Flickering candle lamp

A self contained battery operated table lamp for use in restaurants, and the like. The lamp includes an electric light which is energized on an intermittent basis by a switching circuit to assure long battery life. A feed back loop is included in the switching circuit for establishing the duty cycle of the energizing power intermittingly applied to the lamp. A flicker signal generator is connected to the energizing circuit of the light to introduce a flicker into the output of the light. The flicker signal generator incorporates a plurality of independent oscillators, each operating at a slightly different frequency. The outputs of the various oscillators are summed in a summing network with each being given a slightly different weighting factor, and the resulting signal is injected into a feedback loop to modify the average voltage of the light. The lamp is caused to provide a pseudo-random candle simulating effect.

BACKGROUND OF THE INVENTION 
A self-contained battery operated electric lamp is provided for use as a 
table lamp in restaurants, and which is intended to replace existing 
candle holders. The lamp provides a flickering light which simulates a 
candle. 
SUMMARY OF THE INVENTION 
A self-contained battery operated table lamp unit for use in restaurants. 
The lamp is energized on an intermittent basis to assure long battery 
life. A plurality of electronic signal generators are incorporated into 
the unit to provide a pseudotype random candle simulating flicker effect 
for the lamp.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
The lamp shown in FIGS. 1 and 4 includes a housing 10 which may be formed 
of plastic, or any other appropriate material, and a cap 11 removably 
mounted on the open top of the housing. A light bulb 12 is supported on a 
printed circuit board 14 mounted within the housing 10 and the light bulb 
projects upwardly through the top of the housing to be enclosed by a lens 
16. Lens 16, for example, may be composed of clear plastic. An on-off 
switch 18 is also supported on the circuit board 14 and protrudes 
outwardly through the opening 19 in the top of the housing. 
A replaceable battery pack 22 (FIG. 2) is contained within housing 10, and 
is connected to the electronics mounted on the underside of circuit board 
14 by means of appropriate connectors 24A, 24B. The battery pack may, for 
example, be "C" cell batteries connected by leads 26A to connector 24A, as 
shown in FIG. 2. Connector 24B is connected to the printed circuit on the 
underside of circuit board 14 by leads 26B, as shown in FIG. 4. 
In the embodiment of FIG. 4, the printed circuit board 14 fits into the top 
of the housing 10. The board is held in place by removable cap 11, and the 
bulb 12 protrudes through the cap and into the transparent lens 16. The 
cap 12 is mounted on and removed from housing 10, for example, by a 1/4 
turn lock. 
The lamp may be inserted into an appropriate holder 30, as shown in FIG. 3, 
which is free standing; and a transparent globe 32 may be inserted into 
the holder to surround the lamp. 
In the circuit diagram of FIG. 5, terminals P1 and P2 of the circuit are 
connected to the battery connector 24B of FIG. 4. Terminal P2 is connected 
to a positive power lead 100 through the switch 18 of FIG. 1, which is a 
single pole double throw switch designated SW1 in FIG. 5. Lead P2 is 
connected to the negative power terminal 102. Power lead 100 is connected 
to the emitter of a PNP switching transistor Q1 which may be of the type 
designated 2N4403. The collector of the transistor is connected to the 
lamp 12, which is also connected to the negative power lead 102. The power 
lead 100 is also connected to a 20 kilo ohms resistor R16 which, in turn, 
is connected through a 75 kilo ohm resistor R12 and a 100 kilo ohm trimmer 
potentiometer VR1 to a 75 kilo ohm resistor R17. Resistor R17 is connected 
to the negative power lead 102. 
The collector of transistor of Q1 is also connected through a 3 kilo ohm 
resistor R19 to a 2.2 microfarad capacitor C7, which, in turn, is 
connected to the negative power lead 102. 
A 5.1 kilo ohm resistor R11 is connected between the emitter and base of 
transistor Q1. A 39 kilo ohm resistor R13 is connected to a 13 kilo ohm 
resistor R14 which, in turn, is connected to a 36 kilo ohm resistor R15 
connected to the negative power lead 102. The junction of resistors R14 
and R15 is connected to the base of an NPN transistor Q2 which may be of 
the type designated 2N5088. The emitter of transistor of Q2 is connected 
to the negative power lead 102. The collector of transistor Q2, together 
with the collector of an NPN transistor Q3, is connected to the base of an 
NPN transistor Q4. Transistors Q3 and Q4 may each be of the type 
designated 2N5088. The collector of transistor Q4 is connected to the base 
of transistor Q1, and the emitter of transistor Q4 is connected to a 100 
ohm resistor R18 which is connected to the negative lead 102. 
The base of transistor Q3 is connected to a 360 kilo ohm resistor R20 
which, in turn, is connected to a 510 kilo ohm resistor R21. Resistor 21 
is connected to the negative power lead 102. The base of transistor Q3 is 
also connected to the moveable contact of potentiometer of VR1. 
