliseconds. 
The signals 62 and 64 like signals 54 and 56 of FIG. 7 have a ZERO portion 
respectively represented by, (1) a waveshape having a positive 
steady-state value essentially corresponding to the peak value of signal 
62, and (2) a positive steady-state value essentially corresponding to the 
peak value of signal 64 and exceeding the reference voltage V.sub.REF. The 
ZERO conditions of signals 62 and 64 are representative that the voltage 
across capacitor C1 is remaining at peak value, that is, is not 
periodically changing and thus capacitor C1 needs to be discharged. 
The comparator 46 in response to the ZERO portion of signal 64 develops its 
ZERO portion of waveshape 58 in a manner similar to that described for 
FIG. 7. Similarly, one-shot 48 in response to the ZERO portion of signal 
58 develops its ZERO portion of waveshape 60 in a manner similar to that 
described for FIG. 7. Further, the transistor 50 in response to the ZERO 
portion of both signals 58 and 60 applies a signal via the optical coupler 
52 to the gate (G) electrode of device 38 so as to render device 38 
conductive. The conductive device 38 causes one end of capacitor C1 to be 
coupled to the bleed-off resistor R1 so that the unwanted stored energy of 
capacitor C1 is substantially discharged. 
It should now be appreciated that the present invention provides an 
improved general service incandescent lamp employing a low voltage 
filament and having various embodiments of capacitive ballast circuits. 
The various embodiments of the ballast circuit each have means for quickly 
discharging unwanted energy that may be stored across capacitive elements. 
The various embodiments of the present invention provide such quick 
discharge without the need of continuously dissipative resistive elements 
that might otherwise degrade the efficacy of the improved general service 
incandescent lamp.