The lamp 12 of FIGS. 1 and 4 is intended for use with replacement C cell 
battery pack 22, shown in FIG. 2. The normal battery life of the lamp is 
about 350 hours. The lamp may also be designed for use with a D cell 
battery pack, with approximately 450 hours of battery life. The latter 
embodiment may incorporate the battery unit as an integral part of the 
whole unit, rather than a replacement cartridge. 
As mentioned above, the transistor Q1 is a switching transistor. When the 
transistor Q1 is conductive, the lamp 12 is connected across the battery 
leads 100 and 102. Conversely, when the transistor Q1 is non-conductive, 
the lamp 12 is disconnected from the battery. Transistor Q1 is switched on 
and off approximately 300 times a second. The actual rate at which the 
transistor Q1 is switched on and off is controlled by resistor R19 and 
capacitor C7. The duty cycle is determined by a feedback loop which 
includes transistors Q3 and Q4. 
Neglecting for the moment the operation of a plurality of flicker signal 
generators 110 which are included in the circuit, and which will be 
described, the duty cycle normally adjusts itself so that the average 
voltage across the lamp 12 is approximately 1.5 volts. The trim 
potentiometer VR1 is manually adjusted to establish that voltage. The lamp 
and circuit characteristics are such that the true RMS energy fed into the 
lamp is not constant as the battery discharges from 4.5 volts to 2 volts. 
To reduce variations in brightness versus battery voltage, the resistor 
R16 applies a small error-reducing current into the duty cycle circuit. 
To further reduce operating current, the current controlling the switching 
transistor Q1 is made independent of battery voltage. This is achieved by 
the addition of transistor Q2 and resistors R14 and R15. 
Flicker is introduced into the lamp 12 by modifying the duty cycle on a 
pseudo-random basis at a low frequency rate which is visible to the eye. 
Five independent oscillators are included in the plurality designated 110, 
and each operates at a slightly different frequency. Each oscillator 
includes an operational amplifier which is 1/6 of an integrated circuit U1 
of the type designated 74HC14. A 22 microfarad capacitor C1 is connected 
across the battery leads 100 and 102. Battery lead 100 is connected to an 
operational amplifier which also constitutes 1/6 of the integrated 
circuit 74HC14, which, in turn, is connected to a series of 1 microfarad 
capacitors C2, C3, C4, C5 and C6. 
Capacitor C2 is connected to input terminal 3 of operational amplifier U1, 
whose output terminal 4 is connected to 680 ohm resistor R6. Capacitor C3 
is connected to input terminal 5 of operational amplifier U1, whose output 
terminal 6 is connected to a 910 kilo ohm resistor R7. Capacitor C4 is 
connected to input terminal 9 of operational amplifier U1, whose output 
terminal 8 is connected to an 820 kilo ohm resistor R8. Capacitor C5 is 
connected to input terminal 11 of operational amplifier U1, whose output 
terminal 10 is connected a 750 kilo ohm resistor R9. 
Capacitor C6 is connected to input terminal 13 of operational amplifier U1, 
whose output terminal 12 is connected to a 1 meg a hyphen (-) ohm resistor 
R10. Resistors R6, R7, R8, R9 and R10 constitute summing resistors, and 
all are connected to the junction of resistors R20 and R21. Resistors R20 
and R21 are limiting resistors which serve to limit the influence of the 
flicking signal generators 110 on the lamp 12. 
Output terminal 4 is connected back to input terminal 3 of operational 
amplifier U1 through an 820 kilo ohm resistor R1. Output terminal 6 is 
connected back to terminal 5 through a 910 kilo ohm resistor R2. Output 
terminal 8 is connected back to input terminal 9 through a 1 meg ohm 
resistor R3. Output terminal 10 is connected back to input terminal 11 
through a 1.1 meg resistor R4. Output terminal 12 is connected back to 
input terminal 13 through a 1.3 meg resistor R5. 
The circuits described above constitute five independent oscillators, each 
operating at a slightly different frequency. The output signals from the 
five oscillators are summed with each given a slightly different weighting 
factor through resistors R6-R10. The resulting signal is injected into the 
feedback loop of the transistors Q3 and Q4, and it serves to modify the 
average voltage of the lamp. This results in a flicker which is 
discernable by the eye of an observer. The circuit will operate from 4.5 
volts to just below 2 volts, at which point the flicker signal generator 
will cease operating. The circuits should be adjusted by the trim 
potentiometer VR1 so that the duty cycle across the lamp 12 with 3 volts 
at the input is 50%. Adjusting for a higher duty cycle will increase lamp 
brightness, but will shorten lamp life significantly and battery life 
slightly. Adjusting for a lower duty cycle will extend lamp life 
significantly, and battery life slightly. 
The invention provides, therefore, an improved self-contained table lamp 
which may be used to simulate a candle holder, and which provides a 
flickering light. The lamp of the invention has a feature in that it 
exhibits extremely long battery life, and in that it is readily portable 
and easy to operate and to maintain. 
It will be appreciated that while particular embodiments of the invention 
have been shown and described, modifications may be made. It is intended 
in the claims to cover all modifications which come within the true spirit 
and scope of the invention.